Index Schematics Acronyms Discussion Mail to a friend Post a message. DSP drives speed and accuracy; coherence saves the day - DSP techniques lead to faster, less costly frequency-response tests and enable the use of a powerful concept, the coherence function, which acts as a watchdog to help identify and quantify common but easy-to-miss measurement errors. Best of all, this watchdog works for free. Smart signal conditioners compensate for the errors and extract the true signals from the dross.

Pressure transducers, accelerometers, temperature sensors, and linear-position sensors are often imperfect devices, prone to nonlinearities and gain and offset errors. Rate this link Tech Tips: Rate this link Using a multimeter - A meter is a measuring instrument. An ammeter measures current, a voltmeter measures the potential difference voltage between two points, and an ohmmeter measures resistance.

A multimeter combines these functions, and possibly some additional ones as well, into a single instrument. Rate this link Using a Volt Ohm Meter - A very handy tool for trouble shooting problems is a VOM Volt Ohm Meter - also called a Multi-Meter. It can be used to test cables, AC power levels and Batteries.

You'll often find yourself out on the road with problems that are causing you grief, but you aren't quite sure why. Rate this link What is a decibel? The ratio may be power, or voltage or intensity or several other things. Rate this link Measuring instrument interfaces IEEE is propably the mostly adopted communication bus and protocol used in electronic measusing equioment.

Inthe IEEE adopted the bus structure and communication protocol that it named IEEE Some others call it GPIB general-purpose instrumentation bus. The bus's original name was HPIB Hewlett-Packard instrumentation bus. Until the advent of the HPIB, no standardized methods existed for interfacing instruments with computers. IEEE remained for more than two decades the industry's primary standard for enabling instruments and computers to talk with one another. IEEE standard did a good job of defining the communications hardware, it initially gave short shrift to interfacing's software aspects.

More than a decade elapsed before the evolution of the necessary software standards, particularly SCPI standard commands for programmable instruments. IEEE was not the only interface used. RS ports have became popular on slower instruments. The two top contenders for the instrument-interfacing standard of the future are Ethernet and USB.

You can find one or both in many instruments. Scopes that offer communication ports other than IEEE are becoming increasingly common. The current and most likely future leader in replacing IEEE is Ethernet. USB will also play a major role. The most obvious reasons for turning to computer-standard interfaces in place of IEEE for instruments are cost, size, cable length of instrument networks, and increasing difficulty of installing specialized peripheral controllers in newer PCs.

For test instruments, an advantage of an Ethernet connection over a USB or IEEE connection is Ethernet's much greater allowable cable length. USB and IEEE are limited to tens of feet. Don't be fooled by the new protocols' high nominal bit rates; instrument interfacing usually involves short messages.

In such service, IEEE can be significantly faster than protocols that at first appear to be much faster than IEEE Using an instrument as a Web server is a new aspect in interfacing. Rate this link Oscilloscopes Every scientist, engineer, and technician involved in any form of electronics has used an oscilloscope.

Scope displays of amplitude as a function of time provide intuitive and easily interpreted pictures of signals. Oscilloscope is one of the most important test instruments foravailable engineers. It is useful for very many electronics measurement.

The main purpose of an oscilloscope is to display the level of a signal relative to changes in time. You can use an oscilloscope to analyze signal waveform, get some idea of signal frequency and many other details.

Scopes are ment for looking at the qualitative aspects of the signal like signal waveform, esitence of signal, etc. For making quantitative measurements, a scope is "usually" a bad choice for example multimeter is more accurate tool to measure DC voltage levels than a scope. It is quite typical for the scope to be out by a percent or two or three but if you're counting on that kind of accuracy, you're using the wrong tool.

Traditional oscilloscopes used a CRT screen and were completely analogue devices. Those analogue oscilloscopes are still very usable devicesnowadays. Analogue oscilloscopes work very well as general testing instrumentfor viewing repetitive signals.

Many simple and cheap analogue oscilloscopes have typical bandwidth of 20 MHz. Some better ones go to Mhz or higher in bandwidth. Even a 20MHz analogue scope will produce some response at a higher frequency but of course it will be at a lower level because it is outside of the calibrated specified bandwidth.

Digital oscilloscopes are digital versions of that analogue instruments. Digital oscilloscopes sample signals using a fast analog-to-digital converter ADC. The digitized signals aresotred to the scope memory and shown on the scope screen or at computer screen. The benefit of the digital technology is thatthe waveforms can be captured to memory and then analyzed, immediatlyor later, in many ways.

Digital oscilloscopes can be used to capturerepetitive signals as well as transient signals. Oscilloscope bandwidth is generally listed as the dB point in oscilloscope frequency response. Traditionally, oscilloscopes have exhibited a Gaussian frequency response. A Gaussian response results from the scope design's combining many circuit elements that have similar frequency responses.

Analog oscilloscopes achieve their frequency response in this manner, thanks to chains of amplifiers from the input BNCs to the CRT display. Analog oscilloscopes used the input signal to directly deflect the electron beam in a CRT. This architecture required amplifying the input signal by three orders of magnitude and driving the large capacitive load that the CRT deflection plates presented.

The properties of Gaussian-response oscilloscopes are fairly well-taught and well-understood throughout the industry. Bandwidth is defined as the frequency at which the response is down 3 dB relative to dc. Another commonly used property of Gaussian systems is the overall system bandwidth, which is the rms value of the individual bandwidths. Oscilloscope probes are often designed to have sufficiently higher bandwidth than the oscilloscope bandwidth, so that the above formula is usually not necessary.

Most oscilloscopes are built so that the signal input connector is BNC connector. The input impedance in the connetion is typically around 1 megaohm in typical normal oscilloscopes and 50 ohms in many high speed oscilloscopes check what you have from scope manual.

The connector ground side outer shield is normally connected to the equipment case ground which is generally wired to mains ground through mains connector. This means that the grounds of all channels are genrally connected together and then wired to mains ground unless you power your scope through safety isolation transformer which isolated your scope from ground.

Oscilloscopes are intended to be operated with their chassis at ground potntial. There are good technical and safety resons for this. If you are measuring some mains powered device, it is a very good idea to power the device through an isolation transformer. When working with mains powered equipment, the equipment you measure should be isolated from mains voltage for safety reasons.

When doing the meausrement the right grounding is important for meaningful results. A good oscilloscope probe has a removeable ground lead, that allows the user to ground it to circuit board or not depending on what is needed in that specific meaurement.

In general case the measurements are made better and more accurate with the ground lead connected. If you do not connect the ground lead then the display will show allthe noise the probe cable picks up cable acts like antenna that picks up noise nearby.

If you want rid of this you connect the ground lead to the low of the circuit you are trying to monitor. The oscilloscope ground lead will eventually find its way back to the mains earth of the oscilloscope. If you are trying to make measurements, you must have a reference against which to measure. Without that, "Pissing against the wind" comes to mind, as acomparison.

There are some potential dangers when the circuit ground is at a potential with respect to oscilloscope ground then current will flow in the oscilloscope through the measuring cable shield. There are also some special oscilloscopes expensive ones with inputs that are not connected to ground usually referred as differential inputs.

This kind of scope can be safely connected to almost any electronics circuit. You can get the same performance with a normal scope also if you use a differential proble connected to a normal oscilloscope.

In some cases the battery powered small oscilloscopes are very handly because those devices are completely floating.

If you want to make accurate measurements, you need to have your oscilloscope calibrated. There's a whole lot of difference between a calibrated and un-calibratedscope, but you wouldn't usually know it unless you have a source of precision calibration signals to compare against. Once calibrated, an instrument should be re-calibrated within years since the adjustments can in fact vary a surprising amount over time the time interval could vary somewhat depending on scope type and needed calibration accuracy.

A scope requires significantly more maintenance than simpler measurement instruments like a multi-meter or signal generator. CRT based oscilloscopes are complex instruments. Much more complex than almost any other piece of test instrumentation and the circuitry is not selfadjusting for the most part.

Most scope problems are revealed in the calibrationprocedure in which the tech can choose to either ignore or repair. Sometimes the repairs are trivial, sometimes not. Becauses the cost of maintaining older oscilloscopes accurately many so-called "working" units find themselves on the surplus market. The oscilloscope probe used to establish a connection between the circuit under test and the measuring instrument.

A probe can be any conductor used to establish a connection between the circuit under test and the measuring instrument.

This conductor could be a piece of bare wire, a multimeter lead or a piece of unterminated coaxial cable. These "simple probes," however, do not fulfill the essential purpose of a probe; that is, "to extract minimal energy from the circuit under test and transfer it to a measuring instrument with maximum fidelity. The bare wire can load the input amplifier with its high capacitance and inductance or even cause a short circuit; multimeter leads are unshielded and are often susceptible to stray pickup The unterminated coax will severely capacitively load the circuit under test pF per meter typically.

Also, the unterminated coax is usually resonant at certain frequencies and does not allow faithful transfer of the signal to the test instrument due to reflections.

A simplest probe type is is "x1" probe that just consists of probe tip, grounding conductor and low capacitance coaxial cable to the oscilloscope. The unterminated coax will severely capacitively load the circuit under test.

Typical capacitance of "x1" probe is tens of picofarads. For DC measurements the input resistance is the same the resistance of the oscilloscope input typically 1 Mohm on traditional CRO-type oscilloscopes, 50 ohm on some high frequency models. Attenuating Passive Voltage Probes are the most commonly used probes today.

The "x10" setting gives you reduced sensitivity and reduced capacitace the load capacitance is around one tenth of "x1" setting. This means a typical input capacitance of around pF.

The 10X passive voltage probe presents a high impedance to the circuit under test at low frequencies approximately 5 MHz and lower. Their main disadvantage is a decreasing impedance level with increasing frequency i. FET probes include active components field effect transistors or other active devices rather than passive components. The FET input results in a higher input impedance without loss of signal, i. Since FET probes have a 50 ohm output impedance, they can drive a 50?

Downside of FET probes are that they are typically expensive and need operating power to work either supplied by oscilloscope using properietary methods or powered with batteries. Several high voltage probes are available, and they typically provide X or X compensated dividers. Because of the larger attenuation factors required for high voltage applications, the input capacitance is typically reduced to approximately 3 pF.

The simplest 50 ohm divider probe consists of just one 1 kohm or 2. Current probes provide a method to measure the current flowing in a circuit. Two types of current probes are available, the traditional AC only probes and the "Hall Effect" semiconductor type. AC only current probes use a transformer to convert current flux into AC signals. Combining a "Hall Effect" device with an AC transformer provides a frequency response from DC up to many MHz range.

Because of its "non-invasive" nature, a current probe typically imposes less loading than other probe types. The AC current probes can be just passive devices, while the models with "Hall Effect" device need some operating power typically provided by local battery on the probe. Proper probe selection will extend and enhance an instrument's performance, while imprudent probe selection often reduces your system's performance.

When making measurements make sure not to exceed the maximum allowable input ratings of the oscilloscope input ports.

This will prevent costly damage and provide reliable measurements. Rememeber also not to exceed the input voltage ratigns of oscilloscope probes as well, because this can damage the probes and cause severe safety risk to the person using those probes. A proper oscilloscope probe grounding is essential requirement to get meaningful measuring results with normal oscilloscope probes.

The measured the current must always form a loop. The signal beign measured cannot exit the measured circuit and go to the oscilloscope input without having a path through which it may return. If you are measuring a "floating" circuit, then the return would go through a parasitic capacitance directly between the oscillator and the scope.

This capacitance varies depending how the devices are positiones, which means that the position of the probe cable will have an effect on the shape of the signals you see on the scope! Another nasty artifact of a no-ground probe arrangement is the resonance associated with the combination of the rather large inductance of cable, and the input capacitance of the probe.

This resonance is called a probe resonance and can cause considerable measurement errors. A short, explicit ground connection made between the scope ground and the equipment under test shunts those capacitances and inductances, eliminating their influence on the measured result and pushing the probe resonance up and out of the band of interest. All good probes come with short, tiny ground attachments to prevent such problems. For single-ended measurements, don't depend on mysterious ground connections.

Always use a good, short ground connection. Oscilloscopes are used for very many different kind of measurements. In telecommunication and data communications applications you can often see results of eye diagram and eye pattern measurement. An eye pattern is an oscilloscope display in which a pseudorandom digital data signal from a receiver is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep.

System performance information can be derived by analyzing the display. An open eye pattern corresponds to minimal signal distortion. Distortion of the signal waveform due to intersymbol interference and noise appears as closure of the eye pattern. Many modern digital oscilloscopes allow you to show you signal waveforms and even store the recorded signal for later inspection.

Old analogue oscilloscopes lacked the ability to store the picture on the screen, unless you took a picture of the screen with a normal film camera not very convient, camera settings needs to be right.

If you happen to have an old analogue oscilloscope and need to store the waveform on the screen, then you might be able to use modern inexpensive digital camera connected to computer instead of old traditional film camera. You can for example have an usb pc camera mounted on a tripod at the?

With the bundled software installed on your computer Windows 98se,or neveryou can view the image on your computer screen and save the image on the oscilloscope screen to you hard disk for example to be included to your laboratory documents later. You see it all in real time well almost It work, usually well. This could be an useful trick for those technicians out there with limited funds and equipment.

Digital cameras and webcams are nowadays quite cheap compared to a modern digital oscilloscope. To capture and measure these complex signals, you need powerful instruments tailored for this application. But, because of the variety of video standards, you also need a general-purpose instrument that can provide accurate information - quickly and easily.

Some work-arounds not only can mislead, but also can kill. True differential measurements are safe and accurate, however. Rate this link Digital oscilloscopes: Examples are given of how to use the benefits of a DSO in examining phase shift keying, frequency shift keying, full duplex, etc.

Rate this link DSO Displays: As clock speeds in communications and semiconductors continue to increase, timing margins get even narrower. As clock frequencies increase, a parameter that has even greater impact on measurement needs is edge speed. Rate this link Importance of X10 Probes - A scope probe is built to minimize ringing by adding resistance.

A X10 probe has the effect of reducing capacitance by a factor of ten. The trade-off is that is also attenuates the signal by a factor of ten. Yet, in many cases, monitoring the physical layer with a digital oscilloscope can pinpoint precious information that may not be revealed by protocol analyzers.

Rate this link Mysterious ground - For single-ended measurements, don't depend on mysterious ground connections. Rate this link Probe Loading - This document collection describes how an oscilloscope probles can affect the circuit being measured.

Many different types of effects and probes as described. Rate this link Probe Tutorial: It may just mean you need a better probe to see what is really happening in the circuit. Rate this link Relating wideband DSO rise time to bandwidth: Therefore, the old rules that relate rise time to frequency response no longer apply. That is the question - New active-probe architectures make multigigahertz signal-integrity measurements easier and more accurate but only for those who understand how the probes work and the trade-offs among the topologies.

Rate this link Smart scopes: Spot the secrets within waveforms - DSOs? Wider bandwidth, quicker ADCs, and deeper memories are only part of the story. Giving designers insights and answers when they need them now requires more intelligence. These pages give information on and images of old Tek scopes up to about Lots of pictures, descriptions of the various parts of the scope, and some troubleshooting information, too.

Links to other sites dealing with the Tek The main objective is to assure that any tape recorded on the VTR can be played on another similar machine without requiring any adjustments. The video tracking adjustment, typically done with an analog oscilloscope, requires a lively, gray-scale display. Rate this link Evaluating oscilloscopes: Dig deeper - Read between the lines of banner specifications?

Even though the information is digital in nature, the actual signals are analog. A true digital pulse signal only possesses two states, either "zero" or "one. To design, characterize, and troubleshoot gigabit-per-second systems, engineers and technicians eventually need to observe the actual system pulse waveforms.

To make this measurement, engineers generally use a photodetector and an oscilloscope. Rate this link Mysterious ground - This article describes new way of thinking about oscilloscope probe grounding. Rate this link Understanding Scope Probes - A probe can be any conductor used to establish a connection between the circuit under test and the measuring instrument. Miniature TV converted to simple oscilloscope - Notes on converting that old compact tv set or computer monitor into an oscilloscope.

Proves very useful in line quality monitoring and other low frequency applications. Wiring within the probe connects the probe's reference lead to the shell of the BNC. When you plug the probe into the scope, the reference lead becomes electrically common with the scope's chassis.

The power cord's ground conductor connects the chassis to earth ground. In most oscilloscope applications the inability to make anything except single-ended measurements poses no problems. But oscilloscopes' single-ended inputs present challenges when you try to view signals that are not referenced to ground. A common example is the voltage across the switching device in an off-line switching power supply. Another type of signal that you must measure differentially is a balanced signal.

Simplest way of doing differential measurements is to use two normal 10X probes conencted to two oscilloscope inputs and the "minus" operation to show the difference of signals between them.

The normal 10X probe has a typical accuracy of? Using this 10X probe, the common mode rejection ratio of a scope and probe combination would be no better than True differential measurements are safe and accurate way to measure signals that are not ground referenced. To make those measurements you need a differential probe. Unlike a conventional scope probe, a differential amplifier ijn differential probe has an input that is only implicitly referenced to ground.

As the name implies, a differential measurement produces a waveform that represents the difference in voltage between the two inputs. Ground does not enter into the measurement. Differential amplifiers ignore potentials that are equal in amplitude and phase and appear on both inputs.

This characteristic is known as "common-mode rejection" CMR. An ideal differential amplifier totally rejects the common-mode component. The other key feature of a differential amplifier is balanced input impedance both inputs have identical impedance to ground, typically high impedance.

A true differential probe has typically adjustments and electronics to provide common mode rejection ratios of 10, Differential measurements accurately catch signals without risking your life - Oscilloscopes' single-ended inputs present challenges when you try to view signals that are not referenced to ground.

Rate this link Making Differential Probes for sensing audio signal voltages across devices which are not ground referenced - These "differential" type probes can be used in the same ways as the normal resistor probes, with some exceptions.

Rate this link Probing for the truth - Will the real multigigahertz signal please stand up? Ultra-wideband digital scopes' 50 ohm inputs often make probes essential. All manufacturers of ultra-high-bandwidth scopes also make probes and all now offer differential active probes appropriate to scopes with bandwidths as high as 6 GHz. Rate this link Building oscilloscope probes A probe can be any conductor used to establish a connection between the circuit under test and the measuring instrument.

They provide a convenient and extremely rugged, yet inexpensive, way to acquire signals from your device under test. The FET input results in a higher input impedance without loss of signal. Modified oscilloscope probe tests surface-mount assemblies - small sizes and pad areas of surface-mount components make them difficult to probe but this simple tip helps it.

Rate this link Probing High-Speed Digital Designs - shown circuit diagrams of norma 1: This allows you to quite easily measure signal amplitude and look at the moduleation AM modulation. Rapidly changing voltages and currents in electrical and electronic equipment can easily result in radiated and conducted noise. Electromagnetic interference EMI can be difficult to locate and correct in electronic equipment.

A miniature EMI "sniffer probe" and an oscilloscope can help to locate and identify magnetic-field sources of EMI.

Typical EMI probles consist of some form of elecrical field sensing circuit voltage proble and some form of small coil H-field probe. With suitable accessories usully special sync circuitsa normal oscilloscope can be used as a very nice video signal analyzing instrument. To accurately measure period jitter using an oscilloscope, you must subtract the oscilloscope jitter from the measured jitter. However, oscilloscopes rarely have a jitter specification, so you must determine the oscilloscope jitter.

One method of measuring oscilloscope jitter is to use the oscilloscope to measure the jitter of a pulse generator with known jitter. The ideal generator for measuring oscilloscope jitter would have zero jitter. This article shows a circuit for generating a calibration signal with near-zero timing jitter.

However, they have no internal delay line, so they can't display the pulse that triggers the sweep. Moreover, early laboratory scopes contain delay lines having insufficient delay to display such pulses during a uniform portion of the sweep.

With such oscilloscopes, the true pulse shape remains a mystery. You can circumvent these limitations if you add an external delay line and equalizer.

The scope can then display the exact trigger-point trace. The instrument then becomes easier to use, and the measurements become more trustworthy. Rate this link Matching pads - This article describes some impedance matching circuit for measurements. Today, the PC can acquire, analyze, and present data at increasing frequencies, resolutions, and sampling rates.

In the dim and distant past, engineers recorded measurements with pencil and paper - a slow and error-prone method. Today, 20 years after the introduction of the IBM PC, two types of instruments - inboard and outboard - take measurements and move data into a host computer. PC technology has become the backbone of automated test and measurement systems. Today virtual instruments are superseding the traditional kind by revolutionizing how measurements are made and the data shared.

History of virtual instrumentation began over 15 years ago as PCs started coming into use in test and measurement as instrument controllers.

The PC is now the most powerful and cost-effective approach to building instruments. Virtual instrumentation leverages the power, flexibility, and programmability of the computer and thus brings a wide variety of benefits. Laptop computers have further encouraged this trend with a form factor ideal for many portable applications.

Even a basic normal modern PC can be used to do many different kinds of measurements with no extra hardware. The soundcard found in most PCs can be used for various applications, althrough those applications are limited to audio frequencies and have usually quite limited absolute accuracy PC soundcards are not designedprecise calibrated measureemnt instruments.

With suitable software and soundcard you can use your PC as a signal generator that gan generate different waveform signals. You can generate practically any waveform within audio frequnecy band limits if you use some suitable sample editor software or mathematics software to generate the signal waveform and then play it out through soundcard. With suitable software a PC with a soundcard can be used as a multi-purpose audio frequency signal analyser.

You can for example use PC as audio signal oscilloscope, VU meter, spectrum analyzer, frequency response analyzer. PC can also used as a very convient recording device that can record and play back any audio signal. There are also special measuring instruments that can be connected to PC to expand it's capabilities.

There are varieties that connect to PC bus or some PC interfacing port like parallel or serial port. The oscilloscope products that connect to PC through a slow port serial, parallel etc. The device has a buffer memory in it. When the device starts sampling manual start or automatic triggerit then samples it's memory fullat the given sample rare. After the data is sampled to memory itis stransferred to the PC.

And the process can start all over. What comes to the software that controls commercial PC based measurign instruments there is one software that is more popular than anything else in the field: LabView from National Instruments.

Agilent has it's own VEE software competing on the same field. There are also measuring instrument manufacturer specific control software that is supplied with the instruments. It provides amplification and protection against high voltage input signals. The software is very simple to use and the control is straight forward. Rate this link PC instrumentation through the ages - Events beyond technology helped shape the way engineers use computers to automate measurements.

This article tells what has heppened in this field. Rate this link Rundenz? A CRT display would sweep out terminal behavior current versus voltage from which you could derive mathematical models. From the displays, you could determine the bias points for optimum design performance.

Today, however, you rarely find the classic curve tracers in the lab. Instead, you find design-simulation software, such as Spice, that's removed from hands-on, empirical analysis. Spice models now exist for almost all electronic components. Characterization analyzers still make the voltage-current measurements but not at the design-engineer level. This low-cost circuit allows you to return to the hands-on approach by using your PC as a limited curve tracer. This curve tracer sweeps out seven logarithmic-scaled currents from 1?

A to 1 mA while measuring the voltage, 0 to 5V 3. Digital Oscilloscope Uses PC Sound Card for Input - Oscilloscope for Windows is a Windows application that converts your PC into a powerful dual-trace oscilloscope. Oscilloscope uses your PC's sound card as an Analog-to-Digital Converter ADC to digitize any input waveform speech, music, electric signal, etc. Rate this link PC Soundcard Software Links - This page has links to many PC soundcard software, including waveform geenrators, oscilloscope and signal analyzing software.

With suitable software this allows a sound card to be used as a simple multimeter or oscilloscope that can measure also DC signals. There ideas described here sould be also adaptable to other sound card models as well. Rate this link Transmission line measurements There are applications where you need to measure long cable lines that are used as transmission lines for various signals.

There are many techniques related to transmission line measurements, because there are various factors that needs to be measured. Most commonly measured transmission line characteristics are the following: Part of the cable is buried under ground, some of it runs through walls and floors. You measure one end of the cable with an ohmmeter, and it reads about an ohm.

So the cable is shorted. Hoping for the best, you cut off the connector and measure just the cable. Still reads about an ohm, so the short is somewhere else along the cable. If you could locate the short, you could save a lot of time and money by repairing just that one spot, rather than pulling in a whole new cable.

TDR to the rescue! You can use Time Domain Reflectometry to look at the characteristic impedance along the entire length of the cable. Cables used to carry high frequency electrical signals are generally analysed as a form of Transmission Line. The Characteristic Impedance depends upon the ratio of the values of the capacitance per metre and inductance per metre.

To understand its meaning, consider a very long run of cable that stretches away towards infinity from a signal source. The result, when the signal power vanishes, never to be seen again, is that the cable behaves like a resistive load of an effective resistance set by the cable itself. This value is called the Characteristic Impedance, of the cable. Return loss RL is a measure of the reflected energy caused by impedance mismatches in the cabling system. Reflections create an unwanted disturbance signal or "noise" on the cabling link that potentially interferes with the reliable transmission over the link.

As a noise source, return loss is measured and evaluated to assure that the reflected signal energy is sufficiently small in reference to the transmitted signal such that the reliability of the transmission is not negatively impacted. Return loss is an important characteristic for any transmission line because it may be responsible for a significant noise component that hinders the ability of the receiver when the data is extracted from the signal.

It directly affects "jitter. Poor cable return loss can show cable manufacturing defects and installation defects cable damaged on installation. With a good quality coaxial cable in good condition you generally get better than dB return loss, and you should generally not got much worse than dB.

Return loss is especially important for applications that use simultaneous bidirectional transmission. Opens, shorts or less-severe impedance discontinuities have a way of showing up on cables in strange places - places you might never suspect. These can occur on coaxial transmission lines or twisted-pair lines.

Such opens, shorts or other impedance discontinuities are called faults. The location of faults cannot be determined with simple ohmmeters. Even the existence of certain faults cannot be determined with an ohmmeter. Time domain reflectomer is an instrument often used ot locate such faults. Time Domain Reflectometry measurements sometimes called Time Domain Spectroscopy techniques work by injecting a short duration fast rise time pulse into the cable under test.

The effect on the cable is measured with an oscilloscope. The injected pulse radiates down the cable and at the point where the cable ends some portion of the signal pulse is reflected back to the injection point. The amount of the reflected energy is a function of the condition at the end of the cable. If the cable is in an open condition the energy pulse reflected back is a significant portion of the injected signal in the same polarity as the injected pulse.

If the end of the cable is shorted to ground or to the return cable, the energy reflected is in the opposite polarity to the injected signal. If the end of the cable is terminated into a resistor with a value matching the characteristic impedance of the cable, all of the injected energy will be absorbed by the terminating resistor and no reflection will be generated.

Should the cable be terminated by some value different from the characteristic impedance of the cable the amount of energy reflected back to the cable start point would be the portion of the pulse not absorbed by the termination. Also any change in the cable impedance due to a connection, major kink or other problem will generate a reflection in addition to the reflection from the end of the cable.

By timing the delay between the original pulse and the reflection it is possible to discern the point on the cable length where an anomaly exists. The cable type governs this signal propagation speed. Other cable characteristics are usually easier to measure and can be done with more conventional instruments.

Cable conductor resistance can be measured in installed cable by shorting the cable on one end short center wire to shield on coax, short two wires in wire pair on twisted pair cable etc. Cable capacitance can be measured with a capacitance meter by leaving one end of the cable not connected anywhere all wired free and connecting the meter to the other end of the cable.

Cable insulation is typically measured with an insulation resistance meter. The cable is typically not connected anywhere or connected to equipment that do not cause error in anzac day 2016 shop trading hours qld and do not get damaged by measuring. Insulation resistance meter typically applies some quite high voltage DC V, V, V, V to the line between two wires and measure if there is any leakeage.

The leakage current is measured and the result is converted to resistance usually in megaohms to gigaohms range.

The measuring voltage needs to be selected based on the ratings of the wiring and equipment if such are connected. Low voltage telecom wiring and similar is typically tested with V or V voltage. Higher voltages westfield doncaster trading hours anzac day usually used when testing the insulation on the mains power carrying cables and some radio transmitter coaxial cable systems.

The measurin voltage needs to be right for the intended application. Too low voltage might not reveal insulation problems, but too high voltage can damage wiring and equipment connected to it. Line attenuation can be measured by connecting the signal source used in the application or test instrument generating suitable signal and signal receiver on other end receiving equipment or terminating resistor.

Then you just mesure the signal level on the transmitting and receiving ends using a suitable multimeter or oscilloscope or similar instrument. The difference on those tells how much the cable attenuates the signal.

In some applications you need to do measurement with different frequencies, recording how cable attenuates on different freuqncies. Some cable TV system measurements use a wideband noise source as the transmitter and a spectrum analyzer as the receiver difference on the signal spectrum on the transmitting and receiving ends tells the attenuation on different frequencies. Amount of noise coupled to the line is measured with the indended equipment or suitable line terminators connected to the ends of the cable.

If you use equipment they need to be turned off so that they do niot send anything to the line. Any signal that is now measured on the line is the amount of coupled noise.

Rate this link Measure open-circuited cables using a multimeter - You can use a multimeter with capacitance-measurement capability to measure the length of wire or cable to an open circuit. The capacitance of a pair of wires or a wire to a shield is directly proportional to the length of the wire.

If you know the capacitance per foot of wire, then you can calculate how far it is to the open circuit. What factors caused the 1929 stock market crash document includes good TDR trace example pictures. The cabling system needs to bemeasured after installation and the results of those measurementsshould be documented for later use.

Measurement is also exchange rate chf vs inr today use when cabling problems are suspected. The most common cable fault is easy way to get money in yoville open circuit, usually due toproblems close to or at the ends of the cables.

A simple ohm metertest generally suffices. For multiplair cables where make money enter yourname@yourkeywords ends are many wires inside, a simplemultimeter is bothersome. For those applications multi-pair cabletestes which find showrt circuits and broken wires are a good choise. In some application you need to measure the cable length.

Dependingon the cable characteristics you know and the measuremenet instrumentsyou have, you can use a multimeter resistance measurementRLC meter capacitance measurement. General information Application notes and published papers from Riserbond - Very many cable fault locating documents.

This method is sometimes impractical, however, because it cannot check for short circuits or you need to make very many test to measureresistance between very many wire combinations. To solvel thos problem on multi-conductor cables, there are specialcable testing trading hours e mini futures designed for this.

Cable tester is fast and cheap - This simple microcontroller based cable tester verifies the correct wiring of the cable, up to 8 conductor cables. Rate this link Simple method tests cables - Engineers have long known how to test a cable for continuity by simply connecting all conductors in series and checking with an ohmmeter.

This method is sometimes impractical, however, because it cannot check for short circuits. This simple method solves the short-circuit detection problem. Connecting LED indicators at each shorting loop provides a visual indication. The unit consists of an audible signal monitor for "listening" to the signals present in an electronic device such as an audio system, receiver, amplifier, or tape deck at circuit points inside these devices.

It also includes an RF detector vwap forex and signal generator. You need special tools and proceduresto successfuly and safely measure high voltages. A simple high voltage probe for a DMM or VOM may be constructed from a pair ofresistors.

This kind of devices are sold as ready made devices for example Tektronix, Agilent and Fluke sell those. Follow safety precautions when working around high voltages. Usually some form of equipment protection should be considered whenworking with high voltages. Higher voltages not only cannot be indicated, but will also destroy the instrument.

However, the range of any voltmeter can easily be extended using extra series resistance. Rate this banc de binary android app Electronic high voltage meters - Common voltmeters, digital or analog, usually range to some hundred volts maximum. Rate this link Frequency measurements Frequency counter is a necessary instrument to check that certain circuit operated at thr right frequency.

Frequency counter is an useful tool when you need to tune oscillators, measure some input signal frequency and when youplay with radio devices. Inexpensive frequency counters that will measure frequency well into the microwave range are available share price disparity in chinese stock markets the hobbyist today.

A frequency counter is an excellent means of accurately determining the frequency of unknown signals, or to see if an oscillator or a multiplier stage in a receiver or transmitter is working. However, one must watch out as what is really being measured and exactly what the counter is "seeing".

General information Frequency Counter Measurement Techniques - Inexpensive frequency counters that will measure frequency well into the microwave work from home jobs statesville nc are available to the hobbyist today.

Rate this link Frequency counter circuits Fr? Rate this link Prescaler circuits Prescalers are circuit which are used to extend the meausrement range of other frequency measuring circuits. If you have for example a frequency coutner which can count up 10 Mhz, then with suitable prescaler circuit you can extend the measurement range to higher frequencies. For example suitable 1: And prescaler with higher division factor will enable you to measure even higher frequencies.

It consists of just one IC, a TV tuner prescaler, the Philips SABA, which can divide by 64 or by The device sensitivity is about 10mV RMS over the range 70 - Mhz, and the output is typically 1V p-p. The input resistance varies from down to 30 Ohms, and the input capacitance, excluding the PCB, no more than 5pF.

Frequency to voltage converters are not usually as accurate as real frequency counter circuits, but they are still useful in many applications. Rate this link Idea for a car tachometer - A nifty trading holidays 2013 is simply a means of counting the engine revolutions of an automobile engine.

In this suggested idea a NE timer is configured as a monostable or one shot. The timer receives trigger pulses from the distributor points. Integration of the variable duty cycle by the meter movement produces a visible indication of the automobiles engine hdfc option trading charges. Rate this link Pulse period to voltage converter - This circuit converts a square wave input signal into a voltage proportional to the time between edges period of the signal, not the frequency, the range is from uS to to 10mS, which produces a voltage from mV to 10 volts.

Rate this link Frequency comparators Frequency comparator - This circuit uses a 74HCT74, 74HCT00, and a LM to form a frequency comparator.

A functional feature, retriggering, of a monostable, one-shot 74xx multivibrator can yield frequency discrimination.

This circuit is a frequency discriminator that determines the relation of input-pulse frequency to a reference frequency. It tells if the input frequency is above or below the reference frequency. Rate this link Time measurements Got the Time? Rate this link Time-tag impulses with zero-crossing circuit - A "constant-fraction discriminator" usually performs the time-tagging of impulsive events, which have a peaking time of the signal amplitude.

Rate this link Audio measurements Audio volume is the most commonly measured audio signal property. VU and dB meters both the best forex exit strategy the audio power involved in recording and they both use logarithmic scales to report that power. When measuring electrical signals the following is true: Breakout strategy forex trading is short for "volume units" and it is a measure of average audio power.

A VU meter responds relatively slowly and considers the sound volume over a period of time. A dB meter responds very rapidly and considers the audio power at each instant. When measuring electrical signals decibel is the difference or ratio between two signal levels; used to describe the effect of system devices on signal strength. A signal strength or power level; 0 dBm is defined as 1 mW japanese stock market nikkei of power into a terminating load.

When measuring audio signal power vibrations in air the following measurements are made: The decibel abbreviated dB is the unit used to measure the intensity of a sound. On the decibel scale, the smallest audible sound near total silence is 0 dB. A sound 10 times more powerful is 10 dB.

A sound times more powerful than near total silence is 20 dB. What does 0 dB mean? This level occurs when the measured intensity is equal to the reference level. In this case we have equation: Most typically harmonic distortion needs to be measured. Harmonic distortion describes a nonlinear property of systemswhere the output of the system has added energy at frequenciesthat are at integer multiples of the frequencies input to thesystem. The traditional technique is to input a single frequency F into the system under test, forex trading training in tamil take the output, apply a filter thateliminates F, and measure everything that's left over.

This is usually done with a twin-T, high-G notch filter centered on F. Nowadays computer techniques can be applied where a more detailed analysis can be made usually based on FFT methods where harmonic and non-harmonic componentscan be identified. Measuring audio music voltages on an AC voltmeter will give meaninglessresults as the voltmeter measures the forex education sinhala, over a fairly longintegrating time.

This means that the level indicated will depend totally onthe programme content of the CD being played. Most multimeters are designed for AC power line work and DC measurements, so perfomance up to Hz or little bit over it is enough. To make any meaningful measurement, you need to us a CD with single frequency tones, and, unless you know that the meter measures well at higher frequencies, keep to a low frequency, ideally 50Hz, but generally up to acouple of hundred Hz will be OK.

Most CD players give out 2 V AC from a fully modulated CD. Some of the "RMS" digital units might be useful ifthe frequency response is extended and flat enough. Money exchange rates canada usa multimeters vary in performance, so it is worth to pilling and co stockbrokers their performance on this even some cheap ones can perform accpetably on audio frequencies if a very good absolute accuracy is not needed.

It produces fantastic displays on three LED bars that can be individually adjusted for any particular frequency range. Rate this link ABX Double Blind Audio Tester - This project describes the construction of test equipment for double-blind or ABX testing of source components - preamplifiers, tuners, DACs etc. Double-blind and ABX tests do not allow the listener to know which component they are listening to, and furthermore don't allow the test controller to know either.

This guards against visual cues to the audience including body language. This feature is adequate to prevent clipping but does a poor job of reading the average automated forex trading algorithms, or loudness, level. A high-resolution, average- not peak- reading volume-unit meter produces an accurate reading of loudness. The design is unique in that it detects both stereo channels on a single peak-hold capacitor.

All the adjustments in the circuit simultaneously apply to both left and right stereo inputs. The output is suitable for driving a bar-graph display or for analog-to-digital conversion and display with a microprocessor. The circuit operates as a dual positive-peak-detector circuit.

If you do you will need a good signal tracer, a device capable of amplifing minute amounts of audio to a point where they can be "read out" on a pair of monitoring headphones. Such a gadget is shown in the accompanying schematic.

These components may develop excessive signal attenuation and losses, or poor isolation between inputs and outputs. These components can be tested using a RF signal source, termination resistors, and the Frequency Selective Voltmeter. Rate this link Power and field strength meters A field strength meter is perhaps the simplest piece of RF test newark cattle market co ltd that can be built.

Used for checking transmitters, antenna experimentation, and testing RF oscillators, field strength meters provide an indication of the presence of RF energy. They are generally not frequency sensitive and are useful where indication of a change in level is more important than the actual strength of the signal indicated. The meter works by converting any RF signal present at the antenna to a DC voltage.

This voltage drives a meter movement to give an indication of relative RF. Usually the meter includes a control to reduce its sensitivity where required. An RF field monitor - This is the oddest application of a neon glow lamp, that is used as a electromagnetic field detector.

In fact the trigger voltage of these lamps is a little bit lower in presence of a strong field. A UJT transistor and a transformer a common low power AC transformer are used to produce a high voltage of about Vac. This voltage is reduced by the trimmer to a value just below the trigger voltage of the lamp. In presence of a strong field the trigger voltage drops and the lamp lights. Rate this link 2. Beloq 1 GHz this proe has very flat response. Rate this link Clip-on RF Current Meter - Circuit description is in Japanese, but pictures and circuit diagram usable.

This is an useful tool for RF interference troubleshooting! For EMC investigations, you can also clip this meter on to coaxial cables, rotator cables and other wiring in your shack, to find out where the RF currents are flowing, and how big they are. Rate this link Designing RF Probes - An RF probe is used to directly measure the level of RF voltage present at a particular point and is one of the most useful test instrument in the hands of the home brewer.

It is normally used with a digital multi meter to indicate the voltage level as citigroup stock exchange symbol voltage which is equivalent to the RMS value of the RF voltage being measured. However, the level of RF voltage being measured provides useful information only when the probe has been designed for use with a specific multi meter.

The design of the RF probe is a function of the DC input resistance of the meter we intend to use with it. If a new meter with a different input resistance is used with the probe the reading will be inaccurate. Rate this link Field-Strength Meter - Simple circuit based on old issue of "73 Radio Electronics", changed a few components to get better sensitivity. Rate this link Field Strength Meter - This RF field strength meter use only few parts, a printed circuit board is moneymakeredge avis necessary; components can simply be soldered to one another.

Rate this link Field-Strength Meter I - This circuit is a electromagnetic field meter which can be used for meaturing of transmitters output power. Rate this link Field-Strength Meter II - This circuit is an electromagnetic field meter which can be used for meaturing of transmitters output power. Rate this link Field Strength Meter, VHF Band - This circuit measures radio field strength by converting the signal to DC and amplifying it.

This field strength meter was designed for VHF frequencies in the range 80 - MHz. Rate this link Funky Fresh?

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LED RF Signal Meter - a high quality RF signal meter based around the Analog Devices AD 0. This circuit uses the AD, a high-frequency true-power detector.

Rate this link N5FC's Ballpoint RF Probe - This is a small RF probe that connects to a multimeter. This one is used in conjunction with a high-impedance-input Voltmeter or Digital Voltmeter DVM. Rate this link N5FC's Classic RF Probe - The RF Probe is one of the handiest accessories you can have around the shack.

Using only 3 electronic components, it may rank as one of the simplest and cheapest homebrew projects. When used with a high-impedance DC Voltmeter, it can be used to measure RF voltage and powertrace RF signals in a new design, and troubleshoot malfunctioning RF circuits.

Rate this link RF Probe Up to UHF band - This circuit will read pretty close to the RMS value of the voltage. The RF detector circuit has built-in scaling to give approximate RMS readings for sine wave signals. The voltage marshal gethrforexception vb net will not be accurate, since this is a rectifier probe, but the measurements are good enough for you to be able to determine possible buyout stocks the RF stops, or if a stage is not giving the gain you think it should.

The unit is cheap and fairly basic, but perfectly adequate for its intended purpose. However, the output is not a pure sine wave. The unit covers a frequency range of KHz to 12MHz over five ranges shown below. It is therefore suited to the alignment of RF and IF sections of AM MW and LW sets, as well as the IF sections of FM VHF circuits. It may also be used for RF alignment of SW circuits from 25 to 49 metres. The output may be amplitude modulated by an internal Hz audio tone approx. The output level is adjustable in two ranges up to a maximum of about 4V pk-pk.

The unit is mains powered V AC. Rate this link Impedance measurements Couplers Couplers are passive devices used in cable systems to divide and combine radio frequency signals. Many RF systems use directional test points and non directional test points. Directional coupler separate inbound and outbound signals separately. A non-directional coupler allows the measuring technician to see both forward and reverse signals at the same time sum of them. This situation allows only one test point to be used for forward and reverse, but there is potential possibility for measuring errors due to reflections from the bad cable or passive.

Reflections can add or subtract to the actual levels. The non directional coupler is a device presenting a fairly high impedance to the circuit being measured, minimizing the loading effects.

Non-directional couplers are generally implemented as high forex converter yahoo towards the line resistive attenuation taps wired to the line.

They typically have quite high attenuation dB typical. Directional coupler is a perfect solutions work from home bangalore coupling device for separately sampling through a known coupling loss either the forward incident or the backward reflected wave in a transmission line.

A directional coupler may be used to sample either a forward or backward wave in a transmission line. A unidirectional coupler has available terminals or connections for sampling only one direction of transmission; a bidirectional coupler has available terminals for sampling both directions. Directional couplers are used in a wide variety of applications and can satisfy almost any requirement for sampling incident and reflected RF or microwave power conveniently and accurately with minimal disturbance to the transmission line.

Some general stock broker penny stocks for directional couplers include line monitoring, power measurements and load stock trading guide gta 5 isolators.

A directional coupler has at least three ports: The signal passes between line in and line out ports with loss referred to as the insertion loss.

How much money does a high school teacher make in ontario small portion of the signal power applied to the line in port passes to the tap port. A signal applied to the tap port is passed to the line in port less the tap attenuation value. The tap signals are isolated from the line out port to prevent reflections. A signal applied to the line out port passes to the line in port and is isolated from the tap port.

Building a Non Directional bi directional Coupler - A non directional coupler sees forward and reflected power at the same time, from either direction. A non directional coupler can be built from a common drop splitter provisions of companies act pertaining to buyback of shares directional coupler.

The tap output is attenuated by 30 dB. Rate this link Directional Coupler Those coupled lines are used to construct directional couplers. Generally, in design of directional couplers microstrip and stripline forms are used.

There are many kinds of directional couplers in different forms. The best theoretical performance available from a directional coupler, using ideal transformers, is a function of the turns ratio, and the terminating impedances. At VHF and UHF frequencies, wire gauge and core material can be chosen to closely approximate the response based on the solution of these equations. Rate this link Stripline Directional Coupler Software - This is a stripline design software written in Ansi-C.

The software comes in ascii-text and an X Windows interface using Motif. Rate this link RF Isolator Uses Differential Amplifiers - An RF isolator is a seemingly magic device that allows signals to pass in only one direction.

Signals applied to the input port are sent to the test port and signals coming into the test port can only go to the output port. This is an active RF isolator capable of handling signals approaching 16 dBm and frequencies from well below 1 MHz to above MHz. The circuit really emulates an isolator in that the actual signal energy is not passed from port to port and the signal levels must be fairly low. The circuit is well suited for testing the SWR of a variety of devices connected to the test port.

Rate this link RF spectrum analyzers A mong the many measurement tools sought by the amateur radio experimenter, the most desired - but generally considered the least accessible - is the radio-frequency spectrum analyzer. Spectrum Analyzer is intended for visual inspection of the spectrum of an investigated signal on the oscilloscope screen. The signal can be continuous or pulsed. A Spectrum Analyzer for the Radio Amateur - Here?

Now you can have it - without spending a fortune. A mong the many measurement tools sought by the amateur radio experimenter, the most desired - but generally considered the least accessible - is the radio-frequency spectrum analyzer or SA.

This need not be. Simple and easily duplicated, this homebuilt analyzer is capable of useful measure-ments in the 50 kHz to 70 MHz region. The design can be extended easily radio button selected jquery check the VHF and UHF region. This is an information package for those who want to homebrew a simple Spectrum Analyzer by using one ot more TV CATV tuners as a frontends.

Rate this link Look before you leap: Html set selected option javascript this link Microwave Spectrum Analyzer on a budget - A practical approach to microwave signal analysis for the home experimenter. Rate this link VCR and TV-tuners - This side will explain TUNER and Homebrew Spectrum Analyzer Project.

The need for standard values can be met by using one or the other. Attenuators with equal terminations have a minimum attenuation of 0 dB. Unequal terminations place a lower limit on the attenuation. Rate this link Adapters Matching 75 Ohms to 50 Ohms - The easiest way is to use resistors.

A two way matching network uses a It also includes an RF detector probe for use with HF modulated signals, such as those found on an antenna, RF amplifier, or IF section of a receiver.

Rate this link Radioacivity There are many defices to detect radio active radiation. Geiger counters are devices to detect and measure ionizing radiation, as emitted scotia itrade stock screener radioactive sources. The heart of descargar curso dominando forex geiger counter is rite aid stock price today Geiger-Mueller-Tube.

This is a gas filled tube, to which a voltage of several V is applied. Normally, the gas insulates and no current is drawn. When a radiation particle or quantum passes the tube, it triggers a gas discharge, i. The resulting current option clash for package inputenc lyx can be amplified and made visible or hearable "clicking".

Glas mantle tubes are only suitable for beta and gamma rays, as any alphas are absorbed in the glass. Window tubes have a window usually at one endwhich is sealed with a very thin foil or mica. Alphas can penetrate this window, and thus be detected, as well as betas and gammas. There are also diode based radioactive dosage meters in use.

Adding heat to a system causes its temperature to rise. While there is no maximum theoretically reachable temperature, there is a minimum temperature, known as absolute zero, at which all molecular motion stops. Temperatures are commonly measured in the Kelvin or Celsius scales, with Fahrenheit still in common use in the Unites States. There are many ways to measure temperature elecronically. A thermocouple is a very commonly used sensor for measuring temperature.

It consists of two dissimilar metals, joined together at one end, which produce a small unique voltage at a given temperature.

This voltage is measured and interpreted by a thermocouple thermometer. In practical applications the so called cold side of the junction is kept close to ambient temperature by bonding it to a temperature stable mass. The hot side of the junction is exposed to the temperature to be measured. Because thermocouples measure in wide temperature ranges and can be relatively rugged, they are very often used in industry.

Thermocouple is a A temperature sensing device made by joining two dissimilar metals. This junction produces an electrical voltage in proportion to the difference in temperature between the hot junction sensing junction and the leadwire connection to the instrument cold junction. In typical applications the the hot side is in the end of sensor wire and the cold juction in the temperature measurement device near the sensor connector.

In many cheap meters this cold junction is just in the same temperature as the meter itself, and it's temperature is measured in other means to compensate the effect of changes in cold php mysql select option example temperature. Thermocouple detectors have low impedance. Thermocouples are available in different combinations of metals or calibrations. The four most common calibrations are J, K, T and E.

Each calibration has a different temperature range and environment. Propably the most commonly used type is K-type thermocouple, which is a Ni-Cr-sensor very suiable for degress celsius temteperature measurements can be used from to celsius.

The accuracy of any circuit or system that uses a thermocouple to determine the temperature of a process is limited by the accuracy of the method used to perform cold-junction compensation. In a thermocouple measurement, two wires of dissimilar metal join together at the "hot," or measurement, junction.

The isothermal termination of the thermocouple wires provides a second "cold," or reference, junction. The potential across the thermocouple is proportional to the temperature difference between the two junctions. Thus, to determine the absolute temperature of the hot junction, you must also know the absolute temperature of the cold junction. Resistance Temperature Detector RTD is a sensor that uses the resistance temperature characteristic to measure temperature.

There are two basic types of RTDs: The wire RTD is a positive make money collecting email addresses coefficient sensor only, while the thermistor can have either a negative NTC or positive PTC temperature coefficient. A resistive thermal device RTD can measure temperatures as high as ?

C over a great distance and without expensive signal conditioning. The most popular RTD is a standardized platinum temperature sensor called the PT, which exhibits ohms resistance at 0? C and a linear temperature coefficient of 0. C characteristic appears almost linear over a narrow range. A PRTD's transfer function of resistance vs.

C, are approximated by the equation: Unlike thermocouples, which deliver voltages that represent the difference between two temperatures, the resistance of an RTD represents the absolute temperature of that resistance. Measurement is typically accomplished by driving a current of 1mA to 2mA through the sensor and measuring the voltage drop across it. Also semiconductors can be used as termperature sensors because semiconductor PN junction characteristics change when temperature changes.

This change is well defined and this can be used in some temperature measurement applications. The temperature - versus - bulk resistance characteristics of semiconductor materials allow the manufacture of fapturbo forex robot reviews temperature sensors using standard silicon semiconductor fabrication equipment.

The ordinary semiconductor diode may be used as a temperature sensor because a forward biased voltage across a silicon diode has a temperature coefficient of about the exact trade and audio signals for binary options. C and is reasonably linear. The forward basing can be done with for example around 1 mA current through the diode.

To improve the performance of the diode as a temperature sensor, two diode voltages can be measured with two different currents typically selected to be about 1: The transistor sensor is used in diode mode by connecting the base and collector together or sensor is wired between base and emitter.

Semiconductor temperature sensors are available from a number of manufacturers. There are no generic types. The semiconductor msn money earnings per share IC for integrated circuit temperature sensor is an electronic device fabricated in a similar way to other modern electronic semiconductor components such as microprocessors.

C typicallow cost, good accuracy if calibrated but also poor interchangeability. In general, the semiconductor temperature sensor is best suited for embedded applications - that is, for use within equipment.

This is because they tend to be electrically and mechanically more delicate than most other temperature sensor types. The "out of the box" or interchangeability accuracy of most semiconductor temperature sensors is not particularly good.

If individual sensors are calibrated, significantly better measurement accuracy is possible tyically a two point calibration or three point calibration is used. Due to the high sensitivity of some sensors, they can be very good in measuring small temperature changes as opposed to absolute measurement. Bimetallic thermometers are contact temperature sensors found in several forms what stocks are listed on nasdaq you know where to look, e.

They typically consist of a strip of bi-metal that has some electrical contacts affixed to it. The temperature changes cause the strip to bend, making or breaking the connection as needed.

You will often find long bimetallic strips coiled into spirals. This is the typical layout of a backyard dial thermometer. By coiling a very long strip it becomes much can you legitimately make money from home sensitive to small temperature changes.

In some applications temperature sensing needs to be done without contact to the measured subject. Those measurements use infrared IR techniques. Radiation Thermometers Pyrometers, if you will are non-contact temperature sensors that measure temperature from the amount of thermal electromagnetic radiation received from a spot on the object of measurement.

There are two types of commonly used sensors for this kind of applicatons: Pyroelectric Infrared Detectors and Thermopile detectors. Pyroelectric Infrared Detectors PIR convert the changes in incoming infrared light to electric signals.

The pyroelectric detectors output is proportional to rate of change of incident radiation. This means that pyroelectric detectors can only be used to detect temperature changes.

This kind of PIR sensors are used for example in movement detectors where they sense the moving hot object like human through special optics this optics makes the movement of hot object change the radiation that gets to sensor change sharply when object moves. Pyroelectric detectors have very high impedance requiring an internal impedance converting buffer to make them useable. Thermopile detector output is proportional to incident radiation.

A thermopile is a number of thermocouples connected in series. The so called cold side of the junction is kept close to ambient temperature by bonding it to a temperature stable mass. The hot side of the junction is exposed typing jobs from home without investment online incident radiation. Some thermopile the cattle market car park kingston have a built-in thermistor which provides measurement of the ambient temperature thus allowing the temperature of the target to be calculated.

A thermopile sensor generates a voltage, which is proportional to the incident infrared IR radiation power. Because every object emits IR radiation with a power, which is a strict function of its temperature, one can deduct the object? This method is called pyrometry. Thermopile-type infrared and thermal detectors are used in a number of applications, including infrared spectroscopy, radiometry, security systems, and many consumer products. Although they do not provide vision-quality images as in the case of quantum detectors, thermopiles are still attractive for many low-cost commercial and industrial applications, mainly because they do not need cooling for operation and the technologies are relativly simple.

Thermopile detectors have low impedance. In addition to those some applications use Thermal Infrared imaging camera. Thermal Infrared imaging camera is a camera that responds to the infrared signals instead of normal light. Thermal infrared imaging cameras are detector and precision optics platforms that give us a visual representation of infrared energy emitted by all objects.

Typical applications for this type of cameras are night vision,wildlife observation, search and rescue, victim location, wild fire recon, predictive maintenance in power transmission and machinery, carona detection, process control and printed Circuit Board evaluation. Depending the applications the IR radiation can be shown as normal grayscale video or through real time color infrared output. The color conversion converts different radiation intensities to different colors for easy visual inspection of picture.

With a well calibrated camera, those different colors on picture can be directly mapped to different temperatures.

Thermal infrared imaging cameras are expensive devices bceause they need special imaging sensors that needs to be cooled down to download bop money makes the world go round them operate correctly. This is the Seebeck Effect, discovered by Thomas Seebeck in The effect is multiplied when there are a number of junctions in series in the circuit, with alternate junctions in close thermal contact with each other.

The Differential Thermopile was invented by Macedonio Mellonian Italian physicist who worked in France and Italy. Schematics, mounting instructions and step-by-step instructions included. Rate this link ECEFast Technical Papers - A selection of temperature measurement information document platinum resistance temperature detectors, thermocouple fundamentals, noncontact thermometers and infrared systems.

Also information on water characteristics measurement conductivity, exygen, pH. This technique is a very good way to detect the temperature of a person's eardrum. Rate this link International Thermocouple Colour Codes: Rate this link Measuring temperatures on computer chips with speed and accuracy-a new approach using silicon sensors and off-chip processing - Silicon sensors are becoming increasingly important transducers in electronic systems.

As systems become more complex, more compact, and denser-and run faster and hotter-it becomes increasingly vital to monitor critical temperatures. Traditional sensor techniques, such as thermocouples, thermistors, and RTDs, are now being displaced by silicon sensors, with their ease of integration and use.

Silicon sensors, on the other hand, are linear, accurate, low-cost, and can be integrated on the same IC as amplifiers and any other required processing functions. The actual sensing element in a silicon sensor is a simple P-N transistor junction. C and this fact may be used to develop a temperature measuring system.

Rate this link Omega Technial Reference Section - Lots of technical documents on temperature measurement sensors. Rate this link Practical Temperature Measurements - This short document compares thermocouple, RTD, thermistor and IC sensor technologies. Rate this link Pyroelectric detectors - Pyroelectric Infrared Detectors PIR convert the changes in incoming infrared light to electric signals.

Rate this link Remote diodes yield accurate temperature measurements - All of today's PC designs require thermal management.

Heat generation is a problem for PC-system designers. To prevent failures, you must incorporate thermal-management features in your design. You can control temperatures by, for example, lowering device voltages and reducing clock rates so that devices generate less heat, or by increasing airflow so that the system can better dissipate heat into its environment. Because die temperature is a critical parameter, some devices incorporate a means to allow you to measure it.

It is aimed at engineer, student, scientist, and technologist alike. Rate this link Temperatures. Rate this link Thermocouples Introduction - The Thermocouple is a thermoelectric temperature sensor which consists of two dissimilar metallic wires, e.

These two wires are connected at two different junctions, one for temperature measurement and the other for reference. Rate this link Track multisite temperatures on your PC - This low-cost circuit allows you to track four remote temperatures with thermistor sensors through the parallel port on your PC. C and a resolution of better than?

VBE for a bipolar transistor is a linear function of the absolute Kelvin temperature, T. You can use this truism to make accurate temperature measurements. Rate this link Circuit provides accurate RTD measurements - This circuit is an efficient measuring circuit for PT RTD elements. The circuit provides analogue voltage output. Rate this link mA Loop Powered Temperature Sensor - A simple circuit that allows a mA to power an analog temperature sensor.

Rate this link A precision interface for a Resistance Temperature Detector RTD - Resistance Temperature Detectors RTDs are temperature sensors that make use of the temperature dependence of a metal's resistance. They are used in a wide variety of temperature measurement and control instrumentation. It was originally set up for logging temperatures from the Dallas Semiconductor One Wire Weather Station and up to 20 additional DS18S20 One-Wire Thermometers.

It has since evolved to also read one Dallas Semiconductor One Wire Rain Gauge and Dallas Semiconductor One Wire Humidity Sensors. Rate this link Digital Remote Thermometer - Remote sensor sends data via mains supply, temperature range The Dallas Semiconductor DS digital thermometer allows measurement resolution as fine as 0. C in digital form and with linear response. The accuracy specification is only 2? C, but you can improve this figure by careful calibration.

Rate this link Qiozl's Temperature Sensor Project - Just a handful of components builds an 8-pin microcontroller based circuit for temperature logging via a serial port; small, fast, and acceptably accurate. The circuit monitors the temperature of the pc board and the die temperature of a CPU, an FPGA, or another IC with an on-chip temperature-sensing transistor.

But most thermistors' resistance-versus-temperature characteristics are highly nonlinear and need correction for applications that require a linear response. Using a thermistor as a sensor, the simple circuit presented in this article provides a time period varying linearly with temperature with a nonlinearity error of less than 0.

You can use a frequency counter to convert the period into a digital output. Rate this link Simplify Isolated Temperature Sensing With Single Wire Sensors - Many temperature sensing applications require galvanic isolation of the sensor.

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Fortunately, several low-cost temperature-sensing integrated circuits ICs are easy to isolate. This application note shows two approaches to isolating temperature sensors. Rate this link Selecting temperature sensors Temperature Sensor ICs Simplify Designs - When you set out to select a temperature sensor, you are no longer limited to either an analog-output or a digital-output device. There is now a broad selection of sensor types, one of which should match your system's needs.

Rate this link Tradeoffs in Selecting IC Temperature Sensors - A discussion of IC temperature sensors has become timely and important because electronic systems are increasingly dense, power-hungry, and hot. Temperature sensors also have a lot of gadget appeal.

Many ICs perform highly abstract functions. Included are seven segment decoders, display drivers, a reference, and a clock. The ICL is designed to interface with a liquid crystal display LCD and includes a multiplexed backplane drive; the ICL will directly drive an instrument size light emitting diode LED display. It contains an internal voltage reference, high isolation analog switches, sequential control logic, and the display drivers. The auto-zero adjust ensures zero reading for 0 volts input.

This how this circuit uses that IC to make a voltage meter. Rate this link Digital Volt meter with video output - This design awarded the third international prize in the Elektor Electronics Microprocessor and Microcontrollers Design Contest.

Rate this link Circuit yields accurate absolute values - This circuit delivers the absolute value of the input signal with an accuracy better than 10 ppm of the full-scale range. This technique usually works well unless your design requires operation higher than a few kilohertz. In designs requiring such operation, the accuracy of the circuit severely deteriorates unless at least one of the amplifiers has a high slew rate and frequency response extending to tens or even hundreds of megahertz.

This circuit uses a moderately fast, inexpensive comparator instead of a high-slew-rate op amp to implement the peak detector. This circuit provides wide bandwidth and high accuracy without the use of precision components, and it's simple and inexpensive.

It is not an "Average" voltage and its mathematical relationship to peak voltage varies depending on the type of waveform. By definition, RMS Value, also called the effective or heating value of AC, is equivalent to a DC voltage that would provide the same amount of heat generation in a resistor as the AC voltage would if applied to that same resistor.

True RMS allows the user to obtain accurate measurements of voltage at any waveform. True RMS meter work for non-sinusoidal AC voltage and current waveform found in controls and circuits. A True RMS meter uses a complex RMS converter to read RMS for any type of AC waveform. Normally True RMS reading meters are very expensive. The typical multi-meter is not a True RMS reading meter.

It does this by measuring average voltage and multiplying by 1. Trying to use this type of meter with any waveform other than a sine wave will result in erroneous RMS readings. Improper measurement can easily lead someone to believe that a modified sinewave or square wave inverter is not putting out its rated power.

A few handy things to keep in mind about RMS values that apply when dealing with a sine wave, are as follows: Peak Volts AC x. As a result it will only produce misleading voltage readings when trying to measure anything other than a DC signal or sine wave.

This will be indicated by a flashing light-emitting diode LED. This circuit is based on two LEDs and one lamp. Due to the lamp's filament behaviour, any voltage in the 1. For those high voltage, special techniques and probes are needed. Electronic high voltage meters - Common voltmeters, digital or analog, usually range to some hundred volts maximum. Rate this link Measuring high voltages by spark length - The simplest way to get at least a rough value of tension is to measure the maximum distance the voltage can arc over.

The maximum spark length is determined by applying the high voltage to a pair of electrodes and bringing the electrodes closer to each other until a spark jumps over. Rate this link Current measurements Measuring electrical current can be done using many methods. There are three rival technologies that are typically used for measuring current: Each have attributes that differentiate them on a cost versus performance scale. A general characteristics of different current measurement methods: The voltage drop over thisresistor is determined by the current and the resistor value.

If you select a small resistence, you do not cause much voltage drop over it, so measung does not considerably affectthe measured circuit. When measuring high currents on mains power cables devices called "current transformers" are used. Their main purpose is to produce, from the primary current, a proportional secondary current that can easily be measured or used to control various circuits. The primary winding is connected in series with the source current to be measured, while the secondary winding is normally connected to a meter, relay, or a burden resistor to develop a low level voltage that is amplified for control purposes.

When using just one wire going through the core, that wire can easily made thick enough to be able to handle large currents. Current transformers are relatively simple to implement and are passive devicesthat do not require driving circuitry to operate. The primary current AC will generate a magnetic field that is coupled into a secondary coil by Faraday's Law. The magnitude of the secondary current is proportional to the number of turns in the coil, which is typically as high as turns or even more.

The secondary current is then sensed through a sense resistor to convert the output into a voltage. The voltage measured over selected burden resistor resistor connected between the current transformer output coil outputs gives the indicationof the current voltage directly proportional to the current.

The selected burden resistor value is usually defined with help of transformer data and experimenting. When a suitable burden resistor value is selected, a general experimental transformation ratio is calculated for thisapplication ratio from input current to output voltage with given current transformer and burden resistor.

When using current transformers on high current circuits, make sure that the current transformer is never run without a proper burden resistor. If there is a high current going on transformer primary and many turns on secondary, the open circuit voltage of current transformer can become very high, even to several kilovolts range that can cause operation danger and damage the current transformer secondary insulation.

In current transformer applications where the measuring equipment needs to be service, the output of current transformer should be short circuited before removing the burden resistor load. In some SMPS designs current transformer usually made using a ferrite toroid helps to track the current in the control circuit's feedback loop.

This current is then used to determine how the future behavior of the SMPS will be modified. Many clamp-on multimeters and clamp-on current measuring adapters that can measure AC current are built as current transformers. A simple current adaptor can only consist of the transformer core which can be openedthe transformer secondary coil and suitable burden resistor. Some clamp-on multimeters can also measure DC currents. The hall sensor in the air gap measures the magnetic field cause by the wire running through the toroidal core.

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There are two techniques for sensing current using Hall effect devices: In an open loop topology, the Hall element output is simply amplified and the output is read as a voltage that represents the measured current through a scaling.

In a closed loop topology, the output of the Hall element drives a secondary coil that will generate a magnetic field to cancel the primary current field. The secondary current, scaled proportional to the primary current by the secondary coil ratio, can then be measured as voltage across a sense resistor. By keeping the resultant field at zero, the errors associated with offset drift, sensitivity drift and saturation of the magnetic core will also be effectively canceled. Closed-loop Hall effect current sensors also provide the fastest response times.

However, with a secondary coil that may be needed to drive up to several milli-amps of current, power consumption is much higher in closed loop Hall effect devices than open loop topologies. Current clamp meters and clamp adapters are especially suited to measure DC and AC currents, in all instruments and systems, without interruption of the circuit.

In practice there are many systems where it is not possible or safe to disconnect systems for the purpose of measuring the current flowing. Therefore, with the use of a Clamp Meter the current can be measured without any interruption whatsoever. Generally clamp-on multimeters need the toroidal type core to be closed to get measurements. Lately there has become available "open jaw" style Electrical Tester for measuring current using measurement device which does not need the fully closed core. Clamps and clamp adapters are easy to use.

The conductor is completely surrounded by the current clamp. The measurement value appears on the analogue or digital display and can be read immediately. Most cheap clamp meters are designed to measure the current value of current that have sinewave shape. More sophisticated circuitry is required for measuring the True RMS value of AC or currents with complex waveforms. The RMS value is important for all non-sinus shaped currents, e. Generally, the measurement value displayed on conventional clamps is smaller than the actual measurement current present when the waveform is non-sinusoidal.

Clamp-on nmultimeters are typically designed to measure currents in range from few amperes to several hundred amperes some meter go beyond A. The cheapest clamp-on meters have measuring resolution of around mA. There are more expensive meters that have higher resolution like 10 mA or 1 mA suitable to measure for example current industrial mA current loops.

High resolution mini current clamps for leakage currents from 10? Leakage currents which do not return via an electrical conductor e. N, PE can be quickly, easily and safely measured by surrounding all active conductors e.

L1, L2, L3, N or L1, N. With traditional clamp-on current meters, measurements can only be made on single conductors.

If you need to measure current in multipair cables for example mains cablesthis usually needs covers to be moved to gain access to individual wires. To measure the current consumption of an instrument, the individual wires of a cable had to be opened using e.

From the safety aspect, this procedure was not without problems and relatively difficult to perform. Some new special multimeters can measures current in multi-core cables and power cords without the need to split them.

This kind of multimeter use techologies which are called dending on manufacturer with names like Flexiclamp, multi-core digital clampmeter, duplex clamp and SMF Technology. Different manufacturers use slightly different technologies. Unitest uses in their duplex clamp technology that has several sensor coils are positioned at a certain distance and direction.

With this coil layout, the field direction of the current within a lead can be filtered with respect to the neighbouring lead. Thus, current measurement within a multi-lead cable is possible, without opening. A new technology for AC current measuring is Rogowski coil.

Rogowski coil current transducers can measure alternating currents in a frequency range from less than 0. Their measurement range is impressive ranging from a few milliamps to over 1 million amps. These transducers have an excellent transient response capability and they can be used for measurements on very large or unusually-shaped conductors.

A Rogowski coil is an 'air-cored' toroidal coil placed round the conductor. The alternating magnetic field produced by the current induces a voltage in the coil which is proportional to the rate of change of current. The combination of a coil and an integrator provides an exceptionally versatile current-measuring system which can be designed to accommodate a vast range of frequencies, current levels and conductor sizes. The output is independent of frequency, has an accurate phase response and can measure complex current waveforms and transients.

One of the most important properties of a Rogowski coil measuring system is that it is inherently linear. The coil contains no saturable components and the output increases linearly in proportion to current right up to the operating limit determined by voltage breakdown. The integrator is also inherently linear up to the point where the electronics saturates.

Linearity makes Rogowski coils easy to calibrate because a transducer can be calibrated at any convenient current level and the calibration will be accurate for all currents including very large ones.

Also, because of their linearity, the transducers have a very wide dynamic range and an excellent transient response. Some designs of coil can be fitted on the conductor without the need to disconnect the conductor. Most flexible coils can be fitted this way and it is also possible to build split rigid coils. When measuring current on mains wires please note that most AC current meters are designed to give right current ratings only when they are connected to pure sinusoidal mains current.

Pulse-width motor control systems, SCR and triac controllers and switchmode power supplies, for example, add high frequency HF components to the 50Hz mains that can cause false readings on traditional multimeters. Instruments with True RMS employ circuitry that rejects the HF signals and correctly calculate and display the RMS value. Solar Panel Current Meter - This circuit is used to measure the current from a solar panel. It has very low power loss for currents in the A range.

It also works as a general purpose DC current meter. The circuit can be used on either the positive or negative side of a DC circuit. The circuit works with DC circuits at any practical voltage. Rate this link Real Time Rotor Bar Current Measurements Using a Rogowski Coil Transmitted Using Wireless Technology - Rotor bar current measurement is a valuable step in verifying the theory of electrical machines design and control.

Rate this link AC Line Current Detector - This circuit will detect AC line currents of about mA or more without making any electrical connections to the line. The coil output voltage is integrated electronically so that the output from the integrator is a voltage that accurately reproduces the current waveform of the wire going through the coil.

This document describes both open loop and closed loop Hall current sensors operation. Rate this link Measure power-on current transients on ac line - For any electronic or electrical system, you usually determine the ac-line fuse rating based on the steady-state current. However, the power-on current surge is an important parameter in determining the fuse's I 2 t rating.

The I 2 t rating is a measure of the energy required to blow a fuse in pulsed conditions. Rate this link Picoammeter circuit with 4 ranges - This circuit uses a CA BiMOS op amp to form a picoammeter with 4 ranges and exceptionally low input current typically 0.

The probe is "clamped" around the current carrying conductor to perform non contact current measurement. This technology allows "open jaw" and "multi-core digital clampmeter". The key to the performance of this new sensor is a series of planer magnetic coils placed in a specified layout around the conductor.

The magnetic field created by the current in the conductor induces a voltage in the magnetic coils, which is proportional to the magnetic field of the conductor.

Rate this link Current Transformer Measurements - This document has information on Current Error ratio errorPhase Angle error and Basic Calibration Circuits.

Rate this link Field Adjustment of Current Transformer Ratio - The ratio of current transformers can be field adjusted to fulfill the needs of the application. Passing more secondary turns or more primary turns through the window will increase or decrease the turns ratio. Rate this link Selecting ANSI Class Metering Current Transformers - One of the most common uses of current transformers are in metering and power usage, where a 5 Amp secondary current transformer is applied to a panel meter or a power meter for displaying amperage or recording power.

When extremely accurate measurement is required, or when revenue is generated from a power meter, ANSI class current transformers are generally selected.

Rate this link Precision Rectifier Circuit for CT Signal Conditioning - Many times, the designer wishes to generate a DC signal from an AC current transformer for input to a PLC or data acquisition system, or even as part of a current or motor controller. Creating DC from an AC source creates problems with diode voltage drops and the variances over temperature and current. This circuit provides an accurate method for creating this DC signal.

Rate this link Low Cost Fan Control with Hysteresis - This application can be used to control many different devices. In this example, a compressor current is sensed, and when it reaches a selected set point, the circuit turns on a relay, which controls a fan motor.

The circuit is generated with a minimum number of parts, and includes hysteresis. Rate this link An Analysis of Current Transformer Ratio and Phase Angle Error - A technical discussion of the current transformers including equivalent circuits, phasor diagrams and Thevenin equivalents. Rate this link Application Guide - A general application guide that covers most areas of electrical current monitoring using current and voltage transformers.

The primary purpose of this guide is to give the reader a basic understanding of how to apply instrument transformers in a practical way while observing good engineering practice. A special effort will be made to keep to a minimum technical terms and language.

Rate this link Practical Aspects of Rogowski Current Transducer Performance - This paper examines the frequency response for a 10MHz bandwidth Rogowski transducer. The transducer was tested with currents from a tuned LC circuit for frequencies between 0. The current sensing requirement is a more difficult problem.

Not only does the current sensor require a wider measurement dynamic range, it also needs to handle a wider frequency range because of the rich harmonic contents in the current waveform.

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Rate this link High-Precision Rogowski Coils for Improved Relay Protection, Control and Measurements - Rogowski coils were first introduced to measure magnetic fields. They could not be used for current measurements because coil output voltage and power were not sufficient to drive measuring equipment. Rogowski coils have many advantages over conventional current transformers.

Rate this link How Do Rogowski Coils Work? Rate this link Using Rogowski coils for transient current measurements - In recent years the Rogowski-coil method of measuring electric current has developed from a "laboratory curiosity" to a versatile measuring system with many applications throughout industry and in research.

The technique possesses many features which offer an advantage over iron-cored current measuring devices and these are well illustrated by considering how it can be used for measuring transient currents The paper describes the principle of operation of Rogowski coils and the practical aspects of using them and gives several examples of their use in making transient measurements.

But metering technologies have been the Cinderellas of energy infrastructure - they work hard as cash registers for the utilities, using electromechanical designs which have altered little for the past 30 years.

However, the utility market is changing, and as the cost of digital microelectronic devices comes down, the opportunities offered by solid-state meters are looking increasingly attractive for more intelligent metering systems. Rate this link Rogowski Loop Designs for NSTX - The Rogowski Loop is one of the most important diagnostics from a plasma current measurement and control aspect of tokamak operation.

On the National Spherical Torus Experiment NSTXthe plasma current Rogowski Loop had the constraints of the very limited space available on the center stack, volt isolation and flexibility requirements.

This paper tells about the coil design.

Rate this link Sensor Design for Leakage Current Measurement on ADSS Fiber-Optic Cable - All-Dielectric-Self-Supporting ADSS fiber-optic cables are installed on high voltage transmission lines for communication purposes. When the cables become polluted and wet, a conductive layer is formed on the cables, and leakage currents are induced on their leading to dry-band arcing.

Knowledge of the leakage current levels on the cable surface before dry-band arcing can be used to predict cable failure. Monitoring the leakage current can also yield information on the aging of the cable. This paper presents a review of three different current sensors that can be used on ADSS cables, which include a simple shunt resistor, an active Rogowski coil, and a double core sensor.

Rate this link Rogowski Coils - Rogowski coils are used for measuring alternating current. They work by sensing the magnetic field caused by the current without the need to make an electrical contact with the conductor. These coils have been used in various forms for detecting and measuring electric currents for decades but it is only in recent years that their potential is being realised on a commercial scale. By using the right technique it is now possible to wind both flexible and solid coils with sufficient uniformity for them to be used in a wide range of applications including those demanding precision measurements.

Rate this link Current sensing for energy metering - All energy meters contain advantages comparing with the other current sensing solutions. This is a general introduction to the current measuring topics. Rate this link Current measurement with electrical isolation - The principal advantage of using current transformers to measure current in electric circuits is that the measurement circuit can be electrically isolated from the circuit under test.

Isolation can be a particular benefit where high voltages are present. Current transformers impose a negligible burden on the circuit under investigation and their use has an insignificant effect on the performance of the circuits examined.

They are passive devices. Rate this link Rogowski Coils and Current Transformers - There is considerable confusion over various forms of Rogowski coils and current transformers CTs. In fact the devices are closely related. Both of them are used to measure or detect currents by mutual coupling the primary circuit to the secondary circuit. The Rogowski coil, rfct Rogowski coil and a CT are all basically the same device. When it operates to low impedance it is a RFCT Rogowski coil or a conventional CT.

The terminating impedance controls the frequency where the device changes from a Rogowski coil to current transformer.

Rogowski coils tend to be air cored devices and current transformers tend to have magnetic material cores laminated iron or ferritebut this is by no means certain as it is possible to design air cored CT's and magnetic cored Rogowski coils.

Rate this link Electrical power measurements Measuring power is useful when you want to know how many wattscertain electronic device takes power. If the device is powered from DC voltage, determinign the power iseasy: Measuring AC power is harder. If you just measure the current and voltage with two multimeters, you will get the currentand voltage values.

The real poweris the sum of those calculations. This more complexpower measurement method works also for non-sine waveforms. Power meters provide an early warning of thermal overload by monitoring power consumption in high-reliability systems. Power monitoring is especially suitable for motor controllers, industrial heating systems, and other systems in which the load voltage and current are both variable.

Rate this link Resistance measurements The two instruments most commonly used to check the continuity a complete circuitor to measure the resistance of a circuit or circuit element, are the ohm meter and the megohm meter. The ohmmeter is widely used to measure resistance and check the continuity of electrical circuits and devices.

Typical ohmmeter range usually extends to only a few megohms. When hugher resistances need to be tested, megaohm meter is is used for this. There are two basic methods of measuring resistance. One is to apply a known voltage to the unknown and measure the current. The other is to apply a known current and measure the voltage. Both of those methods are used in different resistance measurement instruments.

When you use your ohmmeter to measure the resistance of a wire you touch one meter lead to each end of the wire and you get a resistance measurment. Your ohmmeter forces a current through the wire, measures the voltage that develops, calculates the resistance, and displays the result. To do all this your ohmmeter must have a current source and volt meter.

A basic analogue ohmmeter typically consists of a dc ammeter, a dc source of potential usually a 3-volt battery and few resistors. Digital multimeters generally measure resistance by applying a known current to the resistor and measuring the voltage drop over it directly proportional to the resistance value. The measuring current can vary between different ranges measuring current is usually few milliamperes or less, but can be higher on some low resistance measuring ranges.

When you make a 2-wire resistance measurement with your multimeter your meter uses only two leads to connect to the device under test. This setup has the advantage of using just two wires to connect to the DUT but what is the actual resistance it's measuring?

Two-wire measurements actually measure the DUT resistance plus the test lead resistance plus contact resistance. You will find that the resistance varies depending on how hard you hold your lest leads to the wire ends. This variation in resistance comes from the point of contact between the device under test and your multimeter measuring lead contacts. This resistance variation from measurement to measurement can add significantly to a learned resistance and will get worse as the mating connectors wear.

When resistors have considerable resistance and the resistance of measuring wires are quite low, things work accurately enough with two wire method. The Two-wire technique is typically used in automotive wiring, computer cables and other low specification applications to merely verify that an item is wired correctly and not to verify the integrity or performance of a cable.

The methods descrubed above are good for measuring resistances that are few ohms or higher, but when measuring very small resistance values, those methods with two measuring wires have their weaknesses. When making resistance measurements for resistances below 1 ohm, the resistance of the multimeter measuring leads plus the resistances on the contacts banana contacts to multimeter plus contacts to item being measured can be so high that they cause easily considerable error to resistance readings those contact resistances can vary easily quite much over time.

Some ohmmeters have four connections to overcome the limitations of two wire system. In four wire measuring system two wires come from the current source sometimes called the "force" leadsand two other come from the voltmeter usually called the "sense" leads. Four wire measurement using the Kelvin Clip reduces the IR drop in test leads that can cause measurement inaccuracies. With four connections you choose where to connect the voltmeter so you are in control over exactly what resistance you want to measure, and the resistances on the wires and connections do not cause considerable error.

The 4-wire testing eliminates the resistance of your interface cabling, which will will greatly improve accuracy if your measuring cable plus contacts resistance is a significant part of the total resistance.

It allows you to measure lower resistance values than 2-wire testing with for example with 1A measuring current you can measure up to milliohms range with soem instruments, one milliom resistance will then show 1 mV voltage. The disadvantage of 4-wire testing is it takes four connections to do the test but it does give you an accurate resistance measurement of the DUT without the resistance of the test leads.

Many continuity testers require 4-wire testing to accurately measure resistances under 1 ohm. The Four-wire measurement technique is found in some higher specification ATE, more commonly known as Kelvin measurement. When measuring low resistance measurements using the four-wire technique the test lead or test interface wiring will be automatically nulled out.

Most Aerospace and Defence companies have adopted the Four-wire continuity measurement technique as the industry standard, because many of the cables being tested in the aerospace sector are of very low resistance and they need to be measured accurately. Different techniques also come into use when very high resistance values are needed to be measured. The megger is a special instrument that is widely used for measuring insulation resistance, such as between a wire and the outer surface of the insulation, and insulation resistance of cables and insulators.

The range of a megger may extend to more than megohms. Megger has the same operation principle, but it generally uses a much higher measurement voltage, typicallyor volts DC. Those high voltage ranges are often used to test the quality of the insulation in electrical cables and equipments safety checks. The output is using two LEDs. Test in this circuit is in Finnish. This document is in pdf format.

Rate this link Latching Continuity Tester - A continuity tester is a must on every service bench for testing cables, pcboards, switches, motors, plugs, jacks, relays, and many other kinds of components. But there are times when a simple continuity test or your multi-meter doesn't tell the whole story. For example, vibration-induced problems in automobile wiring can be extremely difficult to detect because a short or open is not maintained long enough for a non-latching tester to respond.

This Latching Continuity Tester can help you locate those difficult-to-find intermittent short and opens that other testers always seem to miss.

This circuit uses four-wire measurement technique to make more accurate measurements. Rate this link Megger - The megger is a portable instrument used to measure insulation resistance. The megger consists of a hand-driven DC generator and a direct reading ohm meter. A simplified circuit diagram of the instrument is shown in this document. The right circuit topology makes it possible to eliminate most error terms while measuring ohms, leaving the accuracy to be determined by just a single reference resistor.

Rate this link 4-Wire "Kelvin" Testing - If you've used an ohmmeter to make resistance measurements you've probably heard terms such as "2-wire measurement" and "4-wire kelvin measurement. As the connection between a probe and the track surface can easily reach or exceed the track resistance, certain techniques and precautions must be observed in making the measurement. These will involve the use of a "Four Terminal" or "Kelvin Sensing" ohm meter. These circuits are based on using a ohm Platinum RTD PRTDversions of which are readily available from many sources.

Rate this link Insulation testing The importance of sound electrical insulation systems has been acknowledged from the early days of electricity. Insulation failure can cause electrical shocks, creating a real hazard to personnel and machinery. Insulation testing is a common requirement as part of UK, European and International standards.