Measuring and testing

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This item came up and I ordered it thinking I was ordering snack-pak size sacks. This simple method solves the short-circuit detection problem. The probe is "clamped" around the current carrying conductor to perform non contact current measurement. To prevent failures, you must incorporate thermal-management features in your design. As far as for snacks, these are horrible. If you select a small resistence, you do not cause much voltage drop over it, so measung does not considerably affectthe measured circuit.

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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 measurement 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 are 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. This 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 usefulduring use when cabling problems are suspected. The most common cable fault is an open circuit, usually due toproblems close to or at the ends of the cables. A simple ohm metertest generally suffices.

For multiplair cables where cable 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 measurement , RLC 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 instuments 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 probe and signal generator. You need special tools and proceduresto successfuly and safely measure high voltages. 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 link 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 to 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 range 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. 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 tachometer 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 speed. 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.

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 measure the audio power involved in recording and they both use logarithmic scales to report that power. When measuring electrical signals the following is true: VU 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 milliWatt 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, then 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 average, 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.

Some of the "RMS" digital units might be useful ifthe frequency response is extended and flat enough. The multimeters vary in performance, so it is worth to check 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.

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 volume, 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 equipment 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. 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 dc 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 not 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 Funky Fresh? This circuit uses the AD, a high-frequency true-power detector. 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 power , trace RF signals in a new design, and troubleshoot malfunctioning RF circuits. The voltage shown will not be accurate, since this is a rectifier probe, but the measurements are good enough for you to be able to determine where 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 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 impedance towards the line resistive attenuation taps wired to the line. They typically have quite high attenuation dB typical. Directional coupler is a transmission 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 applications for directional couplers include line monitoring, power measurements and load source 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. A 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 or 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. The software comes in ascii-text and an X Windows interface using Motif.

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. 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. 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. Rate this link Look before you leap: Rate this link Microwave Spectrum Analyzer on a budget - A practical approach to microwave signal analysis for the home experimenter. 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. A two way matching network uses a 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 by radioactive sources. The heart of a geiger counter is the 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 impulse 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 end , which 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 junction 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: 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 simple 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 2. 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 or 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 typical , low 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 if 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 more 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 to incident radiation. Some thermopile sensors 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 make 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. 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 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. The circuit provides analogue voltage output.

They are used in a wide variety of temperature measurement and control instrumentation. 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. 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. 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. 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. 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 opened , the 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.

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.

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