Progettazione e Costruzione Apparecchiature Elettroniche



DESIGN IDEA

General information

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 for available 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.

Oscilloscopes are intended to be operated with their chassis at ground potential. 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.

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

Digital oscilloscopes are digital versions of that analogue instruments. Digital oscilloscopes sample signals using a fast analog-to-digital converter (ADC). The digitized signals are sotred to the scope memory and shown on the scope screen or at computer screen. The benefit of the digital technology is that the waveforms can be captured to memory and then analyzed, immediatly or later, in many ways. Digital oscilloscopes can be used to capture repetitive signals as well as transient signals.

Using PC as a measurement instrument

In those early years of computer-based measurement and automation, the desktop computer, linked by the General Purpose Interface Bus (GPIB), played an auxiliary role; however, the increasingly powerful PC has changed all of that. 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.

Transmission line measurements

Cables used to carry high frequency electrical signals are generally analysed as a form of Transmission Line. The amount of capacitance/metre and inductance/metre depends mainly upon the size and shape of the conductors. 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." Return loss is especially important for applications that use simultaneous bidirectional transmission.

Cable wiring testers

Proper testing of wiring system after installation is essential to guarantee good operation later. The cabling system needs to be measured after installation and the results of those measurements should be documented for later use. Measurement is also useful during use when cabling problems are suspected. The most common cable fault is an open circuit, usually due to problems close to or at the ends of the cables. A simple ohm meter test generally suffices.

For multiplair cables where cable ends are many wires inside, a simple multimeter is bothersome. For those applications multi-pair cable testes which find showrt circuits and broken wires are a good choise.

In some application you need to measure the cable length. Depending on the cable characteristics you know and the measuremenet instruments you have, you can use a multimeter (resistance measurement), RLC meter (capacitance measurement). time domain reflectometer (pulse tesing) or signal ateenuation testing (signal source and level meter) to measure the lenght of the cable you have installes somewhere.

    General information

    • Bicotest Application Notes and Technical Bulletins - information on locating cable faults
    • Copper Cable Testing - Twisted pair alternatives have replaced coaxial cabling on today’s LANs. At the Category 5 performance level or above, there are a bewildering number of options. All standards require that installed links pass three tests: wire map (end-to-end pin-to-pin connectivity), attenuation and near end crosstalk (NEXT).
    • Impedance-Based Cable Tester - idea how short and open circuits can be located relatively easily

    Simple single wire testing

    Multi-wire cable testers

    • Cable tester is fast and cheap - simple microcontroller based cable tester verifies the correct wiring of the cable, up to 8 conductor cables
    • TP Cable Tester - circuit that consists of transmitter and receiver and can test 4 pair (8 wire) UTP wiring as used in structures cabling systems (for example CAT-5 LAN cabling)

    Cable test tone senders

    • Signal Tracer and Injector - This audio signal tracer/injector will undoubtedly prove to be very useful for many routine servicing operations. 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.
    • Microphone Circuit Test Oscillator - 440 Hz tone generator for testing XLR microphone lines

    Long line measurements

    • Cable Reflection Tester - a schematic for a homebrew cable reflection tester from the December 1996 issue of Electronics Now, useful for checking coax cable runs for shorts or even impedance mismatches
    • Ring oscillator measures cable length - ECL exclusive-NOR gate (F100107) and a length of cable form a simple ring oscillator, the delay from the cable and the gate determine the ring oscillators frequency, 100m cable yields approximately a 1 MHz oscillation frequency
    • Time Domain Reflectometer (TDR) - simple TDR circuit to be used with an oscilloscope
    • Time Domain Reflectometry Analysis - analysis of a conductor which can be used for example to detect telephone tapping devices

High voltage measurements

DMMs may not be particularly forgiving of voltages on their inputs exceeding their specifications. You need special tools and procedures to successfuly and safely measure high voltages. A simple high voltage probe for a DMM or VOM may be constructed from a pair of resistors. 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 when working with high voltages.

Frequency measurements

Time measurements

Audio measurements

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 100 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. i.e., it is the sound level corresponding to 0.02 mPa. In this case we have equation:

sound level = 20 log (pmeasured/preference) = 20 log 1 = 0 dB

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.

Transducer testing and measuring

  • Mixed-signal algorithm tests transducers - simple test procedure allows you to measure damping coefficient beta in electromechanical transducers, such as speakers, microphones, and seismic geophones
  • Simple procedure tests transducer - testing electromechanical transducers can be as simple as measuring a dc voltage with this circuit, enables you to measure the damping coefficient ([beta]) of speakers, microphones, seismic geophones, and other transducers that exploit electromagnetic phenomena

Radio measurements

Radioacivity

Temperature

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. Because thermocouples measure in wide temperature ranges and can be relatively rugged, they are very often used in industry.

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 0-200 degress celsius temteperature measurements (can be used from -200 to 1250 celsius).

Other commonly used temperature sensors are NTC and PTC resistors, which change their resistance according to the temperature. Also semiconductors can be used as termperature sensors (semiconductor PN junction characteristics change when temperature changes and this is used in some temperature measurement applications).

Voltage measurements

Current measurements

Measuring electrical current can be done using many methods. The most commonly used method for measuring current is to run the current through a know resistor. The voltage drop over this resistor 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 affect the measured circuit.

When measuring high currents on mains 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. In many high current applications the primary coil is just wire going through the toroidal core of the current transformer (=equivalent to one turn primary coil). Many clamp-on multimeters and clamp-on current measuring adapters that can measure AC current are built in this way.

Some clamp-on multimeters can also measure DC currents. Those application use torid cares, where the Hall generator/sensor is placed within air gap of a magnetic core to measure the current. The hall sensor in the air gap measures the magnetic field cause by the wire runnign through the toroidal core.

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.

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.

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 cables), this usually needs covers to be moved to gain access to individual wires. 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 and SMF Technology.

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.

Electrical power measurements

Measuring power is useful when you want to know how many watts certain electronic device takes power. If the device is powered from DC voltage, determinign the power is easy: measure the voltage going to the device and the current going to the device (just connect two multimeters to the powering circuit). Then calculate the power using formula power = voltage * current.

Measuring AC power is harder. The equation power = voltage * current does still hold, but you can't necessarily do the measurement easily with two multimeters. If you just measure the current and voltage with two multimeters, you will get the current and voltage values. You can calculate the power wil formula power = voltage * current (power in VA unit), but remeber that this power is not a real power taken by the device. Depending the phase angel of the current and voltage, the real power taken by the device can be anythign between zero and the power calulated with formula power = voltage * current when current and voltage are measured with multimeter. Power meters which measure real power, need to measure the instantaneous voltage and current many times in a AC power phase, and with every measurement need to do the calculation of voltage * current. The real power is the sum of those calculations. This more complex power 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.

  • 3½-digit DVM IC measures power factor - circuit to measure power factor to 0.1% resolution and operate from a single 9Vdc supply
  • Make a low-cost benchtop power meter - with a few inexpensive ICs and passive components, you can easily make a multirange power meter suitable for use on your benchtop
  • Power meter is ±1% accurate - Power meters can 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.

Resistance measurements

The two instruments most commonly used to check the continuity (a complete circuit), or to measure the resistance of a circuit or circuit element, are the OHMMETER and the MEGGER (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.

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. 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).

Megger is less often needed instrument. The megger 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 1,000 megohms. Megger has the same operation principle, but it generally uses a much higher measurement voltage, typically 250, 500 or 1000 volts DC. Those high voltage ranges are often used to test the quality of the insulation in electrical cables and equipments (safety checks).

  • Continuity Tester - audible output if resistance is less than 300 ohms
  • Digital position encoder does away with ADC - converts the change in resistance of a potentiometer into a digital value without using an expensive A/D converter
  • High-Voltage Insulation Tester - This is the circuit for a high-voltage insulation tester. The circuit is very straightforward and seems to be east to built. This circuit was originally designed for testing high-voltage capacitors used in transmitter tank circuits , it is very useful for checking the flash-over voltage for air-spaced variable capacitors used in high-power aerial tuning units.
  • Johtavuusilmaisin - A simple resistance measurement circuit which shows if resistance is smaller or higher than the threshold set to circuit. The output is using two LEDs. Test in this circuit is in Finnish.
  • Johtavuusilmaisin - A simple resistance measurement circuit which shows if resistance is smaller or higher than the threshold set to circuit. The output is using two LEDs. Test in this circuit is in Finnish. This document is in pdf format.
  • Low-Ohm Meter - article which describes few different low resistance measuring circuits
  • Low Resistance Adapter For DMMs - When the resistances to be measured a very low, say 0.1 ohms, analog meters are useless because the reading becomes indistinguishable from zero. A four and a half digit DMM may have 1/100 ohm resolution but the resistance of the connecting leads, the contact resistance where the leads plug into the meter and where the leads clip to the unknown is significant compared to the unknown. This circuit uses four-wire measurement technique to make more accurate measurements.
  • 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.
  • Ohmmeter - Introduction to ohmmeters
  • Testing Solid Insulation of Electrical Equipment - The megger test method for determining the condition of electrical insulation has been widely used for many years as a general nondestructive test method.

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. A regular program of testing insulation resistance is strongly recommended to prevent this danger, as well as to allow timely maintenance and repair work to take place before catastrophic failure. All new equipment, motors, transformers, switch gears, and wiring should be tested before being put into service. This test record will be useful for future comparisons in regular maintenance testing.

High potential insulation tests are "go no-go" tests. The cable or equipment is required to withstand the specified voltage for the specified time duration. These tests will normally reveal gross imperfections due to improper handling or construction.

The megger 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 1,000 megohms. Megger has the same operation principle, but it generally uses a much higher measurement voltage, typically 250, 500 and 1000 volts DC. Those voltage ranges are often used to test the quality of the insulation in electrical cables and equipments (safety checks). For high voltage testing typically votages 2500 and 5000 volts DC are used. Those high voltage ranges are often used to test the quality of the insulation in electrical cables.

All old wiring and equipment should be carefully checked (for safety), both visually and with an insulation tester. In particular the insulation resistance between live connections and any exposed metal parts should be checked with a high voltage tester ("Megger"- is this just a UK term?) at 500V for 230V equipment and 250V for 110V. If there is any leakage worse than about 50 megohms then track it down.

HiPot testing is a special insulation testing. Some people refer to this as Insulation Testing but this can lead to the mistake of making a resistance measurement using 500Vdc. While this is good practice and useful (to identify potential failures in filters) it does not test insulation strenghnesss. For production, voltages between 1,500 and 2,500 Volts are necessary to verify that insulation is in place. Anything less may “Pass” faulty insulation. Some standards allow AC or DC HiPot testers. DC testing should always be the preference because measurements are not affected by filter capacitance. But do make sure there is an indication that the external load is discharged after testing.

Multimeters

A meter is a measuring instrument that combines functions of ammeter, voltmeter and ohmmeter , and possibly some additional ones as well, into a single instrument. Multimeters are designed and mass produced for electronics engineers. Multimeters are commonly used to measure voltage and resistance between two points. Current is more rarely measured because you must alter the circuit to measure the current (except if you use a clamp type meter which is available for high current measurements).

An analogue meter moves a needle along a scale. Digital meters give an output in numbers, usually on a liquid crystal display. Most modern multimeters are digital and traditional analogue types are destined to become obsolete.

Here is how a typical measurement are made in typical digital multimeter nowadays:

  • DC voltage: The A/D circuitry in the multimeter is designed to directly show DC voltage values typically in few volts range. For higher voltages the input voltage is divided by a voltage divider network. For lower voltages the voltage is amplified with amplifier.
  • AC voltage: Basically same idea as the DC measurement, except that the input voltage is rectified somewhere in the process.
  • DC current: Input current is run through a known low ohm resistance, which converts the input current to a small voltage drop. This voltage is fed to the DC voltage measurement circuitry.
  • AC current: This is measures in the same way as DC current, except that the voltage is fed to the AC voltage measurement electronics.
  • Diode test: A low current (typically less than 1 mA) is fed to the measurement leads (output voltage limited to few volts). The voltage between measurement leads is measurement with DC voltage measurement electronics.
  • Resistance measurement: An accurately known low current (varied dependign on ohms range) is fed to the measurement leads. The voltage (directly proprortional to the resistance conencted) between measurement leads is measured.
Some multimeters can have some of the following functionalities in addition to the basic ones described above:
  • Continuity tester: Works like the resistance measurement measurement, If the voltage between measurement leads is lower than specified value (usually 50 to 300 ohms) would give, make the beeper to signal.
  • Frequency: Input signal is converted to square wave first. The multimeter has either pulse counter (count pulses for one second gifes ouput in Hz) or frequency to voltage converter (output od converter measured with DC voltage measurement circuitry)
  • Capacitance: Feed known frequency low amplitude signal through the capacitance. Measure the AC current which go through the capacitor. Other option is to measure the capacitor charge and discharge times.
  • Temperature: Voltage from thermocouple sensor is amplified and processed. Then the result is fed to DC voltage measurement electronics.

Please note that the information give above are just general statements. The implementation may vary between multimeter brands and models.

If you measure low voltage circuits and do not need very accurate results, some cheap multimeter could be a good choise. You do need to worry much on the meter and measurement wires. If you are going to measure mains voltage circuits, then I recommend to get a good reliable multimeter (IEC 1010 and CE compliant) with safe test leads (1000V rated PVC or silicone insulation, safety banana plug connectors, IEC 1010 and CE compliant). If you are going to measure high current circuit (something with high short-circuit current) be sure that you have a properly fused multimeter (all scales fused) and prefereably fused test probes also.

Almost multimeters owadays have safety banana connecors in then which can accpet both normal banana plugs and safety banana plugs (bananas with plastic "tube" insulation surrounding the plug tip). Please note that there are several different versions of safety banana connectors in use. The banana plug metal tip part inside insulator is similar, but there can be differences in the mechaical construction of the insulation (inner and outer diameter, length of the insulating part etc.). Those differences cause that you might not be able to interchange measuring leads between different multimeter brands and you can't use all available multimeter measuring leads with your multimeter because of this compatibility issue.

    General information

    • Check The Specs For Safety - When working with test equipment, it’s important to understand category ratings. The most important single concept to understand about safety standards is the Overvoltage Installation Category, defined as Categories (CAT) I through IV.
    • Dictionary of Multimeter terminology
    • Playing it safe with your DMM - Taking safe measurements starts with choosing the right meter for the application and the environment in which it will be used. There are a lot of safety issues to think about, from clothing to tools to procedures. Here’s a sampling of just some of the things you should consider on your DMM safety checklist.
    • Selecting the clamp for your job - Choosing the right type of clamp meter is critical when you want to ensure proper power supply to all electrical equipment on a circuit. Current clamps are a simple and reliable means to verify if current is flowing, and if there is continuity between contacts or points of connection. The current clamp has been a mainstay of the electrical technician's toolbox for decades, because it is a cost-effective, simple and accurate means to measure current.
    • The Effect of Meter Resistance - All meters have resistance. The value of this resistance depends upon the voltage range selected. A typical moving coil meter has a SENSITIVITY of 20,000 ohms per volt. Digital multimeter have typically higher resistance (input impedance typically around 10 megaohms on many ranges on good digital multimeters).When the meter is connected to a circuit to measure voltage, this resistance will affect the circuit and therefore the accuracy of the measurement obtained.
    • Using the Multimeter to Measure Voltage and Resistance - Multimeters are commonly used to measure voltage and resistance between two points. Current is rarely measured because you must alter the circuit to measure the current.
    • Using the Multimeter to Measure Voltage and Resistance - Multimeters are commonly used to measure voltage and resistance between two points. Current is rarely measured because you must alter the circuit to measure the current.
    • 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.
    • Why "True-RMS"? - Many modern loads - including solid state motor drives and heating controls - often conduct non-sinusoidal (distorted current). Since the current wave shape can have a drastic effect on a current clamp reading, troubleshooting with an average responding meter will be wrong. In these cases, a True-rms reading is the only option to get accurate measurement results.

    Multimeter circuits

    • Basic Multimeter - A number of shunts and multipliers selected by a switch can be used in association with a single basic meter to form a multirange instrument, known as a multimeter. this is capable of measuring volts, current and resistance. A multirange meter can be constructed in two units, the first containing the 0-1mA meter movement with switches to select various shunt and series resistors to give six d.c. current ranges up to 1 amp and eight d.c. voltage ranges up to 1000 volts. An internal battery provides an ohms range readable up to 200,000 ohms which corresponds with the first division of the meter (0.02mA)
    • Metex M890G Circuit Diagram - This is a circuit diagram of a commercial digital multimeter.

    Accessories

    • Build your own Gaussmeter - Have you ever wanted to find out how strong a magnet really was, or how the strength of the magnetic field varied as you changed the distance from the magnet or the temperature of the magnet, or how well a shield placed in front of the magnet worked? This circuit is a hand-held Gaussmeter for measuring the polarity and strength of a magnetic field. This circuit is a very simple, inexpensive Hall effect device Gaussmeter you can build for as little as $6. This circuit uses a normal multimeter as the display device.
    • Inductance Meter Adapter - a circuit that, when connected to a digital multimeter, lets you measure low-value inductances
    • N5FC's Ballpoint RF Probe - small RF probe that connects to a multimeter
    • Power Meter/Dummy Load - adapter to measure small transmitter power with normal multimeter

    Computer software for multimeters

    • JMM (Java Multi Meter) - JMM is data-acquisition software for digital multimeters equipped with a rs-232 port, such as the Metex 3850 and many others. The software is very simple to use and the control is straight forward.

Bargraph display circuits

Pressure

pH measurements

Strain gage

Electronics components measuring

    Impedance measurements

    Impedance is and AC equivalent to what resistance is for DC. To measure inductance you generally need some signal measuring instruments and a signla source which gives out measurement at the frequency you want to do the impedance measurement at. Usually the impedance more or less varies dependign on the frequency.

    General semiconductor testing

    General measurement for testing all kind of semicondictors is to measure the PN-junctions in the component. You can perform this measurement with a multimerter, but please note that analog and digital meters behave quite differently when testing nonlinear devices like diodes and transistors. On a (digital) DMM, there will usually be a diode test mode. Using this, a silicon diode should read between .5 to .8 V in the forward direction and open in reverse. This test can show catastrophic failures like shorts and opens on diodes, bipolar transistors, SCRs and MOSFETs.

    Curve tracers are pieces of electronic test equipment similar to an oscilloscope. They can not only test transistors and other devices but evaluate the functional specifications as well.

    Transistor testing

    Genral transistor tests are checking semiconductor junctions and measuring gain of a transistor. Typical basic in-circuit transistor testers measure the collector-base or base-emitter junctions. This kind of tester can determine the polarity (npn or pnp) and function of a transistor (a very useful feature in measuring unknown transistors). Transistor gain can be easily measured with many modern multimeters or specialized circuits (like a curve tracer).

    Capacitance and capacitor measurements

    There are many techniques for measuring capacitance. Some of these techniques require a function generator to provide either a sinusoidal, or step-function voltage source. Some measureemtn techniques measure the time for the capacitor to charge to a known voltage when it is charged with a known current.

    Inductor measurements

    • Filter Choke Analyzer - It's more than just an inductance meter.
    • Inductance Meter Adapter - a circuit that, when connected to a digital multimeter, lets you measure low-value inductances
    • Inductance Meter Adapter - a circuit that, when connected to a digital multimeter, lets you measure low-value inductances
    • Inductor self-resonance tester - with aid of an oscilloscope and a signal generator this circuit will allow you to measure resonant frequencies from kilohertz to over 10 megahertz, adds only few picofarads of parallel capacitance to inductor, pdf file
    • LCR/Impedance measurement basics - pdf file from Agilent
    • Method simplifies testing high-Q devices - The design of low-phase-noise oscillators requires careful attention to resonator unloaded Q. In the construction of a low-phase-noise, high-frequency oscillator, the goal is to achieve an unloaded-Q figure greater than 400 in a reasonable package. This simple test set uses nothing more than the voltage-divider relation with the device under test embedded as a series trap network to test inductor.

    Transformer measurements

    Magentic material testing

    Connector measuring

    • Measuring connectors - would like to replace one connector type with a different, less expensive model. How do I prove the two connectors have the same electrical characteristics? Also, how will the power and ground-pin assignments within the connector affect its performance?

    Optoelectronics component testing

    • Diode and LED Tester - simple and cheap unit for testing diodes and LED's for forward conduction and reverse blocking

    IC testing

    • IC Tester - IC Tester is electronic device for testing ics (integrated circuits) and may test some others electronic elements with appropriate addon. Device is connecting to parallel (printer) port at computer, currently you can connect it to PC and amiga computers.
    • Logic ChipTester - ChipTester presented here is used with an IBM compatible PC, and will test nearly all logic devices, providing they operate from a single 5V supply and have no more than 24 pins, Originally published in the 1995 Cirkit Catalogue

Circuitboard testing

Analogue circuit testing

Digital circuit testing

Optoelectronics

Calibration

  • Calibration Forum - to discuss the problems related to the calibration of optical, electrical and photometric calibration in industry

Metal detectors

Special detector circuits

Spectrum analyzer

ESD

Electromagnetic field

  • AC-power monitor uses remote sensing - This circuit senses the main power loss through the radiated power-line signal. The battery-operated circuit has a quiescent-current drain of approximately 2 µA.
  • A Simple Fluxgate Sensor - The fluxgate is one kind of magnetic field sensor which combines good sensitivity with relative ease of construction. The basic principle is to compare the drive-coil current needed to saturate the core in one direction as opposed to the opposite direction. The difference is due to the external field.
  • Build a Magnetic Field Immunity Tester - a precompliance test system can help you determine whether your products comply with standards such as the CE Marking
  • Build your own Gaussmeter - Have you ever wanted to find out how strong a magnet really was, or how the strength of the magnetic field varied as you changed the distance from the magnet or the temperature of the magnet, or how well a shield placed in front of the magnet worked? This circuit is a hand-held Gaussmeter for measuring the polarity and strength of a magnetic field. This circuit is a very simple, inexpensive Hall effect device Gaussmeter you can build for as little as $6. This circuit uses a normal multimeter as the display device.
  • Detecting the Earth's Electricity - HOMEMADE FIELD MILL measures fluctuations in the earth's electric field, article from Scientific American
  • DIY probes for checking E & M fields - probes from very lof frequencies to 200 MHz, also so electric field probes
  • Electric Field and Leakage Detector - detects very small currents such as those caused by leakage and changing electric fields
  • Electric Field Detector - this circuit will come handy when you have to follow the mains wires buried in the wall or even water pipes provided they are not too far away (2-4cm max)
  • Electromagnetic Field Detector - This circuit uses a radial type inductor as a probe and responds well to low frequency changing magnetic and electric fields. Ordinary headphones are used to for detection.
  • Electromagnetic Field Probe with Meter Output - designed to locate stray electromagnetic (EM) fields, response from 50Hz to about 100kHz, will easily detect both audio and RF signals
  • Electromagnetic sensors put a spin on compasses - determining direction using the earth's weak magnetic field entails the use of clever magnetic techniques and devices
  • Induction Receivers - This induction receiver is very sensitive and can serve a variety of purposes. It is excellent for tracing wiring behind walls, receiving audio from an induction transmitter, hearing lightning and other electric discharges, and monitoring a telephone or other device that produces an audio magnetic field ("telephone pickup coil").
  • Live Wire Detector - The short antenna held near any mains-carrying cable will detect a current flow. This will be indicated by a flashing light-emitting diode (LED).
  • Magnetic field probes, ELF (extremely low frequency) - circuits you would use for measuring 60 Hz line problems, the field from the vertical drive coils on TV's, monitors, etc.
  • Noncontact device tests power supplies - a probelike device for strong magnetic field detection as a quick go-no-go test for step-down power supplies
  • RC network eliminates precision reference - this circuit uses a magneto-resistive sensor to detect small magnet displacements without resorting to a precision voltage reference
  • Sensitive Geomagnetic Field - a rather sensitive circuit which will detect minute variations of a magnetic field, particularly the Earth magnetic field
  • Static Electricity / Negative Ion Detector

Distance measurement

Fluid level and humidity

  • Capacitance type liquid level monitor - originally designed to monitor the level of liquid natural gas in a tank but it can be used to also measure almost any liquid, uses two custom insulated metal tubes form a capacitor plate, capacitance between the two tubes increases as the level of the liquid rises, circuit converts an increase of capacitance into a positive voltage change, pdf file
  • Capacitance type liquid level monitor - This circuit was originally designed to monitor the level of liquid natural gas in a tank but it can be used to also measure almost any liquid. This document is in pdf format.
  • Fluid Level Sensor - uses an ac-sensing signal to eliminate electrolytic corrosion on the probe
  • Hot Water Tank Indicator - uses bead thermistors sticked to to the tank as sensors
  • Low-cost relative-humidity transmitter uses single logic IC - This low-cost percentage-relative-humidity radio transmitter operates in a cold-storage warehouse for vegetable storage at temperatures of 1 to 5°C. The transmitter design is simple: It uses a readily available, capacitor-type percentage-relative-humidity sensor for which the capacitor value increases with humidity. The circuit can be tuned to operate at 10- to 50-MHz RF band.
  • Measure humidity and temperature on one TTL line - By combining the responses of an Analog Devices AD590 temperature sensor and a Humirel HS1101 humidity sensor, you can generate a single TTL-level signal containing information from both sensors.
  • Moisture Alarm
  • One-wire bus powers water-level sensor - You can use the simple sensor circuit to remotely monitor the level of liquid water in a vessel such as a swimming pool. A host PC or µC reads the output of the pulse counter via the Dallas Semiconductor one-wire bus.
  • Piezo crystal monitors liquid level - simple and inexpensive circuit monitors the liquid level in a container
  • RF/Capacitance Level Instrumentation - Capacitance level detectors are also referred to as radio frequency (RF) or admittance level sensors. They operate in the low MHz radio frequency range, measuring admittance of an alternating current (ac) circuit that varies with level. Admittance is a measured.
  • Signal conditioning precisely indicates humidity - translates the level of humidity from 0 to 100% into a stable, respective dc signal of 0 to 100 mV
  • Sonarlike method detects fluid level - a simple, cost-effective method of measuring the height of fluid in a column by using ultrasonic waves
  • Water-Level Sensor Uses Hysteresis

Lie detector

Electrical wiring testing

  • Ethernet 10BaseT simulator jig yields zero emissions - tool to evaluate emissions from Ethernet unshielded-twisted-pair (UTP) 10BaseT LAN-interface devices without contaminating the measured results with its own RF emissions, this cirucit generates 10BaseT equipment link test pulses without RF emissions so that 10BaseT equipment will keep sending data
  • Fleapower circuit detects short circuits - a short-circuit tester that supplies a low current to the device under test (DUT) and also uses voltages lower than 100 mV to prevent conduction of semiconductors
  • Multicore Cable Tracer - unit is designed to help when establishing the connections in multicore cables or when identifying a large number of cables contained in a trunking or conduit, supports up to 63 channels up to 100 meters or more, Originally published in ETI, August 1995
  • RJ45 Network Cable Tester -
  • Test Plug - circuit which indicates whether your mains socket is wired correctly, for 220-240V systems, Originally published in Electronics in Action, March 1994

Motor measurements

Instrumention circuits

    General information on instrumentation

    • 4-20mA.com - current loop information
    • A System Designer's Guide to Isolation Devices - Isolation amplifiers provide galvanic isolation of the incoming signal to safeguard equipment and personnel, but the world of isolation, with its own terminology, technologies, and standards, is unfamiliar to many designers. This article reviews the basic concepts and technology of isolation devices and discusses the various options available to the system designer.
    • Beware of under- or overspecifying your next sensor - to choose the best photoelectric sensor for your application, you need to consider a number of criteria, including sensor configuration; environment; and the placement, nature, and speed of the target
    • Circuit makes simple FSK modulator - The need for a compact telemetry system poses a challenge for designing a small, light, low-component-count system. Commercial FSK (frequency-shift-keying) modulators are bulky and need many passive components. This circuit uses a single NOT gate (inverter), an On Semiconductor NL27WZ14 in a surface-mount package, to generate continuous FSK data from TTL-level signals. This circuit is designed to provide 2400 Hz / 1200 Hz FSK, but can be adapted for other frequencies up to an operating frequency of approximately 80 kHz.
    • 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).
    • Fault protection saves multiplexers, switches, and downstream circuitry - For most situations in which fault conditions are possible, a fault-protected switch, multiplexer, or signal-line circuit protector offers a more practical approach to protection than discrete components.
    • Fight Corruption, perserve purity with ANALOG-SIGNAL isolation - analog-signal isolation can dramatically reduce noise and artifacts that corrupt sensitive measurements
    • Ground Loops and Their Cures - DC power systems used for instrument and loop power are subject to a number of possible ground loops. The method to solving ground loop problems is generally twofold. Remove any extra grounds so that there is one ground in the system. If there must be more than one ground, make sure to isolate each from other(s).
    • Improved amplifier drives differential-input ADCs - ADCs with differential inputs are becoming increasingly popular. This popularity isn't surprising, because differential inputs in the ADC offer several advantages: good common-mode noise rejection, a doubling of the available dynamic range without doubling the supply voltage, and cancellation of even-order harmonics that accrue with a single-ended input. This document shows shows two easy ways to create a differential-input differential-output instrumentation amplifier.
    • Isolation techniques for high-resolution data-acquisition systems - You can implement isolation using optical, digital, and magnetic techniques.
    • Noise and disturbances in process control
    • Testing MEMS: Don't reinvent the wheel - but take little on faith - MEMS, which not only condition signals but also move, require consummate care in handling. But the manufacturers have figured out much of what you must know to successfully apply the devices. So be highly selective in choosing where to independently build up your private body of knowledge.
    • Understanding pH measurement - In the process world, pH is an important parameter to be measured and controlled. The pH of a solution indicates how acidic or basic (alkaline) it is. The formal mathematical definition of pH is the negative logarithm of hydrogen ion activity. A pH measurement loop is made up of three components, the pH sensor, which includes a measuring electrode, a reference electrode, and a temperature sensor; a preamplifier; and an analyzer or transmitter. A pH measurement loop is essentially a battery where the positive terminal is the measuring electrode and the negative terminal is the reference electrode. The measuring electrode, which is sensitive to the hydrogen ion, develops a potential (voltage) directly related to the hydrogen ion concentration of the solution. The reference electrode provides a stable potential against which the measuring electrode can be compared.
    • Understanding pH measurement - In the process world, pH is an important parameter to be measured and controlled. The pH of a solution indicates how acidic or basic (alkaline) it is. A pH measurement loop is essentially a battery where the positive terminal is the measuring electrode and the negative terminal is the reference electrode. The measuring electrode, which is sensitive to the hydrogen ion, develops a potential (voltage) directly related to the hydrogen ion concentration of the solution. The reference electrode provides a stable potential against which the measuring electrode can be compared.
    • Why 4-20mA for industrial analog communications? - Why was 4-20mA chosen as the main industrial analog communications protocol?
    • Wiring For Trouble Free Signal Conditioning - Signal conditioning equipment for process signals has kept pace with modern technology, but many users never realize the full potential of the equipment because of poor installation and wiring practices. Such practices can degrade equipment performance from a small percentage of error to the point where the equipment is unusable.
    • Wiring For Trouble Free Signal Conditioning - Article published in European Process Engineer Magazine and In-Tech Magazine

    Insrumentation amplifiers

    The symbol for an instrumentation amplifier may look similar to that of an opamp and may have a broadly similar function: differential amplification of its inputs, but it is an entirely different creature. An opamp is designed to be used in a negative feedback topology, both to achieve a uniform gain and to compensate for amplifier imperfections. An instrumentation amplifier, on the other hand, is used for open loop differential amplification, and has been designed with this in mind. It provides a smaller gain that is typically set by one external resistor. It is often used as a "pre-amp" for signals that are too low-level for an ordinary opamp buffer. Instrumentation amplifiers can be built out of individual opamps or you can use a single-chip implementation.

    Typical Instrumentation Amplifier monitors voltages from a few millivolts (DC or AC). It has several switch settings to allow you to select the best gain. It can be used with may measurement devices like A/D converter cards, programmable logic etc.

    Voltage to frequency conversion

    Other signal format converters

    • Circuit converts pulse width to voltage - This circuit converts pulse information to a clean dc voltage by the end of a single incoming pulse. In another technique, an RC filter can convert a PWM signal to an averaged dc voltage, but this method is slow in responding. This circuit works better and faster.

    Current loop interfacing

    4-20mA is an analog current loop protocol which has become the defacto U.S. standard for supplying DC power to a field transducer, and receiving a scaled return signal. DC power is typically supplied via an unregulated +10 to +30Vdc supply. Many industrial current-loop data acquisition systems operate on a 24V or 28V single supply. The field transducer controls the current flow, and is often referred to as a 2-wire "transmitter". You can easily receive 4-20 mA signals by passing the current through 100 ohm resistor, so you get 0.4-2V voltage over the resistor (if you select 250 ohm resistor, you will get 1V to 5V reading).

    Sensor and measuring circuit ideas

    • Autoreferencing circuit nulls out sensor errors - This autoreferencing circuit nulls out the error of a sensor, such as a pressure transducer, at its reference level, for example, at ambient pressure. The circuit is an analog-digital-feedback control system that uses a digitally programmable potentiometer to provide the variability.
    • Data-acquisition circuit measures almost everything - Using a product developed for PC-motherboard environmental monitoring, you can configure a low-cost, general-purpose DAS (data-acquisition system)
    • Design approach simplifies signal conditioning - low cost and wide availability of 8-bit microcontrollers, such as Motorola's MC68HC11, allow you to easily incorporate intelligence in pressure-measurement systems, your main challenge is to signal-condition the sensor's small, differential bridge signal into a single-ended output voltage that the µC's A/D converter
    • Dual comparators stabilize proximity detector - circuit transforms distance/capacitance into a proportional voltage
    • Home-brewed circuits tailor sensor outputs to specialized needs - use an untrimmed unit and customize it with a signal conditioner based on two or three op amps to get specially trimmed customized sensors
    • How to build instruments for hang gliders - pressure sensors and altimeter
    • Method offers fail-safe variable-reluctance sensors - Variable-reluctance sensors are preferred for industrial and automotive environments, because they sustain mechanical vibration and operation to 300°C. In most applications, they sense a steel target that is part of a rotating assembly. Because the unprocessed signal amplitude is proportional to target speed, a sensor whose signal-processing circuitry is designed for high speed ceases to function at some lower rate of rotation. Hall-effect sensors are preferable for speeds of several pulses per second, but they require the attachment of a magnet to the rotating assembly. Neither variable-reluctance nor Hall-effect sensors offers fail-safe detection of the processed signal in the event of failure in the cable or sensor. This circuit is a fail-safe variable-reluctance sensor for low- to medium-speed operation.
    • Network imitates thermocouples - Thermocouples find widespread use for temperature measurement in systems. During system design or testing, you must observe the system's response at different temperatures. However, it's inconvenient to heat a thermocouple every time you need to check a system's performance. This simple circuit allows you to set a number of voltages equal to the thermocouples' outputs at given temperatures.
    • Programmable Pressure Transducer
    • µC uses simple tool for angle measurements - uses a 2V, 2250-Hz resolver as an angle sensor and provides up to 11 bits resolution for angle measurements

Telecommunication measurements

Weather circuits

  • A lightning flash counter - This page contains instructions to build a lightning flash counter and how to interface it to your PC.
  • Detecting the Earth's Electricity - HOMEMADE FIELD MILL measures fluctuations in the earth's electric field
  • Lightning Detectors - VLF receiver tuned to 300 kHz designed to detect the crackle of approaching lightning
  • Lighting detector - pdf file
  • Lightning Detector - a VLF receiver tuned to 300 kHz designed to detect the crackle of approaching lightning
  • Lightning Detector - VLF receiver tuned to 300 kHz designed to detect the crackle of approaching lightning
  • PC hardware monitor reports the weather - You usually use PC hardware monitors to keep a close eye on power-supply voltage levels, the speed of system cooling fans, and even the temperature of the CPU. However, now that low-cost hardware monitoring ASICs are available, advanced hardware monitoring has become a standard feature in most new PCs. And hardware monitors are now finding their way into diverse applications, such as weather stations. This weather station measures wind speed, humidity and temperature. Circuit connextgs to PC parallel port.
  • Weather circuits - in pdf format

Pulse measurements and conversion

Mains power measurements

Ultrasonics

Flow measurements

Motor rotation speed

  • 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 NE555 timer is configured as a monostable or one shot. The 555 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.
  • Tacho generator motor speed feedback - This page is a bit different from most in that it covers the use of tacho generators as feedback elements in motor control systems. This page covers tacho generator rectifier circuit for 4QD Pro-120 electric motor controllers.

Misc