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Introduction

On the top of this page you can find an overview of all brands that supply measurement devices.

Electronic test equipment (sometimes called "testgear") is used to create signals and capture responses from electronic Devices Under Test (DUTs). In this way, the proper operation of the DUT can be proven or faults in the device can be traced and repaired. Use of electronic test equipment is essential to any serious work on electronics systems.

Practical electronics engineering and assembly requires the use of many different kinds of electronic test equipment ranging from the very simple and inexpensive (such as a test light consisting of just a light bulb and a test lead) to extremely complex and sophisticated such as Automatic Test Equipment.

Generally, more advanced test gear is necessary when developing circuits and systems than is needed when doing production testing or when troubleshooting existing production units in the field.

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Types of test equipment

Basic equipment

The following items are used for basic measurement of voltages, currents, and components in the circuit under test.

  • Voltmeter (Measures voltage)
  • Ohmmeter (Measures resistance)
  • Ammeter, e.g. Galvanometer or Milliameter (Measures current)
  • Multimeter e.g., VOM (Volt-Ohm-Milliameter) or DVM (Digital "Volt" Meter) (Measures all of the above)

The following are used for stimulus of the circuit under test:

  • Power supplies
  • Signal generator
  • Digital pattern generator
  • Pulse generator

The following analyze the response of the circuit under test:

  • Oscilloscope (Measures all of the above as they change over time)
  • Frequency counter (Measures frequency)

And connecting it all together:

  • Test probes

Advanced or less commonly used equipment

  • Meters
    • Solenoid voltmeter (Wiggy)
    • Clamp meter (current transducer)
    • Wheatstone bridge (Precisely measures resistance)
    • Capacitance meter (Measures capacitance)
    • LCR meter (Measures inductance, capacitance, resistance and combinations thereof)
    • EMF Meter (Measures Electric and Magnetic Fields)
    • Electrometer (Measures charge)
  • Probes
    • RF probe
    • Signal tracer

  • Analyzers
    • Logic analyzer (Tests digital circuits)
    • Spectrum analyzer (SA) (Measures spectral energy of signals)
    • Protocol analyzer (Tests functionality, performance and conformance of protocols)
    • Vector signal analyzer (VSA) (Like the SA but it can also perform many more useful digital demodulation functions)
    • Time-domain reflectometer for testing integrity of long cables
  • Signal-generating devices
    • Signal generator
    • Frequency synthesiser
    • Function generator
    • Digital pattern generator
    • Pulse generator
    • Signal injector

Miscellaneous devices

  • Continuity tester
  • Cable tester
  • Hipot tester
  • Network analyzer (used to characterize components or complete computer networks)
  • Test light
  • Transistor tester
  • The Energy Detective

Ammeter

An ammeter is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes (A), hence the name.

The earliest design is the D'Arsonval galvanometer or moving coil ammeter. It uses magnetic deflection, where current passing through a coil causes the coil to move in a magnetic field. The voltage drop across the coil is kept to a minimum to minimize resistance across the ammeter in any circuit into which it is inserted.

Moving iron ammeters use a piece of iron which moves when acted upon by the electromagnetic force of a fixed coil of wire. This type of meter responds to both direct and alternating currents (as opposed to the moving coil ammeter, which works on direct current only).

To measure larger currents, a resistor called a shunt is placed in parallel with the meter. Most of the current flows through the shunt, and only a small fraction flows through the meter. This allows the meter to measure large currents. Traditionally, the meter used with a shunt has a full-scale deflection (FSD) of 50 mV, so shunts are typically designed to produce a voltage drop of 50 mV when carrying their full rated current.

Zero-center ammeters are used for applications requiring current to be measured with both polarities, common in scientific and industrial equipment. Zero-center ammeters are also commonly placed in series with a battery. In this application, the charging of the battery deflects the needle to one side of the scale (commonly, the right side) and the discharging of the battery deflects the needle to the other side.

Digital ammeter designs use an analog to digital converter (ADC) to measure the voltage across the shunt resistor; the digital display is calibrated to read the current through the shunt.

Since the ammeter shunt has a very low resistance, mistakenly wiring the ammeter in parallel with a voltage source will cause a short circuit, at best blowing a fuse, possibly damaging the instrument and wiring, and exposing an observer to injury. In AC circuits, a current transformer converts the magnetic field around a conductor into a small AC current, typically either 1 or 5 Amps at full rated current, that can be easily read by a meter. In a similar way, accurate AC/DC non-contact ammeters have been constructed using Hall effect magnetic field sensors. A portable hand-held clamp-on ammeter is a common tool for maintenance of industrial and commercial electrical equipment, which is temporarily clipped over a wire to measure current.

Avometer

The Avometer was a British brand multimeter. The most recent version, in production from 1950s until 2008, was the Model 8 Mk 7 by Megger.

It is often called simply an AVO and derives its name from the first letter of the words amperes, volts, ohms. It was conceived by a Post Office engineer Donald Macadie in 1923.

meter

It was by far the best instrument of its kind in the UK from 1923 to at least the 1960s. Almost uniquely for a radio repairman's multimeter it measures alternating current up to 10 A as well as the standard AC and DC voltages up to 1000 V; as an ohmeter it measures from 0.1 up to 200 k in three ranges. The instrument had an accuracy of plusminus 1% of FSD on DC ranges and plusminus 2% on AC ranges. Its maximum current consumption was 50 (corresponding to 20,000 ohms per volt), which was sufficient (in most circuits) to reduce the voltage measurement error, caused by connection of the meter, to an acceptable level. A pair of rotary switches are used to select the range to be measured, being arranged in such a way as to minimise the risk of damage to the instrument should the wrong range be selected. Further protection is provided by an overload cut-out and fuses for each mode. It was a superb example of British radio engineering in its heyday and was found in virtually every radio repair workshop throughout the country and can still be found in regular use.

Despite continuing demand from the customers the production was stopped in 2008 due to increasing problems with suppliers of mechanical parts.

Multimeter

A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. There are two categories of multimeters, analog multimeters (or analogue multimeters in British English) and digital multimeters (often abbreviated DMM or DVOM.)

meter

A multimeter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as batteries, motor controls, appliances, power supplies, and wiring systems.

Multimeters are available in a wide ranges of features and prices. Cheap multimeters can cost less than US$10, while the top of the line multimeters can cost more than US$5000.

History

Early Avometer.Scientists originally used galvanometers to measure current. A galvanometer may be wired to measure resistance (given a known voltage source) or voltage (given a fixed resistance). While appropriate for primitive lab use, switching from one setup to another is inconvenient in the field.

Multimeters were invented in the early 1920s as radio receivers and other vacuum tube electronic devices became more common. The invention of the first multimeter is attributed to a Post Office engineer Donald Macadie[1], who became dissatisfied with having to carry many separate instruments required for the maintenance of the telecommunication circuits. Macadie invented a first instrument, which could measure Amps, Volts and Ohms, so the multifunctional meter was then named Avometer. The meter comprised of a galvanometer, voltage and resistance references, and a switch to select appropriate circuit for the input under test.

Macadie took his idea to the Automatic Coil Winder and Electrical Equipment Company (ACWEEC, founded probably in 1923) The first AVO was put on sale in 1923, and although it was initially a DC-only instrument many of its features remained almost unaltered right through to the last Model 8.

As modern systems become more complicated, the multimeter is becoming more complex or may be supplemented by more specialized equipment in a technician's toolkit. For example, where a general-purpose multimeter might only test for short-circuits, conductor resistance and some coarse measure of insulation quality, a modern technician may use a hand-held analyzer to test several parameters in order to validate the performance of a network cable.

Quantities measured

Contemporary multimeters can measure many quantities. The common ones are:

  • Voltage in volts.
  • Current in amperes.
  • Resistance in ohms.

Additionally, multimeters may also measure:

  • Capacitance in farads.
  • Frequency in hertz
  • Duty cycle as a percentage.
  • emperature in degrees Celsius or Fahrenheit.
  • Conductance in siemens.
  • Inductance in henrys
  • Audio signal levels in decibels.

Digital multimeters may also include circuits for:

  • Continuity that beeps when a circuit conducts.
  • Diodes and Transistors

Various sensors can be attached to multimeters to take measurements such as:

  • Light level
  • Acidity/Alkalinity(pH)
  • Wind speed
  • Relative humidity

Oscilloscope

An oscilloscope (commonly abbreviated to scope or O-scope) is a type of electronic test instrument that allows signal voltages to be viewed, usually as a two-dimensional graph of one or more electrical potential differences (vertical axis) plotted as a function of time or of some other voltage (horizontal axis). Although an oscilloscope displays voltage on its vertical axis, any other quantity that can be converted to a voltage can be displayed as well. In most instances, oscilloscopes show events that repeat with either no change, or change slowly. The oscilloscope is one of the most versatile and widely-used electronic instruments.

meter

Oscilloscopes are widely used when it is desired to observe the exact wave shape of an electrical signal. In addition to the amplitude of the signal, an oscilloscope can measure the frequency, show distortion, show the time between two events (such as pulse width or pulse rise time), and show the relative timing of two related signals. Some better modern digital oscilloscopes can analyze and display the spectrum of a repetitive event. Special-purpose oscilloscopes, called spectrum analyzers, have sensitive inputs and can display spectra well into the GHz range. A few oscilloscopes that accept plug-ins can display spectra in the audio range.

Oscilloscopes are used in the sciences, medicine, engineering, telecommunications, and industry. General-purpose instruments are used for maintenance of electronic equipment and laboratory work. Special-purpose oscilloscopes may be used for such purposes as analyzing an automotive ignition system, or to display the waveform of the heartbeat.

Originally all oscilloscopes used cathode ray tubes as their display element and linear amplifiers for signal processing, but modern oscilloscopes can have LCD or LED screens, high-speed analog-to-digital converters and digital signal processors. Although not as commonplace, some oscilloscopes used storage CRTs to capture single events and display them for a limited time. Oscilloscope peripheral modules for general purpose laptop or desktop personal computers use the computer's display, and can turn them into useful and flexible test instruments.

Examples of use

One of the most frequent uses of scopes is troubleshooting malfunctioning electronic equipment. One of the advantages of a scope is that it can graphically show signals: where a voltmeter may show a totally unexpected voltage, a scope may reveal that the circuit is oscillating. In other cases the precise shape or timing of a pulse is important.

In a piece of electronic equipment, for example, the connections between stages (e.g. electronic mixers, electronic oscillators, amplifiers) may be 'probed' for the expected signal, using the scope as a simple signal tracer. If the expected signal is absent or incorrect, some preceding stage of the electronics is not operating correctly. Since most failures occur because of a single faulty component, each measurement can prove that half of the stages of a complex piece of equipment either work, or probably did not cause the fault.

Once the faulty stage is found, further probing can usually tell a skilled technician exactly which component has failed. Once the component is replaced, the unit can be restored to service, or at least the next fault can be isolated. This sort of troubleshooting is typical of radio and TV receivers, as well as audio amplifiers, but can apply to quite-different devices such as electronic motor drives.

Another use is to check newly designed circuitry. Very often a newly designed circuit will misbehave because of design errors, bad voltage levels, electrical noise etc. Digital electronics usually operate from a clock, so a dual-trace scope which shows both the clock signal and a test signal dependent upon the clock is useful. Storage scopes are helpful for "capturing" rare electronic events that cause defective operation.

Another use is for software engineers who must program electronics. Often a scope is the only way to see if the software is running the electronics properly.

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