Editing Multimeter (section)

== Features ==
[[File:Clampmeter Fluke 337.jpg|thumb|upright|A [[clamp meter]]]]

Any meter will load the circuit under test to some extent. For example, a multimeter using a moving coil movement with full-scale deflection current of 50 [[ampere|microamps]] (μA), the highest sensitivity commonly available, must draw at least 50&nbsp;μA from the circuit under test for the meter to reach the top end of its scale. This may load a high-impedance circuit so much as to affect the circuit, thereby giving a low reading. The full-scale deflection current may also be expressed in terms of "ohms per volt" (Ω/V). The ohms per volt figure is often called the "sensitivity" of the instrument. Thus a meter with a 50&nbsp;μA movement will have a "sensitivity" of 20,000&nbsp;Ω/V. "Per volt" refers to the fact that the impedance the meter presents to the circuit under test will be 20,000&nbsp;Ω multiplied by the full-scale voltage to which the meter is set. For example, if the meter is set to a range of 300&nbsp;V full scale, the meter's impedance will be 6&nbsp;MΩ. 20,000&nbsp;Ω/V is the best (highest) sensitivity available for typical analog multimeters that lack internal amplifiers. For meters that do have internal amplifiers (VTVMs, FETVMs, etc.), the input impedance is fixed by the amplifier circuit.

Additional scales such as [[decibel]]s, and measurement functions such as [[capacitance]], [[Transistor#Simplified operation|transistor gain]], [[frequency]], [[duty cycle]], display hold, and continuity which sounds a [[buzzer]] when the measured resistance is small have been included on many multimeters. While multimeters may be supplemented by more specialized equipment in a technician's toolkit, some multimeters include additional functions for specialized applications (temperature with a [[thermocouple]] probe, [[inductance]], connectivity to a [[computer]], speaking measured value, etc.).

Contemporary multimeters can measure many values.<ref>{{Cite book |last1=Crecraft |first1=David |url=https://books.google.com/books?id=Hn90DwAAQBAJ&dq=Contemporary+multimeters+can+measure+many+values.&pg=PA4 |title=Electronics |last2=Gorham |first2=David |date=2018-10-03 |publisher=CRC Press |isbn=978-1-351-99109-4 |pages=4 |language=en}}</ref><ref>{{Cite book |last=SOLANKI |first=CHETAN SINGH |url=https://books.google.com/books?id=48tNl8L1awkC&dq=Contemporary+multimeters+can+measure+many+values&pg=PA13 |title=SOLAR PHOTOVOLTAIC TECHNOLOGY AND SYSTEMS: A Manual for Technicians, Trainers and Engineers |date=2013-01-11 |publisher=PHI Learning Pvt. Ltd. |isbn=978-81-203-4711-3 |pages=13 |language=en}}</ref> The most common are:

* [[Voltage]], [[Alternating current|alternating]] and [[Direct current|direct]], in [[volt]]s.
* [[Electric current|Current]], alternating and direct, in [[ampere]]s. The [[frequency]] range for which AC measurements are accurate is important, depends on the circuitry design and construction, and should be specified, so users can evaluate the readings they take. Some meters measure currents as low as milliamps or even microamps. All meters have a [[burden voltage]] (caused by the combination of the shunt used and the meter's circuit design), and some (even expensive ones) have sufficiently high burden voltages that low current readings are seriously impaired. Meter specifications should include the burden voltage of the meter.
* [[Electrical resistance and conductance|Resistance]] in [[ohm]]s.
Additionally, some multimeters also measure:
* [[Capacitance]] in [[farad]]s, but usually the limitations of the range are between a few hundred or thousand micro farads and a few pico farads. Very few general purpose multimeters can measure other important aspects of capacitor status such as [[Equivalent series resistance|ESR]], [[dissipation factor]], or leakage.
* [[Electrical resistance and conductance|Conductance]] in [[Siemens (unit)|siemens]], which is the inverse of the resistance measured.
* [[Decibel]]s in circuitry, rarely in sound.
* [[Duty cycle]] as a [[percentage]].
* [[Utility frequency|Frequency]] in [[hertz]].
* [[Inductance]] in [[Henry (unit)|henries]].  Like capacitance measurement, this is usually better handled by a purpose designed inductance / capacitance meter.
* [[Temperature]] in degrees [[Celsius]] or [[Fahrenheit]], with an appropriate temperature [[test probe]], often a [[thermocouple]].

Digital multimeters may also include circuits for:

* [[Continuity tester]]; a buzzer sounds when a circuit's resistance is low enough (just how low is enough varies from meter to meter), so the test must be treated as inexact.
* [[Diode]]s (measuring forward drop of diode junctions).
* [[Transistor]]s (measuring [[current gain]] and other [[parameters]] in some kinds of transistors)
* Battery checking for simple 1.5&nbsp;V and 9&nbsp;V batteries. This is a current-loaded measurement, which simulates in-use battery loads; normal voltage ranges draw very little current from the battery.

Various [[sensor]]s can be attached to (or included in) multimeters to take measurements such as:

* [[Luminance]]
* [[Sound pressure]] level
* [[pH]]
* [[Relative humidity]]
* Very small current flow (down to nanoamps with some adapters)
* Very small resistances (down to micro ohms for some adapters)
* Large currents: adapters are available which use inductance (AC current only) or [[Hall effect]] sensors (both AC and DC current), usually through insulated clamp jaws to avoid direct contact with high current capacity circuits which can be dangerous, to the meter and to the operator
* Very high voltages: adapters are available which form a [[voltage divider]] with the meter's internal resistance, allowing measurement into the thousands of volts.  However, very high voltages often have surprising behavior, aside from effects on the operator (perhaps fatal); high voltages which actually reach a meter's internal circuitry may internal damage parts, perhaps destroying the meter or permanently ruining its performance.