Editing Multimeter (section)

== Components ==

=== Probes ===
{{main|Test probe}}
[[File:Multimeter test leads.JPG|thumb|left|Multimeter test leads]]

A multimeter can use many different test probes to connect to the circuit or device under test. [[Crocodile clip]]s, retractable hook clips, and pointed probes are the three most common types. [[Tweezer#Types|Tweezer probes]] are used for closely spaced test points, as for instance [[surface-mount device]]s. The connectors are attached to flexible, well insulated leads terminated with connectors appropriate for the meter. Probes are connected to portable meters typically by shrouded or recessed [[banana connector|banana jacks]], while benchtop meters may use [[banana jacks]] or [[BNC connector]]s. 2&nbsp;mm plugs and [[binding posts]] have also been used at times, but are less commonly used today.  Indeed, safety ratings now require shrouded banana jacks.

The banana jacks are typically placed with a standardized center-to-center distance of {{convert|3/4|inch|mm|sigfig=2|abbr=on}}, to allow standard adapters or devices such as voltage multiplier or thermocouple probes to be plugged in.

[[Clamp meter]]s clamp around a [[electrical conductor|conductor]] carrying a current to measure without the need to connect the meter in series with the circuit, or make metallic contact at all. Those for AC measurement use the transformer principle; clamp-on meters to measure small current or direct current require more exotic sensors, such as; hall effect based systems that measure the nonchanging magnetic field to determine the current.

=== Power supply ===
Analog meters can measure voltage and current by using power from the test circuit, but require a supplementary internal voltage source for resistance testing, while electronic meters always require an internal power supply to run their internal circuitry.  Hand-held meters use batteries, while bench meters usually use mains power; either arrangement allows the meter to test devices. Testing often requires that the component under test be isolated from the circuit in which they are mounted, as otherwise stray or leakage current paths may distort measurements.  In some cases, the voltage from the multimeter may turn active devices on, distorting a measurement, or in extreme cases even damage an element in the circuit being investigated.

=== Safety ===
[[File:Fluke 28 Multimeter Input Protection.jpg|right|thumb|An example of input protection on a multimeter]]
Most multimeters include a [[fuse (electrical)|fuse]], or two fuses, which will sometimes prevent damage to the multimeter from a current overload on the highest current range. (For added safety, test leads with fuses built in are available.) A common error when operating a multimeter is to set the meter to measure resistance or current, and then connect it directly to a low-impedance voltage source. Unfused meters are often quickly destroyed by such errors; fused meters often survive. Fuses used in meters must carry the maximum measuring current of the instrument, but are intended to disconnect if operator error exposes the meter to a low-impedance fault. Meters with inadequate or unsafe fusing were not uncommon; this situation has led to the creation of the [[measurement category|IEC61010 categories]] to rate the safety and robustness of meters.

Digital meters are rated into four categories based on their intended application, as set forth by IEC 61010-1<ref>{{cite web|url=http://www.gossenmetrawatt.com/english/seiten/newsafetystandardiec61010-1since0.htm|archive-url=https://web.archive.org/web/20061202071525/http://www.gossenmetrawatt.com/english/seiten/newsafetystandardiec61010-1since0.htm|url-status=dead|archive-date=2006-12-02|title=Safety Standard IEC 61010-1 since 1.1.2004}}</ref> and echoed by country and regional standards groups such as the [[European Committee for Standardization|CEN]] EN61010 standard.<ref>{{cite book|title=Safety requirements for electrical equipment for measurement, control and laboratory use. General requirements|isbn=0-580-22433-3|year=1993|publisher=B S I Standards }}</ref>

* Category I: used where equipment is not directly connected to the mains
* Category II: used on single phase mains final subcircuits
* Category III: used on permanently installed loads such as distribution panels, motors, and three-phase appliance outlets
* Category IV: used on locations where fault current levels can be very high, such as supply service entrances, main panels, supply meters, and primary over-voltage protection equipment

Each Category rating also specifies maximum safe transient voltages for selected measuring ranges in the meter.<ref>{{cite book|page=285|title=Survey of Instrumentation and Measurement|year=2001|last=Dyer|first=Stephen|publisher=Wiley |isbn=0-471-39484-X}}</ref><ref>{{cite web|url=https://electronicshacks.com/how-to-check-240-voltage-with-a-multimeter |title=Anatomy of a high-quality meter |access-date=2015-11-05 |url-status=live |archive-url=https://web.archive.org/web/20061018221940/https://electronicshacks.com/how-to-check-240-voltage-with-a-multimeter |archive-date=18 October 2006 }}</ref> Category-rated meters also feature protections from over-current faults.<ref>{{cite book|last = Mullin|first = Ray|title=Electrical Wiring: Residential|publisher=Thompson Delmar Learning|year=2005|page=6|isbn=1-4018-5020-0}}</ref> On meters that allow interfacing with computers, [[Opto-isolator|optical isolation]] may be used to protect attached equipment against high voltage in the measured circuit.

Good quality multimeters designed to meet Category II and above standards include high rupture capacity (HRC) ceramic fuses typically rated at more than 20&nbsp;A capacity; these are much less likely to fail explosively than more common glass fuses. They will also include high energy overvoltage MOV (Metal Oxide [[Varistor]]) protection, and circuit over-current protection in the form of a [[Polyswitch]].{{Citation needed|date=February 2022}}

Meters intended for testing in [[electrical equipment in hazardous areas|hazardous locations]] or for use on [[blasting machine|blasting circuits]] may require use of a manufacturer-specified battery to maintain their safety rating.{{Citation needed|date=February 2022}}