How do I review a DMM

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Some reviews focus on verifying as many ranges as possible on the DMM, in my reviews I will not use much space on that. Instead I will focus on what ranges and functions it supports, including a schema that show the most important ranges.

DMMschema1

The first part will show all the common ranges with the maximum reading for each range. When possible I will verify the maximum reading and include the value I see (Many DMM's allows a little bit higher reading than specified).
If I find some range with strange behavior or large errors I will mark them with a red background.

DMMschema2

For DMM's with temperature function this section will contain data. The first line will show the possible formats, i.e. where the comma is placed.
The second line will show the supported sensors. Any DMM that supports a thermocoupler (the letters) will have a built-in sensor, but it may not be possible to read it directly (Shorting the thermocoupler input will always show the reading).
The "Build-in" means that the meter can directly show internal temperature.

DMMschema3

This is a list of various functions that the meter supports.

DMMschema4

If I test a meter with interface this will show what is supported:
DMMschema5

Tolerances for some of the ranges. Both lines are for 25C (or thereabouts) and without special function activated. Function like Low-Z and VFC will usual reduce precision.

DMMschema6

This is the data sheet values for frequency for voltage, current and frequency counter input. A rms meter will usual be able to measure sinus voltage at considerable higher frequency.

DMMschema7

How much voltage is dropped across the meter when measure current. To make it easy to compare meters I have selected some fixed current, not the maxium for the ranges.


Equipment

Even though I do not verify all ranges I do some checking.

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This meter secures that I have enough precision, even without a reference.
It can also do 4 terminal ohm, making it easy to get precise resistance measurements of the probes.

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To generate precise currents and voltage this meter is very useful. It can also be used as a ohm meter.

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For frequency, RMS/average and other test where I need AC or pulses I uses this generator.

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Probes may be fine for voltage measurement, but when testing the frequency counter into the MHz range, it is not a good solution.
The DMM range will depend on input voltage, to keep that fairly predictable I use a coax cable from my generator and first convert to banana plugs at the DMM connectors.

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For DC voltages in the 0-10V range this handy little reference works very well.

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For testing resistance and capacity I have a box with fairly precise resistors and capacitors.

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For checking when the DMM change range and continuity this decade box is more useful.

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And for capacity a decade box is also useful, together with some loose electrolytic capacitors for the high values.

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When checking continuity speed I use a MOSFET driven from a pulse generator. To make it easier to use I have put the MOSFET in a box.
I try to find the pulse with where it beeps each time.

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I have power supplied that can deliver a lot of current (50A), but when testing a clamp meter it is not enough. This small coil makes it very easy to check a clamp for a few hundred amperes. Because I do not now the exact number of turns (It is about 200) I do not know exactly what it is supposed to show, but I can see how it behaves at maximum current.



CAT rating

DMM's usual has a CAT rating printed on them, this defines where it can be safely used and for what voltage.

The ratings are (Explanation is simplified):
The difference between the above CAT's is transient voltage and impedance.

CatRatings

A CAT III 1000V or CAT IV 600V meter must be able to handle 8000V from 2ohm (i.e. up to 4000A) on any range, including the ohm and current ranges. This requires some good protection and fuses that can break high current.