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When selecting a multimeter, what should one look for in terms of safety features and measurement capabilities?

What can you look for in the specifications to tell a good meter from a crappy one (besides price)?

I'm looking at cheaper multimeters for hobby use - so I don't need super high accuracy, and am not planning to measure any higher voltages than normal household power. But I want something that's a little better than the $10 one I have from Canadian Tire.

I'm not looking for specific product recommendations, just what to look for in choosing a multimeter.

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Question is too vague. –  Leon Heller Aug 24 '12 at 13:02
    
Tried to make it a little less vague. –  Grant Aug 24 '12 at 13:12
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If you don't what you need from a multimeter probably any one would do. –  Bruno Ferreira Aug 24 '12 at 13:40
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@Bruno - Me no agree. It's not because you don't know about all the features that they can't be relevant. When you tell that repair engineer with his manual-ranging meter that they now also have autoranging meters, and explain what they do, he'll buy one on the spot. –  stevenvh Aug 24 '12 at 14:49
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When I got my first digital multimeter (they were pretty new then) I made sure to get one that measured to 0.01 ohm, since I was working with motors at the time. If you have specific areas of interest, read up on what types of measurements you're liable to want to do, and make sure to get a meter that will handle that. –  mickeyf Aug 25 '12 at 3:16

6 Answers 6

up vote 13 down vote accepted

Accuracy. Which is something else completely than resolution. Your meter may have 4 digits, that's a 0.1 % resolution, but if its accuracy is only 1 % that last digit is useless.

Accuracy is given by two numbers, an absolute error and a relative error. The relative error is the one expressed in %, like 0.5 %. The absolute error is expressed in digits, like 2 digits. If you have a 0.5 % meter, +/- 2 digits, that means that a reading of "100.0" may as well be (100.0 + 0.2) * 1.005 = 100.7. Engineers fresh from uni often neglect or underestimate measurement error due to the number of digits the meter gives them.

The absolute error becomes less important when the reading gets larger, like for a 900.0 reading 2 digits are relatively less (0.022 %) than for a 100.0 reading (0.2 %).

RMS. If you need to measure non-sinusoidal waveforms you'll need that. Non-RMS meters assume your waveform is a sine, and will only produce correct results if it actually is.

Autoranging. You don't want to put your probe aside all the time to turn the knob.

USB interface. May sound as luxurious, but can be handy to log a whole series of measurements in the computer.

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"that last digit is useless"...Not strictly true. If you're comparing voltage at two nodes, and you want to know which one's higher (but don't care so much the exact values) then the last digit can be useful. –  The Photon Aug 24 '12 at 15:16
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@ThePhoton - I guess that depends on what causes the error. If it's component tolerance, then I agree; then the error won't vary between measurements. If it would be caused by, let's say, noise, I'm not so sure. –  stevenvh Aug 24 '12 at 15:20
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Exactly. If the accuracy limitation is because of noise, you're right...the last digit is basically useless (but you should also see the display jumping around). If it's a systematic error, there's still some value to having the extra precision. –  The Photon Aug 24 '12 at 15:32
    
How to test accuracy of a multimeter once you get it (this can help you determine if the battery needs to be replaced; the accuracy drops when the battery level does): electronics.stackexchange.com/questions/78768/… –  Annonomus Penguin Aug 12 '13 at 22:53

In addition to stehenvh's answer you might want to check EEVblog #75 – Digital Multimeter Buying Guide (52min. running time).

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If you are completely clueless (as am I), this video does a great job of explaining the typical features of a multimeter and why they may be useful to you. –  Zak Jan 21 '13 at 17:48

Autoranging, as stevenvh said, is very useful.

I always miss the ability to measure unusual things like capacitance when I don't have it. Some meters also have temperature probes, or ability to measure inductance.

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Frequency & duty-cycle. Useful for sanity-checks on signals at the interface of a u-controller, timing software loops (complement an output bit on every loop execution), timing a function (raise & lower an output on entry & exit). I probably use this one function as much as all of the rest combined.

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Good things to look for if you may be tempted to poke at light switches, wall outlets power supplies etc or anything over 50V or that might be near something > 50V once in a blue moon.

  1. Safety - HRC fuses, MOVs, creepage/clearance distances, overlapping case halves.
  2. Separate sockets for A (uA/mA, A) and V - Safety.
  3. Jack alert - don't want to measure 240V using the A socket. Safety.
  4. Flexible test leads/probes with marked credible safety rating.

Good things to look for in general

  1. Clear display with good contrast - $1000 meter no good if can't read it.
  2. Stable stand - see above.
  3. Autoranging
  4. Accuracy - not as important as you might think but 0.5% better than 1%
  5. Microamps range - One day you might be curious about base current on a BJT.
  6. Touch-Hold (not Data Hold) - press button, look at DUT, connect probes, hear beep.
  7. Fast, latched continuity buzzer.
  8. True RMS - if you need accurate measurements of non-sinusoidal AC.
  9. Bar graph.

Things that may be unimportant

  1. Capacitance range - few measure down to 1 pF caps. Buy a $10 cap meter kit.
  2. Diode test - don't think you can test LEDs with it.

Bad things to look for and avoid

  1. Transistor test - invariably a sign of a cheap unsafe meter.
  2. Glass fuses (or no fuses)
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I was about to ask this same question. I did some research and found this really insightful article. Answered many questions I had.

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Sorry for the issue with the previous answer. Just linked it here. –  Thomas May 26 '13 at 3:25

protected by W5VO Aug 24 '12 at 17:25

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