What to look for in a multimeter?

Question

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.

Answer 1

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.

Answer 2

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)

Answer 3

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.

Answer 4

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.