8
\$\begingroup\$

I know electronics testing with digital multimeters is easier than analog, but I'm wondering whether there is any electronic testing which can done with only "Analog" multimeters? For example measuring AC voltage with a square waveform: some people say it can't done with a digital multimeter because they are made for measuring sine waves from the grid. If that's right, are there any other tests that require analog multimeters?

\$\endgroup\$
  • 3
    \$\begingroup\$ Anyway, regardless of whether the display is analog or digital, the same assumptions go into both types of meters with regard to how they are calibrated with respect to different waveforms. \$\endgroup\$ – Dave Tweed Sep 28 '17 at 22:11
  • 2
    \$\begingroup\$ AC meter voltage tends to measure peak and assumes sine wave to display rms, but not accurate for pulses \$\endgroup\$ – Sunnyskyguy EE75 Sep 28 '17 at 22:18
  • 8
    \$\begingroup\$ I think an analog meter is somewhat better than digital for finding intermittent poor connections - it is easier to see a wiggling meter needle than to read flickering digits. \$\endgroup\$ – Peter Bennett Sep 28 '17 at 22:40
  • 1
    \$\begingroup\$ @PeterBennett Exactly. It was that behavior, in fact, that I was thinking about when I wrote my answer. I thought about mentioning my motivation, but then felt it would require too much added explanation. \$\endgroup\$ – jonk Sep 28 '17 at 22:41
  • 1
    \$\begingroup\$ An analog multimeter will be more likely to show you a fair average value if you do not know the specs of the multimeter or the signal ** there are techniques allowing digital meters to measure "irregular" signals, but you need to know the specs ** An analog meter can be built get the power from the signal it is measuring, digital meters are not made to do so ** An analog meter likely loads your signal more than a digital meter does, so for precise measurements you need to take that into account (and use a wheatstone bridge measurement if needed). \$\endgroup\$ – le_top Sep 28 '17 at 23:14
21
\$\begingroup\$

You didn't ask for a complete exposition about the differences, so I'm not going to try and tabulate anything here. You asked about where an analog meter might be better (or should be preferred.)

Probably one of the better cases to try, if you are seriously looking to see where a very high quality digital meter (such as a Fluke 87) does far more poorly than a very cheap (nearly free, by comparison) analog voltmeter (such as a TekPower TP7040 -- an inexpensive, fine unit that includes the meter mirror strip [and in my opinion is better than the TekPower TP7050]), is to set up a signal generator to provide a sine wave at \$1\:\textrm{Hz}\$ that varies from about \$3\:\textrm{V}\$ to about \$7\:\textrm{V}\$ (in short, it has a DC bias to it that you ALSO want to see.) Now, hook up both meters.

A digital voltmeter (DVM) will spend all of its time rooting around, going from ERR to who knows what, trying to "auto-range." And, in effect, pretty much NEVER telling you anything useful at all except perhaps that the signal is "difficult." Meanwhile, the cheap analog voltmeter will very nicely swing back and forth between the two values and clearly show you a LOT better detail about what is taking place. You will even have a decent idea about the minimum and maximum values and that it moves smoothly between them.

It's like night and day.


Setting a DVM to manual mode and to the appropriate DC range (when both these features are available) stops the auto-ranging behavior and allows periodic display updates of the measurement. But the values appear to be taken "at random." It's much easier to see what is going on with the analog display, for some kinds of measurements. If also available in manual mode and also with the appropriate DC range selected, setting a DVM to use still faster display update rates improves this situation, too. (My Tektronix DMM916 allows this.) But the point remains for observing some situations. Besides, all we are doing here is narrowing cases by spending more money on the DVM.

\$\endgroup\$
  • \$\begingroup\$ Of course, you can always just manual range the '87. \$\endgroup\$ – Peter Sep 28 '17 at 22:58
  • \$\begingroup\$ @PeterK Yes. But the Fluke 87 was only offered as an example. I could remove it (and perhaps I should) from what I wrote without changing the meaning. \$\endgroup\$ – jonk Sep 28 '17 at 23:08
  • \$\begingroup\$ Some DMMs have a bargraph in addition to the digital display, which would let you visually see the swing of slowly changing signal, much like the needle of an analog meter. \$\endgroup\$ – jwygralak67 Sep 29 '17 at 19:07
  • \$\begingroup\$ @jwygralak67 They do. And I didn't mention it, though I knew about it. One of the reasons I mentioned the Fluke 87, in particular, is because it actually has one of these bargraph displays that works "pretty good." (Better than a lot of them.) But it still isn't nearly as good as an analog meter needle -- in some cases, anyway. \$\endgroup\$ – jonk Sep 29 '17 at 19:10
9
\$\begingroup\$

When the service manual calls out to use an analog meter (such as the venerable Simpson 260) and loading would be different using a digital meter.

Some better digital meters have an analog-like segmented LCD display that mimics a meter movement (with a relatively high sample rate) so restores some of the advantages you would see following varying signals.

You an pick up variations visually from an analog meter easily- whereas digital meters flicker in the least significant digit is just about as distracting as flicker in any other digit.

Digital meters and analog-like displays that auto-range can be even worse. Usually you can turn it off.

In some cases digital meters have very high impedance (tens of M or even G\$\Omega\$) which can lead to confusing results, whereas analog meters- those that don't contain amplifiers take a fair amount of current to crank the needle around against the torque of the hairspring.

\$\endgroup\$
  • \$\begingroup\$ What about AC voltage "frequency" limitation? my old digital multimeter burned when i measure 150V AC voltage with very high frequency some thing more than 10KHz (square wave), here i should use analog, yes? \$\endgroup\$ – mousa Sep 29 '17 at 10:28
  • \$\begingroup\$ Whatever you use you have to know the limitations. I don't think the display technology is necessarily completely decisive. RF voltmeters usually have an amplifier and then either a digital or analog display. Consider this vs. this \$\endgroup\$ – Spehro Pefhany Sep 29 '17 at 15:29
6
\$\begingroup\$

Analog multimeters have the advantage of no battery required for measuring voltage and current. Thus they can be used in the field without worrying about batteries going bad. They are also very useful for making adjustments on circuits that require setting to a minimum or maximum. It is much easier to see such settings on an analog scale then with a digital readout. However, as far as AC voltages go, most analog meters are calibrated to read the RMS value of a sine wave and will be inaccurate with other waveforms. Many digital meters, however, have RMS to DC converters, and will read the correct RMS value for sine waves and most other AC waveforms including triangles and square.

\$\endgroup\$
  • 1
    \$\begingroup\$ Many digital meters are also inaccurate with other waveforms. \$\endgroup\$ – immibis Sep 29 '17 at 1:43
  • \$\begingroup\$ @immibis Which is why I specified meters with an RMS to DC converter. \$\endgroup\$ – Barry Sep 29 '17 at 12:12
4
\$\begingroup\$

An analog meter is useful for instantly recognizing the scale of the signal when it rapidly changes so the brain can interpret time varying patterns faster than deciphering contantly changing slow sampled digits that may appear to be confusing but with less accuracy for stable readings on a DMM. Although some DMM’s have Min/Max stored as well or sample and hold reading after probe removed. DMM’s vary from 1M to 10M while analog coils are rated in Ohms/V or its inverse in uA full scale (e.g. 50 uA) then scaled with series R and shunts for volts and amps.

The instant recognition is like comparing an analog clock to digital one and how quickly your brain is trained to interpret it. Thus for audio, VU meters are preferred over DMM’s. Digital audio meters need a peak memory and decay time with a bar graph display, which is like analog.

  • There are voltage and frequency limitations for both and all meters. You would never use either for 150Vac 10kHz ,rather use a special 10:1 probe matched to the meter impedance or a non-inductive voltage divider of suitable R values or a C divider using suitable parts that would not load or resonate with the circuit. (i.e. SRF >> f)

    • In some cases smps boost transformers may have a tertiary small winding for sampling the output voltage.

    • Similarly, for HiV or UHV ac lines, you would never use a resistive divider due to the power loss implications and length of the conductor for flashover. Rather you might use a capacitive divider which tend to be large gapped small C's into large value C shunts rated for transients expected for grid voltages with large ratios.

    • You would never use either meter on a 600Vac catIII line because a transient would cause an arc flash that could vaporize or seriously burn the user causing death. Nor would you use on RF unless it had an impedance matched termination rated for that band and power level.

\$\endgroup\$
3
\$\begingroup\$

Measuring noise amplitude presents two problems:

  • Most often, RMS measurements are wanted (to measure noise power) which analog meters generally don't provide. Bummer.

  • Noisy waveforms can be much more easily averaged by eye on analog meters. Flashing digits are horrible to average by eye. Very few true-RMS digital meters allow you to change their RMS averaging time constant. Spectrum analyzers offer a "video filter" variable time constant.

I favour the analog meter, because the RMS conversion factor can be calculated to scale the average reading to RMS. And errors due to a fluctuating meter needle can be estimated more easily. Spectrum analyzers are probably the ultimate for noise measurements.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.