Analog meter VS a DMM?

[etstudent]

I'm waiting for my analog meter to arrive before starting my next set of challenges. The next ones are linear integrated circuits. You can't use a DMM, it say specifically not to, and in bold letters to use an analog meter only. What are the main differences between the two, and are there circumstances an analog meter is to be used only over a DMM? Thanks for the info I'm sure you guys have.

[FenderBender]

I'm no expert myself BUT an analog meter should give you better sensitivity to small changes in (whatever you are measuring) because as it says...it's analog...there's no ADC to turn it into a digital number. An analog meter can read an infinite amount of values in a range...technically.

I'm not sure exactly what you are using it for but that's part of the reason to use an analog meter over a DMM. However, most of the time a DMM is your best friend.

Also, what analog meter did you get? Even a mid-priced analog meter doesn't always cut it.

[ejeffrey]

Analog is easier to see quantities that are changing in the few Hz range.  Digital displays become useless when they are changing every update, for instance if a quantity is flickering between 6.99 and 7.00 is very hard to read, especially if the meter has a high update rate.  Most DMMs have an averaging mode to provide a more stable reading.  With an analog meter on the other hand, you can see both the average value and notice that the needle is oscillating back and forth.

Traditional analog meters are much less ideal than digital meters.  Their voltage modes have lower impedance, their current modes have higher impedance, and their resistance modes have less control over the injected current.  There are analog meters with FET preamps that solve some of these problems.

Analog meters are more delicate.  Overcurrent through the movements coil can damage it, so you have to be careful to make sure you are on the right range.  They are also more susceptible to mechanical shock.

Analog meters require more care by the user to get an accurate reading.  You need to use the mirror scale to eliminate parallax error and even then you get at best resolution equivalent to a few hundred counts.  A careless user can have much worse.

[poptones]

I don't even have a digital meter right now. And a very good analog meter can be quite affordable.

http://www.ebay.com/sch/i.html?_trksid=p3984.m570.l1313&_nkw=simpson+260&_sacat=0&_from=R40

[etstudent]

Thanks guys, I forgot about analog meters being better with fast changing voltages. Interesting info guys, thanks a lot.

[SeanB]

I would guess forcing them to use an analogue meter is to reinforce the idea that precision is not just a digital idea, but that it is an analogue thing, and as well to teach about measuring accuracy and the importance of observer training and bias in getting an accurate reading.

[hepcat]

An analog meter would most likely be better for testing the resistance of contactor and relay contacts, because its short circuit current flow is substantially higher than a DMM.  As an example, my Agilent U1272A puts out about 640 microamps, as measured by my Fluke 189.  According to the data sheet, a Simpson 260 puts out 125 milliamps on the RX1 scale.  There are some situations, such as relay contacts, where you actually want to 'stress' the connection.  A DMM, with its miniscule current flow, may be harder pressed to give a true and definitive reading in such situations.

Regards,


Jason

[alm]

This highly depends on your definition of a 'true and definitive reading'. Is 125 mA a good test for a relay in a test equipment switching matrix, for example? Or a telephone exchange (in the days that they still used relays)? Is it a good test for a relay switching a large motor that draws tens of amps? Dry circuit testing is actually a fairly common test for connectors and switches, since it measures the oxides and contamination that might form. Testing at 125 mA is likely to remove the contamination, making the test useless.

[w2aew]

As stated in earlier replies, analog meters are very nice in a couple of instances...  It is much easier to watch the movement of an analog meter when you are adjusting or tuning a circuit parameter. I used on in my PLL video and the video on using diodes as switches.  It's much easier to watch a meter move up/down vs. trying to watch digits increment up and down.

Also, the meter movement, due to its inertia, will tend to filter signals that are wiggling about.

They are great for these circumstances when a relative reading is helpful, rather than a precise, accurate value.  For the latter, a DMM is generally better.

In my lab, I'll always have both.

[madshaman]

As stated in earlier replies, analog meters are very nice in a couple of instances...  It is much easier to watch the movement of an analog meter when you are adjusting or tuning a circuit parameter. I used on in my PLL video and the video on using diodes as switches.  It's much easier to watch a meter move up/down vs. trying to watch digits increment up and down.

Also, the meter movement, due to its inertia, will tend to filter signals that are wiggling about.

They are great for these circumstances when a relative reading is helpful, rather than a precise, accurate value.  For the latter, a DMM is generally better.

In my lab, I'll always have both.

That being said, who makes good analog meters and who makes bad ones?

[Spawn]

Gossen make good ones and top of the range model is around 900USD:
http://www.gossenmetrawatt.com/english/produkte/analogmultimeters.htm

and bad ones... I think there is a lot bad ones out there. Just stay with a known name and you will be good. It does not have to be new either.

I got 2 analog meters last year, not new they are 38 years old now but still working nice:
https://www.eevblog.com/forum/reviews/philips-multimeter-pm2505-teardown/

[w2aew]

As stated in earlier replies, analog meters are very nice in a couple of instances...  It is much easier to watch the movement of an analog meter when you are adjusting or tuning a circuit parameter. I used on in my PLL video and the video on using diodes as switches.  It's much easier to watch a meter move up/down vs. trying to watch digits increment up and down.

Also, the meter movement, due to its inertia, will tend to filter signals that are wiggling about.

They are great for these circumstances when a relative reading is helpful, rather than a precise, accurate value.  For the latter, a DMM is generally better.

In my lab, I'll always have both.

That being said, who makes good analog meters and who makes bad ones?

I love my old Simpson 260. Standard in the industry for 30-40? years.

[rsjsouza]

Another use that I think VOMs are unbeatable is to find the polarity of the windings in unmarked transformers - the coil movement is really subtle but clearly indicates if it is going above or below zero. Something that is very difficult to see in a DMM, even with the bargraph.

[robrenz]

Another use that I think VOMs are unbeatable is to find the polarity of the windings in unmarked transformers - the coil movement is really subtle but clearly indicates if it is going above or below zero. Something that is very difficult to see in a DMM, even with the bargraph.

Please explain, I didn't know transformer windings had polarity.

[rsjsouza]

Well, "polarity" is how I learned, but it may not be the most accurate term in English.

It is simply the relative direction of the windings of a transformer between primary and secondary, or sometimes multiple primaries. The page 7 of this document explains a bit more.

As a more practical example, some dual-voltage transformers have two primary coils that must be connected in parallel (if using 110~127V) or in series (if using 220~240V) - however, if you connect the two coils in reversed "polarity", nothing comes out of the other end.  This other link illustrates this and other cases.

To quickly find the relative direction of the windings, you simply put the VOM in parallel with one winding, and "scratch" the other winding in the terminals of a DC battery (check the "ASCII art" below). If the VOM deflects positively, then you know the Battery + and the VOM + are in phase. If it deflects negatively, then they are reversed.

    [VOM +] ------- | |
                  | | |
                  C | |
          110V    C | |
          Primary C | | ---------
                  C | | |
                  | | | C
    [VOM -] ------- | | C
                    | | C   Secondary
[Battery +] ------- | | C
                  | | | C
                  C | | C
        110V      C | | |
      Primary     C | | ---------
                  C | |
                  | | |
[Battery -] ------- | |

[robrenz]

Thanks, I always like learning something new.

[rsjsouza]

To quickly find the relative direction of the windings, you simply put the VOM in parallel with one winding, and "scratch" the other winding in the terminals of a DC battery (check the "ASCII art" below). If the VOM deflects positively, then you know the Battery + and the VOM + are in phase. If it deflects negatively, then they are reversed.

Actually, I should have clarified something: "If the VOM deflects positively when the battery is connected and negatively when the battery is disconnected, then you know the Battery + and the VOM + are in phase."

[Tepe]

I got 2 analog meters last year, not new they are 38 years old now but still working nice:
https://www.eevblog.com/forum/reviews/philips-multimeter-pm2505-teardown/

I've had this one since the late 70s:

[madshaman]

I love my old Simpson 260. Standard in the industry for 30-40? years.

Thanks for the recommendation, and also those of others!

When I started as a kid, all I had was a hand me down analog meter (whose brand I don't even remember) and an ancient health kit scope built out of tubes from my grandfather.

Don't have an analog meter anymore, my childhood equipment and projects are long gone due to unfortunate circumstances, but I think I'll pick one up!

[nanofrog]

I love my old Simpson 260. Standard in the industry for 30-40? years.

Thanks for the recommendation, and also those of others!

When I started as a kid, all I had was a hand me down analog meter (whose brand I don't even remember) and an ancient health kit scope built out of tubes from my grandfather.

Don't have an analog meter anymore, my childhood equipment and projects are long gone due to unfortunate circumstances, but I think I'll pick one up!

You might want to take a close look at http://simpson260.com/ for buying a used one, as it sorts out the differences between the revisions and models.

Simpson still makes them though, so there's that option as well.   

[ivan747]

I still don't understand what are the advantages of an analog multimeter vs. a digital multimeter with a fast updating bar-graph display. And the second thing I don't understand is why are they restricting students only to use almost obsolete, limited technology with low input impedance.

[CraigHB]

I was going to say the same thing.  I have a high end DMM that has a bar graph as well as a digital display.  It seems to be able to do the same thing an analog meter can. 

[w2aew]

I still don't understand what are the advantages of an analog multimeter vs. a digital multimeter with a fast updating bar-graph display. And the second thing I don't understand is why are they restricting students only to use almost obsolete, limited technology with low input impedance.

A couple of reasons they want you to use an analog meter.
- the analog meter movement has 'infinite' resolution, no discrete segments of a bar graph.
- the bar graph doesn't work real well when watching a parameter that crosses an auto-range boundary.

From an educational standpoint, the analog meter forces you to THINK more about what your circuit is doing.  You need to think about the polarity of what your measuring, and what approximate voltage level you expect to see. A modern, auto-ranging DMM eliminates most of the thinking part except picking the right mode.

[CraigHB]

A couple of reasons they want you to use an analog meter.
- the analog meter movement has 'infinite' resolution, no discrete segments of a bar graph.
- the bar graph doesn't work real well when watching a parameter that crosses an auto-range boundary.

True on the first point, but it may be hard to notice the movement in a needle that would represent one bar segment to the next.  Such small deflections can be hard to see.

On the second point, I can set my meter to range manually which would eliminate any change in scale due to a range shift.

In terms of educational value, I can see where an analog meter might be desireable, but practically, I don't see a huge advantage over a meter that provides a graphical representation of a gauge.

[ivan747]

A couple of reasons they want you to use an analog meter.
- the analog meter movement has 'infinite' resolution, no discrete segments of a bar graph.
- the bar graph doesn't work real well when watching a parameter that crosses an auto-range boundary.

True on the first point, but it may be hard to notice the movement in a needle that would represent one bar segment to the next.  Such small deflections can be hard to see.

On the second point, I can set my meter to range manually which would eliminate any change in scale due to a range shift.

In terms of educational value, I can see where an analog meter might be desireable, but practically, I don't see a huge advantage over a meter that provides a graphical representation of a gauge.

My thoughts exactly. And considering good quality analog multimeters can cost as much as their digital counterparts, I think they are losing their place.

About the infinite resolution: I don't think it's going to be easy to see a 5mV change on a 5V scale, that's 0.1% of the full scale. Assuming the needle can swing 135 degrees. That is 135/360=0.375*100=37.5% of a full circle. Let's assume the needle is 5cm long. The radius of out circle is 5cm. The total perimeter of the arc that forms the circle is 5*2*pi= ~31.41. The length of our 135 degree arc is 0.375*31.41= ~7.779. That is the distance the needle moves when you apply the maximum voltage your range allows. We said earlier that on a 5V range, a 5mV change is 0.1% or the full scale, so: 7.779*0.001=0.00779cm or 77.9µm (0.0779mm). That's 3 mils, the same size of a pixel in an iPhone Retina display or as small as board manufacturers go on trace width.