DMM vs Analog Multimeter

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Bob Lewis:
The question is not analog vs. digital. It is input impedance. An inexpensive or an older analog meter like the Simpson 260 will have a lower input impedance than most digital meters and that will tend to load down high impedance circuits when trying to make measurements.

As for the usability of the readout, analog meters make it easier to make an alignment adjustment for a certain value while digital meters make it easier to read a single value to see if it is in the proper range. You'll find some digital meters that also have an uncalibrated bar graph (analog) for making peaking adjustments.

Personally I just use a digital meter. Some of the newer digital meters even include frequency, capacitance, and other measurements and are pretty reasonably priced.

Chuck Guenther:
I have taught circuit theory both at the engineering and technician levels since 1982.  I always skip the lab exercises involving analog meters.  Even the cheapest DMM's are more accurate and present much higher impedances than a Simpson 260.  

When I designed circuits for a living back in the late 60's and early 70's, we used Simpson 260's for continuity checking, that's all.  Even then we used DVM's (with Nixie tube displays) for any measurements important enough to write down.    

If the 260 were all I had, sure I'd use it.

Chuck  NI0C

Stephen L Crook:
A VTVM or FET analog meter will have the high input impedance of a DVM, typically 10-22 Megohms, a Simpson 260 or other analog VOM will be much lower input impedance however, 5,000 to 20,000 ohms/volt typical, higher for a good meter like the 260, lower for small, low cost meters generally (usually listed on the bottom of the meter scale in fine print). For low voltage low impedence sources (automotive, AC line power, etc. the 260 would be fine, for high impedance, (often high voltage) applications, e.g vacuum tube circuits, high the 260 may load down the source too much, so a VTVM, (or FET) or DVM (or o'scope & 10X probe) would be preferred.

The DVM will give more precise readings, the analog will be better suited to peaking/dipping/nulling applications (where absolute voltage is less important), viewing varying voltages/values (e.g. an S meter or watt meter), or as a quick reference  (a glance is all that's required to see if you're in the right range) -- each has their place.  

Nelson Derks:
'Scuze the minor diversion... 40-ish years ago the Simpson 260 and Triplett Model 60 were the workhorses of the electrical trades. Considering the kit manufacturer tested a properly working sample with a DMM, best bet would be to replicate that setup as closely as possible for a proper comparison to factory spec's.

Could a Simpson 260 do as well? Sure, but there will be more circuit loading and if you know which way to compensate for the meter, no prob. There's the rub... Which direction and how much?

I've used analog meters for years, but the DMM has me so spoiled that going back is like tying one hand to my foot. Auto-Ranging and Fluke's Touch Hold feature are very easy to get used to.

As for accuracy, yeah, even a cheap DMM has the edge.

But... Sitting in front of me as I type this is an original Westinghouse Type PY-5 Portable Volt-Ammeter.

Mine is similar to the pic, but has three additional terminals in the lower right corner for volts and labeled 150, 300 and 600 respectively. The three terminals along the top edge are labeled +/-, 10 and 5 (amps). Inside the cover is a hand typed certification sheet signed by M Donnelly on September 11, 1939.

Tells me the meter is of the moving vane type and correct to 1/2 of 1% between 15 and 133 cycles AC from 10 to 35 degrees Centigrade. DC accuracy is 1% of full scale. Considering the age... I'd say that's not bad.

Resistance of the 150 volt range is 4,680 ohms, 300 volt range 9,360 ohms. Inductance of the 150 and 300 volt ranges is 360 millihenries. Let's just say this meter would not be my first choice for audio or RF work, but it was definitely "built"... By the Westinghouse Newark Works in Newark, NJ.

Bonus Points: If you had a newspaper from 9/11/1939, what would be the big story near the top of the front page?

Pat Bailey:
Simpson 260 (any series) typically has an input impedance of 20K ohms per volt on the DC ranges, and 5K ohms per volt on AC ranges).

As far as accuracy, I've seen 260s and their military equivalents, the AN/PSM-4 series, reading just as accurately as a typical DMM such as a Fluke 87.  A digital display is often equated with "accuracy", but it ain't necessarily so.  It might be highly precise and still be highly wrong.  Any meter of any type requires periodic calibration in order for its indications to have any qualitative meaning.


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