How many still carry an analog meter in their meter arsenal?

With the sensitivity and false readings a DVM can give, I think it is a must to have something at your disposal (besides a solenoid type indicator) that can see the actual voltage.

Roger

I've always though that DVM's should have a high ohm shunt resistor across the leads to "bleed off" phantom voltages and readings from capacative or inductive effects of parallel wires.

A switch could be there so the resistor was optional and the leads could be shunted if something seemed odd. Then nobody would need an analog meter.

Apparently I have one in my arsenal. I found it the other day when I was going through the van looking for knock out fillers. I don't know if it still works.

I feel that it is necessary to have more than one different type of tester at your disposal. Where one tester does not produce reliable readings, a different one will produce an accurate reading. Also, it is my understanding that in extremely cold temperatures, a digital meter is almost useless.

I still have several, including my trusty old Avo 8 and a Simpson 260.

In some electronics work you need to adjust for a null or a peak, and an analog movement makes that much easier than trying to keep up with the constantly changing digits of a DVM. The analog movement is also much easier to follow for voltages which are varying too quickly for a DVM to "keep up" (but not quick enough to require a 'scope).

While my day to day diagnostics are gathered through a older Greenlee DVC6 I've always liked the "throw away" analog multimeter. Just about the cheapest I've found has come from Radio Shack. That way, if I drive over it, drop it, or (most likely ) forget to change the scale back from Ohms before contacting a live circuit, I'm not out much. I keep two on the truck.

A modest input impedance d'Arsonval analog meter smoothes out the "jitter" of the step-wise digital world

... I had a Simpson,..gave it to my father when I found it was a pain to read,..then got me a DMM, now I have an "Archer" analog set from Radio Shack that I "built" myself,...don't use it much any more tho'...took out the batteries while storing it...
Russ

I had to ring out a multi conductor flex cable the other day. One circuit was a flasher. Digital meter was next to usless, found it with an analog in a couple of seconds.

Use a variety of Low, Medium and High input Impedance Analog Voltage Meters + Multimeters, in conjunction to the DVMs and DMMs.

Also use my old Analog type "Amprobe" clamp-on Ammeter, in conjunction with the Digital counterparts.

The Analog display - with the sweeping "Needle" - makes a great visual aid when levels are fluctuating.

My most simple fix, as to tame peaks shown on a High input Impedance DVM is to connect my Wiggy in Parallel with the DVM's leads.
Aligator clip the DVM's leads to the circuit, then place the Wiggy's leads in the same circuit.
Dumps the Cap. charge safely, and no shunt Resistor is needed!

Scott35

Crash said:


Yes, I've noticed that LCDs (liquid crystal displays) don't like cold weather.

They turn purple. Used to have that happen a lot with a digital-tuning radio with L.C. display where it would get dark if I carried it around in cold weather. Once I got inside it would return to normal grey.

I've got a little analog VOM that I picked up for $12 at a DIY shed a few months back.

About the size of a packet of cigarettes, it needs a pen-light battery for use as an ohm-meter, but works fine as is when used as a voltmeter, which is OK for quick-n-dirty readings of light sockets or other current sources, etc.

Don't forget that we can also have high-impedance analog meters, again used regularly in the past in radio/electronics work in the form of the VTVM (Vacuum Tube Volt Meter), or the more modern version with an FET (Field Effect Transistor) input.

Scott,
You'd probably appreciate an old lab-type DVM I have here. Built by the British Solartron company in the early 1970s, it's in a 19" rack cabinet which weighs a ton, and has inch-high Nixie tubes for the readout. Input impedance on the lowest range is over 2000 megohms, and it has built-in calibrators, 50Hz filters, variable-rate or one-shot sampling, maximum/minimum hold etc. I got it for just a few pounds, but it must have cost a fortune when new!

[There is a good spoof on Nixie displays at http://www.gpstime.com/nixie.html]

On high-impedance voltmeters and "ghost" readings, NEMA engineering bulletin 88 dated Oct 1998 suggesting a parallel resistor. The concept is valid but their recommended RESISTOR CAN BE DEADLY.
http://www.nema.org/engineering/papers/PhanBull88.html

Their Feb 2003 revision of engineering bulletin 88 quietly axed the resistor suggestion.
http://www.nema.org/docuploads/97F7D189-813B-4EFB-95A878ADAD82F954//bul88.pdf

What exactly is the safety concern over a shunt resistor?

The only two things I can see are the following:

1. There's a remote possibility of the resistor shorting-out, resulting in a near zero-ohm condition between the probes. That objection could be overcome by using fused test leads, as are commonly fitted to industrial meters these days anyway.

2. There will be a much lower resistance between the leads, and thus a greater risk of shock if someone is touching one probe while the other is being connected to a hot terminal. But that's just down to proper procedure: I always make sure the second lead is safe while connecting the first anyway.

I have no argument with the concept of a shunt resistor, but someone at NEMA had their head up their hind end when recommending 500-1000 ohms.

From http://www.nema.org/engineering/papers/PhanBull88.html

• NEMA recommends placing a resistor of approximately 500 to 1000 ohms across high-impedance multimeters.

OK, so 500 ohms across 120V results in a power dissipation of ~29 watts.

And, 1000 ohms across 240V results in power dissipation of ~58 watts.

In either case, it’s very likely that a ½-watt resistor from a Radio Shack blister pack will deflagrate in the process.

Increase the resistor by a factor of 100. Even 50,000 ohms across 240V is a power dissipation of ~1.2 watts, which will cook a ½-watt resistor if left connected for any significant amount of time.

This makes a mockery of kilovolt-impulse withstands in IEC-1010 overvoltage categories, for use with multimeters on all but the smallest of power circuits.




[This message has been edited by Bjarney (edited 03-30-2004).]

Point taken if someone tried to use a 1/2-watt resistor.

The principle is still good though, and it wouldn't be hard to construct a little feed-thru box with terminals each end to insert between meter and probe leads. Inside could be a suitable series-parallel resistor bank of wirewound resistors.

I carry a Tripplet 310 in the plant for general troubleshooting of control circuits, after all its free since the co provides and if it falls from a crane I don't see the loss, however if I have to go to the CNCs or any high energy circuit I go get my personal Fluke 87III.