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Author Topic: DMM vs Analog VOM  (Read 5834 times)
N3BSZ
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« on: March 20, 2012, 07:28:25 PM »

I have a Fluke 87 meter, and I am wondering if I should look into purchasing an analog meter like a Simpson 260.  I was searching ebay and noticed there are many flavors of the 260.

Are there better versions than others?  Do I need an analog meter to work on boat anchors?

Tom
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KQ6EA
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« Reply #1 on: March 20, 2012, 07:52:36 PM »

I think that analog meters have an edge when it comes to peaking circuits. To my tired, old eyes, it's easier to "see" the peak on an analog meter as I swing the circuit adjustment, than it is to track the changing numbers on a DMM.
I have both high-end Fluke and HP DMM's with the little bar graph on the display, and I still prefer an analog meter.
In the early days of digital meters, I think VTVM's had an higher input impedance, but I don't think that holds true anymore.
I've also had "digital noise" injected into certain circuits by cheap DMM's, but I don't recall my Fluke or HP having ever done that.
I guess it all comes down to personal preference, and for some things I prefer an analog meter.
73, Jim
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K2OWK
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« Reply #2 on: March 20, 2012, 09:28:21 PM »

Hello Tom, The Simpson 260 was the standard of the time. Super rugged and accurate. I have seen them dropped the case cracked and the meter face broken and they still worked. The available Simpson types were, standard good accuracy. mirrored meter for better accuracy. Different sizes and fancy leather cases for them. There was another popular meter at the time that was said to be more accurate, but not as rugged, called a Triplet.

As Simone mentioned they a much better for reading peaks when tuning circuits.
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AC5UP
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« Reply #3 on: March 21, 2012, 02:59:20 AM »

If I was starting from scratch I think I'd be tempted to buy a good DMM in combo with a used oscilloscope in the $100 range. While a VOM or VTVM set to center scale Zero was the standard of the day for aligning FM discriminator circuits and the like, it can be done with a DMM. On a 'scope you can't miss a null and peaks are usually obvious, but whether you go with an an analog meter or other device there's still a learning curve on how to take the measurement. It's one thing to know what to look for and sometimes another in finding something worth looking at.

BTW: While we're throwing meter names around, check this: http://www.amprobe.com/amprobe/usen/Multimeters/AM-500-Digital-Multimeter-Series/AM-550.htm?PID=74037

Notice the features like temperature, capacitance and Lo-Z, Lo-Pass mode plus True RMS on AC measurements. Web site says the price range is $29.95 to $109.95 for the series. I'd have thought significantly more. The Lo-Z thing caught my eye as a Simpson 260 is a 20,000 Ohms per volt device which does load down the circuit under test more than a VTVM. Which explains why vintage schematics tend to mention the meter type used to take the test readings. Unless I'm assuming too much, it looks like the Amprobe meters have a Simpson 260 mode........ (?)

It also boggles my mind to see a spec like resistance to 60 megs. At that level the actual DC test voltage seen by the meter has to be in the microvolt range. How do you reject stray noise on the probes to get reliable readings at that level? Could be a case of sometimes you do, sometimes you don't........  Wink
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N4NYY
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« Reply #4 on: March 21, 2012, 05:21:21 AM »

You need a needle to peak/tune a radio. Trust me on that. For all other aspects, I use a DMM. For tuning, I use a VTVM.
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W4AUE
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« Reply #5 on: March 21, 2012, 05:45:19 AM »

Morning Tom,

I have a scope, VTVM and DMM on the bench (collected over the years) and each has its use. Use them pretty much in the order listed.  For some reason I've never really trusted DMM - think its because the early units where really flaky - the current models are much better. 

Practically, I can watch the scope or VTVM out of the corner of my eye, but the DMM requires a little more focus to interpret. No question that a good high impedance analogue meter is better for peaking or tuning L/C etc. A 260 may not meet your needs for high impedance.

A Simpson 260 is a great tool - carried one for years as a tech and engineer (power company) - last one I personally had was stolen (probably wound up on Ebay???)

But if you are going to be working with Tube type stuff - get a good scope and learn to use it. 
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WB2WIK
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« Reply #6 on: March 21, 2012, 09:49:28 AM »

A VOM is a great and handy portable instrument and some Simpson 260-series (I have three of them, and they're all old!) are really versatile and will measure 5,000Vdc and 10Adc right out of the box, in addition to all the other standard scales.  They also had (maybe still do, I haven't looked) a broad series of plug-in attachments for the 260 series which created expanded ranges; those just "snap on" to the front lower part of the meter and use the existing "banana jacks" for connections, and can expand almost every range there is.  I have several of those, but they're all 20-30 years old.

However, when working with "boat anchors" which are all tube gear, in most places, other than measuring power supply voltages or possibly a low-Z audio output line, you really can't use a 260 for much and a VTVM is a lot more useful for measuring high impedance circuits without loading them.  For "boat anchor" bench gear, I use a standard VTVM, sometimes a specialty AC VTVM, a scope, and AF and RF signal generators more than anything else.   
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AA4PB
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« Reply #7 on: March 21, 2012, 10:24:52 AM »

There are digital multimeters that have a sliding bar (uncalibrated) that can be used for adjusting circuits. This gives you the best of both worlds - the accuracy of a modern digital meter and the ability to peak/dip circuits.
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G3RZP
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« Reply #8 on: March 21, 2012, 10:33:10 AM »

There may be DMMs that don't go mad when working on PA stages, especially big amplifiers. I just haven't seen one. So I keep an analogue meter for that use.
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KE3WD
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« Reply #9 on: March 21, 2012, 02:18:33 PM »

You need a needle to peak/tune a radio. Trust me on that. For all other aspects, I use a DMM. For tuning, I use a VTVM.

There are indeed DMMs that feature an analog bar scale along the bottom of the display, for just this purpose. 


73
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N4NYY
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« Reply #10 on: March 21, 2012, 02:51:16 PM »

Quote
There are indeed DMMs that feature an analog bar scale along the bottom of the display, for just this purpose.

I had a Fluke 87 that did this. And I hate to say it, it was not as good as an analog needle. That is, unless the resolution has gotten much better.
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AC5UP
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« Reply #11 on: March 21, 2012, 03:17:10 PM »

Pssssssssssst.......... Vinnie.............. Sometimes when you're tuning for a peak on a DMM, watching the last digit is not the way to go... It twitches too much. So you watch the next to last (10's) digit instead. Tune for the spot where it reads the highest value and will hold steady on that value. That's your peak, and that's close enough.

Now, before you go ballistic telling me an analog meter is the only one true way to find the absolute peak value........ I dare you, no, I defy you, to give me one good example of any toobular gear that can hold an absolute perfect (and I mean perfect!) alignment for more than a few hours.

Been there, done that, anything with tubes will start to drift out of alignment as soon as you get the covers back in place. And will tend to approach perfection while warming up and may slide past that point a few times as you're using it. So what's the point of tweaking down to a gnat's eyelash with a meter that has its own warm-up accuracy curve?

Because it gives you a warm fuzzy that's gone faster than you suspect........      Tongue
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N4NYY
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« Reply #12 on: March 21, 2012, 05:10:01 PM »

Quote
Pssssssssssst.......... Vinnie.............. Sometimes when you're tuning for a peak on a DMM, watching the last digit is not the way to go... It twitches too much. So you watch the next to last (10's) digit instead. Tune for the spot where it reads the highest value and will hold steady on that value. That's your peak, and that's close enough.

The Fluke 87 had a analog bar graph at the bottom, and it went back and forth like a needle. That is what I meant. The problem was sometime the bar graph needle was 2 or 3 segment wide during fast movement, which made the resolution crap. But that was the last one I used with a bar graph.
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KE3WD
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« Reply #13 on: March 21, 2012, 08:01:59 PM »

... The problem was sometime the bar graph needle was 2 or 3 segment wide during fast movement, which made the resolution crap. But that was the last one I used with a bar graph.

It was trying to tell you that it was time to change the input scaling to suit...

Look, I have lived through the time when the VTVM was the king bench meter, then lived through the FET analog meters, now I use DMMs exclusively and they can indeed do the job as well or better than their predecessors.  But if you happen to like the big old meters, and have the room for 'em on your bench, no harm or foul from using one of those either.  Just stop propagating rumor an propaganda that use of the DMM for the task is not apropos or possible, that just ain't true. 


73
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N4NYY
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« Reply #14 on: March 21, 2012, 08:15:26 PM »

Quote
It was trying to tell you that it was time to change the input scaling to suit...

Look, I have lived through the time when the VTVM was the king bench meter, then lived through the FET analog meters, now I use DMMs exclusively and they can indeed do the job as well or better than their predecessors.  But if you happen to like the big old meters, and have the room for 'em on your bench, no harm or foul from using one of those either.  Just stop propagating rumor an propaganda that use of the DMM for the task is not apropos or possible, that just ain't true.

I have not used that meter since the mid 1990's, and I am not sure it even exists anymore. But I started out peaking with a DMM. I just found it far easier with an analog needle. That is the only use which I use it for.
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