Freaky Amazing DMM?!



Makes sense but do you concede that understanding the conditions matters more than the meter? What matters in wiring that is capacitatively or inductively coupled but not directly so, is that some kind of light load is placed on the line, and the voltage measured across that load. Only when that load needs to be a simple resistance can it be assumed that it is the meter's job to include it. In all other cases it can be assumed that the meter should tax the circuit as lightly as possible while analysing an external load chosen to fit the analysis needed. Which in turn directly implies that in the hands of someone who knows electricity, especially AC and frequency dependent behaviour, the high impedance meter is the way to go. Ideally with a plug-in load module or two, just as meters used to come with plug-in current shunts.
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Who said anything about it being *analogue* ?
Impedance is a property of the input of the meter not the display type.
I've used high and low impedance analogue meters and the same in digital form.
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says...>

Jump into a discussion late, with both feet, often?

Read the thread.

Wow! I'm impressed! For a sparky, you're pretty sharp, there.
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krw used his keyboard to write :

I didn't say you had to use an analog meter. I said that they do not have the same problem. An analog meter "IS A LOAD" a DMM is NOT.
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Arlowe wrote:

Really? They both use resistive divider networks across the DUT.
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wrote:

>>>>>>>>>>>>>>>
I really don't understand the resistance (if you will excuse the expression) to Arloe.
Of course both analog and digital meters (excluding, for practical purposes, the original topic) have resistive input. For the purposes Arloe uses a meter, the intentionally high impedance of most digital meters is a liability. The lower impedance of an analog meter, and some digital meters, is an advantage.
alt.home.repair gets more electric power questions than this newsgroup, with the OP usually less technical savvy (some at a.e.e that aren't either). It is rather common for someone to ask why there is 83 volts on a wire that should be dead. The common response is it is a "phantom voltage" picked up by using a high impedance digital meter and to use an analog meter (or light bulb). As Arloe said "An analog meter 'IS A LOAD' a DMM is NOT."
Arloe is just saying to use the appropriate tool. In addition, he can't kludge a lower impedance onto a high impedance meter. He may meter power circuits that have an available fault current of tens of thousands of amps. In the US you may need to wear a "flash suit" to merely meter the voltage. The meter must be designed to safely fail on those circuits.
Same applies to responses to Stewart, who is speaking from professional experience.

Posted through googlegroups (yech) because my news source apparently doesn't like cross posting.
-- bud--
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In article <fe2bb820-867e-48c1-add6-7ba1757c7ff1

>>>>>>>>>>>>>>>
The issue is his (and others') insistence that a high impedance meter (and indeed even a digital meter) cannot be used in these circumstances. The fact is that it can, though one has to understand that what one is reading may not be correct. These errors are easily prevented/corrected, something the sparkys simply cannot understand.

Of course, "analog" has nothing to do with it (as some have claimed). How does he know that even the analog meter isn't lying to him for similar reasons? The fact is that one has to understand the tools and work with them. A "load" is easy. Preventing a low impedance meter from loading a circuit is difficult.

No, he's saying that that is the only tool possible. The fact is that a high impedance meter *can* be used, though one has to be careful. Something evidently beyond the average sparky.

That isn't the issue, and you know it.

Perhaps "professional" experience, but limited knowledge.

Get a new one. They're cheap.
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Arloe understands that it can and understands what one is reading may not be correct. Arloe understands that if he reads 83 volts with a high impedance meter he doesnt know if the voltage is real or phantom. So how is the measurement useful? Maybe electricians are too fussy about knowing whether the circuits the work on are live?

Arloe does understand. That is why he uses an appropriate tool. And I am a licensed master electrician. I guess I must not understand either.
A high impedance meter reads 83 volts. What do you know? How do you prevent? How do you correct?

The term analog is used because (without an amplifier) they are inherently low impedance in the context of the measurements Arloe is making. (With a good 50 microamp movement you might still see some phantom voltage. AC ranges are likely way under 20k ohms/volt.)

Arloe does understand the tools. That is why he wants to use a lower impedance meter on power circuits.
Not explained - how do you work with a high impedance meter? What is the work with procedure if you measure 83 volts?

How do you easily provide a load if you are measuring power circuits with a high impedance meter?

Of course. If you have a high impedance circuit you use a high impedance meter. Use the appropriate tool.
Power circuits are not high impedance.

He is saying that a low impedance meter is the appropriate tool for the measurements he is making.

Arloe measures 83 volts with a high impedance meter. What does that tell him?

May or may not be. You havent explained how you work with a high impedance meter. What is the work with procedure if you measure 83 volts?

Your Ouija board is very accurate and, of course, is the appropriate tool. Is it high impedance?
-- bud--
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wrote:

It *is* a phantom voltage. It's not so much that measurement is useful but the fact that it's not. How to take the measurement to *not* get this reading is the point. That takes some brains he ain't got, apparently.

No, apparently they're too dumb to use the instruments correctly and to know when to *not* take what they're reading as fact.

No, he doesn't understand. His "low" impedance meter isn't all that low and can still have these measurement artifacts. He's too stupid to understand what he's seeing.

That it most likely ain't 83V.

A number of things. Mainly, no matter what the meter, not to trust it.

Load the circuit. Turn on a light bulb. Use a resistor. Any number of things, depending on the circuit and the wire in question.

They can still be thousands of ohms per volt.

No, he's been told what tools to use. He understands nothing. A high impedance meter can certainly be used, though one has to know what he's doing. Arloe is clueless.

I told you, several times. I can't help it of you're in Arloe's league.

Maybe a light will come on.

No, *understand* your tool *AND* your business.

They certainly are, if not connected.

No, that's not what he's saying. You're coming in in the middle here.

How many times are you going to ask this silly question?

I have many times. I can't help it if you, like Arloe, are too dumb to read.

No, it's what sparkys use, apparently.
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bud-- was thinking very hard :

You are wasting you time with this idiot.
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In article

They, like all the *sensible* engineers I have come across, have a desire to reach the age where they are able to draw and enjoy their pensions.
<SNIP for brevity>

The Avometer Model 8, which I still have, has an impedance of 1000 ohms/volt on AC. It has switched ranges to 1000V f.s.d and a further range, via separate terminals, to allow measurement to 2500V f.s.d
The AVO model 40, which was favourite when working more on the "power engineering" side, was lower. I cannot quote an exact figure but I believe it was more like 200 ohms/volt. The most sensitive AC current range was 12mA f.s.d.
<SNIP>

<SNIP>
And he is absolutely right.
<SNIP>

Should anyone care:
I spent the best part of 40 years as a transmitter engineer maintaining, repairing and caring for, transmitting and associated plant for the BBC.
I have worked on everything from DC to 7GHz (They wouldn't buy me the test gear to repair anything higher in frequency than that but since we only had a few links at higher frequencies it probably made economic sense to return to manufacturer to repair).
I have covered everything from milliwatts to megawatts and battery power to 11kV distribution systems. (Perhaps KRW would like to take his favourite high-Z DMM and try testing the spouts on an 11kV switch-gear panel) I was qualified as an "authorised" person for the purposes of the HV rules.
I have repaired everything from the simplest DC power supply to the latest digital TV and radio transmission equipment. I have worked on cooling plant, rotary converters, standby power plant and done design and prototype work. I doubt there is a single piece of electrical/electronic test equipment which I have not handled and known the *proper* usage of, at some point in that time. (not forgetting general workshop equipment such as lathes, drills, milling machines....)
Stuart
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bud-- wrote:

Only if you don't know how to interpret the better meter. Its a dumbed down toy for wire pullers. I've seen too many over the years that couldn't find an open neutral, or bad connection unless it was on fire.

If you are reading 83 volts, either it is a phantom voltage, or you have a 40 volt drop in a 120 volt circuit, or 160 volt drop in a 240 volt circuit, which is damn unlikely. If you can't see this, you don't know what you're doing.

The appropriate tools start with a well trained brain. Otherwise, you are a monkey throwing crap at the problem.
If is working with what you described, it certainly won't be 'low impedance', because the the current flow required, times the voltage being read would be so high that the meter would need to be in a 55 gallon drum of transformer oil, and able to dissipater several kilowatts. All this would weigh several hundred pounds.

My experience is a broadcast engineer, (The largest was at a 5 MW UHF TV site.) industrial electrical work, and specialized electronics that you'll never see, without going to the International Space Station.
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And both extremly impressive too, yet apparently in disagreement.
I don't think that high an experience is needed to understand this anyway, I learned it at 14 when an aging friend of the family taught me how to build my own (and first) multimeter.
Ohm's law.
And a bit of awareness of insulation strength when high volts are involved.
If you're using a low resistance input you might have to take it into account for accurate measurements but on mains, the error is small, so it's worth keeping inputs resistance low for meters dedicated to such systems, for reasons plenty of posts have explained, so I won't flog that horse now.
If you have strong insulation, you can probe an HV circuit without trouble, just make sure you understand what the meter says. If a meter designed to tax the system as lightly as possible says 83V it means 83V, the problem isn't the meter, you just have to know enough to interpret the truth it tell you. (Mike Terrell got this one right). If you also need to know current through the same meter, you could do it by measuring small voltage across a part of one conductor, then measuring resistance of that part after removing power. Most current meters just do this internally anyway, but they 'know' the resistance of their shunts so they calculate correctly anyway.
So the question isn't who is the most experienced, it's who is right? And take care, because if two people with real experience start arguing over something as basic as Ohm's law, they'll do each other's reputation harm, as well as making it hard for newcomers to trust what they read here.
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wrote:

Is it a phantom voltage? Do you have an open neutral? Voltage coming back through another device? One of many other possibilities?
Arloe can eliminate one of them real fast because he knows what he is doing.

How fortunate that Arloe and Stewart and I are well educated and know what we are doing.

If you followed the thread you might understand how low impedance is being used.
-- bud--
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bud-- wrote:

Easy enough to identify.

I would have full voltage on the supply side.

Not difficult to troubleshoot.

How about high harmonics on the neutral of a three phase service in an office or server room? Do you know why the neutral has to be larger than the supply lines? This has been well documented for over 25 years. Buildings wired to earlier NEC codes have had major electrical fires.
All easy to troubleshoot, if you have common sense and a true understanding of electricity. Try working in a 'zero downtime' job sometime, where you may only have seconds to find a problem to avoid costly repairs, or expensive damage to the entire facility rather than simple monkey work where you can spend hours or days tracking down a problem. Places where preventative maintenance can save lives.

So can I. I've done it for over 40+ years.

Sure you are. Yet you can't figure out how to do it without a dumbed down tool.

I followed the thread, even though it loops in multiple, ridiculous circles. Either you can work with available tools, or you need your hand held, and your mommy to wipe both ends for you.
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wrote:

Even easier for Arloe.

Its the favorite nobody-knows-anything-but-Michael argument.
Not the issue, of course. Any tool can be used. The question is what is appropriate and efficient. High z meters do not help you on power circuits, but you can use what you want. Arloe is entirely reasonable to use a low z meter.
-- bud--
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bud-- wrote:

Proof that its easier for him?

You are starting to sound like your hero, the cut & paste 'surge protector W_Tom'.
Arloe can use anything he wants to. No one else cares, but a lot of what he posts is old wives tales.
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Michael A. Terrell formulated the question :

Bullshit. Prove me wrong.
It is not uncommon to read mains voltage, not some BS 83VAC like some have referred to, but MAINS VOLTAGE on a conductor that is isolated.
When you have a panel where the active cables are segregated form the neutrals, you can get very strong, alternating magnetic fields depending on the current draw.
If you put an isolated cable in that field you will measure voltage on that cable with a DMM. An electrician can not rely on reading an "incorrect" voltage as an assurance that the cable is dead. He has to be able to PROVE IT. Some will use an analog meter, I don't, I use test lamps that have the correct CAT rating for the enviroment. I follow up by testing my lamps on a "known supply" ie. a supply that I verified live before I performed any testing, just to prove the test lamps are functionimg as intended.
Call it crude, I don't give a fuck, it works, it is failsafe and it is fast.
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Arlowe wrote:

So does a screwdriver against the case, and to a buss bar, but I won't do it.
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Michael A. Terrell used his keyboard to write :

??????? Don't be stupid.
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