Re: Freaky Amazing DMM?!

[krw]

Who said anything about it being *analogue* ?

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

Impedance is a property of the input of the meter not the display type.

Read the thread.

I've used high and low impedance analogue meters and the same in digital
form.

Wow! I'm impressed! For a sparky, you're pretty sharp, there.

 

[Archimedes' Lever]

Nice to know someone round here knows what they are doing!

Both of you are idiotic to think that there is some inherent error or
danger in using a DMM to observe an AC line.

 

[bud--]

krw used his keyboard to write :

35g2000pry.googlegroups.com>, [email protected] says...>



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

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.

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

Posted through googlegroups (yech) because my news source apparently
doesn't like cross posting.

 

[krw]

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.

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.

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."

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.

Arloe is just saying to use the appropriate tool.

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.

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.

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

Same applies to responses to Stewart, who is speaking from
professional experience.

Perhaps "professional" experience, but limited knowledge.

Posted through googlegroups (yech) because my news source apparently
doesn't like cross posting.

Get a new one. They're cheap.

 

[Archimedes' Lever]

The meter must be designed
to safely fail on those circuits.

High impedance DMMs "safely fail" on ALL equipment as well.

And no, it matters not that there is a high current capacity available.
If the operator does not know how to take measurements in such
environments, he should not even be in such an environment, much less be
there attempting to take readings from power equipment. With ANY meter.

 

[bud--]

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.

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 doesn’t 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?

These
errors are easily prevented/corrected, something the sparkys simply
cannot understand.

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?

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 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.)

The fact is that one has to understand
the tools and work with them.

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?

A "load" is easy.

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

Preventing a low
impedance meter from loading a circuit is difficult.

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.

No, he's saying that that is the only tool possible.

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

The fact is
that a high impedance meter *can* be used, though one has to be
careful. Something evidently beyond the average sparky.

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

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

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

Perhaps "professional" experience, but limited knowledge.

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

 

[bud--]

High impedance DMMs "safely fail" on ALL equipment as well.

Only if they are designed for high energy circuits.

And no, it matters not that there is a high current capacity available.

It matters greatly that there is high current capacity available.

There is a meter classification based on available current. (Category
1, 2, 3; probably from the IEC.)

If you are in the workplace and covered by (US) OSHA using the wrong
type of meter could be real expensive.

And if you don't use the appropriate tool you could wind up wearing
the meter. You could also wind up wearing the equipment you are
metering.

If the operator does not know how to take measurements in such
environments, he should not even be in such an environment, much less be
there attempting to take readings from power equipment. With ANY meter.

Of course. But a competent person working high energy circuits will
use a meter that has been designed and rated for high energy circuits.
If you are poking around in a PC it doesn't much matter.

 

[krw]

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 doesn’t know if the voltage is real or “phantom”. So how is
the measurement useful?

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.

Maybe electricians are too fussy about knowing whether the circuits
the work on are live?

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

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.

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.

A high impedance meter reads 83 volts.
What do you know?

That it most likely ain't 83V.

How do you prevent?

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

How do you correct?

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

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.)

They can still be thousands of ohms per volt.

Arloe does understand the tools. That is why he wants to use a lower
impedance meter on power circuits.

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.

Not explained - how do you “work with” a high impedance meter?
What is the “work with” procedure if you measure 83 volts?

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

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

Maybe a light will come on.

Of course. If you have a high impedance circuit you use a high
impedance meter. Use the appropriate tool.

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

Power circuits are not high impedance.

They certainly are, if not connected.

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

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

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

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

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

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

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

No, it's what sparkys use, apparently.

 

[Archimedes' Lever]

It matters greatly that there is high current capacity available.

Most meter leads for standard voltage measurements are very small gauge.
Not much will pass across those.

When I read current, I make my own 10Ga. Silver Plated Copper short
jumpers that allow a current reading without changing the circuit much.

The meter, however is limited internally on current readings by one or
even two fuses, and the voltage is limited by the breakdown voltage of
the inputs, and yes, it is isolated to 400 or 600 or more volts.

 

[Archimedes' Lever]

And if you don't use the appropriate tool you could wind up wearing
the meter. You could also wind up wearing the equipment you are
metering.

You're an idiot. Even for an HV reading, one would be required to use
an HV probe, so no threat is posed to the meter itself under proper
operation yet again.

Dead shorting a modern meter amounts to the few joules it takes to blow
the internal circuits or explicit fuse. There is no energy greater than
that that you can pump into one.

Take typical meter probes and a big copper shorting bar. Hook up to
power. The leads flash. Likely before the friggin fuse even blows.
The meter will flash open far sooner than the leads will.

 

[Archimedes' Lever]

They can still be thousands of ohms per volt.

Most analog meters are pretty high impedance as well. On the order of
nearly 10M Ohms per volt.

My first Heathkit meter was.

 

[Archimedes' Lever]

bud-- was thinking very hard :

You are wasting you time with this idiot.

Well then take your stupid ass somewhere else, 'this idiot'.

We don't need your kind around here, 'this idiot'.

That is a very good moniker for you though, 'this idiot'. You should
stick with it.

 

[David L. Jones]

Most analog meters are pretty high impedance as well. On the order of
nearly 10M Ohms per volt.

On what planet??

Almost all analog meters on the market are in the oder of 10's of
Kohms / Volt.
My Triplett 630, a very typically rated industry standard analog meter
for example is 10-20K/V on DC and 5-10K/V on AC volts.
The most sensitive analog meter I've ever owned (and from memory, saw)
was rated at 100Kohms/V.

Those that are higher are FET input meters and they are NOT rated in
ohms/volts, as the impedance is no longer based on the meter movement.
My Tandy FET analog meter is 10Mohms fixed on DC volts, and non-FET
input on AC, rated once again in 10's of K per volt.

You might need to go back to basics:
http://en.wikipedia.org/wiki/Multimeter

Dave.

 

[Sjouke Burry]

On what planet??

This one. Yamato Y3 2Kohm/V ac & dc.
Bought around 1963.
Still works perfectly.
Also it survived 2 digital meters.

 

[David L. Jones]

This one. Yamato Y3 2Kohm/V ac & dc.

Yes, they are Kohms/V on this planet, as I said.
"Archimedes' Lever" must live on another planet were analog meters
have Mohms/V sensitivity!
"krw" must be lusting after one of those! :->

Dave.

 

[Spehro Pefhany]

Most analog meters are pretty high impedance as well. On the order of
nearly 10M Ohms per volt.

My first Heathkit meter was.

http://www.heathkit-museum.com/test/hvmv-7a.shtml




Best regards,
Spehro Pefhany

 

[Archimedes' Lever]

You might need to go back to basics:

Nice reply except for this bit of baby bullshit.

You might need to **** off and die.

 

[Archimedes' Lever]

http://www.heathkit-museum.com/test/hvmv-7a.shtml

No FET front end on that!

Bwuahahahahah!

 

[krw]

I had one too.

No FET front end on that!

An indirectly heated cathode Field Effect Tube.

 

[David L. Jones]

No FET front end on that!

Bwuahahahahah!

So it's a vacuum tube front end instead - same thing, same result.
A fixed 11Mohm input, not 10M/volt as you foolishly claimed.

Dave.