Freaky Amazing DMM?!

[YD]

Late at night, by candle light, "David L. Jones" <altzone@gmail.com>
penned this immortal opus:

On Jan 21, 11:05 am, YD <ydtech...@techie.com> wrote:
Late at night, by candle light, Arlowe <bare.ar...@gmail.com> penned
this immortal opus:



krw used his keyboard to write :
In article <mn.a5307d9188b78d0d.90...@gmail.com>,
bare.ar...@gmail.com says...
krw explained on 19/01/2009 :
On Sun, 18 Jan 2009 19:35:00 +1100, Arlowe <bare.ar...@gmail.com
wrote:

on 16/01/2009, Paul supposed :
On Jan 15, 2:19 pm, "David L. Jones" <altz...@gmail.com> wrote:
"Paul" <energymo...@gmail.com> wrote in message

news:54c2d7cf-c506-4647-b272-17d608c8854a@x8g2000yqk.googlegroups.com...

I'm testing a new DMM I purchased, AM-240 by Amprobe. It claims *over*
100Mohm impedance in 400.0mV mode.

Nothing new there, many DMM's have selectable "high impedance" or "HI-Z"
modes on the mV range. e.g. the Fluke 87.

I've looked at the specs of ~ 30 DMM's today, include a lot of
fluke's, and never seen anything near 14Gohms impedance. Keithley has
an electrometer that's probably higher. Most DMM's are around 10Mohms
(not gigaohms) input impedance. Don't you think 14 gigaohms is a bit
high?

PL

The evil thing about Voltmeters with very high impedance is they will
read induced voltages that analog meters wouldn't.
It makes a voltmeter useless for checking for live circuits in a
crowded panel.

A craftsman never blames tools for his failures. Hackers, on the
other hand...

If you work with electricity you had better know the limitations of
your tools or you will find them...the hard way.

That is certainly true (though perhaps your heirs are the ones who
will find you), but doesn't modify my statement. In this case, the
tool *can* be used as long as the one using it knows what he's
doing.

Ok....everything seems to pass right over your head....
I pointed out a limitation of a DMM and you seem to be inferring that I
am somehow a hack who blames his tools...
BTW> I am not a "craftsman" I am an electrcian..
You don't do what I do for as many years as I have without knowing what
the fuck you are doing.

What's wrong with using a hi Z voltmeter in a live panel?

It's not the right tool for the job.
A meter which gives you a false reading with bad (or no) contact is a
BAD idea in dangerous high voltage/high energy circuits.
That is why proper meters with low impedance (Kohms) modes exist for
the job, e.g. Fluke 113, 110 series, 289 etc.

The circuits are loaded, so any bad contacts will certainly affect the
reading. Which is the way I like it. Any funny readings, move up to
the next point in the line and check there.

I do know better than to measure an unloaded line without sticking
some suitable load across it.

Anyways, AIUI, this started with a meter with Hi-Z in the mV range,
most DVMs use a 10M or 1M divider at higher ranges.

- YD.

--
File corruption detected. Select option:
1 - Call the cops
2 - Call the press
3 - Bribe it

Remove HAT if replying by mail.

 

[Stuart]

In article <MPG.23e106a07e05d19698986b@news.individual.net>,
krw <krw@att.zzzzzzzzz> wrote:

If your
field strength is enough to saturate the innards there isn't much
that can be done.

Doesn't need to get into the innards directly, you can screen that, but
you've got a pair of leads forming an aerial and most likely a diode at
the junction of the test lead and the DVM socket. A low impedance input
attenuator will load that down to something insignificant compared with
what you are measuring.

 

[krw]

In article <5021388151Spambin@argonet.co.uk>, Spambin@argonet.co.uk
says...>

In article <MPG.23e106a07e05d19698986b@news.individual.net>,
krw <krw@att.zzzzzzzzz> wrote:
If your
field strength is enough to saturate the innards there isn't much
that can be done.

Doesn't need to get into the innards directly, you can screen that, but
you've got a pair of leads forming an aerial and most likely a diode at
the junction of the test lead and the DVM socket.

Nonsense. There are many things that can be done to eliminate any
external factors. Add a shunt resistor and you have your low
impedance meter.

A low impedance input
attenuator will load that down to something insignificant compared with
what you are measuring.

Nonsense. If an input resistor will load down your circuit so will
your low impedance meter. It's *exactly* the same thing, except
the user gets the choice.

 

[Stuart]

In article <MPG.23e12cd4f25b41dc989871@news.individual.net>,
krw <krw@att.zzzzzzzzz> wrote:

Nonsense. There are many things that can be done to eliminate any
external factors. Add a shunt resistor and you have your low
impedance meter.

A low impedance input
attenuator will load that down to something insignificant compared with
what you are measuring.

Nonsense. If an input resistor will load down your circuit so will
your low impedance meter. It's *exactly* the same thing, except
the user gets the choice.

Go get some practical experience.

 

[krw]

In article <5021420b76Spambin@argonet.co.uk>, Spambin@argonet.co.uk
says...>

In article <MPG.23e12cd4f25b41dc989871@news.individual.net>,
krw <krw@att.zzzzzzzzz> wrote:
Nonsense. There are many things that can be done to eliminate any
external factors. Add a shunt resistor and you have your low
impedance meter.

A low impedance input
attenuator will load that down to something insignificant compared with
what you are measuring.

Nonsense. If an input resistor will load down your circuit so will
your low impedance meter. It's *exactly* the same thing, except
the user gets the choice.

Go get some practical experience.

I certainly have more than you.

 

[Lostgallifreyan]

Daniel <nidan.danny@gmail.com> wrote in news:e8f56b53-9c0c-49cd-b6b5-
e77d8000ad67@i24g2000prf.googlegroups.com:

A craftsman never blames tools for his failures.  Hackers, on the
other hand...- Hide quoted text -

- Show quoted text -

This is an oft used but seldom understood saying. The reason a
craftsman supposedly never blames his tools is because a craftsman
tends to buy quality tools in the first place.

I thought it was to do with a craftsman knowing the limits of his tools, thus
not blaming them for over-reaching.

Related to that, I find the best definition of a toolmaker is one who
achieves greater accuracy than was provided, and makes a system to easily
repeat that gain.

 

[Daniel]

On Jan 19, 7:06 am, krw <k...@att.bizzzzzzzzzzz> wrote:

On Sun, 18 Jan 2009 19:35:00 +1100, Arlowe <bare.ar...@gmail.com
wrote:





on 16/01/2009, Paul supposed :
On Jan 15, 2:19 pm, "David L. Jones" <altz...@gmail.com> wrote:
"Paul" <energymo...@gmail.com> wrote in message

news:54c2d7cf-c506-4647-b272-17d608c8854a@x8g2000yqk.googlegroups.com....

I'm testing a new DMM I purchased, AM-240 by Amprobe. It claims *over*
100Mohm impedance in 400.0mV mode.

Nothing new there, many DMM's have selectable "high impedance" or "HI-Z"
modes on the mV range. e.g. the Fluke 87.

I've looked at the specs of ~ 30 DMM's today, include a lot of
fluke's, and never seen anything near 14Gohms impedance. Keithley has
an electrometer that's probably higher. Most DMM's are around 10Mohms
(not gigaohms) input impedance. Don't you think 14 gigaohms is a bit
high?

PL

The evil thing about Voltmeters with very high impedance is they will
read induced voltages that analog meters wouldn't.
It makes a voltmeter useless for checking for live circuits in a
crowded panel.

A craftsman never blames tools for his failures.  Hackers, on the
other hand...- Hide quoted text -

- Show quoted text -

This is an oft used but seldom understood saying. The reason a
craftsman supposedly never blames his tools is because a craftsman
tends to buy quality tools in the first place.

 

[David L. Jones]

On Jan 21, 10:40 pm, krw <k...@att.zzzzzzzzz> wrote:

In article <9caaa5aa-54e2-4f21-a324-1f2ca8bdd389
@n33g2000pri.googlegroups.com>, altz...@gmail.com says...



On Jan 21, 2:09 pm, krw <k...@att.bizzzzzzzzzzz> wrote:
On Tue, 20 Jan 2009 19:06:15 -0800 (PST), "David L. Jones"

altz...@gmail.com> wrote:
On Jan 21, 12:22 pm, krw <k...@att.bizzzzzzzzzzz> wrote:
On Tue, 20 Jan 2009 22:05:27 -0300, YD <ydtech...@techie.com> wrote:
Late at night, by candle light, Arlowe <bare.ar...@gmail.com> penned
this immortal opus:

krw used his keyboard to write :
In article <mn.a5307d9188b78d0d.90...@gmail.com>,
bare.ar...@gmail.com says...
krw explained on 19/01/2009 :
On Sun, 18 Jan 2009 19:35:00 +1100, Arlowe <bare.ar...@gmail.com
wrote:

on 16/01/2009, Paul supposed :
On Jan 15, 2:19 pm, "David L. Jones" <altz...@gmail.com> wrote:
"Paul" <energymo...@gmail.com> wrote in message

news:54c2d7cf-c506-4647-b272-17d608c8854a@x8g2000yqk.googlegroups.com...

I'm testing a new DMM I purchased, AM-240 by Amprobe. It claims *over*
100Mohm impedance in 400.0mV mode.

Nothing new there, many DMM's have selectable "high impedance" or "HI-Z"
modes on the mV range. e.g. the Fluke 87.

I've looked at the specs of ~ 30 DMM's today, include a lot of
fluke's, and never seen anything near 14Gohms impedance. Keithley has
an electrometer that's probably higher. Most DMM's are around 10Mohms
(not gigaohms) input impedance. Don't you think 14 gigaohms is a bit
high?

PL

The evil thing about Voltmeters with very high impedance is they will
read induced voltages that analog meters wouldn't.
It makes a voltmeter useless for checking for live circuits in a
crowded panel.

A craftsman never blames tools for his failures. Hackers, on the
other hand...

If you work with electricity you had better know the limitations of
your tools or you will find them...the hard way.

That is certainly true (though perhaps your heirs are the ones who
will find you), but doesn't modify my statement. In this case, the
tool *can* be used as long as the one using it knows what he's
doing.

Ok....everything seems to pass right over your head....
I pointed out a limitation of a DMM and you seem to be inferring that I
am somehow a hack who blames his tools...
BTW> I am not a "craftsman" I am an electrcian..
You don't do what I do for as many years as I have without knowing what
the fuck you are doing.

What's wrong with using a hi Z voltmeter in a live panel? I do it more
often than I really care for, and never have a problem.

There isn't anything wrong with it. Analog meters are dead. High
impedance digital meters are only a problem if there is a loose nut
inside the panel, holding the leads.

Then I suppose Fluke and others make all those purpose designed Low-Z
electrical meters for loose nuts then?

...and electricians who know nothing about electricity, perhaps.

But at least smart enough to chose the right tool for the job.

For an electrician who know nothing about electricity (99.44% of
them, apparently), or if that's all one is ever going to do with
the meter, perhaps.

Yes, electricians generally just do just the one similar job. That's
why they make meters designed for just such specific purposes.
Giving your average electrician say a Fluke 289 is a bit overkill and
would likely not be as productive as a more job specific instrument.

For anyone who knows anything about
electricity or wants a tool that has more than one use, the high
impedance meter is a better choice.

That's why many good meters have selectable Low-Z and High-Z modes.

Dave.

 

[David L. Jones]

On Jan 22, 2:21 am, krw <k...@att.zzzzzzzzz> wrote:

In article <31f7ee1b-796f-4a26-a7e4-7755648e2ad2@
35g2000pry.googlegroups.com>, energymo...@gmail.com says...



On Jan 21, 8:17 am, Paul <energymo...@gmail.com> wrote:
On Jan 21, 7:34 am, Stuart <Spam...@argonet.co.uk> wrote:

In article <MPG.23e0f291d9e4acfc989...@news.individual.net>,
krw <k...@att.zzzzzzzzz> wrote:

Totally useless in areas of high RF.
Wrong.

That statement simply exposes another large hole in your knowledge and
experience.

I spent 20 years on a high power HF transmitting station - believe me - I
*know*

As the man says, the proper tool for the job

I would agree. Take two meters. One is 1Kohms. The other is 1Gohms. If
the load is low impedance, say 100 ohms, then there's an appreciable
error with the low impedance meter-- simple ohms law. While the error
associate with the high impedance meter is unmeasurable.

People are probably confusing the fact that a high impedance meter
while unconnected to anything will pick up signals, for obvious
reasons.

Paul

Sorry, I didn't pay much attention who I was replying to. I'm not
taking sides, but I am saying that high impedance meters are better.

Right. It's easy to lower the effective impedance of a high
impedance meter.

Safely, in a dangerous situation?
What part of using the right tool for the job don't you understand?

Yes, High-Z meters are good (more useful in more cases), but Low-Z
meters have their place too.
There simply isn't any argument here, if you need a Low-Z meter, use
one. If you need a High-Z meter, use one. "Making do" without the
right tool in serious situations is stupid.

Going the other way is a lot harder.

Agreed. That's why if you have serious needs you either have a dual
purpose meter, with Low-Z and High-Z modes, or you have two meters.

Dave.

 

[krw]

In article <6c4c61b0-5a1e-4425-a47d-0a883437bc57
@l33g2000pri.googlegroups.com>, altzone@gmail.com says...>

On Jan 22, 2:21 am, krw <k...@att.zzzzzzzzz> wrote:
In article <31f7ee1b-796f-4a26-a7e4-7755648e2ad2@
35g2000pry.googlegroups.com>, energymo...@gmail.com says...



On Jan 21, 8:17 am, Paul <energymo...@gmail.com> wrote:
On Jan 21, 7:34 am, Stuart <Spam...@argonet.co.uk> wrote:

In article <MPG.23e0f291d9e4acfc989...@news.individual.net>,
krw <k...@att.zzzzzzzzz> wrote:

Totally useless in areas of high RF.
Wrong.

That statement simply exposes another large hole in your knowledge and
experience.

I spent 20 years on a high power HF transmitting station - believe me - I
*know*

As the man says, the proper tool for the job

I would agree. Take two meters. One is 1Kohms. The other is 1Gohms. If
the load is low impedance, say 100 ohms, then there's an appreciable
error with the low impedance meter-- simple ohms law. While the error
associate with the high impedance meter is unmeasurable.

People are probably confusing the fact that a high impedance meter
while unconnected to anything will pick up signals, for obvious
reasons.

Paul

Sorry, I didn't pay much attention who I was replying to. I'm not
taking sides, but I am saying that high impedance meters are better.

Right. It's easy to lower the effective impedance of a high
impedance meter.

Safely, in a dangerous situation?

It's easy to do safely.

What part of using the right tool for the job don't you understand?

What part of understanding electricity don't you understand?

Yes, High-Z meters are good (more useful in more cases), but Low-Z
meters have their place too.

If you're a sparky and all you do is wiring, sure. There is no
reason to have a high impedance meter. That doesn't mean that a
high impedance meter can't be used safely and accurately.

There simply isn't any argument here, if you need a Low-Z meter, use
one. If you need a High-Z meter, use one. "Making do" without the
right tool in serious situations is stupid.

If you have a meter for every job, sure. If you don't, a little
knowledge goes long way.

Going the other way is a lot harder.

Nice snip. That's known as a lie in many corners.

Agreed. That's why if you have serious needs you either have a dual
purpose meter, with Low-Z and High-Z modes, or you have two meters.

No, you understand what you have and use it appropriately.
....something there is an obvious shortage around here.

 

[krw]

In article <2933ea53-af2a-43a8-86c7-d9e2ec400d99@
35g2000pry.googlegroups.com>, altzone@gmail.com says...>

On Jan 21, 10:40 pm, krw <k...@att.zzzzzzzzz> wrote:
In article <9caaa5aa-54e2-4f21-a324-1f2ca8bdd389
@n33g2000pri.googlegroups.com>, altz...@gmail.com says...



On Jan 21, 2:09 pm, krw <k...@att.bizzzzzzzzzzz> wrote:
On Tue, 20 Jan 2009 19:06:15 -0800 (PST), "David L. Jones"

altz...@gmail.com> wrote:
On Jan 21, 12:22 pm, krw <k...@att.bizzzzzzzzzzz> wrote:
On Tue, 20 Jan 2009 22:05:27 -0300, YD <ydtech...@techie.com> wrote:
Late at night, by candle light, Arlowe <bare.ar...@gmail.com> penned
this immortal opus:

krw used his keyboard to write :
In article <mn.a5307d9188b78d0d.90...@gmail.com>,
bare.ar...@gmail.com says...
krw explained on 19/01/2009 :
On Sun, 18 Jan 2009 19:35:00 +1100, Arlowe <bare.ar...@gmail.com
wrote:

on 16/01/2009, Paul supposed :
On Jan 15, 2:19 pm, "David L. Jones" <altz...@gmail.com> wrote:
"Paul" <energymo...@gmail.com> wrote in message

news:54c2d7cf-c506-4647-b272-17d608c8854a@x8g2000yqk.googlegroups.com...

I'm testing a new DMM I purchased, AM-240 by Amprobe. It claims *over*
100Mohm impedance in 400.0mV mode.

Nothing new there, many DMM's have selectable "high impedance" or "HI-Z"
modes on the mV range. e.g. the Fluke 87.

I've looked at the specs of ~ 30 DMM's today, include a lot of
fluke's, and never seen anything near 14Gohms impedance. Keithley has
an electrometer that's probably higher. Most DMM's are around 10Mohms
(not gigaohms) input impedance. Don't you think 14 gigaohms is a bit
high?

PL

The evil thing about Voltmeters with very high impedance is they will
read induced voltages that analog meters wouldn't.
It makes a voltmeter useless for checking for live circuits in a
crowded panel.

A craftsman never blames tools for his failures. Hackers, on the
other hand...

If you work with electricity you had better know the limitations of
your tools or you will find them...the hard way.

That is certainly true (though perhaps your heirs are the ones who
will find you), but doesn't modify my statement. In this case, the
tool *can* be used as long as the one using it knows what he's
doing.

Ok....everything seems to pass right over your head....
I pointed out a limitation of a DMM and you seem to be inferring that I
am somehow a hack who blames his tools...
BTW> I am not a "craftsman" I am an electrcian..
You don't do what I do for as many years as I have without knowing what
the fuck you are doing.

What's wrong with using a hi Z voltmeter in a live panel? I do it more
often than I really care for, and never have a problem.

There isn't anything wrong with it. Analog meters are dead. High
impedance digital meters are only a problem if there is a loose nut
inside the panel, holding the leads.

Then I suppose Fluke and others make all those purpose designed Low-Z
electrical meters for loose nuts then?

...and electricians who know nothing about electricity, perhaps.

But at least smart enough to chose the right tool for the job.

For an electrician who know nothing about electricity (99.44% of
them, apparently), or if that's all one is ever going to do with
the meter, perhaps.

Yes, electricians generally just do just the one similar job. That's
why they make meters designed for just such specific purposes.
Giving your average electrician say a Fluke 289 is a bit overkill and
would likely not be as productive as a more job specific instrument.

That wasn't at issue here. The statement was made that a high
impedance meter couldn't be used and that a low impedance *ANALOG*
meter was a necessity. It's certainly not true, though one has to
understand what one is doing, again a rarity in this group.

For anyone who knows anything about
electricity or wants a tool that has more than one use, the high
impedance meter is a better choice.

That's why many good meters have selectable Low-Z and High-Z modes.

Most *good* meters don't. Many sparky meters might.

 

[Archimedes' Lever]

On Wed, 21 Jan 2009 17:22:31 +0000 (GMT), Stuart <Spambin@argonet.co.uk>
wrote:

In article <MPG.23e106a07e05d19698986b@news.individual.net>,
krw <krw@att.zzzzzzzzz> wrote:
If your
field strength is enough to saturate the innards there isn't much
that can be done.

Doesn't need to get into the innards directly, you can screen that, but
you've got a pair of leads forming an aerial and most likely a diode at
the junction of the test lead and the DVM socket.

The antenna I get. A diode? Are you sure that you are familiar with
modern multi-meter construction?

A low impedance input
attenuator will load that down to something insignificant compared with
what you are measuring.

Low Z meters are dumbed down so that dopes can artificially SUPPRESS
what they term as "noise" when reading power sources in an EMI rich
environment, such that they can take "reasonably reliable" readings on a
power source. They are NOT made for getting true reading on small signal
sources in any way shape or form. The same thing can be accomplished by
changing the sample rate or chop the input and average. The same
canceling can also be gotten by twisting the meter leads together. Note
that nearly all "sense line" attachments are of the twisted pair variety.
There is a reason for that, and it is not so that the wires stay bundled
together.

The Fluke Low Z model has the capacity to REMOVE the low Z shunt from
the meter's lead-in circuit, giving the user back an actual, accurate,
high Z meter.

Placing a shunt across your voltage measurement cannot be done on a
source where such a low impedance will load the source. Either way, you
get a flawed reading.

High impedance metrology is akin to actually getting the test data
without touching or modifying the circuit. As we all know, this is a
very hard thing to accomplish. High Z meters are a GOOD thing. Anyone
that thinks they are not needs their head examined.

 

[Archimedes' Lever]

On Wed, 21 Jan 2009 14:24:30 -0300, YD <ydtechHAT@techie.com> wrote:

Late at night, by candle light, "David L. Jones" <altzone@gmail.com
penned this immortal opus:

On Jan 21, 11:05 am, YD <ydtech...@techie.com> wrote:
Late at night, by candle light, Arlowe <bare.ar...@gmail.com> penned
this immortal opus:



krw used his keyboard to write :
In article <mn.a5307d9188b78d0d.90...@gmail.com>,
bare.ar...@gmail.com says...
krw explained on 19/01/2009 :
On Sun, 18 Jan 2009 19:35:00 +1100, Arlowe <bare.ar...@gmail.com
wrote:

on 16/01/2009, Paul supposed :
On Jan 15, 2:19 pm, "David L. Jones" <altz...@gmail.com> wrote:
"Paul" <energymo...@gmail.com> wrote in message

news:54c2d7cf-c506-4647-b272-17d608c8854a@x8g2000yqk.googlegroups.com...

I'm testing a new DMM I purchased, AM-240 by Amprobe. It claims *over*
100Mohm impedance in 400.0mV mode.

Nothing new there, many DMM's have selectable "high impedance" or "HI-Z"
modes on the mV range. e.g. the Fluke 87.

I've looked at the specs of ~ 30 DMM's today, include a lot of
fluke's, and never seen anything near 14Gohms impedance. Keithley has
an electrometer that's probably higher. Most DMM's are around 10Mohms
(not gigaohms) input impedance. Don't you think 14 gigaohms is a bit
high?

PL

The evil thing about Voltmeters with very high impedance is they will
read induced voltages that analog meters wouldn't.
It makes a voltmeter useless for checking for live circuits in a
crowded panel.

A craftsman never blames tools for his failures. Hackers, on the
other hand...

If you work with electricity you had better know the limitations of
your tools or you will find them...the hard way.

That is certainly true (though perhaps your heirs are the ones who
will find you), but doesn't modify my statement. In this case, the
tool *can* be used as long as the one using it knows what he's
doing.

Ok....everything seems to pass right over your head....
I pointed out a limitation of a DMM and you seem to be inferring that I
am somehow a hack who blames his tools...
BTW> I am not a "craftsman" I am an electrcian..
You don't do what I do for as many years as I have without knowing what
the fuck you are doing.

What's wrong with using a hi Z voltmeter in a live panel?

It's not the right tool for the job.
A meter which gives you a false reading with bad (or no) contact is a
BAD idea in dangerous high voltage/high energy circuits.
That is why proper meters with low impedance (Kohms) modes exist for
the job, e.g. Fluke 113, 110 series, 289 etc.


The circuits are loaded, so any bad contacts will certainly affect the
reading. Which is the way I like it. Any funny readings, move up to
the next point in the line and check there.

I do know better than to measure an unloaded line without sticking
some suitable load across it.

Anyways, AIUI, this started with a meter with Hi-Z in the mV range,
most DVMs use a 10M or 1M divider at higher ranges.

- YD.

Most modern meters are high Z on nearly every range.

 

[Archimedes' Lever]

On Wed, 21 Jan 2009 19:06:47 +0000 (GMT), Stuart <Spambin@argonet.co.uk>
wrote:

In article <MPG.23e12cd4f25b41dc989871@news.individual.net>,
krw <krw@att.zzzzzzzzz> wrote:
Nonsense. There are many things that can be done to eliminate any
external factors. Add a shunt resistor and you have your low
impedance meter.

A low impedance input
attenuator will load that down to something insignificant compared with
what you are measuring.

Nonsense. If an input resistor will load down your circuit so will
your low impedance meter. It's *exactly* the same thing, except
the user gets the choice.

Go get some practical experience.

Loaded...

Unloaded...

Something stinks in here either way.

You have been out of the loop too long. Even your feedback has been
self attenuated. No gain whatsoever.

 

[Archimedes' Lever]

On Wed, 21 Jan 2009 14:08:31 -0800 (PST), "David L. Jones"
<altzone@gmail.com> wrote:

On Jan 22, 2:21 am, krw <k...@att.zzzzzzzzz> wrote:
In article <31f7ee1b-796f-4a26-a7e4-7755648e2ad2@
35g2000pry.googlegroups.com>, energymo...@gmail.com says...



On Jan 21, 8:17 am, Paul <energymo...@gmail.com> wrote:
On Jan 21, 7:34 am, Stuart <Spam...@argonet.co.uk> wrote:

In article <MPG.23e0f291d9e4acfc989...@news.individual.net>,
krw <k...@att.zzzzzzzzz> wrote:

Totally useless in areas of high RF.
Wrong.

That statement simply exposes another large hole in your knowledge and
experience.

I spent 20 years on a high power HF transmitting station - believe me - I
*know*

As the man says, the proper tool for the job

I would agree. Take two meters. One is 1Kohms. The other is 1Gohms. If
the load is low impedance, say 100 ohms, then there's an appreciable
error with the low impedance meter-- simple ohms law. While the error
associate with the high impedance meter is unmeasurable.

People are probably confusing the fact that a high impedance meter
while unconnected to anything will pick up signals, for obvious
reasons.

Paul

Sorry, I didn't pay much attention who I was replying to. I'm not
taking sides, but I am saying that high impedance meters are better.

Right. It's easy to lower the effective impedance of a high
impedance meter.

Safely, in a dangerous situation?
What part of using the right tool for the job don't you understand?

Who said anything about a dangerous situation? If a pro is taking a
reading, his chosen job is not dangerous to him, and he knows how to take
the reading properly. That is why certain skills are taught.

Yes, High-Z meters are good (more useful in more cases), but Low-Z
meters have their place too.
There simply isn't any argument here, if you need a Low-Z meter, use
one.

All low Z meters simply have their low Z rated value utilized as a
direct shunt across the input leads. That is ALL low Z meters.
That is how it is done... in EVERY CASE. SO it is NOT unsafe to CREATE
your own low Z input by doing the same thing. You simply must ALSO be
sure to observe and obey all proximity rules and exposed node
precautions, like any pro would do anyway.

If you need a High-Z meter, use one. "Making do" without the
right tool in serious situations is stupid.

Low Z meters ARE high Z meters with a shunt. In almost every case, but
the cheap Harbor Frieght crap.

Going the other way is a lot harder.

Going from having high Z and getting low is not a problem. The other
way is simple too. All you need to do is go buy a high Z meter.

Agreed. That's why if you have serious needs you either have a dual
purpose meter, with Low-Z and High-Z modes, or you have two meters.

A good "low Z meter"<sic> will allow turning the shunt off. Shitty

brands do not.


Get a good, High Z meter, and if you need Low Z input impedance, set it
up right and perform you measurements. It really is that simple. Proper
set-up.. proper reading.

 

[krw]

On Wed, 21 Jan 2009 13:50:29 -0800 (PST), Daniel
<nidan.danny@gmail.com> wrote:

On Jan 19, 7:06 am, krw <k...@att.bizzzzzzzzzzz> wrote:
On Sun, 18 Jan 2009 19:35:00 +1100, Arlowe <bare.ar...@gmail.com
wrote:





on 16/01/2009, Paul supposed :
On Jan 15, 2:19 pm, "David L. Jones" <altz...@gmail.com> wrote:
"Paul" <energymo...@gmail.com> wrote in message

news:54c2d7cf-c506-4647-b272-17d608c8854a@x8g2000yqk.googlegroups.com...

I'm testing a new DMM I purchased, AM-240 by Amprobe. It claims *over*
100Mohm impedance in 400.0mV mode.

Nothing new there, many DMM's have selectable "high impedance" or "HI-Z"
modes on the mV range. e.g. the Fluke 87.

I've looked at the specs of ~ 30 DMM's today, include a lot of
fluke's, and never seen anything near 14Gohms impedance. Keithley has
an electrometer that's probably higher. Most DMM's are around 10Mohms
(not gigaohms) input impedance. Don't you think 14 gigaohms is a bit
high?

PL

The evil thing about Voltmeters with very high impedance is they will
read induced voltages that analog meters wouldn't.
It makes a voltmeter useless for checking for live circuits in a
crowded panel.

A craftsman never blames tools for his failures.  Hackers, on the
other hand...- Hide quoted text -

- Show quoted text -

This is an oft used but seldom understood saying. The reason a
craftsman supposedly never blames his tools is because a craftsman
tends to buy quality tools in the first place.

No, that's the backhand side of the expression. He doesn't blame his
tools because he understands when he makes a mistake it's his. Hackers
blame everyone else, and the tools (even if they have the best).

 

[krw]

On Wed, 21 Jan 2009 17:04:38 -0800 (PST), "David L. Jones"
<altzone@gmail.com> wrote:

On Jan 22, 10:10 am, krw <k...@att.zzzzzzzzz> wrote:
That wasn't at issue here. The statement was made that a high
impedance meter couldn't be used and that a low impedance *ANALOG*
meter was a necessity.

Ok, I haven't followed the entire silly thread.
From my side I've only been proposing that high impedance meters can
be a problem, and the solution is using the right tool for the job.

Yes, they can be a problem if YOU DON'T UNDERSTAND WHAT YOU'RE DOING.
If you know what you're doing you can get the right reading form a
high impedance meter just as well as one that has been crippled by the
manufacturer. If necessary, you can cripple it yourself, though that
is rarely needed.

 

[David L. Jones]

On Jan 22, 10:10 am, krw <k...@att.zzzzzzzzz> wrote:

That wasn't at issue here. The statement was made that a high
impedance meter couldn't be used and that a low impedance *ANALOG*
meter was a necessity.

Ok, I haven't followed the entire silly thread.
From my side I've only been proposing that high impedance meters can
be a problem, and the solution is using the right tool for the job.

Dave.

 

[Archimedes' Lever]

On Wed, 21 Jan 2009 19:41:04 -0600, krw <krw@att.bizzzzzzzzzzz> wrote:

On Wed, 21 Jan 2009 17:04:38 -0800 (PST), "David L. Jones"
altzone@gmail.com> wrote:

On Jan 22, 10:10 am, krw <k...@att.zzzzzzzzz> wrote:
That wasn't at issue here. The statement was made that a high
impedance meter couldn't be used and that a low impedance *ANALOG*
meter was a necessity.

Ok, I haven't followed the entire silly thread.
From my side I've only been proposing that high impedance meters can
be a problem, and the solution is using the right tool for the job.

Yes, they can be a problem if YOU DON'T UNDERSTAND WHAT YOU'RE DOING.
If you know what you're doing you can get the right reading form a
high impedance meter just as well as one that has been crippled by the
manufacturer. If necessary, you can cripple it yourself, though that
is rarely needed.

Absolutely correctly worded.

 

[David L. Jones]

On Jan 22, 11:41 am, krw <k...@att.bizzzzzzzzzzz> wrote:

On Wed, 21 Jan 2009 17:04:38 -0800 (PST), "David L. Jones"

altz...@gmail.com> wrote:
On Jan 22, 10:10 am, krw <k...@att.zzzzzzzzz> wrote:
That wasn't at issue here. The statement was made that a high
impedance meter couldn't be used and that a low impedance *ANALOG*
meter was a necessity.

Ok, I haven't followed the entire silly thread.
From my side I've only been proposing that high impedance meters can
be a problem, and the solution is using the right tool for the job.

Yes, they can be a problem if YOU DON'T UNDERSTAND WHAT YOU'RE DOING.

The same with ANY measurement instrument, nothing unique here at all.

If you know what you're doing you can get the right reading form a
high impedance meter just as well as one that has been crippled by the
manufacturer.

Crippled? Hardly the right term, try purposely designed.
Just like you wouldn't go around saying a meters DC range is
"crippled" because it's 0.5% when they could have made it 0.1%.
Or a meters current range is "crippled" because it has a burden
voltage of 10mV/mA instead of 1mV/mA.
etc.

Usually, with meters, a lower spec is done to meet a lower price
point. But in the case in question it is done for the purpose of
meeting a (niche) market need. A tool is not crippled just because it
doesn't meet YOUR job spec.

Dave.