9 mV noise on AC voltmeter

A

Andre Majorel

Guest
I've got a Chauvin Arnoux C.A 5220 DMM that bottoms out at 9 mV.
Even with the inputs shorted and in "Velec" mode (270 k input
impedance), it never goes below 9 mV.

The problem is only for AC. In DC mode, it *does* go down to 0.

Any idea what could be the problem ?

It's built around a JRC NJU9210BFC.

--
André Majorel <URL:http://www.teaser.fr/~amajorel/>
"Je regrette le Concorde. Au moins il vous amenait directement ŕ
l'hôtel." -- Cyrano
 
On Wed, 1 Oct 2008 12:24:49 +0000 (UTC), Andre Majorel
<cheney@halliburton.com> wrote:

On 2008-10-01, William Sommerwerck <grizzledgeezer@comcast.net> wrote:
On 2008-10-01, Andre Majorel <cheney@halliburton.com> wrote:

I've got a Chauvin Arnoux C.A 5220 DMM that bottoms out at 9 mV.
Even with the inputs shorted and in "Velec" mode (270 k input
impedance), it never goes below 9 mV.

The problem is only for AC. In DC mode, it *does* go down to 0.

Obviously, "something" is noisy. (Duh...)

Looks like it's 50 Hz because when trying to measure a 50 Hz
sine from a sound card, the voltage slowly oscillates by about
+/-10 mV around a mean value (fraction of Hz beating against the
sound card).

Have you asked the manufacturer?

No. It's long out of warranty.
It is possible that the shorted leads are acting as a loop antenna and
Click to expand...
the 9 mv is legitimate. Does it change if you go outside? Does it
change if you use shorter leads? Coil the leads?
 
On 2008-10-01, William Sommerwerck <grizzledgeezer@comcast.net> wrote:
On 2008-10-01, Andre Majorel <cheney@halliburton.com> wrote:

I've got a Chauvin Arnoux C.A 5220 DMM that bottoms out at 9 mV.
Even with the inputs shorted and in "Velec" mode (270 k input
impedance), it never goes below 9 mV.

The problem is only for AC. In DC mode, it *does* go down to 0.

Obviously, "something" is noisy. (Duh...)
Click to expand...
Looks like it's 50 Hz because when trying to measure a 50 Hz
sine from a sound card, the voltage slowly oscillates by about
+/-10 mV around a mean value (fraction of Hz beating against the
sound card).

Have you asked the manufacturer?
Click to expand...
No. It's long out of warranty.

--
André Majorel <URL:http://www.teaser.fr/~amajorel/>
"Je regrette le Concorde. Au moins il vous amenait directement ŕ
l'hôtel." -- Cyrano
 
On 2008-10-01, greenpjs <greenpjs@neo.rr.com> wrote:
On Wed, 1 Oct 2008 12:24:49 +0000 (UTC), Andre Majorel
cheney@halliburton.com> wrote:
On 2008-10-01, William Sommerwerck <grizzledgeezer@comcast.net> wrote:
On 2008-10-01, Andre Majorel <cheney@halliburton.com> wrote:

I've got a Chauvin Arnoux C.A 5220 DMM that bottoms out at 9 mV.
Even with the inputs shorted and in "Velec" mode (270 k input
impedance), it never goes below 9 mV.

The problem is only for AC. In DC mode, it *does* go down to 0.

Obviously, "something" is noisy. (Duh...)

Looks like it's 50 Hz because when trying to measure a 50 Hz
sine from a sound card, the voltage slowly oscillates by about
+/-10 mV around a mean value (fraction of Hz beating against the
sound card).

It is possible that the shorted leads are acting as a loop
antenna and the 9 mv is legitimate. Does it change if you go
outside?
Click to expand...
It keeps changing until you hold everything perfectly still. But
even outside, it never goes below 9 mV.

Does it change if you use shorter leads?
Coil the leads?
Click to expand...
Not appreciably.

Just tried putting everything in a tin biscuit box and still get
the parasitic reading. Obviously, I couldn't close the box
completely.

--
André Majorel <URL:http://www.teaser.fr/~amajorel/>
"Je regrette le Concorde. Au moins il vous amenait directement ŕ
l'hôtel." -- Cyrano
 
Andre Majorel wrote:

I've got a Chauvin Arnoux C.A 5220 DMM that bottoms out at 9 mV.
Even with the inputs shorted and in "Velec" mode (270 k input
impedance), it never goes below 9 mV.

The problem is only for AC. In DC mode, it *does* go down to 0.

Any idea what could be the problem ?

It's built around a JRC NJU9210BFC.

Sounds normal for a cheap meter to me! :)
Click to expand...


http://webpages.charter.net/jamie_5"
 
On Oct 1, 6:31 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
Andre Majorel wrote:
I've got a Chauvin Arnoux C.A 5220 DMM that bottoms out at 9 mV.
Even with the inputs shorted and in "Velec" mode (270 k input
impedance), it never goes below 9 mV.

The problem is only for AC. In DC mode, it *does* go down to 0.

Any idea what could be the problem ?

It's built around a JRC NJU9210BFC.

Sounds normal for a cheap meter to me! :)

http://webpages.charter.net/jamie_5"
Click to expand...
Could it be that this meter needs to be calibrated? That is, nulled
out on the AC mode? Are there any zero adjustments inside for low AC?
Try putting a very short piece of wire across the input and ground.
That will eliminate the "antenna" effect and pretty much prove that
the noise is inherent in the meter amplifier. Lenny
 
On 2008-10-02, captainvideo462002@yahoo.com
<captainvideo462002@yahoo.com> wrote:
On Oct 1, 6:31 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
Andre Majorel wrote:
I've got a Chauvin Arnoux C.A 5220 DMM that bottoms out at 9 mV.
Even with the inputs shorted and in "Velec" mode (270 k input
impedance), it never goes below 9 mV.

The problem is only for AC. In DC mode, it *does* go down to 0.

Any idea what could be the problem ?

It's built around a JRC NJU9210BFC.

Sounds normal for a cheap meter to me! :)
Click to expand...
Ugh ! Fortunately for me, none of the other cheap meters I've
used ever did something like that.

Could it be that this meter needs to be calibrated? That is, nulled
out on the AC mode? Are there any zero adjustments inside for low AC?
Try putting a very short piece of wire across the input and ground.
That will eliminate the "antenna" effect and pretty much prove that
the noise is inherent in the meter amplifier.
Click to expand...
Did that and the problem is still there. There are four presets
inside but I'd rather not touch them without knowing what they
do. Chauvin-Arnoux do not seem to believe in offering service
manuals on their site (when it is not down). I've asked them,
we'll see...

--
André Majorel <URL:http://www.teaser.fr/~amajorel/>
"Je regrette le Concorde. Au moins il vous amenait directement ŕ
l'hôtel." -- Cyrano
 
Andre Majorel schrieb:

....
What I don't get is how, after shorting the plugs with a 2-cm
long piece of wire, switching to "Velec" mode (270 k input
impedance), switching off all monitors and fluorescent lamps in
the vicinity and going outside, you *still* get 9 mV.
Click to expand...
I have an old (~1980) 4.5 digit true rms DMM; given accuracy for
ACV: 0.25% rd. + 20D!

300 mV AC range, input shorted -> display 000.12 (mV)
300 mV DC range, input shorted -> display 000.00 (mV)

Your reading could be normal for this type of DMM. What says the
manual?

Just my 2 cents

Reinhard
 
It is normal that on the very low voltage AC scale and the leads are
terminated, the meter will read something. The reading my be in the
area of a small number of millivolts. The higher end meters tend to
have this effect on their lowest scale.

The lead wires can act as a small antenna and can pick up noise. The
input circuit on the meter can also pick up its own internal noise.

My Fluke meters all do that type of effect. I have these serviced and
calibrated at least once per year. If I remember correctly, this
effect is explained in the Leitch meter instruction book.


Jerry G.


On Oct 1, 6:05 am, Andre Majorel <che...@halliburton.com> wrote:
I've got a Chauvin Arnoux C.A 5220 DMM that bottoms out at 9 mV.
Even with the inputs shorted and in "Velec" mode (270 k input
impedance), it never goes below 9 mV.

The problem is only for AC. In DC mode, it *does* go down to 0.

Any idea what could be the problem ?

It's built around a JRC NJU9210BFC.

--
André Majorel <URL:http://www.teaser.fr/~amajorel/
"Je regrette le Concorde. Au moins il vous amenait directement ŕ
l'hôtel." -- Cyrano
Click to expand...
 
It is normal that on the very low voltage AC scale and the leads
are terminated, the meter will read something. The reading may
be in the area of a small number of millivolts.
Click to expand...
True, but the OP stated that the reading was the same whether or not the
leads were shorted.

I checked my Fluke 87 set to 4.5 digits. With the leads open, I get a
residual of about 3mV (though this varies with the lead position and
separation, of course). When the test leads are shorted, the reading drops
to less than 2mV and stays there.

I'd say there's definitely something wrong with the OP's meter. Whether it's
significant is another matter.
 
I have three Fluke meters, bought them at pawn shops years ago_One of
them has a plug in thermister wire.They all need new batteries.I use Ray
O Vac alkaline batteries.I don't like keeping up with recharging
rechargable batteries.I al Lazy.
cuhulin
 
On 2008-10-04, William Sommerwerck <grizzledgeezer@comcast.net> wrote:
It is normal that on the very low voltage AC scale and the leads
are terminated, the meter will read something. The reading may
be in the area of a small number of millivolts.

True, but the OP stated that the reading was the same whether
or not the leads were shorted.
Click to expand...
I didn't make myself clear. With the leads open, you get on the
order of 1 V, which doesn't surprise me considering the 10 M
input impedance of the meter.

What I don't get is how, after shorting the plugs with a 2-cm
long piece of wire, switching to "Velec" mode (270 k input
impedance), switching off all monitors and fluorescent lamps in
the vicinity and going outside, you *still* get 9 mV.

Still no service manual forthcoming from Chauvin-Arnoux. What.
A. Surprise.

I checked my Fluke 87 set to 4.5 digits. With the leads open,
I get a residual of about 3mV (though this varies with the
lead position and separation, of course). When the test leads
are shorted, the reading drops to less than 2mV and stays
there.

I'd say there's definitely something wrong with the OP's
meter. Whether it's significant is another matter.
Click to expand...
--
André Majorel <URL:http://www.teaser.fr/~amajorel/>
You measure democracy by the freedom it gives its dissidents, not
the freedom it gives its assimilated conformists -- Abbie Hoffman.
 
On 2008-10-03, Reinhard Zwirner <reinhard_zwirner@web.de> wrote:
Andre Majorel schrieb:

...
What I don't get is how, after shorting the plugs with a 2-cm
long piece of wire, switching to "Velec" mode (270 k input
impedance), switching off all monitors and fluorescent lamps in
the vicinity and going outside, you *still* get 9 mV.

I have an old (~1980) 4.5 digit true rms DMM; given accuracy for
ACV: 0.25% rd. + 20D!

300 mV AC range, input shorted -> display 000.12 (mV)
300 mV DC range, input shorted -> display 000.00 (mV)

Your reading could be normal for this type of DMM. What says the
manual?
Click to expand...
This is a 4000-point meter. For AC voltages, the spec is
"+/-1.5% reading +/-1 count".

I'm not sure what "reading" means in this context. If it means
"whatever number is on the display", 1.5% of 9 mV is 135 ľV so
the actual voltage could be anywhere between 7.865 mV and 10.135 mV.

--
André Majorel <URL:http://www.teaser.fr/~amajorel/>
You measure democracy by the freedom it gives its dissidents, not
the freedom it gives its assimilated conformists -- Abbie Hoffman.
 
Andre Majorel wrote:
On 2008-10-03, Reinhard Zwirner <reinhard_zwirner@web.de> wrote:
Andre Majorel schrieb:

...
What I don't get is how, after shorting the plugs with a 2-cm
long piece of wire, switching to "Velec" mode (270 k input
impedance), switching off all monitors and fluorescent lamps in
the vicinity and going outside, you *still* get 9 mV.

I have an old (~1980) 4.5 digit true rms DMM; given accuracy for
ACV: 0.25% rd. + 20D!

300 mV AC range, input shorted -> display 000.12 (mV)
300 mV DC range, input shorted -> display 000.00 (mV)

Your reading could be normal for this type of DMM. What says the
manual?

This is a 4000-point meter. For AC voltages, the spec is
"+/-1.5% reading +/-1 count".

I'm not sure what "reading" means in this context. If it means
"whatever number is on the display", 1.5% of 9 mV is 135 ľV so
the actual voltage could be anywhere between 7.865 mV and 10.135 mV.
Click to expand...

Just subtract that 9 mV from your readings when using that range.
Unless the thing can be NIST or similar certification for lab work, you
are going to have to put up with it.


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The crazy, and the insane.
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