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 "Je regrette le Concorde. Au moins il vous amenait directement à l\'hôtel." -- Cyrano
Obviously, "something" is noisy. (Duh...)
Have you asked the manufacturer?
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).No. It's long out of warranty.
-- André Majorel "Je regrette le Concorde. Au moins il vous amenait directement à l\'hôtel." -- Cyrano
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? Does it change if you use shorter leads? Coil the leads?
It keeps changing until you hold everything perfectly still. But even outside, it never goes below 9 mV.
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 "Je regrette le Concorde. Au moins il vous amenait directement à l\'hôtel." -- Cyrano
Sounds normal for a cheap meter to me! :)
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
What does that have to do with it?
Ugh ! Fortunately for me, none of the other cheap meters I've used ever did something like that.
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 "Je regrette le Concorde. Au moins il vous amenait directement à l\'hôtel." -- Cyrano
Andre Majorel schrieb: ...
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.
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
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.
-- André Majorel You measure democracy by the freedom it gives its dissidents, not the freedom it gives its assimilated conformists -- Abbie Hoffman.
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 µV so the actual voltage could be anywhere between 7.865 mV and 10.135 mV.
-- André Majorel You measure democracy by the freedom it gives its dissidents, not the freedom it gives its assimilated conformists -- Abbie Hoffman.
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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