Multi-meters showing the wrong reading?

[ericmark]

With voltage we know what it should be, and if the meter is out, we would soon know, my solar software tells me voltage is 247.6, so I would soon realise if one of my meters were out, I have so many meters which read volts. Ohms again my eyesight is not that good reading resistance colour codes, so tend to verify with meter, so would soon realise is out.

But amps not that easy, why I put both on same cables I don't know, likely red one correct, and likely some rubbish on the jaws causing yellow one to be out. But I rarely put two ammeters on the same supply and the amps could have been out on the yellow meter from the day it was bought, in Hong Kong before the take-over, so getting on a bit now, however so is the AVO Mk8 that was got in the early 80s.

The volts are correct on yellow meter, so I had never questioned if amps correct.

 

[bernardgreen]

Why are there two tails ( Live and Neutral ? ) in the jaws ?

If they are Live and Neutral then the meters will indicate the dfference between the two currents,

The difference in readings may be due the way the meters handle currents that do not have a sinusoidal waveform..

 

[EFLImpudence]

What does the red meter read when set to 20A range; the same as the yellow one?

 

[ericmark]

I was trying to measure earth leakage.

The difference in readings may be due the way the meters handle currents that do not have a sinusoidal waveform..

That was something I had not considered, the new meter can measure DC, so likely more technology in it.

What does the red meter read when set to 20A range; the same as the yellow one?

I will have to repeat the measurements. I am sure I can set up a test, but just did not consider meters may be wrong. Know volts are correct, did not consider the clamp could give a different result.

 

[JohnW2]

That was something I had not considered, the new meter can measure DC, so likely more technology in it.

Waveform sensitivity could possibly be an issue. DC current measurement with a 'clamp' meter presumably uses totally different technology.

I will have to repeat the measurements. I am sure I can set up a test, but just did not consider meters may be wrong.

That sounds a little on the naive side Anything electronic 'may be wrong'!

Know volts are correct, did not consider the clamp could give a different result.

You are talking about 'clamp' meters, and I suspect that one cannot really expect them to give more than an approximate answer. If one wants accurate current measurements, then one really needs to 'break' the circuit and insert some sort of in-line current meter.

Furthermore, what you're trying to do is 'worse' than simple clamp meter measurement of current - you're trying to detect (using 'clamp technology' a very small difference between two (probably) fairly high currents. In any measurement (or even mathematical) context, looking at very small differences between very large things is always potentially very problematical.

 

[Rodders53]

Yellow meter: CHY 903 spec states:
ACA 20A/200A/600A 0.01A ±(1.5%+4dgts)

So the display of 0.04 could well be anything from 0.000 to 0.040 Amps

Similarly the other meter (maker manual download doesn't allow cut/paste)
2A AC is resolution 1mA, accuracy +/-3% +10digits. {Or +/-4.0% + 10 in V.F.C. mode}
So it could be anything between, say 8 and 20 mA actual?
Quoted Accuracy is only for 5-100% of range
2A DC is also 1mA, but +/-2% +8 digits.

TBH I'd not expect any two meters like that to measure the same for such an indirectly measured current. Even fresh from Calibration.

 

[JohnW2]

Yellow meter: CHY 903 spec states:
ACA 20A/200A/600A 0.01A ±(1.5%+4dgts)
So the display of 0.04 could well be anything from 0.000 to 0.040 Amps

The display of the yellow meter is to 2 decimal places, so "4dgts" is 0.04, which surely means that a display of 0.04 could be anything from 0.00 to slightly over 0.08 Amps?

Similarly the other meter (maker manual download doesn't allow cut/paste)
2A AC is resolution 1mA, accuracy +/-3% +10digits. {Or +/-4.0% + 10 in V.F.C. mode}
So it could be anything between, say 8 and 20 mA actual?

In the case, the display is to 3 decimal places, so "10digits" is 0.01, which means that a display of 0.015 could be anything from slightly under 0.050 to slightly above 0.025 Amps ?

If the above is correct, then the difference in the currents displayed by the two meters is well within the range that could be expected from the claimed accuracy of the two meters.

TBH I'd not expect any two meters like that to measure the same for such an indirectly measured current. Even fresh from Calibration.

Indeed - as I wrote, I really don't think that such "indirectly measured currents" can (or should) be regarded as anything more than 'approximate'