Error of % + digits?

[Commander Kinsey]

I just bought an amp clamp meter, and it states the error is "+/- 1.9% + 3 digits". What does the "3 digits" part mean?

[Commander Kinsey]

No, I paid 30 quid as I needed one with DC current. The fiver ones only do AC.

[Commander Kinsey]

I luckily noticed it in the descriptions, I checked carefully due to my electric company's watt meter only doing AC, which I had tried to use to check for current in my car wiring and it read zero when I knew it wasn't. They say "AC/DC clamp meter for voltage and current" in the title, but in the description the combination of AC and amps is missing. I'm guessing they use a cheaper sensor. Mine says it uses the hall effect. The cheap ones are presumably just using half a transformer so need AC.

[Commander Kinsey]

Answering my own question, I found this page, it means aswell as the percentage error, the last digit (eg the 2 in 147.2V) can vary by 3.:

[Mark Lloyd]

I would expect +/- 3 times the resolution of the least significant digit, as in a reading of 180 could be mean an actual value as low as

177 or as high as 183.

[alan_m]

It means that its less accurate at low readings.

Assume that you are on the range 0.00 to 1.99Amps

If what you are measuring on that range was 0.10 Amps the error would be dominated by the +/- 3 digits (the 1.9% error is insignificant). The error would be +/-0.03 Amps or an uncertainty in the reading of +/-30%.

If however you are measuring 1.50Amp on that range the error would still be the +/- 0.03 Amps (the +/- 3 digits) plus +/-1.9% of the actual reading which is another +/- 0.03 Amps (rounded up). So 1.50 Amps +/-

0.06 Amps or an uncertainty of 4%

This is why if you clamp meter has more than one range you need to select the range the closest to what you are measuring without it going overrange.

How many digits does the display have and how many, and what are the ranges that you can select.

[Chris Green]

What's this "DC current" of which you speak? :-)

(just DC is sufficient)

[Commander Kinsey]

I hadn't thought of it like that, and was thinking about 3 seperate digits, as in 1s, 10s, 100s, which didn't make sense.

[Commander Kinsey]

Ah that makes sense. As for the ranges, it has two ranges, but it actually quotes three lots of error margins. I think perhaps one of the ranges auto-ranges within it.

[Commander Kinsey]

No, because you can get a meter which has a setting for DC volts. You would list the settings as: DC Volts DC Amps AC Volts AC Amps It wouldn't be marked as D Amps. And if it was marked as DC, is it measuring current or volts?

[Chris Green]

Read Scroggie! He used ZF rather than DC, much more explicit.

However what's wrong with DV, DC, AV and AC ?

[Commander Kinsey]

I've never seen those, but I have seen DCV and ACV. Historical I guess. I would also expect to hear "my house is supplied with AC voltage" not "my house is supplied with alternating voltage".

Anyway, unless you have OCD, it's quite clear what DC volts is.

[Chris Green]

Surely what one actually says is "my house supply is AC"

:-) I am, I'm afraid, a bit OCD.

[Bob Eager]

According to Westinghouse, DC stood for Direct to Cemetery

[alan_m]

Surely not... didn't they prove that AC was responsible for fatalities - by killing an elephant?

[Brian Gaff (Sofa]

That is ridiculous I was using hall effect sensors for autostops in cassette decks to replace reed switches in the 1980s, surely they are cheap as chips, indeed they are chips!

Brian

[Rod Speed]

Brian Gaff (Sofa) [e-mail]> wrote

But not necessarily that cheap with the accuracy you need for a meter.

[Commander Kinsey]

Maybe, I've never said or heard it, since they all are. But I might say "there's an AC voltage present on this terminal". I certainly wouldn't say "an A voltage", or even an "alternating voltage". In fact if I heard "alternating voltage", I'd think it meant one that was varying due to a fault.

Can't you get that fixed? It's all in the mind anyway, just stop doing it.

[Commander Kinsey]

Maybe getting an accurate reading off a hall effect sensor is more expensive? You were presumably just checking for the presence of something. The meter has to give a figure from 0.1 to 600 amps.

[Rod Speed]

That's as silly as you stopping being a psychopath, stupid.