On Sat, 11 May 2019 19:00:52 +0100, alan_m wrote:

On 11/05/2019 14:33, Commander Kinsey wrote:
I got hold of a second hand one of these:
https://www.torontosurplus.com/rs-co...lampmeter.html

A HEME 100 clamp meter.
I can't find specs for it online, only a HEME 1010.
I've tried reading a few currents with it (using a brand new battery in
it), and it seems to underread a fair bit on DC (0.56A instead of 0.62A)
and AC (7.5A instead of 8.5A). It's also susceptible to wires near it -
for example if you put the live inside the clamp but the neutral is an
inch or so from the outside of the clamp, it reads a bit of that too and
gives a higher reading. Are these things supposed to be accurate? Can
I adjust it?

How are you measuring the reference currents of 0.62A and 8.5A?

The 0.62A was with a decent multimeter connected in the circuit.

The 8.5A was measured both with one of those energy efficiency meters on my house's meter tail, and by knowing what devices were running.

Using the specification of the HEME 1010

It's a HEME 100, not 1010.

You are on the 400Amp range with a resolution of 0.1A

There is no range selectable, it's automatic?

The accuracy is +/-5 digits (+/- 0.5 Amps) plus 1.3% of reading (0.1A)
so the reading is 6A +/-0.6A

That's a hell of an error margin, but still way less than what I'm getting.

Also, taking the same reading in the same circuit repeatedly is giving widely varying readings, between 50% too low and 10% too low. I've thrown it in the bin.

If you are using a multimeter as the comparison it may be equally
inaccurate, especially if the internal battery is failing. Often a
failing battery in a multimeter gives high readings.

I know the multimeter is accurate, I've tested it on all sorts of things.