ACM22A True RMS AC/DC Current Clamp Meter for $21?

[upsss]

Has anyone seen or better yet have one of these? https://www.ebay.com/itm/ACM22A-True-RMS-AC-DC-Current-Clamp-Meter-w-Capacitance-Tester-Handheld-MX/264323251839?hash=item3d8ae4be7f:g:KRUAAOSwOKFc26Rl

It looks like a brand new generic True RMS AC/DC current clamp meter, no reviews or any other reference to it.  Almost sounds too good to be true for $21 shipped free from the US.  A similar AC/DC clamp meter from UNI-T cost twice as much and nothing else in between.  Aliexpress sell it under BSIDE ACM22A brand.

[balage]

Well, I have bought a UNI-T 210E. I think one should not go below that. There are a lot of forum threads on it and seems worth the price.

[upsss]

Looks like they dropped the clamp price today to ~$19.  I just watched a YouTube video of the BSIDE ACM03 clamp which looks like an older model version, not True RMS and only 4000 count display.  The review wasn't bad and the built quality was similar to many other cheap Chinese DVMs like the ANENGs and some UNI-Ts which I have and they aren't that bad.  At this point it looks like it’s better than no AC/DC clamp meter which is what I have now.  I will never use it as my main DVM so for occasional use as an AC/DC clamp meter for <$20 I will give it a shoot.

[bob91343]

With a 40A current range it has limited application.

[balage]

Actually I use my own UNI-T for only clamping.

Let us know what is your meter like once you have it.

[bob91343]

I got my clip-on dc millammeter HP 428A working again.  Now I can measure low currents.  Its lowest range is 3 mA full scale, analog.

The manual says you can thread, say, three turns through the probe and increase the sensitivity.  All well and good, but if I am going to do that I have lost the value of clip-on and might as well use a common milliammeter.

[Kleinstein]

Even with 3 or 5 loop through the probe one still has the isolation and if the cable is long enough one can do that without opening the circuit / changing the ohmic drop.

[bob91343]

I have several meters that offer isolation so that isn't unique to the clamp unit.  But you are correct that there may be situations where it could be of use to run a few turns through.  Or even just one turn.

With so much fine test equipment I have usurped all the room on my work bench and so can't work on anything.

[edavid]

With a 40A current range it has limited application.

The ACM22A is a 6000 count meter, with a low current range of 60A (10mA/count).  Obviously the UT210E is 10X more sensitive, but it does drift quite a bit on the the low range.

I got my clip-on dc millammeter HP 428A working again.  Now I can measure low currents.  Its lowest range is 3 mA full scale, analog.

The disadvantage of the HP 428A, especially on the low ranges, is that it injects AC noise into the circuit under test.

[Kleinstein]

There are 2 ways to do DC current sensing with a clamp on meter. One is using a DC magnetic field sensor, like hall effect and a very soft core. However this is limited in accuracy by the coercitivty  of the core. The smaller clamp of the UT210E helps here.

The other way is using the core more like a flux gate sensor or DC current comparator. This superimpose some AC, but this way suppresses core coercitivty. The HP 428 seems to be such a meter. This method also needs quite some extra power - so not that suitable for battery operation.

[coppice]

There are 2 ways to do DC current sensing with a clamp on meter. One is using a DC magnetic field sensor, like hall effect and a very soft core. However this is limited in accuracy by the coercitivty  of the core. The smaller clamp of the UT210E helps here.

The other way is using the core more like a flux gate sensor or DC current comparator. This superimpose some AC, but this way suppresses core coercitivty. The HP 428 seems to be such a meter. This method also needs quite some extra power - so not that suitable for battery operation.

Flux gates traditionally use a lot of power, but I've seen prototypes of integrated flux gates that claim very low consumption and low cost. I haven't worked with them, so I can't comment on how well they work, but they do appear to exist.

Some suppliers of GMR sensors have been working on using those for AC and DC current measurement. I don't know how well that is working out, but GMR sensors are cheap.

[Kleinstein]

If a magnetic core is used the coercivity of the core would be limiting in a DC reading sensor (e.g. hall or GMR). There may be option to use low amplitude AC if needed for demagnetization.  Just GMR sensors without a core would likely be sensitive to external fields.

Flux gate sensors can be made relatively low power (like some 100 mW), but this is for relatively small cores. Another option would be a kind of slow, pulsated mode operation.  Those small cores usually should be closed and the small extra air gap from a movable core can be a slight problem.

[upsss]

Just received the clamp and it is CRAP.  No way to reset the clamp to "0".  Stray DC clamp reading anywhere from 80mA to 150mA.  I should have known better!

[balage]

Sorry to hear that. At least nobody else read this will buy that.