Accurate Low Amp Current Probe Advice

[Martin72]

Finally, a few pictures with AC signals, current is 2mA/div., various frequencies/waveforms.
With/without averaging.
Devices involved:
DC linear supply, Tektronix A6302 with AM501A unit in TM501 housing, various real resistors, SDG2122X, SDS3104X HD, “special adapter” for the A6302 for the AC measurements.
Pictures of the setup will follow.

[Martin72]

Setup from the afternoon(SDG2122X not shown)....

[tautech]

One only hopes screenshots get taken with A/div settings....... 

[Martin72]

That's why I marked the pictures accordingly.

[Phil1977]

Just to show how bad it can be with cheap equipment:



Ch1 is the output of a signal generator with a squarewave with 10V_pp. It is connected to a 330 resistor, so ca. 33mA_pp are flowing. Ch2 is the output of the Peaktech 4250. The screenshot speaks for itself - if really needed you may estimate the amplitude of the waveform by filtering & cursors - but it´s just not suited for such a job.

As a DMM attachment it is a little more useful for small currents. But definitely not comparable to the very decent results of Martin72s gear.

Maybe I can try the same test with the Micsig CP2100B end of the week, but last time I compared them against each other there was not a huge difference.

[Kean]

Just to show how bad it can be with cheap equipment:

FYI, there are some potential improvements you can try
https://www.eevblog.com/forum/testgear/peaktech-4250-acdc-current-clamp-teardown-and-repair/
Not sure if they will help with low current measurements.

[nctnico]

Just to show how bad it can be with cheap equipment:

FYI, there are some potential improvements you can try
https://www.eevblog.com/forum/testgear/peaktech-4250-acdc-current-clamp-teardown-and-repair/
Not sure if they will help with low current measurements.

I don't think so. With a range of 60A, the noise is just too much to measure in single digit mA range. However, I think the lower range clamp which KungFuJosh has tested a few posts up, has the ability to measure currents in the mA range. Only nulling it precisely will be tricky and noise will need to be filtered / averaged.

[Martin72]

Maybe I can try the same test with the Micsig CP2100B end of the week, but last time I compared them against each other there was not a huge difference.

I had once opened a thread about a Micsig CP2100, with various tests:

https://www.eevblog.com/forum/testgear/micsig-current-probe-cp2100b-tests-and-comparing/msg3070834/#msg3070834

(and the following pages)

[DaneLaw]

Tried with the Hantek CC65 (also 60A rated clamp) to see if it could muster minute current clamp values.
The setup is as crude as it gets..
Top of a washing machine, no shielding..
Sig gen DG800PRO 50Hz sine, sq w. with a cheap BNC cable to alligator fitted with 10R metal film resistor.
1mA pr div. (as low as the scope will go) with lpfiltering & avg.
The noise from the clamp can be cleaned up quite a bit on these Micsig scopes with both variable bandwidth filtering and averaging, so even minute mA, triggered..






Setup.

[Sensorcat]

Tried with the Hantek CC65 (also 60A rated clamp) to see if it could muster minute current clamp values.

Could you please explain your setup in more detail (the video is a bit blurred)? I'm a bit puzzled trying to get the numbers together: The Hantek has, in its more sensitive range, 1 mV / 10mA, which is equivalent to 100µV / 1mA. I checked the Micsig range at Batronix and could not find a model with a sensitivity higher than 1mV/DIV. The 2nd screenshot tells 1.52mA PK-PK and the trace covers about 1.5DIVs. Doesn't that require a 100µV/DIV range? OTOH, the AWG seems to read 700mV, and, if I understand correctly, you used a 10Ω resistor as load? With 50Ω output impedance, this would lead to 700mV/60Ω = 11.67mA. Should this be the actual current, the resolution of the measurement would still be impressive, especially because of the stable triggering, since the cleanup through averaging cannot happen without stable triggering on the single acquisition to average. So please tell something on the variable filtering your instrument has!

[DaneLaw]

The pictures aint consistent, it cycles between 1x and 10x, the vpp-values on the sig-gen, also vary.
It was more an attempt to see how little noise it could muster at relatively low values, the LP-bandwidth filters do make quite an impact...
Yes 1mV/10mA on CC65, scope with 30KHz LP, with averaging and 10 Ohm resistor as load...
The values in itself, take it with a pinch of salt, its 9v battery was down in the high 6v region, so far from ideal but the only 9v I had on hand.
Will try to take a look at both ETCR007A and CC65 when I get some 9v batteries..

CC65 (60A 20KHz) 2 settings. [1mV/10mA & 1mV/100mA]
ETCR-007A (50A 100KHz) 2 settings [10mV/A & 100mV/A]

[KungFuJosh]

I have a CC65 coming today to play with. I'll see how it does compared to the crappy one I'm returning today. 😉

[BILLPOD]

My CC-65 gives me VERY inconsistent results.   I test it with known small currents
of under 10 mA and some times it's right on the money, and sometimes it is off by 20 mA.  I find that I can't trust it's results.   I've tried it with high end DMMs and oscilloscopes.

[Conrad Hoffman]

I'll mention the HP428 again. It has a full scale range of 1 mA. They're not uncommon and can often be had for under a hundred bucks. A DC instrument. Some detailed info:
https://www.prc68.com/I/HP428.html
https://www.diyaudio.com/community/threads/modernized-hp428-clone.270510/

[KungFuJosh]

The CC65 arrived today, and my expectations are that it will be better than the other crappy probe, and besides that, probably still pretty crappy.

I ordered the Tek TM502A / AM503B / A6302 Probe on eBay. I expect that to be a little better.

Thanks,
Josh

[Martin72]

I expect that to be a little better.

YMMD...

[KungFuJosh]

 

I'm actually surprised; the CC65 is lightyears better than the other piece of crap. I dunno about repeatability or accuracy or anything that matters, but I couldn't get the other probe to do even this...

I have the SDG2122X connected with some mini-grabbers to a piece of copper wire going through the current probe. Settings are 1kHz, 1Vpp. Probe set to 100mV/A.

ETA: ignore the filename, the last screenshot has averaging turned off.

[KungFuJosh]

The low mA range on the CC-65 is mediocre, but better than the previous piece of junk.

Switching to the 10mA/V setting, the CC-65 was pretty consistent with the DCA stepping through to 6A.

[Martin72]

One more thing:
The termination impedance is not 50 ohms, as far as I can remember regarding the CC-65.....

[KungFuJosh]

Their amazing manual says typical load is 10kΩ.

Here's a capture with DC1M on CH1.

[KungFuJosh]

Holy shit, Batman! Martin, when you said this thing was big, I had no idea how ridiculous it is. 🤣🤣🤣



Only problem is that the probe that came with the set has a small issue with the switch. 

[tautech]

Only problem is that the probe that came with the set has a small issue with the switch. 

Which forms part of the jaw locking device.......

[Martin72]

I still have a few parts...

[KungFuJosh]

I set the SDG2122X output to 369mV at 1kHz, and that measured 5.00mA on my SDM3065X.

Then I setup the AM503B at 1mA/DIV with 20M limit.

This looks pretty good, right? Did I do anything stupid in my setup? 🤔

...because after reconnecting to the SDM, I'm getting 1.713mA. I assume there's an equation I should know here. 😉

[Martin72]

As I mentioned before, you set 10mV/div, 1:1 and 50Ohm on the scope itself and leave it as it is.
Everything else (bandwidth limitation, scaling, AC, DC) is set on the 503B.

I set the SDG2122X output to 369mV at 1kHz, and that measured 5.00mA on my SDM3065X.

So you used a 73.8 ohm resistor as a load?