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Hantek CC-65 AC/DC Current Probe Teardown and Testing
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Noy:
So now we can change to another Sensor / better bin grade to improve the clamp?
myf:
Hello,

I want to test the mains and laptop power supplies. I already have multimeter and uni-t210 ampmeter clamp, and don't have oscilloscope and clamp for DSO yet.
Do you think I shall be able to use this clamp for this ? I don't know what frequency I shall see on the DSO-display. (my future DSO should be rigol-1054 or siglent-1104).

Many thanks for your answers to this too elementary question !

F.
Zhao:
Even if you replace them with HW101A bin G, which is the highest sensitivity part available, you only increase the sensitivity by 40%, which translates to a slightly lower noise floor as less amplification is needed. There are other ways to increase sensitivity without replacing any parts, such as reducing the air gap between the halves of the cores. Although this will also reduce max current level due to earlier core saturation.

It will be very interesting if we can improve its bandwidth to at least a few MHz. Although I afraid the stock core (which appears to be made of laminated permalloy) is not gonna have any permeability at such frequencies.


--- Quote from: Noy on October 10, 2020, 09:03:25 am ---So now we can change to another Sensor / better bin grade to improve the clamp?

--- End quote ---
Zhao:
BTW, I suspect the same sensor is used in the legendary UT210E clamp meter (see the photos in joeqsmith's post, quoted below). I would not recommend converting a UT210E to an oscilloscope current probe though, as it appears to use a pair of silicon steel core instead of permalloy core, according to the teardown from DiodeGoneWild (photo attached).


--- Quote from: joeqsmith on December 29, 2016, 05:15:19 am ---John and Jesse, this was my first attempt.  As I mentioned, the first problem is in the clamp.    Jaw was glued but I was able to cut it apart with an X-acto knife and not damage the plastic too bad.  There are two sensors, one at each end.  Core is a little strange.

--- End quote ---

jrf:
myf,

1/ A current clamp is only required if you want to measure current while isolated from the voltage, do not want to influence the circuit resistance or the current is very high.
ie it's more accurate & sensitive to measure current using a series resistance.
At mains potential a 1 volt drop across a series resistance to measure current is negligible but your OSC needs to be isolated from this voltage. Historically I have used an isolation transformer, in my case a small old 240-110V step down transformer I had. GREAT CARE MUST be taken!
I can now use a tablet on a battery powered USB OSC.
Alternatively there are now available isolated current sensor IC's that eliminate these issues. ie ACS712, 714 or 758 series. Available for +/- DC current.

2/ The RMS current drawn by a laptop supply is ~0.2A. I suspect most newer supplies have yet to include active power factor correction as they are small. So The current waveform should look like a standard bridge rectified capacitor charge circuit. ie large spike of current towards the peak of the AC voltage. Its peak value will be >1amp, under full charge rate conditions, so this current clamp will work well with it.  I just use a short mains extension lead with the 3 wires loose.

Basically if you want to look accurately at currents less than 100-200mA this is not the way to go. There could be 10-20mA of noise present. This clamp is sensitive to magnetic fields so for sensitive measurements it needs to be away from sources of interference! ie the mains! unless you are only interested in higher frequencies & the mains can be filtered out.

Good luck
John.
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