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Hantek CC-65 AC/DC Current Probe Teardown and Testing

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jrf:
This is my 'final' schematic with corrections & updated voltage readings.
Schematic: -  CC-65 CLAMP2.pdf (21.33 kB - downloaded 409 times.)
Also the capacitors marked 100nF are 'unknown' small brown ones! 0.5-100nF range.
I had always assumed they where all the same as the same colour but may be not!
Reading indicates they could be anything!!! What a mess! One way of making life difficult for repairers!

Cheers,
John.

jrf:
Here is the Schematic with extra notes after some playing with it & experiments.
 CC-65 CLAMP3.pdf (22.24 kB - downloaded 434 times.)

NOTE: I have not measured any of the small ceramic capacitors. Brown or white.
My meter works fine so I will not be desoldering them to find out!

From photos & comments on the net I am doubtful there is any reliable better cheap option.
Cheap < 300US. ie you can pay a lot more than this one ($50US) for little to no gain.

Some use 3V batteries. This implies they use switch mode power supplies. Most likely NOISY!

I have also noted physical copies of name brand units (ie fluke/tektronix), often with different specs!
Regardless I doubt they come close to the originals.  They may even have the same electronics but are unlikely to have the same core & sensor head.
Some clamps are copies of copies & don't even use correctly rated components. So not only do they not meet the specs they have poor performance overall & give wildly inaccurate readings at different frequencies. BEWARE!

So, Best of Luck,
John.

RodgerTheBadger:
Hello.

Firstly thank you for the work on the CC-65 clamp schematic, it has proven to be both interesting and informative.

I was just wondering if you could explain the variable resitors VR5 and VR6.  You mention that they are used to adjust fr reading changes when rotating the clamp.  Is this due to the earth's magnetic field?  If so why is there a change in reading if the magnetic field is constant?  I was wondering if it is because the two hall effect sensors ahve different sentitivty?  But even then wouldn't they just everage out?

Any help would be appreciated as I can work out the rest of the circuit now :D

Thanks,

Rodger

CDaniel:
I received my probe ... so I hooked up the signal generator at the sensors output . Indeed , the circuit is limiting the max frequency , it is perfectly linear up to 10KHz . Of course if the amplitude is low the bandwidth could be even worse .

jrf:
Rodger,
Good Question!
RE: VR5-6 function.
Circuit:
Hall sensors used: 4 wire - ~1V-grd power on 2 & +/- signal on the other 2.
Signal +ve of one & -ve of other go to either side of VR5, & the others to VR6.
The halls are mounted at the ends of the C cores forming the clamp such that a field running say clockwise around the core creates a positive output in both. ie If both mounted at each end of one core then one will be upside down to the other.
They are trying to only measure the field created in the core by the current flowing through it.
Common mode fields, ie fields in the environment passing through both sensors are undesirable & need to be cancelled out.
Ideally both sensors have similar characteristics & just summing their outputs equally in opposite directions will do the trick, hence most photos of meters will show the pots VR5-6 centrally located. ie everything was within specs... As are mine.
If rotating the meter 180' about ANY axis in free air, away from all metal, creates any large reading differences then the 2 halls are not balanced, or there is a circuit fault.  Mine changes by about 2mV. Not enough to worry about given the fluctuations due to temperature & close magnetic fields when taking measurements are similar. ie large >10mv say.
I do not know how they are factory calibrated & can see that it would be difficult to get a 'perfect' balance here.
Other clamps & clamp meters with similar Halls use similar circuits & include the 'balancing' VR's. Some only one. I suspect 2 may be overkill.
Another observation is why the C11 capacitor on one of the 4 signal wire resistors & not the others? Suspect it made an improvement during commissioning. Possibly not 'designed' as such.

Anyhow I hope this gives you a better understanding of the circuit function & remember to make sure your clamp is not magnetised before starting ANY adjustments.  This is my one significant complaint with all these 'cheap' clamps. A strong DC current will magnetise the core! My zero moved 20mV. Reversing the current, in a similar way to its initial application, will mostly remove it, but appling a large AC current & then winding it slowly to zero will work better. A 'degauss' circuit from an old CRT screen does a good job as well, from what I have seen on google. My Fluke clampmeter is unaffected by magnets or fields but does not have a CRO output... Similar sensitivity though.

Good Luck,
John.

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