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

[Mechatrommer]

quick and simple current measurement setup...
* poorman's FG 5.88Vpp sine wave into 52.88ohm (measured with DMM) load/termination
* dso channel 1 (yellow) is reading volt across load resistor.
* cc-65 probe setting at 1mV/10mA, plugged into channel 2 (blue) of dso.
* dso acquisition is averaged 8
* theoritically the reading should be (5.88Vpp/52.88ohm = 111mA, ie 11.1mVpp reading at channel 2)
* theoritical -3dB reading is @ 11.1mVpp / 1.414 = 7.86mVpp

result:
reading floor at 5mA (500uVpp), ie no current/wire pass inside hall sensor (refer to 4KHz open.png)
-3dB BW is excess of 23KHz, hence the claim in the spec (20KHz BW) is valid. (refer to 23KHz test 52.88ohm.png)

teardown pictures as attached...
http://www.dx.com/p/hantek-cc-65-ac-dc-current-clamp-meter-multimeter-with-bnc-connector-blue-black-197938#.VG4o3sZNJ8E

(edit 240411)
some useful posts (imho) to consider modding your probe: (please inform me if i miss other useful info) ymmv
1) mickab: https://www.eevblog.com/forum/testgear/hantek-cc-65-acdc-current-probe-teardown-and-testing/msg3320244/#msg3320244
2) toli: https://www.eevblog.com/forum/testgear/hantek-cc-65-acdc-current-probe-teardown-and-testing/msg3625496/#msg3625496

[bdivi]

Hello Mechatrommer,

Thank you for the mini review.

This Hantek clamp is one of the very few affordable DC milliamp clamps on the market and I bought myself one a couple of months ago.
I was however disappointed with the performance. As you noted AC is good to above 20KHz (I measured 28KHz -3dB). The clamp DC nulling on the other hand is hopeless - I have to press the button numerous times in order to get it close to 0 and after that it drifts all over . It goes +/- 50mA in several minutes and on top of that it measures 5-6% above the actual value.

I was in contact with Hantek support asking them for calibration/repair manual and schematic but could not get anything so far.

I am sure that if we get hold of the schematics we will be able to improve the performance - it is amazing how they managed to put so many low quality trimpots in this package.

Cheers
bdivi

[R_G_B_]

Best way to test this is to use a square wave. I think it works up to around 2khz square wave. Then it gets out of shape and distorts the amutude and phase response.

R_G_B

[Lightages]

I also have one of these and have been meaning to do a review of it too. Other things have gotten in the way. I also am not very impressed with the performance. I hold zero hope of getting any kind of help from Hantek, but you never know.

[IDEngineer]

Just picked up a Hantek CC-65 current probe. I'm working on some motor sensing circuitry and have a precise onboard current sensing circuit. I clamped the CC-65 around one of the motor leads and connected it to my scope's CH4. The onboard circuit is connected to my scope's CH1. I've attached a screenshot of the two traces, offset a bit for comparison. (CH1's cutoff on the first peak is due to saturation - the motor was drawing more current than the circuit could report. It was within the CC-65's range, though, so its output isn't truncated.)

I'd say, for the money, the CC-65 does a pretty good job of tracking what the onboard circuit reports. Would I like to have a nice Tek current probe with its standalone amplifier? Sure! But for many applications I think the CC-65 is a heck of a deal.

[Ivan7enych]

Hi,

I've got this Hantek CC-65 Current Probe.

At first test it appears, this probe outputs some parasitic oscillation (see yellow trace, blue trace is an output from UNI-T 210E current probe). On top of rectangular signal (2KHz, 200mA peak-to-peak), one can see some oscillations. Without signal the oscillations are better visible.

I've found, that inside there's a 7V stabilizer (U5B chip on top od the board, marked as PAO1), it generated some oscillations. I've added 100mkF capacitor between 7V output and ground, oscillations disappeared.

After the fix, output signal looks much better and cleaner. Probe noise is ~10mA.

[GSteuerwald]

Hi,
I own meanwhile 2 of these current clamps and confirm the oscillation on the output signal. HANTEK knew the problem and proposed to replace the capacitors C1 and C7 by 47uF/10V tantalum capacitors.
My solution: I added two low esr-elkos with 100uF/16V in parallel to the existing capacitors and the problem was solved.
Regards
GSteuerwald

Pic 1 and 2: Additional capacitors built in
Pic 3: Measured DC current: oscillation before change (green trace)
Pic 4: Measured DC current: signal after change (green trace)

[GSteuerwald]

Hi again,
one more pic showing the PCB without change and the polarity signs.
Regards
GSteuerwald

[rpress]

I bought a CC-650 with the same unstable supply.  I'm my case to solve the problem I put a 0.1uF cap in pins 1&2 of the pads for U5.

[mkee]

Just received a cc-65 as well with the same power oscillation. Smoothed that one out thanks to comments here. Would be great to be able to find out what's causing the significant and fairly quick drift. And why it needs so many attempts to get it to zero out in the first place.

[rpress]

The zero button is actually charging a cap up while it's pressed.  So try holding it down longer.

[mkee]

Of course...just realized that too...my mistake for not looking just a little closer before making that comment

[mkee]

Just thought I'd mention an observation in case someone is looking for a comparison in the future. Or if someone is trying to improve this. Seems like the drift stabilizes at around -800mA (relative to calibrated state) on high sensitivity (1mV/10mA), and -550mA on the lower sensitivity (1mV/100mA). At least noise is much improved after modification though.

[enyone]

Has anyone else noticed this behaviour of Hantek's CC-65 dc offset "walk" (see attached graph) ? There is some intervals where strange things happen and between those intervals measured values are quite static. I was wondering if it was my scope's ADC causing this but then I repeat same measurements at my multimeter and similar behaviour occured.

Test setup is one 10 watt 12 volt automotive light bulb connected to full 17Ah 12 volt gel lead acid battery (attached photo has 2 similar of them but only the one behind the the on in front is used). Plot data collected with Rigol DS1054Z which was self calibrated before measurement. Lamp was powered cold when measurement started. Hantek's clamp was "nulled" to 0 DC offset when measurement started.

[nctnico]

I see the same effect with a DC clamp from another brand. I think this has to do with the leakage of the capacitor + surrounding circuit that is charged during DC offset nulling. In other words: it is not suitable for doing long term measurements.

[bb1]

Attached is the report of testing Hantek CC-65 bought in October 2018.
Screenshots show frequency response for square and sinusoidal signals, as well as measured current amplitudes for actual currents up to 65A.
No unwanted oscillations are observed.
Saturation at 20A is reported for 1mV/10mA CC-65 setting.

[KlausF]

Does anybody has the schematics and knows where to get it?
I sought and sought but couldn´t find.

[Mechatrommer]

i just checked my topic list to find old friends but it surprised me when seeing this thread. there have been many replies throughout the years but iirc i havent get any single notification of new reply to this thread. my worst nightmare is when somebody asked me in forum and i dont see it in my "unread post" thread list i dont even know the un-oscillating capacitor hack posted 2 years ago until today i've been using this current probe in its original form happily since. and then i tried to make modification to increase bandwidth and learn its circuitry early this year, but failed since i thought, there is no room for improvement, iirc the bottleneck is the hall sensor bandwidth, you'll need to pay more for higher BW hall effect sensor. btw, i attached some of my (failed) hack attempt record if anyone interested. this is not in anyway will make you understand the circuit any better, its just showing how i tried to do it, my methodology and i think the last image is partially developed schematic from reverse engineering it i dont think i will proceed since there is not much point to it, build it? this device is cheap enough go buy it, you can spend more by getting each individual components imho. you wont get anything meaningfull but iirc this device built on several 272 opamps...

pic #1: i marked the opamp/ic orientation before desoldering them out, so i can better see traces underneath
pic #2: the pcb under the light for better visualization. opamps removed.
pic #3: the spaghetty mess try to understand it all
pic #4: the half breed schematics, i dont remember it anymore.

fwiw and cheers...

[harrimansat]

In mine, this lead of variable resistor was not soldered. One of the scales was out intermittently

[harrimansat]

The other side was not soldered on the bottom either. Once soldered it has not failed again 

[KlausF]

That is what I am interested in, in those variable resistors. What is adjusted with them ?

[electro-56]

I was unable to get the full calibration procedure out of Hantek, but when pressed they offered this:
VR1 adjusts the scaling of the 1mV/10mA range (they called it the 100mA range), and VR2 adjusts the scaling of the 1mV/100mA range (which they called the 10A range). They also suggested squeezing the clamp jaws together while pressing the "zero" button to improve the accuracy.
howie

[harrimansat]

What type of hall sensors are used? It seems a magnetoresistive bridge type no?

[Mechatrommer]

What type of hall sensors are used? It seems a magnetoresistive bridge type no?

its in the OP picture, not sure what, it has SE marking on it...

[harrimansat]

The other HP clamp that I have is colsed loop with inductor and hall. I don´t know how this clamp works. There´s more hall sensors in PCB?

[Mechatrommer]

not on the pcb, i marked earlier only to indicate the connection to it. hall effect sensor is to sense magnetic field so it must be near that metal core loop, so thats what you see, there are 2 of them as in the picture, nothing more.

[maxspb69]

Maybe useful for someone...
https://yadi.sk/i/qGA6hIVvvBYOPg

[macboy]

The other HP clamp that I have is colsed loop with inductor and hall. I don´t know how this clamp works. There´s more hall sensors in PCB?

Your HP clamp is probably a much better instrument than this. Hall sensors have limited bandwidth; they work from DC to some 10's or maybe 100's of kHz. In contrast, a traditional current transformer can be designed to have 10's MHz bandwidth, but can't give output at DC.  A high bandwidth AC/DC current clamp will combine both techniques, and use other interesting methods to give good measurements. For one thing, the core materials necessary for high bandwidth will saturate at a relatively low DC value, and will distort the waveform even with a DC bias lower than saturation. For that reason, those probes will use the Hall sensor output to drive a DC current into the sense coil (or another coil), to offset the magnetic flux created by the DC current. It will always try to drive the (low frequency component of) Hall sensor output to zero. Then, the magnitude of this "correction" current (not the Hall sensor output) is measured to give DC/LF current measurement, and is combined with the output from the coil for the AC/HF components, giving an overall AC+DC measurement. This gives a good DC current measurement linearity, even if the Hall sensor is non-linear, it prevents saturation of the core, it helps prevents DC current from magnetizing the core thus causing hysteresis errors, and it prevents DC bias from distorting the AC portion of the waveform.  It's also why a "real" AC/DC current probe is so expensive.

[KlausF]

Огромное вам Спасибо. я очень рад.

[KlausF]

Maybe useful for someone...
https://yadi.sk/i/qGA6hIVvvBYOPg

Огромное вам Спасибо. я очень рад.

[mrprecision]

Hantek Current Probe Frequency Response:

[jrf]

Thanks for the Schematic.
I have been looking at options for a clamp & all the cheap ones look to use almost the same circuit, with the same issues, so I wanted one with a circuit I could modify &/or repair.
To this end I hunted for info & from partial schematics, photos, & descriptions I have prepared the attached schematic with notes.

This is not 100% accurate.

I have ordered a clamp but it is still 4-6 weeks away.
If anyone has any suggestions or corrections please help!

Cheers,
John.

[jrf]

Did not see my attachment in last post so will try it this way.

 cc-65-CLAMP.pdf (21.08 kB - downloaded 662 times.)

Cheers,
John.

[belzrebuth]

Isn't this able to perform better with some circuit change or something or it's at the limit of the topology used?
I'm slightly surprised this hasn't be done yet, given how many people have it and its target price.

I mean even exchanging some parts for more expensive ones should still render this tool a great value for hobbyists.
Since it's analog there shouldn't be much in terms of tedious reversing and they must be some known good designs that the hantek could be adapted to.
I know what I say is vague and I admit I don't know much if anything about current probes but I'd expect this would be a nice hacking candidate for knowledgeable people.

[jrf]

If you look at CC-65-clamp.pdf, available above, you could try replicating part of the circuit U3-1&2 & U4-1 on a breadboard. Feed it power & signal from the clamp. By changing U3 & U4 to amps with 10x the bandwidth you may be able to determine the upper limit of the Hall sensors. I have seen others reach 100KHz with similar sensors. BUT to go further best use an AC clamp. With modern cro's just adding the output from AC & Hantek would give the complete picture. This is the approach used in early model AC/DC MHz range probes. Not sure what is used now.  Remember the material used for the core of the clamp will also affect its response. AC ones are likely to start at 20KHz but go to a GigHz if you spend enough! & thats the point. If you spend a lot of time & energy you may be able to push this to 100KHz but it will use more battery power & it all depends on how much more usefull that is! Also  other clamps like this from PICO etc are using basically the same circuit. It is probably an obsolete design from the 80's just using more modern  components built on price/performance compromise.

Also note the capacitors are just a guess. I actually suspect the small ones to be closer to 0.01uF rather than 0.1uF but as I am still waiting on my clamp from AliEXPRESS or Ali-snailmail (7 weeks & yet to leave China!- & can't complain till 100 days!) I can not measure them or some other parts of the circuit to confirm accuracy.

Good luck,
john

[CDaniel]

I ordered one too ... AC bandwidth is anyway much better than an usual clampmeter ~400Hz - 1KHz
It should be easy to test what is limiting the bandwidth by replacing the hall outputs with the signal generator ... But the quality of the core is very important so I don't think the circuit is the limiting factor .

[belzrebuth]

I was also going to order one; that's how I found this thread but I'm kind of reluctant since I was going to use it for taking screenshots of current plots directly from my scope.
Since I want the waveforms to be as accurate/nice as possible this is just not going to cut it unfortunately.

Maybe I would be better off with plotting software than this.

See here:
https://youtu.be/uZTicR_eC9A?t=521

I'm not sure if the triangular waveform would actually look like a triangle if frequency was lower..
If signal is okay for say a frequency of 10k that's fine enough for me at least.
Perhaps someone who has this probe could post some screenshots in different frequency ranges.

[CDaniel]

This is usefull only when you can't interrupt the circuit , otherwise a proper shunt will give you all the bandwidth ...
As I see it , it is suitable for field measurements with a portable oscilloscope , not in the lab .

[Noy]

Which Opamps are used within the clamp?

[belzrebuth]

Which Opamps are used within the clamp?

I believe it's mentioned in this video
TLC272 & TL062

[Martin72]

Hi,

Had the CC-65 too, it´s behaviour in general was worser than the owon cp-05, which I got too (still have it).
The noisefloor kills it, probably this should be only used by multimeter.
Also the offset correction wasn´t stable.
The owon costs about 170€ incl. tax and is usable from 1A/div upwards, because of the noisefloor, the hantek in my memory too.
I wouldn´t recommending both, but the hantek is so cheap, it could be worth trying to improve it´s behaviour.

But the quality of the core is very important so I don't think the circuit is the limiting factor .

Remember the tektronix current probes.
With their external, large supply/amplifier, the circuit does matter too.
It´s got current compensating measuring method, so in theory, the core would not get into saturation.
(Current compensation: A winding is on the core, the hall sensor detect the current flowing through the core and feed it into a regular circuit which controls the compensation winding on the core.
A compensating current will be generated which rises up until the current through the core is zero, which means that the core couldn´t get in saturation - this compensating current will be forwarded to the measure output.
If 1A is flowing through the core, then compensating current will be 1A - And this is, what you measure.
Also this method allows you to do easily degaussing.)
But the saturation also depends from the frequency of the current, so the material of the core is mostly not a single one, it´s a mix, an compound of several ones to get as high as possible.

Current Clamps like the hantek or owon or many others, even when they costs 1000, 2000 bucks, don´t have it at all, what current compensating/ degaussing concerns.
What you can do is to reduce the noisefloor, maybe shifting a little bit the bandwith.

[belzrebuth]

Had the CC-65 too, it´s behaviour in general was worser than the owon cp-05, which I got too (still have it).
The noisefloor kills it, probably this should be only used by multimeter.

Have you tried increasing/adding capacitors as described in this thread?

[Martin72]

To be honest, no. Got it, test it, give it away...
Must read the thread completely, what the capacitors concerns.

[jrf]

CC-65-CLAMP.pdf above shows one capacitor solution as described in this blog, labled NEW caps in the power supply.
These caps are specified by the voltage regulator manufacturer but where not fitted, from what I can understand.
As stated on CC-65 CLAMP.pdf it should be possible to put in a multi-turn trim pot to replace the Zero push button. Then so long as the unit is at 'temperature' & under steady state conditions the zero should be reasonably stable, unlike a charged capacitor zero circuit! Pots where used on all the name-brand clamps & I suspect the push button was used to simplify the unit for rapid use in non-tech fields, copying its use in meters. Unfortunately meters are able to use a computer to do Zero, & do not drift compared to this solution!

I have read here about the coils used in some clamps. On reading a repair blog I found a 10MHz unit said the coil actually measured AC & the Hall the DC component. This makes sense. A coil could also be used to 'zero' the hall reading to reduce DC-saturation, but does nothing for AC saturation. The photos on this blog clearly show steel laminations. The frequency response of these would probably affect the linearity of the clamp at higher frequencies.

The op-amps used & the current circuit will only do as specified. Op-amps with 10x the frequency response are available but with typically higher current draw or more $$.

John.

[Noy]

Do somebody know pincompatible better ones (Opamp)?

[jrf]

Most dual opamps are pin compatible & available in that case size.
Important things you need to look at:
Operation Voltage range. ie same or better than existing.
Frequency response. 10x existing.
most of the other specs equivalent or better.
Availability.

Changing just the op-amps may not change the frequency response of the overall circuit as some of the capacitors in the circuit may act as filters as well.  Breadboard a circuit & experiment with what needs to be changed or just look up a 'standard' instrument amp circuit with the desired frequency response & modify to suit this applictaion.  Capacitors are often added for compensation & can depend on the opamp used.

John.

[belzrebuth]

@jrf
Could you do a basic test when you receive the unit and post a couple of screenshots here?
Maybe post something like a square into a load and the current rising and falling at half its stated BW and close to 20k?
I'd very much like to know when things start to break up.
With other words I wonder what could be the max frequency at which you can get a pretty looking waveform before discontinuities or other artifacts appear.

[jrf]

Look at the posts on this blog for that! Lots of photos of outputs.
10KHz bandwidth means that a 10KHz sign wave is at 3db down (1/2 expected voltage) at 10KHz.
So a 1KHz square wave, which is made up of 1KHz, 3KHz, 5KHz, 7KHz, 9khz etc sign waves,  will be mostly square.
But by 10KHz all you get is a mostly 1/2 voltage 10KHz sign wave.

John.

[jrf]

Well Aliexpress have delivered my Clamp & ,after a few quick measurements, the circuit is as I drew.
Scematic -  CC-65 CLAMP1.pdf (20.94 kB - downloaded 410 times.)
I have updated the voltage regulator values.

I shorted the 470uF zero cap for 30sec & then powered on & the output was 2mv at 1mV/10mA.
I then zeroed the unit & the cap chaged to ~10mv to offset this to zero.
2mV zero error is what I would expect. The temperature of my unit was ~20'c.
I would expect up to +/- 5mV based on temperature fluctuations & existing mag fields.
I turned off the unit for 2 hours & then back on (the capacitor charge should not be affected by the power switch pos).
It then read 1mV. So 1mV drift. (equiv to 10mA.) Very good.
Noise was ~1mV p-p without any mods. Have yet to test adding caps. I think 1mVp-p is reasonable!

I also put a magnet near the head. Big reading.
So if you short the Zero Cap & get a large value (zero offset) then the head may need demagnetising.
My Fluke is unafected by external mag fields!
If demagnetised & still high zero offset then may need to adjust Zero - step 6. VR3-4

Checking the calibration, mine looks to read 10-20% high!
Only tried DC to 2A. Will try AC & if the same error will calibrate to full scale on DC on both ranges.
(as described in the SChematic attached. Last section only, ie no need to adjust hall sensors, so just Steps 7 & 8.)

Further testing/calibration tomorrow.

Cheers,
John.

[Martin72]

Do you know the name of the op-amps ?

[jrf]

Try reading the posts above or looking at the PDF schematic attached above.
ie TLC272 & TL062 as marked on drawing.

JRF

[jrf]

Further testing of CC-65:
AC: 50Hz
Dodgy is the best way to describe the performance of the clamp.  At 65A it worked well. But at low currents ie <6A it was poor. The Zero offset was high & took a long time to stabilise. ie Zero of 400mA common.
DC:
At low currents accuracy +/- 10%. ie <2Amps.
Above this accuracy improved. At 60Amps it was good.
BUT 60A DC magnetisd the head. So when removed it still read 2A.
Reversing the current direction through the meter re-zeroed it.
I also put it back on 60A AC to make sure. (I used a Microwave transformer converted to a spot welder pluged into a variac to generate the current. I could do 1000A if I had a big enough variac & was fast enough.) Search for info on DIY spot welders.
I used a Fluke clamp meter & multimeter to compare. The Fluke uses more modern systems & is not affected by magnetic fields etc. It indicates down to 10ma but drifts up to 50ma over 10min. So the CC-65 is more sensitive & stable at low readings so long as not phisically moved.

Verdict: It does the job it was designed to do. ie Automotive testing.
It is not a accurate measuring instrument. It is an indicator. It shows what is going on.
As such I am happy. For $72AU it does the job I need.
Looking at what else is available I would need to pay 10-20X that to get something better enough to make a difference.

Cheers,
John

[mqsaharan]

Hi jrf,
Thanks for the schematic. I think the 3.3k resistor attached to Zero button and 470uF capacitor marked as R34 is actually R24 and I also have doubts about the R269, its assigned number as well as its value. Please reconfirm it before making any changes.

I don't own this clamp. I have Peaktech 4250, instead. And the schematic is almost the same with difference in some component values.
The power supply ripple was horrible at the output of its voltage regulator U5. I did replace C1A, C7A and C9A with double values but the ripple remained there. Then I installed a 6.8uF capacitor at the input of U5 and all the ripple was gone.
I didn't install 100nF capacitors that you suggested in your schematic. The little testing that I have done with this probe, I think these are not needed.

Regards,
Qasim.

[jrf]

Agreed R34 is actually R24, Typo. Thanks! Good to see others interested enough to check & let me know.
R269 is on the bottom of the board & clearly marked on the photos I have.
Colours Brown-black-black-green---brown(I think).  Looks like 1-2W.  2 other schematics here show it but one says 100M.
(will not dismantle again, now, as the power switch can be a pain if the wipers fall off!)
Not sure why it is there, under the board as well as in the circuit, or the size!??
Often large capacitors have dischage resistors to make them safe to work on some time after the power is removed or for ballancing but neither apply in this circuit.

I agree adding 100nF after the reg is actually in parrallel with C9, so is unlikely to do much. Missed that!. C1 has nothing to do with the regulator ripple & C7 is large already.
By putting a capacitor on the input to the reg it implies a resistance in the battery supply circuit. ie dirty switch contacts? or poor battery, but that is often why capacitors are put there! ie my second new 100nF. May be undersized!. Did you put it to battery -ve or circuit gnd? Not impressed with the power/selector switch at all! Designed to give problems!.

Cheers,
John.

Cheers,
John.

[Martin72]

Here is the schematic I´ve drawn from my owon cp-05+ (200Khz, 4/40/400A, appx 170€):

https://www.eevblog.com/forum/testgear/pintek-pa622-current-probe-crap-or-just-cheap/msg2220903/#msg2220903

It seems, it´s nearly the same design regardless of the price.

[mqsaharan]

Agreed R34 is actually R24, Typo. Thanks! Good to see others interested enough to check & let me know.
R269 is on the bottom of the board & clearly marked on the photos I have.
Colours Brown-black-black-green---brown(I think).  Looks like 1-2W.  2 other schematics here show it but one says 100M.
(will not dismantle again, now, as the power switch can be a pain if the wipers fall off!)
Not sure why it is there, under the board as well as in the circuit, or the size!??
Often large capacitors have dischage resistors to make them safe to work on some time after the power is removed or for ballancing but neither apply in this circuit.

I agree adding 100nF after the reg is actually in parrallel with C9, so is unlikely to do much. Missed that!. C1 has nothing to do with the regulator ripple & C7 is large already.
By putting a capacitor on the input to the reg it implies a resistance in the battery supply circuit. ie dirty switch contacts? or poor battery, but that is often why capacitors are put there! ie my second new 100nF. May be undersized!. Did you put it to battery -ve or circuit gnd? Not impressed with the power/selector switch at all! Designed to give problems!.

Cheers,
John.

Cheers,
John.

Hi John,
I am sorry I missed that through hole resistor. I do have seen those pictures but I forgot it is on the other side of the board.
As I mentioned before my current probe is Peaktech 4250. It does not have any component on the other side of the board except for two LEDs, the physical Zero switch and on/off switch contacts. I have attached pictures here borrowed from the other thread (https://www.eevblog.com/forum/testgear/peaktech-4250-acdc-current-clamp-teardown-and-repair/).

What I am calling ripple is actually oscillations due to lack of a capacitor at the regulator input terminals. The one that is in Peaktech seems to be unstable without the input capacitor. I tried 100n first, then 1uF but these didn't make much difference. The next up with me was 6.8uF and it did the trick.
I added the capacitor at the input of U5 and circuit ground. And it removed all the oscillations and regulator started giving clean output.

Regards,
Qasim.

[mqsaharan]

Here is the schematic I´ve drawn from my owon cp-05+ (200Khz, 4/40/400A, appx 170€):

https://www.eevblog.com/forum/testgear/pintek-pa622-current-probe-crap-or-just-cheap/msg2220903/#msg2220903

It seems, it´s nearly the same design regardless of the price.

Hi Martin,
Thanks for the review of CP05. Some pictures from your forum thread are not showing up.
Did you happen to test the probe with increased supply voltage? Did it perform any better?
You are right. MC33078 does need 5 volts minimum dual supply. I don't know why the designer couldn't find any other part that can work at 3v like other op amps used in this clamp. Or why didn't he made sure of the proper supply voltage for this particular part.

Regards,
Qasim.

[Martin72]

Hi Qasim,

No, increasing the supply didn´t take any effect  - Except that I´d burned out the hall sensors...
Fortunately they´ve send me a second one without any questions...

Some pictures from your forum thread are not showing up.

Hm, I still can se all of them (Browser: Edge)....

Martin

[mqsaharan]

Hi Quasim,

No, increasing the supply didn´t take any effect  - Except that I´d burned out the hall sensors...
Fortunately they´ve send me a second one without any questions...

Some pictures from your forum thread are not showing up.

Hm, I still can se all of them (Browser: Edge)....

Martin

My bad. Never mind. I forgot to check the rest of the pages of your thread.
Pictures on page 1 where you announced that you've received the CP-05 are missing as well as in the post after the next post. But its all right.
I am using Firefox on Ubuntu.

I just read that you have already checked with higher voltages with no difference in performance. This begs the question, have the designer made some arrangement to make up for the supply of MC33078 or what trick he used to make this op amp work at lower voltages. Or perhaps this op amp can work at lower voltages with minor decrease in performance.

Anyway, good luck with your current probe project.

Qasim.

[jrf]

Martin72,
If you want to test at 5v then you need to modify the voltage regulation circuit feeding the halls. This is normally temperature compensated at about 0.8v. ie maintain -3v at R11-10k or change the 10k to maintain the same voltage at the halls. Can't see any temp comp in that circuit. Any noise on that 3V will be reflected to a degree in the readings. Although your halls supply is +/- the same voltage. A bit of common mode rejection? C4 may cause a low frequency ripple, depending on size, if any noise on -3v there. Cap is required as all circuits have it.
Yes most of these circuits using 4 pin halls only will be very similar. Looks like yours also has a auto zero at power on?
I also would like to have a spec on the halls used!!!
How is yours affected by large DC currents? ie magnetized? Zero shift?

Qasim,
Thanks. Will look at that cap as low dropout regs are known for needing low impedance supplies & oscillation is common. Better to have & not need than have random issues. More testing rqd...

Cheers,
John

[jrf]

Well did some testing today. Very interesting. Much better results on the scope than on the multimeter.
My CC-65 does not seem to suffer the issues others have experienced. ie Zero error is minimal & as such drifts slowly.
It is important not to move the clamp afer zeroing!
Also there is no need for extra capacitors on mine. Noise level changes little when power is applied to meter.

I logged some results using Sign waves & square from 1KHz to 50KHz using about +/- 100mA.

10mA was the smallest current waveform that showed up on the scope. As such I am very happy.

Cheers,
John

[Martin72]

This is what I would expect from a clamp, only showing it´s limited bandwith and not such a crap like the cp-05 does:

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg3125996/#msg3125996

There must be something going in resonance or whatever.
Nevertheless, the hantek beats it for more than half of the price.

[jrf]

Martin72,
I have seen similar, just can't remember when/why. Will ask around. It rings bells! That certainly looks to come from a filter. Quite a high Q in your frequency annalysis. May give good single frequency sine wave responce but hopeless for square waves!!.
Possibly an active filter & would certainly not help the noise responce of the clamp. ie ampifying it! In reality, when you look at the phase lag of CP05 & CC-65 with the CC-65 90' at about 40-50KHz compared to 25KHz for CP-05.
I believe my CC-65 uses the output coax as part of the filter circuit. Filtering out much of the HF noise present when looking at the meter signals directly with a 10x probe.
Also I failed to mention the Scope I used for the pictures was a LOTO-OSC482M. This USB unit works with a PC & Android. $120AU.
And the RMS current readings from the scope agreed with my 4 digit RMS meter within unit accuracy. Impressed. So my earlier comments about AC readings with a meter do not apply when using a osc.

So Conclusion:
Pros:
My CC-65 works up to 10KHz with a bandwidth of about 45KHz.
Its zero is stable & gives accurate readings from 30-50ma & up.
Noise is within acceptable limits. Only slightly higher than background.
Cheapest low current OSC clamp I could find at $72AU.
Does the job it was designed for as advertised.

Cons:
High DC currents will magnetise the head, resulting in a large zero offset. (but still read that current correctly!)
This can be reversed by reversing the current through the clamp or using a large AC current. ie I was testing at 60A AC & DC & zero moved ~20mv on 1mv/100mA scale.
Leaving the clamp for a few hours should give a zero offset with discharged capacitor. If > 5mv or so then the head is possibly still magnetised,picking up stray fields in close metal or the meter was poorly zeroed inititally.
The meter picks up magnetic fields & should not be moved once zeroed prior to taking measurements.
Need to hold the zero button for several seconds, 5-10, to stabilise the capacitor charge.

Conclusion: Worth the money if it meets your spec.

Happy,
John.

[Martin72]

On the first (defective) one I began to desolder all the components for having a free look to the printed circuit, therefore I´ve measured most of the caps.

It makes me wonder if there is not a fault with your clamp.

Yes, this is my opinion too - When I got time to investigate, I´ll do it in the "right" thread then.

Martin

[Martin72]

Transport it to the CP-05 thread:

https://www.eevblog.com/forum/testgear/pintek-pa622-current-probe-crap-or-just-cheap/msg3128474/#msg3128474

[jrf]

This is my 'final' schematic with corrections & updated voltage readings.
Schematic: -  CC-65 CLAMP2.pdf (21.33 kB - downloaded 325 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 356 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

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.

[CDaniel]

I don't have a Fluke DC clampmeter , but from videos I see that the behaviour could be better , but in essence the same , drift , magnetising effect if you pass a large current . That's why there is a zero offset button .
Yea , the idea of using 2 sensors should cancel out common magnetic fields like earth magnetic field ... for some reason not all core magnetising can be canceled this way
If the sensors are not balanced right than + and - currents are not the same ( putting the wire in the opposite way through the clamp ) , so if you adjust the pots for this than should be good for any common mode fields .

[jrf]

Any magnetising of the core, within the core, will pass a common mode field through both sensors! ie a field circulating around within the core.
Hence the zero offset.
A large external field passes through the core & sensors with minimal circulating effect, passing through the sensors in differential mode, & hopefully being cancelled out. ie like parallel lines through the whole area of the clamp.
If the Hall sensors are not flat in the same plane then this field will give different signals from the sensors & be more difficult if not impossible to 'balance' out.
Small fields like a magnet close to the clamp will read more in one sensor than the other, hence giving a reading.

The description of the orientation of the sensors in my previous essay above may not be 100% but the logic & function is correct.

I avoid using the zero Push Button as it will result in reading drift with time. My USB oscilloscope has zero offset ability on its inputs so I use that.
If the offset >5mv I can just trim VR3 to zero it. A magnetised head will result in large zero offsets & significant drift if the Push button is used to 'correct' it. The push button is a poor replacement for the potentiometer, especially as it hides a magnetised head unless you short the 470uF cap or leave the unit for many hours to discharge completely. When I switch mine on it is usually within 2mV of zero. It changes 2-3mV depending on orientation & proximity to metal.

Cheers,
john.

[CDaniel]

Doesn't seems logic at all to replace a pot with a push button for some bias voltage and achive good results ... more likely the voltage/current small pulse when you press the button and the output of the op amp is "high" is somehow reseting the sensors  ( not very logic either way )
The cap is discharged anyway by the 10M resistor and internal leakage relatively fast , so the output of the amp should go slowly back to 0V . Why would you want this effect if this a bias

[dcac]

The "sample and hold" circuit used for zeroing has rather strange time constants and a I don't think I've seen an electrolytic timing capacitor before, usually you'd use a low leakage film capacitor for that.

When Zero button is pressed C4 is charged through R24, so 3.3K x 470u = 1.55s - so that could explain needing to hold the button a few seconds to achieve zero - remember you need 5x that time to charge the capacitor to >99%.

And the discharge time through R269, 10M x 470u = 4700s or about 1.5h, so a (slow) offset drift is unavoidable - unless you were lucky and C4 was charged to 0 volts. But then leakage and dielectric absorption in C4 can still cause offset drift.

[CDaniel]

OK , that OUT on the inverting input is like ground and fooled me 
Should be a better way of compensating the drift of this amplifier

[jrf]

R24 is just a surge current limit to protect the op-amp U4-2. Good work on calculating why we need a 10sec press to get a good zero.
The 10M R269 may be another 'commissioning'  part. It may be a 'bypass' leakage current resistor for the op-amp & without it the capacitor may actually change. Size & location do not make sense.
Regardless if the zero offset is only +/-5mv then the drift is slow & workable, once the capacitor has been charged for a time. Unfortunately it discharges exponentially, so will drift faster initially, & not good for larger offsets. ie when magnetised.

A better way to Zero is as mentioned on my Schematic & as used on all original & many new clamps. ie a potentiometer.
VR7 was probably the original zero adjuster before the PB capacitor was added. ie simply add a wire from the wiper of VR7, replaced with a potentiometer with shaft,  to the U1-1 side of the Push Button, & remove/disable the PB. It may be possible with resistors to range adjust the new VR7 to be single turn.

john.

 

[CDaniel]

In theory with the cap discharged if you can tweek the pots for zero output and measuring right positive and negative currents  then you have the basic adjustments  right .
So far not so easy in my case because the 2 hall sensors are not perfectly equals

[dcac]

It might be an idea to experiment with the value of R24 (3.3K). I’m pretty sure it can be lowered to perhaps 1K or so for a faster setting time.

But it seems this circuit was mostly intended short time measurements. If you want stability over a longer period you probably, as already mentioned, need to remove/replace C4 and rely on the trim pots. And when measuring with a DMM you can then also use REL to clear the offset.

[CDaniel]

Not very sure how the pot could work without some modifications , since the circuit is made to zero the output with no input , that's why is momentarily connected . With the button pressed you can't measure , it is just showing zero , when released and the wire removed from clamp it will show that last current value as the new zero level .
If you don't want that function just remove R23 and use REL all the time .

[jrf]

CDaniel,
When balancing the halls, VR5-6, the idea is not to zero the output but to nullify the difference as the clamp is rotated about a post.
Any change within 2-5mv is probably reasonable.
Once adjusted then Zero, Calibrate the clamp.

Replace VR7 with a pot mounted for shaft access externally. Connect wiper to output of PB going to Zero Circuit Cap. Done!
As I mentioned you may use balancing resistors to change the voltage to/from the pot to achieve a good central zero position on average using a single turn pot. (actually one could just solder wires to either side of VR7 & a third, wiper, to the 470uF side of the PB & connect to an external 10K pot to test. Do not use the PB as will not work! Range +/-0.25V I think giving +/-25mv zero adjust.)
From memory the voltage across the Cap is 10x the zero offset voltage required. ie 10mv zero requires 100mv on cap.
VR7 ranges from +/-0.5V, by my calcs.

John.

[RodgerTheBadger]

John,

Many thanks, that makes sense now.

I suspect two variable resistors are used to try and keep the temp co. the same on each side?  If fixed resistors were used on one side and a trim on the other they would probably have different temperature coefficients, leading to inbalance with temperature change.  Or maybe it is just to keep the parts list down to make assembly cheaper.

Anyway, thank you for your reply


Rodger

[dcac]

Not very sure how the pot could work without some modifications , since the circuit is made to zero the output with no input , that's why is momentarily connected . With the button pressed you can't measure , it is just showing zero , when released and the wire removed from clamp it will show that last current value as the new zero level .
If you don't want that function just remove R23 and use REL all the time .

Keep in mind you can only use REL as long as the offset is not too high. i.e. if you have a 50000 count meter and want to measure in the 50mV range - but you have 20mV offset canceled out with REL - you can then only measure up to 30mV before you get out of range.

[Elasia]

Hmmm I've had one of these in a drawer for some years now... maybe i'll mod it... thing drifts so much its useless really less i want an instant measurement and only that one instant measurement..

[Elasia]

I slapped a 10uF chip cap right on the output to make it semi usable and cut the fuzz down

It still drifts to no end making it utterly useless for time based tests less that charge cap is modded out

[jrf]

Most of the time when I switch mine on at normal room temperature it is with in +/-1mV of Zero volts. (especially after tweaking VR3).
Hence no point using zero button. The button should never be used for timed tests.

This unit is not designed for 'measurements' below 50mA. It gives an indication below 50mA but not something I would trust, given the noise threshold of +/-10-15mA.

Drift is caused by temperature change, using the Zero PB, or physically moving the clamp.
So eliminating those issues will reduce drift to within +/-1mV.
Given that most long term measurements involve measuring the change then initial zero is not critical.
Adding an output filter for slow measurements to reduce the +/-10-15ma noise is also fine.

Remember this unit is not a precision instrument. It is a cheep automotive clamp mostly used to measure currents above 100mA or to show the relative timing of switching events. ie injectors ect...

Precision instrument amplifiers, circuitry & design layout COST & are hard to duplicate when the clamp heads core is included.

This serves the purpose for which is was designed very well & is the cheapest reasonable option I have found. Pico sell a unit, with what I believe is basically the same circuit, for 2-3 times the cost & one can spend 5x the cost on other units for no gain.

At about 10x the cost some units start to out perform it, but one needs to pay at least $700US to get a unit that may be designed to minimise the noise & achieve good accuracy, sensitivity & frequency response.  These units will usually have two separate but complimentary measuring systems for the DC & AC components.

One gets what one pays for has never been truer!

Cheers,
John.

[Elasia]

Part true minus the expensive alternative / cost bit

I actually do have the pico model I bought years ago before knowing they were on aliexpress, it is the same board, just a rebadge

The best current clamp I've seen for the money is micsig's CP2100A for about $200 and goes up to 800 KHz or CP2100B for about $400 and goes up to 2.5 MHz

These blow this design out of the water although it is still good for a dmm and single use / point testing and now is only $60 bucks or so

The micsig's only came out in the last 2 years or so while this design has been around for 5 years or so?

I've been using several CP2100B for multi phase power and they all work fantastic

[Martin72]

Plus the unbelivable building quality of the micsigs.
I don´t know how they managed it, but you wouldn´t believe they´re so cheap when you don´t know their prices.
800khz and 2.5Mhz....Look around, at which price you normally do get this.
Unbelievable.

[jrf]

Looks very good if you need the frequency. That seems to be the only significant positive. (can work around zero offsets)
Noise level is about the same, 4x cost & needs external 5V.
I have seen reviews indicating some of the better clamps having 1/10 the noise levels of this?

How does it handle magnetic fields???
Does it self magnetise on high DC currents, if NOT then a BIG plus!

Oh & the Hantek design is ancient! Looks like based on clamps from the 80-90's just using more modern components.

Cheers,
John.

[Elasia]

Martin could probly answer that, you can see the noise levels here

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

[jrf]

Noise no better than CC-65 from that $400 unit. Much better Freq! though, but for a bit $ more I would hope the noise would be a bit less!

John

[Martin72]

If it´s so, congrats to hantek.

Here a comparison between much more expensive models like lecroy and tektronix, they´re "of course" better but not far away:

[Elasia]

Case of you get what you pay for.. mine is the noisy cricket lol.. have to use a large averager but that improved greatly after i slapped some chip caps on the output, still picks up on a lot of hfq noise but not as bad filtering it out

Mine also loves to drift off into space constantly, i'll slap a constant voltage via a trim pot voltage divider + fixed resistor next time i tinker with it

[jrf]

Thanks for those comparisons.  The best shot showing relative noise I could come up was from my Tektronix with Ch2 shorted & CH1 CC-65.

I have scaled both inputs to 5mV/div=50mA/div as per yours.
It puts into perspective my relative view. ie noise not an issue given my equipment. My USB scope shows less!
I have not 'zeroed' the clamp. Just switched it on, after powered off 24hr, & the recorded result.
No complaints.

Anyone with feedback on external fields/magnetic etc on other clamps? or magnetisation when using DC?

This seems to be the worst feature of a clamp to be used on cars, DC, or switched DC currents only!

Cheers,
John.

[Circlotron]

I bought mine to look at the primary current in car ignition coils. Typically (some exceptions) not much more than 10 amps, often lower. In that application the DC current goes to zero every switching cycle so you only have to adjust the scope so the zero line corresponds to a horizontal graticule line and you're done. Accuracy, drift, noise and frequency response is quite good enough for this, so in this instance it is fit for purpose and I am quite happy with it. I can understand why others may not be completely satisfied though.

[dcac]

I tried a spice simulation on the frequency response of the 272 op-amps. I guessed C6 to 1nF as this was the only value that gave a somewhat reasonable response in high gain mode:

EDIT: please disregard these traces - see next post.





But in low gain mode the response perhaps starts to drop of too quickly:

[dcac]

(lol) Well when I actually started looking at the caps values and the surrounding resistors it slowly hit me "100n" likely was just a 'place holder' for a sooner to be determined more accurate value.

So after some searching I found my CC-65 and decided to measure the caps 'in circuit' - using a technique with a signal gen, a variable series  resistor, a 10x amplifier and a DMM. The purpose of the amplifier was so I only needed to apply 25mV P-P from the signal gen and still be able to get an accurate reading on the DMM, the series resistor was set to match the resistance in parallel with the caps. This so I could measure the signal drop when probing the cap on the PCB. I could use 20Khz sine wave to get good readings on the DMM and i.e. swapping the probes over the caps only changed the reading about 10%.

So here are the measured/calculated caps values:
C5 = 2n2
C6 = 1n  (hey! I guessed it)
C8 = 2n2
C11 = 22n
C14 = 27n

I cannot swear by these values but they're likely better than ball park figures.

Spice Simulation to follow...

[dcac]

Here's the spice simulation - in high gain mode (6.5A) BW is about 23KHz - and in low gain (65A) about 34KHz.

High gain



Low gain


I have no spice model for the hall sensors so these are just simulated with sine generators with 500 ohms output impedance.

Do we know anything more specific about these sensors other than they appear to be in sot-143 size?

[dcac]

While I had my 10x amplifier handy I tried to measure the signal directly from the hall sensors - between pin 1-3 on HALL 1.

My amp can also be set to 100x and is based on OP37 so it has quite low noise and BW is about 250KHz.

The hall sensors seems to have allot of noise however - about 100uV P-P - but it wasn’t an easy measurement as CC-65 has no shielding to speak of - so I really had to fight with the 50Hz mains pickup.

It’s interesting there seem to be frequency peaking already at the hall input formed by R11//C13. When measuring 50mA RMS with the clamp I got:

500Hz = 120uV
1KHz = 123uV
5Khz  = 132uV
10Khz = 153uV
20Khz = 214uV

RMS from the hall sensors. This is then amplified about 50x by the 272s in high gain mode and about 5x in low gain.

[Elasia]

Yeah it has no shielding at all practically... picks up damn near anything, even the earth lol

[dcac]

I wonder why they chosen to frequency limit the 272s - well, they're limited with C5-C6 - but then peaking is applied with C8 and C14. I will try a simulation later without the caps.

Also why does U3-1-2 not have symmetrical feedback resistors R22 and R15 - one is 11K the other 7.5K.

[dcac]

I found the ut210e schematics and it does not seem to have any frequency compensation in the diff amp. From picture of the PCB C13 does not seem to be populated.

[dcac]

Red line = Spice simulation without any caps - BW is now about 115Khz in high gain mode. Question is how much more noise this would let through.

[dcac]

And for good measures - 10Khz square wave.

Red trace = without any caps in the 272 diff amp.




Remember this does not show the actual response with the HALL sensors - only what the amplifier look like in a spice simulation.

[dcac]

New Schematic with caps values added and some notes.

EDIT: Newer version of the Schematics here: https://www.eevblog.com/forum/testgear/hantek-cc-65-acdc-current-probe-teardown-and-testing/msg3545210/#msg3545210

 CC-65 CLAMP4.pdf

[Zhao]

The Hall sensor marked SE is likely to be HE12AF1D12U, a knockoff version of HW101A. "E" indicates that its sensitivity is in bin E (228-274mv @ 50mT).

Marking of HE12AF1D12U chip:

Taken from http://blog.sina.com.cn/s/blog_7d2f0f0a0100tv93.html

Datasheet of HW101A:
https://www.akm.com/content/dam/documents/products/magnetic-sensor/hall-element/in-sb-ultra-high-sensitivity/hw101a/hw101a-en-datasheet.pdf

[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.

So now we can change to another Sensor / better bin grade to improve the clamp?

[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).

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.

[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.

[mickab]

Hello,

I'm currently searching a solution to increase the bandwidth of the clamp. The hall effect sensor seems to response up to 3MHz but the mod is design for +/- 1Mhz (Power supply design)
My first glance on this topic was very helpful.

I have simulated the signal conditioning stage of the hall-effect sensor on Spice with a rudimentary model. An OPA2350 is used for U3 (high speed, low noise, single supply...) and a OPA2192 (high C-Load capacity) for the output stage.
The simulation is based on the schematic "cc-65-CLAMP.pdf" wich seems right except the capacitor value. I correct some cap value with few measurements. The correction is into the .pdf.

Push to the limit we can obtain 2.3MHz with +/- 170° phase shift and -3dB (see picture)

I will make a comparison soon with a new clamp vs modified. 

[jrf]

Mickab,

Very impressive, especially if the osc pages shown where actual measurements of your modified clamp in operation.
Simulation certainly has come a long way!
I would not have expected such a good result given the iron laminations in the head.
Shows how similar circuits from other suppliers can achieve good results, with better spec & correct components.
I am sure none of the original designs where optimised with a simulator.

PS: The version of cc-65-CLAMP.pdf used is not the latest on the site. ie some corrections & updates & most capacitor values updated, but not surprisingly a little different to your measurements. I suspect errors, changes or quality will change these with batches.

Cheers,
John.

[Mechatrommer]

The hall effect sensor seems to response up to 3MHz but the mod is design for +/- 1Mhz (Power supply design)

yeah good job. the reason i didnt pursue modding my clamp is because i saw some datasheets about cheap grade hall sensor their BW rating always in KHz region, the opamps used in the clamp is in MHz BW region iirc. so i concluded the bottleneck is the hall sensor and any mod attempt on circuit or IC will be futile. good to hear that i'm wrong.

[mickab]

Hello,

See in the .PDF the full test comparison. 
 

[Mechatrommer]

Hello,
See in the .PDF the full test comparison. 

in your pdf stated to change U4 with OPA2195. i cant find what is OPA2195, no datasheet in internet... but in your earlier picture, suggesting to change U4 with OPA2192, so i guess OPA2195 is a typo?... i'm currently adding stuffs into lcsc cart, so i want to add this stock as well. i can find OPA2350 for U1,U3 but i cant find OPA2192 in DGK (vsop/pdso) package, only soic8. is there any specific reason why we cant use all U1,U3,U4 = OPA2350? why must U4 = OPA2192? kudos to your work and cheers.

edit: i just noticed your OPA2192 high C-load remark. so we cant use OPA2350? i'll check on this thanks.
edit2: checking schematics, there is no C-load directly subjected to U4, at least 1Kohm impedance in the middle.

observation:
OPA2350 is 7V max opamp (5.5V recommended operating voltage), battery in CC-65 is 9V so i think  need to buck down operating voltage to 5V, this probably will reduce maximum current spec from 6.5A to maybe 3A in lower range and 65A to 30A in upper range. for myself, i dont think thats a big problem, i never need to measure high current so far.

[mickab]

Indeed this is a typo error for the OPA195.

In first place U4 was an OPA2350 but the response wasn't great due to the poor capability of driving capacitive load.
C15 represent the C-Load and is needed for noise attenuation.

Good observations Mechatrommer the OPA2350 can't work at 9V but the regulator of the clamp is set at 7V.
I think we can replace all op amp with OPA2192. This will need some simulation and testing but it is possible.
Tell me if you're interested. 

[Mechatrommer]

In first place U4 was an OPA2350 but the response wasn't great due to the poor capability of driving capacitive load.
C15 represent the C-Load and is needed for noise attenuation.

but there is R18 1Kohm separating them. this is a bit surprise for me. maybe i will figure out how to reduce noise from that output later.

Good observations Mechatrommer the OPA2350 can't work at 9V but the regulator of the clamp is set at 7V.
I think we can replace all op amp with OPA2192. This will need some simulation and testing but it is possible.
Tell me if you're interested. 

yes interested. as i'm going to order some parts from lcsc, i will add few parts for this mod as well (save shipping cost). but i can only find OPA2350 and another opamp that can get supply from ±12V, but 15MHz GBW only, i wont name it as its limited supply so i dont want somebody to outrun me  (its 2-3X the OPA2350 price anyway) if really the bottleneck is in opamp BW, i'm suspecting U3 will need high BW since its in sort of high gain differential (instrumentation) mode from schematics you guys provided. i cant figure out what gain, but lets say gain 10, OPA2350 38MHz GBW still can give 3MHz+ BW, so i think its a wise choice. where the rest of opamps are mostly for Voffset correction i guess. if my eye and mind is correct U4-1 is only gain 4 differencing opamp, so 15MHz GBW opamp still can give 15/4 = 3MHz+ BW. unfortunately, i cant make order for OPA2192 since lcsc doesnt stock this opamp, i will try with whats available in lcsc first. ordering separately from digikey for this particular mod will result in shipping cost damage on my side. cheers.

[mawyatt]

Hello,

I'm currently searching a solution to increase the bandwidth of the clamp. The hall effect sensor seems to response up to 3MHz but the mod is design for +/- 1Mhz (Power supply design)
My first glance on this topic was very helpful.

I have simulated the signal conditioning stage of the hall-effect sensor on Spice with a rudimentary model. An OPA2350 is used for U3 (high speed, low noise, single supply...) and a OPA2192 (high C-Load capacity) for the output stage.
The simulation is based on the schematic "cc-65-CLAMP.pdf" wich seems right except the capacitor value. I correct some cap value with few measurements. The correction is into the .pdf.

Push to the limit we can obtain 2.3MHz with +/- 170° phase shift and -3dB (see picture)

I will make a comparison soon with a new clamp vs modified. 

Interesting modifications, thanks for posting. I have a couple questions:

1) Since R18 isolates the output capacitance due to the load, is the added 22pf is to help stabilize U4-1?

2) Shouldn't another 22pf like capacitor be added across R20 to balance the differential amplifier?

3) With R18 isolating the capacitive loading to U4-1, then just about any good op-amp can be used that has rail to rail I/O at +- 3V rails and sufficient BW. The 22pf added capacitance may need to be changed depending on the op-amp selected.

4) With the leakage in C4 and R269 bleed resistor, wonder if another type cap and larger resistor value could work? Or removing R269 and placing back to back low leakage diodes (CB junction of bipolar) might work better drift-wise? If the drift is dominated by the Hall Effect sensor then this wouldn't matter.

5) What did you find in relative BW before and after the mods, maybe you could post images showing such if it's not too much trouble?

Anyway, great work and many thanks for showing

Best,

[masterx81]

Bought one of this, as soon as it arrives, i'll do the mods. Thanks for sharing! Nice result!
I've readed on other threads that this clamp have a lot of noise, but i see only ~1mv of noise (around 10ma), seem quite good.

[maxspb69]

Today I made all the modifications exactly according to the mickab 's description. The result is in the pictures below.

  1 - original device,
2 - modified device.

Test conditions: 6Vp-p amp, 50Ω load, 3 turns of wire on  hantek cc-65.

The band has expanded to up to 2.4MHz (-3dB).
If only to remove the amplitude jumps in the 1.0-2.5MHz range, the frequency response would be generally very beautiful! But this jumps within 1db are quite acceptable, I think...

(I think I can save a lot on the Micsig CP2100B current probe purchase  ) 

Thank a lot for the detailed instructions!

[Noy]

Argh.. currently i will also do the modification, but still waiting for the opamp..
Unfortunally i purchased a Micsig last year November already.. 800k one..

[Bluegizmo83]

I bought a CC-650 with the same unstable supply.  I'm my case to solve the problem I put a 0.1uF cap in pins 1&2 of the pads for U5.

Hey I know you posted this several years ago, but can you recall what type and voltage the capacitor was that you used for this for the CC-650?

[Bluegizmo83]

I bought a CC-650 with the same unstable supply.  I'm my case to solve the problem I put a 0.1uF cap in pins 1&2 of the pads for U5.

Just a heads up... I just did this mod on my CC-650 and I don't see any difference at all. I placed a 0.1uF electrolytic capacitor on pins 1 and 2 of U5. No change at all.

[maxspb69]

0.1uF electrolytic???

[Bluegizmo83]

0.1uF electrolytic???

Yes... Why? That's what someone else said they used...

[Bob Sava]

Indeed this is a typo error for the OPA195.

In first place U4 was an OPA2350 but the response wasn't great due to the poor capability of driving capacitive load.
C15 represent the C-Load and is needed for noise attenuation.

Good observations Mechatrommer the OPA2350 can't work at 9V but the regulator of the clamp is set at 7V.
I think we can replace all op amp with OPA2192. This will need some simulation and testing but it is possible.
Tell me if you're interested. 

If capacitive load on U4-1 is an issue - is resistor R18 different than 1k?

[Noy]

So whats best now?
Every opamp OPA2192 or mixed with OPA2350?

[newbieswe]

Does anyone have a parts list for the caps used in the modded schematic?
I'm about to order but don't know which size specs to choose.
If anyone have a complete parts list, that would help a lot.

[Noy]

All 0603 ones. The caps you need are all so small that you can choose X7R or They are only available as C0G.. So you can use >25V types..
All OPAMPS are MSOP..

[toli]

Glad to have found this thread. I've ordered a unit yesterday, and was looking for the schematic in the hope of extending the BW further.

Looking at the schematic posted on page 5 of this thread, some things seem a bit odd. Did anyone else trace out to circuit to see this schematic is correct?

Most of all the output difference amplifier around U4 seems strange, but a few other things can be extended in BW too.
1 - R18, which in theory should help isolate the amplifier from the capacitive load, is wrapped inside the feedback loop which means it doesn't isolate the amp from the capacitive load, it can actually make stability worse. I would expect R18 to be located after the feedback point (or in other words, for R17 and its added bypass cap to connect to the output of U4 instead of after R18).
2 - C15 seems very high in value. R18 + C15 will create a low-pass-filter with a pole at 1.6KHz with the values shown. Since its inside the feedback loop, the opamp will try to compensate for it, but with the limited GBW of the opamp it will only be able to do this for a limited BW (and even that only with small signal amplitude). Since the measurement results people have posted seem to show fairly high BW compared to this 1.6KHz, the value of C15 is probably quite a bit lower than this. Perhaps its 100pF and its a typo only?
3 - 22pF in parallel to R17 will add a pole at ~280KHz, and I'd expect to see a matching capacitor to bypass R20 for a typical difference amplifier structure. This could perhaps explain some of the uneven response seen at >100Khz.
4 - The first stage around U3 also has C5/C6 which are 8.1pF (8.2?) following the mod, so in parallel with 11Kohm its a pole at ~1.8MHz. That is assuming an opamp with high enough GBW. At the low current range the gain at this stage is probably ~X20 so we need an opamp with GBW on the order of 36MHz to get to this 1.8MHz limit in this case. In the PDF file attached a few posts later I see these caps are 15pF, this will limit the BW further to ~1MHz, so a GBW of ~20MHz should suffice in this case.

A few thoughts (which I can't do anything about until I get my unit ):
1 - My first guess would be that the value of C15 is off and its actually much lower in capacitance. Even then, it can probably be omitted completely after the mod. If we assume ~100pF load (cable + scope input) and R18 of 1K its a pole at 1.6MHz already, so adding additional capacitance will limit this further. R18 can probably be made smaller in value quite a bit (say 330R) to push out the pole its creating with the load capacitance, which would allow extended BW.
2 - The feedback for U4 will be taken (we can modify that fairly easily if it isn't the case) from output of U4 instead of after R18. In this case the 22pF in parallel to R17 can potentially be omitted completely, which would align R17 with R20 with no bypass and should result in a more even response at >100KHz and better CM rejection at the frequencies. If some capacitance is still needed there, we can scale down R16/17/19/20 to extend BW, which would make this stage less sensitive to parasitic capacitance if this is a problem. It will also reduce noise for this stage which can help in the high current range where first stage gain is reduced.
3 - This one is more of a trade-off. Currently the first stage seems to be operating with a gain of >X20 in the low current range (this is assuming the trimmer in the schematic is roughly in the center position), while the output stage has a gain of ~2.5 (for the low current range only, in the high current range the first stage gain is lower). This means the first stage needs to have a higher GBW as its more limiting in terms of BW. Moving more of the gain to the second stage can help extend BW further in the first stage which would improve overall BW. The down side here is that it will result in some noise degradation. A possible solution to this can be to move the gain switching to the second stage, and leave first stage with a constant gain of X5-X8 that will render noise of second stage non-dominant, but that's a bit more work.

[DaneLaw]

Also got one of these CC65 and been positively surprised with this unit, my first Hantek product.
Purchased the 4 cheapest AC & DC current probes I could find in China at one of their pre-NY-sales and some of them could likely work great with a new Micsig scope I had just purchased at the start of 2020.. So I ended up with 4 budget AC/DC current probes, and saw it as cheap entry tools to learn from, and compare one to the other and get an idea of frequency-rating and the noise and all that jazz..
The total price' a tad over 100 bucks' and it were more or less the same ballpark f I should have purchased Fx a Hantek CC65 inside Europe from a regional seller with danish +25%VAT.

ETCR007AD 100KHz (was the most expensive at 45USD delivered it has a +/- wheel on the side, while the Hantek have a degauss-button)
Hantek CC65 35USD 20KHz
AllSun EM264 25USD ?? Hz  (dedicated zero button, like the Hantek CC65)
HoldPeak HP605A 13USD ?? Hz
All 4 were AC+DC

ETCR007 at the top waveform and CC65 at the bottom. (spotwelder)

The Hantek CC65 of the 4 AC/DC current probes' got way the cleanest signal.. the other AC/DC like 605A and the EM264 is primarily for DMM's and quite high amps.

Here a vid with the 13USD Holdpeak AC/DC 605A  https://i.imgur.com/yUrAeXz.mp4

and here the 20KHz Hantek CC65 below and the 100KHz ETCR007 at the top.. noisy to say the least.. can be seen when going full BW like I have on the CC65 at the bottom.. (load is a USB colorchanging RGB diode with like +/-150mA.) https://i.imgur.com/Cj2B5AJ.mp4

But its very likely Im doing something wrong (rookie) but so far the Hantek CC65 has been the one I been most satisfied with, and to an extent that I even wondered about getting the CC650 but the noise will be that higher, and most of my use-cases are in the lower amp-segment so decided to pass on the CC650 but CC65 have been a pleasant first purchase from the brand "Hantek".

[dcac]

1 - My first guess would be that the value of C15 is off and its actually much lower in capacitance. Even then, it can probably be omitted completely after the mod. If we assume ~100pF load (cable + scope input) and R18 of 1K its a pole at 1.6MHz already, so adding additional capacitance will limit this further. R18 can probably be made smaller in value quite a bit (say 330R) to push out the pole its creating with the load capacitance, which would allow extended BW.

Yeah I probably missed C15 when I measured the other caps - the 100nF value is just an arbitrary value from the first versions of the schematics. And I also notice neither R18 or C15 was included in the spice simulation I did here: https://www.eevblog.com/forum/testgear/hantek-cc-65-acdc-current-probe-teardown-and-testing/msg3158118/#msg3158118

Adding C15-R18 to the simulation it will actually cause some signal peaking as C15 'steals' part of the signal from the feedback loop. And question is still what exact value C15 is - I agree 100nF seems pretty big.

[dcac]

Measuring C15 + the output cable which sits in parallel - it seems to be about 3nF.

I used the same technique as I did before using a low level sine wave at 10mV RMS and measuring the -3dB point it forms as a RC network with a known resistor value.

Below is the simulation with R18-C15 added - it didn't make that much difference in the frequency response. Though there is peaking of about 3.1dB at 100KHz. The lower blue trace is with C15 set to 0nF.

[toli]

Thanks for the reply, 3nF sounds much closer to expected value as this will add a pole at around 50KHz.

The peaking is probably due to stability of the feedback network now that this pole is there. It should improve peaking if you move the feedback to the other side of R18 which is the opamp output.

[dcac]

Not quite sure what you mean about moving the feedback.

I any case the schematics with regard to R18 and C15 placement seems correct. I haven't opened my cc-65 again but i.e. loading the output with a 1K resistor the signal level doesn't drop - suggesting R18 is inside the feedback loop. And adding capacitance in parallel with the output (and in parallel with C15) causes additional peaking or in other words an increased level at increased frequency. This scenario is of course only valid until the opamp saturates.

[toli]

I meant moving R18 outside the feedback loop (connecting R17 at the left side of R18 instead of the right side) would fix the stability issue.
For 20KHz this isnt a big problem probably, but for extended BW this is needed obviously.

[dcac]

Oh I get it now, yeah for a higher bandwidth the current configuration is far from ideal.

[toli]

Thanks dcac for your help so far, appreciate it 
I will be sure to update here when I have a chance to play with my probe when it gets here in a few weeks time.

The parts used really makes you wonder why they aren't offering a higher spec unit for slightly more.
For instance, from a noise density standpoint, the amplifiers used there are the P272 if I understand correctly from the pictures online. These are 25nV/Hz, the resistors in the feedback loop of the first stage will give some extra noise but its not dominant compared to the opamps used. So if we take 2 such opamps for the instrumentation amp input we get ~35nV/rt(Hz). Lets round that up to 40nV/rt(Hz) with the feedback resistors + second stage + resistors infront of it which are ~1K in series to each sensor on each side. For the lower current range given the gain of both stages (x60 combined gain assumed) and translation to equivalent input signal this will result in ~24uA/rt(Hz). As a sanity check, assuming ~20KHz -3dB BW, single pole means noiseBW is ~30KHz. So 24uA/rt(Hz) * rt(30K) will give ~4.25mArms noise which seems reasonable from the info shared in this thread.
With the replacement opamps suggested here in this thread (OPA2350) the noise of the opamps is no longer dominant at 5nV/rt(Hz) per amplifier. So now the opamps and resistors will be more balanced, and the overall noise density will be ~X3 (10dB) lower than the original. If we modify the feedback network around U3 to use lower value resistors we can get this down further by another 2-3dB.
A similar argument could be made for the BW. These opamps have a GBW of >1MHz (the stock units), so its possible to get well over 20KHz from this unit. Splitting the gain evenly across the stages could achieve ~150KHz BW at the cost of noise (I didn't measure slew rate limitation though, so this might only suffice for limited amplitude). A better opamp would not cost much and will give higher BW with lower noise floor with minimal circuit modifications.

The main down-side to using higher spec opamps (BW and noise) would be the current consumption which is X2-X3 higher and will reduce battery life. But this one could have been easily solved in a higher price unit with an integrated battery of higher capacity. The higher integrated noise can also be circumvented by a BW limit switch, so that a much lower noise can be achieved for a limited BW.

All the noise numbers above are for high frequency. It does rise rapidly at low frequency, and at low frequency (<300Hz) the OPA2350 is actually noisier than the P272. As a possible alternative, I quite like the OPA2156. A quick look at it seems promising with lower noise across the band, sufficient GBW, sufficient max voltage rating, etc.

BTW, looking at the teardown photos, R18 doesn't seem like a resistor at all. Edit: yep, its a PTC indeed/EDIT. That would explain why its inside the feedback loop (to limit amplitude and timing distortion due to its non linearity) despite the fact it has an undesired effect on stability of this stage.

[dcac]

Nice job identifying the PTC - that seems rather sophisticated choice for a device at this price point - I think I paid about 32 GBP for it a couple of years ago. Not that PTCs are really expensive but that they actually bothered to add that extra protection as supposed to just having a resistor there.

With regard to improving the probe I’ve made two mods to mine - I replaced C4 with a 1000uF/10V high quality cap - this have lower leakage and lower dielectric absorption so the zeroing process is and bit more distinct now and the larger value cap means less/slower drift. And then I lowered R24 to 1K to compensate for the increased charge time of C4 and to make zeroing slightly quicker again. But I never really measured the actual overall improvement except for the leakage in C4 which was significantly lower in the new cap and as it was an easy dropin mod in it went and then a 1.5K resistor in parallel with the 3.3K R24.

[toli]

Replacing the cap is probably a good idea actually since its the dominant leakage source at this point, only problem is getting a cap with low enough leakage. This can be a bit of a trial and error perhaps. Did you find one that fits and has a good spec on the leakage or did you pick one based on measurements?

[dcac]

It was just one I had in my caps box - I believe it's an Elna low ESR type so not really the specifically low leakage variants. I really only wanted to compare the leakage with the mounted 470uF/25V and that 1000uF/10V I found not only had double the capacitance but also considerable lower leakage and it was the same diameter 10mm but slightly taller 20mm vs 13.5mm but still no issue to fit it.

The drift now is less than 0.5mV after 5 minutes in high gain mode so often plenty of time to make the measurement but of course not stable enough for any logging purpose. And it's easier getting it to zero - with the original cap you had to hold the button for more than a couple of secs and then often press it again and again to really get it to zero - now it locks on much quicker.

[dcac]

Updated Schematics - just an updated value for C15 and that R18 is a PTC - also added possible types for the HALL sensors (suggested by Zhao).

C15 is set to 2.7nF - I measured it earlier to 3nF but forgot to subtract 120pF for my test coax cable. And the fixed output coax on CC-65 is probably 100-150pF and is also in parallel with C15.

[dcac]

I had a look at the noise performance and wanted to compare with what the spice simulation shows.

I measured CC-65 output noise in high gain mode to be about 2.5mV P-P but this is on a 100Mhz oscilloscope. My Fluke 45 shows it as about 0.5mV RMS. But I noticed how sensitive CC-65 is to EMI - just holding the probe in my hand I can get almost 3mV P-P 50Hz hum signal. Interestingly the front of the probe - or the actual clamp section - isn’t that sensitive to EMI so adding some shielding around the amplifier section should really be worthwhile if you plan to measure low level signals.

Simulating the noise in Micro-cap 12 I get about 133uV RMS output noise at 50KHz BW. This is with the Hall element simulated as generators with 400 ohms source resistance and with the TLC272 opamps.

If replace the opamps with TLC2272 which is an improved version that has lower noise at 9nV/sqrt(Hz) compared to 25nV/sqrt(Hz). I get 104uV RMS noise - so some improvement compared to 133uV RMS. But compared with the output noise I measured from CC-65 (roughly) 500uV RMS the overall improvement will probably not be noticeable as the Hall elements seems to contribute the majority of the noise them self.

And the simulated current consumption increased from 2.9mA to 3.3mA with the TLC2272

But keep in mind the measured noise is more a ball park value as the BW it represent isn’t well known. But from my previous experiences with Micro-cap noise simulations they seem to mimic the real world pretty well.

Below are RMS noise traces for TLC272 and TLC2272 - I only changed opamps at U3-1-2 as these stand for the majority of the amplification.

EDIT: There seem to be an error in the TLC272 simulation - there are four different spice models for these parts, it has to do with the supply voltage level and I don't think I selected correct model.

[toli]

The noise density of 25nV/rtHz even if we assume this is the only source of noise (that is U3-1 and U3-2), we still get 35nV/rtHz. For a -3dB BW of >20KHz, and single pole response the noise-BW is 30KHz. The gain of the first stage would be (R22+R15)/(R6+VR1) (I've neglected the path via VR2 here). The second stage is R17/R16. So overall gain assuming VR1 is about half its max value would be (18.6/1.06)*(26.1/11) which is >40. I wrote it down explicitly just so that its easy to check my math in case there's an error.
We can calculate the total RMS noise as:
Input noise density * gain * sqrt(BW), and we use only the white noise density which is somewhat optimistic but reasonable. So we get 35e-9 * 40 * sqrt(30000) = ~0.25mV. Since we have a transfer gain of 10mA/mV this is ~2.5mArms.
This all assumed only U3 noise is relevant, and that its a white noise source. So in practice this will probably be higher than this value.
C5/C6 will add a pole, but C14 seems to offset this partially. This will therefore result in lower noise-BW, but with limited benefit, perhaps 20% at most. So that's not too far out of your simulations, about 3-4dB difference.

The TLC2272 does look significantly better than the original unit with good power consumption too. Another good option might be the OPA2196. It has lower noise (15nV/rtHz wide band noise), similar BW (2.5MHz GBW), lower offset (100uV max), can swing closer to the supply rails (might allow extending output range further in the sensitive range), and lower power consumption (140uA typical per channel). If extending BW to 100KHz is sufficient, it might be an excellent match for this application.
I've also given this some more thought in the mean-time while waiting for my unit to get here. My aim is to extend BW among other things, and I want to see how far I can effectively stretch it with minimal effort. Therefore I'm willing to pay for it with some power. My current plan is to go with the OPA1652 for U3, which has a few benefits in addition to noise density. As far as noise is concerned though, it should reduce noise density by about 10dB for the overall transfer function if my math is correct, this should be easy enough to measure on my typical audio measurement setup that covers this frequency range. I have a few other modifications planned, I will get to it when I get my probe and order the replacement parts for it. I will be sure to update here as well as post about it with some background on my blog like I typically do for such things.

Regarding sensitivity to EMI, I wonder at what frequency is it most sensitive? Perhaps at a few KHz and above? Looking at the schematic, the possible problem with this structure as I see it is that it ignores the reason we have the 2 sensors to begin with. By bypassing R13 with C11, the input signal to the instrumentation amplifier is no longer an average of the two sensors like it is at low frequency. This means we no longer attenuate ambient magnetic field by averaging the two sensors in reverse polarity. Therefore, if it was me, I'd remove this bypass capacitor and modify the amplifier transfer function to get around it if needed.

[dcac]

In my previous post - there seem to be an error in the TLC272 simulation - there are four different spice models for these parts, it has to do with the supply voltage level and I don't think I selected correct model.

I'll post new simulations when I figured out which model is relevant for the CC65 circuit.

EDIT:
I think this should now be correct. The TLC272 error was quite substantial - simulated RMS noise is now 256uV compared to 133uV previously. Still though compared to the overall noise from the CC65 it would not make that much difference.

So Simulated RMS noise at 50KHz BW:
TLC272 = 256uV
TLC2272 = 108uV
OPA1652 = 67uV

Simulated current draw:
TLC272 = 2.9mA
TLC2272 = 3.3mA
OPA1652 = 5.0mA

Below are the traces for RMS noise and the Output frequency response - interestingly OPA1652 has slightly better reach even with the same capacitor values around the U3 lowpass filter.

TLC272 = Purple trace
TLC2272 = Blue trace
OPA1652 = Red trace

[toli]

Thanks, that now matches my calculations much better

BTW, don't forget the current consumption of the sensor bias. This can be a few mA per sensor (the spread is quite wide and sensitive to temperature) and we have 2 of them.

[dcac]

Yeah it was your calculation that made me check the simulation again.

The simulation only includes active elements U3-1-2 and U4-1 to do the Noise and Frequency response, so none of the Hall, DC control or Regulator current is accounted for.

[dcac]

I measure CC-65 total current draw to 10mA at 9.6V. So upgrading U3 really shouldn't make that much difference.

A rechargeable battery really is preferable in any case - else it will kinda ruin your day if you forgot to switch the probe off.

[toli]

My probe arrived. I'm yet to make any significant measurements on it, and no mods yet (will need to order parts first). However, I've probed inside of it for a few minutes just to fill some gaps I've had.
First, as far as the LDO stability is concerned, I don't see any oscillations at the output. Nor do I see any oscillations at the bias of the sensors which U1-2 regulates. This is good, although I still don't like this structure of the bias circuit, it has 2 poles which can cause instability or at the very least noise peaking which might still be inside the BW of the amplifier after it. I will try to remember to probe this with the audio measurement setup, to observe the spectrum there, might reveal something more interesting that way.

The current draw of my unit is ~11.4mA, which is higher than the 10mA you've measured, but its expected there would be variation among units, especially with the value of the sensors resistance varying so much. Still, not too impressive life time out of it.

What I found interesting is the value of the DC rails. The positive rail I've measured at 3.22V, so ok for a 3.3V LDO with slightly lower voltage than nominal (I see the schematic marks it as 3.2 nominal, in which case its almost spot on). The negative rail though is -3.8V, so D4 might be a 3.9V variant (I see the schematic you've posted is marked with 4.2V, also possible as these have a fairly soft knee and a few percent tolerance - I admit I was too lazy to check). Why do they plan for such a significant voltage for the negative rail? The bias of the sensors, and as a result the CM voltage at the inputs of the op-amps are derived from positive rail, so I'd expect them to shift the rails in favor of the positive rail if anything, not the negative rail. 3.2V+3.8V = 7V, so if we leave a bit of headroom the battery must have >7.2V for normal operation, seems like inefficient use of battery energy.
Additionally, because of the way the low battery threshold is sensed, the positive rails needs to drop quite a bit for this indicator to light up. So this only happened at 6.8V in my unit at which point the positive rails was already 0.3V lower than nominal at 2.95V. This means that performance might degrade even before the low battery indicator lights up.

Might be of value to replace D4 with a lower voltage shunt regulator (just so its sharper than a zener, but a zener is ok too), perhaps 2.5V for instance. Then move the voltage sensing for low battery to 3.5V instead of 3V. Then 3.5V+2.5V would allow operation with a 6V supply instead of 7.2V.

It'll probably take a little while before I order and get the parts for mods, but I will post if I see anything interesting before any changes are made to it.

BTW, what I found quite funny is that if the battery voltage drops slightly lower than the value designed as the limit, the LED turns off. Probably because U6 has very limited ability to drive positive output voltage, so that combined with the LED drop is too much. So at 6.8V it lights up, but at 6.5V you can barely see it 

[toli]

I replaced C4 with a 1000uF/10V high quality cap

Did you use a bipolar cap or still a polarized cap?

I see the original capacitor is polarized, which means the negative voltage range is very limited if we want leakage to remain low. However, if we go to a bipolar cap, we can live with an increased voltage over this cap,
which means we can reduce its weight in the circuit (increase value of R23). This will make it less sensitive to leakage of this capacitor. There's still the effort of finding a cap with low leakage though.
Edit: its possible to do the same trick with a polarized cap obviously, but then there a risk of the reverse voltage being large enough to cause increased current.
If we go too far we might need to increase R269 too, and then there's the question of how the leakage of the cap depends on the voltage over it when the applied voltage is so much lower than rated voltage

[Fraser]

I just ordered a Hantek CC65 from AliExpress delivered to the UK for £40. That was the best price I could find as we now pay VAT

Hantek can produce some very competitively priced test equipment and I own a few of their TME products (USB DSO, USB  ARB FG, USB LA) but sadly it is the software side of things that often lets them down. Thankfully the CC65 does not need firmware or software to do its job 

Thank you to all those forum members who have helped to reverse engineer, analyze and improve this current clamp. Your efforts are much appreciated. I intend to use this current clamp with my new MICSIG ATO1102 DSO for both automotive and lab measurements. I repair thermal imaging cameras and you can learn a lot about a thermal camera by monitoring its current draw during start-up. This CC65 probe appears to be the best value for money solution on the market and, thanks to this thread, may be improved if desired.

My one disappointment with the design is the poor implementation of the Zeroing function. My higher current Beckman AC/DC clamp uses a conventional potentiometer adjustment which I prefer. This charging an electrolytic capacitor lark seems somewhat over complicated and flawed. I will see how my probe behaves when it arrives and may fit a manual zeroing control.

Regarding magnetisation of the clamp head, I have seen at least one automotive video where the tech using a similar looking clamp declared it in need of replacement due to a permanent current offset that was not zero’d out by the Zero button. Sadly I suspect many perfectly functional clamps go in the bin when all they need is a good degaussing. I would be interested to hear what others use to degauss their clamp heads. I think I have a tape head degausser somewhere. I note that in one review I saw of the CC65, the presenter thought the Zeroing button activated an internal degaussing circuit but we know the truth about that function now.

Before I ‘pulled the trigger’ on the CC-65 purchase, I bought a HEME LEM LTA 50P / SP1 AC/DC current transducer. It cost me £10 and offers 50A nominal operating AC current, 160A Max AC current and +/-50A DC current monitoring and measurement at DC to 100KHz. The unit offers both current and voltage output. Current is 1000:1 ratio and the voltage output is 100mV/1A. It seems like a neat little unit to have mounted on my lab power supply positive output cable to monitor DUT current draw behaviour on my DSO. LEM are known to make some decent Current sensors. I just need to set the sensor up with a +/-15V power supply. It will be interesting to compare the LTA 50P performance with that of the CC65 probe..... very different formats of sensor but each with its own applications.

Fraser

[rhb]

Hmm,

I just got one today and came wandering over here looking for more information.  From an initial inspection it appears to be eminently hackable. And in need of it ;-)

So far I have just skimmed this thread, but I'll more closely read backwards from here.  I observed a lot of flux on the unit, so I recommend a scrub with isopropyl.  There was no residue on mine on the other side and you *really* don't want to tangle with the switch contacts!

I don't understand the charge on a capacitor bit.  If it's just a reference voltage, the cheapest voltage reference and voltage divider would do  that.  It seems to me far better.

But I don't yet understand how it works in sufficient detail to build one from scratch.  So I'll stop until I know more.

Have Fun!
Reg

[dcac]

I replaced C4 with a 1000uF/10V high quality cap

Did you use a bipolar cap or still a polarized cap?

I see the original capacitor is polarized, which means the negative voltage range is very limited if we want leakage to remain low. However, if we go to a bipolar cap, we can live with an increased voltage over this cap,
which means we can reduce its weight in the circuit (increase value of R23). This will make it less sensitive to leakage of this capacitor. There's still the effort of finding a cap with low leakage though.
Edit: its possible to do the same trick with a polarized cap obviously, but then there a risk of the reverse voltage being large enough to cause increased current.
If we go too far we might need to increase R269 too, and then there's the question of how the leakage of the cap depends on the voltage over it when the applied voltage is so much lower than rated voltage

Sorry for the late reply, I used a regular polarized cap, I didn't actually think about possible reverse polarity when testing the replacement cap - only that it seemed to have much less leakage - or perhaps mainly less dielectric absorption like when a cap is acting a bit like a battery. The replacement cap seemed to settle much faster on the 'sample' voltage when the zero button was pressed. Even though it was twice the capacitance, 1000uF compared to 470uF for the original.

[toli]

Been while since I was able to find the time to play with this probe. I've had a free hour to do so tonight, so I looked into a few of the things that were of interest to me. First, the gain seems to be off by >10% on my unit (DC current measurement), so well outside the spec. Its easy enough to adjust, but somewhat disappointing non the less. I see there is also ~2% error between polarities, so I think it would also make sense to adjust the balance of the two sensors when I get to adjusting the gain.

What I was interested in for the moment was the LDO output voltage to check for any instability. I've observed it with the scope, and there was something there (at ~3.5KHz, although nothing too extreme), so I've connected to my audio measurement setup which is better suited for such low frequencies.
See 2 first attached images, first is time domain, second is the spectrum of that same signal. Notice this is with a 40dB gain so scale Y axis accordingly. Placing some decoupling at the input has improved it somewhat as can be seen in the 2 last images attached. The peak was reduced by ~7dB, and total RMS value at <100KHz is ~6dB lower (<200uVrms integrated noise up to 100KHz which is fairly typical figure for a low power LDO). Modifying the amount of capacitance further had negligible effect, as did modifying decoupling at the output and to the negative rail. This is a "free" improvement over what was there before the change, and nothing too extreme, but still something I might revisit when I have a chance. Perhaps replace with another LDO (one I actually know the part# for ) such as the LP2980/1. This tone at 3.5KHz can standout over the noise, and therefore I'd prefer to get rid of it completely if its cheap and quick.

I hope to get to the more interesting stuff of extending BW and reducing noise in the next few weeks. The shortage of parts is affecting this too, as some of the opamps I wanted to use cannot be obtained for a while now, with no solution in the near future. I will most likely go for plan B with other parts of lesser spec, or else this will probably never get done. Will try to keep posting when I have additional data.

[toli]

In case it will be of interest to anyone, I've posted on my blog about the measurements and modifications I did to my probe.
In the blog post(s) I go into much more detail as there's no one there to stop me , but I'll try to summarize this briefly here as well.

The changes included:
- Extension of -3dB BW to 1MHz. This can be stretched to a few MHz if desired, but I chose not to do so as for my needs it will result in increased noise with no practical use.
- Reduction on noise density. At 10KHz it is now ~12dB (X4) lower than it previously was.
- Removal of the tone observed at the supply (and output) of the probe. This was caused partially by instability of the LDO (which capacitor at its input fixed), and more dominantly by instability of the bias circuit which was also apparent at the LDO output due to limited load regulation. This was fixed by adding local negative feedback in the bias circuit by an additional capacitor, that has also reduced bias loop BW and noise.
- Reduction of minimum operating voltage to 6V by modifying the negative rail to have a 2.5V shunt regulator instead of the zener diode.
as well as a few other tweaks that are mostly nice to have.

I'm attaching a few images:
1 - Schematic I've implemented (with the exception of the part in green which I've selected not to implement, at least not for the moment). The green part is there to stabilize the offset drift over temperature, which I didn't see as a major drawback for the moment.
2 - Measured frequency response after the modifications for both ranges
3 - Transient response (with 4A pulse so it has some reasonable swing at the output, and not only small signal measurement) before mods
4 - Same as (3) after mods
5 - 1KHz 3mArms sine wave before mods (192KSPS so BW limited to ~90KHz, although probe BW limits this much earlier with 26KHz -3dB point before mods)
6 - Same as (5) with the probe after mods (far higher noise BW since now its limited to ~90KHz by the measurement setup)
7 - Same as (6), but this time with 48KSPS so BW is limited to <24KHz which is somewhat closer to the stock BW, just for comparison.

[Maciej]

I would like to better understand supply / bias of Hall sensor.
At first, opamp U1-2 seems to have positive feedback thru R1, R2, or just circuit drawing mistake?
As I understand the Hall is current driven. Hall input resistance is in this case the current sensing resistance, diode D1 provides reference.
Input resistance of Hall changes exponentialy with falling temperature, if we look at here:
" alt="" class="bbc_img" />
Would it be better to stabilise supply current with just another resistor?
I thing that bandwidth of U1-2 regulator should be nearly as low as temperature changes. It would help to cut off lot of noise. Just an idea.

[toli]

R1/R2 provide negative feedback, the PNP device adds its gain which is inverting.

Making the loop slower for reduced noise is indeed a valid point (but the question is where the noise is coming from, at the input to the amplifier, or due to the components in the current path at which case the BW should actually be higher to clean it). In this case you are indeed right, its better to make it slower, which is exactly what I did in my probe via the new 1uF capacitor which reduced noise significantly. It provides local negative feedback, stabilizing the loop, but also making the BW far lower in the process which improved noise further.

I'm not sure I understood your question about the change of bias circuit with just a resistor, do you mean remove the diode completely for zero tempco? Generally speaking, depending on the range of temperature of use and the sensor used, the temp-co of the biasing circuit will need to be adjusted. In this case we are only guessing the sensor (and therefore tempco), but typically VH starts falling as you increase temperature of the sensor above room temp, so increasing the bias voltage to offset for this is a reasonable way of compensating for this.
This one has a reasonably readable figure for this: https://www.nicera.co.jp/wordpress/wp-content/uploads/2019/06/NHE520Fe.pdf so if we assume this data is more or less representative, it actually makes sense to use a positive tempco for the bias voltage to offset the reduced signal. That is assuming we are at or above room temp.

[Maciej]

The biasing circuit looks like this:
" alt="" class="bbc_img" />
with R3 and R4 as Hall sensors. Voltage input is here stabilised at 2*Vref
Spatially and thermally both sensors are preety distanced.
Looking at ambient temperature curve for voltage driving "Vc Const" I see no chance to compensate it with linear Vref tempco.
" alt="" class="bbc_img" />
" alt="" class="bbc_img" />
Both sensor candidates NHE520 and HW101A look very similar is voltage mode. I cannot compare current mode "Ic const" because graphs are not to scale.
BTW. When using P-N junction tempco it is recommended to use BJT junction rather than standard true diode.

[toli]

Using the diode is a simple way to improve temperature stability over a limited temperature range where the signal drops with a given slope (above room temp if we trust the figures from the sensors we think are of interest). It needn't be perfect, simply better than nothing. Is using a constant voltage instead of one with this tempco better for the temperature range in question? No idea, to know for sure we need to know the exact spec of the sensor used, or to measure tempco ourselves.
Seems like some sort of such correction as in this one is included in other similar probes too, so without measuring this to know better, I think it makes sense to leave this tempco there.

[HardyKefes]

Hello, does anyone know whether the ESI 695 current probe is more accurate than the Hantek cc65?
Also, How is the TECPEL CA-60 AC/DC compared to the Hantek?

[Glowas]

Hi Guys,

I've decided to find all components and upgrade my CC-65 current probe. I have problem to get OPA1652AIDGK. Is anybody have proposal for direct substitute for this part ?
I thought about OPA1642AIDGKT but Im not sure  Many thanks for any advice.

Best regards,
Pawel

[apirltag]

OPA1678 is a fully compatible replacement.

[dcac]

I just noticed member MikePie had drawn in the differences between cc65 and the Peaktech 4250 clamp, found here: https://www.eevblog.com/forum/testgear/peaktech-4250-acdc-current-clamp-teardown-and-repair/msg4565725/#msg4565725

And as I always thought the circuit for the zero button on cc65 was a bit odd and not really configured as a regular “sample and hold" like the Peaktech 4250 seems to be. I tried to implement the same circuit on cc65 by removing the 10M resistor and but in a 220n filmcapacitor instead of the bulky 470uF electrolyte.

But this just resulted in a huge drift and the clamp could not hold zero for more than a couple of seconds. I’d already checked the U1-1 272C op amp datasheets from a few different manufactures and they suggested input bias to be something like 2 to 6 pico-amp. So 220n capacitor should be able to withstand this for quite some time without much change to the “sampled” voltage level. But when I measured the output on U1-1 the voltage was dropping very quickly. So ruling out possible faulty capacitor and measuring the resistance on U1-1 input to ‘infinity’. The only thing left was the 272C being faulty - but with the original circuit configuration with the 470uF cap it worked as it should.

So removing the cap again and measured the input bias, and yeah.. about 1800 pico-amp. So I’m thinking these 272C are fake or very bad quality. Anyhow... this can explain why the cc65 is prone to drift - more than it should - and why they used this huge 470u electrolytic capacitor, that has problems like leakage and dielectric absorption. The Peaktech zero circuit is probably much more stable using a filmcapacitor and probably genuine 272C op amps.

 
           

[Fraser]

An interesting discovery. Thank you 

Are you intending to fit genuine/correct quality 272C op-amps in your unit now, or just leave it as manufactured, with the large electrolytic capacitor ?

Fraser

[dcac]

Yes, I think I have a couple of tlc2272 laying around, somewhere. They should not only be a direct replacement but also a noticeable improvement to the 272. Both lower noise and lower input bias current, only 1pA, so they would be worth a try when I find them.