Oscilloscope Current Probe

Thread Starter

Joster

Joined Jun 12, 2013
95
Hi All,

I am testing a pulse charge battery charger. It has a cap bank that is charged up then discharge quickly into the battery. I need to get a current probe for my scope to be able to see the transient current pulses. All the probes I see on ebay (the good ones at least) are pretty expensive. Is there anyway to do this on the cheap or should I just start saving?

Thanks,

Joster
 

Lestraveled

Joined May 19, 2014
1,946
Why not just put a small resistor in series with the charger common terminal and measure the voltage across it?
Because in a high energy pulse environment, common mode and parasitic noise can easily overwhelm a reading using a resistor. I learned the hard way that a Pearson current transformer or a non-contact current probe is the only way to get accurate pulse current measurements.


Joster, start saving.
 

Thread Starter

Joster

Joined Jun 12, 2013
95
Because in a high energy pulse environment, common mode and parasitic noise can easily overwhelm a reading using a resistor. I learned the hard way that a Pearson current transformer or a non-contact current probe is the only way to get accurate pulse current measurements.


Joster, start saving.

ok so ur recommendation is that the diy version will not cut it and I should start saving then?..I have a good connection with good electronics surplus dealer who is hopefully going to have 1 or two.
 

Lestraveled

Joined May 19, 2014
1,946
Here are some examples:

9 us pulse width, 6 amps

- The top trace is the voltage across a .01 ohm non-inductive resistor.
- Bottom trace is the output from a Pearson current sensor (model 4100, 1Volt/amp)



Below
- Same signal, different scale on the top trace.


If you did not know what to look for in the top trace, by having seen the bottom trace, you would have little chance of getting any useful measurements.

The Pearson 4100 current transformer that I used.
 

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Lestraveled

Joined May 19, 2014
1,946
I tried and failed several times to build my own current transformer (similar design as the above white paper). Pulse widths over a few hundred microseconds, no problem. Under 100 microseconds, forget about it.

There is a reason that the new list price for a Pearson CT is around $1000. I bought my 4100 used on E-Bay for a little over $100. It is worth every penny.
 

Janis59

Joined Aug 21, 2017
1,827
Hmmm, when the low frequency, there any resistor or coil will be good enough. But when one have a deal with high frequency, at least I was incapable to solve this thing well. I tried a noninductive resistors, I tried a capacitative dividers, I tried an impedance compensated adjustable circuits, but anyway I got that I utilize the many-fold more power out of my `black-box` than it consumes from PS, where to DC ampermeter I can believe absolutely. Thus, I decide any current probe for RF may be considered only to show the +/- 1000% accuracy, and this is the best case scenario.
 
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