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Current probe signal attenuation?

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Current probe signal attenuation?

Postby tinwelp » Fri Nov 13, 2009 4:46 pm

Hello all,
my newest and most interesting problem of the day is an issue I've just discovered whilst using a Picoscope2203 with a LEM PR430 current clamp. I'm driving an inductive load with a very fast MOSFET, measuring the peak current just at the point of switch-off (14V drive, 1ms on, 20ms off). Everything seems to be sensible, including the current profile during the on period, except if I measure using the Picoscope and a Tek TDS210 in parallel... 31.2A on the Picoscope, 34.7A on the Tek!

I've checked the probe function by injecting a known and loved square-edged pulse, monitoring on both 'scopes... same result.

I've run separate tests, just with the Picoscope and just with the Tek, running an accurate re-calibration of the current probe before each test... same result.

Injecting the 5V square-wave calibration signal from the Tek into the Pico gives an excellent response, confirming all is well with the Pico, but I cannot find an explaination for the disparity.

As additional information, the current profile reported on the Tek is that of a classical pure inductive load: absolutely triangular in shape with almost no variation of gradient. With the Pico, the first 80% of the profile is identical, but the gradient flattens out significantly in the last 20%, accounting for the entire disparity between the two 'scopes.

Does anyone have any experience of this? Fully open to suggestions at this point, be they reasoned or otherwise; I just need a solution!!

Thanks in advance.

Cheers... Paul
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Re: Current probe signal attenuation?

Postby ziko » Tue Dec 08, 2009 12:21 pm

Hi could you send a .psdata or even an screen capture?

Kind regards
Ziko

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