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NI9205 Shows Incorrect Value

Hi everyone,


I want to measure the performance of an isolated DC-DC converter.


Please  see attached file......


Voltage at the input and the output (Vin+, Vin-, Vout+, Vout-) of the converter are sensed by NI9205.

Current at the input and the output (Iin+, Iin-, Iout+, Iout-) are also measured by NI9205

using 2 current sensors (1 milli Ohm resistors).

10 kOhm resisters are bias-resistor connected to the COM port.

The each measurement are performed by "dfferential mode".


I actually confirmed that the test circuit work well or not.

But the values were incorrect immediately after the converter started up!


Could you tell me why NI9205 showed incorrecd value and the solution?

Is it EMC problem...?


Thank you




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Message 1 of 4

What do you expect to see?

What do you actually see?

If you measure the same points with a DMM, do you see what you expect to see or what the 9205 shows?

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Message 2 of 4

Dear natasftw,


I expected to see Vin=3 V, Vout =5 V, Iin=0 A, and Iout is 0 A.

But in actually, all values were meaningless and bullshit

(for examle, Vin=1 V, Vout =6 V, Iin=200 A, and Iout is 50 A)


A DMM showed correct value,

so i think bad guy is NI9205......


Thank you

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Message 3 of 4

Instead of a DMM better have a look with a fast (analog?) scope.

Switched power converter are not as easy to measure as batteries 🙂

The dynamics and timings are important.

I strongly recommend reading the appnotes from Jim Williams about switched power converters.....

an25 is a nice starting point...

Greetings from Germany

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

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Message 4 of 4