connecting a HV differential probe to a USB-6341

[Jens_K]

Hi,
I have a NI USB-6341 and need to measure a 20KHz, 700V signal.
I am planning to use a high voltage differential probe like the TA041 from Pico.
Do I need to worry about the output impedance of the probe? Those probes are designed to be used with oscilloscopes which have 1MOhm impedance. According to the datasheet the 6341 has >10GOhm impedance.

Jens

[HeinzG.]

Hi Jens,

the devices wouldn't be damaged or anything like that if you don't apply more than 10V to the USB-6341. BUT you won't get accurate measurements either! 

Probes are designed to be a volage devider with the accurate resistor in the Oscilloscope. See the second picture in this link. The input resistor in the USB-6341 is "unknown", inaccurate (of course you can mesure it) and it will lead not to the deviding factor you expect. Thus I wouldn't recomment to do the measurement this way. For that purpose you should rather use a NI-SCOPE:

http://sine.ni.com/nips/cds/view/p/lang/de/nid/12638

Hope this helps,

Heinz

[Henrik_Volkers]

RTFMspec : It says output impedance of this activ probe is about 1Ohm to 8Ohm up to 1MHz 🙂

So I wouldn't expect problems with that. But also take a brief look into the USB-6341 spec .seems like a multiplexed card so keep in mind the source impedance error versus sample-time (no problem if all inputs are buffered with an activ probe 😉 ) And if you read more channels check crosstalk!