Oscillator and Analog Input (NI 9205) in parallel?

[Camell]

I have a NI 9205 analog input module. I want to verify that the read values are ok and that acquisation is fast enough (because I have some values that make quite big steps within 1ms and I am not sure if this corresponds to the real hardware signal).

Therefore I put an oscilloscope in parallel with an analog input and my voltage source (low impedance). But then the read values are not correct (almost 0). I changed the oscilloscope impedance from 50 Ohm to 1MOhm, but it's still the same. The values on the oscilloscope are correct.

Is there any possibility to have an oscilloscope in parallel with an analog input?

I am not the best expert in electrics ... 

[ReginaW]

Hi,

In generall you can use the oszilloscope to measure the Voltage over time at this cRIO module.

The Problem in this case is that the inputimpedance of the cRIO Moduel is larger than 10GOhm, when the module is powered.

Normally the impedance of the oszilloscope and of the cRIO Module should be almost the same.

In this case they are completely different which results in a measured voltage which is wrong.

To do what you want to do I think you need the have an oszilloskope with an higher impedance.

Best Regards

Regina

National Instruments

[Camell · Accepted solution]

Thanks for your reply.

Actually it worked. I measured a wrong voltage because all of grounds of the BNC connection at the oscilloscope are connected. I didn't keep that in mind ...