PXIe-6341 and SCB-68 analog inputs question

[SevenSeeds5]

Hi everyone,

I'm trying to use SCB-68 along with PXIe-6341 to acquire photodiode output in the analog channel. I have a really weird problem that I just cannot seem to figure out.

1. If I hook up +ve of the photodiode with AI0 on SCB-68 and the ground of the photodiode to AI-GND, I cannot seem to acquire any signals (through the NI-MAX test panel software).

2. If I hook up +ve of the photodiode with AI1 on SCB-68 and the ground to AI-GND, then I get photodiode response traces in the analog channels.

3. I tried different combinations of analog input locations and AI-GND ports and I seem to be able to only pick up photodiode responses in only certain combinations.

 (AI6 and AI-GND have also worked for me)

What's going on? Am I setting something up wrong? I am using RSE measurement as I have a ground and +ve.

[santo_13]

Check if you're configuring the input configuration correctly.

DAQ analog inputs require a signal source with low output impedance. It would be best to add some buffer/amplifier for the Photodiode, typically an I-V converter because the Photodiode generates current.

https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1003

https://www.ti.com/lit/an/sboa220b/sboa220b.pdf

https://www.optosigma.com/us_en/photodiode-amplifier-PDA-1%20-%20PDA-1.html