Constant Offset Voltage with USB-6008 and PIN Photodiode

[hendrix]

I am measuring the output voltage from a PIN photodiode (see link below) with a USB-6008 across a 10K load resistor. I measure a constant 93mV signal in both RSE and differential modes that I cannot seem to eliminate. Is this something that can be eliminated with a different connection configuration?


Photodiode datasheet:
http://www.thorlabs.com/thorcat/2200/2201-S01.pdf

[GarPar]

Hello hendrix-

     A different connection configuration shouldn't change the signal if you have already read 93 mV using both differential and RSE.

     Is the 6008 reading 93 mV regardless of what the PIN photodiode is outputting, or does the 93 mV fluctuate with a changing input to the photodiode?

     Try these three things:

1. Measure the photodiode on another input channel to the 6008.

2. Measure the photodiode with a handheld DMM - do you get the same reading?

3. Measure a battery with your 6008 - does it read correctly?

     These steps will allow us to figure out if the issue lies with the photodiode or with the 6008.

     I hope this helps lead to a resolution!

Regards,

[hendrix]

Hi Gary,

I tried your suggestions and it seems that different input channels produce the same behavior, a direct measurement with a DMM does not reproduce the behavior and the DAQ reads the voltage from a battery correctly.  

These results did not indicate an obvious problem with either device but I found another brand of photodiode in our lab that works well without this behavior.  I'm still not certain what was going on there but at least it can be taken care of by switching out the PD.

Thanks for your help!

[GarPar]

Hendrix-

     I am glad to hear that your setup is up and running. 

     That is curious about the other PD.  I wonder if there was some sort of a grounding issue - is the new PD grounded the exact same way as the other PD?  It could have been that some connections were loose, switched, etc.

     Either way, I am glad to hear that it is working now.  Best of luck with your application!

Regards,