Multifunction DAQ

cancel
Showing results for 
Search instead for 
Did you mean: 

Cross-talk with PCI-6221/BNC-2110

Hi all,

We are attempting laser absorption measurements that require simultaneous input from a detector photodiode and a spectrum analyzer.  The spectrum analyzer signal (ai0), which is 50ohm output impedance and only reaches 5 V, is imprinted on (and generally overwhelms) the photodiode signal (ai1), which is about 5% - 10% of the strength of the analyzer signal.


The same effect occurs whether the spectrum analyzer (which is a ground-referenced signal) is acquired as a differential signal (BNC block set to FS) or an RSE signal (BNC block set to GS) with device ground appropriately tied to AIGND.  The photodiode is always a differential signal, and is configured as such both at the BNC-2110 and in the software.

The eight available input channels on the BNC-2110 block are read in one LabWindows call to DAQmxReadAnalogF64() with default settling time (which, from the forums, I understand to be the maximum possible settling time).  These are single-point, software-driven acquisitions, not waveform acquisitions.

We are using a SHC68-68-EPM cable between the BNC-2110 and the PCI-6122.

Is this likely to be a configuration problem, or is there an electrical fault somewhere in the BNC-2110 or the PCI-6122 that could be causing this behavior?
0 Kudos
Message 1 of 2
(2,847 Views)

Dear Mzwier,

What are you setting as your input range? You will set the range when you create the channel (example: DAQmxCreateAIVoltageChan). Set the range on the channels to be as small as possible. For example. Create a channel for ai0 where the min and max are +/- .5V. Then create another channel for ai1 where the min and max are +/- 10V. This should help with the crosstalk. Also, try inputting the channels on ai0 and ai2, instead of ai1. Please let me know if you have any questions. Have a great day!

Sincerely,

Marni S.

0 Kudos
Message 2 of 2
(2,825 Views)