DAQmx Sample Clock (on-board clock) effects

[Broken_Arrow]

Why would I get slightly different readings when using the Sample Clock (onboard clock) and not using it? On several different cards, I've noticed slightly lower levels of analog input when using the Sample Clock and not using it.

thanks

[Doug_L._Bear]

What cards have you seen this on?  What are you measuring?  Are you seeing this in Measurement and Automation Explorer or LabVIEW?

[Broken_Arrow]

Thanks Doug. In LabVIEW, on a SCXI-1102 and a 1502. (DAQ is a PCI-6221).

I understand the benefit of the DAQmx buffer that gets setup when you use Sample Cock, but if I'm just taking "1Chan 1Samp" samples, I wouldn't expect a difference. The sample taken with the Sample Cock included in the Task is a few tenths of a volt less than a the reading taken from a Task not including the Sample Clock (on a ~1V signal).

Message Edited by Broken Arrow on 01-14-2009 04:21 PM

[Jordan F]

Try measuring your signal using test panels in Measurement and Automation Explorer to see if you receive the same behavior.  Also, remove all the other devices from the scxi system (leave one module to acquire from, ex. 1102)  and see if you receive the expected input. 

What is the signal you are reading?  Was removing the sample clock the only change you made to your program?