Noise in hardware timed sampling sequence USB 6212 Multifunction DAQ

[Linkster]

I am using a 6212 USB Multifunction DAQ Board to sample 2 analog inputs and 1 counter.  I pull single samples using DAQMX read single channel single sample for each of the analog inputs and they are not noisy.  But when I switch to a task that reads both the inputs and 1 counter, I get a noisy signal on the analog input.

 The task is timed out by the other counter set to output at a certain clocking frequency.  I have the clocking frequency set to the same value as the sampling frequency I'm using to take measurements.

Any ideas on why the signal becomes noisy when I switch to a task?

[Linkster]

*Correction:  I meant to say it is the internal timer is clocking the other functions.

[Paul_C.]

Hi Linkster,

I'm afraid this could be due to a number of reasons.  Can you provide me a little more information about what type of Noise you are seeing?  Perhaps if you could take a screenshot that would be helpful. There is a knowledgebase here that has some great information you might find useful.  Also, the field wiring and noise considerations article, found here, is very useful for reducing noise.  It is likely that the noise is due to the fact that we use a multiplexer to switch between channels on the USB 6212.  This can sometimes cause something called "ghosting" to occur.  If what you are seeing is indeed ghosting, I would take a look at the article here for some ideas on reducing the effect.

I hope this helps,
Paul C.