DAQ Card is inducing noise on an external clock signal resulting in false triggering

[WM_John_Weeks]

Naturally, if it were something to do with your large motor (or whatever) the noise should coincide with starting or stopping the device. I would also think about solenoids and such.

It sounds like you have lots of experience with proper shielding and such, so that's probably fine.

How about noise carried on the AC lines? You might want to supply some of your instrumentation via an isolation transformer.

[Henrik_Volkers]

One suggestion for a test:

Scope your output grounded with 10k (or lower, just what the ST can drive) at dig ground. 

Than scope R connected to the DAQ input and dig grnd and finally  your ST output connected.

What is your pulsrate? How big is your phase margin?  (Just thinking about some C s to shortcut the spikes)

[OSU_Mech_Eng]

Thanks to all who posted advice and responses.

I never managed to actually fix the problem, but using the counter I have been able to enforce a minimum pulse that will get through to clock my measurements.

This is my first post with a problem and I am very impressed with the quality of advice.  I will try to make time in the future to scan the message board and chime in with advice of my own.