Digital Filter Minimum Pulse Width for CO Arm Start Trigger on USB-6212

[AndrewJerome]

Hi All, 

I'm trying to use the digital filter to overcome a noise problem that is causing "false" Arm Start Triggers on my counter output task, using DAQmxSetDigEdgeArmStartTrigDigFltrMinPulseWidth. Although I've successfully used this with a custom value (0.5ms) in the past on a different device (cDAQ), my USB-6212 is not really allowing me to use this property and giving a -200077 error that the value is not supported.

Strangely, I've actually gotten it to work by using the 6.425us preset value used for the counter input digital debounce filter, but I need a much larger pulse width for the noise I am experiencing, and the other preset values that I've found in the documentation of M and X series devices of 2.55ms and 2.54ms give me the same error. 

Any thoughts, explanations, workarounds would be tremendously helpful at this point.

Best regards, 

Andrew

[Kevin_Price]

1. Your M-series USB-6212 doesn't directly support differential encoder signals.  To make them compatible, you can convert them to single-ended TTL.

2. You must have a pretty significant noise problem if it takes a digital filter at 0.5 msec to suppress it.  I'd strongly advise also looking for ways to reduce the noise source or its coupling into your DAQ system.

3. Have you seen this article?  It sounds like M-series may not directly support filtering a signal use as a trigger, but there's an indirect method shown at the link

-Kevin P

[AndrewJerome]

Thanks very much for your input and assistance, Kevin!

1. This is not an encoder application, but analog voltage data acquisition from an instrument requiring synchronization with some motion control. The arm start trigger is used for this purpose.

2. Total agreement, however that part is out of my control for the time being and the hardware is a few thousand  miles away. Surprisingly, the analog voltage data does not appear to have a noise problem. 

3. I hadn't seen that article until you brought it to my attention, but that was the key: "For M Series devices the valid values for the minimum digital pulse width are 0s, 2.56ms, 6.425us and 125ns." I saw 2.54 and 2.55 ms elsewhere but those values didn't work. When I use 2.56ms it works as needed!

Thanks again, 

Andrew