DAQmx reference trigger and hysteresis

[GS]

>>Perhaps such a high value of hysteresis is needed for stable triggering when PFI 0 is used because the comparator in this circuit has only 8 bits of resolution.<<

Thanks for confirming the behavior. I didn't realize that PFI0 only uses 8 bits.

>>But, to use ai0 as a reference trigger source, it must be the only channel in your task.<<

That's a problem. In my real application I have several channels to convert.
Well at least you've given me a road to go down to investigate further. Thanks.

[grivilla]

Thayles:

Looking for the solution for a problem with trigger time I found following answer you gave in the past:

"Perhaps such a high value of hysteresis is needed for stable triggering when PFI 0 is used because the comparator in this circuit has only 8 bits of resolution. Plus, this circuit has a fixed range of 20V (+/- 10). This gives a resolution of only 75mV. When you use ai0 as your trigger source, you use the 12 bit ADC of the device as well as its gain stage. But, to use ai0 as a reference trigger source, it must be the only channel in your task"

I'm not sure whether I well undestand. Does it means that the trigger will only be accepted when the input signal at PFI 0 is bigger than 75mV independently of the slope of the signal?  in other words: what is exactly the definition of a "rising edge"?

My problem is trying to find the time between 0 Volts and the Trigger "Zwitch time".

Thanks

Alberto

[thayles]

With a resolution of 75 mV, a rising edge would be seen if a signal currently at voltage V was seen to increase to at least V + 75 mV.

To measure elapsed time from 0V to the trigger, you need to figure out how to start a counter task at 0V time and use the Analog Comparison Event as the Sample Clock (GATE). You may be able to use the trigger Hysteresis setting to get the Analog Comparison Event to change state at 0V and the trigger Level setting to get the ACE to change state again at the trigger point.