The Analog Input Trigger Resolution of Multifunction DAQ

Issue Details

I am using an analog trigger to start an input acquisition on my NI 60xxE, 62xx or 63xx (formerly E, M, or X Series) device module. I set my trigger level to a certain voltage and notice that there is a margin of error between the value of the first sample of my data and the trigger level. What factors affect the resolution of the analog trigger?

Solution

First and foremost, the table below has a list of our Multifunction DAQ boards and their respective trigger resolution:
 

Board	Trigger Resolution
E Series	8-bit
M Series	10-bit
X Series	16-bit

As you can see from the table, the trigger resolution on our DAQ boards is lower than the resolution of the analog inputs.  This means that the voltages steps across the range are larger and you might see a larger difference between your trigger level and when the trigger is asserted.  Even with reduced resolution, there are still some things that you can do to improve your results when using an analog trigger.

Unfortunately, the trigger circuit is not calibrated and you cannot pick trigger levels that fall on the resolution steps.  The best you can do is account for the fact that the maximum voltage difference between your trigger level and level the trigger is actually asserted on is the range divided by 2^(trigger resolution). 

To confirm the trigger resolution on your device, refer to the specifications document.
 

Additional Information

Difference between Analog Input Channels and APFI lines:
The major difference between analog inputs and the APFI lines is the fact that your analog inputs will take the range into consideration and apply gain.  If you configure the analog input channel for a signal between -1V and 1V, a gain of 10 will be applied to amplify your signal across the full scale range of the card (+/-10V).  The APFI lines will always use the +/-10V range regardless of the input signal levels and range settings.