Is relativeInitialX valid for externally triggered measurements? NI PXIE 5122 64MB per channel

[blakney]

For instance when using the following commands

niScope_ConfigureDigitial (with a positive delay time)

NiScope_SetAttributeViInt32 ( NISCOPE_ATTR_FETCH_RELATIVE_TO to NISCOPE_VAL_READ_POINTER)

followed by

niScope_FetchBinary16 (looped to retrieve data plus wfmInfo)

What will the value of the wfmInfo.relativeInitialX prior to the external trigger?  Is it defined?  Is it set to a fixed number to indicate triggering has not occurred until the trigger has been received and then it becomes accurate after the trigger has been received?

I would like to use this to do a modified FecthForever but synchronized to an external trigger for waveforms up to about a  minute.

It seems the trigger delay for the 5122 should be able to hande a minimum trigger delay of about 170 seconds (at max sample rate more at lower rates), so the data I would need could all be borrowed from the prefetch buffers of the externally triggered and properly post trigger delayed measurement.

Thanks in advance for any advice.

Greg

[Nathan-P · Accepted solution]

In the case that you are fetching pre-trigger data (fetching data before a trigger has occured., relativeInitialX will be the same value as absoluteInitialX.  

Regards,

Nathan

[blakney]

You are exactly correct. I will use the transition from equality to inequality to signify the physical trigger location.