Want to insert a programmable delay between trigger and start of channel DAQ.

[sean_dowling]

I have an external signal conditioner/piezo pressure transducer hooked up to AI0 of a PXIe-6366 in a PXIe-1073 chassis.  Currently I am sampling at full speed for the AI (2MS/s) but am interested in splitting the input channel to some (if not all) of the remaining 7 AI channel inputs and sampling those channels also at 2MS/s, but with a short (several ns) programmable delay so that all the channels are slightly out of phase with each other (effectively increasing the sample rate of the mirrored signal).  The goal of this exercise is to ensure I am not missing the peak of the high-speed pressure event I am recording.  Following DAQ, rather than assemble the traces, I would simply take the trace which recorded the highest peak as the data set for that event.

[Chris-NI]

Hi Sean,

Unfortunately, X Series does not support the measurement you are needing to implement.  All of our X Series DAQ cards have only one analog input timing engine, which requires that all channels be reserved on the same task.  Although you can implement a start delay (number of ticks of the timebase after start trigger before acquisition begins), this cannot be done on a per channels basis in one task.  As such, all channels in your analog input task will be in phase, sharing one sample clock from the same timing engine.

As I understand from speaking with some other Applications Engineers here that worked with you on this, you need to sample at 12 MS/s (please let me know if this spec is incorrect).  To achieve this sort of sampling rate sampling rate, there are a few options, most of which fall into the category or oscilloscopes/digitizers:

Good: PXI-6115

Potentially sufficient sampling rate if 10 MS/s is okay, but may not have the required bandwidth to capture pulse

Better: PXI-5114

Should have sufficient bandwidth and sampling rate, but perhaps not enough vertical resolution

Best: PXI(e)-5122

Should meet your requirements for bandwidth and peak searching

An additional specification that would be helpful to know is what frequency components you expect to see in your pulse, so that we can understand what sort of bandwidth we need here.  If the pulse width is on the order of 100 ns or smaller, then your signal will have frequency components in the 10s of MHz or higher.  Even a card, such as the 6115, sampling at 10 MS/s will not capture these small transients.  Even if you adhere to Nyquist and sample at twice the highest frequency, you will still not capture the peak's position or amplitude with any certainty.  Because of this, I would recommend that we focus on finding a scope that has sufficient bandwidth for your signal and then sample as quickly as you need timing resolution for the peak's location.  The cards I listed above are a good start, but may not be the final/best solution once we hammer out all of your requirements.

Regards,