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How to stack a signal with microseconds drift

Hello,

 

I have a CRIO-9014 with 2 modules: 9401 an 9239.

I feed the DI with a PPS from a GPS. I record the delay between the PPS and the first analog measurement following.

The FPGA clock isn't 40 MHz exactly. The 9239 is a timed module then follow the FPGA clock then I have few microseconds drift every seconds.

By example, one second I will get the first measurement at 10 us and the next second will be at 13 us.

 

I would like to stack the data .... add together values of few seconds of data and divide by the number of data.

The problem is : I need to shift data depending time of measuremet otherwise the stacking will be wrong

 

I have tried different options: use the time in a waveform (doesn't work), use a 1M array ( too big, too slow).

 

Anybody has got an idea?

 

Mathieu

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Hi Mathieu,

 

I am going to cheat and quotethis kb:

 

"You can use the SMB connector of cRIO-9012/9014/9074 controllers to connect a digital device to the controller. For example, if you connect the pulse-per-second (PPS) output of a GPS device to the SMB connector of a cRIO-9012/9014/9074 , you can use the GPS device to correct for drift of the system clock of the controller. You can also use the SMB connector as a general purpose digital I/O line."

 

It looks like you want to use the SMB pin for GPS drift correction.

National Instruments
RIO Embedded Hardware PSE

CompactRIO Developers Guide
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