High-Speed Digitizers

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Fastest way to measure voltage with PXI-5153 and LabWindows/CVI

Hi Folks,


I'm using six PXI-5153s in a PXI chassis to measure voltages. I know it seems like overkill, but the original plan changed, and I'm stuck using these parts.


I have 60 microseconds to sample a voltage level three times. My current measurement using niScope routines to set up a bunch of measurement parameters, and then niScope_read to get the scalar result takes about 30 milliseconds, so I'm nowhere close. Next thing I'm going to try is moving the setup routines out of the measurement routine. That should help a lot.


I inherited the code, and am fairly new to LabWindows/CVI. Does anyone know a really fast way to get a voltage measurement? Would it be fastest to use the 5153 to average three measurements, or should I get the values and average them myself?


Any thoughts someone has would be appreciated!


Thanks in advance!


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Message 1 of 5

Have you looked through the NI Example Finder for LabWindows/CVI?  There are several examples for voltage measurements.


Example Path:

NI Example Finder > Hardware Input and Output > Modular Instruments > NI-SCOPE (High-Speed Digitizers)


Why are you trying to average 3 measurements?

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Message 2 of 5

Hi Red,


Thanks for the reply. It's not a question about MAKING the measurement; that's not difficult, and I am familiar with the examples. My question is more along the lines of the finding the fastest way to do that. I only have 60 uSecs to make three measurements of the same pulsed signal. The requirements specify the average of 3 measurements, so that's why.


I have to repeat this every 50 milliseconds. It takes at least 15 to 20 mS to setup the measurement, toggle some switches, and arm the digitizers for an external trigger.

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Message 3 of 5

From what I’m understanding what you are trying to do should be possible.  You should be able to send a trigger to the PXI-5153 every 50 milliseconds to acquire 3 samples at the rate you need.  Then the program will wait until it receives each trigger until you terminate the acquisition.


Do you have a device or card you could use to send triggers to all your PXI-5153 cards?

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Message 4 of 5

Hi Red,


Yes, I have an IRIG-B board to match our time with the rest of the system, and I'll be using PXI_Trig0 to propagate the trigger input from the controller in the PXI chassis to the PXI-5153s.


I did some more timing tests and can see that the setup of the measurement, which is currently done each time a measurement is made, takes a lot longer than the actual measurement itself. I'm moving all of the setup calls into their own routine, and I'll only have to call that every now and then, I think.


That way, I can call the setup routine when needed, and use the measurement routine by itself most of the time. That will work.

Thanks for your help, Red. I appreciate it!


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Message 5 of 5