PXI-6624 Pulse Frequency measurement

[TarunT]

Hi.  I'm working with a PXI-6624 and am interested in doing pulse frequency measurements to get both frequency and duty cycle on its inputs using DAQmx.  

Whenever I go to create the virtual channel however, I get error -200431:

"Selected physical channel does not support the measurement type required by the virtual channel you are creating."

"Requested Value: Pulse Frequency"

"You Can Select: Frequency, Period, Pulse Width, Semi Period, Two Edge Seperation, Position:..."

Is this card really not capable of doing these pulse frequency measurements?  

[John_P1 · Accepted solution]

Yes, the "Pulse" (not to be confused with "Pulse Width") measurement was introduced with NI's STC3 devices including X Series and CompactDAQ.  

Pulse Measurement:

However, you should still be able to measure frequency and duty cycle on your card with a semi-period measurement:

Semi-Period Measurement:

Images are from the X Series User Manual.

The difference between the two modes comes down to how the data is stored and buffered on the card--with the semi-period method the hardware doesn't distinguish between high and low samples and puts everything into a single buffer.  However, if you start the counter off the appropriate edge (see below property node), then you would know in software the order of high and low samples and can pretty easily calculate frequency and duty cycle from this.

Best Regards,

[TarunT]

Hi John.  That sounds like a good work around.  I'll give this a try.  Thanks.