Dear all,
Overview:
I am using NI PXI 6722(Multifunction DAQ card) to count the no of pulses generated from source.
it has two counter I/P channel. I configure "Count edge" to count the no of pulses generated.
http://www.ni.com/pdf/manuals/370735f.pdf
My source signal Frequency ranges from 1HZ to 10 HZ. signal waveform is Square waveform. Low state is 0V and High State is 5V
Issue : Getting extra no of pulses than expected. (Ex :For 10HZ, Expected 600 pulse/min but actual 800+ pulse/min)
Observation/workaround :
NI PXI 6722 has two Onboard clocks(100KHZ and 20MHZ). I am not using any external clock so far for this requirement.
I assume, By default the card is taking 100KHZ clock as ref clock. So it is looking for the change for every 10us.
I tried with three different sources with the same frequency(10Hz). Two sources out of three sources rising time is less than 10us which counts(600/min) are perfect as per the frequency. The third source (Actual source)raise time is 50us so its giving extra no than expected.
I assume, this issue will get over if I use 50KHZ or less than 50KHZ as a clock ref.
Please suggest me whether my observation is making sense or not.
Thanks,
Kumaran
