I am using the digital impulse counter of the NI USB-6212 DAQ. The external device generating the square wave pulses is a flow-rate sensor. For flow rates of about 200 ml/min I am reading the pulses at about 400 pulses/second, but for a lower flow rate, say 80 ml/min, the counter shows 0 pulses/second (and 0 pulses total of output data). If I read the output of the flow sensor through an analog input and plot the result in time, it is clear that the flow sensor is still outputting square wave pulses with a frequency <110Hz.
Any idea why the counter is outputting 0? I am using DAQmx
Cl Cnt Edges
Start
Read as Counter U32, 1Samp (as the 'read').
Is there a lower pulse rate limit on the digital I/O counter? Are the pulses too wide now to measure, causing counter time-out? It would be really odd if the counter couldn't read low freq. pulses. If there are too many 0 counts does the counter give-up counting? I don't have a read time-out wired, but if I did, i'd still get a VI output error. I'm sure there's something really simple I'm missing. Any ideas?
