Reading Digital Pulses from a Flowmeter

Question

I have a flowmeter that puts out 0 to 5 VDC pulses and has a calibration factor of 50.99 pulses per CC. I do not have a counter card, but have a digital input card and an Analog Input card.
What will be accurate method to read these pulses from the flowmeter?

Answer 1

The Detect All Triggers.vi is not included, so I cannot tell what it is doing.
Several things may affect your results.
1. It appears that you have the DAQ assistant set to sample at 250,000 samples per second and to acquire 100,000 samples. It creates the task, configures the timing, acquires data, stops and clears the task on every iteration of the loop. The only part which needs to be inside the loop is the acquire data part. All the rest should be outside the loop. You can open up the DAQ Assistant and pull the parts out to do this.
2. The samples you acquire take about 0.4 seconds but you have a 1 second elapsed time test in the loop. It appears that you are only looking at about 40% of the data available because you do not accumulate the data while waiting for the elapsed time.
3. The Detect All Triggers boolean output which connects to the case structure where Counter is updated only allows Counter to increment once pper iteration of the while loop, maximum, regardless of the number of pulses detected in the dataset. Unless you never get more than one pulse in 400 ms Counter cannot accurately represent the number of pulses produced by the flowmeter.
4. Get rid of the local variables. The are not needed and often contribute to race conditions.
5. Learn about dataflow. The "initialization" of the chart history and local variables at the left of the diagram could occur after the while loop has started or even completed. The sequence structure in the True case is probably not needed either. Shift registers are your friend
Lynn