Multiple digital triggers

[VeritasAequitas]

Hi I am using a cRIO 9012 with the chassis NI9101 and a digital input card NI 9421. I am trying to read in a signal from a magnetic pickup. From the input I am trying to find the number of revolutions that occur within 1 minute. The problem I am having is that I am reading multiple highs from a single pulse or that it misses the pulse entirely. We have a drill press mounted spinning an object in front of the sensor at a constant 760 RPM. I either get around 500 or 600 RPM or way to high. I tried using a method node set on wait on rising edge. I am new at using this type of data acquisition so any help will be greatly appreciated.

[charris]

Hello!

What kind of signal output does your sensor have? Is it simply the current induced by the magnet? If so, it's possible that the pulse train may not be picked up by the DIO module, depending on how steep the rising edges are and the magnitude of the pulses.

It also looks like you're doing your frequency calculations on the real-time controller. You might be seeing aliasing of some kind if the controller can't keep up with the angular speed of the sensor. If you slow down the drill press, are your results more accurate? If so, you may consider offloading some of the processing to the FPGA so that the logic can keep up with the input signal.

Good luck!