Hello All, I am reading RPM from a square wave generated from a BLDC motor. The signal is carrying some noise that I am unable to eliminate. I am sending the signal to USB-6363 DAQ. The problem is that the DAQ is reading the noise spikes and including them in the count. I replaced the signal from the motor with a signal from a waveform generator and I get RPM readings right where they should be. Hook up the motor signal and I get readings in the seven digit range. The frequency range is around 75-150Hz. The noise is being carried on the high and low sides of the waveform. Cleaning up the signal coming from the motor is not an option as it would entail a product redesign. Is there a way to filter the signal programmatically? I have attached my code. Any help would be greatly appreciated.

I very slightly modified the code you posted to add digital filtering, with a default min pulse width of 2 msec. Give it a try. -Kevin P

LabVIEW

How to Filter Noise

Solved!

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Hi Kevin,

I couldn't figure out why the filtering didn't work. So, I re-grouped and revisited it. Seems after 30 plus years doing this type of work I still haven't learned one of the fundamental lessons one should never forget; ATTENTION to DETAIL. When I configured the channel node I selected Digital Input instead of Counter Input for the enabling and filter. Duh!

When set up correctly it worked great. I also cleaned up the signal some with a couple capacitors. FYI....I also installed a ferrite core just like the picture in the Ni user manual. It made no difference. I didn't think it would as this problem is not noise (which what ferrite cores are for) but rather a PWM signal embedded in a PWM signal as I stated earlier. Two different critters.

Thank you for your help!