Hi,
I am Abbishek and I am a graduate student in the Department of Aerospace Engineering in Auburn University. I am using a stepper motor to rotate a shaft and a rotary encoder to measure the position of the shaft and hence determine the RPM. The encoder I am using is a quadrature encoder (REV-11-1271). Initially, I was using the "Measure Angular Position - modKP.vi" program to get the position of the shaft from the encoder and then determine the RPM of the shaft from that. The DAQ system I am using is the NI-6218. When I run the program and use the X4 decoding, I observed a lot of fluctuations. So, I used an X1 decoding, and the fluctuations reduced a bit. But I observed something peculiar in the RPM measurement. It was seen that the fluctuations about the mean RPM were always about 0.3 RPM, irrespective of the motor rotation rate, the acquisition rate or the microstepping. To check further, I changed the program and used the other VI which has been uploaded here. In that VI, I counted the edges over 1 second to determine the frequency of the pulses and got the RPM from there (our encoder has 2048 pulses per revolution). But, there I observed that the encoder is outputting varying frequencies due to which the RPM is varying as well.
I wanted to know that why am I getting this kind of fluctuations (only 0.3 RPM magnitude). Does it have something to do with the acquisition parameters or how we are acquiring the data? Please help me out with this issue.
Thank you
Regards,
Abbishek