Alternative to digital rotary encoder

[DaveX]

@backflip

I cannot make sense of your calculation. 123 rpm is close to 120 rpm, and it is two revolutions each second. It makes one revolution in 0.5 second and 0.55 second is shown in plot.

You are correct. I was wrong and flipped things around while doing the RPM & sec/rev units conversions.

@backflip

I do have some step responses when the speed reference to the control loop is given a step. Is this what you like to see?

I think so -- from an admittedly external, top level control system point of view of a person without any experience with your hardware, the time constant of the plant/system/DeviceUnderTest seems like it would be much much longer than the dt=0.000020s(?) of your control loop.