frequency to RPM

[gihlutax]

I need a RPM measurement of a BLDC. I have Hall input signals. I use a cRIO and I program on the FPGA.

So I measure the frequency of one hall input signal using a single timed loop on the FPGA.

In another loop I calculate the rpm from the frequency. This according to the number of poles.

When the motor is running, I can see the number of ticks changing, but the calculated RPM is not changing, it's fixed at 5299,41 RPM.

I hope someone can help me.

[crossrulz · Accepted solution]

What is the settings for your Fixed Point data type?  I think you are just hitting the limits of the fixed point settings.  You might need to convert it to a floating point and order to do all of the math.

[gihlutax]

It was indeed the fxp configuration of on of the data operations that caused the problem. Thank you!