LabVIEW FPGA - Control PID - LM35

[Silvane]

Hi,

I'm using the plataform myRIO of National Instruments. I have to use the LabVIEW FPGA. And I'm applying an PID control into a DC motor based an temperature in of LM35.

But I had some problems.

The first is that the measured temperature is too varying, up until 10ºC.

The second problem is that to drive the motor I'm applying a PWM signal. How can I do this in the LabVIEW FPGA?

Thanks,

Silvane

[Sam_Sharp]

For PWM in FPGA, just turn on a digital output, wait your 'on' time, turn off your digital output and wait your 'off' time. The ratio of the on time to the off time is your duty cycle and the sum of the on and off time gives your PWM frequency.

This isn't the most efficient solution, but it's one of the easiest to see what's happening:

[Silvane]

I get it, but how can I connect the PID output to the PWM signal?

Tanks

[GerdW]

Hi silvane,

the PID should output a duty cycle value. You just calculate ON/OFF time from this duty value…

[Silvane]

But, the output PID do not is a duty cicle? I don't understand

Thanks,

Silvane

[Sam_Sharp]

Duty cycle is a % from 0 to 100 - 0 being always off, 100 being always on and anywhere in between is the ratio of on-time to off-time.

Scale your PID output maximum values from 0 to 100.

Then calculate the on/off time (the reverse of the calculations I've shown in my snippet) and use that in your PWM.