update Duty Cycle in PID/PWM temperature control

[HessenMob]

Hi fellow Labview users,

I am controlling the temperature in a box by reading the temperature (voltage) of a PT100 element and outputting PWM pulses through the PCI 6221 counter to close the circuit of a solid state relay to power my heater.

By using PID (not tuned quite yet in the code attached below), I would expect the duty cycle to also adapt according to how close we are to the setpoint value (i.e. it would be fine tuning the out put pulses to not be 50% when its close to the setpoint, but instead be like 10% so it doesnt overshoot). Right now my code does nothing the moment the process variable goes above the setpoint (I have the duty cycle set to 1E-5 in this case, essentially off, since if I dont do this, the counter still outputs pulses...)

How do I incorporate the update of the PWM pulses in my code?

Thanks!

HessenMob

[HessenMob · Accepted solution]

I think I have solved the problem.

 As a new person to these forums, I didnt know how to delete my post...

An updated version is attached below!

 Any thoughts on how to tune the K_p, K_i, K_d parameters??

Thanks,

HessenMob

[Nirali]

Hello guys,

I am controlling the temperature in small prototype of a house by reading the temperature (voltage) from the LM 34 temperture sensor and outputting PWM pulses through the cDAQ 9072 counter to control the voltage applied to a pump which pumps hot water to a heat exchanger which is placed infront of a fan.

Basically, I am using PID in Labview to do this. I have seen your code and it is very much the same. I have designed the PID sub VI, unfortunately, the PID is not responding to the change int he process variable. I have checked my code and the problem seems to be that there is not iteration from the while loop. when I connect the Iteration icon (the small bule i in the corner) to an indicator, the loop doesn't iterate!!!.

The LM 34 sensor has a linear output voltage to the change in temperture but it has a very slow response to a step change in temperture. Any suggests on using other type of sensors??

I am attaching the code for the PID sub VI. Can any body help me?

Thank you