PID Temperature Controller working with an ON/OFF time cycle

[viga01]

Hi,

I trying to reproduce into LabView a PID temperature controller that you buy from omega for intance.

I want to use the PID build in VI. The PID output from 0-100% will be multiply by a time cycle value (e.g. 5 sec). If the output of the PID is 50% and the time cycle is 5 sec, that means that my heater will be ON for 2.5 sec. Heater ON means that I'm sending a DO signal to a relay, which turn on the heater.

I don't know how to program this. Anyone could help? 

[Nate.H]

Dear Viga,

What hardware are you working with?  (input and output)

Do you have the PID toolkit for LabVIEW?

To do PID control with a digital output (on/off), you will want to do PWM (pulse width modulation), which is what I believe is what you are describing in your post.

There are multiple LabVIEW shipping examples that show you how to do PWM, depending on which hardware you have. I would check out one of these examples appropriate to your hardware, and add PID control to it, based on your input. 

If you have a multi-function DAQ card, then I recommend looking at the PWM-Counter Output example VI, which actually implements proportional control. You would just have to replace the proportional control subVI with a PID VI and make a couple other small changes to adapt the example to your application.

Hope this helps,

~Nate