PWM Cycle Time for Heaters

[thingstodo]

There's nothing to it...
1. Feed it the 0-100% CV from the PID
2. Set the cycle time
3. Set the min/max time
4. Set the min/max percent, typically 50/100%

Don't make this harder than it should be. Unless you just really want to.

+1 on that.

My advice is to start as simple as you can, and work from there. You have several suggestions on this thread.

I have had grand plans in the past .. that get flushed down the drain after the first field test when things are not-quite-as-the-customer described ...

It's an iterative process. Document your assumptions. Document how the situation changes - measurements, equipment, staffing - and document what you tried, what worked and what did not.

You won't remember any of these details 6 months after it works. Make it easier on yourself later .. on on the next guy after you move on.

 

[Peter Nachtwey]

Peter is going to smack my hand for asking this.

Do you need ramping? Does the SP change?

I think you are sweating the small stuff unless the time constant of the system is very short. Do you know what it is? That is what will determine your PID update time. The PID update time should be at least time times faster than the system time constant. As stated above, the PWM rate needs to be at least 100 times faster than the PID update rate to get 1% resolution.

What we don't know is the system time constant.
I don't like your calculation about F/min. It only considers adding heat and not the heat that is lost as temperature increases.