PID discussion for one input (thermocouple) and two control outputs (damper and fan)?


 

J.Diggs

New member
The heatermeter is a bit unique in that the PID method(s) that CapnBry uses can control two outputs, a fan and a damper.

When I was doing PID stuff back in the dark ages I think I mostly set up controllers with one input (temperature, pressure, flow, whatever) and one output (valve, burner, heater, vent, whatever).

Is there a discussion somewhere on single input multiple control output algorithms and methods? Maybe even somewhere where CapnBry discussed what he did in the heatermeter?

looking around the googleverse, there's lots of discussions and course-level stuff on single in single out. Almost all the multiple out uses some sort of proportional slaving from one output to the other. Or else feeding the input to separate separate PID controllers for each output.

I can certainly go into the source (thank you Capn for leaving it up and available) but if there was already higher level discussions that would be a better place to start.

Where I'm ruminating on going with this is maybe prototyping an ESP32 based controller for my kamado just for fun. And it beats mowing the yard....which is not fun 8).

Thanks!
 
Although there may be two electrical outputs, there is really only one degree of freedom -temperature- that is being controlled with somewhat of a "staged" or perhaps "paralleled" single output. The PID itself doesn't really decide which output to use and how much. The user determines for a given PID output, what amount of each output am I going to ask the Heatermeter to apply or at what threshold am I going to ask the heater meter switch on the second output. In fact for my application of a Weber Kettle, I only use the single servo output to control the factory installed louvers on the bottom of the kettle. No fan needed.

Here's a snapshot of the Heatermeter PID configuration that I found somewhere on this forum. Ignore the red box. The green box is mine. You'll see there is only one PID output, but you can control when the servo/fan either kick in or max out independently of each other.
1744715666067.png

Often times with a two input/two output type of PID you may be thinking of, you're controlling a 2 DOF system and therefore need to measure and constrain both of those degrees.
 

 

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