Pids and variable temp

I'm trying to build a controller. I wanted to put a pid heater and a variable heater. Is there any reason to put a variable on the pid also?

gr3 said:

I'm trying to build a controller. I wanted to put a pid heater and a variable heater. Is there any reason to put a variable on the pid also?

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Perhaps if you want more control over your boil. PID is useful for holding exact temps below boiling. After the water is boiling, you are better by controlling the duty cycle yourself if you can. Most PIDs have a manual feature that you can use to alter it.

For the boil control I've removed the PID and replaced it with this from Auber...

http://www.auberins.com/index.php?main_page=product_info&cPath=2_30&products_id=444

Makes boil control simple, especially when I have people helping and having them learn the buttons on the PID was impractical.

For the boil you do not need any of the PID features. What I do miss is using the alarm for when the temp is approaching a boil, but I just use one of the other controllers in my setup for that, so I get both solutions. If I want to do something like kettle souring at keep temps at 110 for a few days I just plug the kettle element into one of the other outlets controlled by a PID and use the probe cable form that PID for control. Best of all worlds.

Would there be times that being able to regulate temp as well as voltage to burner at same time. I was thinking of pid inline with switch that you could turn on to reg voltage if you needed. I was going to have a switch that I could switch to second burner output and use 2 temp probes.

Might as well just use the manual setting on the PID. If you really wanted to you could create a switch circuit to choose what controller you wanted to run the element, but that's a lot of extra parts for no reason. The manual setting on the PID is how I did that for years.