PID controlled heating mat

Hello

I have a 230V 85W small heating mat that i would like to be controlled by a PID controller for my fermentation container project.
Can someone who made maybe something similar give me examples of PID controllers that would be the best fit for this please or maybe a complete schematic.

Thanks in advance

Hi,

Is the purpose to maintain a constant-ish temperature? Probably not the solution you're after as you're asking about PID. If I were to make a simple analog circuit to do that, I might initially consider trying with a window detector fed by a temperature IC, the window detector controlling a comparator with hysterisis which in turn controls a transistor, which turns a relay on and off to control the 230V (AC?) mat. Others may suggest more sophisticated designs using microcontrollers.

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Hi,

I apologise for any errors in this, I had to rush the schematic, but you'll get the general picture, and others can improve upon the basic idea, if you're lucky. It doesn't even need an envelope detector, just a temp IC, a comparator/op amp as comparator, a transistor and the relay.

Driving a relays by a comparator without hysteresis is basically a bad idea, because it's likely to cause relays chatter near the threshold. There must be a hysteresis, as suggested in the post.

An on-off controller will always cause oscillating behavior in combination with the control process low-pass characteristic and dead time. If you don't want it, at least a proportional P or PI controller is required. D action is usually not needed for a temperature controller with constant set point.

Superimposing a slow triangle or sawtooth wave (period e.g. 5 - 30 seconds with relays output, less with triac control) to the set point signal can turn an on-off controller in a linear P controller with PWM output.