question re PID's and STC's

[PD]

I am now quite comfortable with wiring an stc1000 up for a brew fridge etc ( after trial and errors and one blown stc ! )
I've never used a PID and am wondering if anyone can tell me simply what the difference between the two are, when would I choose to use a PID over an stc ? Is the witing the same ? Basically what is the difference ?

Thanks

 

[LeithR]

Mornin PD,
An STC is a simple on off heat cool controller within a set difference range. A PID (Proportional + Integral + Differential) controller is a much more sophisticated beast. HERE'sthe wiki definition which is much better than I could attempt.

 

[adomant]

PID is useful for say HERMS where it has to stay well ahead of the game and anticipate what heat needs to be applied in advance of strike temperatures. PID devices are also used to switching (pulsing) rapidly to fine tune temperature.

STC is off / on only and has no brain and will probably blow up if you gave it too much thinking or frequent switching to do.

 

[Dr Mike]

As Adomant says, a PID can vary the power by pulsing on and off very rapidly while an STC is all or nothing on/off. In a homebrew setting this means that you can't use a PID to control a fridge - the motor would not enjoy being pulsed on and off very much. Also, when using a PID to control a heating element you need to use a solid-state relay to control the high voltage side. A mechanical relay would destroy itself pretty quickly!