On Fri, 27 Nov 2020 16:59:36 +0000, Caecilius wrote:

The advantage of PID is that it should aim to keep wherever you
place
the thermocouple at a constant temperature - it'll 'learn' the
dynamics
of the room and the heater to avoid peaks and troughs as it
overheats
and then overcools.

Get the three control variables and it should run flat out until it
starts to approach the target temp then it'll throttle back to hit
the target temp with no overshoot. It'll then hold the temp there as
required, possibly very finely.

I'm surprised that a PID controller uses a simple SSR output. I would
have thought that a "dimmer" type circuit using a triac for switching
would be better for that.

A SSR can be driven with a PWM signal, you have to be a bit careful
with the underlying pulse frequency otherwise the PWM waveform beats
with the 50 Hz mains meaning the power delivered varies at the beat
frequency at some settings. Looks like the pump speed controller I
have runs at 3 Hz.

What do you think is in a SSR? B-)

I guess you could drive a triac directly, some how. You'd have to
provide the isolation, zero crossing stuff etc...

--
Cheers
Dave.