On 27 Nov 2020 16:43:09 +0000 (GMT), Theo
wrote:

Caecilius wrote:
Thanks for that link: although the 0.2A capacity means it won't work
with a 2KW heater there may be similar units available that do what I
want.

I think the takeaway is solid-state switching plus low hysteresis.

If you don't mind DIYing a case, there are PID controllers, eg:

https://www.ebay.co.uk/itm/REX-C100-...t/363129928297
(they're all clones of clones of clones)

That's interesting. PID control might be a bit OTT for my
application, but it's cheap enough.

I wouldn't trust the SSR with 40A but 8A mains should be ok.

Yes, I've seen enough big Clive videos to know how optimistic these
ratings are. But as you say a 2KW pure resitive load should be well
within it's capabilities.

I don't know if the thermocouples would be accurate enough - quite a
difference in +/- 2C for room temperature. You might be able to manually
offset it (ie ask 20C and get 22, so ask for 18C instead).

I'd hope that there's something with a smaller temp range (0 - 1300 C
looks like it's designed for a kiln) and an associated increase in
accuracy. I'd like something like 0.5 C or maybe even 0.1 C if
possible.

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.

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.

Theo