Harry Bloomfield wrote
Rod Speed wrote
Onetap wrote
Graham. wrote

The other thing Onetap might consider is that the resistor body
is physically in contact with strip (at least it is on this old
Satchwell I have on the desk), so the design was to heat the strip
by conduction primarily.

So the resistor is in contact with the bi-mettalic strip. The
bi-metallic strip dissipates the heat to the air by convection
and to the surroundings by radiation. The convection causes
air currents to pass through the air vents. Anyone still having
difficulty with that one? I don't think it's that hard to grasp.

Different matter entirely to why the heater is there at all and why
bi metallic strip thermostats work fine if you disconnect the heater.

The ONLY effect you get when you do that is that the hystersis increases.

You do NOT get a set point shift.

The fact that the heater is only on when the load is has probably
got something to do with the high thermal capacity of the metal
and the high radiant emissivity of the metal surfaces.

Nope, nothing to do with that at all.

It actually allows the bi metallic strip to see what the temperature of the air is.

Metal surfaces are usually colder than the air temperature,

Not even possible.

and usually are the first to attract condensation.

Thats wrong too.

Then again, I didn't design the things and have never used one.

Thats always been obvious.

Some control technicians thought the heater was effective for some applications..

And its completely trivial to prove that the heater does reduce the
hysteresis as it was designed to do by whoever invented that approach.

They wouldnt add an extra cost item like that if it didnt do something;

You are wasting your time with providing explanations to this poster!

True, but I do that in case anyone considers that he might be right.

And you did so yourself too.