On Sat, 20 Oct 2007 22:42:37 +0100, Baron
wrote:

John Fields wrote:

On Sat, 20 Oct 2007 00:15:56 GMT, "Farticus"
wrote:


"John Fields" wrote in message
...

From the point of view of cost, I like the idea of a single
phase-controlled TRIAC driving both heaters in parallel since the
pair of heaters, in parallel, will only need 10A from the mains and,
with proper timing, the loads will never see more than 120V.

When one is unplugged, of course, the TRIAC need only pass 5A.
Even better.

But what's a simerstat? Is it a device with feedback which will
maintain a temperature once set, or is it like an open-loop lamp
dimmer?


--
JF
A simerstat is the term given by electrical wholesalers for a control
typically used to control a cooker plate. It is open loop.
The simmerstat has a bi-metal strip built into it that does the
"control". The simerstat usually incorporates a 1amp(or thereabouts)
rated contact that is used to control the cooker plate (element).
F.

---
I'm confused.

If the simerstat is used to control temperature and the bimetallic
switch is used to switch the element on and off in order to maintain
that temperature, then that's closed loop.

An example of 'open loop' would be a lamp dimmer where there is no
feedback used to control the brightness of a lamp. Or, for another
example, a VARIAC.

Hi John,

The simmerstat is only open loop in the sense you describe. There is no
sensing of the actual hotplate temperature. The current through the
hotplate passes through a secondary heater wound around a bimetallic
strip. This simply makes/breaks the circuit. A cam controls the
distance the bimetallic moves.

---
Got it, thanks! :-)


--
JF