old electric cookers - power circuitry

OT, I know, so feel free not to answer;
Does anyone know how, prior to thermistors being so easy to use, how electric cookers used to vary the power to the heating rings?
e.g.
http://www.espares.co.uk/part/cookers-and-hobs/hotpoint/p/1092/808/0/0/1020660/1800-watt-electric-hob-el.html
The oven is thermostatic, so that's on-off, but the rings were almost always fully variable.
So how was that done in (say) 1950?
BugBear
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On Mon, 31 Jan 2011 16:02:22 +0000, bugbear

Simmerstat (q.v.)
HTH -
--
Frank Erskine

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bugbear wrote:

http://www.espares.co.uk/part/cookers-and-hobs/hotpoint/p/1092/808/0/0/1020660/1800-watt-electric-hob-el.html
I don't think that thermistors are used today - Thyristors or more like Triacs maybe.
Prior to that that it was a variable duty cycle so like the oven they were on or off.
Bob
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On Mon, 31 Jan 2011 16:02:22 +0000, bugbear

Bimetal strip controlling the contacts with a heating element around it . Element in parallel with the load. Cam to alter strip pre-load or contact position to alter duty cycle.
AKA simmerstat.
Mark Rand RTFM
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"bugbear" wrote in message
OT, I know, so feel free not to answer;
Does anyone know how, prior to thermistors being so easy to use, how electric cookers used to vary the power to the heating rings?
e.g.
http://www.espares.co.uk/part/cookers-and-hobs/hotpoint/p/1092/808/0/0/1020660/1800-watt-electric-hob-el.html
The oven is thermostatic, so that's on-off, but the rings were almost always fully variable.
So how was that done in (say) 1950?
BugBear
Thermostatic blade in the controller. The higher the setting, the longer they stay turned on.
Steve R.
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http://www.espares.co.uk/part/cookers-and-hobs/hotpoint/p/1092/808/0/0/1020660/1800-watt-electric-hob-el.html
longer
Goggle 'Simmerstat' and all will be revealed. Basically a bi-metallic strip bends as a small heating element wrapped round it warms up - this breaks a current carrying contact that not only turns off the small element, but also the ring it controlled. Bimetallic strip then cools and remakes the circuit starting the cycle again. Turning the cooker control knob varies the bias pressure on the bimetallic strip. Thermal inertia of the element makes the process seem continuous.
AWEM
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Andrew Mawson wrote:

So a small electro-mechnical mark-space device (like a variable car indicator thingy).
Thanks to all.
BugBear
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