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  1. #16
    Join Date
    Dec 2007
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    The 'potentiometer' used in most kilns is actually a simmerstat - and was commonly used in domestic electric cookers, simmerstats operate by varying the time on vs time off ratio. Back in the early 70's I took a year or so off uni and worked as lab tech in a senior college, I was called to 'service' the kilns in the art rooms a few times - mostly to replace elements but once to replace a simmerstat on a small benchtop kiln used for enameling jewelry, being so long ago my memory is a bit hazy but I believe the larger kilns used a mechanical cutoff where a small piece of pottery held a latch open - once the required temp had been reached - determined by the properties of the small piece of pottery - the piece collapsed allowing the latch to swing down, hit a switch and shut off the power - it was quite crude and often used in conjunction with a slump cone - a small cone shaped piece of pottery was put into the kiln along the bits being fired - once the cone collapsed the temp had been reached - a visual confirmation of correct temperature, if you were within earshot of the kiln you could hear the latch dropping and hitting the switch and could go and have a quick look to see if the cone had collapsed - a quick google search showed these things are still in use they are called pyrometric bars and cones.

  2. #17
    BobL is online now Member: Blue and white apron brigade
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    Feb 2006
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    Perth
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    Quote Originally Posted by familyguy View Post
    The 'potentiometer' used in most kilns is actually a simmerstat - and was commonly used in domestic electric cookers, simmerstats operate by varying the time on vs time off ratio.
    That's the way many of our larger lab hotplates worked. In the 1980's smaller ones started being controlled (not very well) by conventional incandescent lamp dimmers.

    In 1970 one of the simmerstat hotplates was inside a PVC fume hood and its simmerstat short circuited went to full power and melted through the PVC fume hood into a cupboard underneath containing organics (ethanol, chloroform, ether etc) the resulting fire and fume damage was about $200,000 which was lot of money back then. The blackened simmerstat mounted on a polished wooden plinth is still in the staff trophy room or at least it was when I was last in there.

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