The electrical heating resistance, for operation at high temperatures, incorporates a temperature probe, which can be connected to the control and regulating circuit for the supply to the resistance. The temperature probe may comprise a thermocouple, with the hot junction positioned within the heating resistance, so as to be at the same temperature as the latter. The circuit connected to the temperature probe pref. provides a signal when the temperature of the heating resistance reaches the upper working limit, this signal used to cutloff the supply to the heating resistance, the supply being re-connected when this signal disappears.
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