Temperature control system for electric surface heater

摘要

A temperature control system for electric surface heater of piled layers of a heating element across which a commercial AC source current is fed and a thermosensitive electrode opposing the element through thermosensitive element showing negative impedance characteristics with temperature rise. In the system, an AC signal voltage different from the source current is applied between the heating element and the thermosensitive electrode, and excessive variations in the signal voltage responsive to the negative impedance of the thermosensitive element is detected to disconnect or connect the heating element and the source.