A Design for Electrical Regulation of High Temperature Ovens

In growing Tellurium crystals, a temperature within a few degrees of 450 centigrade must be maintained constantly. The electrical oven available consisted of a porcelain tube five centimeters in diameter and thirty centimeters long, covered with asbestos. The need for making a regulator arose from the fact that nowhere in the catalogues available was there a regulator advertised that would, be contained within the tube without completely closing it. Nearly all temperature regulators for electrically heated apparatus break the heating current when the temperature rises to a given point, and make it when the apparatus cools, and the difference between these two temperatures is the regulation of the device. It requires 10 amperes to heat this particular oven to 500 degrees centigrade, and simple expansion could not be relied upon to make a gap sufficiently wide to prevent sparking and at the same time give any very close regulation.