GB1211429A - Process and apparatus for electrically heating and controlling the temperature of thin layers - Google Patents

Abstract

1,211,429. 429. Automatic temperature control systems. FARBENFABRIKEN BAYER A. G. June 10, 1968, No.27422/68. Heading G3R An arrangement for controlling the temperature of insulating material e.g. glass, porcelain, enamelled or oxidized metal, which has been plated or vapour coated with thin electrically conducting layers having resistance dependent upon temperature, comprises passing a heating current through the layer and simultaneously a measuring current which is electrically separate from and smaller than the heating current. The currents may be alternating and of differing frequencies. A D.C. source 4 may supply current to terminals 3 connected to the layer through a variable resistor 6 and an indicating or recording device 5. The measuring current is provided by an A.C. generator 8 also fed through an indicator or recorder 9, a resistor 10 and D.C. isolating capacitors 12. A fraction of the voltage across resistor 10 is compared with a reference 11 the difference controlling a servomotor M adjusting the value of resistor 6. The conducting layer may be arranged in a bridge circuit which may have a second layer in another arm. The latter arrangement may be used to compare the melting points of two substances one of which is known. The resistor 10 may be adjusted by a programme device. An object may be heated by interposition between layers having conductive coatings, see Fig. 5 (not shown) and the conductive layer may be coated with at least one protective layer. The layer may be optically transparent and may heat a part of an optical apparatus e.g. a microscope table or a spectroscope.