GB372007A - Improvements in and relating to temperature control systems - Google Patents

Abstract

372,007. Thermostats. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Kelly, H. R.; R.D. No. 4, Schenectady, New York, U.S.A.) Feb. 25, 1931, No. 5935. Convention date, Feb. 26, 1930. [Class 64 (ii).] An automatic temperature control system comprises a temperature-responsive device and a galvanometer operated thereby, controlling the exposure of a photo-electric cell to a source of light, the current traversing the photoelectric cell being applied to the grid circuit of a three-element vapour electric discharge device such as that known under the registered Trade Mark " Thyratron," which controls a heating circuit. An electric furnace 10 is heated by a resistance 11 supplied through a switch 12 which is biased to the open position by a spring 14 and closed by an electromagnet 15. A thermocouple 19 is connected to the moving coil 20 of a galvanometer having a pointer 35'integral with an arcuate strip 36. A photo-electric cell 16 and lamp 18 are mounted in a common structure carried by a rod 24 rotatable in the same axis as the galvanometer pointer. The strip 36 is adapted, at a predetermined temperature, to intercept the light passing from the lamp 18 to the cell 16, and the temperature at which this occurs may be varied by rotating the lamp structure about its axis, until the pointer 37 indicates the desired temperature on the scale 38. The electric discharge device 17 is of the kind which forms a mercury vapour arc between the anode 40 and cathode 41 at certain critical voltages on the grid 42, the arc continuing independently of the grid voltage as long as the anode is positive. The arc is prevented from starting when the grid voltage is more negative than a critical value. The device 17 is energized from the central section 50 of a transformer 49, and the cell 16 is connected so as to vary the phase of the grid voltage with respect to the anode voltage. A resistance 44, condenser 46, and grid leak 52 are connected as shown. When the discharge device operates, a pulsating current passes through the coil 15 and the switch 12 closes to energize the heater 11. In a modified construction, Fig. 2, the index 55 of the galvanometer carries a mirror 56 which controls the reflection of light from a source 57 to a photo-electric cell 58, which is adjustable along a graduated slot 60. Specifications 255,405, [Class 64 (ii), Heating systems &c.], and 357,572, [Group XL], are referred to.