GB750898A - Improvements in electrical control systems - Google Patents

Abstract

750,898. Automatic temperature control systems. SANGAMO WESTON, Ltd. Dec. 23, 1952 [Jan. 21, 1952], No. 32642/52. Class 38 (4). In Fig. 4 the direct voltage output of a thermocouple 13 responsive to the temperature of a liquid bath, is applied in opposition to a source of reference potential 35 to a moving coil 31 of a D.C. to A.C. converter 30 of the type described in Specification 604,312, [Group XL (c)]. A valve 45 is maintained in oscillation by feedback through the right-hand section of a double triode 40. On deviation of temperature from a value determined by the setting of a potentiometer 43, coil 31 moves from a central zero position so that further feedback occurs through the left-hand section of valve 40 to cause the oscillation frequency to increase or decrease according to the sense and magnitude of temperature deviation. The oscillator output is applied through a transformer 47 to a frequency discriminator, including a doublediode 49, which produces a direct voltage dependent in polarity and magnitude on the sense and magnitude of the deviation. This direct voltage is applied to biased triodes 22, one or other of which conducts according to the polarity when the temperature deviation reaches a predetermined value, to pass current in the appropriate direction through a resistance 36, the voltage across which constitutes negative feedback reducing amplifier gain for temperature deviations outside predetermined limits. An instrument 50 indicates or records deviations between these limits. A relay 16 in the anode circuit of one of the diodes 22 operates to switch off electric heating of the bath when the temperature rises above a predetermined limit. Specification 749,251, [Group XL (c)], also is referred to.