GB827701A - Thermal controller - Google Patents

Abstract

827,701. Automatic thermal control systems. ADDRESSOGRAPH - MULTIGRAPH CORPORATION. April 17, 1958 [May 22, 1957; Jan. 29, 1958], No. 12213/58. Class 38 (4). In a thermal controller for an image transfer printing machine, a Wheatstone bridge 47 supplied at a low voltage from the secondary of a mains frequency transformer 42 has shunted across one arm a thermistor 54 kept at platen temperature. The out-of-balance signal from the bridge is amplified by a triode 63 and applied to the grid of a thyratron 71. When the out-of-balance signal exceeds a predetermined value and is in phase with the anode voltage of the thyratron derived from the primary of the transformer 42, a relay coil 98 is energized and a pair of contacts 98A, 98B, in parallel, close the supply to a platen heater, not shown. The amplified out-of-balance signal is also rectified by a diode 143 and the resultant negative-going pulses are applied to the grid of a triode 70 which is cathode biased from the primary of the transformer 42 through a resistor 155. At a predetermined amplitude, the negative going pulses on the grid reduce the anode current of the valve 70 so that a relay 91 is de-energized, cutting off the supply to the machine drive control circuit, not shown. The platen temperature is adjusted by a variable resistance 57, and a variable resistance 148 adjusts the platen temperature limits at which the machine drive control circuit is energized. In another embodiment, Fig. 2, not shown, the triode 70 is self-biased and the rectifier diode is so arranged that an increase in the rectified out-of-balance signal applied to the control grid energizes the relay coil 91 and break the supply to the machine drive control circuit. Specifications 703,336 and 782,633, [both in Group XVI], are referred to.