GB828975A - Improvements in or relating to electrothermic indicating apparatus - Google Patents

Abstract

828,975. Electrothermic indicating apparatus. KALLE, K. T. Nov. 22, 1957 [Dec. 5, 1956], No. 36510/57. Class 40 (1). In a system in which one of a pair of thermally self-interrupting contacts 12, 11 is moved towards and away from the other by a variable to be measured such as temperature, pressure, position, so that the average current through the contacts represents the value of the variable, the contacts are kept clean by continuously vibrating one of them transversely electromagnetically. As shown, a Bourdon tube 26 actuated by a temperature-sensitive probe 24 determines the position of contact 12. That of contact 11 is determined by the length of a wire 19 heated by a coil 13 in series with the interrupter contacts and with a thermally operated indicator 22. The transverse vibration is imparted to the contact 12 by a magnetic plate 29 which as shown is mounted near to a groove in the magnetic circuit of the supply transformer. Alternatively, plate 29 may be arranged near to a gap in a magnetic circuit provided by magnetic extensions from the transformer core, Fig. 4 (not shown). To reduce sparking, the self-interrupting circuit is shunted by a resistor 10. As a further alternative, the interrupter contacts may be in the primary circuit of the transformer and the heater and indicator in the secondary circuit.