GB557445A - Improvements in and relating to electrical regulators for the automatic control of a variable condition or characteristic - Google Patents

Abstract

557,445. Automatic control systems for furnaces &c. BRITISH THOMSON-HOUSTON CO., Ltd. March 18, 1942, No. 3582. Convention date, March 20, 1941. [Class 38 (iv)] Temperature &c.-Anti-hunting means, in a system in which change in conductivity of a grid controlled valve indicates correction or departure of a variable condition from a desired value comprises a condenser in the grid circuit and switching means to initiate simultaneously the charging thereof whereby the conductivity of the valve may be restored in substantially the time taken in correcting a moderate departure. As an example, a photo-electric cell 13, responsive to the temperature of strip steel 10 issuing from a furnace 11 and controlling the speed of a motor 14 driving the strip, may be associated with an amplifying valve 20 to produce a current change, in a resistor 32 determining the relative potentials of cathode and grid in each of two valves 21, 22, when a departure from a desired strip temperature occurs. The values are arranged so that under correct conditions 21 is non-conducting and 22 conducting so that relay contacts 23a, 24a are both open. When a temperature rise increases the current through the amplifier, valve 21 becomes conducting, contact 23a closes and the speed of the motor 14 is increased. At the same time contact 23b connects a negative potention to one electrode of condenser 35 through a resistance 37 whereby a charge is built up which eventually restores the initial condition of conductivity of both valves. This operation may be arranged to match, in time, the cycle of the correcting process so that only a single correcting operation occurs upon a departure from the correct temperature.