GB601121A - Apparatus for maintaining a variable at a substantially constant value - Google Patents

Abstract

601,121. Automatic control systems. IGRANIC ELECTRIC CO., Ltd. Feb. 9,1945, No. 3296. Convention date, Feb. 9, 1944. [Class 38 (iv)] Variables in general.-In an automatic control system in which the value of a variable is determined by the rate of flow of a medium, the rate of flow of the medium is controlled in accordance with the value of the variable and with the rate of change of the variable, the latter effect being obtained by using a ring type liquid drag device. The Figure shows an arrangement for maintaining the calorific. value of a gas flowing in pipe 10 constant by mixing it with a proportion of air from pipe 11. The air regulating valve 13 is controlled by calorimetric device 16 which rotates shaft 18 in accordance with the calorific value of the mixed gases in pipe 12. Rotation of shaft 18 causes member 39 to rotate so that gears 43 and 44 mounted on a common freely mounted shaft 42-and meshing with segments 45 and 46 cause freely mounted member 50 to rotate, owing to the resistance of the liquid drag device 23, 24 to which segment 45 is attached and also to the increase in tension in one of springs 30 and 31. Rotation of member 50 results in the closure of one of contacts 97g and 97e preparing the circuit of one of relays 95 and 96 for energization, and the displacement of arm 61, 65, arm 61, 65 controls the phase relation between cam 76, which is continuously rotated by motor 64 through planet gears 68, 67 and 71, and directly driven cam 77, by moving planet gear 67 round the motor shaft. If there is no displacement of the system, contacts 78 and 79 associated with cams 76 and 77 remain open ; if the system is displaced however these contacts are periodically closed for a period dependent on the degree of phase displacement, so that one or other of relays 95 and 96 is periodically energized. Relays 96 and 95 control servo-motor 14 operating valve 13, so that closure of the appropriate relay contacts causes the motor to adjust the valve and restore the correct calorific value. Visual indication of any deviation is given by pointer 17 moving over scale 21. In a modification, Fig. 4 (not shown) a cam mounted on the shaft of the planet which engages a fixed follower in such a manner that arm 61 is periodically disengaged from member 57. Member 57 is given a stepped configuration, member 61 being suitably shaped to engage it.