Patent GB-456348-A (GB)
Title: Improvements in or relating to temperature controlling arrangements
IPC: G05D23/24
Filed: 1935-05-07
Abstract: 456,348. Automatic control of temperature. ASSOCIATED ELECTRIC LABORATORIES, Inc., 1033, West Van Buren Street, Chicago, U.S.A. May 7, 1935, No. 13437. Convention date, May 9, 1934. [Class 38 (iv)] To avoid appreciable heating of the measuring resistances in a Wheatstone bridge, employed in a temperature control system to determine the resistance change in a temperature testing unit, potential is applied to the bridge automatically at intervals. As shown in Fig. 1 a vibrating pendulum relay 2 determines these intervals and a chain of relays operating in association with a sensitive relay SR of the galvanometer type effects the control. In the modification shown in Fig. 2 a motor driven cam 42 applies the potential to the bridge and other cams operate swtiches associated with the galvanometer relay. The arrangement according to Fig. 1 is adapted to maintain the temperature in a room or laboratory within very close limits. The temperature testing element 13 of the bridge WB is preferably a single layer coil with spaced turns and its total resistance may be divided between coils in different parts of the room. A heating or cooling sytem, or both, may be controlled, for example an electric heater and a fan energized respectively by relays 22, 23. On starting the system the relay 23 starts the fan and a slowoperating relay 4 closes the galvanometer circuit. Slow-operating relays 5 and 6 then operate in succession. The last energizes a magnet 19 depressing the pointer of the relay SR and cuts off the current supply to the bridge. The pointer controls the contact 20 which determines the condition of the heating and /or cooling apparatus and the slow-operating relay 7, also energized by the relay 6, cuts this contact into circuit and also two coils of a testing relay 9, one of which is in series with the contact 20. With the contact 20 not operated by the magnet 19 and galvanometer pointer, due to low temperature, the relay 9 will operate and lock up, thus stopping the fan and energizing the heating relay 22. Slow-operating relay 8 is energized also by relay 7 ; the testing relay is thus disconnected and a circuit for the vibrating relay 2 is closed ; relay 3 is energized by its left-hand contact. The bridge circuit is opened at a second point and relay 4 de-energized so that relays 4 to 8 inclusive restore in succession. The relay 2 is thus de-energized after an interval, whereupon it vibrates and sends impulses maintaining relay 3 operated for a period determined by the characteristics and adjustment of the relay 2, by which the temperature tests are principally timed. When the relay 3 eventually falls back potential is applied to the bridge and the cycle is repeated until the temperature is sufficient to cause contact 20 to be closed ; the differential winding of the relay 9 is then energized and its contacts drop, to cause the fan to operate instead of the heating sources. The modification shown in Fig. 2 is adapted to control the temperature in a resistance. The temperature testing comprises a main control resistance 64 which may be in sections in different rooms, a resistance 65 subject to the temperature of the source of heat and a resistance 63 subject to outdoor temperature, and its effect is to give anticipatory control action to a degree determined by the proportioning of the resistances 63 .. 65.