Patent GB-501917-A (GB)
Title: Improvements in or relating to control devices comprising a galvanometer
IPC: H01H47/00
Filed: 1937-08-04
Abstract: 501,917. Automatic control systems. QUEYRAS, J. F. AUGIER-. Aug. 4, 1937, Nos. 21517, 21518, and 21519. Convention dates, Aug. 5, 1936, Aug. 14, 1936, and Aug. 14, 1936. [Class 38 (iv)] Electromotive force: temperature &c.-In a control system in which a contact carried by a deflectable member of a galvanometer cooperates with a fixed contact and controls an electromagnetic relay, normally closed contacts of the relay are arranged in series with the fixed and movable contacts of the galvanometer in the relay coil circuit so as to open this circuit when the relay is energized, and normally open contacts of the relay are arranged to close a holding circuit for the relay in shunt with the series circuit consisting of the normally closed contacts and the galvanometer operated contacts. The defection of the galvanometer is proportional to the value of a physical state or condition such as temperature or voltage. A galvanometer winding G in the circuit of a bridge one resistance, R4 of which is sensitive to temperature, controls a movable contact A operating between fixed contacts C2, C1. Contact C1 controls the energization of a relay 1 through a contact 16 and resistance 21. Operation of the relay closes a holding circuit over a contact 15 whilst contact 16 is opened. At the same time a contact 17 closes and a contact 18 opens, both contacts being in series and being closed together for a short time to permit the passage of a short pulse of current through the galvanometer winding G in the reverse direction to separate contacts A and C1 or, in a modification, in the same direction so as to separate them by elastic re-bound. Contacts 14 are closed to control the heating means in the appropriate direction. Closure of contact A on C2 causes short-circuiting of relay 1 over a contact 13. Relay 1 de-energizes and opens its various controlling and holding circuits, but at the same time operates contacts 11, 12 in series so that they are both closed together for a short period so as to send a "kick-off" impulse through the winding G to separate contacts A, C2. The relay may be de-energized by providing an additional winding of opposite effect to the energizing winding. The " kick-off " current may be obtained direct from the battery instead of through the contacts C1, C2. The galvanometer winding may be supplied from an A.C. source through a rectifier for controlling the voltage of the source. In a modification, re-bound of the needle A is obtained by momentary short-circuiting of part of a resistance in series with the A.C. supply to the rectifier when contacts equivalent to 17, 18 are closed together. In order to limit the "kick-off" torque, the holding circuit of the relay 1 may be interrupted periodically so that the condition to be controlled is tested at short intervals. The current in the galvanometer is interrupted in the intervals between tests. Such an arrangement, Fig. 7, controls the voltage of an A.C. circuit, in which a galvanometer of the single contact side zero type controls a relay 1 which, when energized operates contacts 15 to bring a voltage reducing means M into operation whereas normally voltage increasing means M1 are operative. The circuits of the means M, M1 of the relay 1 and of the galvanometer are controlled by contacts 21, 22, 23 periodically operated by a cam 2. The means M, M1 may be constituted by a reversible motor. " Kickoff " current, holding &c. circuits are provided as before. As applied to temperature control, a centre zero galvanometer operates two sets of contacts C1, C2, each of which controls n separate relay such as 1. The relays are electrically interlocked and separately control means such as M, M1 for raising or lowering the temperature. Cam-operated contacts are provided in the galvanometer coil and relay coil circuits. In an arrangement, Fig. 9, for voltage control a single contact galvanometer controls a relay 1 as above described. The relay controls, at contacts 15, a further relay 2 which controls regulating devices R, R1 at contacts 23, a holding circuit for itself at contacts 21 and a motor M at contacts 22. The motor M operates a cam 3 which controls contacts 31 completing the holding circuit of the relay 2, contacts 32 which open the holding circuit of the relay 1 and contacts 33 which shunt the contacts 22 of the relay 2. Thus, as long as the voltage is sufficient to energize relay 1, relay 2 remains energized and the motor rotates, although the relay 1 is de-energized at contacts 32 of the cam after each test. Cam contacts 33 ensure the return of the cam 3 to a fixed position after the relay 2 is de-energized. Relay 2 may be of the slow-acting type. In a modification, Fig. 10 (not shown), cam-operated contacts are replaced by the combination of a bi-metallic, heated relay and an electromagnetic relay so as to produce periodic closure of contacts on the latter which control the holding circuits of relays such as 1 and 2 in Fig. 9. Such a system is described in connection with a temperature control arrangement in which the galvanometer pointer operates between two contacts so that a set of relays such as 1 and 2 in Fig. 9 are provided for each contact, the two relays such as 1, Fig. 9, being electrically interlocked. The system may be used in a heating system in which three burners are used, all of which are operative when the temperature is below a desired value, one being operative when the temperature is above another desired value and two being operative when it is between these values. In a further arrangement in which a number of tests are made of the value of the condition, the sensitivity of the galvanometer is decreased after each operation of the controlling relay. Such an arrangement, Fig. 11, applied to a temperature controlling arrangement giving selective control of two relays 1, 2 comprises a galvanometer, the coil G of which is connected to a temperature sensitive bridge through resistances 7, 8. Resistance 7 is of sufficient value to render the galvanometer ineffective and is short-circuited periodically by a continuously driven cam C having two cam rises 5, 6 in order of operation, controlling contacts 51, 52 and 61-63 respectively. The arrangement is such that if, when contacts 51 are closed by cam 5, the temperature is such that arm A contacts with contact C1, relay 2 is energized and thereafter held energized over a circuit including cam contacts 51. Relay 2 initiates the control action at contacts 28 and opens contacts 26 which insert resistance 8 in the galvanometer circuit to reduce its sensitivity. A " kick-off " impulse is also produced. The cam rise 6 closes contacts 61-63 whilst contacts 51-52 are also closed for a short period. If, at this time, needle A is still in contact with contact C1, i.e. temperature is higher than reduced sensitivity of the galvanometer permits, a relay 4 is energized over contacts 51, 63 and contacts 27 of relay 2. Relay 4 closes holding circuits for itself over cam contacts 61, 63 and sends a further " kick-off " impulse through the galvanometer coil. It also closes a circuit over contacts 61, 45 and 21 which ensure holding of the relay 2. The regulating action of contacts 28 of relay 2 therefore persists over the period determined by the cam rise 6, after which the apparatus is re-set to normal and a further test repeated. Relays 1, 3 operate in a similar manner if contacts A, C2 are closed. If desired, additional cam rises may be provided and the sensitivity of the galvanometer may be reduced further in additional steps. This system is also described as applied to voltage control in Fig. 12 (not shown).