Patent GB-408625-A (GB)
Title: Improvements in or relating to traffic signalling systems
IPC: G08G1/085
Filed: 1932-10-08
Abstract: 408,625. Valve circuits. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and ESPLEY, D. C., c/o General Electric Co., Wembley, Middlesex. Oct. 8, 1932, No. 28067. [Class 40 (v).] In impulsers and timers for the operation of traffic signals the timing element includes a thermionic tube and the period of the device is determined by the values of a condenser C, resistance R and the operating current of a relay A in the anode circuit of the valve, the resistance R being in series with the condenser C. The arrangement is supplied with D.C. from a potentiometer P and one terminal of the condenser C and one end of the resistance R are connected to different points on the potentiometer. In an impulser, shown in Fig. 1, the thermionic valve is connected across part of the potentiometer P, the junction of the condenser C and resistance R being connected to the grid of the valve, a switch a<1> in series with a resistance r being arranged to short circuit the condenser C when the relay A operates. With a<1> closed the grid of the valve is made negative and relay A is de-energised. The condenser C now charges up through the resistance R and raises the grid potential until the anode current is sufficient to operate the relay A and close the contact a<1> when the cycle begins again. Auxiliary contacts on the relay A operate external apparatus. In order that the period of the arrangement may be independent of the supply voltage the operating current of the relay A is so chosen that when the supply voltage is normal the grid voltage which corresponds to the relay operating current is given by v1 = - E1/m, where v1, is the requisite grid voltage, E1 is the normal anode voltage and m the magnification of the triode. This condition can be satisfied by choosing the position of the point P on the potentiometer, i.e. by choosing E1. The duration of the impulse delivered to the external circuit by the relay A may be adjusted by variation of the discharge resistance r of the condenser. An impulse winding on the relay A may be connected in series with the resistance v. Where the arrangement is used as a timer whereby it performs only one cycle of operation a signal operates a relay which closes the energizing circuit of the arrangement whose relay A operates after a predetermined period and closes the contact a1 and also a contact a2 (not shown) in the circuit of a holding winding on the relay A. The holding circuit is only opened on the arrival of a second signal which operates a contact in the holding circuit. This contact and that effecting initial energization may be controlled by the same or different relays. A contact may be included in series with the resistance R which contact is controlled by an impulse so that the period of the timer is increased by the presence of this contact in the ratio of the whole period of its controlling impulse to the duration of an impulse. The cathode of the thermionic valve may be supplied in series in the potentiometer circuit P provided the period of the circuit is longer than the time required for heating up of the cathode. In a modification, Fig. 3, the grid potential of the triode is fixed and the condenser voltage is impressed upon the anode of the triode. When the arrangement functions as a timer the relay controlling contact c<1> for energizing the circuit also controls a contact c<2> in shunt with the condenser C so that when contacts c<1> are closed, contacts c<2> are open and vice versa. When the arrangement is to function as an impulser the contact c<2> is permanently open and contact c<1> closed. This modification operates by raising and lowering of the anode potential of the valve and the condition of independance of the period of the circuit and the supply voltage is obtained by choosing the potentiometer tappings so that e = - V1 /m where e is the fixed grid voltage with normal supply voltage, V, the anode voltage necessary, with normal supply voltage, to operate the relay A. British Specifications 260,291, [Class 40 (v)], 349,983 ; 355,666, [Group XXXV] ; 395,373 and 408,624, and U.S.A. Specification 1,869,500 are referred to.