Patent GB-801142-A (GB)
Title: Improvements relating to transductor trigger circuits
IPC: H03K3/45
Filed: 1955-06-20
Abstract: 801,142. Non-contact-making relays. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd., KING, K. G., and TUCKER, A. W. June 6, 1956 [June 20, 1955], No. 17715/55. Class 40 (9). A transductor with alternating current windings 2 supplies a load 5 with current proportional to that in the A.C. windings and has a feedback winding 3 supplied with D.C. from a rectifier 7 energized by a voltage proportional to that across the load 5, a saturable impedance 8 being connected in series with the A.C. terminals of the rectifier such that the transductor is bi-stable. The transductor may be controlled by means of a D.C. winding 4, or by a control D.C. applied to the feedback winding 3, or by D.C. applied to saturate the impedance 8. The circuit constants may be chosen so that the transductor characteristic is symmetrical about the control current axis, in which case the transductor may be changed from one stable state to another by means of a D.C. control pulse of appropriate polarity, or the bistable part of the characteristic may be made to lie to one side of the control current axis so that to attain one stable state a continuous D.C. control signal must be applied. To reduce the effect of even harmonic flowing in the feedback winding 3, a resistor 9 may be included in series, a capacitor may be placed in parallel, or a short-circuited winding may be wound on the transductor core. To permit as good an insulation as possible for the A.C. windings these may be made of a few turns of heavy gauge and to achieve this separate transformer coupling between the A.C. source, the transductor cores, the load and the feedback rectifier is necessary (see Fig. 2, not shown). To protect the transductor cores from saturation due to increase in voltage or decrease in frequency of the A.C. supply, the A.C. may be applied to the circuit over a transformer having a sharply inclined saturation characteristic. A fuse may be included in the A.C. circuit. Alternatively, a resistance with a fuse in circuit may be used. If the load 5 includes a rectifier, deterioration of its forward resistance will increase feedback and the sensitivity of the trigger circuit will increase and produce spurious output signals. To avoid this the load 5 may be fed in parallel with a shunt resistance in the A.C. circuit such that the shunt takes most of the A.C. in the windings 2 (Fig. 3, not shown). Alternatively, the load 5 may be fed in parallel with the primary of a transformer, the secondary of which is connected across a shunt, or the load 5 may be placed across the secondary and the shunt across the primary. Where the load is isolated by transformer coupling, increase in sensitivity due to deterioration of a load rectifier may be offset by making the coupling transformer take a heavy magnetizing current. A further alternative, to reduce such an increase in sensitivity, is to incorporate the load rectifier in series with the feedback circuit or to connect the load in series or parallel with the output of the feedback rectifier 7. The choke 8 may be replaced by a saturable transformer 18, Fig. 5. connected with an unsaturable transformer 19 and fed in parallel with a resistor 13 in series with A.C. windings 2. When 18 is unsaturated secondary voltages from 18 and 19 cancel out.