Patent GB-907991-A (GB)
Title: Improvements in computing apparatus for railway marshalling yards
IPC: B61L17/00
Filed: 1960-03-14
Abstract: 907,991. Retarder control systems. WESTINGHOUSE AIR BRAKE CO. March 14, 1960 [March 27, 1959], No. 8869/60. Class 105. In a hump yard retarder control system in which an average value of rolling resistance is used to control the operation of group retarders when a measured value is not available, the average value is continuously modified in dependence upon available measured values of rolling resistance. Unit 10, Figs. 2 and 3, corresponds to a curved track rolling resistance computer of the type described in Specification 903,742, and produces between terminals c and d a signal representing the measured value of rolling resistance of each cut of vehicles descending the hump. If a cut leaves the preceding master retarder at the correct speed and if its length is within a predetermined limit, relay CLVP operates and as the cut enters a track section preceding that containing the group retarder relay TC releases and the measured value of rolling  resistance is applied via lead 30 to a group retarder control computer 32. If the cut does not meet the above conditions average values of rolling resistance for light, medium and heavy weight cuts, which are stored in a network including potentiometers 34 and 36 and battery 38, are available on leads 44, 58 and 50, respectively and the required value is selected by cut weight relays RLP and RHP which are energized respectively by light and heavy weight cuts and which are both energized by medium weight cuts. The required value selected by contacts f, relay RHP and contacts f and g, relay RLP, is passed via cathode follower V3, b.c. (back contact) a, relay CLVP, and b.c. a, relay TC, to computer 32. Since the stored average values should approximate closely the measured values and since the value of rolling resistance varies with weather conditions &c., the stored average values are compared and adjusted in accordance with measured values which meet the previously stated conditions. Assuming a light-weight cut a measured value of rolling resistance (Em) is applied via (front contact) f.c. a, relay CLVP, to one end of resistance network R1, R2 and the stored lightweight average value (Es) is applied via lead 44, f.c. g, relay RLP, b.c. f, relay RHP, cathode follower V3 and lead 108 to the other end of the network. The voltage at the junction of the two resistances and since the value of R2/R1+R2 is chosen equal to 0.11, the voltage Ed equals the stored average value plus 11 % of the difference between the stored and measured values. This voltage Ed represents the new average value of rolling resistance for light-weight cuts and is applied via f.c. d, relay RLP, to a storage unit 69 which is of the type described in Specification 853,908. When the cut enters the track section including the group retarder relay RITP picks up and energizes relay RL1 via f.c. b relay CLVP, b.c. a, relay RHP, f.c. a, relay RLP, and f.c. a, relay RITP. The cathode circuit of differential amplifier V2A and V2B, which includes V4  acting as a constant current device, is now completed via b.c. c, relay RHP, f.c. a, relay RL1, and b.c. b, relay RL2. The new average value appearing at output terminal c of storage unit 69 is applied to the grid of V2A via amplifier V1A and the stored average value, appearing at the cathode of valve V3 is applied via f.c. b, relay RL1, and amplifier V1B to the grid of valve V2B. Assuming the new value to be greater than the stored value the current through V2A and coil 74 is greater than that through V2B and coil 74a whereby differential relay 75 energizes to close contacts a and b. Relay RL3 energizes over these closed contacts and in picking up energizes relay RL2, these relays provide a holding circuit for relay RL1  at their front contacts a. In addition servomotor 66 controlling the tap of potentiometer 34 is energized via contacts a and b, relay 75, and f.c. b, relay RLP, and drives the tap to a new position in which it supplies the new stored average value of rolling resistance for lightweight cuts. When the tap reaches this position the equality in the voltages at the grids of V2A and V2B produces an equal current through coils 74 and 74a, whereby contacts a and b, relay 75, release, stopping the servomotor and releasing relays RL3 and RL2. When the rear of the cut vacates the track section preceding that containing the group retarded relays CLVP and RLP become de-energized whereby relay RL1 releases. In a similar manner the tap on potentiometer 36 is adjusted to provide a new stored average value for heavy-weight cuts. No adjustment is performed for medium-weight cuts. Specifications 903,741 and 903,743 also are referred to.