Patent GB-893525-A (GB)
Title: Improvements in or relating to telemetering systems
Inventor: DAVIES ALEXANDER ORME
IPC: G08B25/00
Filed: 1959-10-31
Abstract: 893,525. Telemetering. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Oct. 27, 1960 [Oct. 31, 1959], No. 37029/59. Class 40 (1). In a telemetering system in which electrical pulses whose duration represents the value of a measured electrical quantity, e.g. the output of an electrical machine, are transmitted from a remote station to a control station where they are converted into an electrical quantity which represents the measured quantity and which is indicated on a display device, pulses continue to be transmitted if the value of the measured quantity falls to zero, and means are provided at the control station for recognizing the absence of pulses as an indication of failure in the system. A number of electrical quantities to be monitored may be cyclically connected by a scanner to a common transmitter at the remote station, the output of the pulse converter at the control station being connected by a distributer to each of a similar number of display device circuits in turn. Remote station. Transmitter. Fig. 1.-A high-speed telegraph relay 1A controlled by the difference in anode currents of valves VT1, VT2, is in the condition shown when the grid of VT2, which is biased by connection to 50 v. positive, and on which signal voltages are impressed via lead ML, is more positive than the grid of VT1. A capacitor C1 charges from a 90 v. source until its charge, which is applied to the grid of VT1, exceeds the voltage on the grid of VT2; during the charging period a relay X remains energized causing a pulse to be transmitted along a lead SL. When the current in relay 1A reverses, relays AX and AY come up and relay X releases, terminating the pulse. C1 quickly discharges through a low-value resistor R6, and the grid of VT1 is placed at the potential of the junction of resistors R7, R8, shunted across the 50 v. supply, which potential is lower by the voltage drop in R7 than the minimum potential on the grid of VT2, i.e. that when the signal voltage on ML is zero. Relay AX releases slowly to provide an inter-pulse period of constant duration. Scanner.-Each time AX comes up, 50 v. is applied via a lead DL to a counting-chain, Fig. 3, comprising relays A, B, ... N, which are energized in succession and which prepare circuits for relays AS, BS, ... NS, which come up when AX releases to connect signal voltages on lines MAL, MBL, ... MNL in turn to lead ML. At the (N+1)th inter-pulse pause, relay L is energized, followed by relay LS which connects ML via a lead LSL to a voltage higher than any signal voltage. This produces a synchronizing pulse the length of which may be further increased by connecting an additional resistor in the charging circuit of C1 Next, relay S comes up, followed by relay SS which disconnects LSL from ML, causing a " zero " pulse to be transmitted, and releasing relays A . - - L and ultimately S and SS. Control station. Receiver. Fig. 2.-Each signal pulse operates relay AR to connect a capacitor C2 to a 90 v. charging circuit and to energize a relay BR which in turn energizes a slow-releasing relay PF. At the end of the pulse AR releases, transferring the charge on C2 to a capacitor C3, and thus applying it to the grid of valve VT3, the anode of which is connected to one terminal of a voltmeter VM, the other terminal of which is connected to the tapping-point of a potentiometer R15 placed across 250 v., which is adjusted to enable VM to show a zero reading when the shortest pulses are received. Failure to receive a pulse for a period beyond the delay time of relay PF causes contacts pf to operate to discharge C3 through a resistor R16; this produces a negative indication on VM and disconnects a lead AL from 50 v. positive, setting off an audible alarm. Distributer, Fig. 4.-At the beginning of each inter-pulse period, 50 v. positive is applied via lead RL to a counting-chain comprising relays RA, RB, ... RN which prepare circuits for relays RAR, RBR, . . . RNR, which operate at the end of the inter-pulse period to connect capacitor C2 (Fig. 2) in turn to individual capacitors C3, each associated with a voltmeter circuit. Also during each pulse-pause, a relay PFA is energized; this relay has a slugging circuit C6, R17 which prevents it from falling back during signal pulses but permits it to so do during the long synchronizing pulse, when contacts pfa open to unlock the counting- chain. During the next pause, relay RS operates to prepare a circuit for relay RSR, which operates during the " zero " pulse to prepare a circuit for relay RA to commence a new cycle.