Patent GB-906703-A (GB)
Title: Improvements in or relating to systems for remote supervisory control of plant and equipment
Inventor: MONTGOMERIE, GEORGE ALAN
IPC: G05D3/12
Filed: 1959-05-13
Abstract: 906,703. Electric selective signalling systems. SERCK Ltd. May 2, 1960 [May 13, 1959], No. 16386/59. Drawings to Specification. Class 40 (1). General.-In a remote control and supervisory system the control end comprises means for transmitting sequentially to the plant end one or more selection pulse trains which comprise redundant pulses followed by pulses characteristic in number of the channel to be selected, and the plant end comprises means for transmitting back a verification pulse train characteristic of the actual channel selected, and means is provided at the control end for determining from the selection and verification trains whether or not the channel selected is the desired one, and if so causing an activation signal to be transmitted to operate a device connected to the channel selected, and if not, to prevent the transmission of an activation signal. The system described is constructed entirely from transistor NOR gates except for output contactor relays at the plant end. Operation.-The channels are selected in sequence for control and indication purposes or one particular channel is selected by a pushbutton to be repeatedly monitored until the button is released. In the former mode of operation, one of thirty-two channels is selected by a counter-controlled scanner, clock pulses are supplied to a further counter (called a d stributer) and are transmitted as the selection train until the count registered in the distributer corresponds to the channel marked by the scanner. The selection trains comprise 45 redundant pulses followed by the characteristic pulses interleaved with groups of 5 further redundant pulses so that a total of 45+6n pulses are transmitted to select channel n. A distributer at the plant end, similar to that at the control end counts the pulses of the selection train, and if the number of pulses received lies between 3 less and 2 more than the total number allocated to the desired channel, selection of the correct channel takes place, and if not, an incorrect selection occurs. At the end of the selection train, detected by the absence of five consecutive pulses, clock pulses are supplied to the plant end distributer and are also transmitted (as the verification train) to the control end where they are supplied to the distributer. The plant end distributer causes transmission of the verification train to be stopped when its count reaches 298, its capacity being 299. If the control end distributer stands at zero + 0-5 at the end of the verification train as it should if correct selection has occurred, an activation pulse or pulse train is transmitted to the plant end where it is routed to operate a device in the selected channel, e.g. a valve or motor, and also to permit information concerning the channel to be transmitted back to the control end. This information may, for example, be a train of pulses representing in number the value of a variable such as temperature or rate of flow or the " on " or " off " positions of a valve. The value of the variable is transmitted to the control end by transmitting a pulse train of variable frequency for a predetermined time, e.g. while the plant end distrubuter is stepped from 48 to 298 by clock pulses. The control end distributer having been reset (if it was not already zero) at the end of the verification train now counts the pulses of the information train, and when this train is completed, gating circuits previously primed by the scanner are opened to supply the output of the distributer to light lamps giving a numerical or other e.g. " on " or " off " display of the variaable. The number of pulses in the information train is preferably such that the distributer is always stopped in its second cycle, an odd number of cycles of the distributer being detected and the lamps being extinguished to prevent an incorrect indication being made. The cycle is then repeated for the next channel in the scanning cycle. If a push-button is pressed, however, the channel selected is repeatedly monitored to provide an indication of the associated variable, and the automatic scanner is prevented from stepping on after each cycle. When the button is released, scanning may recommence where it left off or begin at the start of the scanning cycle. If a fault occurs in a channel during an automatic scanning cycle, the faulty operation is detected and the indicator lamps of that channel are extinguished, the scanner then selecting the next channel. If the fault clears itself the indication is restored when the channel is sampled in the next cycle. If the channel selected by a push-button becomes faulty, the indication remains extinguished until the fault is cleared.