GB776779A - Improvements in or relating to remote indicating systems - Google Patents

Abstract

776,779. Remote indicating systems. ELECTRIC & MUSICAL INDUSTRIES, Ltd. June 25 1954 [March 25, 1953], No. 8178/53. Class 40 (1). In a remote indicating system wherein information from a number of sources, e.g. meters and lamps, is transmitted to a receiving station by a multiplex transmitting system, there being provided at the receiving station means for reproducing the transmitted signals, check signals also representing the information are transmitted, so that information reproduced at the receiving station from the first-mentioned signals is cyclically checked. As shown, the signals to be transmitted are applied at 1 as analogue potentials to a high-speed selector switch 2, the check signals being applied to a low-speed selector switch 3 whose output is applied to the input of selector switch 2. The selector switch 2 may comprise rings of thermionic valves. A master frequency generator 4 through a selector timing device 5 controls switches 2 and 3, and also controls a pulse width modulator 6, providing pulses having widths proportional to the analogue potentials. The modulator 6 includes in its output circuit a differentiating circuit whereby for each signal a positive and negative pulse is produced having a spacing proportional to the analogue voltage, which are applied to a line 7. Synchronizing signals having a pulse width greater than the maximum analogue signal are applied at 30, and are separated from the signal pulses by a discriminator 10. The signal pulses are fed to a demodulator 16 and through a distributer 17 provide potentials at 17a corresponding to the analogue inputs. Synchronizing pulses are fed from the discriminator 10 to a ring counter 18 to control the distributor 17. To check for modulation and demodulation check potentials are applied to channels 20 and 21 at the transmitter, e.g. zero and a standard potential, and at the receiver the corresponding outputs are stored at 22 and 23 and compared with similar check potentials, an alarm being operated if the deviation exceeds a preset tolerance. To check the information provided at the distributer 17 the inputs 1 are also supplied to the low-speed selector switch 3 which samples in turns one input for every complete cycle of the selector switch 2, the check signals being supplied over channel 1a to be stored in the receiver at 24 and applied to a comparator 25. The output signals 17a are also applied to the comparator 25 via a low-speed selector switch 26 operating in synchronism with the switch 3 and controlled by synchronizing pulses supplied over a channel 27 via sync. separator 28. If the difference of the two signals at the comparator exceeds a preset tolerance an alarm C is operated. To avoid the possibility of raising a false alarm a channel 29 is used to inhibit the alarm system when an analogue potential is changing appreciably during one cycle of selector switch 2. Standby equipment may be brought into operation automatically by switches 30a, 31, at the transmitter and 32, 33, at the receiver.