Patent GB-865237-A (GB)
Title: Improvements in or relating to electrical supervisory equipment
Inventor: WEIR DONALD ADAMS
IPC: H03M1/00
Filed: 1958-06-20
Abstract: 865,237. Electric selective-signalling systems. STANDARD TELEPHONES & CABLES Ltd. June 19, 1959 [June 20, 1958], No. 19832/58. Class 40 (1). A multiplex system for monitoring the condition of a number of measuring devices each producing an electrical output dependent upon the parameter being measured comprises means for cyclically scanning the measuring devices, equipment for converting the scanner output to an electrical digital code combination, and means for storing said code. General operation.-Voltage pulses received from a cyclic scanning of 600 thermocouples are amplified and passed to a digitizer to be transformed into binary numbers representative of the temperatures at the thermocouples. Each temperature number passes to a logic circuit which compares it with preset data, and from data of the previous cycle determines the rate of increase of temperature, an alarm being sounded if certain limits are exceeded. The data is also recorded on punched or magnetic tape. A large store holds data for the last four cycles, and should an alarm be given this is fed to a high-speed magnetic/punched tape. Numerous pieces of apparatus are duplicated to provide checking means. Detailed description.-Pairs of thermocoupled TC1 . . . TC600, Fig. 1A, are connected in turn through three hundred pairs of contacts, e.g. SA1, SA2, to two amplifier systems, each comprising a pair of amplifiers in parallel, e.g. DCA, DCB, and a comparator CA to check that the amplifiers give the same amplification of one pulse. An alarm is given if discrepancies occur. These two systems are connected to a point K through two contacts α, #, which are synchronized with switches SA1, SA2 . . . to produce a succession of six hundred voltages, one for each thermocouple, in turn at K. Each voltage passes through two binary digitizers DA, DB whose outputs are compared by a comparator CC which sounds an alarm if a significant difference is detected. A switch ASD1 is synchronized to select one of the 600 rows of a ferro-magnetic store SS each corresponding to a particular thermocouple, and as the binary number passes to a logic circuit LC, the corresponding temperature of the previous cycle, and its rate of change, also pass to LC from store SS. In addition, preset limits pass from switches PD to the logic circuit. As well as passing to the logic circuit, the data of SS passes to a row of a 2400 row store LS, selected by contacts AS2 synchronized with AS1, which row has been cleared prior to the entry of new data. Store LS has four rows for each thermocouple and so stores data for four previous cycles. The logic circuit operates, in known manner, to compare new temperatures with a predetermined limit, to subtract the new temperature from the old and shift one place to the right to find average rate of increase per minute, (since one complete cycle takes 2 minutes), and to compare these results with predetermined limits and to sound an alarm should these limits be exceeded. The new temperature and its rate of change is fed into store SS, to give in combination with LS a recording of the temperatures at all the thermocouples over the last ten minutes, i.e. the last five scanning cycles; the new information is also converted to decimal form by CV1 and passed to buffer stores OBCA, OBCB, OBCC, until it is required for printing or punched tape, the time may also be printed from a timer TCC. When an alarm occurs all data in the store LS is printed out via converter CV2 and buffer OBCD by a high-speed punch or magnetic tape machine. Switch AS3 is controlled so that it runs in time with AS1. Should two alarms be sounded successively, in which case the tape printer would be in use from the first alarm, AS3 is stopped at the row related to the second alarm, so acting as a marker, and allows further printing out when the printer has completed its operation with respect to the first alarm. The digitizer.-When a thermocouple 1, Fig. 2, is selected a pulse from the scanning control equipment 2 starts a saw-tooth generator 3 which feeds a linear rising voltage to a comparator 7 and supplies a start pulse to a binary counter 4. The counter counts oscillations from the oscillator 5 until it receives a stop pulse from the comparator which is supplied when the voltages of the scanning circuit and the saw-tooth generator are equal. Thus the binary number is directly proportional to the input voltage from the thermocouple. In a modification two comparators are used to further accuracy. Specification 796,488 is referred to.