Patent GB-878475-A (GB)
Title: System for telemetering a plurality of values of vaniable magnitude over a single transmission line
IPC: G08C15/00
Filed: 1959-04-17
Abstract: 878,475. Electric telemetering systems. ALLMANNA SVENSKA ELEKTRISKA A.B. April 17, 1959 [April 19, 1958], No. 13121/59. Class 40 (1). [Also in Group XL (c)] A system for telemetering the values of several variables each of which has been converted into a proportional D.C. voltage, comprises a transmitter consisting of a free-running transistor multivibrator, the duration of each state being proportional to the amplitude of one of the measuring voltages as selected in a particular sequence by a stepping switch, and a receiver wherein voltages proportional to the duration of each pulse and each interval separately are directed by a stepping switch to an appropriate amplifier and meter, each variable being transmitted as at least one pulse and one interval in the series, and the receiving amplifiers adding their values to give continuous indications. A special pulse and interval is sent to ensure synchronism. Transmitter (Fig. 1).-The measuring voltages in transducers MG1-MG4 are connected as shown to the terminals of two banks VS1, VS2 of a stepping switch VS. The multivibrator comprises two transistors 13, 14 and associated components, including a polarized relay SR. Initially a capacitor 2 is being charged from terminal 6, the charging current flowing through the base circuit of transistor 14 to make it conductive. As the collector of transistor 14 is substantially at zero potential, diode 16 is also conductive, and capacitor 1 is short-circuited by diode 16 and transistor 14 so that transistor 13 is non-conductive. When the voltage across capacitor 2 is equal to that at first input terminal 12 diode 10 becomes conductive, the charging current stops, transistor 14 becomes non-conductive, its collector potential is equal to that at terminal 19, so that diode 16 ceases to be conductive, and capacitor 1 starts to charge, making transistor 13 conductive. This continues until the voltage on capacitor 1 is equal to that at the second input terminal 9, when the transistors change over again. When transistor 13 is conductive, current flows through the left-hand winding of relay SR to close contacts SR1-SR3, sending a pulse along line 22, whose duration is equal to the charging time of capacitor 1, which is substantially proportional to the voltage at terminal 9. When transistor 14 is conductive, current flows through the right-hand winding of relay SR to open contacts SR1-SR3, and an interval is transmitted along line 22 whose duration is equal to the charging time of capacitor 2, which is substantially proportional to the voltage at terminal 12. The stepping switch VS1, VS2 is moved each time contacts SR3 open, i.e. after each pulse on line 22, so that with the connections shown a series of five intervals and pulses are transmitted along line 22, proportional to the signal voltages in transducers MG1-MG4 in a predetermined sequence, each signal being repeated in at least one interval and one pulse. The switch VS homes to position 0, where a fixed 20 volts is connected on bank VS2, and contacts VSH are open to reduce the charging current to capacitor 2 and produce a very long interval followed by a short pulse determined by the 5 volts connected to diode 23. This pulse period at the homing position is used to synchronize the receiver. Receiver (Fig. 2).-The measuring pulses and intervals are received on line 38 where they selectively operate relays MR, OR, UR, SYP and SYJ, so that a capacitor 26 is charged at a constant rate for the interval durations, and a capacitor 27 is charged at a constant rate for the pulse durations, the voltages being transferred to appropriate amplifier K1-K4, each of which stores the sum of its two inputs and indicates the value on a meter 32. The receiver stepping switch VM is stepped at the end of each pulse. When it reaches the homing position 0, only the very long interval and short pulse sent to synchronize the receiver can act on lagged relay SYP to step the switch VM to its next position, whilst contacts SYP3, SYP4 open to prevent erroneous signals being sent to the amplifiers K1-K4. If the synchronizing signal is received when the switch VM is not in the homing position the lagged relay SYP operates during the extra long interval to disconnect the amplifiers K1-K4 and step the switch by its self-driving contact VMS to the homing position, hence re-establishing synchronism.