GB1024823A - Transmission and receiving system for signals representing process variables - Google Patents

Abstract

1,024,823. Electric measuring systems. HITACHI SEISAKUSHO KABUSHIKI KAISHA. Dec. 14,1962 [Dec. 16, 1961], No. 47298/62. Heading G1N. [Also in Division H4]. A system for transmitting and receiving a plurality of electric signals, representing by their frequencies a plurality of process variables, in turn through a single transmission line, comprises a plurality of gates which are selectively opened to transmit the corresponding signal through the line, the signals each having a different amplitude and a plurality of relays at the receiver selectively operated by the different signal amplitudes to switch the signals to the corresponding channels. An oscillator 3, has a coil 6 whose inductance is varied by the variable being monitored. A gate 9, is operated by an electronic switching circuit 7 through an amplifier 8 1 . The amplitude of the output from gate 9 1 is limited by Zener diodes 11 1 , and the output is passed through terminal b 1 to a common matching circuit and line L. A similar arrangement is provided for each variable, the amplitudes of the different outputs being limited to different levels. In the receiver the signal is rectified, amplified and applied to a circuit 18 including Zener diodes 17 1 , 17 2 , 17 3 and 17 4 , resistors R1, R2, and R3 of equal values, and resistors R1<SP>1</SP>, R2<SP>1</SP>, R3<SP>1</SP> and R4<SP>1</SP>. The lowest amplitude signal is arranged to be sufficient to make diode 17 1 conductive. The voltage drop across R1<SP>1</SP> then appears between terminals C1, C2, and differentially connected transistors 20 1 , 20 2 operate to close relay 22 1 and close the circuit of meter 14 1 . This meter then receives the output from frequency-voltage converter 13. Similarly the next lowest amplitude signal makes diodes 17 1 and 172 conductive so that a voltage drop exists between terminals C2, C3 to close the circuit of meter 142, and so on. Oscillators 3 may produce sine waves or pulses. Switch 7 may be selectively operable, or may switch at a constant speed.