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Two-wire signal transmission system

  • US 3,959,772 A
  • Filed: 06/17/1975
  • Issued: 05/25/1976
  • Est. Priority Date: 06/20/1974
  • Status: Expired due to Term
First Claim
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1. A signal transmission system of the type used in process control systems for conveying a signal between a field instrument and a central controller, or between a central controller and a process control device, comprising:

  • a transmitter arranged to accept an input signal;

    converter means in the transmitter for developing a pulse width signal with a duration corresponding in a predetermined manner to the value of the input signal;

    means in the transmitter for providing a transmission signal with two states, said means being responsive to the converter means to cause the duration of one of the transmission signal states to correspond to the duration of the pulse width signal;

    a transmission line for carrying the transmission signal;

    a receiver for receiving the transmission signal;

    means in the receiver for developing an output signal with a duration corresponding to the duration of the one transmission signal state, whereby the duration of the output signal corresponds in said predetermined manner to the value of the input signal;

    means, in one of the transmitter or receiver, for supplying power for the transmission signal; and

    means, in the other of the transmitter or receiver, for deriving operational power from the transmission signal;

    whereby the signal transmission system is able to convey signals less affected by noise, and is also able to convey operational power.

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