Abstract: Disclosed is a low current binary input subsystem for providing a binary input signal to a data acquisition system. The binary input subsystem monitors the open/close state of a field contact and provides galvanic isolation of noisy field contacts, high noise immunity, a steady state current of approximately 1.2 milliamps resulting in power dissipation of approximately 0.25 watts for a 125 VDC input, and a momentary high current pulse of approximately 150 milliamps for a duration of approximately 4 milliseconds during field contact closure to aid in cleaning of oxides from the field contact.

Abstract: A fiber optic data interchange network comprising a plurality of nodes, or drops 10a, 10b, 10c . . . , interconnected by fiber optic cable 12 (FIG. 1 ). Encoded data signals originating at any node are circulated around the network, allowing multipoint (or multidrop) data interchange. Each node includes a data encoder, transmitter, fiber optic receiver, data decoder, clock recovery circuit, and a repeater, i.e., a combination of the fiber optic receiver, an invertor (providing pulse width distortion correction) and the fiber optic transmitter. Thus each node is capable of originating data transmissions and receiving/relaying transmissions from a preceding node.

Abstract: A differential protective relay system includes protective relays 19A and 19B at the terminals of a protected transmission line segment 21. Analog signals QL1 and QL2 are sampled at the respective ends of the protected line segment 21, digitally encoded using delta modulation and biphase-mark encoding, multiplexed and transmitted over a 1.544 Mbps T1 communication channel 20 to the other end of the line where they are decoded and compared with the local signal at that end. Power is removed from the protected line segment if the difference between the local and remote signals exceeds a predefined value. Biphase-mark encoding is employed so that a clock signal may be recovered from the decoded signals.