Importance

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Abstract

A balancing resistor and thermistor network for telephone circuits, and combination with an external relay, which reliably handles all three levels of adverse conditions, automatically resets under certain conditions, is physically small in size, and is strong. It is a flat ceramic substrate on both surfaces of which are screen-printed thick-film balancing resistor films. Also screen-printed on both surfaces are termination traces having portions so located that when the substrate substantially instantaneously fractures it reliably and substantially instantaneously breaks the circuits through the resistive films, the fracture occurring in response to a sudden high-voltage overload. Accordingly, there is no damage to, or melting or burning of, small wires in the telephone circuits at points near to or remote from the balancing resistor network. A thermistor film is screen-printed directly onto the substrate at a central region where there is no resistive film. The thermistor is connected to a relay and its associated circuitry on the telephone line card (circuit board), acting as a sensor to control the relay so that the latter resettably interrupts current flow through the entire circuit board and thus through the balancing resistor network.

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First Claim