Customer services terminal method and apparatus for testing a plurality of interface circuits and telephone lines that are connected thereto

Abstract

Customer services terminal input connected between telephone exchange and outputs. Interface circuits provide service between input and outputs Test means applies test conditions to interface circuits and/or to outputs associated with the interface circuits, and/or to ring/tip pairs associated with interface circuits, and/or to telephone lines associated with interface circuits Other interface circuits service input to other outputs Test means analog-to-digital converter includes reference input, analog measuring input, ground potential input, and test output Normally de-energized calibration relay has normally-closed switches and normally-open switches. Normally-closed switch connects reference voltage to reference input. Another normally-closed switch connects analog measuring input to test means generated voltage. Calibration switching means energizes calibration relay to connect analog measuring input to reference voltage via normally-open switch, to connect reference input to source of ground potential via another normally-open switch to generate calibration output useful for determining test results output when calibration relay is de-energized.