Patent ID: 6870902

Claim:
A telecommunications customer services terminal comprising: an input for connection to a telephone exchange; a plurality of outputs; each of said outputs including a tip/ring pair for connection to one of a plurality of telephone lines, each telephone line having a tip lead and a ring lead; a plurality of interface circuits; each of said interface circuits providing telecommunications services between said input and one of said plurality of outputs; test means for selectively applying test conditions to at least one of said interface circuits, and/or to an output that is associated with said at least one interface circuit, and/or to a ring/tip pair that is associated with said at least one interface circuit, and/or to a telephone line that is associated with said at least one interface circuit; said test means including; an analog-to-digital converter having a reference input, an analog measuring input, a ground potential input connected to a source of ground potential, and a multi-bit digital test results output for providing a test-results output; a normally-de-energized calibration relay having first and second normally-closed switches and first and second normally-open switches; a reference voltage connected to said reference input by way of said first normally-closed switch; means including said second normally-closed switch connecting said analog measuring input to an analog voltage that is generated by said test means; and calibration switching means for temporarily energizing said calibration relay, to thereby temporarily connect said analog measuring input to said reference voltage by way of said first normally-open switch, to thereby temporarily connect said reference input to said source of ground potential by way of said second normally-open switch, and to thereby temporarily generate a multi-bit digital calibration output for use in thereafter determining said multi-bit digital test results output when said calibration relay is de-energized.