Hitachi, Ltd.

Nippon Telegraph and Telephone Public Corporation

Kenzo Tamaki

Takafumi Kojima

Shiro Yokota

A system for testing subscriber lines and terminals by leading the subscriber line to the testing system through an associated semiconductor switch of a type driven by a constant current. The system includes a circuit for varying a current fed through the switch from the subscriber line to be tested, a circuit for measuring current values corresponding to the circuit states of the circuit, and a circuit for determining on the basis of the measured values derived from the measuring circuit a current value from which the constant current component for driving the switch is eliminated.

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Yokohama, Japan

Kenzo Tamaki