PURPOSE: To obtain a lightweight, soundless, long-life and highly reliable polarity detecting circuit, by forming a calling loop of a communication line in a test device, and using a photocoupler as a detecting element of the current flowing into the calling loop.
CONSTITUTION: Since rectifiers D0, D1 are actuated in the forward and backward directions respectively when the polarity detecting circuit 1 is connected to a calling current supplying circuit, the current is made flow into a light emitting diode of the photocoupler PCO, a photodetecting transistor(TR) of the PCO is conducted, a terminal POL-E is earthed, and the information is sent to the test device. Since the current is not made flow into a light emitting diode of a photocoupler PC1, a photodetecting TR of the photocoupler PC1 is not conducted, +5V is applied to a terminal POL-F and the information is sent to the test device.
| JPS59226550 | DIGITAL CONFERENCE TESTING SYSTEM |
| JPH06338910 | PRIVATE BRANCH EXCHANGE |
| JPS6039964 | TEST SYSTEM OF EMERGENCY CONTROL CIRCIUT |
YAMAMOTO KUNIO
NAKADA HIROSHI
| JP49080608B | ||||
| JPS57111161A | 1982-07-10 |
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