| 摘要 |
A battery powered tester has an electrical testing circuit combining continuity, polarity, and voltage amplitude circuits. The testing circuit for measuring a test voltage or relative continuity has first and second inputs to which first and second test points can be respectively coupled by RED and BLACK prods. The continuity, polarity, and voltage amplitude circuits are coupled in parallel to the first and second inputs, the polarity circuit being symmetrically coupled to the inputs. The polarity circuit has first and second polarity lamps and a sensing circuit for lighting the first polarity lamp when the test voltage is positive and lighting the second polarity lamp when the test voltage is negative. The continuity circuit has a continuity lamp separate from the polarity lamps and a driving circuit for lighting the continuity lamp whenever a zero or low passive impedance is coupled to the first and second inputs. A transistorized switching circuit monitors the difference in voltage between the first and second inputs, and if the difference equals or exceeds a predetermined continuity limit voltage, the switching circuit disables the signal to the driving circuit. The voltage amplitude circuit uses a solenoid-type voltmeter coupled between the first and second inputs by a bilateral silicon switch to measure the absolute amplitude of the test voltage.
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