| 摘要 |
A portable test instrument for testing electrical continuity, and diode polarity, AC and DC voltage amplitudes and DC voltage polarity. An electronic switch device has main electrodes connected in an indicating circuit with an electrical supply, a light-emitting diode and a current-limiting resistor. A double pole, double throw switch is manually switchable between continuity and voltage test positions, and with four resistors defines an input circuit interposed between the control electrode of the electronic switch device and probes connectible to a circuit or the like to be tested. In both the voltage and continuity test modes of the instrument, the light-emitting diode is energized only by current from the electrical supply within the indicating circuit. Though proper circuit operation is obtained by manual manipulation of the mode switch between its voltage and continuity positions, the light-emitting diode is automatically protected from damage should the test probes engage a voltage circuit (within the operating voltage range of the instrument) while the instrument is in continuity mode.
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