| 摘要 |
PURPOSE:To easily detect an operating voltage being applied to a terminal device and to facilitate installation construction and maintenance by dividing an applied source voltage and comparing it with a reference voltage, and deciding their large-small relation and turning a pilot lamp on and off. CONSTITUTION:The source voltage applied to a terminal T1 is divided by a variable resistor Rv and compared by a differential amplifier 1 with the reference voltage Vr applied to a terminal T2; when the input voltage Vi of the differential amplifier 1 is larger than the reference voltage Vr, a positive voltage is applied to an inverter 2 when smaller, a negative voltage is applied. The same voltage as the 'H'-level voltage of the output of the inverter 2 is applied to a terminal T3 and a light emitting diode 3 lights when the output of the inverter 2 is at 'L' level (in grounded state), but does not light when at 'H' level. For the purpose, the variable resistor Rv is adjusted to let Vi=Vr when the applied source voltage is as high as the minimum operating voltage of the terminal device, thereby easily knowing the applied source voltage being sufficient on the light emitting diode 3.
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