| 摘要 |
A signal amplitude monitor and relay driver circuit. The input signal is applied to a plurality of diodes connected in series with a set of normally closed relay contacts and a first resistor. A second resistor is connected in parallel with the series connected diodes through a set of normally open contacts of the relay. A third resistor is connected in parallel with the combination of the first resistor and normally closed contacts. A transistor circuit is connected with its emitter-base circuit responsive to the signal developed across the first resistor. The transistor output drives an amplifier which energizes the relay coil. When the normally closed contacts are closed the input signal must exceed a first predetermined level before the transistor circuit becomes conductive causing the amplifier to energize the relay coil. When the relay operates the first resistor is taken out of the circuit because the normally closed contacts open, and the second resistor is connected in the circuit because the normally open contacts close. Under these conditions the transistor circuit will remain conductive until the input signal falls below a second predetermined level, the second predetermined level being lower than the first predetermined level.
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