| 摘要 |
A circuit for activating an alarm device, for example a buzzer or a lamp, with a predetermined period, is insensitive to noise pulses in the circuit. An input of a reference voltage generating circuit (7) is driven by the output contact of a relay (2), the exciter winding of which is controlled by a comparator. The inverting input of the comparator (1) is connected to the output of the reference voltage generating circuit (7). A time constant circuit (3, 4) is provided between the contact (2a) of the relay (2) and the non-inverting input of the comparator (1). The delay time of the relay (2) is utilised as protection against noise voltages. <IMAGE>
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