| 摘要 |
<p>An audible alarm device for use primarily with domestic freezers to provide an audible warning system as a malfunction of the freezer is disclosed. The device comprises a sensor circuit including a Wheatstone bridge having a negative temperature coefficient thermistor in one branch, and a high gain differential amplifier to sense voltage differential across the bridge, and a transistor between the amplifier and an audible signal device. A primary power source normally powers the circuit with low voltage direct current from a transformer having a rectified secondary winding, and the device also has a secondary power source of low voltage direct current which comprises a battery providing reserve power for powering the circuit and activating the alarm device upon failure of the primary power source. In use, the thermistor which is positioned directly within the freezer compartment senses temperature increase in the compartment and triggers activation of the audible alarm and as an indicator of freezer malfunction.</p> |
