| 摘要 |
PURPOSE:To provide a frosting detector provided with defrosting function and can be made electronically and compactedly with high reliability by utilizing the electrical characteristic of a thermistor of which the temp. is elevated by frosting in detecting frosting and performing defrosting. CONSTITUTION:When a power source V is turned on, the contact T1a of a timer T1 is made into electrical conduction for warming up an initially cold thermistor Th up to a reference temp. The contact T1a opens upon ending of the warming- up, then the contact T1b of a relay DF closes and the emission of a defrosting command is kept standing-by. The constant current in the thermistor Th balances with the ambient air temp., wind velocity, etc. and the thermistor maintains a specified temp. in the initial time when the current begins to flow to the thermistor. When frosts are successively deposited on fins 3, the temp. in the ambient is below the freezing point and therefore the frosts provide a odiabatic effect and the flow of the wind between the fins 3 is decreased. The quantity of the heat radiated from the thermistor Th is suppressed by the above-deseribed effect and decrease and the temp. of the thermistor Th rises. When the voltage of the thermistor Th drops to a prescribed voltage or below, the relay for defrosting command is energized, by which a defrosting device is driven. |
