Frost and dew sensor
First Claim
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1. A frost and dew sensor comprising:
- (a) a thermosensitive resistor capable of generating heat by itself due to a given current supplied thereto, said thermosensitive resistor having a resistance varying according to the change of temperature of said thermosensitive resistor;
(b) a power source for changing the temperature of said thermosensitive resistor periodically, said power source including a variable constant-current source for alternately supplying a heat-generating current and a comparative reference current to said thermosensitive resistor, said comparative reference current being such that it causes a temperature increase of said thermosensitive resistor to only a negligible extent with respect to the temperature increase due to the heat-generating current; and
(c) an arithmetic circuit for fetching a temperature of said thermosensitive resistor as an output voltage according to a resistance corresponding to the temperature and for generating a frost-and-dew signal according to a difference between the output voltage during the heat-generating current is being supplied to said thermosensitive resistor and the output voltage during the comparative reference current is being supplied to said thermosensitive resistor, whereby the frost-and-dew signal is issued as presumed that said thermosensitive resistor is covered with frost or dew when a differential temperature of said thermosensitive resistor in such two durations is lowered.
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Abstract
In a frost and dew sensor composed of two thermosensitive resistors, a power source and an arithmetic circuit, frost or dew is detected from the change of a differential temperature between the two thermosensitive resistors as two different currents from the power source are supplied to the respective thermosensitive resistors. In an alternative form, the sensor has a single thermosensitive resistor, which is energized as two different currents are alternately supplied from the power source so that frost or dew is detected by comparison of the time-lags between the two outputs from the thermosensitive resistor.
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Citations
8 Claims
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1. A frost and dew sensor comprising:
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(a) a thermosensitive resistor capable of generating heat by itself due to a given current supplied thereto, said thermosensitive resistor having a resistance varying according to the change of temperature of said thermosensitive resistor; (b) a power source for changing the temperature of said thermosensitive resistor periodically, said power source including a variable constant-current source for alternately supplying a heat-generating current and a comparative reference current to said thermosensitive resistor, said comparative reference current being such that it causes a temperature increase of said thermosensitive resistor to only a negligible extent with respect to the temperature increase due to the heat-generating current; and (c) an arithmetic circuit for fetching a temperature of said thermosensitive resistor as an output voltage according to a resistance corresponding to the temperature and for generating a frost-and-dew signal according to a difference between the output voltage during the heat-generating current is being supplied to said thermosensitive resistor and the output voltage during the comparative reference current is being supplied to said thermosensitive resistor, whereby the frost-and-dew signal is issued as presumed that said thermosensitive resistor is covered with frost or dew when a differential temperature of said thermosensitive resistor in such two durations is lowered. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification