Frost sensor employing self-heating thermistor as sensor element
AssigneeEaton Corporation
InventorJames R. Jaeschke
Life of this patent
Estimating the term…
Abstract
A frost sensor circuit which employs a thermistor (10, 20) to sense the amount of frost present on the cooling coils of a refrigerator, air conditioner, or the like, and to inhibit defrosting that would otherwise occur at regular intervals, in those cases where the frost present is not enough to justify a defrost function thereby to limit defrost heating to those cycles requiring it, thus saving electrical energy. This is done by mounting the thermistor at or on the coils to collect the same amount of frost as the coils and to have the defrost cycle control (11) energize the same for a timed interval, melting the frost thereon and thereby determining the amount of frost build-up.
Claims22
In a cooling system having cooling coils, a defrost heater for defrosting said coils, and a defrost cycle control for periodically energizing said defrost heater from an electric source to defrost said coils, a frost sensor circuit comprising:
- impedance means, the value of which changes according to its temperature, located so as to collect substantially the same amount of frost as said cooling coils;
- and
- a timing circuit, including switching means for energizing said defrost heater at the end of the time interval measured by said circuit, connected with said impedance means in circuit with said defrost cycle control and said defrost heater;
- such that if sufficient frost is present on said coils to justify a defrost cycle, said switching means energizes said defrost heater after said time interval measured by said timing circuit, whereas if insufficient frost is present, said impedance causes disabling of said timing circuit to prevent energizing said defrost heater.
In a cooling system having cooling coils, defrost means for defrosting said coils, and a cooling control system for controlling said coils and defrost means, a frost sensor comprising:
- a timer having "START" and "STOP" inputs, said "START" input being connected to said control system;
- first and second impedance means, in series between said timer and ground, one of said impedance means being located so as to accumulate substantially the same amount of frost as said cooling coils, the value of said one of said impedance means varying according to its temperature;
- and
- comparator means for comparing the voltage at the junction between said first and second impedances with a predetermined voltage supplied by said control system, and for energizing said "STOP" input of said timer when said junction voltage reaches said predetermined voltage;
- such that said "START" input is energized at the same time as current begins to flow from said timer output through said first impedance, the heat from said current melting any frost accumulated on said impedance, and when that frost is melted said comparator energizing said "STOP" input of said timer, which in turn indicates to said control system the amount of time necessary for said defrost means to be energized in order to defrost said cooling coils.
In a cooling system having cooling coils, a defrost heater for defrosting said coils, and a defrost cycle control operable to normally periodically energize said defrost heater, means for inhibiting defrosting when frost accumulation is insufficient to require it, thereby to save energy, comprising:
- frost sampling means, located so as to accumulate substantially the same amount of frost as is accumulated on said cooling coils, and responsive to the operation of said defrost cycle control for sampling said frost;
- and
- control means for inhibiting said defrost cycle control from energizing said defrost heater if the amount of frost accumulated on said frost sampling means is less than a predetermined amount.
Dependencies are inferred from the claim text.