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US 5,214,310 AGranted
Timing mechanism with a PTC thermistor
AssigneeEmerson Electric Co.
InventorGeorge W. Adams
Life of this patent
Estimating the term…
Abstract
A timing mechanism has cams operating switches which control the functions of an appliance and another cam operating another switch supplying short pulses to a separate function such as a warning buzzer. A PTC thermistor is in series with the switch supplying the short pulses which when applied to the buzzer electrical circuit provides a short controlled "on" time to the buzzer even though power is applied to the complete switching system for an extended period of time by the timing mechanism.
Claims4
A method for controlling a load in an appliance to indicate end of an appliance function cycle, comprising the steps of:
- (a) controlling the appliance function cycle with a first cam means and first switch means responsive to said first cam means;
- (b) controlling application of power to a PTC thermistor with a second cam means and second switch means responsive to said second cam means;
- (c) providing said PTC thermistor connected in a series circuit with said second switch means, the load and a bleeding resistor connected in parallel with the load;
- (d) adjusting current flow through said PTC thermistor and thereby the time required for said PTC thermistor to internally heat and reach an abrupt increase in resistance with said bleeding resistor;
- (e) switching power "off" to the load by said PTC thermistor abruptly increasing resistance as a result of internal heating caused by current flow through said PTC thermistor to the load and said bleeding resistor;
- and,
- (f) switching power "on" to the load by said PTC thermistor abruptly decreasing resistance as a result of internal cooling caused by decreasing current flow through said PTC thermistor to the load and said bleeding resistor.
4 more elements
Dependencies are inferred from the claim text.