Thermostat with load activation detection feature
First Claim
1. A thermostat for an environmental temperature control system having an AC system power source, a temperature load comprising one or more members of the group consisting of heating loads and cooling loads to which electrical power from a low voltage side of the AC system power source can be selectively applied through latching relays, the thermostat being operatively coupled to the latching relays to selectively control the application of power from the low voltage side of the AC system power source to the temperature load, the improvement comprising the thermostat having:
- a sensor coupled to the temperature load and generating a first indicator signal indicative of power being applied to the load; and
a controller having a load sensing input and a load controlling output, the load sensing input being coupled to the first indicator signal for causing the load controlling output to pulse the latching relays when the sensed power applied to the load does not correspond to that selected by the thermostat.
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Accused Products
Abstract
A thermostat for control of an AC-operated HVAC unit (or a unit providing only heating or only cooling) is provided with load activation detection sensing for increased reliability of latching relay activation. The thermostat includes a sensing transformer in series with the heating or cooling load (or both, if both are in the system), so that, when activation of the load is called for by the thermostat, current flows in a primary winding of the transformer, inducing a current in the secondary winding. A voltage derived from the current in the secondary winding is sensed by the thermostat controller and used to determine whether the heating or cooling load has been properly activated or deactivated. Sensing of the AC power source in the HVAC unit may also be provided, so that the controller can confirm that the absence of the voltage derived from the current in the secondary winding is actually due to the state of the latching relays rather than to a failure of the AC power source. When the sensed voltage derived from the current in the secondary winding does not correspond to that expected when the latching relays are in their expected states, the thermostat controller provides additional pulses, twice as long in duration as the original pulses and emitted at spaced intervals, to attempt to correct the fault by placing the relays into their correct states. Power for the thermostat controller may be derived, at appropriate times, from the current flowing in the secondary winding.
119 Citations
22 Claims
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1. A thermostat for an environmental temperature control system having an AC system power source, a temperature load comprising one or more members of the group consisting of heating loads and cooling loads to which electrical power from a low voltage side of the AC system power source can be selectively applied through latching relays, the thermostat being operatively coupled to the latching relays to selectively control the application of power from the low voltage side of the AC system power source to the temperature load, the improvement comprising the thermostat having:
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a sensor coupled to the temperature load and generating a first indicator signal indicative of power being applied to the load; and a controller having a load sensing input and a load controlling output, the load sensing input being coupled to the first indicator signal for causing the load controlling output to pulse the latching relays when the sensed power applied to the load does not correspond to that selected by the thermostat. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A thermostat for an AC-powered environmental temperature control system comprising:
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a temperature sensor; a sensing transformer having a primary winding and a secondary winding, the primary winding being in circuit with a temperature load, so that when power to the temperature load from a low voltage side of the AC-powered environmental temperature control system is switched on, an alternating current flows through the primary winding to thereby induce a voltage across the secondary winding; a controller coupled to the temperature sensor and configured to provide a signal to selectively switch power to the temperature load in response to the temperature sensor, the controller also being coupled to the secondary winding and configured to sense the voltage across the secondary winding to confirm the switching of power. - View Dependent Claims (13, 14, 15)
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16. A method for controlling an environmental temperature control system with a thermostat, and having a temperature load powered by a low voltage side of the environmental temperature control system, the method comprising:
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pulsing a latching relay to control the temperature load to an operating state selected by the thermostat; sensing a current drawn through the temperature load to generate a signal indicative of an operating state of the temperature load; and repeating the pulsing step when the signal indicative of the operating state of the temperature load is inconsistent with the selected operating state. - View Dependent Claims (17, 18, 19, 20, 21, 22)
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Specification