Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Reexamination Certificate
1998-12-17
2001-03-20
Martin, David (Department: 2839)
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
C392S498000
Reexamination Certificate
active
06204623
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention relates generally to a device controller, and more particularly relates to a control circuit for variably controlling power to an appliance such as a heater, a humidifier and/or a fan.
2. Description Of The Prior Art
It is known in the art to control the velocity of a fan or power to a heater in response to changes in temperature and/or humidity. Generally, in a temperature control circuit, a transducer senses changes in temperature and a control circuit adjusts the power to a fan or power to a heater in response to the temperature changes. a humidifier control circuit generally has a humidity sensor and a control circuit that responds to changes in humidity by controlling the flow of air over a wick filter or by controlling the temperature of an evaporative water tank. The temperature and humidity control circuits typically include a triac which is used to control the AC power to the fan or heater.
Traditional control circuits consist of numerous discrete components. The use of discrete components tends to provide temperature and/or humidity control which is less accurate and less reliable. The poor accuracy is due to changing part tolerances and due to limitations within the discrete component circuit design.
Modem control circuits often include microcomputer type devices such as a microprocessor, a microcontroller or a digital signal processor. These control circuits typically result in improved accuracy and speed, but tend to be more costly. They involve numerous support logic such as address decode devices, memory devices and analog to digital converters, which increase the cost of the control circuitry. It would therefore be advantageous to have a sophisticated means for quickly and accurately adjusting fan velocity or heater power at a cost substantially less than that of the typical modern control circuit. It would also be advantageous to have a sophisticated means for adjusting fan velocity or power to a heating element that comprises substantially fewer components than that of the typical modern control circuits.
Conventional control circuits also react to changes in temperature and/or humidity by either switching the appliance On and Off or by switching between fixed appliance speeds, such as High and Low. This results in the actual temperature and/or humidity overshooting and/or undershooting the desired level. It would therefore be advantageous to have a control circuit that could variably control power to an appliance based on continuous monitoring and evaluation of the input parameter.
Thus, the present invention is directed toward overcoming the disadvantages of conventional temperature control circuits which have been discussed above.
OBJECTS AND SUMMARY OF THE INVENTION
It is the object of the invention to provide a device which can quickly and accurately determine absolute temperature and/or humidity.
It is another object of the present invention to provide a device which can quickly and accurately adjust velocity of a fan motor and/or power to a heating element.
It is a further object of the present invention to provide an apparatus which can quickly and accurately adjust velocity of a fan motor and/or power to a heating element with minimal overshoot and/or undershoot.
It is still another object of the present invention to provide a method for monitoring and measuring analog signals for use in an appliance controller.
It is yet another object of the present invention to provide a method for variably controlling an appliance.
The apparatus formed in accordance with the present invention is capable of controlling appliances such as fans, heaters and humidifiers. A thermistor or humidistat may be used as a sensor which is responsive to changes in ambient temperature or humidity, respectively. a control circuit, including a microcontroller, responds to a signal provided by the sensor and varies the power to a fan or heater accordingly.
Preferably, the control circuit includes a clock oscillator and a variable electrical device, (i.e., a thermistor or humidistat), responsive to an external source, such as ambient temperature and/or humidity. The variable electrical device controls a frequency of the clock oscillator in response to the external source and the microcontroller calculates the ambient parameter in response to the frequency of the clock oscillator and generates a control signal in response to the clock oscillator frequency. The control signal is used to control a fan speed or power provided to a heating element of an appliance. Thus, the present invention provides an apparatus for a variable controller.
More specifically, the microcontroller includes a counter having a counter value associated therewith. The counter value is responsive to the clock oscillator for determining a frequency of the clock oscillator which is responsive to the ambient parameter. The microcontroller may also include a look-up table which allows the calculation of ambient parameters based upon the counter value. The microcontroller further includes an interrupt whereby the counter value is set to zero upon the zero crossing of the interrupt based upon the AC input. The counter value at subsequent zero crossings provides the basis for determining the clock oscillator frequency. As earlier noted, the clock oscillator frequency is used to determine an ambient parameter and for generating a control signal in response thereto. The variable electrical device may take the form of a thermistor, for use in a thermostat or a variable capacitive device or the like for use in a humidistat.
A preferred method of generating a control signal by a microcontroller formed in accordance with the present invention includes the steps of providing a variable controller having the features previously described and controlling a frequency of oscillation of the clock oscillator in response to the external source changing the variable electrical device and generating a control signal in response to a frequency of the clock oscillator. The method may also include calculating ambient temperature in the microcontroller in response to the frequency of the clock oscillator.
More specifically, the preferred method of generating a control signal, especially for use in a thermostat, includes the steps of altering a variable electrical device, such as the thermistor, in response to ambient temperature, controlling a frequency of a clock oscillator in a microcontroller in response to the value of the thermistor, calculating an ambient temperature in the microcontroller in response to the frequency of the clock oscillator, and generating a control signal which responds to the calculated ambient temperature for variably controlling an appliance such as fan motor or a power to a heater element. The microcontroller may also include a counter therein and the method having the step of setting a value in a counter of the microcontroller in response to the frequency of the clock oscillator and comparing the value in the counter to a look-up table in the microcontroller to determine ambient temperature and/or humidity.
A preferred form of the device controller, as well as other embodiments, objects, features and advantages of this invention, will be apparent from the following detailed description of illustrative embodiments, which is to be read in connection with the accompanying drawings.
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Levy William
Polonchak John C.
Sherwood Robert A.
Duda Rina I.
Hoffman & Baron LLP
Marino Francis E.
Martin David
The Holmes Group, Inc.
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