ROBUST APPLIANCE SENSOR
Publication Date: 2014-Nov-14
The IP.com Prior Art Database
The device uses basic discrete circuits to convert the resistance of the thermistor to a signal, such as a digital or frequency signal that can be easily measured by a microprocessor. The resistance of the thermistor can be converted to frequency using a 555 timer or equivalent. Alternatively, the resistance signal can be converted by a 4 bit microprocessor to a digital signal. The conversion of the resistance of the thermistor is performed prior to the signal being outputted. The embodiment described herein minimizes the space needed for the thermistor, increases efficiency and reliability, and decreases costs associated with the thermistor.
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ROBUST APPLIANCE SENSOR
BACKGROUND OF THE INVENTION
The present invention is drawn to modular thermistor signal transformation for an appliance, which could be a refrigerator in one embodiment. Embodiments of the invention as described herein improve reliability of thermistor configurations and address many of the problems encountered by use of a standard thermistor configuration.
Thermistors are thermally sensitive semiconductors whose resistance varies with temperature. They are manufactured from metal-oxide semiconductor material encapsulated in a glass or epoxy bead. Due to their structure, thermistors typically have much higher nominal resistance values than other resistance temperature detectors (anywhere from 2,000 ohms to 10,000 ohms) and can be used for lower currents.
The resistance of a thermistor at cryogenic temperatures may vary between 2,000 and 50,000 ohms whereas the maximum source resistance allowable for a strip chart recorder is around 2,000 ohms. Therefore, a thermistor has a higher performance at cryogenic temperatures greater than 2,000 ohms.
Traditionally, temperature sensing has been accomplished by use of a mechanical device that mechanically changes in response to temperature changes. Due to their design, these mechanical devices often develop reliability problems or vary from their designed operational characteristics.
A standard thermistor configuration comprises a thermistor that is mounted on an appliance. Lead wires are attached to the thermistor, which are then connected to a
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circuit where the circuit includes a meter and its associated circuit. Connected in a parallel fashion to the meter circuit is a standardization resistant circuit. Lastly, a switch is adapted to connect either the standardization resistant circuit or the thermistor circuit. The traditional configurations of the thermistors have caused reliability issues, led to high cost, and have taken up a significant amount of space, all of which embodiments of the present invention provide a better solution for.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an embodiment of a simple discrete circuit capable of converting the thermistor signal using a 555 timer and transmitting the signal along the DC supply. Figure 2 is a graph of the relationship between Kilohertz to temperature for the conversion of the thermistor signal.
An embodiment of the present invention transforms a thermistor signal before output of the signal. The transformed signal then travels along a wire to the motherboard. The present invention will increase reliability and efficiency of the thermistor and decrease the amount of space necessary for the thermistor.
In an embodiment of the invention specific to the improvement of reliability in an appliance by eliminating the effect of connector resistance to temperature measurement, the original thermistor resistance signal is converted to a frequency or digital signal prior to...