Fail safe HVAC temperature and medium presence sensor
First Claim
1. A fail-safe sensor for an HVAC system, comprising:
- a temperature detector operable to measure a temperature of a component or a medium;
a PTC heater operable to heat the sensor to a self-regulating temperature, the heater comprising a resistive element having an electrical impedance which increases with increasing temperature in accordance with a positive temperature coefficient characteristic; and
a sensor housing comprising the PTC heater and the temperature detector therein;
wherein in a heating mode the sensor is heated to the self-regulating temperature by the PTC heater and the temperature is measured by the temperature detector provides a fail-safe confirmation of temperature detector operation in response thereto, and wherein in a cooling mode the sensor cools to a temperature of the medium or component, and the temperature detector provides temperature data indicative of a time constant of the thermal decay rate of the sensor.
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Accused Products
Abstract
A system and method is presented for a fail-safe sensor for an HVAC system. The sensor comprises a temperature detector operable to measure a temperature of a component or a medium present at the sensor, a PTC heater operable to heat the sensor to a self-regulating temperature, the heater comprising a resistive element having an electrical impedance which increases with increasing temperature in accordance with a positive temperature coefficient characteristic, and a sensor housing comprising the PTC heater and the temperature detector provided within a single housing. An algorithm is provided for HVAC systems, wherein the sensor is heated to the self-regulating temperature by the PTC heater and is then measured by the temperature detector to confirm that the temperature detector is operating properly. Further, the sensor may be allowed to cool to a temperature of the surrounding medium or the component for sensing the temperature thereof. Thereafter, by calculating the time constant of the thermal decay rate of the sensor, the presence or absence of the component or medium surrounding the sensor may be determined in a fail-safe manner by an analyzer, for example.
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Citations
67 Claims
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1. A fail-safe sensor for an HVAC system, comprising:
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a temperature detector operable to measure a temperature of a component or a medium;
a PTC heater operable to heat the sensor to a self-regulating temperature, the heater comprising a resistive element having an electrical impedance which increases with increasing temperature in accordance with a positive temperature coefficient characteristic; and
a sensor housing comprising the PTC heater and the temperature detector therein;
wherein in a heating mode the sensor is heated to the self-regulating temperature by the PTC heater and the temperature is measured by the temperature detector provides a fail-safe confirmation of temperature detector operation in response thereto, and wherein in a cooling mode the sensor cools to a temperature of the medium or component, and the temperature detector provides temperature data indicative of a time constant of the thermal decay rate of the sensor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A fail-safe sensor for detecting water temperature and the presence of water in a water boiler,
wherein the sensor comprises a PTC heater and a temperature detector provided in a single housing; -
the PTC heater comprising a resistive element having an electrical impedance which increases with increasing temperature in accordance with a positive temperature coefficient characteristic;
wherein the sensor is located at a low water cut-off level location in the boiler for immersion by the water on a wet side of the sensor housing, and wherein a controller is connected to electrical terminals of the heater and temperature detector on a dry side of the sensor housing; and
wherein the PTC heater is operable in a heating mode to bring the sensor to a self-regulating temperature that is measured by the temperature detector to confirm a fail-safe temperature thereof in response thereto, and wherein the sensor in a cooling mode cools to the temperature of the medium and wherein the temperature detector senses the temperature of the medium, and wherein the controller calculates the time constant of the thermal decay rate of the sensor, and determines the presence of a water or air medium. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
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41. A fail-safe sensor for an HVAC system, comprising:
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a PTC device in a sensor housing operable to heat the sensor to a self-regulating temperature and to measure a temperature of a component or a medium, the PTC device comprising a resistive element having an electrical impedance which increases with increasing temperature in accordance with a positive temperature coefficient characteristic; and
wherein in a heating mode the sensor is heated to the self-regulating temperature by applying a voltage to the PTC device and the temperature associated with a resistance of the PTC device is measured thereat and provides a fail-safe confirmation of the sensor, and wherein in a cooling mode the sensor cools to a temperature of the medium or component, and the resistance of the PTC device provides temperature data indicative of a time constant of the thermal decay rate of the sensor. - View Dependent Claims (42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60)
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61. A method of detecting a temperature or a presence, or both, of a component or a medium within an HVAC system using a fail-safe sensor comprising a PTC heater and a temperature detector, the method comprising:
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applying a voltage to the PTC heater until the sensor heats to a self-regulating temperature;
measuring a first temperature of the sensor, a predetermined time period after applying the voltage;
removing the voltage from the PTC heater and allowing the sensor to cool down to the temperature of the medium;
measuring second temperature of the sensor during the cooling;
computing a time constant TC of the thermal decay rate of the sensor based on the measured first and second temperatures, based on the elapsed time delay between the measurements; and
determining the presence or absence of the medium surrounding or in contact with the sensor by comparing the computed TC of the sensor to a first predetermined TC level corresponding to that of a sensor in contact with the medium. - View Dependent Claims (62, 63, 64, 65, 66)
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67. A method of detecting water temperature and the presence of water in a water boiler using a fail-safe sensor, the method comprising:
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inputting and storing a self-regulating temperature for a PTC heater of the fail-safe sensor, an initial resistance and a temperature coefficient of a thermistor temperature detector based on the sensor part number;
applying a supply voltage to the PTC heater;
waiting while the sensor heats toward the self-regulating temperature for a predetermined time period;
measuring a resistance of the temperature detector at a first temperature of the sensor, after the predetermined time period and after applying the supply voltage;
removing the supply voltage from the PTC heater and allowing the sensor to cool down to the temperature of the medium;
waiting while the sensor cools for a predetermined time delay period;
measuring a resistance of the temperature detector at a second temperature;
computing and storing a time constant TC of the thermal decay rate of the sensor based on the measured first and second temperatures, and the elapsed time between the measurements;
determining whether the sensor is immersed in water by comparing the computed TC of the sensor to a first predetermined TC level corresponding to the TC level of a sensor immersed in water;
generating a low-water cut-off alarm for maintenance of the water boiler, if the computed TC of the sensor has not exceeded the first predetermined TC level, thereby corresponding to a TC level of a sensor in air; and
generating a sensor maintenance alarm if the computed TC of the sensor has not exceeded a second predetermined TC level, or if a predetermined percentage of the second temperature is not achieved within the predetermined time period, thereby providing a fail-safe indication of a possible sensor failure or the prediction thereof.
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Specification