Thermistor circuit calibration
First Claim
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1. An automatically calibrating thermistor circuit comprising:
- a port coupleable to a thermistor exposed to a heated location over which a range of temperatures is expected, and configured to obtain a temperature reading representative of a temperature of said heated location;
a first source, the first source providing a temperature reading associated with one end of said expected range of temperatures; and
detection circuitry having an input selectively coupleable to the port and the first source and having an output, the detection circuitry including an amplifier coupled to the input and having a generally preset gain and a variable offset, the variable offset being set in response to an adjustable offset signal coupled thereto, and an A/D converter coupled to the amplifier and the output by which to provide a digital temperature signal correlated to a temperature reading at the input, the amplifier outputting amplified temperature reading signals across an expected operating range in relation to said expected temperature range of said heated location, the amplifier outputting a minimum value in response to the first source; and
a processor coupled to the detection circuitry output, the processor selectively causing the first source to be coupled to the input of the detection circuitry in a calibration mode and the port to be coupled to the input of the detection circuitry in a normal operation mode, in the calibration mode the processor determining the adjustable offset signal based on the digital temperature signals obtained from the first source, the adjustable offset signal being operatively coupled to the variable offset of the amplifier such that the variable offset of the amplifier is set in response to the adjustable offset signal from the processor so that the variable offset of the amplifier is based on digital temperature signals obtained from the first source whereby to obtain the temperature reading representative of said temperature of said heated location in the normal operation mode.
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Abstract
Temperature detection circuitry is selectively coupled to a thermistor and one of two sources representing the impedance at respective ends of the expected range of temperature to which the thermistor is to be exposed. The offset of an amplifier and a scale factor to account for gain set of the amplifier are determined in an automatic calibration process while coupled to the source(s), and thereafter temperature readings are taken from the thermistor. During the calibration process, if the gain or scale factor are outside of expected ranges, a failure is determined and an alarm given and/or a heater is disabled.
59 Citations
22 Claims
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1. An automatically calibrating thermistor circuit comprising:
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a port coupleable to a thermistor exposed to a heated location over which a range of temperatures is expected, and configured to obtain a temperature reading representative of a temperature of said heated location; a first source, the first source providing a temperature reading associated with one end of said expected range of temperatures; and detection circuitry having an input selectively coupleable to the port and the first source and having an output, the detection circuitry including an amplifier coupled to the input and having a generally preset gain and a variable offset, the variable offset being set in response to an adjustable offset signal coupled thereto, and an A/D converter coupled to the amplifier and the output by which to provide a digital temperature signal correlated to a temperature reading at the input, the amplifier outputting amplified temperature reading signals across an expected operating range in relation to said expected temperature range of said heated location, the amplifier outputting a minimum value in response to the first source; and a processor coupled to the detection circuitry output, the processor selectively causing the first source to be coupled to the input of the detection circuitry in a calibration mode and the port to be coupled to the input of the detection circuitry in a normal operation mode, in the calibration mode the processor determining the adjustable offset signal based on the digital temperature signals obtained from the first source, the adjustable offset signal being operatively coupled to the variable offset of the amplifier such that the variable offset of the amplifier is set in response to the adjustable offset signal from the processor so that the variable offset of the amplifier is based on digital temperature signals obtained from the first source whereby to obtain the temperature reading representative of said temperature of said heated location in the normal operation mode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An automatically calibrating thermistor circuit comprising:
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a port coupleable to a thermistor exposed to a heated location over which a range of temperatures is expected, and configured to obtain a temperature reading representative of a temperature of said heated location; a first source, the first source providing a temperature reading associated with one end of said expected range of temperatures; and detection circuitry having an input selectively coupleable to the port and the first source and having an output, the detection circuitry including an amplifier coupled to the input and having a generally preset gain and a variable offset, the variable offset being set in response to an adjustable offset signal coupled thereto, and an A/D converter coupled to the amplifier and the output by which to provide a digital temperature signal correlated to a temperature reading at the input, the amplifier outputting amplified temperature reading signals across an expected operating range in relation to said expected temperature range of said heated location, the amplifier outputting a minimum value in response to the first source; and a processor coupled to the detection circuitry output, the processor selectively causing the first source to be coupled the input of the detection circuitry in a calibration mode and the port to be coupled to the input of the detection circuitry in a normal operation mode, in the calibration mode the processor determining the adjustable offset signal based on the digital temperature signals obtained from the first source, the processor further indicating failure if the adjustable offset signal determined by the processor is outside of an acceptable range. - View Dependent Claims (14)
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15. A method of automatically calibrating a thermistor circuit in which a thermistor is to be exposed to heat from a heated location, the temperature of which is expected to vary over a range of temperatures comprising:
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operating a processor to selectively couple temperature readings from a first source providing a temperature reading associated with one end of said expected range of temperatures, through an amplifier having a generally preset gain and a variable offset, the variable offset being set in response to an adjustable offset signal coupled thereto, and an A/D converter to generate digital temperature signals corresponding to the temperature readings, the amplifier outputting amplified temperature reading signals across an expected operating range in relation to the expected temperature range, the temperature reading provided by the first source corresponding to a minimum value output of the amplifier; determining with the processor the adjustable offset signal based on digital temperature signals obtained from the first source; automatically setting the variable offset of the amplifier in response to the adjustable offset signal determined by the processor so that the variable offset of the amplifier is based on the digital temperature signals obtained from the first source; thereafter, with the variable offset of the amplifier set in response to the adjustable offset signal determined by the processor, operating the processor to selectively couple temperature readings from the thermistor through the amplifier and the A/D converter to generate digital temperature signals corresponding the temperature readings from the thermistor; and determining with the processor a temperature of said heated location based on the digital temperature signals obtained from the thermistor. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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Specification