Method and apparatus for economical drift compensation in high resolution difference measurements and exemplary low cost, high resolution differential digital thermometer
First Claim
1. A method for compensating electronic difference measurement apparatus for at least one of time and temperature drift of electronic components, comprising the steps of:
- providing a first signal representative of a first value of a physical variable;
providing a second signal representative of a second value of the same physical variable;
providing at least one difference signal amplification means for amplifying the difference between the first and second signals to produce a difference signal;
providing at least one ambient condition signal means responsive to the ambient condition of at least one of a) the physical variable and b) temperature for providing a third signal;
providing analog to digital converter means for converting the difference signal produced by the difference signal amplification means and the third signal provided by the ambient condition signal means into digital form;
providing computer means for compensating the electronic difference measurement apparatus for drift of electronic components;
providing memory means for storing calibration information used for compensating the electronic difference measurement apparatus for drift of electronic components;
operating in a reference calibration mode, in which at least one offset curve representative of offset for electronic components associated with difference signal measurements versus measured ambient condition is acquired over a range of ambient conditions and stored in the memory means, the curve so generated being referred to as a difference reference curve;
operating in a standard calibration mode, in which a difference signal offset that substantially compensates the difference reference curve for drift over time is determined at a current arbitrary ambient condition by comparing difference measurements at the current arbitrary ambient condition to previously stored values on the difference reference curve and at least one of a) translating the difference reference curve in order to substantially compensate the difference reference curve for time drift associated with difference signal measurement, the difference reference curve after translation being referred to as a translated difference reference curve, the translated difference reference curve being used to provide a difference signal offset during an operational mode, that substantially compensates difference measurements for drift, and b) setting the difference signal offset to the difference between an estimated difference reference and an actual difference reference, the difference signal offset being used to linearly translate difference measurements during the operational mode in order to substantially compensate difference measurements for drift of components associated with difference measurement; and
performing at least one difference measurement in the operational mode, in which a measurement representative of current ambient condition provides an ambient condition measurement which is correlated to a difference signal offset measurement, the difference signal offset measurement being at least one of a) determined from the translated difference reference curve at the measured ambient condition measurement, b) equivalent to the difference signal offset determined during the standard calibration mode, and c) derived by empirically comparing values for the difference signal offset at various times during operation in the standard calibration mode at various ambient conditions, and the difference signal offset measurement being used to correct the difference signal for component drift to provide a compensated difference measurement between the first and second values of the physical variable.
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Abstract
A system for measuring differences in a physical variable, such as temperature, by utilizing predictable behavior in the relative time drift of offset curves for various circuit elements, including two sensors connected to a difference signal amplifier, an ambient condition amplifier, and an analog to digital converter. In an initial calibration mode, the system records several offset curves, stored in memory, correlating ambient condition measurements to offset measurements acquired from the ambient condition amplifier and the difference signal amplifier. Offset curves recorded in the initial calibration mode, correlating ambient condition measurements to measurements from the difference signal amplifier, include one curve recorded with both inputs of the difference signal amplifier held at equal potential and another curve recorded with both sensors held at the same value of the physical variable, over a given ambient condition range. Another offset curve correlates ambient condition to measurements from the ambient condition amplifier, with inputs to the ambient condition amplifier connected to voltages from a substantially time stable reference resistance bridge. These offset curves representing drift behavior, among electrical components, can be updated for time drift, at a single, current arbitrary ambient temperature, the measurements for which can be obtained quickly and applied as a time drift correction to the offset curves, without interrupting normal system operation, to provide a compensated difference measurement between the different values of the physical variable measured by the respective sensors. Additionally, the system dynamically tracks cumulative system errors, in order to calculate optimal system resolution, based upon current operating conditions.
86 Citations
68 Claims
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1. A method for compensating electronic difference measurement apparatus for at least one of time and temperature drift of electronic components, comprising the steps of:
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providing a first signal representative of a first value of a physical variable;
providing a second signal representative of a second value of the same physical variable;
providing at least one difference signal amplification means for amplifying the difference between the first and second signals to produce a difference signal;
providing at least one ambient condition signal means responsive to the ambient condition of at least one of a) the physical variable and b) temperature for providing a third signal;
providing analog to digital converter means for converting the difference signal produced by the difference signal amplification means and the third signal provided by the ambient condition signal means into digital form;
providing computer means for compensating the electronic difference measurement apparatus for drift of electronic components;
providing memory means for storing calibration information used for compensating the electronic difference measurement apparatus for drift of electronic components;
operating in a reference calibration mode, in which at least one offset curve representative of offset for electronic components associated with difference signal measurements versus measured ambient condition is acquired over a range of ambient conditions and stored in the memory means, the curve so generated being referred to as a difference reference curve;
operating in a standard calibration mode, in which a difference signal offset that substantially compensates the difference reference curve for drift over time is determined at a current arbitrary ambient condition by comparing difference measurements at the current arbitrary ambient condition to previously stored values on the difference reference curve and at least one of a) translating the difference reference curve in order to substantially compensate the difference reference curve for time drift associated with difference signal measurement, the difference reference curve after translation being referred to as a translated difference reference curve, the translated difference reference curve being used to provide a difference signal offset during an operational mode, that substantially compensates difference measurements for drift, and b) setting the difference signal offset to the difference between an estimated difference reference and an actual difference reference, the difference signal offset being used to linearly translate difference measurements during the operational mode in order to substantially compensate difference measurements for drift of components associated with difference measurement; and
performing at least one difference measurement in the operational mode, in which a measurement representative of current ambient condition provides an ambient condition measurement which is correlated to a difference signal offset measurement, the difference signal offset measurement being at least one of a) determined from the translated difference reference curve at the measured ambient condition measurement, b) equivalent to the difference signal offset determined during the standard calibration mode, and c) derived by empirically comparing values for the difference signal offset at various times during operation in the standard calibration mode at various ambient conditions, and the difference signal offset measurement being used to correct the difference signal for component drift to provide a compensated difference measurement between the first and second values of the physical variable. - 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, 24, 25, 26, 27, 28, 29, 30, 31, 32)
operating in the reference calibration mode, in which offset curves are acquired over a range of ambient conditions and stored in the memory means, the offset curves comprising;
a) at least one curve representative of offset for electronic components associated with ambient condition measurements versus measured ambient condition, the curve so generated being referred to as an ambient reference curve; and
b) the difference reference curve;
operating in the standard calibration mode, in which an ambient signal offset and a difference signal offset that substantially compensate the ambient reference curve and difference reference curve, respectively, for drift over time are determined at a current arbitrary ambient condition by comparing measurements at the current arbitrary ambient condition to previously stored values on the ambient reference curve and difference reference curve and, for both the ambient reference curve and difference reference curve, one of a) translating at least one of the ambient reference curve and difference reference curve in order to substantially compensate the at least one reference curve for time drift associated with ambient condition measurement and difference signal measurement, the respective reference curves after translation being referred to as a translated ambient reference curve and a translated difference reference curve, respectively, and b) determining at least one of an ambient signal offset and difference signal offset by obtaining the difference between an estimated ambient reference measurement and an actual ambient reference measurement, and between an estimated difference reference measurement and an actual difference reference measurement, respectively, the respective signal offset being used to linearly translate ambient condition measurements and difference measurements, respectively, in order to substantially compensate the respective measurements during the operational mode for drift of components associated with ambient condition measurement and difference measurement, respectively; and
performing at least one difference measurement in the operational mode in which a measurement representative of current ambient condition compensated for time drift using at least one of the translated ambient reference curve and ambient signal offset determined during the standard calibration mode provides an ambient condition measurement which is correlated to a difference signal offset measurement, the difference signal offset measurement being at least one of a) determined from the translated difference reference curve at the compensated ambient condition measurement, b) equivalent to the difference signal offset determined during the standard calibration mode, and c) derived by empirically comparing values for the difference signal offset at various times during operation in the standard calibration mode, at various ambient conditions, and the difference signal offset measurement being used to correct the difference signal for component drift to provide a compensated difference measurement between the first and second values of the physical variable.
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31. A method as defined in claim 30 wherein the ambient reference curve and difference reference curve are re-acquired and compared to previous versions of the respective offset curves to at least one of a) estimate error in the linear translations, associated with the standard calibration mode, and b) track trends in drift of the respective offset curves.
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32. A method as defined in claim 30, further comprising the steps of providing a first sensor responsive to the first value of the physical variable for producing the first signal, providing a second sensor responsive to the second value of the physical variable for producing the second signal, storing drift parameters associated with at least one of the first sensor, second sensor, difference signal amplification means, and ambient condition signal means in the memory means, and using the stored drift parameters to determine at least one of a) the ambient reference curve and b) the difference reference curve.
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33. Apparatus for compensating electronic difference measurements for at least one of time and temperature drift of electronic components, comprising:
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means for providing a first signal representative of a first value of a physical variable;
means for providing a second signal representative of a second value of the same physical variable;
at least one difference signal amplification means responsive to the first and second signals for amplifying the difference between the first and second signals to produce a difference signal;
at least one ambient condition signal means responsive to the ambient condition of at least one of a) the physical variable and b) temperature for providing a third signal;
analog to digital converter means connected to the difference signal amplification means and the ambient condition signal means for converting the difference signal produced by the difference signal amplification means and the third signal provided by the ambient condition signal means into digital form;
computer means for compensating the electronic difference measurement apparatus for drift of electronic components;
memory means for storing calibration information used for compensating the electronic difference measurement apparatus for drift of electronic components;
the apparatus being operable in a reference calibration mode, in which at least one offset curve representative of offset for electronic components associated with difference signal measurements versus measured ambient condition is acquired over a range of ambient conditions and stored in the memory means, the curve so generated being referred to as a difference reference curve;
the apparatus additionally being operable in a standard calibration mode, in which a difference signal offset that substantially compensates the difference reference curve for drift over time is determined at a current arbitrary ambient condition by comparing difference measurements at the current arbitrary ambient condition to previously stored values on the difference reference curve and at least one of a) translating the difference reference curve in order to substantially compensate the difference reference curve for time drift associated with difference signal measurement, the difference reference curve after translation being referred to as a translated difference reference curve, the translated difference reference curve being used to provide a difference signal offset during an operational mode, that substantially compensates difference measurements for drift, and b) setting the difference signal offset to the difference between an estimated difference reference and an actual difference reference, the difference signal offset being used to linearly translate difference measurements during the operational mode in order to substantially compensate difference measurements for drift of components associated with difference measurement; and
the apparatus for performing at least one difference measurement in the operational mode, in which a measurement representative of current ambient condition provides an ambient condition measurement which is correlated to a difference signal offset measurement, the difference signal offset measurement being at least one of a) determined from the translated difference reference curve at the measured ambient condition measurement, b) equivalent to the difference signal offset determined during the standard calibration mode, and c) derived by empirically comparing values for the difference signal offset at various times during operation in the standard calibration mode at various ambient conditions, and the difference signal offset measurement being used to correct the difference signal for component drift to provide a compensated difference measurement between the first and second values of the physical variable. - View Dependent Claims (34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68)
the apparatus being operable in a reference calibration mode, in which offset curves are acquired over a range of ambient conditions and stored in the memory means, the offset curves comprising;
a) at least one curve representative of offset for electronic components associated with ambient condition measurements versus measured ambient condition, the curve so generated being referred to as an ambient reference curve; and
b) the difference reference curve;
the apparatus additionally being operable in the standard calibration mode in which an ambient signal offset and a difference signal offset that substantially compensate the ambient reference curve and difference reference curve, respectively, for drift over time are determined at a current arbitrary ambient condition by comparing measurements at the current arbitrary ambient condition to previously stored values on the ambient reference curve and difference reference curve and, for both the ambient reference curve and difference reference curve, one of a) translating at least one of the ambient reference curve and difference reference curve in order to substantially compensate the at least one reference curve for time drift associated with ambient condition measurement and difference signal measurement, respectively, the respective reference curves after translation being referred to as a translated ambient reference curve and a translated difference reference curve, respectively, b) determining at least one of an ambient signal offset and difference signal offset by obtaining the difference between an estimated ambient reference measurement and an actual ambient reference measurement, and between an estimated difference reference measurement and an actual difference reference measurement, respectively, the respective signal offset being used to linearly translate ambient condition measurements and difference measurements, respectively, in order to substantially compensate the respective measurements during the operational mode for drift of components associated with ambient condition measurement and difference measurement, respectively; and
the apparatus for performing at least one difference measurement in the operational mode in which a measurement representative of current ambient condition compensated for time drift using at least one of the translated ambient reference curve and ambient signal offset determined during the standard calibration mode provides an ambient condition measurement which is correlated to a difference signal offset measurement, the difference signal offset measurement being at least one of a) determined from the translated difference reference curve at the compensated ambient condition measurement, b) equivalent to the difference signal offset determined during the standard calibration mode, and c) derived by empirically comparing values for the difference signal offset at various times during operation in the standard calibration mode, at various ambient conditions, and the difference signal offset measurement being used to correct the difference signal for component drift to provide a compensated difference measurement between the first and second values of the physical variable.
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67. Apparatus as defined in claim 66, further comprising a timer and wherein the ambient reference curve and difference reference curve are re-acquired at a known time, relative to the time at which the respective offset curves were last acquired and compared to previous versions of the respective offset curves to at least one of a) estimate error in the linear translations, associated with the standard calibration mode, and b) track trends in drift of the respective offset curves.
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68. Apparatus as defined in claim 66 wherein the means for providing the first signal representative of a first value of the physical variable comprises a first sensor and the means for providing the second signal representative of a second value of the same physical variable comprises a second sensor and wherein drift parameters associated with at least one of the first sensor, second sensor, difference signal amplification means, and ambient condition signal means are stored in the memory means and used to determine at least one of a) the ambient reference curve, and b) the difference reference curve.
Specification