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 either:
- a) a first signal representative of a first value of a physical variable and, a second signal representative of a second value of the same physical variable;
- or
- b) a first signal representative of a difference between a first value of a physical variable and a second value of the same physical variable, and, a second signal available at the location of the measurement and at the location of the apparatus, for purposes of comparison with the first signal, the second signal being one of:
- i.) a system ground potential, so that the said first signal effectively comprises a difference potential in respect to the said second signal which is at a system ground potential;
- or
- ii.) a static potential other than system ground, so that the said first signal effectively comprises a difference potential in respect to the said reference signal which is at the static potential;
- or
- iii.) a dynamic potential, so that the said first signal effectively comprises a difference potential at any point in time in respect to the dynamic potential, at the same point in time, the second signal being the dynamic potential;
- and, providing at least one difference signal means for one of:
- a) obtaining the difference between the first and second signals at a gain factor greater than one, or equal to one, or less than one, to produce a difference signal;
- or
- b) attenuating the difference between the first and second signals using passive components to produce a difference signal;
- or
- c) electrically conveying the first signal, with the second signal being available at the location of the measurement, and at the location of the apparatus for purposes of comparison with the first signal, the second signal being one of:
- i.) a system ground potential, so that the first signal effectively comprises a difference signal in respect to the second signal, which is at a system ground potential;
- or
- ii.) a static potential, other than system ground, so that the first signal effectively comprises a difference signal in respect to the second signal, which is at the static potential;
- or
- iii.) a dynamic potential, so that the first signal effectively comprises a difference signal at any point in time in respect to the second signal, at the same point in time, the second signal being the dynamic potential;
- 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 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.