A method for compensating electronic 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 measurement apparatus, the second signal being one of:
- i) a system ground potential;
- ii) a static potential other than system ground;
- and
- iii) a dynamic potential;
- providing at least one difference signal by 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 the difference signal;
- or
- b) attenuating the difference between the first and second signals using passive components to produce the difference signal;
- or
- c) comparing the first signal with the second signal, the dfference signal being one of:
- i) said first signal is substantially the difference signal in respect to said second signal, which is at the system ground potential;
- or
- ii) the difference between said first signal in respect to the second signal, which is at the static potential;
- or
- iii) the difference beween said first signal in respect to said second signal, at a given time, the second signal being the dynamic potential;
- providing at least one ambient condition signal responsive to the ambient condition of at least one of a) the physical variable and b) temperature for providing an ambient condition signal which when measured provides a measured ambient condition;
- storing calibration information used for compensating the electronic measurement apparatus for drift of electronic components;
- operating in a reference calibration mode, in which at least one reference curve representative of at least one associated difference parameter value versus measured ambient condition is produced, the difference parameter value being either a difference signal measurement or value derived from a difference signal measurement, said curve referred to as a difference parameter reference curve being acquired over a range of ambient conditions and stored, the reference curve so generated in the reference calibration mode being referred to as a difference parameter reference curve, and one or more such difference parameter reference curves being referred to as a set of difference parameter reference curves, and:
- a) if the associated difference parameter value is representative of difference measurement input offset, then the difference parameter reference curve is more specifically referred to as a difference reference curve, and
- b) if the associated difference parameter value is representative of difference measurement gain, then the difference parameter reference curve is more specifically referred to as a difference gain reference curve, and
- c) if the associated difference parameter value is representative of difference measurement common mode, then the difference parameter reference curve is more specifically referred to as a difference CMR reference curve, and
- d) if the associated difference parameter value is representative of difference measurement power supply rejection, then the difference parameter reference curve is more specifically referred to as a difference PSR reference curve;
- operating in a standard calibration mode, in which at least one difference parameter reference curve is substantially compensated for drift over time by an associated difference curve offset value, which is determined at a current arbitrary ambient condition by comparing at least one expected difference parameter value determined from the difference parameter reference curve, at the current arbitrary ambient condition, to at least one determined difference parameter value, measured or derived from a difference signal measurement, at the current arbitrary ambient condition;
- and
- performing at least one difference measurement in the operational mode, in which a measurement representative of current ambient condition provides a measured ambient condition which is correlated to at least one current difference parameter value, the current difference parameter value being associated with the difference parameter reference curve, and the current difference parameter value being at least one of:
- a) determined from a translated difference parameter reference curve at the measured ambient condition, the translated difference parameter reference curve being the difference parameter reference curve after translation by the difference curve offset value associated with the difference parameter reference curve during operation in the standard calibration mode;
- b) determined from the difference parameter reference curve at the measured ambient condition, and translated by the difference curve offset value associated with the difference parameter reference curve as determined in the standard calibration mode;
- c) substantially equivalent to the determined difference parameter value determined during the standard calibration mode and associated with the difference parameter reference curve;
- and
- d) derived by empirically comparing difference parameter values associated with the difference parameter reference curve at various times during operation in the standard calibration mode at various ambient conditions;
- the current difference parameter value being used to correct the difference signal measurement for component drift to provide a compensated difference signal measurement between the first and second values of the physical variable.