Method and apparatus for offset error correction
First Claim
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1. Apparatus for compensating for drift from a null point of a measuring device comprising:
- comparison means for comparing a first signal from said measuring device with a derived second signal and for providing an output signal representative of the difference between said first and second signals;
analog-to-digital converter means to which said output signal is applied, for providing a digital equivalent of said output signal;
digital-to-analog converter means for providing said second signal to said comparison means; and
data processing means coupled to said analog-to-digital converter means and to said digital-to-analog converter means, and operable in an iterative operation to generate a compensating value which, when applied to said digital-to-analog converter means, results in said second signal having a predetermined relationship to said first signal, said compensating value being generated in a plurality of iterations commencing from a predetermined initial value by incrementing said digital-to-analog converter means to change the magnitude of said second signal until said output signal applied to said analog-to-digital converter means by said comparison means attains a predetermined value.
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Abstract
A method and apparatus for correction of null or zero reference offset error occurring in a measuring or transducing device by reason of temperature change, component ageing or other effects. A system including an appropriately programmed microcomputer, an analog-to-digital converter, a digital-to-analog converter and an operational amplifier provides a closed feedback correction loop, controlled by the microcomputer, which can maintain the zero adjustment of an analog transducer and amplifier circuitry over an indefinite period of time.
43 Citations
22 Claims
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1. Apparatus for compensating for drift from a null point of a measuring device comprising:
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comparison means for comparing a first signal from said measuring device with a derived second signal and for providing an output signal representative of the difference between said first and second signals; analog-to-digital converter means to which said output signal is applied, for providing a digital equivalent of said output signal; digital-to-analog converter means for providing said second signal to said comparison means; and data processing means coupled to said analog-to-digital converter means and to said digital-to-analog converter means, and operable in an iterative operation to generate a compensating value which, when applied to said digital-to-analog converter means, results in said second signal having a predetermined relationship to said first signal, said compensating value being generated in a plurality of iterations commencing from a predetermined initial value by incrementing said digital-to-analog converter means to change the magnitude of said second signal until said output signal applied to said analog-to-digital converter means by said comparison means attains a predetermined value. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. Apparatus for compensating for drift from a null point of a measuring device comprising:
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comparison means for comparing a measurement output signal from said measuring device in a noload condition with a compensating signal and for providing a comparison output signal representative of the difference between said measurement output and compensating signals; analog-to-digital converter means to which said comparison output signal is applied, for providing a digital equivalent of said comparison output signal; digital-to-analog converter means coupled to said comparison means for providing said compensating signal thereto; and data processing means coupled to said analog-to-digital converter means and to said digital-to-analog converter means, said data processing means including first storage means for storing a first amount representing the digital equivalent of the previous value of said comparison output signal, second storage means for storing the digital equivalent of the compensating signal, comparing means for comparing the digital equivalent of the comparison output signal with the digital equivalent of the previous value, and incrementing means controlled by the comparing means and capable of incrementing the digital equivalent of the compensating signal to cause said digital-to-analog converter means to provide a modified compensating signal. - View Dependent Claims (9, 10, 11, 12)
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13. A method for compensating for drift from a null point of a measuring device comprising the steps of:
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(a) comparing a measurement output signal from said measuring device with a compensating signal; (b) providing a comparison output signal representative of the difference between said measurement output signal and said compensating signal; (c) comparing said comparison output signal with a previous comparison output signal; (d) modifying the compensating signal by a predetermined amount in the event of a given result of the comparison of step (c); and (e) repeating steps (a) to (d) inclusive with successive modifications of said compensating signal until said comparison output signal attains a predetermined value. - View Dependent Claims (14, 15, 16)
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17. A method for compensating for drift from a null point of a measuring device in a no-load condition comprising the steps of:
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(a) setting a compensating digital value to a predetermined amount; (b) deriving an analog compensating signal from said compensating digital value; (c) comparing a measurement analog signal from said measuring device with said analog compensating signal; (d) providing an output analog signal representative of the difference between said measurement and compensating signals; (e) converting said output analog signal to a digital value; (f) comparing said digital value of said output signal to a prior value of said output signal; (g) incrementing said compensating digital value by a predetermined amount in the event of a given result of said comparison; (h) deriving an updated analog compensating signal from said compensating digital value; and (i) repeating steps (a) to (h) inclusive with successive incrementations of said digital value and corresponding alterations of the magnitude of said analog compensating signal until said output analog signal attains a predetermined value. - View Dependent Claims (18, 19, 20, 21, 22)
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Specification