Self-calibrating automatic zeroing strain gauge circuit
First Claim
1. A circuit for calibrating and providing an output from a strain gauge after said strain gauge is fitted to an object to be measured comprising:
- a constant current source for providing a constant current in said strain gauge;
a source of a reference voltage;
means responsive to an error signal corresponding to a difference between a voltage drop across said strain gauge due to said constant current and said reference voltage during a predetermined time period for adjusting the magnitude of the current from said current source in said strain gauge to reduce said difference between said strain gauge voltage drop and said reference voltage; and
means responsive to a difference between said voltage drop across said strain gauge and said reference voltage after said adjusting of said current in said strain gauge for providing an output of said voltage difference relative to said reference voltage.
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Accused Products
Abstract
A method of and apparatus for calibrating and providing an output from a strain gauge (1) is described. In the method and apparatus there is provided a constant-current source (10). Coupled to the current source (10) is an amplifier (12,13) for providing an output corresponding to the difference between the voltage drop across the strain gauge (1) and a reference voltage from a source (14). The reference voltage is used to adjust the current in the strain gauge (1) from the current source (10). After the current is adjusted, further changes in the voltage drop in the strain gauge (1) relative to the reference voltage is used for providing an output of the voltage difference relative to the reference voltage. The adjusting of the magnitude of the current from the constant-current source (10) is provided by a calibrate-and-zero sample and hold circuit (16) having a sample and hold period sufficient to reduce to negligible levels the effects of the dielectric absorption of an associated capacitive means (20).
32 Citations
13 Claims
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1. A circuit for calibrating and providing an output from a strain gauge after said strain gauge is fitted to an object to be measured comprising:
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a constant current source for providing a constant current in said strain gauge; a source of a reference voltage;
means responsive to an error signal corresponding to a difference between a voltage drop across said strain gauge due to said constant current and said reference voltage during a predetermined time period for adjusting the magnitude of the current from said current source in said strain gauge to reduce said difference between said strain gauge voltage drop and said reference voltage; andmeans responsive to a difference between said voltage drop across said strain gauge and said reference voltage after said adjusting of said current in said strain gauge for providing an output of said voltage difference relative to said reference voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of calibrating and providing an output from a strain gauge after said strain gauge is fitted to an object to be measured comprising the steps of:
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providing a constant current in said strain gauge;
detecting a difference between the voltage drop in said strain gauge due to said current and a reference voltage during a predetermined time period after said strain gauge is fitted to an object to be measured;adjusting the magnitude of said constant current for reducing said voltage difference; and detecting the difference between the voltage drop in said strain gauge due to said current and said reference voltage after said adjusting of the magnitude of said current for providing an output of said voltage difference relative to said reference voltage. - View Dependent Claims (10, 11, 12, 13)
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Specification