Embedded programmable sensor calibration method
First Claim
1. A method for establishing a voltage level for an output signal from a sensor and its associated correction circuit, the sensor having a desired null output level achieved by said correction circuit that is substantially equal to Vo2 and a desired full scale output equal to Vo1, said Vo1 and Vo2 levels being the approximate range of acceptable input to an analog to digital converter that accepts output from said correction circuit, the correction circuit comprising an amplifier having first and second input ports and an output port said output port supplying said output level as its output, and a resistance R1 connected to provide an offset signal to said second input port, the sensor being connected to the first input port, wherein the method for providing a voltage value for said offset signal comprises the steps of:
- (a) connecting the sensor output to a measurement device so as to be able to measure the output signal of the sensor at a zero stimulus level (named Vlo) and at a full scale level (named Vhi), said connection to a measurement device being named a measurement configuration;
(b) measuring the output signal of the sensor at both Vlo and Vhi;
(c) based on these measurements, determining the offset voltage value (named Vr) by calculating the relationship defined as;
space="preserve" listing-type="equation">Vr=(Vhi*Vo2-Vlo*Vo1)/(Vhi-Vo1-Vlo+Vo2);
(d) based again on these measurements and the determined Vr, determining a gain voltage value (named gain'"'"') for correcting the sensor output signal for span error using the equations;
space="preserve" listing-type="equation">Rf=((Vhi-Vo1)*R1)/(Vr-Vhi)
space="preserve" listing-type="equation">gain'"'"'=Rf/R1;
(e) configuring the correction circuit to apply said gain voltage and said offset voltage values to said first input port of said amplifier; and
(f) disconnecting the sensor output from said measurement device.
1 Assignment
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Accused Products
Abstract
A method for quick and low cost calibration of a sensor to remove span and offset errors. Span and offset errors are removed using a circuit which produces a corrected output signal as a function of calculated gain and offset values. The gain and offset values are calculated by first measuring an uncorrected sensor output at no input and at full scale output. These values are then used in an equation to calculate offset and gain values. The circuit includes an amplifier, a switch, a gain circuit, an offset circuit and a memory. The memory, which may be serial written memory including static RAM and a shift register, stores gain and offset coefficients for use by the gain and offset circuits and the amplifier. The gain and offset circuits may include digital to analog converters for converting the stored gain and offset digital values into analog equivalents.
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Citations
4 Claims
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1. A method for establishing a voltage level for an output signal from a sensor and its associated correction circuit, the sensor having a desired null output level achieved by said correction circuit that is substantially equal to Vo2 and a desired full scale output equal to Vo1, said Vo1 and Vo2 levels being the approximate range of acceptable input to an analog to digital converter that accepts output from said correction circuit, the correction circuit comprising an amplifier having first and second input ports and an output port said output port supplying said output level as its output, and a resistance R1 connected to provide an offset signal to said second input port, the sensor being connected to the first input port, wherein the method for providing a voltage value for said offset signal comprises the steps of:
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(a) connecting the sensor output to a measurement device so as to be able to measure the output signal of the sensor at a zero stimulus level (named Vlo) and at a full scale level (named Vhi), said connection to a measurement device being named a measurement configuration; (b) measuring the output signal of the sensor at both Vlo and Vhi; (c) based on these measurements, determining the offset voltage value (named Vr) by calculating the relationship defined as;
space="preserve" listing-type="equation">Vr=(Vhi*Vo2-Vlo*Vo1)/(Vhi-Vo1-Vlo+Vo2);(d) based again on these measurements and the determined Vr, determining a gain voltage value (named gain'"'"') for correcting the sensor output signal for span error using the equations;
space="preserve" listing-type="equation">Rf=((Vhi-Vo1)*R1)/(Vr-Vhi)
space="preserve" listing-type="equation">gain'"'"'=Rf/R1;(e) configuring the correction circuit to apply said gain voltage and said offset voltage values to said first input port of said amplifier; and (f) disconnecting the sensor output from said measurement device. - View Dependent Claims (2, 3, 4)
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Specification