Digitally-temperature-compensated strain-gauge pressure measuring apparatus
First Claim
1. A pressure sensor, comprising:
- a piezoresistive diaphragm having four resistors connected in a bridge configuration, four connection junctions positioned on the bridge, one junction being located between each of the four resistors;
a first resistor connected in series with the bridge at a first one of said four junctions, said first resistor having a first resistance; and
wherein an excitation signal is received at the bridge configuration at the first junction via the first resistor to induce a diaphragm response across opposing second and fourth junctions of said four junctions, the excitation signal having a first voltage; and
wherein a second voltage occurs across the first resistor and a third voltage occurs across said second and fourth junctions of the bridge configuration in response to the excitation signal; and
processing means for executing a first computer program comprising the steps;
calculating a current normalized voltage across the bridge configuration from the second voltage, third voltage and first resistance;
calculating bridge impedance from the first voltage, second voltage and first resistance;
deriving a first-pass estimate of diaphragm temperature based on the calculated bridge impedance;
deriving a first-pass estimate of pressure exerted on the diaphragm from the current normalized voltage and the first-pass temperature estimate;
correcting for temperature-induced errors in the calculated bridge impedance by using the first-pass pressure estimate to derive a corrected bridge impedance;
adjusting the first-pass temperature estimate by using the corrected bridge impedance to derive a corrected estimate of diaphragm temperature;
calculating a temperature offset error and a span error occurring in the diaphragm response;
adjusting the current normalized voltage based on the calculated temperature offset error and span error to generate a corrected current normalized voltage; and
converting the corrected current normalized voltage to a corrected pressure measurement.
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Accused Products
Abstract
A strain gauge exhibits temperature offset errors and span errors which vary from device to device and vary as a function of temperature. A digitally-compensated strain-gauge apparatus executes embedded calibration and compensation programs for improving accuracy over a wide temperature range. Pressure measurement error bands are reduced to approximately to 0.03% of full scale for a 5 psi device over a 0° C. to 50° C. temperature range. A calibration program defines parameters for compensating for such errors. During field operation, a compensation program uses the calibration parameters to generate a more accurate pressure measurement. According to the compensation scheme, current normalized voltage and bridge impedance are derived from the raw data. A first-pass temperature estimate then is derived from the result. The derived first-pass temperature estimate is plugged into a temperature offset error function to find the temperature offset error at the estimated temperature. Such offset error is used to adjust the current normalized voltage. A first-pass pressure estimate is derived from the adjusted current-normalized voltage, then used to correct the bridge impedance. The corrected bridge impedance leads to a corrected temperature estimate, a corrected current normalized voltage and a corrected pressure. The corrected pressure is the compensated pressure measurement.
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Citations
11 Claims
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1. A pressure sensor, comprising:
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a piezoresistive diaphragm having four resistors connected in a bridge configuration, four connection junctions positioned on the bridge, one junction being located between each of the four resistors; a first resistor connected in series with the bridge at a first one of said four junctions, said first resistor having a first resistance; and wherein an excitation signal is received at the bridge configuration at the first junction via the first resistor to induce a diaphragm response across opposing second and fourth junctions of said four junctions, the excitation signal having a first voltage; and wherein a second voltage occurs across the first resistor and a third voltage occurs across said second and fourth junctions of the bridge configuration in response to the excitation signal; and processing means for executing a first computer program comprising the steps; calculating a current normalized voltage across the bridge configuration from the second voltage, third voltage and first resistance; calculating bridge impedance from the first voltage, second voltage and first resistance; deriving a first-pass estimate of diaphragm temperature based on the calculated bridge impedance; deriving a first-pass estimate of pressure exerted on the diaphragm from the current normalized voltage and the first-pass temperature estimate; correcting for temperature-induced errors in the calculated bridge impedance by using the first-pass pressure estimate to derive a corrected bridge impedance; adjusting the first-pass temperature estimate by using the corrected bridge impedance to derive a corrected estimate of diaphragm temperature; calculating a temperature offset error and a span error occurring in the diaphragm response; adjusting the current normalized voltage based on the calculated temperature offset error and span error to generate a corrected current normalized voltage; and converting the corrected current normalized voltage to a corrected pressure measurement. - View Dependent Claims (2, 3, 4, 5)
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6. A pressure measuring apparatus, comprising:
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a piezoresistive diaphragm having four resistors connected in a bridge configuration, four connection junctions positioned on the bridge, one junction being located between each of the four resistors; a first resistor connected in series with the bridge at a first one of said four junctions, said first resistor having a first resistance; means for generating an excitation signal input to the bridge configuration at the first junction via the first resistor, the excitation signal having a supply voltage, the excitation signal inducing a diaphragm response across opposing second and fourth junctions of said four junctions; means for detecting the diaphragm response as a second voltage across opposing second and fourth junctions of said four junctions, said second and fourth junctions not including said first junction; means for detecting a third voltage across the first resistor; and processing means for executing a first computer program comprising the steps; calculating a current normalized voltage across the bridge configuration from the second voltage, third voltage and first resistance; calculating bridge impedance from the supply voltage, third voltage and first resistance; deriving a first-pass estimate of diaphragm temperature based on the calculated bridge impedance; deriving a first-pass estimate of pressure exerted on the diaphragm from the current normalized voltage and the first-pass temperature estimate; correcting for temperature-induced errors in the calculated bridge impedance by using the first-pass pressure estimate to derive a corrected bridge impedance; adjusting the first-pass temperature estimate by using the corrected bridge impedance to derive a corrected estimate of diaphragm temperature; calculating a temperature offset error and a span error occurring in the diaphragm response; adjusting the current normalized voltage based on the calculated temperature offset error and span error to generate a corrected current normalized voltage; and converting the corrected current normalized voltage to a corrected pressure measurement. - View Dependent Claims (7, 8, 9, 10, 11)
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Specification