Correction of a pressure indication in a pressure transducer due to variations of an environmental condition
First Claim
1. Apparatus for measuring pressure, comprising:
- a pressure sensor comprising at least first and second sensing means each having an impedance value which varies with pressure and with a predetermined environmental condition;
impedance means having an impedance value which is substantially unchanged by changes in the predetermined environmental condition;
connection means for alternately connecting the impedance means into operative relation with the first and second sensing means, successively, the sensor and impedance means together providing first and second signals during respective alternative connection of the impedance means with the first and second sensing means, the first and second signals being functions of pressure and the predetermined environmental condition; and
correction means responsive to the first and second signals for correcting a pressure indication for variations of the predetermined environmental condition based upon the first and second signals.
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Accused Products
Abstract
A two-wire transmitter includes a pressure sensor comprising first and second sensing means each having an impedance value which varies with pressure being measured and with a predetermined environmental condition, such as line pressure or temperature. A fixed impedance has an impedance value which is substantially unchanged by variations in the predetermined environmental condition. A switch alternately connects the fixed impedance into operative relation with the first and second sensing means to derive first and second signals which are each functions of pressure being measured and the predetermined environmental condition. A correction circuit processes the first and second signals, such as by a polynomial series or with a lookup table, to derive a corrected pressure signal. In one form, the sensor senses differential pressure and the predetermined environmental condition is line pressure or temperature, and the first and second signals are functions of both differential pressure and either line pressure or temperature, so the correction circuit derives an indication of differential pressure corrected for variations in either line pressure or temperature. In another form, the sensor measures line pressure and is sensitive to temperature changes, in which case the first and second signals are functions of line pressure and temperature and the correction circuit derives a line pressure signal corrected for variations in temperature.
108 Citations
47 Claims
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1. Apparatus for measuring pressure, comprising:
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a pressure sensor comprising at least first and second sensing means each having an impedance value which varies with pressure and with a predetermined environmental condition; impedance means having an impedance value which is substantially unchanged by changes in the predetermined environmental condition; connection means for alternately connecting the impedance means into operative relation with the first and second sensing means, successively, the sensor and impedance means together providing first and second signals during respective alternative connection of the impedance means with the first and second sensing means, the first and second signals being functions of pressure and the predetermined environmental condition; and correction means responsive to the first and second signals for correcting a pressure indication for variations of the predetermined environmental condition based upon the first and second signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A capacitive pressure sensor for sensing differential pressure in a two-wire transmitter, comprising:
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a capacitive pressure transducer having first and second pressure sensors each having a capacitive value varying with variations in pressure and being suitable for being exposed to first and second pressures; fixed capacitor means having a capacitance value which is substantially unchanged by variations in line pressure; a switch alternately connecting the fixed capacitor means into operative relation with the first and second pressure sensors, successively, the transducer and fixed capacitor means together providing first and second signals respectively during alternative connection of the fixed capacitor means with the first and second pressure sensors, the first and second signals being functions of a differential pressure between the first and second pressures and line pressure; and a correction circuit responsive to the first and second signals for correcting a differential pressure signal for variations in line pressure based upon the first and second signals. - View Dependent Claims (27, 28, 29, 30, 31, 32)
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33. A method of measuring a pressure differential comprising the steps:
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sensing a differential pressure with a first pressure sensing means which provides a first value representative of pressure and a predetermined environmental condition and with a second pressure sensing means which provides a second value representative of pressure and the predetermined environmental condition; providing a fixed means having a value which is substantially fixed in relation to variations in the predetermined environmental condition; deriving first and second relationships between said first and second pressure sensing means and said fixed means, the first and second relationships being different from each other wherein the first and second relationships are derived by alternately connecting the fixed means into operative relationship with the first and second pressure sensing means; deriving an indication of differential pressure from said first and second relationships, said indication being representative of differential pressure sensed by said first and second pressure sensing means and independent of variations in the predetermined environmental condition. - View Dependent Claims (34, 35, 36, 37, 38, 39, 40, 41)
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42. A method of measuring a line pressure comprising the steps:
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sensing a line pressure with a first pressure sensing means which provides first a value representative of line pressure and with a second pressure sensing means which provides a second value representative of line pressure, said first and second values being different, the values of the first and second pressure sensing means also being responsive to temperature; providing a fixed means having a value which is substantially fixed in relation to variations in temperature; deriving first and second relationships between said first and second pressure sensing means and said fixed means, the first and second relationships being different from each other; deriving an indication of line pressure from said first and second relationships, said indication being independent of variations in temperature. - View Dependent Claims (43)
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44. A circuit for providing an output signal as a function of a first input condition, the first input condition being in the presence of a second input condition, comprising:
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generating means coupled to the first and second input conditions for providing first and second generator signals, the generating means including first and second sensing means having reactance values which are functions of the first and second input conditions, reactance means having a reactance value which is substantially fixed in relation to variations in the second input condition, and connection means responsive to a control signal for selectively connecting the reactance means to the first and second sensing means in first and second modes so that current through the reactance means is algebraically summed with current through the first sensing means in the first mode and current through the reactance means is algebraically summed with current through the second sensing means in the second mode, the first and second sensing means and the reactance means forming charge packets representative of the first and second input conditions, the first generator signal comprising a first plurality of charge packets formed while the connection means is in its first mode, the second generator signal comprising a second plurality of charge packets formed while the connection means is in its second mode; measurement means coupled to the generating means and responsive to the first and second generator signals for providing respective first and second measurement signals as functions of the first and second generator signals; feedback means coupled to the measurement means for providing the control signal to the generating means as a function of the measurement signal; and output means providing the output signal as a function of counts of numbers of charge packets contained in the first and second generator signals. - View Dependent Claims (45, 46, 47)
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Specification