Transmitter with improved compensation
First Claim
1. A measurement transmitter, comprising:
- conversion circuitry including a first sensor for sensing a process variable within a first span of process variable values the conversion circuitry providing a first digitized output representative of the sensed process variable;
a memory for storing at least two membership functions for the first sensor, each membership function having a non-zero value over a predetermined region of the first process variable span and a substantially zero value over a remainder of the first span;
selection circuitry for selecting only those membership functions which have a non-zero value at the first digitized process variable;
correction circuitry for providing at least one correction value, each correction value calculated from a compensation formula based on a plurality of process variables stored in the memory which corresponds to a selected membership function;
weighting circuitry for weighting each correction value by its corresponding selected membership function, and for combining the weighted correction values to provide a compensated process variable; and
an output circuit for coupling the compensated process variable to a loop circuit.
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Abstract
A circuit for compensating variables in a measurement transmitter. Within the transmitter, a sensor senses a primary process variable such as differential pressure and a converter digitizes the sensed process variable. The sensor senses pressures within a span of pressures values. A memory inside the transmitter stores at least two membership functions, each membership function having a non-zero value over a predetermined region of the process variable span and a substantially zero value over the remainder of the span. The memory also stores a set of compensation formulas, each formula corresponding to a membership function. A selection circuit in the transmitter selects those membership functions which have a non-zero value at the digitized process variable and a correction circuit provides at least one correction value, each correction value calculated from a compensation formula corresponding to a selected membership function. A weighting circuit multiplies each correction value by its corresponding selected membership function, and combines the multiplicands to provide a compensated process variable. The compensated process variable is coupled to a control circuit connecting the transmitter to a control system.
48 Citations
15 Claims
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1. A measurement transmitter, comprising:
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conversion circuitry including a first sensor for sensing a process variable within a first span of process variable values the conversion circuitry providing a first digitized output representative of the sensed process variable; a memory for storing at least two membership functions for the first sensor, each membership function having a non-zero value over a predetermined region of the first process variable span and a substantially zero value over a remainder of the first span; selection circuitry for selecting only those membership functions which have a non-zero value at the first digitized process variable; correction circuitry for providing at least one correction value, each correction value calculated from a compensation formula based on a plurality of process variables stored in the memory which corresponds to a selected membership function; weighting circuitry for weighting each correction value by its corresponding selected membership function, and for combining the weighted correction values to provide a compensated process variable; and an output circuit for coupling the compensated process variable to a loop circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method in a measurement transmitter for calculating compensated process variables, comprising:
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sensing a process variable representative of a process, the process variable taking on values within a predetermined span of process variable values; converting the sensed process variable to a digitized process variable; storing at least two membership functions, each membership function having a non-zero value over a predetermined region of the process variable span and a substantially zero value over the remainder of the span; storing a set of compensation formulas, each formula corresponding to a membership function; selecting only those membership functions which have a non-zero value at the digitized process variable; providing at least one correction value, each correction value calculated from a compensation formula based on a plurality of process variables and corresponding to the selected membership function; weighting each correction value by its corresponding selected membership function, and combining the weighted correction values to provide a compensated process variable; and coupling the compensated process variable to a control circuit.
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Specification