Rosemount Inc.

Scott E Brigham

Gary A Lenz

Jogesh Warrior

Hehong Zou

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.

Transmitter with improved compensation

A process control system controls a non-self regulating process through a control output signal based on a set point and a measured process variable. The process control system includes a control circuit having a set point input, a process variable input and a control output. The control circuit generates the control output signal on the control output as a function of the set point received on the set point input and the measured process variable received on the process variable input. An auto-tuning circuit excites the process, estimates a process model based on an intersection between rising and falling asymptotes of the measured process variable, and then tunes the control function to the process based on the process model. The auto-tuning circuit obtains robust results, but is computationally simple such that the circuit can be implemented with hardware or software in low-power and low-memory applications, such as in field-mounted controllers.

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Saint Paul, MN, United States of America

Scott E Brigham