Analog process variable transmitter with electronic calibration
AssigneeRosemount Inc.
InventorNathan Len Wiater
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Abstract
A process variable transmitter for measuring a process variable includes a process variable sensor configured to sense a process variable and provide a sensor output. Measurement circuitry receives the sensor output and provides a measured output related to the process variable. Output circuitry provides a device output on a two-wire process control loop based upon the measured output. The output circuitry has a transfer function that is a function of an adjustable analog circuit component. A motorized actuator is configured to adjust the adjustable analog circuit component to thereby change the transfer function of the output circuitry. An optional calibration controller is also provided.
Claims18
A process variable transmitter system for measuring a process variable, comprising:
- a process variable sensor configured to sense a process variable and provide a sensor output;
- measurement circuitry configured to receive the sensor output and provide a measured output related to the process variable;
- output circuitry configured to provide a device output on a two-wire process control loop based upon the measured output, the output circuitry having a transfer function that is a function of an adjustable zero setting analog circuit component and an adjustable span setting analog circuit component;
- and
- a motorized zero setting actuator configured to receive a signal received from a calibration controller related to a desired zero setting of the device output and which responsively adjusts the adjustable zero setting analog circuit component to thereby change the transfer function of the output circuitry;
- a motorized span setting actuator configured to receive a signal received from the calibration controller related to a desired span setting of the device output and which responsively adjusts the adjustable span setting analog circuit component to thereby change the transfer function of the output circuitry;
- a transmitter housing and wherein the measurement circuitry, motorized zero setting actuator, motorized span setting actuator and output circuitry are located entirely in a hermetically sealed environment in the transmitter housing and wherein the calibration controller is outside the housing;
- and
- the calibration controller configured to send the signals related to the desired zero and span settings to the motorized zero setting actuator and motorized span setting actuator, respectively.
A method of calibrating a process variable transmitter of the type used to measure a process variable, comprising:
- sensing a process variable with a process variable sensor;
- measuring the sensed process variable;
- providing a device output on a two-wire process control loop based upon the measured process variable and a transfer function of output circuitry;
- and
- changing the transfer function of the output circuitry using a zero setting motorized actuator which receives a signal received from a remote location related to a desired zero setting of the device output and which responsively adjusts an adjustable zero setting analog circuit component of the output circuitry;
- changing the transfer function of the output circuitry using a span setting motorized actuator which receives a signal received from the remote location related to a desired span setting of the device output and which responsively adjusts an adjustable span setting analog circuit component of the output circuitry;
- enclosing the measurement circuitry, motorized zero setting actuator, motorized span setting actuator and the output circuitry entirely in a hermetically sealed housing and wherein the remote location is outside the housing;
- and
- sending the signals related to the desired zero and span settings to the to the process variable transmitter using a calibration controller.
Dependencies are inferred from the claim text.