Process variable transmitter

A method performed in a compensation processer of a process variable transmitter for providing an output signal representing an estimated compensated process variable, the process variable transmitter comprising a process variable sensor configured to provide an analog sensor signal representing a process variable and an analog to digital converter configured to receive the analog sensor signal from the process variable sensor and to convert the analog sensor signal to a digital sensor signal, the analog to digital converter operating at a converter rate, the method comprising:

• receiving an initial digital sensor signal value from the analog to digital converter;
• determining a proxy digital sensor signal value, the proxy digital sensor signal value being different from the initial digital sensor signal value;
• calculating, in a first mode, a compensated process variable value based on the initial digital sensor signal value, wherein the compensated process variable is calculated in the first mode at a first rate slower than the converter rate;
• determining a proxy compensated process variable value by calculating the proxy compensated process variable value based on the proxy digital sensor signal value;
• calculating a compensation factor as a function of the compensated process variable value and the proxy compensated process variable value by calculating the compensation factor as ratio of a first difference to a second difference, the first difference being a difference between the compensated process variable value and the proxy compensated process variable value and the second difference being a difference between the initial digital sensor signal value and the proxy digital sensor signal value, wherein the digital sensor signal values are updated at a second rate as a function of the converter rate and faster than the first rate;
• receiving an updated digital sensor signal value from the analog to digital converter at the second rate;
• calculating, in a second mode, a process variable estimate as a function of the updated digital sensor signal value and the compensation factor, wherein the process variable estimate is calculated in the second mode at the second rate;
• and
• outputting the output signal representing the estimated compensated process variable value based on at least the process variable estimate at approximately the second rate.

A distributed control system comprising:

• a controller configured to control a process;
• an input/output module coupled to the controller and configured to facilitate communication between the controller and a plurality of field devices;
• a process variable transmitter comprising:
• a process variable sensor configured to provide an analog sensor signal representing a process variable;
• an analog to digital converter configured to receive the analog sensor signal from the process variable sensor and to convert the analog sensor signal to a digital sensor signal, the analog to digital converter operating at a converter rate;
• and a compensation processor coupled to the analog to digital converter and configured for:
• receiving an initial digital sensor signal value from the analog to digital converter;
• determining a proxy digital sensor signal value, the proxy digital sensor signal value being different from the initial digital sensor signal value;
• calculating, in a first mode, a compensated process variable value based on the initial digital sensor signal value, wherein the compensated process variable is calculated in the first mode at a first rate slower than the converter rate;
• determining a proxy compensated process variable value by calculating the proxy compensated process variable value based on the proxy digital sensor signal value;
• calculating a compensation factor as a function of the compensated process variable value and the proxy compensated process variable value by calculating the compensation factor as ratio of a first difference to a second difference, the first difference being a difference between the compensated process variable value and the proxy compensated process variable value and the second difference being a difference between the initial digital sensor signal value and the proxy digital sensor signal value, wherein the digital sensor signal values are updated at a second rate as a function of the converter rate and faster than the first rate;
• receiving an updated digital sensor signal value from the analog to digital converter at the second rate;
• calculating, in a second mode, a process variable estimate as a function of the updated digital sensor signal value and the compensation factor, wherein the process variable estimate is calculated in the second mode at the second rate;
• and outputting an output signal representing the process variable estimate at approximately the second rate;
• and an actuator operatively connected to the controller;
• the controller being configured to adjust the actuator based on the output signal to control said process using the actuator.