Setting the Standard for Automation

Loop tuning basics: Integrating processes

Loop tuning basics: Integrating processes

Posted on, authored by James Beall, Principal Process Control Consultant at Emerson Process Management

The two most common categories of process responses in industrial manufacturing processes are self-regulating and integrating. A self-regulating process response to a step input change is characterized by a change of the process variable, which moves to and stabilizes (or self-regulates) at a new value. An integrating process response to a step input change is characterized by a change in the slope of the process variable. From the standpoint of a proportional, integral, derivative (PID) process controller, the output of the PID controller is an input to the process. The output of the process, the process variable (PV), is the input to the PID controller. Figure 1 compares the response of the process variable to a step change of the PID controller output for a self-regulating process and for an integrating response.

Level processes typically have an integrating response, the likely exception being when the outflow of the vessel is gravity driven. Other processes can have an integrating response. For example, a “low-pressure, large-volume” gas pressure control application can have an integrating process. Another example of an integrating process is a reactor temperature controller that cascades to a “jacket water inlet temperature difference” controller. This controller controls the difference between the reactor contents’ temperature and the jacket water inlet’s temperature based on the set point specified by the output of the reactor contents’ temperature controller.

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