How does proportional control work

This gives "bumpless" transfer if the error is zero when the controller is turned on. The set point SP is the target value and process variable PV is the measured value that may deviate from the desired value. The output of a non-integrating process returns to the same steady-state value after an input impulse response. An integrating process does not return to the same steady-state value after the impulse response.

Consider the example of a water bottle with a leak non-integrating system and without a leak integrating system. Conversely, when Kp is negative a reverse acting process , the controller must be direct acting for stable control. Since Kp and Kc always have the same sign for a particular process and stable control requires negative feedback, then:. In most commercial controllers, a positive value of the Kc is always entered. The sign or action of the controller is then assigned by specifying that the controller is either reverse or direct acting to indicate a positive or negative Kc respectively.

If the wrong control action is entered, the controller will quickly drive the final control element e. Proportional Band Some manufacturers use different forms for the same tuning parameter. The popular alternative to Kc found in the marketplace is proportional band, PB.

In many industry applications, both the CO and PV are expressed in units of percent. Given that a controller output signal ranges from a minimum CO min to maximum CO max value, then:. Many case studies on this site assign engineering units to the measured PV because plant software has made the task of unit conversions straightforward. If this is true in your plant, take care when using these conversion formula. We explore P-Only control, offset and other issues for the heat exchanger and the gravity drained tanks processes.

Email : info controlstation. Search Results. Proportional Control. Establish the design level of operation the normal or expected values for set point and major disturbances. This technique is somewhat intuitive: if the temperature is much too low due to initial error, start-up mode, or more material being added , simply turn up the heat by a large amount; if the difference or error is small, apply just enough heat to keep it close to the setpoint. This is called proportional P control.

In fact, this works fairly well, but has limitations, as it has some long-term cumulative sources of error buildup and poorly controlled reaction to upsets, and is also prone to oscillation around the setpoint. To enhance the performance of a proportional controller, two other factors called the integral and derivative terms are added to the closed-loop control approach.