The Tracking Ratio Station

In ratio control, the control objective is to keep the ratio between two signals, normally flow measurements, at a desired value in spite of variations in setpoints and load disturbances, and possible control signal saturations. This paper presents a new ratio control scheme, the Tracking Ratio Station, that manages to handle all these situations. It is also able to keep the ratio when one of the controllers takes a local setpoint or is switched to manual control. The Tracking Ratio Station determines the setpoints of the two flow loops so that the one with the largest control error follows the external setpoint, whereas the one with the smallest control error follows the process output of the opposite control loop. The paper illustrates the properties of the Tracking Ratio Station in terms of both simulations and industrial field tests.