Sensor parametrization and the sensor group

While sensors play an important role in the control loop, in practice they often are considered to be a part of the plant and the explicit interaction between the plant and sensor is disregarded in the further considerations. Based on an input/output perspective, this paper investigates the internal stability property of the control loop when this interface is considered explicitly. As a main result of the paper, we provide a Youla type characterization of all the sensors that renders the loop stable for a fixed plant and controller.