I have set up a control loop, see attachment, and can't find any values for the PID controller once I install the sensor. I adjusted the values without the sensor using the frequency response method and verified them with Nyquist criterion. These methods are valid without a measuring device. The autotuning feature of Simulink keeps giving me incorrect values. In this system, an electromagnet is used to try to keep a metal ball suspended in air. The control loop consists of a controller, current controller (cascade control), process, and sensor. The upper control loop represents the actual control loop, while the lower one represents the linearized form. In both, the sensor is not installed, and the process is still stable.