 Alternatively, PIDs can be modified in more minor ways, such as by changing the parameters (either gain scheduling in different use cases or adaptively modifying them based on performance), improving measurement (higher sampling rate, precision, and accuracy, and low-pass filtering if necessary), or cascading multiple PID controllers.Another problem faced with PID controllers is that they are linear, and in particular symmetric.Thus, performance of PID controllers in non-linear systems (such as HVAC systems) is variable.