Derivative filter is an integral part of PID design

A PID controller is a second-order controller, and as such involves four parameters. However, many available tuning methods design only three parameters, and then use a default choice for the derivative filter factor. In the paper it is pointed out that for a PID controller of series form a default value for the derivative filter makes some sense, since it corresponds to a lead-lag controller. For PID controllers of ideal (or parallel) form default values are much less natural. The main purpose of the paper is to discuss the importance of model-based design methods, treating the derivative filter as an inherent part of the design. For example, it is illustrated how default choices for the derivative filter may lead to excessive control actions.