Investigation on Digital Control Concepts for Dynamic Applications of Electromagnetic Force Compensated Balances

Abstract

This paper deals with the optimization of the dynamic performance of electromagnetic force compensated balances by alternative controller concepts. Concerning uncertainty of measurement and achievable resolution, balances based on the principle of electromagnetic force compensation represent the state of the art. Due to the high achievable resolution, the focus of the implementation is not concentrated on static weighing applications any longer, but also shifted towards dynamic purposes. Typical applications would be check-weigher or metering devices in pharmaceutical or food filling plants. There, the demand is not only to obtain the resolution at a high reproducibility, but also to reach a stable and reliable measurement result in a very short time. One possibility to achieve this goal is an optimization of the controller, whereas a PID controller represents the state of the art. For static applications, the PID controller’s performance is fairly good, but due to the limited number of parameters and the basic concept, the optimization potentialities for dynamic applications are restricted. An alternative approach is to realize the controller digitally. The advantage of this approach is, that the controller and filtering concept can be adapted unrestrictedly to the system to be controlled, and that parameters may be adjusted easily and online. With these concepts, the time to achieve a stable measurement signal can be diminished significantly. In this paper we will present detailed investigations on two commercially available Real-time systems (Controller and FPGA-based) for the implementation of digital control and filtering algorithms. The hardware restrictions were evaluated, and based on these results possible software realizations were tested. In accordance with the determined capabilities and limitations, a controller was designed. These first investigations emphasize the capabilities and potential of digital controllers.