Evaluation of the timing properties of two control networks: CAN and PROFIBUS

Due to the increased availability of low cost network technology, the use of networks to interconnect sensors, actuators and controllers is becoming widely accepted for the implementation of feedback control systems. Such type of feedback implementation, wherein the control loops are closed through a real-time network, are called network controlled systems (NCS). When implementing a NCS, the underlying communication network must provide a timely communication service, which must be adequate to fulfill the control application requirements. Therefore, the assessment of the network responsiveness to the real-time requirements of the control application is a fundamental issue. Both PROFIBUS and CAN networks are usually considered suitable to support small-scale NCS, due to their real-time capabilities. However their temporal responsiveness is highly dependent on both the timing characteristics of the supported message streams, such as its periodicity and the related message lengths. In this paper, we compare the timing properties of both CAN and PROFIBUS control networks. Basically, we assess their capability to support network controlled systems, through the evaluation of the related worst-case message´s response time. A small example of a NCS is then used to assess the capability of the CAN control network to fulfill control application requirements.