Measurement of master node delay in networked control systems

Master node delay is an unavoidable factor in a networked control system (NCS), which will lead to performance deterioration of the system, and large delay may even cause instability. In order to measure the master node delay in NCSs, its influence factors are analyzed and a non-perturbative black-box measurement method is proposed. In this method, a FPGA-based (Field-Programmable Gate Array) measurement device is developed, which sends out testing frames to master node periodically and triggers the master node to send out a response frame for every testing frame. Then the measurement device can get the measurement delay value by calculating the time interval between sending the testing frame and receiving the response frame, which consists of master node delay and some other delay that can be calculated precisely. Therefore, the accurate master node delay can be obtained by further processing the measurement delay value. A set of experiments were carried out and the results show that the proposed method can effectively measure the master node delay without a thorough understanding about its hardware and operating system software, and is not constrained by the type of operating system. Besides, as the master node delay can be measured exactly in the actual working condition without perturbing its user program by using this method, the results can reflect the real-time performance of the master node accurately. So that, it can provide a direct reference for choosing an appropriate master node for NCSs.