Time Constraints in PID Controls with Send-on-Delta

Send-on-delta allows reduction of event rates and better resource utilization in the networked control systems. At the same time, the send-on-delta increases the uncertainty on the system state in the controllers, resulting in such problems as irregular samples, timing of sensor and controller events, and limit cycles. These problems can be solved by limiting the inter-sample intervals with the help of time constraints. This paper analyses the problems of send-on-delta in closed loops with PID controllers under considering of time constraints. Based on this analysis, the tuning rules for selection of time constraints in such loops are proposed.