A safety function response time model for wireless industrial control

Safety function response time is a metric for safety-critical automation systems defined in the IEC 61784-3-3 standard for single input and single output systems communicating over wired technologies. We propose a model to estimate the safety function response time for a multiple input and multiple output feedback control loop system communicating wirelessly over one of the modes defined in the IEEE 802.15.4e standard that was specifically designed for process automation. Our model merges the architecture and safety requirements defined in the IEC 61784-3-3 standard with the communication protocol defined in the IEEE 802.15.4e standard. We present equations for the worst case delay time and watchdog timer of the participating network entities, and demonstrate the application of our model via an example of a multiple input and multiple output system implementing a feedback control loop.