Handling of variable wireless latency and updating frequency in PI controllers

Abstract

In closed loop process control with wireless measurements it must be ensured that communication packet dropouts and variable latency is handled properly with respect to the impact on the controlled process. A procedure for automatic adjustment of the controller parameters is presented. The main property is to maintain the closed loop stability margin in presence of variable communication latency. The sampling rates in wireless instrumentation are usually chosen to be quite slow to save battery power in the transmitters, so both selecting the appropriate sampling rates and handling of the real transmission characteristics in a closed loop process control environment require attention. The presented algorithm can handle typical wireless communication errors, and can also be used to deliberately alter the sampling rate based on the actual disturbance level and by that save battery power in calm periods. The algorithm is based on the SIMC tuning rules.