Patent ID: 7945339

Claim:
A process control system for a process having a process variable, comprising: a field device to transmit a process variable signal indicative of the value of the process variable of the process; and, a controller in communication with the field device, the controller including a processor and a control module that executes periodically at a periodic execution rate on the processor, wherein the controller receives the process variable signal and the control module generates a control signal for the process based on the most recently received process variable signal; wherein the field device wirelessly transmits the process variable signal non-periodically based on whether the value of the process variable has changed by more than a predetermined threshold so that the transmission time between at least two successively transmitted process variable signals is longer than the periodic execution rate and wherein the control module executes to generate a process response signal representing a process response to the control signal based on an elapsed time between transmission of process variable signals and uses the process response signal to generate the control signal.