Evaluation of Delays Induced by Foundation Fieldbus H1 Networks

The delays associated with the use of foundation fieldbus (FF) H1 networks within control loops are investigated in this paper. A Smar IF302 device, a Smar FI302 device, a DeltaV distributed control system (DCS), a Honeywell C300 DCS, and a National Instrument (NI) FF H1 workstation are used to implement test loops with the control-in-the-field architecture. Analytical and experimental evaluations are performed with a test loop using hardwired analog channels as a benchmark. Three segments of FF-H1-network-induced delays are identified, their analytical models are developed, and suggestions to potentially reduce the delays are provided. Furthermore, it is found that an unexpected additional delay of one macrocycle may be introduced, probably depending on whether the analog input (AI) block within the IF302 device is executed as scheduled. In conclusion, significant delays could be introduced if the traditional analog channels of a DCS are replaced by an FF H1 network.