Measuring WirelessHART against wired fieldbus for control

Wireless applications in process automation started in areas where wireless sensors provide rich process information to the automation systems. Shortly after WirelessHART became the international standard, both ISA100.11a and WirelessHART claimed that their respective wireless technology could be applied to control as well. Although both standards provide provisions for supporting control over wireless, actual installations of wireless control systems have been slow to be adopted. Due to people´s wariness of using wireless in combination with the serious nature of control, what is needed is a demonstration of performance and reliability of control when being executed across wireless media. A good starting point is a comparison between a wireless control system and its wired counterpart. In this paper we first study if we can establish a WirelessHART control loop the same way as a wired one; then we study if our WirelessHART control loop could achieve the same execution rates and reliability as a wired Foundation Fieldbus control loop. The experiment affirms that, in most likely cases, control over a WirelessHART network could be as good as control over a wired fieldbus.