In high-speed loops, such as those used for flow and pressure control, battery-powered wireless instruments must balance battery life and data update rates. In cases where battery life is expected to exceed five years, a data update period of 60 seconds may be required. Gareth Johnston, global wireless product manager for ABB, says such a relatively slow update period is not compatible with high-speed loops.
Machine control is not so hot for wireless, says Steve Toteda, vice president and general manager of the wireless business unit at Cooper Industries (www.cooperindustries.com) and chairman of the Wireless Industrial Networking Alliance (WINA). “A lot of people have looked at this, but machine controls have a different set of characteristics for which wireless is not as well suited in most cases.” He adds, however, that using wireless to interconnect machines is a perfect application for the technology.
PID control. According to Johnston, trials are currently being conducted for PID control where wireless loops are involved. As with the high-speed loop issue, the PID applications are also limited by the battery life/update period balance. Despite this issue, he expects PID loops to include wireless instruments in the near future.
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