The Emerson devices also feature channel hopping, a built-in protection against jamming of channels by either intentional or non-intentional sources.
Figure 2 -- High reliability: The wireless devices have
The wireless mesh system has proven to be incredibly reliable (Figure 2). After installation and commissioning, everything comes online within five to 10 minutes and seems to be totally flawless. "We put a Smart Wireless gateway out there, start lighting up the sensors, and they talk. I haven’t had to do any maintenance. It just runs," explains Reese Borel, PPG process control specialist.
Uses of Smart Wireless at the Lake Charles plant, some of which are in test stage, include:
Steam header temperature profiling. Twenty wireless Rosemount transmitters are profiling temperatures on the 175-lb and 400-lb steam headers across the entire plant. Operators watch these data every day to check for cold spots and adjust steam throughput to maintain superheated steam plant-wide. Saturated steam can harm some pieces of equipment.
Redundant tank level measurement. Eight wireless transmitters now monitor caustic tank levels, providing backup for primary radar level measurements. The wireless information goes from the gateway to the plant distributed control system (DCS), where the logistics operators responsible for transferring material into and out of the tanks use those levels to avoid overfilling. These operators no longer have to manually measure the tanks every shift — instead they do it only about once a month when a deviation occurs between wireless signals and radar readings — typically because the radar units have become coated with salt.
Vibration monitoring of centrifuges. To test the ability of wireless to provide vibration data, four transmitters were very quickly installed on Salt Bird centrifuges. They provide a continuous stream of vibration data back to the control room to help operators determine when maintenance is due.
Deluge valve monitoring. Wireless discrete transmitters are deployed in three areas of the plant alongside existing deluge valves (each of which consists of one water and one air valve). The transmitters monitor for low and high pressures using dual independent sensors, and alerts operators to any problem with the deluge systems.
Tank pressure monitoring. Two wireless pressure transmitters now check tank pressures in a remote area of the plant where no wired path was available.
Wireless tablet PCs. The plant is testing these devices to enable personnel to use the AMS Suite: Intelligent Device Manager predictive-maintenance software to check transmitters, look up information on existing valves or transmitters, and remotely view the DCS screens.
Once a test succeeds, the plant adopts the application. In all of these cases, wireless instrumentation was chosen as the best means to save time and money for PPG while delivering useful data from the field.
A Valuable Start
For a site the size of Lake Charles, retrieving data from some areas via wiring is cost prohibitive. In addition, getting conduit and monitoring instruments into areas like steam headers ranges from very difficult to impossible. Wireless technology delivers important data from measurements that previously couldn't have been made. The plant is continually discovering additional applications for wireless to increase process reliability and improve operations.
Tim Gerami is a senior design engineer in the chemicals division of PPG Industries, Lake Charles, La. Jerry Moon is public relations director for Emerson Process Management. Austin, Texas. E-mail them at email@example.com and Jerry.Moon@Emerson.com.