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Here's a wireless alternative to expensive fiberglass cabling

July 21, 2015
WiFi network for chemical plant gas chromatographs saves big compared with fiberoptic cabling connections


The Axiall Corporation chemical plant in Westlake, La., a maker of chlorovinyl products, decided to upgrade several gas chromatographs within an analyzer building. The analyzers monitor chemical streams such as 1,1 ethlylene dichoride and 1,2 ethylene dichloride used primarily in the production of vinyl chlorides. Axiall is North America's second-largest producer of vinyl chloride monomer.

Examples of stream components measured by the online gas chromatographs include methyl chloroform, ethylene, vinyls, butadiene, nitrogen, oxygen, carbon monoxide, and carbon dioxide. The online GC analyzer values are communicated to a central digital computer system (DCS) in the plant control room, primarily for quality control. Operators monitor online data and make adjustments to keep streams within specifications. They also send stream samples to plant laboratories for cross comparisons to check for any drift in data accuracies.
The new analyzers, PGC5000 Process Gas Chromatographs from ABB Measurement & Analytics, require Ethernet output connections to the plant control room. The earlier gas chromatographs used serial twisted-pair connections. Plant engineers first considered the installation of fiberoptic cabling between analyzer sites and the control room. But that turned out to be prohibitively expensive.


Working with the plant's Process Control Department, engineers decided to take advantage of an existing nearby plant-wide Ethernet network using WiFi wireless interconnection. A wireless Ethernet access point was already positioned outdoors about 100 yards from the analyzer building. The output Ethernet cable from the new gas chromatographs now connects to an Ubiquiti Bullet 5.8 GHz WiFi radio. The radio resides within an air-purged housing due to area hazard classification.

A Power over Ethernet (PoE) adapter allows a single Ethernet cable to provide both data connection and electrical power for the radio. A PoE network switch also powers the Ethernet wireless access point. The radio's N-type RF output plugs into the directional antenna mounted outside the analyzer building. The Ubiquiti radio incorporates a signal strength LED meter to aid antenna alignment, which is line-of-sight. The directional antenna provides more than sufficient range to reach the Ethernet access point. The WiFi network relies on WPA2 encryption for security.


Preliminary estimates yield a savings of over $450,000 based on the installation of fiberoptic cabling for all the plant's gas chromatographs and on the plant's experience with actual WiFi Ethernet interconnections for six gas chromatographs. This includes cases where Ethernet WiFi access points and infrastructure will have to be added. 

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