Intrinsic safety helps keep propane tanks in check

Preparing for barbecuing season usually means making sure your propane tanks are filled and ready for outdoor grilling.

For Decoe Inc. (Elkin, NC), an industrial automation and electrical contracting company, the upcoming spring and summer means specifying, integrating, and building machines that recondition, wash, paint, fill, and label new and used, 20-lb propane cylinders, so its customers will have enough tanks ready for the rush. This process includes Decoe’s automated propane cylinder decal-sleeving system, ‘Sleeve-O-Matic,’ which is PLC-driven and uses pneumatics in a smooth, quiet, low maintenance operation that places perforated stretch film over the cylinders.

However, in late 2001, Decoe decided a more economical method was needed for wiring solenoid devices, pushbuttons, photoeyes, and limit switches in its sleeving system. This posed a challenge because Sleeve-O-Matic must be located in a Class I, Div 1 hazardous location that requires explosion-proof cabinets and wiring methods to electrically connect its input/output (I/O) devices in a cost-efficient manner. Once the machine is finished and shipped to users, they previously had to hire an electrical contractor to install it on-site using rigid conduit with seal-offs and explosion-proof flex cabling. ‘We wanted to market the machine as ready-to-run and save customers the time and money of installing the rigid conduit,’ says Scott Sebastian, Decoe’s vp.

To accomplish this innovation, Decoe decided to use intrinsically safe (IS) barriers from Phoenix Contact (Harrisburg, PA) in the control panel. IS barriers limit energy levels in hazardous area circuits to prevent arcs, sparks or thermal effects from causing an ignition. Designed and approved for I/O signals from Div 1 and/or Div 2 hazardous area locations, they are also approved for installation in the safe area or directly in Class I, Div 2 (Groups A, B, C and D) hazardous locations. This eliminates the need for bulky, expensive explosion-proof/purged enclosures, sealed conduits, glands, and fittings that have been typically used.

In addition, Phoenix’s IS barriers are galvanically isolated, eliminating the need for high-integrity intrinsic safety grounding and maintenance associated when using zener barriers. Using the barriers allowed all I/O devices to run with cable rather than the rigid conduit, saving Decoe the material costs of electrical connections by conduit in a hazardous location. ‘The barriers also allowed our customers to see significant cost savings, as well as a simplified installation,’ adds Mr. Sebastian.

Eliminating the bulky enclosure added further savings. ‘When using a control panel in a hazardous area, space gets very expensive,’ explains Mr. Sebastian. ‘Explosion-proof enclosures are costly, approximately 15 times the cost of a standard NEMA 4 enclosure.’

Also, the significant space savings were a result of Phoenix’s dual-channel solenoid driver. Because of this dual-channel device, Decoe only had to buy half as many IS barriers compared to using IS barriers with only one solenoid. All the pushbuttons, photoeyes, and limit switches (simple devices) in the Div 1 location were integrated into the control system via dual-channel, digital input, intrinsically safe isolators with relay contacts on the safe side.

In addition, explosion-proof enclosures are also very heavy, especially in larger sizes. IS barriers allowed Decoe to keep its enclosure small and save valuable floor space.

Finally, easy-to-use LED indicators and wiring diagrams on the front face of the devices aid in troubleshooting, while technical specifications printed on the housing provide a simple reference check. ‘These barriers will pay for themselves in the very first machine we build,’ Mr. Sebastian concludes. And, immediate savings for Decoe means the same for its customers.

For more information, visit www.phoenixcon.com or www.decoeinc.com

-Control Engineering StaffComments or questions, contact:Mark Hoske, editor in chief, MHoske@cfemedia.com

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