Installing a display monitor or a PC in a hazardous area used to be a very expensive proposition, but new technologies are easing implementation. Thin clients can be used for the operator interface tasks of displaying information and entering commands, often via a touchscreen. They don't require much processing power, don't consume much energy, and don't generate a lot of heat. This makes it possible for manufacturers to provide thin clients in sealed enclosures suitable for installation in Class I, Div. 2 applications.
A major international oil company has a facility near San Francisco Bay where oil from tankers is transferred to storage tank farms. The company wanted to place six industrial workstations in the field near the transfer points for easy operator access, and connect these workstations back to a control room 500 feet away through a series of industrial switches.
The solution was to link the thin-client workstations back to the Honeywell DCS in the control room. "This installation is in a Class I, Div. 2 outdoor environment with year-round outdoor use and no purge system is needed," relates Louis Szabo, business development manager for the HMI and purge business unit at Pepperl+Fuchs.
"Our certified VisuNet IND OIT workstations met the required price point and hazardous requirements. A 22-in. touchscreen was selected for compatibility with the HMI widescreen graphics already developed for the control room," adds Szabo.
Although a thin-client architecture works well for extending operator interface capabilities from protected areas, such as control rooms to hazardous areas, other applications are more suited to solutions that simply extend the distance from the PC to the display monitor—often by miles.
In these situations, a KVM extender is often the best choice, as it requires very little in the way of design, just the installation of KVM hardware at the source and destination. A chemical company in the Houston area used this technology to install two workstations in a Class I, Div. 2 area, and link them to a remote Siemens PCS 7 control system.
The workstations are under a roof in an open-air environment, and the requirements were for two Class I, Div. 2-certified workstations, each with a wide-screen, glove-friendly touch display, a keyboard and a trackball. All the components needed to be housed in a stainless steel enclosure and pedestal to meet NEMA 4X requirements. The client didn't want to use a purge system, so all of these components had to be rated for use in Class I, Div. 2, including a fiber-optic KVM receiver.
A fiber-optic KVM extender was installed at the control room miles away from the workstations. The solution was built by Pepperl+Fuchs SEC group, and certified under UL's 698A NNNY panel program to meet the primary customer's concerns about the hazardous-area mounting of a certified system, exposure to both hazardous and potentially corrosive environments and temperatures over 115 °F.
For remote operator interface applications in hazardous environments, a thin client is the most economical solution, followed by a KVM extender. The most expensive is to install a PC, often with peripherals such as a printer, but in some applications that's what's needed.
A good solution in these cases is to use non-rated components installed in a purged enclosure. Depending on the type of purge system, this can allow non-rated components installed in standard NEMA 12 enclosures to be used in hazardous environments up to Class I, Div. 1.
"Purging and pressurization systems may be integrated or mounted separately, and the application can include any variety of exposed or remote devices such as pushbuttons, keyboards and barcode scanners," says Mike Baucom, CEO, Bebco Industries. "Depending on the application, the devices can be protected by safety barriers within the pressurized enclosure to render them intrinsically safe."