Bus system drives remote I/O into hazardous areas

Turck Banner has developed a decentralised, remote I/O system that allows large numbers of addressable channels to be installed in Zone 1 hazardous areas.

Traditionally, providing I/O in hazardous areas has been tricky for several reasons, including the high energy requirements of intrinsically safe (IS) analogue (4-20mA) equipment, and the need to use short lengths of cable in the Ex area. This meant that groups of no more than four devices had to be wired separately to a flameproof marshalling box and then, via a barrier, to the control device outside the hazardous area. These systems were bulky, and costly and time-consuming to install.

The new modular system, called Excom, is based on an IS interface that allows up to 128 digital or 64 analogue channels to be connected to a single field bus cable. Modules containing four analogue or eight digital I/O are mounted on racks, linked via a backplane bus. Each backplane acts as an independent, self-contained barrier, with its own power supplies, gateways and barriers. There are three versions of the racks, accommodating five, nine or 18 modules.

Field devices can be connected - and power supplies, gateways and I/O modules exchanged - while the system is operating. The modules, which are addressed using three decimal coded rotary switches, incorporate short-circuit, wire-break, and overload fault detection.

The I/O system includes a Profibus-DP link and offers an IS interface to Zone 0 areas. It allows online parameter setting and configuration. Dual redundancy is an option for the 24V DC or 115/230V AC power supplies.