Irish gas board switches to wireless

Middleton, Republic of Ireland  - Emerson’s Smart Wireless technology is being used to help monitor a natural gas pipeline transmission system. The work is part of an upgrade to Bord Gáis’ Above Ground Installations (AGIs) in Ireland. Rosemount wireless devices have replaced ageing hard-wired devices as part of a trial to decide the future specification of such sites and for other sites that are due upgrades.

Existing AGIs have between three and 12 pressure transmitters measuring both inlet and outlet pressure. The cooling effect as a result of pressure reduction is also measured using temperature transmitters. These devices are connected, by hardwiring, to an onsite Remote Terminal Unit (RTU) that transmits data back to a SCADA system Master Terminal Unit at the central monitoring station in Cork. Should thresholds be exceeded to pressure or temperature, alarms are activated.

When Bord Gáis looked to upgrade the facility with new instrumentation, it was decided to use a network of wireless pressure and temperature transmitters. The Middleton site is quite unusual as it is divided by a road. Although cable ducting was already in place and this could have been reused, this facility presented an excellent application to test wireless technology with a view to installing wireless at other AGIs.

Whenever new AGIs are installed to support extensions to the pipeline system, or existing sites are upgraded, Bord Gáis looks to minimise any installation costs. Power and data cabling are usually installed in ducting at the AGIs. However, burying cables can prove to be costly and time consuming. For the upgrade at Middleton, wireless promised to be lower cost, offered faster installation and start up, as well as easy integration into the existing RTUs using Modbus serial communications.

Although there is minimal traffic on the road dividing the Middleton facility, Bord Gáis could not use a line-of-sight wireless solution as the signal may be interrupted by passing cars affecting the reliability of the communications. With the new wireless system, each measurement point has a redundant communication to the RTU via two or three routes.

Wireless devices can act as a router for other nearby devices, passing messages along until they reach their destination. If there is an obstruction, transmissions are simply re-routed along the network until a clear path to the wireless gateway is found. As conditions change or new obstacles are encountered in a plant, such as temporary scaffolding, new equipment, or a parked construction trailer, these wireless networks simply reorganise and find a way to get their signals through.

Because cabling enters into potentially explosive zones, regular checks are required of cable integrity as well as the condition of the EX barriers. This is especially important for older sites where there can be an ageing cabling infrastructure. Wireless removes such concerns and reduces the number of site inspections needed.

At Middleton, Rosemount wireless transmitters include five measuring pressure, one differential pressure, and one temperature; all transmitters have been successfully installed and are sending measurements back to the control room via the RTU. The devices are placed in enclosures, standard practice for all instrumentation used at Bord Gáis AGIs, and the Smart Wireless Gateway is positioned within the instrumentation kiosk, which is effectively a ‘walk-in’ enclosure.