APEX units have been located in each of the twelve old regions and are designed to convert protocols from three different RTU types into a common data format. Two further APEX units at System Control HQ act as ‘hot’ standbys, to take over from any field APEX in the event of a failure.

The second integration phase involves installing twelve APEX units, two in each of the former regions of the South and West, configured as ‘hot’ standby pairs. The APEXs talk to the RTUs that control the medium and low-pressure distribution to consumers. This part of the system converts eight different RTU protocols into the common format.

For convenience and speed of changeover, Transco has worked closely with Arcom to develop a Configuration Tool that allows new protocols and scanning strategies to be downloaded remotely over the network. By using this tool, an operator only needs to make a change at one system node, and the entire communications channel will be automatically configured, together with the host system. This saves the time and cost of a site visit.

The British Gas Transco system makes full use of the multi-session capacity of the TCP/IP interface offered by the APEX. Multiple hosts are able to concurrently connect to the services available from the unit.

APEX also oversees the physical communications links to the existing outstation networks. This is by radio (RF) or by modem links -either dedicated leased-line or public switched telephone network (PTSN) according to the nature of existing communications equipment. APEX effectively moves the overall system towards an open-architecture network, giving great flexibility over future RTU and SCADA strategy.

High-pressure gas distribution for the UK is now managed by a single national SCADA system at British Gas Transco’s System Control headquarters in central England. Four further SCADA systems (situated within the new North, South, East and West operating areas) control the medium and low pressure distribution to consumers. All five SCADA systems are linked via a common wide-area Ethernet network, using mainly microwave communications, in order to access to all data at any location.

As well as providing Transco with flexible system integration, APEX also facilitates a more effective scanning strategy. Each APEX unit is configured to concentrate data locally, notifying the host systems only when changes take place outside pre-programmed limits. This is the more adaptable ‘report-by-exception’ (RBE) strategy. It substantially reduces the processing ‘overhead’ at the host - yet still allows operators to access live data at any point in the network, at any time. This could be for operational, management or maintenance purposes.

For ease in troubleshooting, facilities have been designed into the software system to capture and trace communication exchanges. Sophisticated diagnostic routines can be undertaken by each of the APEX units. Normally these are accessed using a standard Telnet session on the TCP/IP-based Wide-Area Network (WAN). The APEXs also provide SLIP capability. The SLIP feature also allows operators in the field to access the SCADA network, and all its embedded diagnostics, using a standard portable computer and modem link over the PSTN network.

A key element in Transco’s decision to team-up with Arcom was the ‘off-the-shelf’ nature of the APEX family, which is built on open-architecture principles. This is unlike the predominantly proprietary equipment within the existing SCADA system that the APEX units are communicating with. Each APEX uses standard bus-board hardware and modular software techniques, allowing the user to convert process data from one protocol to another, both easily and transparently.

While British Gas provided their own Configuration Tool, APEX is supplied with standard configuration software that runs in the Windows 95 or NT environment. Protocol emulation, once developed, is put into a library from where users can mouse-configure the protocol conversions as intermediate ‘virtual devices’. These enable data from remote equipment to be converted and communicate transparently, via the APEX, into the host system. These virtual devices can also perform powerful data concentration functions, such as storing information in a local database and intelligently retrieving it as required. This allows for the interconnection of diverse equipment in a very cost-effective manner.

For example, the APEX units can accommodate a combination of numerous physical PLC/RTU devices into a single virtual unit, thereby reducing the overhead attributable to the host protocol when data is being retrieved. Additionally, data from remote equipment can be combined into logical groupings - such as all alarm, shutdown, or control signals - so that polling and control strategies within the host can be optimised.Further flexibility is implemented via the provision of a fully IEC-1131-compatible editor/compiler. This allows users to add applications such as interlocks, data derivation, number-type conversion, etc, to the base data store within the APEX unit.