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01 July 2003

Wired for oil

A SCADA architecture based on Foundation fieldbus and Ethernet secures inaccessible land locations and offshore platforms.

By Jonas Berge

It has dawned on most that traditional serial communication is no longer adequate for supervisory control and data acquisition (SCADA) systems. To build a SCADA system based on industrial Ethernet that leverages the more intelligent devices is now the issue.

A SCADA or telemetry system collects data from various remote sites and makes it available in a central location. Examples include everything from the simple electronic gathering of data from oil wells to the remote operation of an unmanned oil or gas platform.

Applications include tank farm management in storage facilities, water and steam injection, transmission pipelines, metering stations, steam production, compressor stations, and others.

Due to the distances involved and the obstacles in the path, the data typically transmits using radio, though sometimes via microwave or satellite. Sometimes dial-up or leased lines are useful.

Apart from the different media, a whole range of mainly proprietary protocols exists. However, Ethernet is the media of choice for wired automation backbones, and it is gaining significant inroads in the SCADA market.

Ethernet over radio, or wireless Ethernet, is already functioning in business applications and is available in industrial versions.

Diagnostics remote locations

This SCADA architecture is a result of close cooperation with different oil and gas companies around the world, fusing their know-how with existing knowledge of fieldbus and industrial Ethernet.

It came about to provide a platform that enables an increase in efficiencies in oil and natural gas production and movement, water reservoir monitoring, and like applications.

It enhances remote applications through improved access to real-time measurements and instrument diagnostics from remote locations. More data requires an increased bandwidth.

For example, production field teams typically monitor hundreds of wells and pumping facilities continuously. As basic measurement couples with device diagnostics and other maintenance information, the result is overwhelming volumes of data.

This new remote operations information architecture is based on high-bandwidth Ethernet networking to handle the volume of data. The new SCADA architecture is ideal for remote unmanned oil and gas production sites, be they inaccessible land locations or offshore platforms.

As a SCADA system grows and operations cover larger areas, diverse systems may have to integrate into a single contiguous system. The use of interoperable standards-based technologies becomes more important.

Standards make it possible to integrate equipment from different suppliers and bring the data all the way into the business environment. By leveraging standards, information architecture can grow, regardless of what the equipment vendors are.

Open information architecture consists of standards-based networking and software. Apart from flow measurement and control, a modern SCADA system also needs full access to device diagnostics and configuration.

Thus, a modern SCADA architecture must be completely digital. The design starts at the field level, where transmitters, valve positioners, and remote I/O for discrete devices must network using Foundation fieldbus (FF) H1 technology rather than 4–20 mA.

FF includes a wide selection of field instruments from a multitude of vendors. Fieldbus linking devices and flow computers take the place of remote terminal units (RTUs) from the past.

The linking devices, in turn, network using FF high-speed Ethernet (HSE), which also benefits from the tight integration of equipment from competing vendors.

Faster than HART

At the field level, using the digital FF protocol for communication with instruments for the primary measurements of static and differential pressure as well as temperature provides greater accuracy and functionality in oil and gas operations than what was possible with 4–20 mA.

Faster than a highway addressable remote transducer (HART), H1 fieldbus transmitters provide better dynamic response than their smart counterparts that have to fall back on analog. FF eliminates the need for conventional I/O expansion cards.

A fieldbus flow computer will be able to accept turbine flowmeters and densitometers based on H1 fieldbus in the future. Discrete I/O, control valves, analog converters, and others can also join in.

Eliminating 4–20 mA removes the errors resulting from digital-to-analog-to-digital conversions in transmitters as well as in old RTUs.

The new architecture combines FF networking technology, wireless industrial Ethernet, and SCADA infrastructure, together with OLE for process control (OPC), to get information into software applications for production, monitoring, instrument maintenance, and asset management.

Fieldbus provides the necessary bandwidth for all of this information.

FF allows multidrop wiring for instruments while maintaining intrinsic safety, which means it is economical to mount the linking device outside the hazardous area where it is easy to access, with only two wires safely going to the instruments in the field.

Industrial Ethernet radios

The wireless Ethernet used for SCADA is different than the IEEE 802.11b Wireless Fidelity (WiFi) standard used in the business environment. WiFi operates at 2.4 gigahertz (GHz) and has high speed (up to 11 megabits per second and increasing), but has a very limited distance, rendering it unsuitable for SCADA applications.

However, using industrial-grade Ethernet radios, you can now communicate 40 kilometers without cable. The reason for the longer distance is that the radio operates in the unlicensed 900-megahertz band, which suffers less attenuation than 2.4 GHz and has much higher gain antennas, higher power transmitters, more sensitive receivers, and lower speed, which is more robust.

Other differences setting industrial wireless apart from WiFi is that the radio end of the technology is usually proprietary, although the wire at the Ethernet end is standard.

Industrial Ethernet is not really for use in mobile applications and is not for roaming. It is a fixed-location technology. Other industrial features include fail-over redundancy (select other radio in case of failure) and serial tunneling for legacy interfaces.

In the past, serial RS-232-based radios for SCADA applications were limited to 19.2 kilobits per second (Kbps), while wireless Ethernet radios now have a bandwidth of 512 Kbps, enabling a far greater data throughput.

The result is more information and faster updates from more sites. It cannot be stressed enough how much simpler Ethernet is to use than traditional RS-232 serial.

With Ethernet, there is no need to configure rate, parity, stop bits, flow control, timeouts, and the rest. In a chain that is typically at least four devices long, eliminating these configuration requirements greatly reduces the number of things that can go wrong.

Wireless Ethernet is completely transparent. The remote device is simply connected to the remote access point.

Addressing is simpler, too. IP addresses assign to the access points using the management tool embedded in the access point, which is running as the Web server. Internet Explorer is the user interface.

The access point automatically detects the remote Ethernet devices connected and displays them in an endpoint list.

Found in DCS and most RTUs

Because industrial Ethernet wireless networking gear is not WiFi compliant, there is no interoperability among vendors. Thus, central and remote sites must use the same brand equipment. Of course, different brands of radios used in different areas can ultimately link together using wired Ethernet.

However, recall that Ethernet interoperability is not as simple as Ethernet TCP/IP. For easy system integration, a standard application layer such as FF or possibly Modbus/TCP is required for different equipment to work together.

Without a standard application layer, communication among different controllers is not possible, and integration into the host computer is more tedious.

FF HSE provides interoperability at the higher level, making it possible to integrate linking devices and gateways, and looks ahead to a future with HSE-based gas chromatographs, variable speed drives, and the like.

Fieldbus provides the necessary bandwidth for all this information. Ethernet eliminates the need for legacy serial interfaces such as RS-232 and RS-485 and eliminates the dependency on proprietary protocols.

Configuration from any fieldbus host supporting HSE is possible, and it can all happen from a central remote location without the need for site visits.

Proprietary technologies found in distributed control systems and most RTUs become very costly because driver development, if at all possible, often costs many tens of thousands of dollars and is difficult to implement.

System virtually impenetrable

Industrial Ethernet access points are frequency-hopping radios. They spend only a few milliseconds at each frequency. This transmission scheme makes detection difficult and is security against spying or overriding data.

Indeed, the primary security is obscurity. Thousands of internal setting combinations for the frequency-hopping pattern make it very difficult to eavesdrop or even detect the radio.

Additionally, this architecture uses 128-bit encryption. Further, by limiting the number of connections, the system is virtually impenetrable. All of these measures incorporate into the radio and require no additional infrastructure.

Remote mounted devices can also incorporate access control based on passwords. As an additional measure, it is possible to use virtual private networks to provide additional security through obfuscation. There is a large selection of IP and Ethernet-based equipment available that makes this architecture real.

Also, remote locations can use various measures of theft prevention such as on-site IP surveillance cameras. These can transmit video sharing the same networking, eliminating a second infrastructure for security. This is important where intruders and theft are concerns.

Other physical security precautions include simple intrusion detection, such as opening fence gates and panel doors; detection of device disconnection or tampering; and audiovisual site alarms.

Stop further investment

The IP platform integrates well with the corporate intranet. Using Ethernet all the way from the linking devices, sufficient bandwidth is ample and exists for current and future information needs.

At the host level in the central control room, Ethernet brings the data to an OPC server that provides the data to workstations for operation, engineering, and maintenance on the same Ethernet.

The operations software may have an SQL-based plant database that stores all data also available to other applications. The maintenance station runs the online plant asset management software.

The software for asset management and the plant information database should be compatible with the Web. This, in turn, will enable the corporate intranet or the Internet to dispense the necessary information through the routers and firewalls.

OPC is the technology of choice in the central control room but not in the field and not in the business environment. The field requires industrial network protocols.

Unlike distributed component object models (such as OPC), Web technologies have no problem with dynamically assigned addresses or firewall security. Web technologies are therefore the ideal interface to an intranet. OPC will be part of the scheme, but it will operate in the central control room, not at remote wells and like sites.

Old sites may have existing equipment based on 4–20 mA instruments and proprietary RTU protocols. These can interface through OPC during a transition period.

For older open technologies such as Modbus/RTU, using the gateway functionality in a linking device or employing a converter for Modbus/TCP will work. That is to say, there is a capability to integrate existing proprietary RTUs during the transition period to a standards-based SCADA infrastructure.

To migrate to an open architecture, the first step is to stop further investment in proprietary technologies. W

Behind the byline

Jonas Berge is general manager at Smar's Asia-Pacific headquarters in Singapore. He has sixteen years of experience in instrumentation and application development. Berge is a senior member of ISA and the author of Fieldbuses for Process Control: Engineering, Operation, and Maintenance (ISA Press 2002).