H1 Fieldbus at the field level takes the place of field and I/O subsystem protocols, and HSE at the host level takes the place of control network and remote I/O. Although the host network is separated from the plant information network using a router, they both use the same network technology which helps to integrate them as one.

So the question may be asked, will H1 disappear into the newer technology HSE?

In the control system architecture H1 Fieldbus is used at the field level to connect transmitters and positioners while HSE is used at a host level between linking devices, gateways and workstations.

H1 has many desirable features that HSE does not have, and there are many good reasons why Ethernet will not replace H1 at the field level. Copper-based Ethernet, for example, is limited to 100 m, which is too short for wiring field instruments. It also requires multi-core cable, which is too costly for long field cable runs.

Ethernet operates from a LAN switch. These are not expensive and many industrially hardened switches are now available, but they are still comparatively costly and space consuming; installers would have to use one port for each field device. Also, with the exception of the new Power over Ethernet (PoE) specification IEEE 802.3af, which is still in its infancy, Ethernet provides no power so installers would need to supply additional wires. Ethernet is not intrinsically safe so it could not be used in hazardous areas such as those found in the chemical and petrochemical industry.

Likewise H1 will never replace the HSE backbone. H1 has too low bandwidth to be used as backbone for the entire plant, and does not have media redundancy making it unwise to make more than a few loops depend on each network. Thus, in a real sense, the two network technologies complement each other.

The emergence of HSE as the host level may create an even greater revolution than what H1 did at the field level. The lack of host level standards has previously prevented easy integration of higher level devices. But now users will be able to 'mix and match' subsystems for basic control, emergency shutdown, quality control, advanced control and compressor control from different suppliers, and control can be done using controllers from different manufacturers.

Try connecting two controllers using Ethernet from different manufactures together, or to the workstation of a third supplier, and you will be gravely disappointed. Why is it that they cannot talk to each other when they are using Ethernet and TCP/IP?

Ethernet and TCP/IP do not eliminate the need for Fieldbus standards, on the contrary, they are a celebration of what can be achieved thanks to standards. The reason they don't integrate is that Ethernet and TCP/IP are only half the story (4/7 to be precise).

Interoperability is more than just connecting two things together on the same wire without conflicts. They must talk to each other too. Ethernet only handles the bottom two layers of the seven layer stack, TCP/IP handle the next two. Ethernet and TCP/IP were specifically designed to handle many different protocols, even at the same time. There are more than two thousand protocols travelling on this platform: http, ftp and pop3 are some of those we use every day on the Internet. It makes Ethernet powerful, but it is at the same time the cause of the interoperability confusion.

Since neither Ethernet nor TCP/IP make up a complete protocol stack, a network technology therefore is required to have an application layer (layer 7) that is an open standard. If not, special drivers are ultimately required to access the data from software or gateways between devices. No doubt you can use standard Ethernet cable, interface and hubs, and that Windows makes the bits and bytes available to your applications, but the data cannot be interpreted unless the application layer is standardised. Most of the Ethernet networks used in control systems today are in fact proprietary because they have their own application layer protocol. Though devices are Ethernet, they can not exchange data with other devices nor be interrogated from a workstation.

Not all industrial Ethernet networks are proprietary. For example, the Modbus/TCP protocol uses Ethernet media and TCP/IP to communicate data using an application layer with the same register method as the familiar Modbus/RTU protocol. Modbus/TCP therefore ensures a fair level of interoperability. Devices from several manufactures use it. Off-the-shelf process visualisation software already supports Modbus/TCP.

Because Modbus is still a de facto standard some small variations exist. Therefore the user must configure several things manually. OPC eliminates this problem as far as workstation software is concerned, but peer-to-peer communication between devices is not possible. Of course this requires that the device supplier provide an OPC server. A limitation of Modbus and other protocols is that they have no standard for programming and configuration download.

Today customers expect more than just interoperability. They want ease of use. That is, it must simply work, without any time consuming manual configuration or parameter mapping. Because 'open ' previously meant 'do it manually, ' many users selected a proprietary system instead. Other users selected open systems because 'integrated ' really means 'inflexible.' You no longer have to chose either or. Foundation HSE Fieldbus uses Ethernet and UDP/IP (the lesser known cousin of TCP/IP which is more suitable for process control system architecture) and takes interoperability to a plug-and-play level. You can have both ease-of-use and interoperability.

HSE includes not only the application layer, but also a standard application process. That is, fieldbus defines not only communication, data types, and object structure, but also a function block diagram programming language that allows users to build control strategies distributed throughout the network into devices from different manufacturers. Devices and subsystems from different sources can talk to each other peer-to-peer. No longer do users need to put up with proprietary languages.

A shutdown can be extremely disruptive as it would have repercussions both upstream and downstream of a long supply chain. Downtime means heavy losses. In order for the system not to be a weak link, the Ethernet must be able to handle multiple faults. Industrial grade networks using dual redundancy, ring topology, and industrial hardened components may be used in order to be able to handle multiple simultaneous faults. Hot-standby redundancy is already part of the HSE protocol specification upper layer. In addition Ethernet ring topology that is 'self-healing ' can be used. With ring topology Ethernet is able to quickly find alternative routes for the communication in case one path fails.

Petrobras's Namorado-I platform off the cost of Brazil uses a combination of Ethernet ring topology and redundant Foundation HSE Fieldbus networks to achieve high availability. This topology ensures there is only one device per wire so that they may be disconnected without disrupting communication or control in other parts, and any wire fault has a very limited effect on the system. Fibre optics in a dual ring topology is used to link the switching hubs in the different areas together over longer distances. The fibre-optic part in addition of being dual is also connected in a ring topology where communication can flow either clockwise or anti-clockwise. This means that the network can sustain multiple faults but still continue to function. Thus the networking is extremely reliable. All parts of the network are duplicated, including the hubs; two independent networks ensure that communication can continue even if one network fails.

Smar has an engineering and maintenance tool called SYSCON that lets the user build the control strategy and configure devices and carry out H1 and HSE network management.

The user can optimise network parameters for devices from different manufacturers. The software auto-detects and identifies new devices on H1 and Ethernet, making commissioning and expansion easy. Bridging between H1 networks is managed, H1 networks can be connected, disconnected and rearranged to other ports.

One advantage of IP that users particularly like is the ability to 'ping' nodes to diagnose the network, particularly when there are many routers and subnets. A log of communications errors can be reviewed any time at the click of a button.

A point where Ethernet and software really meet is at OPC (OLE for Process Control). Of all the special software that exists today for advanced control, simulation, inferential measurement, asset management, auto tuning, linking to business applications, statistical process control (SPC) and plant information, none 'speak ' HSE or Ethernet of any type.

The SYSTEM302 universal Fieldbus bridge, called DFI302, is among other things an H1 to HSE linking device, and it comes with OPC server applications running in redundant server stations that makes all the process and device data available to any OPC client software.

In addition to OPC the configuration tools use an OLE client-server architecture to fill the gap left by the OPC data access. OLE functionality is used for control strategy configuration download and other functions required for device management but not provided by OPC data access. Actually, it can be seen as a precursor to the OPC Complex Data Access specification. The OLE and OPC effectively integrate with the rest of the system. Once a function block is configured in a device from the engineering tool, all its parameters are automatically made available from the OPC server to all clients where they may be selected for display, trending and reporting etc.

Because of the benefits of Ethernet, every protocol suite is now migrating in that direction. At some point there will be a whole bunch of them in addition to Foundation HSE Fieldbus and Modbus/TCP. Don't expect the different flavours to work with each other. In the long run Foundation HSE Fieldbus may be a good choice since it is part of the proposed IEC standard.