FIELD WIRELESS AUTOMATION SOLUTIONS BASED ON THE ISA100-11A STANDARD

Phil Black - PII Editor 18/03/2011

313 7 minutes read

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By – Henk van der Bent – Yokogawa Europe

Communication between field devices and control systems started with 4-20 mA analogue communication, and has evolved via hybrid communication systems such as HART and Brain, to digital communication technologies such as FOUNDATION™ Fieldbus and PROFIBUS, and finally to wireless communication based on the ISA100.11a standard.

These communication technologies have significantly increased the amount of information that can be used for plant operations, and have led to major innovations in field instrumentation. Activities such as asset management and proactive maintenance have been realised using extensive information such as multiple process values and diagnostic results, which can now be sent from field devices to higher-level systems such as Distributed Control Systems (DCS) and Plant Asset Management (PAM) systems.

Field wireless technology that enables wireless communication between field devices and control systems will bring further advanced innovation in the instrumentation sector. Field wireless communication has many advantages, such as the ability to reduce wiring, engineering and commissioning costs, the ability to install devices in areas where wiring is difficult, and the ease of adding or removing devices. By making best use of these advantages, it is possible to use instrumentation to implement functions that were impossible before. Both wireless technology and the instrumentation that makes best use of wireless communication will also continue to evolve.

Standardisation efforts
In order to promote the ISA100.11a wireless communication standard for industrial automation in a comprehensive manner, the ISA100 Committee has set up working groups for specific purposes. These groups include both vendors and users, and are working on developing standards in an equitable manner based on user requirements. As a result of these groups’ activities, the ISA published the ISA100.11a wireless communication standard for industrial automation in September 2009.

As a founding board member of the ISA100 Committee, the Yokogawa Group has been promoting this standardisation process. In addition, as a founding member of the ISA100 Wireless Compliance Institute (WCI) that disseminates the ISA100 standard, the company is playing a central role in disseminating efforts, including the development of a device certification environment to ensure ISA100.11a interoperability, the development of implementation specifications, and support for product development.

The WCI is a non-profit organisation which not only provides certification, verification, education and technical support related to ISA100, but also promotes the dissemination of the ISA100 standard by helping vendors and users reduce the time, cost and risk for the development and adoption of ISA100 products. As a WCI board member, Yokogawa, in co-operation with other companies, aggressively supports the WCI activities through developing test specifications, device descriptions and capability files, and through developing and providing an ISA100.11a function test script and WCI stack conformance and device interoperability test kits.

ISA100.11a system configuration
Fig.1 shows a typical field wireless system configuration based on the ISA100.11a standard, incorporating wireless field devices and a gateway which acts as an interface between the wireless network and its applications and higher-level control and plant asset management systems. The backbone router functions as the interconnect between the wireless field devices and between a wireless field device and gateway. The system manager and security manager control and manage the behaviour and security of the wireless network. As shown in the figure, it is possible to provide redundant paths between the controller and wireless field devices via multiple backbone routers, and to provide multiple communication paths from the wireless field devices to the backbone router. The ISA100.11a standard defines the many basic functions which improve data transfer reliability in communication. Therefore within a ISA100 based wireless network devices can have different roles; I/O (input/output), routing and I/O plus routing.

Based on these general concepts, a practical realisation of an ISA100.11a based field wireless system must achieve three additional goals which can be summarised as “control proof”, “power proof” and “future proof”. “Control proof” means that the wireless architecture meets the requirement for real-time control applications. “Power proof” refers to the ability of Yokogawa’s wireless solution to provide reliable and long lasting power, while “future proof” refers to the ability of the solution to keep up with the rapid changes taking place in the world of IT.

Control proof
To be suitable for control applications, wireless networks must possess the necessary reliability and deterministic data transfer capabilities. ISA100 supports reliable radio technology and offers excellent coexistence with other wireless networks such as Wi-Fi. With bidirectional digital wireless networks based on ISA100, the measurement values, device diagnostics, and parameter data transferred between a control system and field devices are securely encrypted. This wireless technology is ideal for control applications in addition to status monitoring and device diagnostics enabling proactive maintenance.

Network topology also affects performance and reliability. Yokogawa’s field wireless strategy calls for a redundant star topology network. In Yokogawa’s view, redundant star topology (I/O devices communicating in duo cast with redundant backbone routers) provides the best determinism, high communication speed (one-second data transfer), low latency, and multiple route communications needed to provide the level of reliability needed for process control applications.

For less critical applications such as monitoring, where determinism is not required and higher latencies can be tolerated, a mesh network topology or a mix of a star and mesh network could be considered.

Power proof
A primary advantage of wireless transmitters is that they do not require wiring for either data transmission or power supply. However, reliable and long lasting power has been a long-standing challenge for wireless process sensor applications. Yokogawa has addressed this issue with its own “open battery” concept. The company has designed a unique battery case that allows the use of low cost commercially available off-the-shelf general-purpose lithium thionyl chloride batteries in its wireless transmitters. An essential feature of the battery case is that it can easily be replaced, even in a hazardous area environment. The (redundant) star topology network functions highly efficiently and provides low energy consumption, resulting in longer battery life. Yokogawa also plans to develop easy-to-maintain alternative power sources for use with these devices.

Future proof
The ISA100 standard allows for multiple application processes in the application layer of the ISO OSI-model as well as multiple physical layers. This allows the support of multiple protocols moving forward, including HART and FOUNDATION™ Fieldbus and so on, making Yokogawa’s wireless solution future proof. In addition, Yokogawa will continue to be radio agnostic, meaning that alternative suitable radio technologies will be considered when these become available, and will continue to provide a solution that can incorporate changing IT technologies. Part of being future proof also means providing seamless integration of both wired and wireless technologies, as the two will continue to coexist in process plants for many years in the future.

System elements
The initial system elements in Yokogawa’s ISA100.11a field wireless offering include a field wireless integrated gateway/backbone router, a differential pressure/pressure transmitter series and a temperature transmitter.

The YFGW710 field wireless integrated gateway has a gateway function to connect the wireless field instruments with the host system, and has the function of the system manager, security manager, and backbone router specified in the ISA100.11a standard. Communication with the higher-level system utilises a Modbus/TCP protocol, the Modbu
s protocol implemented on top of the Ethernet TCP/IP protocol. A field wireless configurator and field wireless management tool supplied with the YFGW710 are used to build and manage a field wireless network. The PC on which the software is installed is connected to the YFGW710 via Ethernet communication.

The field wireless configurator software is used for setting and maintaining the field wireless network, while the field wireless management tool software manages and monitors the operating status of the field wireless network and field wireless instruments.

The EJX B series differential-pressure/pressure transmitter inherits the features of the existing EJX series, such as the high reliability and stability of the sensor, multi-sensing function, and enhanced self-diagnostic functions, as they are. A low-power consumption electronics design was implemented in order to extend the life of the built-in batteries, while keeping the capabilities and functions of the wired equivalent product.

The YTA510 is a high-performance temperature transmitter that accepts input signals from IEC standard thermocouples (eight types including Type K, E and J), inputs from IEC or other standard resistance temperature detectors (RTD) (three types including Pt100), DC current corresponding to resistance, and DC millivolts.

The devices send measured values to the higher-level system. Furthermore, they send diagnostic information and receive provisioning data and setting parameters via wireless communication. Yokogawa uses the protocol independent open FDT technology for device integration and management in device and plant asset management systems and has developed a communication DTM for its gateway and device DTMs for its devices through which the devices can efficiently be configured and managed in any FDT frame application.

Other existing products which contribute to the overall field wireless solution are a versatile device management tool known as FieldMate, the PRM plant resource manager, a field wireless device OPC server, and the YFGW communication package used to connect the field wireless system to a DCS such as CENTUM VP or SCADA system such as FAST/TOOLS.

Last, but not least, Yokogawa has the expertise to successfully plan and implement wireless networks.

Conclusions
As a member of the ISA100 Standards Committee on Wireless Systems for Automation, Yokogawa will continue to engage in a wide range of activities to promote development of the ISA100.11a international standard. Yokogawa’s next step in its wireless roadmap is to develop a fully redundant wireless system based on ISA100 and to continue to make enhancements to its wireless devices and expand its portfolio.

In the longer term, Yokogawa’s field digital network will cover the entire plant site and provide integration of any sub-networks, both wired and wireless.

References
1.   Field wireless solution based on ISA100.11a to innovate instrumentation; Shuji Yamamoto, Toshiyuki Emori and Kiyoshi Takai; Yokogawa Technical Reports, Volume 53, No.2, 2010
2.   World’s first wireless field instruments based on ISA100.11a; Shuji Yamamoto, Naoki Maeda, Makoto Takeuchi and Masaaki Yonezawa; Yokogawa Technical Reports, Volume 53, No.2, 2010
3.   Yokogawa’s wireless solutions show a long-term commitment to ISA100 standard; ARC Advisory Group, White Paper, February 2011

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