NAMUR advances wireless standards convergence

Leverkusen, Germany – Automation end users group NAMUR has published new recommendations (Full details below) on the convergence of the standard for wireless sensor networks. The move is a response to the competition between three existing standards for wireless sensor networks.

The document, NE 133 “Wireless Sensor Networks: Requirements on the Convergence of existing Standards” was produced together with WIB as well as representatives of ISA, HART Communication Foundation and manufacturers of both WirelessHART and ISA SP100 products,

NE 133 aims to define requirements for wireless sensor network standards, explained NAMUR. The term “wireless sensor network”, it noted, describes all the devices – sensors, actuators, routers, access points, gateways, etc.– within a network as well as the wireless technology and network characteristics.

“Competing standards for the same applications hamper the successful implementation of technologies, as is graphically demonstrated by the field bus, which to this day has failed to maximise its application potential,” said the German-based group.

Namur wants all wireless technology and product suppliers to ensure a secure and sustainable investment environment for wireless in the process industry. Its recomendations, therefore, define minimum requirements on the technology and equipment, as well as instructions and guidance on its implementation in process operations.

As well as focusing on reliability and availability issues, the NAUMR document describes requirements and constraints on the use of wireless communication technology. This includes issues of coexistence, interoperability and interchangeability during the life cycles of the equipment and technology employed.

“This recommendation aims to satisfy different objectives,” said NAMUR. “Firstly, future technological advances must not be hindered by excessively restrictive specifications and, secondly, the requirements set out in this recommendation must enable the operation of wireless networked instrumentation with minimum life cycle costs.

“NE 133 documents a broad consensus among users and manufacturers regarding the standardisation of wireless sensor networks. NAMUR expects that this clear statement and the requirements formulated will enable all those involved in the standardisation process to work together constructively with a view to achieving a converged standard.”

NAMUR Recommendation (First Issue: 06.09.2010)

 Wireless Sensor Networks: Requirements for the Convergence of existing Standards - NE 133

Scope:

The NAMUR recommendations (NE) and worksheets (NA) are working documents and practical reports prepared by the NAMUR members. The NAMUR members are entitled to use the NE and the NA on a non-exclusive basis and for their own commercial purposes only. The same applies to any third parties that obtain access to the NE and the NA.

NAMUR does not warrant that the NE and the NA are complete or accurate. Any use of the NE and the NA by the NAMUR members or by third parties is at the responsibility and the risk of the user. All claims for damages are excluded, except as stipulated by mandatory liability laws.

Details are established in the Articles of Association/Rules of Procedure of NAMUR or in the agreement between NAMUR and a third party.

* User Association for Automation in Process Industries

Members:

Jürgen Brink, Evonik-Degussa GmbH

Christian Klettner, BASF SE

Berry Mulder, Shell

Peter Nicke, Merck KGaA

Stefan Ochs, Bayer Techn. Services GmbH

Alexander Piciorgros, Lanxess Deutschland GmbH

Dirk Püthe, ISP Marl GmbH

Bernd Rastatter, Rösberg Engineering GmbH

Thomas Stachurski, BP Gelsenkirchen GmbH

Martin Schwibach, BASF SE (Chairman)

Supported by:

Sean Keeping, ABB

Frank Fengler , ABB

Martin Zielinski, Emerson

Klaus Peter Lindner, Endress+Hauser

Richard Caro, ISA100.8 Chairman

Patrick Schweitzer, ExxonMobil, ISA100.12 Co-

Chair

Paul Sereiko, E-Senza, ISA100.12 Chairman

Ron Helson, HART Communcation Foundation

Michael Hopfe, Honeywell

Paul McLaughlin, Honeywell

Patricia Brett, Honeywell

Hartmut Wallraf, Invensys

Dr. Gunther Kegel , Pepperl & Fuchs

Michael Kessler, Pepperl & Fuchs

Sicco Dwars, Shell

Ludwig Winkel, Siemens AG

Dr. Kurt Polzer, Siemens AG

Penny Chen, Yokogawa

Toshi Hasegawa, Yokogawa

Dr. Reinhard Hüppe, ZVEI

1. Objective

1.1 General Objectives

The purpose of this NAMUR recommendation is to define requirements for wireless sensor network standards. The term wireless sensor network describes all the devices (Sensors, Actuators, Routers, Access Points, Gateways,…) within a network which are required to achieve the desired functionality and satisfy the use case.

Furthermore the term describes the radio technology and network characteristics. The technology employed and solutions from different vendors ensure that these provide the necessary functions and security of the solution for sustainable use in the process industry. The minimum requirements to be met by the technology and equipment involved are described in this respect. In addition instructions and recommendations are provided for their implementation under actual operational conditions.

An emphasis is placed on the requirements to be met by deterministic applications with regard to reliability and availability. Moreover, additional requirements and marginal conditions for the use of wireless communication technology (e.g. coexistence, interoperability and interchangeability) are illustrated with consideration of the life cycles of the equipment and technology employed.

This recommendation aims to satisfy different objectives. Future technical developments must, on the one hand, not be hindered by excessively

restrictive specifications. On the other hand, the requirements set out in this recommendation must enable the operation of wireless networked instrumentation with a minimum total cost of ownership.

Within the NE133 key requirements from NE124 “Wireless Automation Requirements” [6] are modified and adapted to define and sharpen the requirements for convergence of wireless sensor networks for the needs of the process industry.

1.2 NAMUR / WIB Cooperation

This document serves as an aligned requirement from NAMUR and WIB. It describes the necessary user requirements for convergence of the wireless sensor network standards, including IEC/PAS62591 referred in this document as WirelessHART, WIA-PA (IEC/PAS 62601) and ISA100.11a and any future appearing wireless sensor network standard(s), into one single wireless standard for industrial application use in process automation.

Any technical specifications are not in the scope of this paper.

1.3 Initial Situation / Review

Several wireless standards have appeared in the market place. At least three of these emerging standards specifically address the industrial markets. They are IEC/PAS 62591 (WirelessHART), WIA-PA (IEC/PAS 62601) and ISA100.11a. The recommendation also applies to any future appearing wireless sensor network standard(s), which target process industry use. All of these standards essentially address the same physical space where wireless can be used for

industrial applications.

In the history of wired field networks, supporting multiple network protocols due to competing specifications has increased both operational and capital costs. This severely hampered the widespread implementation of wired field networks.

The user community has therefore strongly recommended that wireless sensor network standards have to converge into one single standard which addresses the long term lifecycle required for an industrial application network installation. This single converged standard has to provide a common network structure that will afford the greatest diversity of wireless instrument applications that can now, or in future, be available to the end users.

1.4 User requirements on convergence of one wireless sensor network standard

1. In the converged standard, all recommendations from the NE 124 “Wireless Automation Requirements” [6] shall be considered. The converged sensor network standard must cover all NAMUR and ISA use classes for wireless applications.

a. NAMUR (A) covers ISA 0

b. NAMUR (B) covers ISA 1-3

c. NAMUR (C) covers ISA 4-5

2. It is not a key requirement that the proposed converged network includes an overall methodology for preserving the integrity of already installed WirelessHART, WIA-PA or ISA100.11a devices.

3. It is expected that the converged standard covers and integrates state of the art technologies and developments.

4. The converged standard must center on a single radio technology for all components within a network such as field devices, routers and gateways

The single converged standard must prescribe how, throughout the entire device lifecycles:

Field instrumentation such as sensor nodes use IEEE 802.15.4 wireless connectivity with other wireless nodes in order to meet the use case-based requirements.

Host system nodes (e.g. gateway, proxy) on the wireless network use same wireless connectivity with these instruments so that the field devices can meet their use case requirements.

Interoperability is to be achieved between field devices such as sensors and in-field routers from vendors A, B and C, without losing wireless link performance and without compromising security when mixing and matching devices from different vendors.

To ensure interoperability between gateways from arbitrary vendor D and field devices from vendors A, B and C

Sensor data (PV’s typically, but also array data, like waveform and spectra) will flow from wireless sensor node into a single list of tags, made available on the plant network upstream of the gateway.

Key performance indicators for network health (described in 3.2) are collected in the field instrument and presented in the network or system manager.

Field sensor devices are configured with the required update rate, measurement type, and values of interest, for example, such values of interest in the WirelessHART standard include PV, SV, TV, QV allocation etc.

2 Areas of application

Use of wireless sensor network technology opens up new areas of application which cannot be realised with conventional, wired technology.

These primarily involve areas of application which require flexibility and mobility. Other applications are created through a wireless alternative to cable-based (wired) solutions. However, it currently cannot be assumed that wireless solutions will replace any existing cable configurations.

Wireless Instrumentation can be used to gather and transmit (bidirectional) information from many process and non-process-centric sensors with different and varying performance requirements.

The wireless network must be able to support the typical amount of points in plants with predictable performance and easy to use maintenance and management tools.

The number of wireless instruments in a plant can range from just a few devices to thousands of devices throughout a plant.

A single converged standard enables users, over a period of decades, to:

1 Install and use wireless sensors for measurements such as temperature, pressure, flow, level, vibration, load, corrosion, voltage, current, frequency, orientation, position, speed, size, air quality, product quality, etc. Such sensors produce bit data (such as switch on/off status or fuse state), process values (PV’s, which are mostly floating point values), file/array data for periodic uploads or a multitude of data, or combinations thereof. Sensor measurements and subsequent wireless sensor signal transmission is executed periodically at predetermined rates, but may also be initiated via the wireless network, on demand, event driven as instantaneously as possible, or may be transmitted at precisely pre-set times.

2 Easily add or remove wireless devices to the wireless networks, irrespective of which vendor supplies the devices

3 Add devices while understanding upfront, without need of further vendor guidance, any potential security and/or performance degradations of earlier installed applications on that same network and on the supporting host infrastructure.

2.1 Flexibility

Temporary, flexible and rapid use of automation solutions is one of the core areas of application for wireless communication technology in process automation. Flexibility enables multiple uses of measurement systems at different locations and, consequently, a reduction in investment and installation costs.

2.2 Mobility

Mobile, transportable automation solutions form the second area of emphasis involving wireless technology in automation engineering. Use case 1: Moving instruments within a wireless network. Use case 2: Moving instruments between different wireless networks.

2.3 Cable replacement

The cost-effectiveness and efficiency of the wireless application must be examined in this respect. Possible areas of application may include:

  Long distances, complex cable laying operations or measuring locations which are difficult to access;

 Measurements conducted on moving objects (e.g. replacement of sliding contacts / trailing cables)

3.1 Application classes

Wireless technology and applications in automation engineering are classified according to NE 124 “Wireless Automation Requirements” [6] use classes that meet ISA use classes as described in 1.4.

Within the different use classes, sample rate and data volume can differ. The standard must meet these requirements. The data volume can differ from single floating point values up to complex signals such as a waveform, spectrum analysis or configuration data.

The standard must provide the means to deliver real time data for different requirements and use cases. A physical network should be able to support devices that have varying performance requirements and operating characteristics concurrently.

To meet the different requirements the wireless solutions has to adapt network topologies to the existing requirements. Topologies could be for example mesh, star or hybrid networks.

The network management has to meet the different requirements (for example management between lower priority deterministic applications and high priority messages) within a physical network.

Definition: Application class A

(functional safety):

Time-critical applications in the area of functional safety, process interventions and interaction with other applications and systems are governed by the requirements of critical safety applications.

Definition: Application class B

(process management / control):

Time-critical, deterministic applications which must meet high requirements with regard to availability and reliability. Interactions with other applications and process interventions are included.

Definition: Application class C

(display / monitoring):

Applications that are not time-critical and exclusively provide additional information.

Interactions with other applications and systems are excluded.

Especially to support use class C applications, the converged standard must support deploying plug and play devices.

3.2 Availability, reliability and real-time capability

The converged standard must define uniform, vendor independent key performance indicators (KPI’s) for characterizing availability, reliability and real-time capability. Related with the application classes of wireless sensor networks appropriate KPI’s must describe the Quality of Service of the network.

The NAMUR recommendation NE 107 “Selfmonitoring and Diagnosis of Field Devices” [5] has to be consulted for basic diagnostic requirements.

Examples of appropriate KPI´s could be:

  Availability:

Availability is the number of packets (in percent) that arrive at the Gateway within a pre-defined period of time.

Latency and Jitter:

Measuring latency can be performed by tracking the time between the generation of packets and their receiving. Jitter can be measured in standard deviations. Latency must be less than 50% of sampling frequency.

Packet Error Rate (PER):

The percentage of erroneous packets received by a device within a pre defined period of time.

Throughput:

Throughput is the average of the number of packets transmitted or received per second.

Buffer usage level:

Buffer usage level provides information on whether there are bottlenecks in the network.

This helps the user to detect critical spots within the network.

3.3 Security

Wireless systems are open systems and must be specially protected through appropriate security measures. Security measures must be a general design objective during conception as well as for the long-term operation of the wireless automation solutions. Minimally, the following measures must

be taken into consideration:

Encryption of transmitted data (minimum 128- bit)

Access control to monitor accessing of wireless equipment (authentication, authorization) and secure linking to master networks.

An operating concept that ensures the quality of the methods employed must be set up that takes into account application information security considerations and the data to be transmitted. The security mechanisms implemented must be documented by the vendor.

The requirements defined in NA 115 “IT-Security for Industrial Automation Systems: Constraints for measures in process industries” [7] have to be met. The VDI/VDE 2182 “IT-security for industrial automation” [8] should also be taken into consideration.

A single converged standard must enable users, over a period of decades, to:

· Exploit identity-based security models, where device credentials (guaranteed unique device identity, public key, certificate etc), and offline authenticateability thereof shall not change ever throughout the device lifecycle. This implies device based certificates, and architecture with a perimeter-less network concept and an internally parameterized security module within each node.

· The new standard must indicate to the user/auditor that all security measures are implemented correctly. Therefore uniform security KPI’s such as unauthorised access or unrestricted join process have to be defined.

3.4 Coexistence

In contrast to cable-based applications, the resources required for signal transmission cannot be provided exclusively for wireless automation. Vendors must ensure the coexistence of the basic technology employed with other radio technologies, taking international standards (e.g. IEEE 802.15.4, IEEE 802.11)into consideration.

In order to evaluate the coexistence, vendor independent, uniform and non-proprietary parameters must be defined within the standard to characterize the coexistence of wireless solutions.

The standard has to be designed as a radio environment friendly technology with attention paid very carefully to:

a) Maintaining coexistence with other radio technologies

b) Minimizing coexistence impact on other existing radio technologies.

Coexistence of basic technologies:

In order to ensure the coexistence of basic technologies uniform and non-proprietary parameters must be defined to characterise the coexistence of wireless solutions.

The converged standard must describe how coexistence of the basic technology employed with other radio technologies is managed.

Coexistence of applications:

The required parameters must be specified to ensure the coexistence of applications. Basic information must include frequency band, channel configuration,  spatial expansion, data rate, loss rate, bandwidth latency / time response  protocol (see NE124)  availability.

Further advice about coexistence of wireless technologies can be found in ZVEI “Coexistence of wireless systems in automation technologies” [12] and VDI2185 “Wireless communication in automation technology” [9].

3.5 Interoperability / Interchangeability

Wireless sensor network devices and radio technology must be based on a uniform international standard. Proprietary, manufacturer-dependent expansions, which impact the interoperability of the devices on the wireless network must be strictly avoided.

The converged standard must ensure vendor independent interoperability within the wireless sensor. The user must be able to add or remove wireless devices to their wireless networks, irrespective of which vendor supplies them.

Additional vendor specific features must not have any negative impact on the basic function of the network as it is described in the converged standard.

The communication regulations utilised by the manufacturer must be accessible for all users.

In addition to the converged communication standard, the following basic conditions must also be met on a non-proprietary basis to ensure interoperability and interchangeability:

Uniform connection technology (plug connections / antennae)

Security measures

 Power supply

3.6 Transparent integration in master automation systems

It must be guaranteed that wireless instrumentation components to be used in automation systems will be integrated easily and transparently into existing integration tools and methods (e.g. FDI, EDDL) The requirements specified in NE105 “Specifications for Integrating Fieldbus Devices in Engineering Tools for Field Devices” [4] have to be applied.

The standard has to support a single device description according to specified device integration tools in host systems.

Additional Software and Hardware tools have to be reduced to a minimum.

The converged standard has to have the ability to integrate into existing infrastructure in order to cover existing technologies (e.g. Foundation Fieldbus, Profibus, Profinet, Ethernet, HART, OPC,…) and to avoid adding double basic network management functions.(e.g. backend security system, network management, …).

The integration must efficient and feasible with minimal effort for the end user.

The converged standard must describe how data generated by the network can be constructed into a single tag database. No update of the host systems should be required.

An update of the host system should not affect the functionality of the wireless network.

3.7 Version and lifecycle management

Hardware, operating system and application software harbour considerable risks for the user during a version change. A lifecycle of 15 years or longer must be assumed for applications in process industry. Dependencies which arise in relation to the standard IT components employed must be minimised by additional measurements.

Manufacturers are responsible to ensure long-term support, maintenance and service as well as migration path for updates and patches.

These must ensure upward and downward compatibility of equipment and systems. Measures taken to ensure sustainability must be documented and made available to the user. The requirements expressed in NE105 “Specifications for Integrating Fieldbus Devices in Engineering Tools for Field Devices” [4] apply.

3.8 Power supply

In contrast to wireless infrastructure components wireless instruments are usually implemented without additional wiring. The following criteria must be observed with regard to the power supply in order to minimise additional costs generated by battery operation:

The batteries used must be easy to replace and meet current industrial standards.

Appropriate measures and procedures for hazardous areas have to be defined by device and component vendors. Explosion protection requirements during battery changing conforming to the regulations in potentially explosive environments

Forecast of battery life-time estimation under typical and current operating conditions.

The acceptable battery service life duration or storage battery service life depends on the respective application. For example, the frequency of battery changes for “wireless sensors“ must be several years even in unfavourable conditions (extreme temperatures, high data rates)

The objective of further development must be that wireless sensors are self-sustaining for their entire life cycle when it comes to power requirements.

3.9 Self-monitoring and diagnosis

Important operational and malfunction conditions must be defined for continuous online monitoring by wireless users and their network connection.

Important and significant status messages have to be classified through adapted diagnostic algorithms. Recommendation NE 107 [5] must be consulted in this respect, insofar as it can be applied to wireless applications.

The following examples show important diagnostic information, that should be supplied by the standard:

  KPI’s for availability, real time, coexistence,… as required in 3.2

  Power supply status (qualitative / quantitative)

  Live signal of all active (authorised) network users and their characteristics (version level)

Optional additional information:

  Topological locations of wireless users

  Identification of errors / attacks by unauthorised users

  EMC issues

3.10 Equipment and components

Equipment must meet those specifications established in the process industry, such as:

- standardised, distinctive, robust and simple connection technology

- insensitivity to harsh ambient conditions (e.g. aggressive atmospheres, ambient temperature, damp, dust, impacting, vibration, EMC) equipment variants designed with gas and dust explosion protection

- uniform and non-proprietary KPI’s for monitoring and diagnosis, functions and operating areas of co-generic wireless components (e.g. congeneric components examples include: field devices, access points, repeaters) interface for the integration of freely-selected standardised electrical signals for measurement of process values (e.g. 4-20mA)  interfaces for system integration (e.g. OPC, Modbus, Profibus, Ethernet) handling with universal tools (with regard to planning, maintenance and plant modification) wireless modules for existing systems and equipment for retrofitting

4 Operation and maintenance

4.1 Configuration / Commissioning

In order to simplify management of configuration parameters for the commissioning, securing and reconstitution of plant configurations, the configuration of wireless components must, as it is the case with other system components in process-related communication technology, be realised with standardised description languages or tools.

The configuration of equipment and systems must be designed to ensure simplicity and clarity. Infrastructure components must remain broadly user transparent in this respect.

4.2 Service and maintenance

A single, uniform configuration and maintenance tool set has to be provided. This toolset must support:

 - Over the air provisioning

 - Common interface device or methodology

 - Handhelds with appropriate access restrictions

The modular structure of equipment facilitates service and maintenance and the replacement of components. After a device is replaced, the new device must integrate automatically with the current configuration data into the overall system.

Configuration data must not be lost in the event of a power failure or replacement of batteries.

User-friendly diagnostic tools and integrated diagnostic routines must contribute to the targeted and efficient narrowing down of error causes.

These tools must enable simple status identification and provide uniform status messages (e.g. conforming to NE 107 [5]).

Interoperable diagnostic tools must be supplied with equipment by the device vendor.

In addition, monitoring of the quality of wireless communication and the components used must be possible using integrated tools of this nature. It must be possible to check against defined requirements (e.g. from Chapter 3) using KPI’s in this context. Diagnostic functionality must also be employable locally on plants.

5 Certification

The adherence to standards assured by vendorsmust be supported by suitable certification processes. Adherence to these criteria can, for example, be assured by non-proprietary certification authorities.

6 Terminology

Coexistence: State in which all wireless communication solutions sharing a common media fulfill all their application communication requirements

Interoperability: The ability of a device to fulfil all designated functions together with other devices via a common communication medium. Adherence to standards is necessary in this context.

Interchangeability: The replaceability requirement of devices. Devices from different manufacturers based on the same technology can be interchanged without a loss of functionality.

Security (information security):The term security encompasses all measures which protect data against manipulation or destruction by unauthorised parties.

Safety (functional safety):Part of overall safety relative to the monitored equipment and the control system that depends on the correct functioning of the E/E/PE-( Electrical / Electronic / Programmable Electronic) related safety system, safety systems of other technology and external risk-reducing equipment.

EMC (electromagnetic compatibility): The capacity of electrical equipment or a system to function satisfactorily in its electromagnetic surroundings without radiating electromagnetic disturbance variables that are unacceptable for other equipment in these surroundings.

ISM band (industrial, scientific, and medical band): The frequently-used ISM band is in the public domain, but its utilisation is not restricted exclusively to automation engineering. Its reliability is deteriorating with the growth in use of the frequency band and the consequent reduction in the number of channels available for wireless equipment.

Vendor: The term vendor in this document is used for the supplier and system integrator and encompasses all service providers who supply plant operators with a wireless application and automation systems and components.

Operator: The operator of a process plant is responsible for the flawless operation of his plant and defines the requirements to be met by and functions of a wireless application. He also specifies the marginal conditions and infrastructure of the wireless application and automation solution for the vendor.

Wireless Sensor Network: The term Wireless Sensor Network describes all the devices within a wireless network sensors, actuators, routers, access points, gateways as well as the radio technology.

7 Literature

[1] NAMUR Recommendation 74

NAMUR Fieldbus Requirements

[2] NAMUR Recommendation 97

Fieldbus for Safety-Related Uses

[3] NAMUR Recommendation 98

Installation Requirements for Achieving EMC

in Production Sites

[4] NAMUR Recommendation 105

Specifications for Integrating Fieldbus Devices

in Engineering Tools for Field Devices

[5] NAMUR Recommendation 107

Self-monitoring and Diagnosis of Field

Devices

[6] NAMUR Recommendation 124

Wireless Automation Requirements

[7] NA 115: IT-Security for Industrial Automation

Systems

Constraints for measures in process industries

[8] VDI/VDE Directive 2182

IT-security for industrial automation

[9] VDI/VDE Directive 2185

Wireless communication in automation technology

[10] DIN IEC 61326-3

Electrical equipment for measurement, control

and laboratory use - EMC requirements

[11] DIN EN 61508 Sheet 4

Functional safety of electrical / electronic / programmable electronic safety-related systems

[12] ZVEI: Coexistence of wireless systems in automation technologies

Frankfurt am Main: ZVEI, 2008

8 Appendix

8.1 Applicable requirements analogous to

fieldbus technology

The common ground shared by fieldbus and wireless technologies when compared with individual connections stems from the common utilisation of a bandwidth-limited transmission medium with suitable limitations in transmission between devices. This means that requirements from existing NAMUR recommendations for fieldbuses also apply as a minimum requirement for wireless automation. The following are examples of NAMUR recommendations for fieldbuses and fieldbus-compatible devices which also apply to wireless automation:

NE 105 “Specifications for Integrating Fieldbus Devices in Engineering Tools for Field Devices” [4]:

3.1 Security of investment

3.2 Version-related problems

4.1 Integration of equipment in configuration tools

4.3 Self-monitoring and diagnostic requirements of field devices

5.5 Standardised data storage

8.2 Applicable IT security requirements

Wireless systems have a lot in common with other IT systems utilised in automation engineering. The following IT security requirements are for this reason also of primary relevance: NA 115 “IT security for industrial automation systems” [7]