Though we are not experiencing another round of "fieldbus wars" on the wireless front, a number of documents in the IEC family of standards and white papers discuss wireless as an important component of Industry 4.0. Like the fieldbus standards, each of the wireless standards is targeted to a particular industry or niche of industries. Most protocols, including fieldbus and wireless standards, follow the Open System Interconnect (OSI), ISO/IEC 7498-1 seven-layer model with the physical layer (Layer 1), data link layer (2) on through application layer (7), and in many cases, a user layer (8). To help you understand which standards have been developed for wireless sensor networks (WSN), below is a summary of each of the documents developed or in progress.
IEC 62591:2010 is the WirelessHART document that specifies the following key components necessary for this and the majority of fieldbus/digital field network communication standards:
- Physical layer service definition and protocol specification (Layer 1); data-link layer service and protocol (Layer 2);
- Application layer service and protocol (Layer 7), with network management, security and communication profiles incorporated in the intervening layers as a common stack that also includes the associated wireless procedures. The standard also defines a gateway to connect the field-level network to the balance of plant.
IEC 62734/Ed1, commonly referred to as ISA 100.11a, is a protocol suite including system management, gateway considerations and security specifications for low-data-rate wireless connectivity with fixed, portable and slowly-moving devices. Though it is intended to support all applications, the target niche is similar to WirelessHART's, that is, focused on process automation monitoring and control where end-to-end communication latencies on the order of at least 100 milliseconds can be tolerated.
Though not well known in North America, China has developed two industrial wireless standards as well. The first is IEC 62601:2011 - WIA-PA, Wireless Networks for Industrial Automation - Process Automation (WIA-PA) that specifies the communication network, communication profile and system architecture built on IEEE STD 802.15.4, which is the same network as WirelessHART and ISA100.11a. As the name implies, this network is intended for the process environment, which typically has requirements of low power availability.
IEC PAS 62948/Ed.1: WIA-FA is the sister standard to IEC 62601, except it is targeted to the factory automation environment and because this case requires higher bandwidth while having access to plant power, it uses the IEEE 802.11 physical layer to communicate.
Two other documents of interest to industrial wireless developers address how to effectively manage wireless networks in an environment where they are competing for limited resources because they share the license-free industry/scientific/medical (ISM) bands with a wide range of devices. The first is a technical specification (TS): IEC TS 62657-1:2014 Part 1: Wireless Communication Requirements and Spectrum Considerations. It addresses how to provide the wireless communication requirements for applications within the broader ISM environment while remaining independent of the wireless technology being used.
TS describe requirements in detail using less technical language than a full specification. In addition to providing broad direction, technical specifications often are published when the subject under question is still under development or when insufficient consensus for approval of an international standard is likely to be achieved. As a result, the TS is often an intermediate step to a full international standard (IS).
Part 2 of this series, IEC 62657-2:2013 on coexistence, started as a TS and then in 2013 was accepted as an IS: IEC 62657-2:2013 Wireless Communication Networks - Part 2, Coexistence Management. It specifies the fundamental assumptions, concepts, parameters and procedure for wireless communication coexistence by providing guidelines, requirements and best practices for wireless communication's availability and performance in an industrial automation plant.
We're all aware that the field level network is only a small part of the full communications requirement for today's integrated control and business systems. Integration of the field level through business systems, including the wireless standards above, are a key part of Industry 4.0.
The IEC has prepared a series of white papers on Industry 4.0 and the Internet of Things (IoT), and the sixth paper in that series, "Internet of Things: Wireless Sensor Networks" discusses the use and evolution of WSNs within the wider context of IoT and provides a review of WSN applications, while also focusing the attention on infrastructure technologies, applications and standards featured in WSN designs. As part of that discussion, the white paper mentions not only the above standards, but also a wide range of other documents, including the ETSI EN 300 220-2 initiative, commonly known as "Listen Before Talk (LBT)" that we have discussed in this column previously. The white paper only reinforces what the range of standards implies, which is that there is no one solution to all the communications challenges we face, and therefore, we must continue to select the right tool(s) for the task(s) at hand.