IEC TR 62918 Edition 1 0 2014 07 TECHNICAL REPORT Nuclear power plants – Instrumentation and control important to safety – Use and selection of wireless devices to be integrated in systems important t[.]
Wireless basics
The integration of wireless technology in nuclear power plants is becoming essential as advancements in this field accelerate, driven by a booming commercial market for wireless products The widespread adoption of wireless technology for personal and home use has led to a robust commercial market, fostering competition among major corporations This competitive landscape has resulted in the standardization and enhancement of wireless component technologies, significantly improving their reliability, security, and power management—key requirements for industrial applications.
Wireless communication is the transfer of information over a distance without the use of electric wires or conductors How does it actually work? In its simplest form, a source device
IEC generates electromagnetic (EM) waves that propagate through the air at nearly the speed of light to reach a target device These waves can originate from any conductive object, such as a wire or antenna, that carries alternating current, producing EM radiation at the same frequency as the current The properties of these waves are defined by their wavelength and frequency, which are inversely related; thus, a shorter wavelength corresponds to a higher frequency.
The wavelength of a 900 MHz device is longer than that of a 2.4 GHz device, allowing signals with longer wavelengths to travel further and penetrate obstacles more effectively Additionally, frequencies closer to visible light exhibit behaviors similar to light itself.
The 900 MHz radio frequency offers superior barrier-penetrating capabilities compared to the 2.4 GHz frequency Generally, higher frequencies provide increased throughput but result in shorter range, leading to necessary trade-offs in performance.
The strength of a received signal diminishes as the distance from the transmitter increases, following the inverse square law (1/r²) In communication systems, this principle indicates that the received signal strength (RSS) decreases with the separation distance (R) between the receiver and transmitter, particularly in line-of-sight scenarios.
Data are modulated or coded using conventional binary data (1s and 0s) onto an RF carrier
Wireless information is conveyed through radio messages that utilize binary code, consisting of 1s and 0s, to represent the actual payload or message This transmission also includes supplementary data that aids in message handling and synchronization.
All industrial communication networks, whether wired or wireless, must connect to systems that display, record, or utilize sensor data in control loops The multi-level Purdue architecture reference model was essential in categorizing systems and their networks in a wired environment However, in today's wireless landscape, all systems operate on the same medium, frequently within the same ISM band and overlapping geographically, leading to competition Consequently, the primary destination for wirelessly captured data in plants is often unclear.
The Purdue model illustrates that in a connected environment, DCS and SCADA systems serve as the central hub for all plant sensor data, where each sensor is represented by a tag and recorded in the plant historian Additionally, asset management and maintenance systems utilize the DCS to access diagnostics from plant instruments.
Wireless systems generate data that is often more pertinent to optimization and maintenance teams than to operators This data is primarily utilized within business networks and is increasingly managed by third-party contractors over the internet.
Cyber security presents a new challenge, particularly in the context of the Purdue model While domain segregation was easily managed in wired environments through firewalls separating office and plant automation networks, the rise of perimeter-less wireless technology complicates this defense Wireless systems can facilitate sensor data collection across all levels of the Purdue model with minimal deployment complexity, yet they must still uphold robust cyber security measures Guidance on maintaining domain segregation between internet, business, and plant networks while allowing wireless systems to effectively transmit data is illustrated in Figure 7.
3 In general situations, the received signal strength decreases as 1/R n
Wireless systems are either providers of wireless connectivity or users of that connectivity
Connectivity providers are, for example, plant-wide WiFi™ access points or cell phone towers
Connectivity users encompass a range of devices, including wireless sensors, tablet PCs, video cameras, and people-tracking systems, as well as wired control loops that require wireless diagnosis and configuration Additionally, tunnels within the classic Purdue model, such as microwave links relaying L2 between offshore platforms and satellite wellheads, serve as connectivity users Notably, some field devices can function as both connectivity providers and users, exemplified by mesh-to-the-edge wireless sensor networks.
Walking counterclockwise around the diagram, the top left component is the sensor, which typically measures variables such as temperature, pressure, and vibration The design is generic and does not differentiate between intrinsic sensors located on the board or other types.
The auxiliary circuitry block, which may function as an Application Specific Integrated Circuit (ASIC), is closely integrated with the sensor and the manufacturer's design Power for the wireless sensor is supplied by the Power System (PS) block, which can either be a battery or incorporate energy harvesting capabilities along with storage solutions.
At this point we have described a generic sensor, or field transmitter, design with no details of the wireless functions
The RF transceiver, a key element of the wireless transport method, plays a crucial role in various operational and performance aspects such as modulation format, operating frequency, transmit power, and receiver sensitivity Wireless sensors, or field transmitters, have existed for years, and historically, transceivers were integrated with complex hybrid circuitry to ensure stable wireless transmission.
Plant production scheduling, operational management, etc
Dispatching production, detailed production scheduling, reliability
Batch control Continuous control Discrete control
Figure 8 – Simplified diagram of a generic wireless sensor design
Industrial wireless sensor networks
In this subclause, field edge devices and the network that provides connectivity for them are detailed Figure 9 depicts the communication areas addressed by IEC PAS 62734 or
IEC 62591, also known as WirelessHART®, outlines standards for industrial wireless communication In this framework, field devices such as sensors, valves, and actuators are represented as circular objects, while rectangular objects symbolize infrastructure devices that connect to the backbone network This backbone, which is not specifically defined by the standard, can include industrial Ethernet or IEEE 802.11 networks A complete network encompasses all necessary components and protocols for secure traffic routing, resource management, and integration with host systems It consists of one or more field networks that connect to a plant network through infrastructure devices Field networks are made up of field devices that communicate wirelessly using the specified protocol stack, with some devices possessing routing capabilities to relay messages from others.
Microcontroller transceiver RF circuitry Aux
Wireless industrial sensor networks (WISNs) are characterized by their scalability and extensibility, enabling simple operation and unlicensed functionality They exhibit robustness against interference from both non-WISNs and other wireless devices in industrial environments WISNs ensure deterministic or contention-free media access and feature self-organizing capabilities with redundant communication pathways from field devices to the plant network Additionally, they incorporate an IP-compatible network layer, robust security measures—including data integrity, encryption, and replay protection—and effective system management for all communication devices Furthermore, WISNs support application processes using standard objects and facilitate tunneling, allowing the transport of other protocols through the wireless network.
Radio frequency
Applications
The deployment and value of industrial wireless is based on two broad application classes: those enabling personnel mobility and those derived from the reduced cost of installation
(e.g., not having to run wires)
Empowering process operators to move throughout the facility while remaining connected to plant information systems enhances their efficiency and provides stationary operators with a clearer understanding of activities across different areas In the field, personnel can access real-time alarms, alerts, process displays, streaming video, and voice communication, along with comprehensive access to enterprise applications that monitor and locate materials, equipment, staff, visitors, contractors, and first responders.
Table 1 – List of “industrial” radio technology standards and their candidate applications
Number “Common” name Operational frequency Unlicensed
802.11 a-z Wi-Fi 2,4 GHz, 5,7 GHz Yes Wireless LAN
802.15.1 Bluetooth 2,4 GHz Yes Wireless PAN
802.15.3 WiMedia ~5 GHz * High data rate, short distance 802.15.4 ZigBee/ISA100.11a/
WiHART 2,4 GHz Yes Low rate industrial sensors
802.15.4a “chirped” 2,4 GHz Yes Low rate sensors and position
(12 GHz-40 GHz) No Broadband, data transport 802.16 WiMAX (WiBro) 2 GHz-11 GHz,
10 GHz-60 GHz No Broadband wireless
802.20 MBWA