Industry 4.0 has imparted machines with more intelligence and automated facilities with more efficiency and flexibility. Industry 4.0 smart machines and modular automation are defined by secure and adaptable connectivity, data collection, continual adjustment of production-process values and machinery-condition monitoring, among others. The wireless technologies to support these functions are based on cellular, Wi-Fi, Bluetooth and IEEE 802.15.4 standards and protocols.
Wireless communication devices can be costlier than wired networks, but they often prove the most cost-effective option over the long run, since there are no costs nor additional time and effort in running cables.
WiFi-based standards for automation
In 1997, the Institute of Electrical and Electronics Engineers (IEEE) released standard 802.11 defining the wireless implementation of local area networks. To ensure its market adoption, the industry consortium Wi-Fi Alliance soon followed, led by wireless-device companies invested in establishing testing and certification programs to maintain cross-supplier product interoperability. Today the Wi-Fi standard as defined by IEEE 802.11 is complemented by additional Wi-Fi Alliance standardisation, for exceptionally reliable compatibility of devices.
Whilst Wi-Fi is quite useful for monitoring applications and connecting machines to enterprise-level systems, its speed, latency and connection stability issues have limited its applications to:
- Barcode scanners that communicate data to manufacturing execution systems, able to tolerate delays of up to two seconds;
- Motion sensors that do not need real-time control; and
- Long-term machine-condition monitoring.
There have been efforts to adapt Wi-Fi to industrial control applications, but with limited success – apart from the Chinese industrial wireless communication standard WIA-PA (Wireless Network for Industrial Automation and Process Automation).
Wi-Fi operates at either 2.4 or 5GHz, with the higher frequencies allowing faster data transfer but at a reduced range, since higher frequencies dissipate quicker when passing through walls and other solid objects. Specialised standards use other frequency bands; for example, IEEE 802.11ah low-data wifi (HaLow wifi) operates around 900MHz and is usually employed in sensors needing extended ranges and very low power consumption. At the other end, IEEE 802.11ad wifi (WiGig) operates at around 60GHz to provide very fast data transfer.
IEEE 802.15.4-based wireless standards
Other wireless options are low-rate wireless personal area networks, or LR-WPANs, as defined by the IEEE 802.15.4 standard. These technologies prioritise low cost and low power over speed and range. With the basic specification allowing data transfer rates of 250kbit/s at ranges to 10m, this type communication links low-cost devices without any additional communications infrastructure. Protocols based on the IEEE 802.15.4 standard such as 6LoWPAN, WirelessHART and ZigBee are fast becoming preferred IIoT protocols.
- WirelessHART: One 802.15.4-based protocol supported by the HART Communications Foundation, ABB, Siemens and others, is WirelessHART – a robust standard for industrial automation applications. Its reliability is maintained using a frequency-hopping mesh network with time synchronisation.
In contrast, most WiFi-based communication protocols use the less-robust star network topology, where all devices connect to a central system. All communications are encrypted using 128-bit AES, and user access can be tightly controlled.
Because WirelessHART uses a mesh topology, data can be routed directly between devices, which extends network range and forms redundant communication paths. That way, if one path fails, the sender automatically switches to another path.
Frequency hopping allows WirelessHART to avoid issues with interference.
- 6LoWPAN: IPv6 over Low-Power Wireless Personal Area Networks, known as 6LoWPAN, is a protocol that allows IPv6 packets to transmit over an IEEE 802.15.4-based network. This means that very low power devices can connect to the Internet, well suited to IoT sensors and other low-powered devices.
- ZigBee: Maintained by the Zigbee Alliance and most widely used in smart-home and building-automation applications, ZigBee is perhaps the most established IEEE 802.15.4-based protocol. It allows nodes to remain in sleep mode most of the time, greatly extending battery life.
ZigBee typically operates in the 2.4GHz band and has a fixed data transfer rate of 250kbit/s. It works with any network topology – star, tree or mesh, with tree and mesh extending its network range.
Bluetooth LE and cellular IoT
Bluetooth Low Energy (BLE) is an alternative to IEEE 802.15.4, with low cost and low power being top priorities on the account of speed and range. It operates at the same 2.4GHz frequency as standard Bluetooth, with its key benefit being the native support it gets from mobile operating systems such as Android, iOS and Windows. Large electronics suppliers such as Logitech have invested greatly in its R&D to make it the primary wireless-connectivity option for consumer devices.
The last few years have seen sensors, remote controls, locks and handheld devices using BLE for industrial automation tasks, a trend likely to increase in the future.
In contrast to BLE and IEEE 802.15.4-based protocols for low-power short-range communications, cellular technologies support long-range wireless communications. 2G GSM has, however, been mostly superseded by 3G and 4G high-speed cellular protocols, commonly found in cellphones and IoT devices. The problem with these is that they require significant power, which in industrial applications (say for machine connectivity) means the system must be permanently connected to a wired power supply.
Cellular LTE categories offer the highest data-transfer rates but at the cost of higher power consumption. LTE Cat-0 and Cat-1 connectivity are suitable for IoT devices. In contrast, LTE-M is a low-power cellular protocol designed specifically for machine-to-machine and IoT applications.
In contrast with its relatively widespread use in cellphones, industrial 5G applications are less mature, because consumers prioritise download speeds whereas IIoT engineers prioritise low latency and ubiquitous coverage. In fact, low latency is of top importance in industrial automation. It’s true that the first 5G networks hold latency to under 30ms, with efforts to bring it down even further, to just 1ms. That’s fast enough for demanding real-time industrial control as well as monitoring — such as transmitting feedback signals in machine tools, for example.
One way that 5G reduces latency is with network slicing, a technique that divides a network’s bandwidth into different virtual lanes which are individually managed. Some lanes are reserved for low-latency transmissions — with only industrial-control applications allowed to use them, for the quickest transmission.
LoRA
Long-range wide-area network modulation (LoRA) is the low-cost wireless protocol of choice for remote and offshore applications in renewable energy, mining and the logistics industries. This is a low-power wireless technology that can communicate over very long ranges on one battery — even to beyond 10km for up to 10 years.
In short, LoRA is a non-cellular technology operating in license-free frequency bands. It employs sub-GHz frequency bands, such as 433 and 915MHz, and spread-spectrum modulation based on chirp spread spectrum (CSS) modulation, making it well suited to IoT devices set in remote locations that only need modest data transfer rates.
LoRA also features 128-bit encryption and authentication protocols. Another useful feature (especially for sensors in IIoT applications) is geolocation using trilateration (a surveying method) between devices.
LoRA uses proprietary technologies developed by Semtech, but has a vast array of open-source elements. It’s supported (and device interoperability ensured) by the LoRa Alliance, a large association that includes IBM, Cisco, TATA, Bosch and Swisscom.
By Rolf Horn, Applications Engineer, Digi-Key Electronics
