There are four factors for a successful industrial wireless system:
- Environmental fit (operating temperature, hazardous atmosphere and substances, vibration…)
- The right protocol for the right application (WirelessHART, ISA100.11a, Bluetooth, Trusted Wireless …)
- Interface with the control system (I/O, RS485, Ethernet, USB…)
- Proper installation (Antennas, types and gains, connectors, cables, surge suppression device…)
The user's focus is always on easy handling and reliability, just as it is for cable-based devices. As a matter of fact, if the wires can be run then that is the most cost effective, safe and reliable method. However, sometimes wireless becomes a more suitable option, especially when cable installations are too expensive, permit costs too high, something is in motion, distance is too high or your application should start quickly.
Considerations when choosing a wireless system:
There are several key factors in determining a technology’s performance: distance, date rate and interference. They are all interdependent; users must find the correct balance for their application.
In practice, various wireless technologies have proved suitable for a range of applications, however there is no “one size fits all” for wireless.
WLAN (IEEE 802.11)
For high-performance infrastructure networks that are also suitable for industrial applications
For transmitting control data in factory automation
For data exchange with unlimited range via mobile phone networks
For signal transmission in the process industry using proven HART communication
Newly released international standard for signal transmission in the process industry
For signal and data transmission in large systems
The Trusted Wireless™ technology was specially developed for industrial applications where long distances need to be achieved and easier interface with control system is a must. The technology which works in the license-free frequency bands 900 MHz and 2.4 GHz offers extremely high reliability and ruggedness. It continues to be characterized by high ranges, good interference and coexistence properties as well as very good diagnostic options.
Ruggedness and freedom of interference
The basis for Trusted Wireless™ wireless communication is a so-called frequency hopping method (FHSS = frequency hopping spread spectrum). In such a method, wireless transmission is carried out over different, narrow-band wireless channels. Here, the transmitter and receiver continuously change the transmission/reception frequency.
The Trusted Wireless™ wireless technology can make use of up to 830 single frequencies, depending on the application, which are jumped to pseudo-randomly across the entire band. With this, it achieves a high degree of freedom of interference and ruggedness.
Reliability and diagnostics
The reliability of Trusted Wireless™ wireless technology is further increased by special software mechanisms in the protocol. Also, Trusted Wireless™ wireless technology offers very good diagnostic options which can be made use of, depending on the product. The status of the wireless connection is diagnosed via the RF LINK signal.
The quality of the wireless path, on the other hand, can be precisely monitored by means of an analogue RSSI signal (Receive Signal Strength Indicator). This signal can be constantly monitored on a system or only used for startup and aligning the antennas. The packet error rate and other parameters can be directly accessed, depending on the product.
The Trusted Wireless™ wireless technology is optimized for medium-sized and long ranges. Can be achieved if suitable antennas are used and if the legal guidelines and the maximum values of the following distances are complied with:
In the 900 MHz band at 1W transmission capacity, typically 20 miles (= 32 kilometers)In the 2.4 GHz band at 10/100mW, typically 3 kilometers.
These values can be exceeded or fallen short of, depending on the application.
Bluetooth was standardized according to IEEE 802.15.1 for the wireless communication of mobile devices of various manufacturers, usually at short distances. Bluetooth uses the 2.4 GHz ISM (Industrial, Scientific and Medical) band as a transmission medium. This cost- and license-free frequency band is available worldwide.
Since interference can occur by occupying this frequency band with other devices, a robust transmission method is required. For this reason, Bluetooth uses the frequency hopping method. Here, the available frequency band is divided into frequencies from 2.402 GHz to 2.480 GHz on 79 channels, each having a bandwidth of 1 MHz.
The transmission channel is changed 1600 times per second (every 625 µs). If interference is caused by any other existing wireless devices (e.g. other Bluetooth or WLAN systems), the telegram is repeated on a new channel afterwards. In most cases, however, the integrated error correction FEC (Forward Error Correction) is able to detect errors and automatically correct them.
The frequency hopping method considerably contributes to the security of the data telegrams since the frequency change is done pseudo-randomly. In addition, 128-bit data encryption guarantees high data integrity. Starting from Bluetooth version 1.2, the adaptive frequency hopping method is used.
Here, static disturbing stations on the frequency band are detected and these frequencies are taken out of the hopping sequence for the next transmissions. This ensures that neither the Bluetooth signal to be transmitted, nor the other radio service is disturbed. Thus, it is easily possible to operate Bluetooth 1.2 and WLAN 802.11 b/g networks in the same wireless field at the same time without interference.
Bluetooth is limited to communication from one master and a maximum of seven slaves. However, as a result of the frequency hopping method, a high local system density (i.e. interference-free parallel operation of many Bluetooth networks) is possible in the same wireless field.
The maximum permissible transmission power for the 2.4 GHz ISM band is limited to 20dBm (100mW). Thus, a range of 200 m can be reached outdoors. Under certain conditions, such as when using directional antennas, the range can be extended even further. In any case, however, it must be considered that the range depends on the surrounding conditions. The Bluetooth devices are divided into three classes according to their transmission capacity, which results in different values for the range.
Independent of the maximum sending capacity, due to the automatic transmission capacity regulation, only that power is emitted which is actually required for the respective connection. The data throughput is relatively low compared to WLAN 802.11 with 1 Mbps, but for many applications, especially in the area of I/O communication, it is completely sufficient.
WLAN (Wireless Local Area Network) is standardized in acc. with IEEE 802.11b/g for local wireless networks. The WLAN uses the 2.4 GHz ISM band (Industrial, Scientific and Medical) as a transmission medium. This cost- and license-free frequency band is available worldwide. There are also IEEE 802.11a/n which is increasing its popularity in industrial applications.
WLAN uses the frequency spread method as the transmission method (DSSS - Direct Sequence Spread Spectrum). Here, the available frequency band is divided into frequencies from 2.401 GHz to 2.483 GHz on 13 channels, each having a bandwidth of 22 MHz. But not all channels are released for use in all countries, however. In Europe, channels 1-13 are permitted, and in the USA and Canada, Channels 1-11.
Illustration caption: Frequencies and channels for IEEE 802.11b
Since the channels overlap each other, not all channels can be used at the same time without the devices interfering with each other. This results in the recommendation to only use channels 1 | 6 | 11. In Europe, one can also use channels 1 | 7 | 13 or 2 | 7 | 12 or even 3 | 8 | 13 in parallel without them influencing each other.
Based on WLAN, high-performance wireless networks can be realized with many devices since theoretically there is no limit to the number of devices. However, the involved devices must share the available bandwidth (shared medium). The data rate can be up to 54 Mbps, depending on the surrounding conditions. Thus, WLAN, for example, is optimally suited for Ethernet communication with mobile controls. Since data is transmitted with a transparent protocol, WLAN systems can be easily integrated in IT networks.
The maximum permissible transmission power for the 2.4 GHz ISM band is limited to 20dBm (100mW). Thus, a range of 200 m can be reached outdoors. Under certain conditions, such as when using directional antennas, the range can be extended even further. In any case, however, it must be considered that the range depends on the surrounding conditions.
In order to guarantee high data security, various encryption mechanisms (WEP, WPA, WPA PSK …) and authentication (EAP) are used.
HART® (Highway Addressable Remote Transducer) protocol is the global standard for smart process instrumentation. More than 30 million HART-enabled devices are currently installed in plants around the world, but only 10 percent of the devices are used to their fullest potential. The WirelessHART™ standard was developed by the HART Foundation to enable users to more effectively utilize the capabilities of their HART-enabled devices. WirelessHART is a subset of the HART 7 standard released in 2007.
One of the goals of this technology is to connect instruments and actuators to a DCS, AMS, PLC or PC. And it can be used in conjunction to a standard 4 to 20mA current loop, however only the main analogue primary variable is available through the cables, where are through WirelessHART hundreds of parameters can be exchanged.
WirelessHART is a Self Organizing & Self Healing Wireless Mesh Network that operates at 2.4GHz ISM and its radio platform is based on IEEE 802.15.4, which is a Direct Sequence Spread Spectrum (DSSS) that hops in 15 available channels.
All devices are routers in the mesh and maintains its own neighbor list, please see picture below.
Distances up to 250m (10dBm) can be achieved with WirelessHART and even higher when instruments are added in the mesh as each instrument is also a repeater in the network. Wireless has also become an international standard IEC 62591.
Very similar with WirelessHART, the ISA100.11a is a new protocol with powerful features that will go beyond process instrumentation applications.
Please see below facts about ISA100:
- ISA100 has no basis in existing standards/protocols
- ISA100 consists of several subgroups
- ISA100.11a is low power mesh technology for field devices/sensors
- ISA100.12 is working on convergence of WirelessHART and ISA100.11a
- ISA100.15 is working on a backhaul wireless standard…and others… wireless power, asset tracking, etc.
- ONLY ISA100.11a is complete at this time!
- released in 2009, with revision in 2011
- IEC approved as a PAS (publicly available specification)
- IEC 62734
|Radio platform||IEEE 802.15.4||IEEE 802.15.4|
|TX power||Up to 10dBm||Up to 17dBm (varies by country)|
|Transmission||DSSS with channel hopping||DSSS with channel hopping|
|Number of channels||15||15|
|Battery life||Up to 5 years||Up to 5 years@10dBm
Up to 2 years@17dBm
Just like WirelessHART, ISA100.11a is a Self Organizing & Self Healing Wireless Mesh Network that operates at 2.4GHz ISM and its radio platform is based on IEEE 802.15.4, which is a Direct Sequence Spread Spectrum (DSSS) that hops in 15 available channels. ISA100.11a has more knobs to turn make the technology more flexible but not as ready out of the box as WirelessHART.
A great feature is that every node has a IP address, which makes the technology very interesting for tunneling applications over various medias and networks.
The ISA100 is working in integrating all the communication methods in the process instrumentation field combining in the same mesh ISA100.11a devices, WirelessHART and Foundation Fieldbus.
Users in the shorter term will have to choose between ISA100.11a and WirelessHART based on device availability as they are both new technologies, with WirelessHART being the first one to be released to the market.
When selecting a wireless system, no one size fits all. Factors such as distance, speed requirements, control system or environment are to be considered. As process instrumentation devices equipped with wireless capabilities are introduced into the market, it is becoming more important for users to understand the differences of these technologies.
WirelessHART, ISA 100 11a and Trusted Wireless are three such technologies that can be used to wirelessly network these process devices to their control system or each other. The technologies each offer advantages and disadvantages depending their intended uses, environment, end user requirements and control system.