12 March 2013
The Highway Addressable Remote Transducer Protocol (HART) is a widely used, standardized communication technology for instrumentation and control in the process industry. About 40 million HART systems are installed worldwide. The new WirelessHART standard was released in 2007 as part of HART 7, the latest version of the HART Specification. This communication protocol is based directly on the HART standard and uses wireless, robust and reliable mesh networks for data exchange.
WirelessHART adds wireless capabilities to the HART protocol while maintaining compatibility with existing HART devices. Radio transmission is based on the wireless communication standard IEEE 802.15.4. WirelessHART operates in the 2.4 GHz Industrial, Scientific, Medical (ISM) radio band, which is a worldwide freely available and license-free frequency band. To ensure high communication security and reliability, WirelessHART employs different mechanisms such as Direct Sequence Spread Spectrum (DSSS) technology and channel hopping as well as TDMA-synchronized, latency-controlled communications between the devices on the network. This technology has been proved in field trials and real plant installations across a broad range of process automation applications. In 2011, more than 40,000 WirelessHART devices were sold worldwide.
Achieving the previously impossible
After initial skepticism from users, wireless data transmission has rapidly gained acceptance. More and more use cases with WirelessHART are being implemented, and plant operators worldwide have recognized the advantages of this technology. For instance, it allows the integration of instruments at plant locations that were previously out of physical or economic reach.
The WirelessHART standard provides a solution to core process automation functionalities for which no appropriate wireless standard existed. WirelessHART therefore supports, in particular, the full range of process monitoring and control applications, including equipment and process monitoring. In addition, WirelessHART is also used for energy management, for example.
WirelessHART is typically employed where long distances need to be covered, such as for monitoring the fill levels of tanks. WirelessHART is also ideal for instruments mounted on rotating or moving parts, or to overcome obstructions in the signal path, as caused e.g. by railroad tracks or rivers. As WirelessHART segments can be seamlessly combined with wired HART networks, WirelessHART allows the addition of field devices at any time – also temporarily. Robust and easy to scale, WirelessHART is perfect for use in dynamic plants in which obstacles like trucks can appear between individual devices. WirelessHART networks are very easy to expand; all it takes is a quick configuration of the device. This has the advantage that devices can be used temporarily and in a relatively mobile way if short-term events occur.
According to a study conducted by analyst firm ARC Advisory Group in fall 2011, these application possibilities make WirelessHART the leading standard for wireless data exchange in process automation. While Europe and North America are the main markets, Asia is also showing an increasing interest in WirelessHART.
WirelessHART module for process automation
A provider of wired industrial communication solutions for more than 30 years, Softing Industrial Automation has now expanded its portfolio by wireless technology. In a first step, Softing deliberately focused on the development of the WD-H module for the integration of the WirelessHART standard into existing and new HART field devices.
Softing's communication module teams proven hardware, based on standard components, with a fully tested protocol stack. The protocol stack has been developed to meet the special requirements of process automation and has been optimized for the WD-H platform used. Membership in the Wireless Industrial Technology Konsortium (WiTECK) enabled Softing to incorporate valuable feedback from leading process automation companies into the development of the stack. Its small form factor and workable interface design make it very easy to integrate the WD-H into field devices. It allows secure and reliable data transmission over long distances, has a low power consumption, and is ideal for use in explosive and harsh process environments. For this purpose, the module is supplied with an appropriate ATEX certification. Radio approvals guarantee conformity with major wireless standards.
The field device and the WD-H communication module perform different subtasks of a WirelessHART device. The field device houses the application itself and the sensor driver. It also provides the HART Maintenance Port supporting the HART commands for parameterizing and configuring the field device. The WD-H module is responsible for managing the WirelessHART protocol and for executing the commands of the WirelessHART Network Manager.
For implementing a WirelessHART device, the WD-H communication module exchanges commands with the field device application. This is done using a high-speed asynchronous interface, which is provided as a 4-wire UART interface. It is based on HART communication and makes use of the framing and the Data Link Layer of the HART 7 standard. The request/response mechanism used is based on HART commands. A wakeup handshake minimizes power consumption.
This implementation approach offers an easy way to develop WirelessHART field devices based on the WD-H communication module. The resulting devices meet all the user requirements on wireless communication.
To download a copy of a whitepaper - WirelessHART in practice: Saving power with proper network and field device configuration - go to:
http://www.controlengeurope.com/white-papers.aspx?ShopItemID=137
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