WirelessHart Introduction of Products for the New Wireless Standard

Editor: Dr. Jörg Kempf

In the late fall of 2009, Namur and the Hart Communication Foundation (HCF) began a field test of WirelessHart technology at BASF in Ludwigshafen/Germany, which was actively supported by Pepperl+Fuchs. This test clearly demonstrated that WirelessHart has great potential, and is ready for mobile and flexible applications. By now, the company has introduced the first products featuring this new wireless technology.

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A possible application of WirelessHART is level measurement. (Pepperl+Fuchs)
A possible application of WirelessHART is level measurement. (Pepperl+Fuchs)

For some time, wireless communication for process automation has been the subject of countless press reports. The early stages of development saw the installation of a number of proprietary systems, which in turn quickly produced the demand for a standard. Namur showed interest in this subject at an early stage, and at the beginning of 2009 published recommendation NE124 describing the organization’s requirements for wireless communication for the worldwide process industries. Three years ago, WirelessHart was introduced as the first wireless standard for process automation. However, until now, no products have been available on the market — for good reason.

Field test clears the way

One major reason for this delay was the need to guarantee interoperability between different WirelessHart devices. The goal is to ensure the seamless combination of devices from multiple manufacturers, so as to avoid dependency on any single manufacturer.

The importance of compatibility has appeared before, during the introduction of fieldbus systems. At that time, fieldbus components that did not conform fully to the standard resulted in unstable systems or even stopped systems operating completely. Clearly, WirelessHart would have to do better.

In cable-based communication systems, every information packet is available for inspection by diagnostic tools. With wireless systems, diagnosing errors is more difficult, since it is not possible to trace the communications path using conventional tools. For this reason, wireless systems must be tested with extra care before they reach the market.

To ensure that all WirelessHart devices are interoperable, the Hart Communication Foundation (HCF), Namur, and BASF teamed up with leading manufacturers of WirelessHart products, including Pepperl+Fuchs, for a field test. With the help of BASF, Namur examined WirelessHart in terms of NE124.

Pepperl+Fuchs took advantage of the test to determine how well its products conformed to the specification. The company submitted its WirelessHart Gateway and WirelessHart Temperature Converter for the test. The WirelessHart Adapter, which also will be offered by Pepperl+Fuchs, was provided by Endress+Hauser.

Strengths and weaknesses

The field test revealed positive results, but also pointed out two aspects needing more attention. On the plus side was the reliability of the wireless communication. WirelessHart is based on a “self-healing” mesh network defined by the worldwide IEEE 802.15.4 standard, and an important part of the test was to find out how reliably messages are routed. Even under adverse operating conditions, communication turned out to be fine. The Pepperl+Fuchs temperature transmitters worked well, even though it had been assumed that their integrated antennas might lead to problems with radio communication.

The security mechanisms of WirelessHart also demonstrated positive results. The 128-bit AES encryption in CCM* mode cannot be switched off. This means, it is practically impossible to hack the key in order to monitor communication. In addition, the key is renewed at regular intervals, which further improves the resistance against hacking attempts. Hacking attacks, as they are known from WLAN networks, are excluded a priori, since the MAC layer does not correspond to that of WLAN and does not accept respective messages right from the start. This means, there is no need for a firewall.

But where there is light, there are also shadows. Unfortunately, the integration of WirelessHart into process control systems is still at the same level as that of the fieldbuses. Tools such as DTM (Device Type Manager) and DD (Device Description) are not yet standardized, and there are different DD versions that do not run on all host systems. As a result, WirelessHart vendors must provide a number of different DD software versions as well as different host systems. An additional problem is that not all combinations will work. The HCF is currently putting maximum effort into solving this issue and standardizing host systems. The goal is that any DD runs flawlessly on any certified host system. To guarantee the seamless integration of WirelessHart devices into process control systems, Pepperl+Fuchs will support all required DD and DTM versions until all hosts become compatible.

Another criticism was the variety of batteries used. Each manufacturer developed its own battery pack optimized for a specific field device. Although there are technical reasons for this, such a development is anything but user-friendly: for plant operators, a variety of batteries increases handling, storage, and maintenance costs. Namur has therefore started an initiative to standardize battery formats. Pepperl+Fuchs realized this problem right from the start, and its WirelessHart temperature converter uses a standardized, D-cell-sized battery that can be exchanged even in Zone 1 environments.

To improve network diagnostics, BASF suggested unified key performance indicators (KPIs) to determine whether a WirelessHart network performs well and to indicate possible sources of problems. Such KPIs would allow users to quickly detect network malfunctions, and perhaps even diagnose problems, without detailed network knowledge or statistics. Pepperl+Fuchs will integrate such KPIs into its products as soon as possible.

A usable technology

Pepperl+Fuchs views the overall result of the field test as positive; WirelessHart can be viewed as a usable technology. Wireless communication between devices from different manufacturers works well, and there are no fundamental objections to the market introduction of WirelessHart.

Integration with DCSs and production control systems certainly still call for some improvements. The support of all DD and DTM versions by Pepperl+Fuchs is one way to overcome this problem until host systems can be properly standardized.

As an expert in communication infrastructures, Pepperl+Fuchs continues to drive the development of this new technology. At the Hanover Fair in April, Pepperl+Fuchs presented its WirelessHart Gateway, WirelessHart Adapter and WirelessHart Temperature Converter as the first products available.

* G. Lohmann is Product Manager and X. Meyer is Technical Editor Global Marketing in the Process Automation Division of Pepperl+Fuchs, Mannheim/Germany.