WirelessHart

Introduction of Products for the New Wireless Standard

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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.

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