An Innovative Distributed Instrument for WirelessHART Testing P. Ferrari, A. Flammini, D. Marioli, S. Rinaldi, E. Sisinni Dept. of Electronics for Automation University of Brescia Via Branze, 38 – 25123 – Brescia, Italy A. Taroni Carlo Cattaneo University Corso Matteotti, 22 – 21053 – Castellanza (VA), Italy [email protected] Abstract—In the last few years solutions adopted in industrial communication have been deeply changed thanks to the adoption of technologies borrowed from completely different areas. In particular, the advent of hybrid wired/wireless networks promises to greatly improve efficiency and scalability. However, their success will depend on the availability of standard solutions, that ensure multivendor compatibility. Recently, the WirelessHART specifications have been released, making it the only available standard for wireless networking in the industrial field. In this paper, authors present an innovative distributed instrument that will make easier the debug and the development of WirelessHART devices and networks. Keywords- WirelessHART, realtime systems, wireless sensor network, low power system, synchronization I. INTRODUCTION The world of industrial communications shows increasing interest toward wireless fieldbuses, that is the use of wireless communications to interconnect devices at field levels: sensors; actuators; instruments; controllers; and so on. Besides some proprietary solutions, some standards are emerging, like WirelessHART or ISA100 [1]. The goal of both proposals is to establish a wireless communication standard for process automation applications. The more known ZigBee, on the contrary, seems unsuitable for this application field as it has not been specifically designed for reliable, real-time, cyclic communications. Although ZigBee, WirelessHART and ISA100 use the same Physical level of IEEE802.15.4, they differ a lot concerning Medium Access Control (MAC) level, practically impeding the use of common devices and tools. Our work focuses on WirelessHART (WH), that is a mesh solution adopting frequency agility and power adaption to improve communication reliability. The WH specifications are available since september 2007, but instruments specifically designed for commissioning or diagnostics of WH systems are still lacking. HART consortium has proposed a sort of sniffer [2], also called Wi-Analys and still in the development stage, that is able to monitor simultaneously more frequency channels in order to support frequency agility and some companies proposes similar solutions for multistandard analysis, like Perytron-C [3]. If we suppose to install a mesh wireless network in a real industrial plant, the idea of a single-probe instrument shows some limits. In fact, only one-hop network can be analyzed, since the area coverage of the instrument itself is on the same order of the area coverage of a single device. In addition, a diagnostic instrument should be able to simultaneously analyze several parts of the plant, to better characterize and adjust the mesh behavior. The ability of a WH node to tune the transmitting power can be effectively used only if there is an instrument that is able to simultaneously measure the quality of communication in several points of the plant. In addition, as it will be clear in the following section, a distributed diagnostic instrument is necessary to help the Network Manager in designing the best graph routing. As we said, even if the physical layer is the same of IEEE802.15.4, traditional distributed protocol analyzer, like the Q51 from Exegin [4] or the 2400-SNA from Daintree [5], cannot be used since they are not able to simultaneously hear all the available channels. This paper is structured as follows. In the Section II a brief resume of WH characteristics is reported. In Section III, the architecture of the new distributed instrument, that can be used for both diagnostic and commissioning of WH systems, is detailed. In Section IV, the probe implementation is discussed and in Section V some experimental results are reported. Finally, some concluding remarks are highlighted. II. THE WIRELESS HART STANDARD WirelessHART (WH) is an extension of the well-known and widespread wired HART protocol; it preserves backwards compatibility and offers new possibilities thanks to greater flexibility and scalability of wireless networking. As previously stated, it is mainly devoted to the process automation; for this reason WH supports applications that have a minimum cycle times on the order of seconds. It is a time-synchronised, ultra low-power, mesh wireless fieldbus. In order to maximize reliability, it uses frequency diversity, time diversity, and spatial diversity, beside allowing transmitting power adaption. The WH specifications follow the OSI layers, and contain a PHYsical, Data Link (that includes Medium Access Control) and NetWorK layers. The Transport and APPlication layer are the same for both wired and wireless HART. A WH network contains different kind of devices (logical and or physical): • one and only one Security Manager, that distributes encryption keys to the Network Manager of each network; I2MTC 2009 - International Instrumentation and Measurement Technology Conference Singapore, 5-7 May 2009978-1-4244-3353-7/09/$25.00 ©2009 IEEEAuthorized licensed use limited to: Univ of Calif Berkeley. Downloaded on January 17, 2010 at 20:36 from IEEE Xplore. Restrictions apply.• one and only one active Network Manager, whose aim is to form the network, schedule resources, configure routing paths etc… • at least one Gateway, whose aim is to interconnect field devices with the plant automation system; • several field devices that are connected with the process, i.e. devices with sensors and actuators. There can be also devices that have no connections with the process but have only communication facilities; they are routers, handheld devices (used for commissioning and/or maintenance purposes) and adapter (used to connect legacy hardware with the wireless network). With regards to the physical layer, the working group has adopted the IEEE802.15.4-2006; i.e., physical devices compliant with this standard can be used to implement WH nodes. This implies that modulation schemas are exactly the same but all other protocol layers are different; this means that there is no compatibility between these standards and interoperability has to be realized at the application