Chemical Processing - May 2008 - (Page 24)

• Send when data change — deliver alarm or alert messages only when they are triggered (time stamp within the instrument); and • Change measurement rates based upon alarm limits — i.e., increase the rate when a value approaches a set limit. Building a WirelessHART network. Once the gateway is commissioned (connected to the host and asset management system), you’re ready to build the WirelessHART network. It’s really a very simple procedure that involves entering three variables into the wireless instrument. This is one example of a commissioning procedure: • Obtain the wireless network name/identity (which would be a value set in the gateway); • Connect the instrument to the process; • Power up the instrument (which could be externally or battery powered); and • Attach a HART hand-held configurator to the maintenance port (terminals within the instrument that look like 4–20-mA connectors). Follow the menu on the hand-held and enter the following: 1. The network name/ID; 2. The instrument refresh rate (i.e., how often the PV is updated); and 3. The network join password. Monitor the instrument as it automatically synchronizes to the network, is authenticated, and successfully joins the network. The gateway automatically optimizes the mesh network and redundant pathways. It continues to monitor the mesh and adapts it as new devices join or the radio environment changes. This self-building and self-healing feature provides the reliability of data communications industry requires. WHY USE WIRELESSHART? Besides providing an open solution for an instrument wireless network, it: • Builds upon the existing HART speciﬁcation used by more than 24 million installed instruments; • Unlocks information stranded inside existing 4–20-mA intelligent ﬁeld instruments by adding a WirelessHART adapter; • Uses existing software tools to conﬁgure and maintain instruments; • Offers simple and low cost installation, reducing cabling and hookup expenses; • Allows measuring of points that were uneconomical to get at in the past; and • Features a self-building and self-healing mesh network. How are the issues of security addressed? Security at chemical plants is a huge topic in its own right (see, e.g., www.ChemicalProcessing.com/articles/2008/046.html, www.ChemicalProcessing.com/articles/2007/152.html and www.ChemicalProcessing.com/articles/2007/095. html). Wireless HART makes security of data transmitted a key part of its core technology. For WirelessHART, security is always switched on. Built-in features address the issues of data security and outside interference. Some of the security methods used include: • Keeping data transmission bursts short (10-msec time slots) (Figure 6). This makes it hard to synchronize and read messages. • Authenticating devices as they try to join the network (join key, device key) and monitoring attempted joins. This will help to stop unauthorized devices joining the network. • Encrypting each message. WirelessHART also allows the user to rotate encryption keys to make it difﬁcult to identify the keys and decode messages. >> Mesh network >> New features HART 7 Time/condition-based reporting PV trending Security Mesh and star All PV with status Long tags Process monitoring Diagnostics Conﬁguration Remote access HART 5 HART 6 4–20-mA loop Wireless Figure 4. Self-building and self-healing mesh adapts to plant changes, even temporary ones for maintenance. 24 • May 2008 Figure 5. The HART 7 speciﬁcation adds wireless connectivity and other features. www.chemicalprocessing.com http://www.ChemicalProcessing.com/articles/2008/046.html http://www.ChemicalProcessing.com/articles/2007/152.html http://www.ChemicalProcessing.com/articles/2007/095.html http://www.ChemicalProcessing.com/articles/2007/095.html http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - May 2008

From the Editor ChemicalProcessing.com Field Notes In Process Energy Saver Compliance Advisor WirelessHART signals a change at plants Avoid costly fabrication mistakes Watch out with variable speed pumping Hot cutover boosts control system migration Plant InSites Process Puzzler Equipment & Services Product Spotlight/Classifieds Ad Index End Point

Chemical Processing - May 2008

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