Chemical Processing - May 2008 - (Page 20)

these costs as there are no (or fewer) cables to run with instruments often being self-powered. During the planning phase for traditional wired instrument loops, it’s common to add up to 20% spare capacity to account for future plant modifications because wired systems are expensive to modify and expand later. However, frequently much of this spare capacity isn’t actually used five or 10 years down the line. A wireless network offers a very scalable solution that can reduce the need for building in and paying for such spare capacity at the onset. The intrinsic low-cost nature of wireless technology now allows you to tackle some of those process problems that only can be solved by measuring new process data or by monitoring device condition. ment process value and compare it to the 4–20-mA value. This can help confirm the instrument calibration status or provide a value when the 4–20-mA signal is out of range. (The WirelessHART value doesn’t depend upon the 4–20-mA value — it comes straight from the digital value.) • Valve condition monitoring. For a positioner you now have access not only to valve position feedback but also to other data to help analyze the valve’s condition. • Advanced diagnostics. You have remote access to instrument information such as asset signatures, level echo trace and other advanced diagnostics. • Full use of complex multivariable instruments. For multivariable instruments (mass flow, for exam- >> Successful demonstration >> Instrument adapter Figure 1. At last year’s ISA show WirelessHART effectively linked instruments from multiple vendors. Figure 2. A plug-in adapter can provide a simple, low cost way to get information from instruments. Target applications The chemical industry historically has been cautious in adopting new technologies. Hopefully WirelessHART will jump-start the use of wireless instrument networks at plants. End-user surveys provide a good guide to likely wireless applications. Upgrading existing instruments. Adding WirelessHART to an existing HART instrument in the field is very simple. Connect the adapter to the instrument at either a spare cable gland or even at a junction box. (The adapter could be self-powered or powered via the loop.) Add the network ID and password to the adapter and it will automatically join the existing WirelessHART mesh network. The original 4-20-mA signal remains intact and you now have remote access to the instrument information. This permits: • Calibration check and over-range reading. For a pressure transmitter you can monitor the instru20 • May 2008 ple), you now can read the process values previously hidden away. Coping with aging infrastructure. The maintenance and support of aging plant often can be a problem, especially when new measurements are required and the spare capacity within cable runs and its condition are unclear. A WirelessHART solution can overcome many of these issues because a wired infrastructure isn’t required and the mesh network overcomes many of the problems of point-to-point wireless topologies. Some examples: • Replacing local gauge indicators. A wireless instrument can provide a low cost way to report process information back to the control room, reducing operator rounds to read local indicators and improving visibility of the process. • Supplanting obsolete field instruments. Installing wireless instruments can obviate difficulties in keeping old instruments working as spares become www.chemicalprocessing.com 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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