Chemical Processing - May 2008 - (Page 23)

forts underway. This does seem to send a confusing message to end users who are looking for a single standard. (Incidentally, instrument vendors also would like a single standard and development path.) However, these groups have made huge strides in working together to allow us to obtain a successful wireless instrument network. HART 7 and ISA. HCF has provided the WirelessHART specification to SP100 — a joint analysis team has already identified a pathway forward to use WirelessHART at the instrument level. Don’t forget that ISA SP100 is a family of protocols; WirelessHART would fit in very well at the instrument level. HART 7 and Fieldbus. The Wireless Cooperation Team (WCT) is working towards a topology where WirelessHART can be used at the instrument level with Foundation Fieldbus or Profibus as the backbone to the host system. The WCT meets regularly and includes experts from all three protocols. With such cooperative efforts progressing and end-user pilots complete, there’s no reason to wait much longer to consider a WirelessHART project. Evolution not revolution The HART 7 specification has built upon the existing HART specification by adding wireless connectivity and other features to ensure reliability, security and simplicity of operation (Figure 5). So, yes, we can employ existing software tools including HART hand-held configurators; yes, the network is self-building and self-healing; and, yes, existing instruments can be used via a WirelessHART adapter. The WirelessHART topology. Every WirelessHART network has three main elements: 1. A gateway: It connects the control system (via Ethernet, Profibus, etc.) to the wireless network; 2. A network manager: This normally is part of the gateway and automatically builds the wireless network and manages its operation; and 3. Field instruments and devices: These usually consist of pressure, temperature, position or other instruments but also can include adapters. WirelessHART is an instrument level network using existing and new HART commands to access information. The instrument network connects to a WirelessHART gateway that builds the mesh topology and also connects to the host system via standard high-speed backbones such as Ethernet. How often is the information updated? The rate at which process information is transmitted over a wireless network directly impacts battery life for those instruments using battery power. WirelessHART offers several mechanisms to maximize battery life and use of the network capacity: • Transmit measurements at different rates for different instruments — for instance, level every 20 or 30 seconds, and flow every 1 or 2 seconds; www.chemicalprocessing.com http://www.discoversolex.com http://www.discoversolex.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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