SP100 Committee Listens to WirelessHART

The ISA SP100 standards committee was presented with WirelessHART specificationas that were voted on by the HART Communications Foundation’s membership in June 2007.

By Dick Caro

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The proposed SP100 Application Layer technology supports HART messages over the wireless network along with data for other protocols providing this “universal” capability for the user, whereas WirelessHART is narrowly focused, only supplying HART data over its unique wireless network. It has also been communicated earlier to the SP100 committee that the Technical Steering Committee of the Fieldbus Foundation has voted to base its future wireless protocol on SP100. A similar response is expected from Profibus International, which previously stated its position to not develop its own wireless protocol, but to influence the design of SP100 to meet its needs.

While most of the field instrumentation suppliers present at the Austin meeting have declared their intent to market both WirelessHART and SP100.11a networks and products, they’ve added that they’ll also make products that support HART protocols in a SP100.11a-compliant wireless network. This means that users will have a wireless network choice for communicating HART protocols with field instruments: a) a WirelessHART only network, b) a SP100.11a only network, or c) both types of networks. Also, it’s expected that some suppliers will make “small modules” available to connect wired HART instruments to an SP100.11a network to capture the diagnostics and communicate them to host systems.

Playing Catch Up

In other news at the Austin meeting, the primary agenda was resolving all problems preventing completion of the standard. At this point, all of the editors are working on creating Principles of Operation (PoO) for each network layer. To complete this document, the scope of the protocol for each layer must be completely defined. This revealed several gaps between layers that were to be resolved during this meeting. This has now occurred, although the resolution is not yet documented in the draft specifications for the respective layers. In general, the document editing work is one or two months behind the original schedule of a completed first draft document by the end of October 2007. Given this, a special editors’ meeting was called in June to get back on schedule for completing the PoO document, which is critical to completing a draft standard by October.

The Application and Gateway specifications, first presented in detail at the Karlsruhe meeting, are now nearing completion as the result of the Austin meeting. The Application Layer has been divided into a Lower Application Layer (LAL) that provides all of the normal AL functions, such as read and write to remote devices, and an Upper Application Layer (UAL) based on EDDL as defined by IEC61804-3 and the draft ISA S104 standard. This allows field devices to exchange data using the common attributes or parameters shared by HART, Foundation Fieldbus and Profibus-PA. These attributes will also be recognized by OPC. Also, the UAL will support a tunneling protocol that will allow transport of other protocols such as Modbus RTU and TCP and CIP common to EtherNet/IP, ControlNet and DeviceNet.

The SP100 Gateway protocol is also being defined to connect directly to any of the supported networks using EDDL with a minimal interface to be specified by each of the supporting organizations. Networks requiring the tunneling support of SP100 will require a Gateway application suited to their own needs where the use of EDDL does not apply, but the wireless portion will be a part of SP100.

Based on these discussions at Austin, the objective of SP100 is to become the universal wireless network for industrial communications supporting HART protocols as well as others. For the process industries, SP100.11a Release 1 is being designed to carry EDD information from smart field devices through the wireless network directly to host systems/networks that are already designed to receive information in this form. By agreement, some of the future standards work necessary for use in factory automation applications needs higher speeds and less object definition, so the standard is also being designed with the tunneling of protocols to serve all of the dominant networks used in these industries.

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