New WirelessHART Gateway Device Simplifies Integration for End User Implementation
By: Ron Helson, Executive Director, HART Communication Foundation; Dave Glanzer, Director of Technology Development, Fieldbus Foundation; Joerg Freitag, President of PI (Profibus & Profinet International).
The process industry’s three leading organizations dedicated to control network technology—the HART Communication Foundation, Fieldbus Foundation, and PI (Profibus & Profinet International)—have joined forces to create an architecture for a new WirelessHART® gateway device. The device will allow a WirelessHART network of devices to communicate bi-directionally with a host automation system via the Fieldbus Foundation High Speed Ethernet (HSE) protocol or the PI protocol, Profibus.
The cooperative project addresses the concerns of industry users by delivering simple and reliable integration of a WirelessHART network with Fieldbus Foundation and PI wired networks. When completed, the architecture and its related specifications provide a standard structure for others in the industry to design and build the gateway device.
The architecture also provides the information needed for creation of gateway configuration software that could reside in either the host automation system or a stand-alone third party product. The gateway device maintains a consistent overall architecture for easy integration of WirelessHART networks and sensors into different host automation systems from different manufacturers.
The specification covers the three primary functions needed for the integration: Gateway Configuration, Wireless Sensor Configuration and System Operation.
GATEWAY CONFIGURATION
Gateway configuration is performed by the gateway engineering application in the host automation system. This application uses client/server communications over HSE or Profibus to configure the I/O mapping of the wireless sensor parameters (such as device address, device tag, process variables, process alarms and other data) into database objects.
The application uses the Device Description (DD) files that are provided by the gateway supplier and the wireless sensor supplier. The DD files are also needed during operation, so they are stored in the host system.
Each object is identified by an object index, and has the DD reference as part of the object data. The object indices are organized into a gateway directory that is used by the operator interface application to display the parameters.
WIRELESS SENSOR CONFIGURATION
Once the gateway is configured, the wireless sensor engineering application is used to bring the wireless sensors online. Wireless sensor configuration uses communication protocols that aren’t understood by the gateway, so the wireless sensor engineering application communicates directly with the wireless sensor via a pass-through function in the gateway.
The application sends the wireless sensor configuration message to the gateway. The gateway forwards the message to the wireless sensor and waits for a response. When the response is received, the gateway passes the response back to the application until the configuration is complete.
The collection of wireless sensors operate and transmit their data in a wireless mesh network, meaning the devices communicate directly to the gateway, or they can communicate by routing their message through another wireless sensor if the primary path is blocked.
For example, if a truck temporarily blocks the communication path of a wireless sensor device to the gateway, the device uses an alternate path through another device to communicate with the gateway. When the truck is moved out of the way, the device reverts to the primary path.
The data flow for ongoing management of the wireless sensor mesh isn’t shown in the Diagram. These data flows include but aren’t limited to update of security keys, frequency hopping settings and mesh diagnostics.
SYSTEM OPERATION
Once the gateways and the wireless sensors are configured, normal system operation can begin. The gateway will scan through its list of wireless devices and request each device to send its parameter data to the gateway. In some wireless sensor networks, the devices can be configured to periodically publish their data to the gateway without the need for the request. In either case, the gateway maintains a local process data cache that can be accessed by the host.
The host uses its gateway directories to maintain its local process data cache. The frequency of update of the host cache is configured by tools provided by the host supplier. The host process data cache can be configured to request data from the gateway process data cache periodically, or on demand by an operator. In some systems, the gateway can be configured to publish data automatically from its process data cache to the host process data cache, either periodically or upon a change of state of a parameter such as an event or an alarm.
The operator interface application in the host uses the data in the host process data cache to graphically display the wireless sensor data to the operator. To properly display the data, the application uses the DD files stored on the host to provide additional information like the label of the parameter, engineering units, help strings, and other data points. This is possible because the DD references were configured into the parameter objects during gateway configuration.
The Diagram shows how data from a wireless mesh sensor network could be integrated into a host automation system.
END USER APPLICATIONS
Many process industry firms have selected WirelessHART as their wireless mesh network standard, and many more will do so in the future. These users need assurances that they will be able to easily integrate their WirelessHART mesh networks and sensors into their host automation systems.
For example, some companies may have different host automation systems at different facilities. The gateway device provides a solution by allowing use of the WirelessHART mesh network with different host automation systems—just so the host automation system supports HSE or Profibus communications.
To ease integration among different host automation systems, the gateway device maintains a consistent overall architecture. Wireless sensor parameter I/O mapping and use of DD files are also consistent among the HSE and Profibus protocols.
Even though inevitable competition exists among network organizations, the HART Communication Foundation, Fieldbus Foundation and PI are working together to proactively address the concerns that competition can create (such as incompatibility issues) through this common architecture development project and other efforts.
About the HART Communication Foundation
The HART Communication Foundation (www.hartcomm.org) is an international, not-for-profit, membership organization supported by more than 250 companies worldwide. Founded in 1993, the Foundation is the technology owner and central authority on the HART Protocol and provides global support for application of the HART technology. The Foundation manages and controls the HART standards including new technology developments and enhancements that benefit and support the needs of the industry. HART is the leading communication technology for smart process instruments with more than 32 million devices installed worldwide.
About the Fieldbus Foundation
The Fieldbus Foundation is a global not-for-profit corporation consisting of leading process end users and automation companies. Within the Fieldbus Foundation, end users, manufacturers, universities and research organizations work together to develop an automation infrastructure that provides process integrity, business intelligence and open scalable integration in a managed environment. For more information, visit their web site at www.fieldbus.org.
About PI (PROFIBUS & PROFINET International)
The Profibus Nutzerorganisation e.V. (PNO) was founded in 1989 as a non-profit organization. The PNO is owner of the PROFIBUS and PROFINET technology and responsible for further developments (www.profibus.com). PROFIBUS and PROFINET International (PI) is an international umbrella organization offering regional support for PROFIBUS and PROFINET. With 27 regional organizations all over the world, 1,400 member companies and about 2,500 different products, PI is currently the world's largest interest group for industrial communication covering all key markets of industrial automation like factory automation, process automation, motion control and safety-related applications. In total, more than 35 million PROFIBUS devices are currently installed worldwide.