Wireless HART Field Device Installation and Configuration
The self-configuring capabilities of WirelessHART networks simplify the installation and configuration of WirelessHART field devices.
|By Moazzam Shamsi MSc, BEng, CEng, MinstMC; Global Solutions Architect with Emerson Process Management|
|WirelessHART devices are based on the HART (Highway Addressable Remote Transducer) protocol, which has become the global standard for sending and receiving digital information using 4-20mA analog wiring between smart devices and handheld devices or host systems. Typical WirelessHART devices include temperature, pressure, flow, level and other process variable transmitters (Figure 1).
Figure 1, wireless transmitters installed in field. This wireless installation measures steam flow injection rates in this oil and gas field by utilizing differential pressure, gauge pressure and temperature measurements. In the foreground are Rosemount 3051S differential pressure and 3051S gauge pressure transmitters. Visible in the background is the temperature connection head for the obscured Rosemount 648 wireless temperature transmitter.
IEC62591 WirelessHART devices are based upon established HART technology. These devices use the WirelessHART bi-directional communication protocol to provide data access between intelligent wireless field instruments and handheld devices or host systems. Host systems can include control, monitoring, asset management or maintenance management systems.
Frequency Planning and Configuration
WirelessHART mesh networks are self-configuring and self-healing, so setup and operation is greatly simplified as compared to networks requiring users to designate communication paths and other parameters. Each device in a WirelessHART network can act as a repeater, creating multiple possible paths of communication among the field devices and the WirelessHART Gateway (Figure 2). The network automatically and dynamically selects the best communication paths to the gateway.
Figure 2, gateway installed in field. This WirelessHART Gateway communicates with multiple WirelessHART field devices via a wireless mesh network, and with host systems via a hard-wired connection.
At least one gateway is required for each installation, with some installations requiring more. Reference 1, the Gateway Capacity Estimator, gives information to assist users in calculating the number of required gateways. There is no frequency planning required for WirelessHART networks. By design, the protocol utilizes every channel in the 2.4 GHz range by channel hopping during the course of normal communications.
Figure 3, Host System in Control Room. Each WirelessHART Gateway is connected to one or more host systems, which are typically installed in the control room.
Configuring a Device to Join the Network
Configuring Host Systems
In some installations, not all data collected from the WirelessHART field devices belongs in the control system, as some points of measurement may just be used for monitoring or asset management. Although most WirelessHART field devices are used for monitoring purposes, they can also be used for real-time control in certain applications.
The host system integration philosophy should be such that data from a WirelessHART field network is delivered to the appropriate end user. The WirelessHART data can be routed though shared network resources. To give some examples:
Properly defining an integration strategy will ensure an efficient collection of data from WirelessHART field devices, and proper dissemination of this information to the right end users. Some end users may be currently using application specific databases into which data is manually collected and uploaded. With the ability to integrate WirelessHART data using standard interface protocols, these existing databases can be automatically populated with information from WirelessHART field devices.
Traditionally, host integration between the gateway and the host systems has been via a Modbus hardwired connection and the OPC protocol. With the release of HART-IP, the familiar HART protocol can be used over a TCP/IP network (which may be wired or wireless) for the host integration connection. This enables direct access to WirelessHART field devices from the host systems without the need to perform any intermediate mapping.
As previously discussed, each WirelessHART device is configured with an update rate which varies from one second to many minutes. The update rate thus affects the time between an alarm condition and when it can be detected.
For the purpose of this discussion, each WirelessHART device is assumed to have a fixed scan rate, which is the pre-configured rate at which the device sensor is energized and a reading of the process variable is made.
When assigning an alarm to a process variable, the following factors should be considered when determining an appropriate scan rate:
Users should set an update time for each WirelessHART device which exceeds the process response time to ensure that any changes or disturbances in the process variable are captured within the planned update time of the field device.
This is the third of a five-article series on wireless instrumentation and infrastructure. This article covered WirelessHART field device installation and configuration. For more detail on these and other subjects listed below, please see Reference 4.
The first article showed how wireless can be used to cut operating expenses in capital-constrained environments. It can be found at:http://www.automation.com/automation-news/wireless-cuts-operating-expenses-in-capital-constrained-environments
The second article covered wireless device system planning, design, test and commissioning. It can be found at: http://www.automation.com/automation-news/todays-featured-news-headlines/wireless-device-network-planning-and-design
The next two articles in this series will be published in the upcoming issues of automation.com as follows:
Article 4, Apr 2016, Reliability and Maintenance of Wired versus Wireless Networks. Discusses reliability and maintenance issues.
Article 5, Jul 2016, Adding to Existing Wireless Networks. A detailed discussion of how to add instruments to existing wireless networks.
Upon conclusion of this five-article series, the reader will be prepared to justify, design, install and maintain wireless instrumentation and wireless networks.
About the Author
Mr. Shamsi has been an automation professional for 25 years and his career spans a broad range of industries, in roles from technical leader to project management. He presently works for Emerson Process Management where he directs Emerson’s global wireless consulting and execution solutions on large capital projects. He specializes in working with clients and contractors to implement technology solutions to improve operational efficiency. Source: automation