HART Communication adapts for the Internet world
A closer look at the benefits offered by HART-IP, which is the latest enhancement to the HART Protocol Specification
To address growing industry demand for accessing data over the Ethernet, the HART Communication Foundation added a new capability to the HART Protocol Specification, HART-IP. HART-IP takes HART technology as it exists today and adapts it for the world of the Internet, allowing the exact same HART protocol to run over an IP-based connection delivering valuable HART data at the speed of Ethernet.
This means that the standard Ethernet infrastructure that is used today in most control systems is now able to run the HART application layer and protocol over the same Ethernet and TCP/IP layer. A HART-IP backhaul network enables software to gain direct access to information in WirelessHART devices for example, without having to perform any data mapping through intermediate Modbus or OPC.
Offering comment on HART-IP, Harry Forbes, senior analyst at ARC Advisory Group, said: "The introduction of an IP backhaul will undoubtedly increase the use of WirelessHART." Frank Fengler, of ABB agrees, saying: "The greater use of HART-IP will lead the way to larger WirelessHART networks because it will be easier to gain access to the intelligent information in HART devices. HART-IP is already being used in many products that have connecting devices - such as gateways, remote I/O and multiplexers so just with the addition of a communication driver, users can gain access to HART-IP."
"In reality, because most WirelessHART networks contain less than 100 devices, multiple networks are created," Forbes went on to explain. "This can present an integration management problem as the number of networks grows, because there will be many different gateways that all need to be integrated. Having an IP backhaul, therefore, makes a huge amount of sense, connecting measurements to the Internet. This will enable users to integrate whatever applications they are using for measurements, over a much larger scale.
"It will also make it possible to centralise the management of multiple networks. Applications consisting of, for example, up to 200 or more wellheads distributed over wide distances, would be able to manage all of the gateways from a single point, connecting to all the measurements," said Forbes. Once the HART-IP-enabled devices are plugged into the corporate network, the information can travel literally anywhere in the world over the corporate VPN allowing remote access of process measurements and device and/or process diagnostics.
With more vendors using HART-IP within their product offerings, Eric Rotvold, distinguished technologist, Emerson Process Management, says that there are now implementations of HART-IP in the real world, and WirelessHART is also being adopted more aggressively by industry. "Many gateways already support HART-IP so its increasing use is a natural progression. There are also devices such as COM DTMs under the FDT umbrella, being developed to talk to these HART-IP gateways and instrumentation, for asset management purposes." Likewise, many HART-enabled device configuration and asset management applications are already HART-IP enabled.
A big benefit of HART-IP is the ability to gain high-speed access to the standard HART diagnostic information and process data using the plant's installed networking infrastructure. Rotvold said: "Although this information has been available for a long time, , up until this point there has not been a great way to get a lot of data out of HART devices and into asset management or enterprise level systems. Multiplexers suffer from data aggregation and with WirelessHART gateways you still need a way to ship all the data up to the host system as quickly as possible. HART-IP provides this capability, allowing for the effective management of many gateways and many thousands of WirelessHART devices."
HART-IP offers the most straightforward way to access all the standard HART information available in a HART device. It allows the information from these devices to be brought up to the Ethernet level easily, without the need to go through any translation processes and with no loss of information.
According to Rotvold, the main barrier to greater implementation of HART-IP is now the system vendors. He said: "If system vendors make HART-IP available in the same way that they do with Modbus TCP, I believe that there would be a dramatic uptake in the use of HART-IP which would result in an even greater uptake of WirelessHART. Emerson's system controllers already support HART-IP and can talk directly to the Emerson gateway via HART-IP. The HART-IP specification was released in 2012 so I expect that we should start to see introductions from other vendors within the next two years."
John Yingst, product manager at Honeywell, believes that HART-IP is an essential tool to increase the distance between the source of HART data (the devices themselves and the control systems they are connected to) and the application user of that data (typically some kind of configuration tool or instrument asset management system). Traditionally, HART multiplexers have used RS485 networks to link these together, which required set-up and configuration of several parameters (baud rates, adapters, wiring polarity, address switch settings, etc.) and posed some distance limitations. HART-IP significantly simplifies the connection configuration and basically eliminates the distance limitations.
Yingst said: "Several emerging Honeywell products will take advantage of HART-IP. For example, the Wireless Device Manager (WDM), a key part of the OneWireless Network solution, offers HART-IP in Release 220. The WDM serves as the gateway for Honeywell's wireless product offering. From its initial release, the WDM had the ability to represent wireless sensor data as HART, OPC, Modbus and Honeywell (Experion PKS) CDA data, allowing applications to transparently use this device data. Extending the HART capability in the WDM to support HART-IP is a natural evolution."
Another development that takes advantage of HART-IP is Honeywell's RTU2020, aimed at the wellhead control and monitoring market. This RTU features a HART-IP server which gives the ability to remotely maintain and diagnose connected HART valves and transmitters. "A maintenance engineer in such applications might be 1,000 km away from the HART device and the closest maintenance camp might be 200 km away. Having HART-IP will allow better decisions to be made about the health of the remote asset, possibly negating the need for an expensive site visit," said Yingst.
HART-IP works with any IP-enabled PHY, including packet radio, SAT-radio, WiFi, cell nets, etc., which makes the HART network - including WirelessHART devices - compatible with commercial and industrial grade LAN switches, fibre optic media converters, Wi-Fi access points, and related equipment.
Because the application layer is the same for HART field devices and HART-IP, time consuming and error-prone data mapping is eliminated, making HART-IP the most suitable backhaul network for WirelessHART gateways and 4-20 mA HART multiplexers.
Implementing HART-IP is really just about organizing the communication path," explained Gerrit Lohmann, manager product group remote systems at Pepperl+Fuchs. "It is nothing new or complex. End users need to do nothing because the HART integration mechanism does not care how the HART message went into the system. It is possible to reuse all the DTMs and DDs - the only additional consideration is the communication path. In the DTM world a communication DTM is created to open the Internet communication path. Of course, the connected DCS or asset management system will also need a physical interface."
Lohmann expects HART-IP implementation to increase in the near future. He said: "HART-IP is now starting to be implemented in DCS systems and asset management systems, which will broaden its usefulness - as these systems will be immediately plugged into the gateway, allowing the HART information to be more widely used."
Pepperl+Fuchs have included a HART-IP interface in its WirelessHART gateway for many years. "Having this Internet based communication capability broadens the application of HART, enabling it to be used in the same way, and parallel to, other Ethernet-based protocols, using the same infrastructure and using the same principles for integration," concluded Lohmann.
Suzanne Gill is editor of Control Engineering Europe.
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