Ethernet is taking the place of RS485 in plants and Ethernet-APL will eventually take the place of 4-20 mA. Ethernet is used for the control network since over 20 years ago. This means multiple protocols; you can use many protocols at the same time. But you also must use multiple protocols. One of these Ethernet application protocols is HART-IP. As I&C engineers are delivering new control systems, modernizing existing control systems, and also execute the digital transformation “use cases” identified for Industrie 4.0, what is the role played by HART-IP? Here are my personal thoughts:
HART-IP Justification
Plants deploy HART-IP to simplify system integration, to support infrastructure an ever growing number of wireless sensors, and in the future to replace 4-20 mA.
Ethernet instead of RS485
Many older control systems do not support HART communication for the 4-20 mA devices. Therefore HART multiplexers (HART MUX) are used to access the non-PV data such as diagnostics. The first generation of HART multiplexers used RS485 backhaul networking to the Intelligent Device Management (IDM) software which requires a RS485 to Ethernet converter to connect to the IDM server. Also, these first generation of HART multiplexers installed in plants are coming of age and have begun to fail and must be replaced. Moreover, RS485 is a bottleneck which slows down field instrument configuration upload and download, as well as diagnostics scanning.
To “future proof” the system and make it easier to manage, replace aging RS485-based HART multiplexers with new HART multiplexers using Ethernet directly. HART-IP is the best protocol for HART instrument data.
DD Instead of data mapping
Mapping data from 4-20 mA/HART and WirelessHART sensors to Modbus/TCP or OPC in a HART multiplexer or WirelessHART gateway is relatively easy for one process variable per device. However, if you also want to display measurement status, device status, detail diagnostics, and internal variables it becomes a lot of work to map it all into the control system when there are many devices.
To reduce system project engineering burden and improve day-to-day ease of use, instead use Intelligent Device Management (IDM) software that uses each device’s Device Description (DD), newer Electronic Device Description Language (EDDL), or latest unified Field Device Integration (FDI) file to automatically display all the device information without manual mapping. HART-IP is the best protocol for HART instrument data as it enables the DD/EDDL/FDI file to be used.
Manage wireless sensors
With Digital Transformation (DX), I&C engineers will deploy operational analytics as well as hundreds or even thousands of WirelessHART sensors to fully instrument equipment to feed data into this analytics to help other departments manage plant equipment like pumps and heat exchangers, energy conservation, process, and HS&E. The I&C engineers also continue to manage the WirelessHART sensors.
To simplify their work and save time in their day-to-day work, I&C engineers manage these WirelessHART sensors using the same IDM software they use for 4-20 mA/HART and fieldbus devices. HART-IP together with DD/EDDL/FDI provide access to the required instrument identification, configuration/setup, and calibration data as well as auxiliary measurements without data mapping, also saving project time.
Second layer of automation
Many of these additional WirelessHART sensors feed data into detail analytics for vibration, corrosion, and steam traps. This is lots of data and some of it in data formats that do not lend itself well to mapping to Modbus or OPC.
By instead using HART-IP direct into the analytics, no data mapping is required to get data into the software, again saving project time.
Pass-through instead of HART multiplexer
Many older Safety Instrumented System (SIS) logic solvers do not support HART communication pass-through for the 4-20 mA devices. Therefore HART multiplexers are used to access the non-PV data.
However, modern SIS logic solver now support pass-through of HART data from 4-20 mA devices to IDM software using HART-IP thereby dramatically simplifying system hardware and engineering, saving project time. In the future Remote Terminal Units (RTU), flow computers, PLC, remote-I/O, and DCS will also support HART-IP.
Ethernet-APL instead of 4-20 mA
4-20 mA, even with HART, imposes many limitations on devices.
In the future plants will use pure digital 2-wire Ethernet-APL (Advanced Physical Layer) instead of 4-20 mA. APL is Single Pair Ethernet (SPE) and avoids the limitations of 4-20 mA. Many Ethernet-APL field instruments will support HART-IP and other application protocols.
HART-IP Technical Description
HART-IP is an application protocol which works over Ethernet and UDP/TCP/IP. Ethernet can be copper cable or fiber-optic. HART-IP can also be carried over links using Wi-Fi and other media supporting UDP/TCP/IP like microwave or satellite. In the future there will be Ethernet-APL field instruments that support HART-IP together with other protocols.
HART-IP devices like HART multiplexers and WirelessHART gateways have an IP address. So will Ethernet-APL devices.
HART-IP uses “well known” port 5094. If there is a firewall, this is the port that needs to be open.
Devices like HART multiplexers and WirelessHART gateways that support HART-IP also support other industrial application protocols such as Modbus/TCP, OPC, EtherNet/IP, and others. For instance, process variables from sensors may be converted to Modbus/TCP, OPC, EtherNet/IP, or PROFINET-IO for use in the DCS or PLC. There will even be proprietary application protocols in parallel for some purposes.
HART-IP is a client-server protocol. The device like a HART multiplexer or WirelessHART gateway is a server. Multiple clients like IDM software or analytics can communicate HART-IP with the device at the same time to get the data they need.
HART multiplexers and WirelessHART gateways simply pass-through HART commands received over HART-IP from IDM software and analytics to the underlying field instrument and return the response. The application protocol remains intact. Only the physical media is changing from Ethernet to Bell 202 (4-20 mA/HART) or IEEE 802.15.4 (WirelessHART).
Future HART-IP field instruments will use the same commands as 4-20 mA/HART and WirelessHART instruments. That is, software or other client use one command to identify the device, another command to read the PV from a sensor, another command to send the setpoint to a valve, and yet another command to read the diagnostics and so on.
Since HART-IP preserves the application protocol when passing through communication with 4-20 mA/HART and WirelessHART instruments, only changing the physical media, IDM software can still use the device DD/EDDL/FDI files to automatically access all the data in the device without the need for manual data mapping.
As an end-user of automation that is probably all you need to know about the HART-IP protocol. Only developers need to know the details.
HART-IP Integration & Architectures
Modbus/TCP, PROFINET-IO, or EtherNet/IP are well established industrial application protocols but better suited for mapping one or two variables per field device but impractical for large volumes of setup/configuration, diagnostics, calibration, and other data from every field instrument. HART-IP is designed specifically to carry data from, 4-20 mA/HART and WirelessHART field instrumentation enabling the full power of field instruments to be used.
HART-IP is already supported in SIS, IDM software, gateways, multiplexers, and operational analytics apps.
Control System and Safety System Pass-Through
For 4-20 mA/HART devices the analog 4-20 mA signal is the real-time value for the process variable from a sensor or the setpoint to a valve. The real-time analog signal is what the DCS is using for Core Process Control (CPC); closed loop control and alarms. The logic solver in an SIS also uses the 4-20 mA signal for the Safety Instrumented Function (SIF). The digital HART communication is a non-real-time “second channel” pass-through from DCS, SIS, or RTU to IDM software to access intelligence in the field instrument. This 2nd channel pass-through can now be implemented via HART-IP. The IDM software may be deployed as part of the Digital Operational Infrastructure (DOI) on the side of the DCS as a second layer of automation as per the NAMUR Open Architecture (NOA) for Industry 4.0. OPC-UA is not used for the 2nd channel because OPC-UA does not support DD/EDDL/FDI.
The HART protocol is only used for setup, calibration, and diagnostics purposes, not for safety critical operation.
Intelligent Device Management (IDM)
IDM software support HART-IP and FOUNDATION fieldbus HSE (FF-HSE) standard protocols from 2nd channel pass-through in third-party systems such as HART multiplexers, SIS, and fieldbus linking devices. IDM software is used for device configuration/setup, diagnostics, calibration management, and to view auxiliary variables.
DD/EDDL/FDI is three generations of technology used to integrate devices into IDM software. DD/EDDL/FDI-based IDM software can access all the unique features in a device. A DD/EDDL/FDI for a 4-20 mA/HART device or WirelessHART sensor can still be used even though the data has been transferred through a gateway over HART-IP because HART-IP preserves the application protocol. It would not be possible to use DD/EDDL/FDI if data has been mapped to Modbus/TCP or OPC.
Another technology to integrate devices into IDM software is Field Device Tool / Device Type Manager (FDT/DTM). FDT-based IDM software rely on three types of DTMs: A deviceDTM for each device type, a gatewayDTM for each type of gateway (including multiplexers and gateways), and a commDTM for the backhaul protocol. A DTM for a 4-20 mA/HART device or WirelessHART sensor can still be used even though the data has been transferred over HART-IP because HART-IP preserves the application protocol. It would not be possible to use FDT/DTM if data has been mapped to Modbus/TCP or OPC.
The IDM software vendor may not have designed the software to support HART-IP or WirelessHART, but with the HART-IP commDTM installed the software now supports HART-IP anyway. And with WirelessHART gatewayDTMs the software now supports WirelessHART sensors.
Any system integrator that has ever attempted to manually map device diagnostic information from a mix of different devices to Modbus registers or OPC, build logic to decode, and build graphics to display it, soon learn it is a lot of work to create and impractical to maintain in the long run. The only practical way to manage intelligent devices is to use IDM software.
WirelessHART Gateways
Many plants now have plant wide WirelessHART coverage with WirelessHART gateways in every plant unit integrated using Ethernet backhaul network. A site may have hundreds and even thousands of WirelessHART sensors for automating manual data collection as part of digitization of how the plant is run and maintained; particularly the maintenance, reliability, integrity, energy efficiency, occupational safety and health work processes. Advanced sensors are key to digitalization of activities. However, all these sensors must be managed. HART-IP enables WirelessHART gateways and IDM software from different vendors to work together.
HART Multiplexers
Many plants still rely on HART multiplexers because HART is not supported in their control system. Modern HART multiplexers use Ethernet backhaul network. HART-IP enables HART multiplexers and IDM software from different vendors to work together without the need for custom driver software.
Operational Analytics
Analytics is a key part of the fourth industrial revolution (4IR). One of the differences between general purpose data analytics and operational analytics purpose-built for industry, is that operational analytics apps support industrial automation protocols like HART-IP and OPC-UA. For instance, apps for vibration, steam trap, and corrosion analytics receive raw data from WirelessHART sensors directly through HART-IP without mapping data to registers. Plant I&C engineers work with automation vendors to select the best solution.
Also note that HART-IP also run straight to the same analytics apps running in the cloud without conversion to MQTT.
Control System
In the future field instruments will use Ethernet-APL instead of 4-20 mA and on-off signals. Some of these Ethernet-APL field instruments will support HART-IP. Control systems today do not support HART-IP but some control systems may support HART-IP in the future. Many control systems may never be upgraded to support HART-IP. However, most control systems support Modbus/TCP which can be used to integrate Ethernet-APL devices in the future. Some control systems also support OPC-UA, EtherNet/IP, or PROFINET-IO. HART-IP, Modbus/TCP, and other application protocols can run in parallel on the same two wires. That is, future Ethernet-APL instruments supporting both Modbus/TCP and HART-IP can integrate sensor process variable and valve setpoint to the control system using Modbus/TCP, and HART-IP as a second channel to IDM software.
There is no need for FDT/DTM program or DD/EDDL/FDI file to map just the sensor process variable or valve setpoint to the control system via Modbus/TCP registers, EtherNet/IP instance & member, OPC group & item, or PROFINET-IO index & sub-index.
HART-IP Interoperability & Interchangeability
Interoperability means devices and software can exchange data without custom programming. Some data mapping may be required, or it could be as simple as loading a DD/EDDL/FDI file. Interchangeability means you can replace a device with another without custom programming, and even without re-mapping data or loading a new DD/EDDL/FDI file or equivalent. In simple terms interchangeability means an instrument technician can replace a device using only a screwdriver, without touching the control system software.
Ethernet or Wi-Fi alone, even with TCP/IP, provides no interoperability. An open application protocol is always required for multi-vendor interoperability. There are thousands of application protocols used over Ethernet for different applications. HART-IP is one of them.
HART-IP supports DD/EDDL/FDI which makes it possible for IDM software to access the large number of data points in a device without the need for manual data mapping. Make sure to use HART multiplexers and WirelessHART gateways supporting HART-IP. Similarly, use IDM software that supports HART-IP and DD/EDDL/FDI, or worst case FDT/DTM. This will provide interoperability making initial device integration easier.
The HART application protocol has mandatory universal commands implemented by all HART devices and these are well suited for transmitters, such as reading the process variable (command 1, 3, and 9). This provides some level of interchangeability for transmitters; to read the PV without system integration work thus making device replacement easier.
The HART application protocol has optional common practice commands implemented by some HART devices, such as writing a device variable (command 79) like the setpoint to a valve. Therefore, for future Ethernet-APL valve positioners, such as for control valves and electric actuators / Motor Operated Valves (MOV), with HART-IP make sure command 79 is implemented to get some degree of interchangeability; to write the SP without system integration work thus making device replacement easier.
Support of device families (device profiles) provide additional interchangeability thus making device replacement easier
Look for HART-IP certification by the FieldComm Group in devices and software.
HART-IP Commissioning & Management
Commissioning a HART-IP device like a HART multiplexer or WirelessHART gateway is primarily about setting its IP address. It is expected that all HART-IP devices, like most Ethernet devices, will have an embedded webserver enabling the IP address and other basic settings to be made using a laptop with a web browser. The web server may provide other administrative tools like network management, backup and restore, and firmware update etc.
Power up the device; for devices using regular Ethernet this is most often separate power, but could be Power over Ethernet (PoE). In the case of future Ethernet-APL devices, power shall be provided by an Ethernet-APL power switch.
Connect a laptop to the device; for devices using regular Ethernet, connect a regular Ethernet cable between the laptop and the device. In the case of future Ethernet-APL devices, connect the laptop through the Ethernet-APL power switch.
The device will be shipped from the manufacturer with a default IP address. Configure the laptop for the same subnet and then type the device’s default address in the web browser. The exact steps to make the required IP settings will be unique to each device. If the device is not at its default address and the correct address cannot be discovered, you may need to hardware reset the device to bring it back to the default address. Anyway, I&C engineers have been working with Ethernet for the past 20 years so they are able to figure out the subtle differences.
HART-IP Cybersecurity
HART-IP is an application protocol on top of the IP network layer protocol. The network over which HART-IP is transported can therefore make use of the wide range of security solutions available for IP; such as Transport Layer Security (TLS) / Secure Socket Layer (SSL) encryption, IEEE 802.1x authentication, firewalls, intrusion detection systems, VPN tunneling, and many others. A system can thus be designed to provide multiple layers of encryption, authentication, authorization, and verification etc. for security with defense in depth. That is, security is not part of the HART-IP protocol itself. Rather, security is at the lower layers which has the additional benefit that other protocols sharing the same network can also benefit from the same mechanisms.
HART-IP Troubleshooting
The most interesting fact is I have not had any problem with HART-IP application protocol itself. Any problems have been with the physical Ethernet connection or IP settings. Make sure any firewalls in the communication route has port 5094 is open for the corresponding addresses. More common issues include missing DD/EDDL/FDI file for the field instruments or 4-20 mA/HART communication errors.
HART-IP Migration
If you are using HART multiplexers with RS485 in your plant today, you may wish to start planning for migration to Ethernet. When the manufacturer of the HART multiplexer announces the model you are using is going obsolete and limited spare parts are available, it is time to upgrade to HART multiplexers with Ethernet. That is, not another HART multiplexer with RS485 and a converter to Ethernet. But rather a HART multiplexer with embedded Ethernet port and support for HART-IP.
HART-IP is easy to deploy because it can use the existing Ethernet infrastructure already available for automation systems in most plants. New Ethernet networking can easily be added using the plethora of industrial grade Ethernet hardware available. Existing intelligent device management software can be upgraded to latest version supporting HART-IP.
In the future DCS may support HART-IP directly to communicate with field instruments, such as future devices based on Ethernet-APL
Specifying HART-IP
Make sure to specify HART-IP backhaul network support for pass-through, wireless gateways, and HART multiplexers when deploying infrastructure in the plant. Well, that’s my personal opinion.
Jonas Berge Senior Director, Applied Technology at Emerson Automation Solutions
