Bridging the gap with HART

19 May 2020

Taking critical plant floor data from smart HART field devices and sharing it with higher level control and information systems no longer has to be difficult or expensive according to Tina Todd.

The rapid growth of industrial Ethernet and wireless networks in process manufacturing plants and automation facilities has resulted in data exchange within a facility and even throughout global corporate networks becoming commonplace. The separate information hierarchy levels, outlined in the ISA 95 model – related to process data exchange within a manufacturing facility – have started to coalesce. Traditionally, data and information that needed to be exchanged between the lowest plant floor levels 0-2 and the upper ERP level 4 required MES products or custom coding; and oftentimes both. This free flow of information has introduced a new set of ubiquitous terms, standards and phrases such as IIoT, Smart Factory, Cloud Automation and Industry 4.0. 

The typical process control model that involves decision making for the process at the local or centralised level by PLCs or BPCS (Basic Process Control System) is changing. These systems were never intended to deal with the amount of data they would have access to in the near future. Streamlining of costs and overheads has left many manufacturers with just enough personnel to keep the plant running, so there is not the time, personnel or resources to analyse data. For this reason third-party companies, and even some of the larger process control vendors, are offering leasing or annual agreements that involve collecting, storing, and analysing process data. 

The challenge remains: how do existing and new manufacturing facilities find a cost-effective way to get critical plant floor data up to higher level information systems? The answer is to take advantage of the digital HART data that is already in many installed instruments.

HART continues to get updated revisions that enhance data exchange capacity, speed, number of devices on a network, support over Ethernet, and wireless capability. It gives end users unfettered access to process and diagnostic data that can be shared with all areas of the new Smart Factory that supports IIoT endeavors.

In many cases, HART instruments were installed simply because they could be configured and diagnosed easily with a HART handheld communicator (HHC). However, the HART digital signal often contains additional process measurements and other variables that may include instrument status, diagnostic data, alarms, calibration values and alert messages. A simple and cost-effective solution for gathering HART information is to use a HART interface device which makes acquiring data a fairly simple proposition. This HART data can then be made available to the control system, asset manager or plant Ethernet backbone where it can then be shared with higher level systems.

Interface options
There are several ways to interface with HART smart field devices to acquire the digital process and diagnostic information.  They vary from HART enabled 4-20mA input cards, HART multiplexer (Mux) systems, slide-in PLC gateway cards, custom coded software interfaces for asset management and MES/ERP systems and standalone gateways that typically convert the HART data to some other proprietary or open industry format. Many PLC and BPCS cards installed in legacy systems don’t have the capability to read the HART data that is superimposed on the 4-20mA signal.  However, each vendor usually has an alternative card that is more expensive or offers a full upgrade path to input cards that read HART. 

HART multiplexers are common and typically their interface is a custom RS-422, RS-485 or RS-232 serial connection which is custom configured for a particular vendor’s hardware interface, asset management system or control system. Some PLC and BPCS companies offer slide-in chassis type gateway cards that read the HART data and offer a proprietary backend communication connection to the system.  Usually each of these options is costly and so is often avoided.  The most expensive, but also most specific HART interface to have is one written by a programmer which can then be customised to exact user and hardware specifications.  

Lastly, there are standalone HART gateways which provide an economical pathway to extracting HART data from field devices and making the data available to higher level systems.  These products usually offer one to four channels or ports that allow several HART devices to be multidropped for maximum data concentration (See Figure 3).

Using the data
Once HART data is extracted from field devices it is essential that the information is made available in an open and easy-to-interface manner. Now that Ethernet backbones have become the standard for in-plant communication links, it seems only reasonable that any interface device that gathers and holds enormous amounts of data should include an Ethernet port.  Likewise, these same devices should support open protocols that run seamlessly over Ethernet networks.  

Employing HART data for process monitoring, control, predictive maintenance, and process optimisation requires that open and vendor neutral industrial protocols be supported. This allows the HART device data to freely flow to most any control, SCADA and monitoring system from any vendor.  Now that HART supports Ethernet with HART-IP, it seems logical that any device supporting the HART protocol with an Ethernet port would support HART-IP devices which typically allow for any HART field device data to be mapped to a number of Device Variables locations for reading by a HART-IP host.

One of the most installed and supported industrial Ethernet protocols is MODBUS/TCP which takes MODBUS data packets and wraps them in a TCP header utilising IP addressing. This makes implementation by both host computer and field device manufacturers quick and abundant. Additionally, Ethernet devices can offer web pages to view the collected HART process and diagnostic data on any PC or mobile device. However, efforts should be made by device vendors to lay the information out in a table format with easy-to-understand headers and address locations (for other supported protocols) so that additional hosts can be configured more easily.

Cybersecurity considerations
IIoT, cloud storage, big data and a host of other interconnecting methods and strategies has led to production and efficiency increases.  However, this has also led to cybersecurity issues. It is therefore important that Ethernet-based devices include safeguards within their products to ensure that network bandwidth is protected, viruses or malware cannot be loaded, unwanted access is not granted, unauthorised reconfiguration of device is not allowed, and unauthorised writes to memory locations are not accepted by the device.  In addition, physical security of such devices must also be restricted to authorised personnel only and process data should be read only – unless the device is required to perform control. It is important that the entire product lifecycle including design, build and test must adhere to tight process and quality assurance requirements. Additionally, post installation considerations should be taken to assist onsite protection of site data and property. At a minimum, a two layer protection scheme should be put in place for the device that includes software and physical hardware restricted access.

Traditionally, end users have had to deal with custom and proprietary configuration packages from vendors for advanced capability devices. This typically requires several custom software packages that users have to learn, become familiar with and get IT support and permission.  Most IIoT capable devices are not simple field instruments and therefore small handheld configurators are not convenient for setup and configuration. Indeed, many HART protocol gateways require complex database mapping and programming software. When sourcing or specifying an IIoT device, investigate what the programming interface will be. There are several open standards and software packages that vendors have access to that prevent the need for custom and sometimes even expensive programming software utilities.

With the acceptance of industrial Ethernet backbones and wireless networks, IIoT HART interface devices with built-in security measures, open industry protocols and ease of programming, provides a quick and seamless way to share process data with the entire corporate infrastructure.

Tina Todd is director of engineering at Moore Industries-International, Inc.

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