Ethernet-Based Multiplexers Provide Cost-Effective Access to HART Diagnostics

Summary

HART devices make up the majority of the installed base of all field devices today, but most end users lack connectivity between HART-provided device diagnostics and the DCS or plant asset management system. This is unfortunate, since this enormous pool of "stranded" diagnostics could be used to reduce routine maintenance costs and costly unplanned shutdowns that could otherwise have been avoided.

Most users will tell you that they would consider using diagnostics for predictive maintenance if they had a cost-effective way to interface their existing HART devices to their systems without having to invest in all new HART I/O. As ARC Advisory Group leaned in a recent briefing by Phoenix Contact, HART multiplexers can – but don't always - provide cost-effective connectivity for older HART devices. The problem is that some multiplexers can require a significant amount of effort to install and utilize.

Ethernet-based HART multiplexers offer the benefits of standard networking technology to provide a cost-effective way to achieve connectivity with the huge number of installed HART devices that does not rely on large-scale replacement of DCS I/O, which may only be possible during a major upgrade or migration project.

 

Value of Remote Diagnostics and Predictive Maintenance

One of the big advantages of protocols such as HART is the ability to access information about a device remotely from the control room, instrument shop, or anywhere the information is needed. Remote access to device diagnostics can save owner-operators a considerable amount of money on maintenance costs and avoided failures.

Access to remote diagnostics is the foundation of a predictive maintenance strategy. Research shows that equipment failure is the second major cause of unreliability in process plants. Equipment failure relates directly to both incident avoidance and maintenance issues, which are aggregated under equipment reliability.

The challenge now is for the process industries to be able to tap into wealth of device diagnostic information now largely stranded in non-connected intelligent devices without requiring a major upgrade or migration project.

Accessing HART Diagnostics

The value proposition of predictive maintenance and device diagnostics is clear, but how can end users avail themselves of the diagnostic capabilities without spending a lot of money? There are several options available in the marketplace today with varying levels of cost and functionality.

Handheld and Mobile Devices

Handheld and other mobile devices are probably the most common method used to access HART data. Most of these devices, however, are typically used for initial instrument commissioning and calibration, rather than predictive maintenance. Since remote access to diagnostic information from the control room or maintenance shop is the foundation of a good predictive maintenance strategy, users still need some level of access to these devices apart from having to go out into the field and access the device directly. There is a place for handhelds, and they should be part of your device maintenance toolkit, but handhelds alone leave a lot of money on the table when it comes to realizing the benefits of predictive maintenance.

 

Approach	Remote Capabilities	Primary Function	Initial Capital Cost	Lifecycle Cost
Handheld and Portable Devices	Used at the Device	Installation and Configuration, Bench Work	Low to Very High	Low
HART Modems	Remote Access to the Device or Used Locally or in the Instrument Shop	Engineering, Installation and Configuration, Bench Work	Very Low	Low
HART I/O	Full Remote Access to HART	All Functions of HART	High	Very Low
Wireless HART Gateways and Adapters	Full Remote Access to HART	All Functions of HART	High	Very Low
HART Multiplexers	Full Remote Access to HART	All Functions of HART	Medium	Very Low

Various Approaches to HART Integration and Their Associated Functions and Costs

HART Modems

HART modems are typically used to interface HART devices to a laptop or device for routine maintenance tasks and often found as part of the maintenance benchtop set of tools. In this case, HART modems are essentially relegated to the same role as handhelds, rather than to connect a large number of field devices to a DCS or plant asset management system.

HART I/O

HART I/O provides a robust option for directly integrating HART devices with control systems and related applications. However, it also tends to be the most costly in terms of initial capital outlay. ARC research indicates it is primarily employed as part of a control system modernization or migration project where significant portions of the existing DCS are being modernized and/or upgraded.

Wireless HART Gateways and Adapters

Wireless HART gateways are the standard for accessing wireless HART data and bringing it up to the plant applications that require it. End users can take their existing wired HART devices, add wireless HART adapters, and bring the diagnostic information in through the wireless gateway. This can also often provide a good solution for retrofitting existing wired HART devices. However, for end users that may want to start small and work their way up, this solution may be cost-prohibitive due to the need to modify existing instrumentation.

HART Multiplexers

HART multiplexers can provide the same benefits of HART I/O at less cost. HART multiplexers also allow end users to interface to the installed base of the HART devices in their plants gradually over time, often using maintenance (rather than capital) budgets. HART multiplexers also allow end users to start using their HART diagnostic data immediately.

HART multiplexers offer one of the most cost effective ways to implement a predictive maintenance strategy. They are relatively inexpensive, can be implemented over time in a phased manner to provide a scalable approach to intelligent device management, and can interface with other standard networks in the plant.

However, HART multiplexers come in different flavors. Traditional serial multiplexers enable users to connect groups of HART devices to the control system via RS485 or other serial link. Alternately, a new generation of HART multiplexers allow the user to connect HART devices to industry-standard, Ethernet-based networks such as HART IP, Profibus, and Ethernet/IP.

Phoenix Contact's GW PL Ethernet Multiplexer

Phoenix Contact recently briefed ARC on the company's new Ethernet HART multiplexer solution. The GW PL modular system provides a simple way to parameterize and monitor HART devices via HART-IP, Profinet, Modbus TCP, and FDT/DTM for easy integration into nearly any host system. It is a modern alternative for traditional RS485 HART multiplexers.

The multiplexer consists of a head station and a variety of HART expansion modules to suit a variety of applications. A digital I/O expansion module enables alarm and status monitoring, as well as actuation of motors, pumps, blowers, and other equipment. Up to five expansion modules can be connected and powered by the head station. The modular design provides a scalable solution for modern distributed control systems and phased rollout. Another feature worth noting is the 1x1 HART master, which means one HART master per channel. This approach allow users to speed up their maintenance routines, specifically for multiple instruments at one maintenance interval.

The GW PL ETH/BASIC-BUS head station communicates directly onto Ethernet networks. Up to five fieldbus-specific expansion modules can be connected, and the field device data can be accessed using FDT/DTM technology, HART IP, and Modbus TCP. The GW PL ETH/UNI-BUS head station also adds PROFINET communication. The head station features an embedded web server for configuring the device, as well as a CommDTM for use with an FDT Frame application such as PACTware or any of the wide range of plant asset management applications offered by the major process automation system suppliers.

HART-IP Support

Significantly, the GW PL multiplexers support HART-IP, the latest networking technology for HART. HART-IP uses a conventional client-server architecture. Servers can be WirelessHART gateways, HART multiplexers, HART Remote I/O, or individual HART devices. Servers listen for client requests on TCP and UDP ports 5094 and must provide service over both UDP and TCP transport. Servers must also support a minimum of two simultaneous client sessions. Any type of applications can be clients. So HART-IP could be used as part of field device management software to configure, manage, and diagnose HART devices or access additional measurement values. Any HART-IP server can be a HART-IP client as well.

HART-IP is essentially a remote HART command interface. HART commands pass through the IP network as payloads and are interpreted and executed by the HART-IP server, which responds to the client. The advantage of a remote command interface is that the server does not need to do any data mapping. The HART-IP specification does not prevent a server from caching HART data. That matter is left up to implementation.

Besides the pass-through of HART commands, HART-IP provides two additional functions. First is a set of identity commands that identify the field devices associated with a HART-IP server. The second is an optional discovery protocol. This function identifies all HART-IP servers within a particular IP network and is implemented using a UDP broadcast.

According to Phoenix Contact executives, a major US chemical company is evaluating this solution as a migration path to enable it to connect the HART devices from older parts of the complex that are not currently connected via either serial HART multiplexers or WirelessHART. This would enable the company to maximize the benefits of HART diagnostics for its predictive maintenance activities by cost-effectively extending remote access to all its HART devices. The GW PL multiplexers provide a faster path to access HART diagnostics and easier integration onto standard Ethernet-based networks. The system is compatible with the phased roll-out nature of the project and provides faster time to benefit.

Conclusions

Ethernet-based HART multiplexers should be considered as part of any intelligent device management strategy that involves tapping into the diagnostic potential of HART devices. These multiplexers are especially well suited for brownfield installations that have a large installed base of HART devices for which the intelligent diagnostic capability is not being used. The ability of Ethernet-based multiplexers to integrate directly to industry standard networks such as HART-IP is an added benefit and offers the potential to greatly reduce installed cost and lifecycle costs.

ARC Advisory Group clients can view the complete report at ARC Client Portal on www.ARCweb.com or Box.com

If you would like to buy this report or obtain information about how to become a client, please Request ARC Info

 

Keywords: Device Diagnostics, HART, Ethernet, Lifecycle Cost, Predictive Maintenance, ARC Advisory Group.