Crossing the Chasm

End users must often deal with multiple fieldbus networks in their plants. This can complicate network design, installation, and maintenance. Courtesy of Profibus International.

Courtesy of Profibus International

Dealing with multiple vendors requires care. “The master unit of one vendor’s network may not be fully compatible with another vendor’s spur blocks,” relates Philip Daniels, an engineer with the Wastewater Treatment Division of King County in Washington.

“One vendor may have the intrinsic barrier located at the master unit, while another may have it at the spur block. If the wrong combination of vendor products is selected, there will be no intrinsic barrier in the circuits,” adds Daniels.

“Another problem is addressing of the units. The Foundation Fieldbus network is just like any other network, and the addresses of the various components must be unique. We ended up addressing field devices just like our office network intranet addressing. Another issue that caused us problems was individual component programming. Each device has unique programming needs, and vendors do not always provide proper documentation,” concludes Daniels.

So how do you get up to speed? One way is to hire a digital fieldbus expert who has prior experience with the design, installation and maintenance of your desired network and your existing control system. Good luck finding such a person.

This is not like the PC world with its true and few interoperable standards, its long track record and its throngs of qualified and certified network engineers. You instead have to deal with multiple incompatible technologies, relatively new products and a paucity of experienced professionals.

If hiring an expert is virtually impossible, the other avenue is for you and your colleagues to become experts. This means getting training, either from a vendor or from a service company.

Training Challenges

The next step is to train the right way. This end user learned the hard way. “Our main challenge with our digital networks was training instrument techs on the more complicated devices” reports Danny Cox, the director of manufacturing systems at AOC Resins, Collierville, Tenn. Cox’s company used Foundation Fieldbus, DeviceNet, AS-i and HART to connect field devices to an Emerson Process Management DeltaV control system.

“We tried vendor training, and it was a total disaster. We now have corporate engineering travel to the plants to provide hands-on training. At least for our situation, in-house training seems to work much better,” he concludes.

AOC Resins has to deal with four different networks and with instruments from 10 different vendors. Sending your entire staff to ten different vendor training sessions is not practical. Better to have an internal company expert learn as much as possible from vendors, from network organizations and from other end users; and then train others.

Another challenge that distinguishes a digital fieldbus network from an office network is the sheer number of people that have to be familiar with it. In an office, a small number of network experts know the network in detail. In a plant, the entire automation group will probably have to deal with at least some part of the network on an on-going basis. Engineers need to know how to set up the network initially. They also need to specify the instrument parameters of interest for the process control and information systems. They need to know how to configure the software packages that receive the network data.

Instrument techs need to know how to use the network for remote calibration. They need to be able to make sense of the instrument data for predictive maintenance. Instrument techs keep calibration records, so they need to know how where that data is stored.

If something goes wrong or if changes need to be made after initial installation, engineers and technicians often need to work together.

So we have a situation where many people within your company must get up to speed on multiple networks, various field devices and at least one control and information system. Proper training is essential so that you can pre-identify some of the gotchas. Read and heed how some of your fellow end users are winning their field bus battles.

Winning the Battle

The big problem with vendor information is that too rosy a picture is painted because vendors want to promote their particular networks. If you listen to vendors married to particular digital fieldbus technologies, you invariably will go in to your project with unrealistic expectations.

There are two main sources of straight dope. The first is other end users, system integrators and engineering firms who have been where you want to go. The is suppliers who make a living helping end users install networks from multiple vendors.

Let’s hear from an end user first. While Richard McCormick was at Ultramar, the company implemented Foundation Fieldbus (FF) on a grass-roots unit. The engineers connected field instruments to a Honeywell Experion PKS automation system through fieldbus interface modules. “We used Honeywell’s asset manager software to gather FF data from the Experion system. I consider such software a must if you want to fully exploit FF.  Because there is so much data available from FF instruments, you need a piece of software that will massage the data prior to presentation to instrument techs. This greatly simplifies their work by providing common root-cause information from different instruments vendors’ embedded diagnostics,” advises McCormick.

Now let’s hear from a vendor who works with many different fieldbus technologies and has no interest in promoting one over another. “Some of most baffling problems occur during startup and are because of improper installation,” reports Desmond Ho, fieldbus applications consultant at MooreHawke in Shanghai, China.

“In many cases, segment terminators are not set properly. All fieldbus segments need proper termination to prevent communications errors through uncontrolled signal reflections. Many subcontractors pay little heed to the terminators and either forget them completely or simply install them everywhere, neither of which allows the segment to operate properly. Often, physical inspection of junction boxes and field enclosures is the only way to locate and correct the terminator position, which is a significant delay to the commissioning process,” continues Ho.

“This problem can be avoided from the beginning simply by specifying newer device couplers with automatic segment terminators such as our device couplers. The automatic segment terminator greatly assists in segment commissioning by eliminating the issue of over or under terminating. If multiple field device couplers are used, the auto-terminator is always activated at the farthest unit and automatically migrates up the segment if that line is disconnected,” concludes Ho.

ARC Advisory Group research director Wil Chin gives some sound advice on dealing with multiple vendor protocols. “A best practice for end users is to pick a supplier with multi-protocol capability. As an alternative, FDT technology should be considered for plant upgrades, particularly when the objective is deploying a plant-wide asset management system.”

The Benefits of Getting it Right

Once AOC Resins figured out how to get their people up to speed, they began to reap the benefits. “The main advantages of digital data are online instrument health monitoring and communication of multivariable information. The best example is looking at the drive gain for our Coriolis meters. If one exceeds a limit, we assume that the meter has gas, and we switch our primary measurement to load cells. In a similar fashion, we verify radar level is not locked on a target by looking at signal strength and this prevents over filling,” relates Cox.

Preventing one over-fill incident with an associated spill, shutdown, and clean-up can go a long way to justifying a digital fieldbus system.

McCormick of Mick Automation says that other key benefits are decentralized control on the wire capabilities, reduced implementation costs, measurements with better precision and predictive maintenance.

“Process plants gain availability of historical data for process analysis, process improvement and real-time management of production,” says Dan Miklovic, the vice president of manufacturing research at Gartner. “Plants can also use simulation to configure soft sensors and thus avoid installing and maintaining hard sensors in hazardous locations.”

Are the benefits of fieldbus worth the costs and risks? It’s your call. Just make sure that you include all of the costs and benefits in your analysis based on good information from unbiased sources.

For more on fieldbuses, go to www.controlglobal.com/fieldbusguide.html

What Makes Digital Fieldbus Difficult to Implement?

• Lack of industry wide expertise
• Too many standards
• Frequent requirement to work with multiple networks and vendors
• Harsh environments
• Huge amounts of data to be handled
• Multiple users must learn how to work with the network
• Vendors promote their favored networks instead of warning users about implementation issues 

How to get up to Speed

• Designate one or more people in your company to become experts
• Have your internal experts train others within your company
• Make sure that operations personnel use the technology early and often
• Find and attend vendor neutral presentations and seminars
• Speak with other end users who have been where you need to go
• Engage an independent system integrator

What you’ll get out of it

• Reduced installation costs
• Faster commissioning
• Remote instrument maintenance
• More instrument data
• Easier to use multivariable instruments
• Better measurement precision
• Enable decentralized control

For more on fieldbuses, go to www.controlglobal.com/fieldbusguide.html