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In everyday life, availability is a relatively simple
matter — can you join us for dinner tomorrow?
However, on the plant floor, availability is a far more serious matter. If a system is available, it’s operating successfully.
If it’s not, critical uptime and productivity are being lost —
and sometimes personnel and equipment put in harm’s way.
More directly, in process automation — especially in
heavy industries — achieving availability generally means
doing your engineering best to make sure nothing gets
lost, stops working or is damaged.
Thanks to ever-evolving technology, expanded product
offerings and design best practices, process industry stakeholders now have more ways to achieve high availability
for process control systems. The catch is that no one-sizefits-all proposition exists. Manufacturers need to examine
each application against their overall business objectives to
determine the solution that best meets their performance
requirements and protects their assets.
Reliability and Maintainability
Availability can be defined as the probability that a system
is operating successfully when needed. Availability is
most often expressed as a percentage. It’s calculated by the
expression A= MTBF/ MTBF + MTTR. Today many suppliers can supply control systems with availability ranging
from 99.9 to 99.9999 percent.
The term high availability encompasses all aspects
related to productivity, especially reliability and maintainability. Reliability is the likelihood that a device will
perform its intended function during the mission time.
An engineer can enlist numerous methods to achieve
reliability. For example, reliability can be designed into the
16 THE JOURNAL | OCTOBER 2010
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system using techniques such as Component Derating and
Design through Six Sigma.
However, even the most reliable system might not be
the most available. To be available, an automation system
also must be easy to troubleshoot, modify and repair during mission time, which may exceed a decade or more. In
other words, it needs to be maintainable.
Personnel should be qualified and trained, and they should
be able to remove and add components to the system without
interrupting the mission. Consequently, replacements should
not require rewiring or reprogramming.
Some features that help improve maintainability include system-level diagnostics, such as controller, network,
I/O, server and field-device diagnostics. To assist with
troubleshooting, users can leverage network-monitoring
tools, products with onboard LED indicators, graphical
programming languages and human-machine interface
(HMI) with built-in alarm displays.
Features that help improve maintainability on the control side include online editing, executing partial downloads, adding I/O online, and removing and inserting
modules under power. Furthermore, the ability to add tags
to the HMI online helps with the availability of the HMI
and information layers.
More Scalable Solutions Tailored
to Meet Specific Needs
New multidiscipline plant process-control systems are
more scalable and more economical for end users and machine builders (OEMs) that provide skid-mounted process
equipment. Equipment suppliers can purchase scalable,
more economical controls to meet their specific requireWWW.ROCKWELLAUTOMATION.COM/THEJOURNAL
The term high availability encompasses
to productivity, especially reliability and
ments, and be able to offer control technology that easily
integrates into the plant control and information systems.
In general, some form of redundancy is used if a control
system shutdown or loss of visibility would cause a major
loss in data, product or revenue damage equipment; or
create a potential hazard.
Redundancy means the duplication or triplication of
equipment needed to operate without disruption, if and
when the primary equipment fails. Redundant HMI,
servers, networks and controllers that include media are
common ways to achieve high availability.
While most users traditionally have achieved high availability through redundancy, this increases the number of
components, thus increasing the number of potential component failures. Therefore, redundancy — if not applied
properly — can decrease system availability.
To avoid weighing down a system with redundancy
overload, process manufacturers should determine the cost
of potential failures and make high availability investments accordingly. For example, would the loss of control,
view, product or data be most devastating? What about
damage to equipment? Is downtime the biggest concern?
Once priorities are defined, users can invest resources
in redundancy in critical areas to achieve high availability
and best protect assets.
Because most processes are enclosed in pipes and tanks
and spread out over large areas, process manufacturers
rely on vision systems and instrumentation to monitor the
processes and systems at work. In an oil and gas refining
process, for example, instrumentation is the only way to
see what’s going on within the pipes and tanks.
Therefore, to achieve high availability, redundant networks, redundant instruments, redundant HMI and alarm
management are critical. These process operations also
require redundant processors, networks and some I/O.
Full system redundancy is necessary for critical operations that can’t be stopped without damaging equipment
or creating a dangerous hazard. For example, an offshore,
unmanned oil platform could lose millions of dollars per
hour if production is halted or tens of millions of dollars if
equipment is destroyed.
In pharmaceutical production, a reactor may contain
hundreds of thousands of dollars worth of product, so
integrity of the product must be maintained. In addition,
FDA and other regulations require constant tracking and
recording of the ingredients and process so redundant
controllers, networks and servers may be critical.
For a food and beverage process operations, FDA regulations require tracking and tracing, so high availability is
required for data and information. To keep track of data,
redundant networks and servers are required. However,
since much of the operations are batch and continuous
control less critical, only certain equipment may require
redundancy of the control system.
>> Rockwell Automation Partners Support Process Safety
For fault-tolerant solutions that help extend the continuity of your control systems, consider the Rockwell
Automation-compatible products from these participating Rockwell Automation EncompassTM Product Partners.
Marathon Technologies
www.rockwellautomation.com/go/p-marathon
Fault tolerant software for Microsoft Windows applications
Moore Industries-International Inc.
www.rockwellautomation.com/go/p-moore
Fault tolerant Foundation Fieldbus connectivity system
NEC Corp. of America
www.rockwellautomation.com/go/p-nec
Fault tolerant servers for Microsoft Windows applications
Phoenix Digital Corp.
www.rockwellautomation.com/go/p-phoenixdigital
Fault tolerant, redundant fiber optic communication
Stratus Technologies
www.rockwellautomation.com/go/p-stratus
Fault tolerant server for Microsoft Windows or Red Hat Linux
operating systems
Ultra Electronics
www.rockwellautomation.com/go/p-ultra_electronics
Fault tolerant, redundant fiber optic communication
18 THE JOURNAL | OCTOBER 2010
WWW.ROCKWELLAUTOMATION.COM/THEJOURNAL
>> New Solutions Make High Availability
Easier, Simpler
all aspects related
maintainability.
Meanwhile, 100% availability may be required for
water wastewater treatment operations because of regulations, and because people depend on water for survival.
In addition to redundancy, process manufacturers can use
design techniques — including for the controller, HMI and
information system — to help achieve high availability, where
redundancy is less critical. In this case, the designer must be
willing to accept the fact that anything can fail, and design the
facility around this notion. This often has been referred to as
modular distributed design, and involves the following areas:
• Distributed control architectures.
• Distributed control design with independent line,
zones, etc.
• Distributed HMI.
• Distributed databases.
For example, in continuous and batch processing operations, following the S88 model helps achieve availability
by allowing recipes and procedures to be ported to various
equipment, lines and plants. Human interface into a process or operation is crucial and, in many cases, a requirement that often is achieved using hardwired indicator
lights and manual controls.
Designing in diversity is another typical method. This
might mean using diverse HMI devices in conjunction
with local indicator lights. Client server configurations
with multiple clients linked with redundant servers provide yet another method.
Technology Driving High Availability
Emerging technologies are coming together to form comprehensive solutions for process manufacturers interested in
achieving high availability — whether they meet that goal
through design, redundancy or other means.
For example, redundant communication interfaces are
becoming available for a variety of network protocols, increasing connectivity down to the field device, and helping
with predictive maintenance and other factors related to
asset management.
Distributed and more available communications can be
accomplished with redundant ControlNet or with a Device
Level Ring EtherNet/IP configuration. Options also exist for
fault tolerance in field device networks, thanks to solutions,
like intelligent junction boxes, that allow continued field
indication or commands with up to two faults in the field.
Rockwell Automation continues to expand its Allen-Bradley ®
PlantPAxTM Process Automation System to help manufacturers
meet high availability demands more easily and cost-effectively.
The expansion includes:
• Allen-Bradley L7x programmable automation controllers and
19.50 firmware: The L7x controllers offer significant improvements in performance and provide faster cross-loading for
redundancy systems.
• 1715 redundant I/O: 1715 fault-tolerant I/O provides SIL
2-rated redundant input and output modules including
analog outputs configured by Rockwell Software® RSLogixTM
5000 software and supporting redundant Ethernet adapters
all with no additional programming required.
• FactoryTalk® Supervisory Edition View 6.0: FactoryTalk View
SE 6.0 supports alarm and event server redundancy for
auto-synchronization of device-based and tag-based alarms
between active and standby servers and a single alarm history configuration.
• EtherNet/IP I/O: DLR, Star and other EtherNet/IP topologies
provide scalable resiliency to meet all network availability,
cost and performance requirements.
Rockwell Automation offers a complete end-to-end high availability solution that helps protect production and product
quality, critical equipment and plant assets, plant personnel, the
environment and surrounding community.
For more information, visit www.rockwellautomation.com/go/prps.
ing, the need is growing for networks to capture more
data, perform additional diagnostics, access all instrumentation and other process device information remotely and
leverage the data across the manufacturing enterprise to
ensure high availability.
With the Device Level Ring topology, the EtherNet/
IP network can be set up without the need for additional
switches and the wiring is daisy-chained from node to
node. This helps to reduce time and costs compared to the
wiring in a star topology.
This means tomorrow’s process plants can tap into
well-established, robust automation networks — making
it easier to connect field instrumentation with the rest of
the enterprise.
Maximizing Availability
System interruptions and losses can threaten the productivity and performance for process manufacturers. With
this in mind, process engineers can leverage emerging
technologies to increase system availability and, in so doing, mitigate potential hazards and risks that could harm
people, machinery or profits.
The Role of EtherNet/IP
Rockwell Automation Process Solutions
As business drivers and regulations become more demand-
www.rockwellautomation.com/go/tj10pr
WWW.ROCKWELLAUTOMATION.COM/THEJOURNAL
OCTOBER 2010 | THE JOURNAL 19