signals a change at plants

signals a change at plants
Watch out with
variable speed pumping
Avoid costly
fabrication mistakes
Hot cutover boosts
control system migration
Cast a cold eye
on columns
WirelessHART
M ay 2 0 0 8
signals a change at plants
271402.indd 14
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Wireless
WirelessHART
signals a change at plants
W
ireless technology is so much a part of our lives that
we use words like Blue-tooth and WiFi systems with
confidence and familiarity. So why has it taken so
long for the chemical industry to take advantage of the benefits
a wireless network can offer?
Some things that we can tolerate as consumers — such
as signal loss when driving through a tunnel or occasional
interference from other wireless networks — are unacceptable
at plants. The chemical industry requires reliable and secure
transmission of information via a technique that’s easy to set
up and flexible enough to adapt to changing conditions. WiFi,
Bluetooth and others simply don’t meet these basic requirements.
The result is that wireless networking has found a few specialized
applications at plants but hasn’t been widely deployed.
The wireless instruments available to date are either proprietary
or early pilot developments that only can exist within a single
vendor network. However, an open approach is emerging.
In September 2007, the Hart Communication Foundation
(HCF), Austin, Texas, released its latest specification, HART
7, which included wireless connectivity. HART 7 provides the
chemical industry with a wireless network that can support
instruments from multiple vendors in an industrial environment.
This WirelessHART specification was demonstrated at last
year’s ISA show in Houston, where a multi-vendor network of
instruments worked together within the same wireless network
connection to asset management applications running on
computer workstations (Figure 1).
271402.indd 15
HART 7 gives plants a real incentive to consider wireless.
So, we’ll examine the advantages and typical applications of
a wireless instrument network, whether now is the right time
to consider a wireless project, and how a WirelessHART
instrument network works.
The advantages
Traditional 4–20-mA field instruments have been using the extremely
successful HART protocol to assist during commissioning and
scheduled maintenance work; in fact, more than 24 million such
instruments have been installed to date. However, some 20 years
since HART 5 became available we’re still not making the best
use of the remote access HART offers — instrument information
remains locked away for the vast majority of users. WirelessHART
can provide the key to unlock this information and allow us to
install instruments at a very much lower cost.
Retrieving stranded instrument and process information.
The vast majority of 4–20-mA instruments installed have no
mechanism to allow remote access to the information they
hold. If you wish to retrofit a communications path back to
an asset management system, then you typically would need to
break into the field wiring to insert a HART multiplexer. This
poses some risk and cost. The use of a WirelessHART plug-in
instrument adapter (Figure 2) offers a more convenient, lower
risk and lower cost alternative.
Reducing installation and planning costs. The need to run
cabling around a plant makes installation and commissioning
7/11/08 4:26:50 PM
>>
Successful demonstration
Figure 1. At last year’s ISA show WirelessHART effectively linked instruments from
multiple vendors.
costly for traditional 4–20-mA analog and fieldbus (Foundation
Fieldbus H1 and Profibus PA) networks. When you consider
routing the cable, mounting cable trays, cutting holes and
tunnelling, and generating the work permits, expenses can run
to $5,000 per point. Wireless networks clearly can reduce these
costs as there are no (or fewer) cables to run with instruments
often being self-powered.
During the planning phase for traditional wired instrument
loops, it’s common to add up to 20% spare capacity to account
for future plant modifications because wired systems are
expensive to modify and expand later. However, frequently
much of this spare capacity isn’t actually used five or 10
years down the line. A wireless network offers a very scalable
solution that can reduce the need for building in and paying for
such spare capacity at the onset.
The intrinsic low-cost nature of wireless technology now
allows you to tackle some of those process problems that only
can be solved by measuring new process data or by monitoring
device condition.
Target applications
The chemical industry historically has been cautious in adopting
new technologies. Hopefully WirelessHART will jump-start the
use of wireless instrument networks at plants. End-user surveys
provide a good guide to likely wireless applications.
Upgrading existing instruments. Adding WirelessHART
to an existing HART instrument in the field is very simple.
Connect the adapter to the instrument at either a spare cable
gland or even at a junction box. (The adapter could be selfpowered or powered via the loop.) Add the network ID and
password to the adapter and it will automatically join the
existing WirelessHART mesh network. The original 4-20-mA
271402.indd 16
>>
Instrument adapter
Figure 2. A plug-in adapter can provide a simple, low cost way to get information from
instruments.
signal remains intact and you now have remote access to the
instrument information. This permits:
• Calibration check and over-range reading. For a pressure
transmitter you can monitor the instrument process
value and compare it to the 4–20-mA value. This can
help confirm the instrument calibration status or provide
a value when the 4–20-mA signal is out of range. (The
WirelessHART value doesn’t depend upon the 4–20-mA
value — it comes straight from the digital value.)
• Valve condition monitoring. For a positioner you now
have access not only to valve position feedback but also
to other data to help analyze the valve’s condition.
• Advanced diagnostics. You have remote access to
instrument information such as asset signatures, level
echo trace and other advanced diagnostics.
• Full use of complex multivariable instruments. For
multivariable instruments (mass flow, for example), you
now can read the process values previously hidden away.
Coping with aging infrastructure. The maintenance and
support of aging plant often can be a problem, especially when new
measurements are required and the spare capacity within cable
runs and its condition are unclear. A WirelessHART solution can
overcome many of these issues because a wired infrastructure isn’t
required and the mesh network overcomes many of the problems
of point-to-point wireless topologies. Some examples:
• Replacing local gauge indicators. A wireless instrument can
provide a low cost way to report process information back
to the control room, reducing operator rounds to read local
indicators and improving visibility of the process.
• Supplanting obsolete field instruments. Installing wireless
instruments can obviate difficulties in keeping old
instruments working as spares become harder to find. Self-
7/11/08 4:26:55 PM
powered or loop-powered, the wireless network provides
an information pathway without other major changes to
wiring or control system hardware.
Short-term monitoring. The low cost nature of wireless
technology allows you to consider temporary measurements
to help diagnose process problems. This could be as simple as
using a strap-on temperature transmitter or replacing a local
pressure gauge with a new pressure transmitter.
To get a sense of how wireless can change the way you
troubleshoot, consider the following issues raised at a refinery
operations morning meeting:
Operator A: “We have a problem in the PP splitter column
(Figure 3). I just don’t have enough information to isolate and
diagnose the problem. What I really need is a new pressure
measurement at the top of the column.”
Traditionally, the engineer responsible for the unit might reply:
“I’ll call a meeting with Instruments and Electrical. We might
have some spare cable pairs and trays up there, but we probably
don’t. We’ll have to call in the construction subcontractors. I’ll
look into it and get back to you later in the week.”
Instead, with WirelessHART, the engineer might say:
“No problem. We have a wireless pressure transmitter. We’ll
stick the transmitter on the piping vent up there and have it
running by lunch time. Just give me the tag and how often you
want the data updated.”
Operator B: “We seem to have more fouling in the pre-heat
exchangers again and I’m not sure which ones to clean. We’re
measuring a few of the temperatures, and there’re even some
spare thermowells, but there aren’t any real data to help me
with this problem.”
Here, the conventional response might be:
“I’ll call a meeting. We’re going to need some new cable
trays in there as we used the last of the spare cable pairs during
>>
Troublesome splitter
Why uSe WIreleSShArT?
Besides providing an open solution for an instrument wireless network, it:
• Builds upon the existing HART specification used by more than 24 million
installed instruments;
• Unlocks information stranded inside existing 4–20-mA intelligent field
instruments by adding a WirelessHART adapter;
• Uses existing software tools to configure and maintain instruments;
• Offers simple and low cost installation, reducing cabling and
hookup expenses;
• Allows measuring of points that were uneconomical to get at in the
past; and
• Features a self-building and self-healing mesh network.
the ‘little learning event’ we had last year. We can probably
find a few spare slots in the input modules but they’ll be spread
out a bit. I don’t like these spaghetti solutions, though, because
they make for trouble later on.”
With WirelessHART, the engineer might instead say:
“I’ve got seven wireless temperature instruments and
thermocouples in stock. I could even borrow some more from
another unit for a few days. They’re all WirelessHART, so
there’s no problem with compatibility. We just need the mobile
platform for access and a list of which ones to fit first. If you
want, I can leave some up there permanently. Let me know
when I can have the ones you don’t need back.”
Closed loop control? One of the clear messages from
customers is that they won’t consider closed loop control using
wireless for at least five years — they want to get experience
with the technology first. While it’s possible to transmit process
data from a measuring device over the mesh to a positioner/
valve, this requires care in setting up the network topology to
reduce time delays. Plus, the positioner would be constantly
modulating the valve and would need significant power, thus
perhaps ruling out a self/battery-power option. Given that the
measuring instrument typically isn’t far away, a local controller
using wired connection to the instrument and positioner
would be a good solution when coupled with instrument
WirelessHART connectivity back to the host.
Meshing efforts
Figure 3. Wireless pressure transmitter offers a quick and simple way to get necessary data.
271402.indd 17
Early adopters of wireless instrument networks have been
using either proprietary solutions (e.g., for tank level or safety
shower operation) or running early pilots of WirelessHART.
The proprietary networks often relied on a star configuration
with single line-of-sight connection to a wireless hub/gateway.
Process plants have steel vessels, exchangers, piping,
structural steel work, reinforced concrete, etc. So, it’s tough to
set up a star wireless network with clear lines of sight from the
gateway to each instrument. Then, what happens in the future
as the plant is modified and maintained with scaffolding being
erected near the wireless network?
7/11/08 4:26:57 PM
>>
Mesh network
>>
New features
Time/condition-based reporting
PV trending
Security
Mesh and star
HART 7
HART 6
All PV with status
Long tags
Process monitoring
Diagnostics
Configuration
Remote access
HART 5
4–20-mA loop
Wireless
Figure 4. Self-building and self-healing mesh adapts to plant changes, even temporary ones for maintenance.
A self-healing mesh network with redundant pathways that
can adapt to changing plant environments avoids such issues
(Figure 4). ABB and other vendors have tested such mesh
networks within plants and observed the mesh adapting to
the changing environment and effectively coping with other
interference sources.
As often is the case with emerging technology, other groups —
here, ISA (via the SP100 Committee) and Foundation Fieldbus
and Profibus — have similar efforts underway. This does seem
to send a confusing message to end users who are looking for
a single standard. (Incidentally, instrument vendors also would
like a single standard and development path.) However, these
groups have made huge strides in working together to allow us
to obtain a successful wireless instrument network.
HART 7 and ISA. HCF has provided the WirelessHART
specification to SP100 — a joint analysis team has already
identified a pathway forward to use WirelessHART at the
instrument level. Don’t forget that ISA SP100 is a family
of protocols; WirelessHART would fit in very well at the
instrument level.
HART 7 and Fieldbus. The Wireless Cooperation Team
(WCT) is working towards a topology where WirelessHART
can be used at the instrument level with Foundation Fieldbus
or Profibus as the backbone to the host system. The WCT meets
regularly and includes experts from all three protocols.
With such cooperative efforts progressing and end-user
pilots complete, there’s no reason to wait much longer to
consider a WirelessHART project.
Evolution not revolution
The HART 7 specification has built upon the existing HART
specification by adding wireless connectivity and other features to
271402.indd 18
Figure 5. The HART 7 specification adds wireless connectivity and other features.
ensure reliability, security and simplicity of operation (Figure 5).
So, yes, we can employ existing software tools including HART
hand-held configurators; yes, the network is self-building and
self-healing; and, yes, existing instruments can be used via a WirelessHART adapter.
The WirelessHART topology. Every WirelessHART network
has three main elements:
1. A gateway: It connects the control system (via Ethernet,
Profibus, etc.) to the wireless network;
2. A network manager: This normally is part of the gateway
and automatically builds the wireless network and
manages its operation; and
3. Field instruments and devices: These usually consist of
pressure, temperature, position or other instruments but
also can include adapters.
WirelessHART is an instrument level network using
existing and new HART commands to access information. The
instrument network connects to a WirelessHART gateway that
builds the mesh topology and also connects to the host system
via standard high-speed backbones such as Ethernet.
How often is the information updated? The rate at which
process information is transmitted over a wireless network
directly impacts battery life for those instruments using battery
power. WirelessHART offers several mechanisms to maximize
battery life and use of the network capacity:
• Transmit measurements at different rates for different
instruments — for instance, level every 20 or 30 seconds,
and flow every 1 or 2 seconds;
• Send when data change — deliver alarm or alert messages
only when they are triggered (time stamp within the
instrument); and
• Change measurement rates based upon alarm limits —
7/11/08 4:26:58 PM
i.e., increase the rate when a value approaches a set limit.
Building a WirelessHART network. Once the gateway is
commissioned (connected to the host and asset management
system), you’re ready to build the WirelessHART network.
It’s really a very simple procedure that involves entering three
variables into the wireless instrument. This is one example of a
commissioning procedure:
• Obtain the wireless network name/identity (which would
be a value set in the gateway);
• Connect the instrument to the process;
• Power up the instrument (which could be externally or
battery powered); and
• Attach a HART hand-held configurator to the maintenance
port (terminals within the instrument that look like 4–20mA connectors). Follow the menu on the hand-held and
enter the following:
1. The network name/ID;
2. The instrument refresh rate (i.e., how often the PV
is updated); and
3. The network join password.
Monitor the instrument as it automatically synchronizes to the
network, is authenticated, and successfully joins the network.
The gateway automatically optimizes the mesh network
and redundant pathways. It continues to monitor the mesh
and adapts it as new devices join or the radio environment
changes. This self-building and self-healing feature provides
the reliability of data communications industry requires.
How are the issues of security addressed? Security at
chemical plants is a huge topic in its own right (see, e.g.,
www.ChemicalProcessing.com/articles/2008/046.html,
www.ChemicalProcessing.com/articles/2007/152.html and
www.ChemicalProcessing.com/articles/2007/095.html).
Wireless HART makes security of data transmitted a key
part of its core technology. For WirelessHART, security is
always switched on. Built-in features address the issues of
data security and outside interference. Some of the security
methods used include:
• Keeping data transmission bursts short (10-msec time
slots) (Figure 6). This makes it hard to synchronize and
read messages.
• Authenticating devices as they try to join the network (join
key, device key) and monitoring attempted joins. This will
help to stop unauthorized devices joining the network.
• Encrypting each message. WirelessHART also allows
the user to rotate encryption keys to make it difficult to
identify the keys and decode messages.
>>
Data security
Frame
Timeslot
Used Timeslot
Figure 6. Use of short and varying-interval time slots for sending data enhances security.
• Authenticating that the data haven’t been altered as they
pass through the mesh network.
• Changing the transmitted channel after each message is
sent, making it hard to snoop at data.
• Requiring a physical connection to the instrument (via a
HART hand-held) for the instrument join procedure.
Time to act
Vendor testing and end user trials have shown that WirelessHART
provides the reliability, security and simplicity that the chemical
industry demands from a wireless network. You can take advantage
of the technology today to improve your vision of the process and to
unlock valuable information hidden within existing instruments.
It’s clear that WirelessHART will complement not displace
4–20-mA loops. We’ve cited some applications, such as shortterm diagnostic measurements, condition checking via adapters
and instrument replacement, worth considering.
The WirelessHART specification is available now. Many
significant instrument vendors (e.g., ABB, Emerson, Siemens and
Yokogawa) are at an advanced stage of product development.
Indeed, WirelessHART instruments and devices will start to
reach the market in the middle of 2008 and the selection will
widen during 2009.
Don’t wait. An open solution for an instrument wireless
network is here. Find a local seminar to build you knowledge
and identify the benefits a WirelessHART solution can provide
for your process. CP
Gareth Johnston is wireless product manager for ABB, St. Neots, U.K. Alan
Munns is product manager, refinery solutions, for ABB, St. Neots, U.K. E-mail
them at [email protected] and [email protected]
Reprinted with permission from Chemical Processing, May 2008. On the Web at www.chemicalprocessing.com.
© PUTMAN. All Rights Reserved. FosteReprints: 866-879-9144, www.marketingreprints.com.
In US contact:
ABB Instrumentation USA
1-800-829-6001 Extension 5
[email protected]
www.abb.com/instrumentation
271402.indd 19
7/11/08 4:27:00 PM
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