VirtualMarshalling
Marshalling With FOUNDATION™ Fieldbus Technology
The key advantages of software-based distributed I/O connectivity
With increasing implementa on of digital
control technologies across the processindustries, as well as the growth of industrial
wireless and network protocols, the successof the F
Fieldbus open automa on
infrastructure is some mes taken for granted.
The global marketplace is s ll experiencing
double-digit growth in the sales of products
and services related to F
Fieldbus.
The technology remains a preferred choice forboth new construc on and plant retrofitprojects.
Perhaps now is a good me to revisit thekey performance advantages that have madeF
Fieldbus technology the leader indigital process fieldbus communica ons.
FFieldbus is a real- me digitalcommunica on network designed specificallyfor process control applica ons. It replaces
analog 4-20 mA and on/oﬀ signals forconnec ng instruments like transmi ers,analyzers, control valve posi oners, and on/oﬀ valves to distributed control systems(DCS), programmable logic controllers (PLC),
remote terminal units (RTU), and otherautoma on systems.
As demonstrated at plants around theworld, the benefits of completely digital

automa on without the limita ons of 4-20
mA and on/oﬀ signals are enormous.
F
Fieldbus technology takes
automa on to the next level by making
control loops en rely digital from end-to-end— from transmi er to posi oner — without
intermediate analog signals, and bycommunica ng mul ple signals frommul ple devices on the same pairs of wires. It
also enables new, more powerful devices,
includingintelligent two-wire on/oﬀ devices withpredic ve diagnos cs.
FFieldbus H1 technology
provides an all-digital solu on from thesensor to actuator, completely elimina ng theneed for analog 4-20 mA signals andsignificantly reducing the overall amount ofequipment needed. It also takes the place of
proprietary protocols previously used withelectric actuators/motor-operated valves(MOV), gas chromatographs, and tank gauging
systems. Communica on is me-synchronized
and scheduled to ensure determinis c
closed-loop digital control. Mul ple devices,each with mul ple I/O signals, share the samebus.
FFieldbus supports long cable

lengths to junc on boxes far into the field, as
well as long spurs for devices. Fieldbus-based
control systems employ two-wire twisted paircable and provide intrinsically safe or
non-incendive device power suitable for all
hazardous areas. Unrestricted access tofield device intelligence enables centralized
configura on/setup and diagnos cs for all
field instruments, including discrete sensors
and actuators. This solu on also supports
temporary masters such as handheld fieldcommunicators, laptops/tablets, anddocumen ng calibrators.
Unlike other digital architectures,
FFieldbus was designed from theground up to enable control-in-the-field (CIF)
strategies across the plant.
FFieldbus started with a few
simple ideas:• Reduce cabling• Simplify marshalling• Enable real- me digital closed-loopcontrol• Ensure mul -vendor interoperability• Expand device intelligence• Allow diagnos cs-based maintenance• Liberate plants from proprietary protocols
Reduced Hardware Requirements:
Lower overall capital expenses
Today, some automa on projects areadop ng various alterna ves to tradi onal I/O
and marshalling technology. But why makephysical marshalling smarter or be er when
you can eliminate iten rely? Many of the func ons provided byhardware in a conven onal control system are
no longer required by a F
Fieldbus
system, or are handled through so wareinstead.
F
Fieldbus technology wasdeveloped from the ground up as a way toeliminate tradi onal marshalling all together
through VirtualMarshalling connec vitysolu ons. In other words, VirtualMarshalling
enables so ware-based distributed I/Oconnec vity in which devices provide
mul ple signals over the same twoterminals. Instead of relying on custom
hardware configura ons to accomplish thefunc ons of tradi onal marshalling,F
Fieldbus accomplishes thesetasks through a so ware-based structure. All
signal linking (block to block) is done inso ware without hardwiring. This approachallows late addi on of feedback andauxiliary measurement and control signals
without the need for addi onal wiring, as
well as change of devices without switching
I/O cards. Burnt shunt resistors are also
eliminated. More devices can be added
without laying more cable.
FFieldbus is par cularly
well-suited for expansions at exis ng sites,
which are running out of tray capacity.
Smaller System Footprint:
Easier design and implementaƟon
Rather than use individual wires for each
Fieldbus connects
device signal, F
mul ple devices in parallel on the same pairof wires recognized by address. A single pair
provides both power and communica on, andcan be intrinsically safe or non-incendive if
required. Long distance is also possible. Field
junc on box hardware is rugged andencapsulated for harsh outdoor field
condi ons, some even passive and op onallyzone 1 cer fied.

FFieldbus technology reduces
the need for cable, cable trays, I/O cards, andassociated labor for installa on, as well as theeﬀort of cu ng, stripping, crimping, labelingand connec ng at every intermediate point.
For example, a bus with 10 instruments — andan average of three signals per device — cantake the place of 30 pairs of wires and I/Ochannels. The resul ng cost is even lower
than remote I/O and local moun ng.
In addi on, F
Fieldbus simplifies
the integra on of devices with mul ple
signals for opera on and feedback. This
includes electric
actuators/MOVs and discrete devices suchas intelligent two-wire intrinsically safe on/oﬀ
valve actuators. In the past, these devices
required one pair of wires and one I/Ochannel for each signal, meaning as many as 3,6, 12 or more pairs per device. In comparison,F
Fieldbus enables a single pair ofwires to support mul ple devices, resul ng indras c wiring reduc on. The reduced numberof I/O cards for auxiliary signals also translates into fewer I/O cabinets, a smaller
footprint, and reduced weight.
Since all device signals can now be
employed at lower cost, plants can fully u lize
device capabili es without being limited to a
subset of signals and func onality. Con nuous

feedback and bumpless transfer (a feature in
virtually all PID
controllers preven ng a sudden jump in
output when the controller’s mode isswitched from manual to auto) on handopera on also becomes available for allvalves.
Thanks to FFieldbus
technology, transmi ers, control valves, andtwo-wire on/oﬀ valves are able to share thesame bus. As a result, there is no need to
select I/O card or barrier types, since all
devices use the same single type of interface
card and barrier, and have the same en ty
parameters — simplifying selec on. At designme, it is not necessary to know the exact
type and quan ty of signal for each device todetermine I/O requirements.
Reduced Device Count:
Lower wiring and installaƟon costs
FFieldbus instruments are notlimited to transmi ng single values in realme. Instead, the technology supports
mul -point devices such as mul -channel
temperature transmi ers with eight sensor
inputs, which are ideal for temperature
profiling applica ons, as well as mul -point
indicators. For dual sensor temperaturetransmi ers, both channels can be used forƵƚŽŵĂƟŽŶ^ǇƐƚĞŵ

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control loops.
The fieldbus solu on allows eight-channel
temperature transmi ers to take the place ofmany hardwired transmi ers, thus reducing
the overall device count as well as associatedwiring and I/O card points. These and other
innova ons oﬀering installa on cost benefits
are not possible with hardwired signals.
Open Network Standard:
Fewer protocols and greaterinteroperability
Proprietary protocols were eliminatedyears ago for simple transmi ers and valve
posi oners. Now, F
Fieldbus canalso eliminate these protocols for electric
actuators/MOVs, gas chromatographs andtank gauging systems.
These fieldbus devices integrate withintelligent device management so ware forsetup/configura on and diagnos cs just liketransmi ers and valve posi oners, enabling
predic ve maintenance and doing away withspecial so ware. Devices also share the samebus infrastructure, elimina ng the need forseparate networks, gateways, and drivers.
As an open network standard,
F
Fieldbus eliminates single vendor
dependency, which limits the ability tointerchange or replace exis ng instrumentswith third-party devices. This means diﬀerent
brand equipment can share the same network orserve as second-source replacement devices.
Faster Commissioning:
Reduced labor and associated errors
With F
Fieldbus, me-consuming manual commissioning tasks and theirassociated errors are no longer a concern.
The same is true of 4-20 mA ranging andsignal distor on; tradi onal five-point loop
tests are replaced by a simple plausibility
check. Technicians can automa cally confirm
the correct device type (model and manufacturer) has been installed. This applies to not
only transmi ers and posi oners, but also
discrete devices such as intelligent two-wire
on/oﬀ valves and electric actuators.
High Signal Integrity:
Be er resolu on and increased accuracy
F
Fieldbus’ pure digital signals
eliminate the digital-to-analog (D/A) andanalog-to-digital (A/D) conversion required indevices and systems u lizing 4-20 mA
technology. Fewer conversions lead to higher
resolu on and accuracy. Errors due to current
calibra on diﬀerences between transmi er
output and DCS input are also eliminated. Thisis par cularly important in flow and levelapplica ons such as tank gauging, wheresmall percentages correspond to significantrevenue.
Using fieldbus, measurement values transmitted digitally cannot be distorted and integrity

errors are immediately detected. Thiscompares with “on-scale” errors associatedwith 4-20 mA signals, which are o en due toundetected ground loop or current restricon issues. Unlike discrete signals whereopen or short circuits may not be recognized,
bus communica on errors are easily
iden fied.
Greater Signal Fidelity:
Increased awareness of abnormal situa onsF
Fieldbus devices are designed
to transmit measurements as a real number inengineering units (not scaled by range),
which are received — unaltered — by acontrol system at the other end.
Transmi er configura on download fromthe DCS is done as partof the device replacement process, thus
ensuring the units, range, and other se ngs
are correct. This approach eliminates theprocess variable value skew that some mes
results from mismatched 4-20 mA range
se ngs between transmi ers and the control
system. Operators gain confidence that thereading, controls, and alarms in the system
are correct.
With fieldbus, measurement values are alsotransmi ed over the full sensor limit withgreater precision and are not limited to anarrow 4-20 mA por on. As such, they do notsaturate at the normal control range, but go
beyond, providing valuable informa on
during abnormal condi ons.
Tighter Control:
Faster response and less variability
Transmi ers, controllers, and valve posi oners are digital — so it only makes sense tohave pure digital signals between them. A
digital bus running 25 mes faster than earlier
hybrids of analog and digital allows a closed
loop that is digital and me-synchronizedfrom end to end, from sensor to valve.
Fieldbus communica on is determinis c andrealme, oﬀering control response mes fasterthan 150 ms in some cases.
Elimina on of analog input (AI) and analog
output (AO) cards and their associated scandelays and ji er also improves control
response me, par cularly compared toremote I/O with addi onal network and link
delays. Reduc ons in process variability allow
set points to be moved closer to the op mal
point of opera on, with less “comfortmargin.” Improvements for each transmi er
and valve, loop, and process unit contribute tobe er plant performance.
Real- me Signal Status:
Fewer trips and increased availability
F
Fieldbus delivers real- me
signal validity indica ng if the value is goodfor control, uncertain, or bad (fault). The
status is then propagated as part of the samedata structure as the value, elimina ng theneed for separate data mapping. This enables
process problems to be dis nguished fromdevice problems, thereby minimizing
nuisance trips of the control loop on sensorfailure and increasing availability. The valve
status includes limit condi ons for override
windup protec on, fault state, bumplesstransfer and more — further improving control.
More Powerful Devices:
New and robust instrument func onality
The electronics in F

Fieldbus

two-wire devices are not restricted toopera on on 4-20 mA. The result: buspowered instruments are able to consume
more power, enabling new and more powerfulfunc onality.
Examples of such devices include two-wireradar level transmi ers with frequency
modulated con nuous wave modula on,
two-wire eight-channel process temperaturetransmi ers, two-wire tank gauging
mul -spot temperature transmi ers withwater bo om level measurement, two-wire
intelligent on/oﬀ valves, and two-wire fieldindicators.
Powerful func on blocks in fieldbus
instruments provide computa on andarithme c whenever there is a need to
calculate or compensate a value in the device
so that it may be shown on a local display.
Enhanced Diagnos cs: Improved
opera ons and maintenance programs
The digital nature of F
Fieldbus
supports centralized device configura on/setup, diagnos cs, and viewing of internalvariables. The technology also allows
two-wire devices to drive more powerfulelectronics and firmware, ensuring moresophis cated self-diagnos cs. This includes
sta s cal process monitoring (SPM) for
mul ple variables across the bus andcon nuous valve performance diagnos cs notfound in 4-20 mA devices.
Faster communica on also means
diagnos cs and configura on/setup pages
load faster.
Predic ve diagnos cs with fieldbus isavailable from two-wire intrinsically safe
intelligent on/oﬀ valves and other discrete
devices not digitally integrated in the past. In
addi on, the technology employs NAMUR
NE107-compliant device alarm ra onaliza on
to no fy the right person without alarm
flooding.
Simple Online Upgrades:
Easier access to new technology
F
Fieldbus instruments not only
communicate faster than older hybrid analog/
digital devices, but they also have the speed
necessary to allow firmware download fromthe system. Devices with dual memory banks
switch bumplessly to new firmware.

The FF
solution employs NAMUR NE107-compliant device
alarm rationalization to notify the right person without alarm flooding.

FieldComm Group™ and FOUNDATION™ Fieldbus are trademarks of FieldComm Group.
Copyright©2015 FieldComm Group. All rights reserved.

Modern fieldbus devices are easily
upgraded to take advantage of features andother improvements in new versions. These
upgrades can be performed without going
into the field to replace the en re circuitboard or connect a laptop.
Greater Ease of Use:
Proven solu ons for projects of all sizes
FFieldbus technology is
con nuously improving based on feedback
from our strong end user advisory council.
The F
Fieldbus specifica on now
includes NAMUR NE107-compliant role-based
and priori zed device diagnos c alarms;
backwards compa bility and easy device
replacement; and graphically enhanced,
device-level electronic device descrip on
language (EDDL) user interface and wizards.
Constantly improved device interoperability
tes ng kits (ITK) and host profile registra on
processes ensure that new devices andsystems meet our specifica ons.