Rockwell Automation 1757-FFLD User Manual
RSFieldbus and the
1757-FFLD Linking
Device
1757-FFLD
Programming Manual
Important User Information
Solid state equipment has operational characteristics differing from those of
electromechanical equipment. Safety Guidelines for the Application, Installation and
Maintenance of Solid State Controls (Publication SGI-1.1 available from your local
Rockwell Automation sales office or online at
http://www.rockwellautomation.com/literature) describes some important
differences between solid state equipment and hard-wired electromechanical devices.
Because of this difference, and also because of the wide variety of uses for solid state
equipment, all persons responsible for applying this equipment must satisfy
themselves that each intended application of this equipment is acceptable.
In no event will Rockwell Automation, Inc. be responsible or liable for indirect or
consequential damages resulting from the use or application of this equipment.
The examples and diagrams in this manual are included solely for illustrative purposes.
Because of the many variables and requirements associated with any particular
installation, Rockwell Automation, Inc. cannot assume responsibility or liability for
actual use based on the examples and diagrams.
No patent liability is assumed by Rockwell Automation, Inc. with respect to use of
information, circuits, equipment, or software described in this manual.
Reproduction of the contents of this manual, in whole or in part, without written
permission of Rockwell Automation, Inc., is prohibited.
Throughout this manual, when necessary, we use notes to make you aware of safety
considerations.
WARNING
IMPORTANT
ATTENTION
SHOCK HAZARD
BURN HAZARD
Identifies information about practices or circumstances that can
cause an explosion in a hazardous environment, which may lead
to personal injury or death, property damage, or economic loss.
Identifies information that is critical for successful application
and understanding of the product.
Identifies information about practices or circumstances that can
lead to personal injury or death, property damage, or economic
loss. Attentions help you identify a hazard, avoid a hazard, and
recognize the consequence
Labels may be located on or inside the equipment (for example,
drive or motor) to alert people that dangerous voltage may be
present.
Labels may be located on or inside the equipment (for example,
drive or motor) to alert people that surfaces may be dangerous
temperatures.
Preface
This programmig manual describes how to use the 1757-FFLD linking device
along with RSFieldbus in applications with the F
network. This document provides technical, network setup and configuration
information with guidelines on application function block use. In addition, this
manual offers references to third party device configuration guidelines for the
Foundation Fieldbus and the linking device. For more information about using
Rockwell Automation products with F
OUNDATION Fieldbus, see Fieldbus
Solutions for Rockwell Automation’s Integrated Architecture, publication
1757-UM006.
RSFieldbus is for use with Microsoft Windows 2000 or XP Professional. This
manual assumes that you are already familiar with navigating and running
applications in a Microsoft Windows 2000 or XP Professional environment.
OUNDATION Fieldbus
Conventions Used in This Manual
Convention Meaning Example
click Click left mouse button once. (Assumes cursor is
positioned on object or selection.)
double-click Click left mouse button twice in quick succession.
(Assumes cursor is positioned on object or selection.)
right-click Click right mouse button once. (Assumes cursor is
positioned on object or selection.)
drag and drop Click and hold the left mouse button on an object, move
the cursor to where you want to move the object, and
release the mouse button.
select Click to highlight a menu item or list choice. Select H1-1 from the drop-down list.
check/uncheck Click to activate/deactivate a checkbox. Check the Do not show this dialog again
⇒
expand Click the + to the left of a given item /folder to show its
Shows nested menu selections as menu name followed
by menu selection.
contents.
This manual uses the following conventions:
Click Browse.
Double-click the H1 icon.
Right-click the Fieldbus Networks icon.
Drag and drop the desired block into the
Strategy window.
checkbox.
Click File ⇒ Page Setup ⇒ Options.
In the H1-1 window, expand the FFLD.
<Enter> Keys to be pressed are shown in angle brackets. Press <Enter>.
>PID Example< Data to be typed at a prompt or in an entry field. Enter >PID Example< for the name.
3 Publication 1757-PM002A-EN-E - June 2006
Preface 4
Related Documentation
For information on the Rockwell Software products found in this manual,
refer to the following publications:
• RSFieldbus Installation Guide, publication RSFBUS-IN001
• RSFieldbus User Manual, publication RSFBUS-UM001
• RSView Supervisory Edition User’s Guide, publication
VIEWSE-UM003C
These FOUNDATION Fieldbus Specification documents contain information
that you may find helpful as you read this manual:
• System Architecture, publication FF-800
• Technical Overview, publication FD-043
• Application Guide 31.25 kbit/s Wiring and Installation, publication
AG-140
• System Engineering Guidelines, publication AG-181
These documents can be purchased from the Fieldbus Foundation as part of
the H1 Communications and User Layer Technical Specification.
For more information go to
http://www.fieldbus.org/ProductsAndServices/FFProductCatalog/
and look under Final Specifications.
Publication 1757-PM002A-EN-E - June 2006
System Requirements
Chapter
1
In This Chapter
Purpose of this Chapter
Foundation Fieldbus Description
For See Page
Purpose of this Chapter 1-1
Foundation Fieldbus Description 1-2
Hardware Requirements 1-4
Software Requirements 1-12
Additional Resources 1-12
This chapter describes the components of a typical fieldbus system, including
the Rockwell Automation Linking Device, 1757-FFLD.
Refer to the Glossary for further explanation of fieldbus terms and concepts.
If you already have a basic understanding of fieldbus concepts, skip to Chapter
2,
Setting Up A System, or if you want to start using RSFieldbus for
applications immediately, skip to Chapter 4, Applications.
The term fieldbus refers to an all-digital, two-way communication system that
connects control systems to instrumentation.
The Fieldbus Foundation is an organization that developed a fieldbus network
standard based on the work and principles of the ISA and IEC. The goal of the
Fieldbus Foundation is to provide multi-vendor interoperable process control
using a single robust industrial network based on standards and other proven
technologies.
FOUNDATION Fieldbus, the communications network created by the Fieldbus
Foundation, is a protocol designed for robust, distributed control of process
control applications. Devices that you connect within a F
Fieldbus network are used for sophisticated, highly distributed Process
Control. F
integrated into Rockwell Automation’s Integrated Architecture through the
linking device.
1 Publication 1757-PM002A-EN-E - June 2006
OUNDATION Fieldbus is an enabling technology that has been
OUNDATION
1-2 System Requirements
Hardware Requirements
To build a simple fieldbus system, you need:
• Power supply
• Power conditioner
• Fieldbus cable
• Field devices
• Connector blocks
• Ter minal blocks
• Ter minators
• 1757- FFLD linking device
• Personal computer
Power Supply
The following power supplies are available according to the referenced
Fieldbus Foundation Physical Layer Profile Specification:
Type 131 Non-I.S. Power supply intended for feeding and I.S. barrier. Output
voltage depends on barrier rating.
Type 132 Non-I.S. Power supply not intended for feeding and I.S. barrier.
Output voltage is 32 VDC Max.
Type 133 I.S. Power supply; complies with recommended I.S.
parameters
You can configure power supplies to provide dual redundancy as long as they
meet the IEC/ISA Physical Layer Standards requirements. It is not acceptable
for example, to merely parallel two power supplies.
A typical power supply for a small network is a SOLA SDN 5-24-100. 5A, 24
VDC output, 110 AC input. For more specifications on power supplies, see the
Power Considerations section on page 2-2.
Power Conditioner
Publication 1757-PM002A-EN-E - June 2006
A power supply impedance matching network is required for Fieldbus use.
This is referred to as a power conditioner. A power conditioner is a
System Requirements 1-3
resistive/inductive network that is either external or built into the fieldbus
power supply.
Fieldbus Cable
The preferred fieldbus cable is specified in the IEC/ISA Physical Layer
Standard, Clause 22.7.2 for conformance testing. It is referred to as type “A”
fieldbus cable. This cable will probably be used in new installations.
Other types of cable can also be used. The alternate preferred fieldbus cable is
a multiple, twisted pair cable with an overall shield. It is referred to as Type
“B” cable. Less preferable types of cable include single or multiple twisted pair
cable without any shield, referred to as Type “C” cable, and multiple conductor
cable without twisted pairs, but with overall shield, referred to as Type “D”
cable.
The following table contains the types of cable identified by the IEC/ISA
Physical Layer Standard and their maximum length values. For information
about spur wire length, see the
page 2-9.
Spur Wire Length Calculations section on
Ty pe Cable Description Size Maximum Length
Type A Shielded, twisted
pair
Type B Multi-twisted pair
with shield
Type C Multi-twisted pair
without shield
Type D Multi-core, without
twisted pairs and
having an overall
shield
#22 AWG
(.8 mm2)
#22 AWG
(.32 mm2)
#26 AWG
(.13 mm2)
#16 AWG
(1.25 mm2)
1900 m
(6232 ft.)
1200 m
(3936 ft.)
400 m
(1312 ft.)
200 m
(656 ft.)
Devices
Fieldbus links smart field devices with automation systems. The devices
generally used in fieldbus networks are type 113 (bus powered) or type 114
(separate power). Examples of these devices are the Rosemount 3051S
pressure Transmitter and the Micro Motion 2700 Flowmeter.
Publication 1757-PM002A-EN-E - June 2006
1-4 System Requirements
Connector Blocks
Connector blocks are optional coupling devices. They can be used to connect
wire to a fieldbus device, or to another section of wire (e.g. at a junction block).
Connector blocks are useful for installations where devices may be periodically
disconnected or moved.
Standard fieldbus connectors are specified in Annex B of the ISA Physical
Layer Standard and Annex A of the IEC Physical Layer Standard.
1757-FFLD Linking Device
The 1757-FFLD, also referred to as the linking device, bridges both
F
OUNDATION Fieldbus™ HSE and Ethernet/IP networks to FOUNDATION
fieldbus H1 device networks. Bridging these networks facilitates information
flow between a Logix system’s control layers.
Terminal Blocks
Terminal blocks typically provide multiple bus connections, so a device can be
wired to any set of bus terminals. They can be the same terminal blocks as
used for 4-20 mA.
Terminators
A terminator is an impedance matching module used at or near each end of a
transmission line. Terminators prevent distortion and signal loss, and are
typically purchased and installed as preassembled, sealed modules. Each
terminator has a value of 50 ohms.
ATTENTION
A trunk is the longest cable path between any two devices on the network. All
connections to the trunk are called spurs. Place the terminators at the ends of
You can use a maximum of two terminators per bus
segment.
Publication 1757-PM002A-EN-E - June 2006
System Requirements 1-5
the trunk. The following illustration shows a sSimple Fieldbus network with
terminators
FFI
Trunk
Software Requirements
FFLD
Wire Pair
T
Terminator Terminator
Signals
T
Fieldbus
Digital
Field
Device
Personal Computer
You need a computer to run RSFieldbus software.
RSFieldbus and RSLogix 5000 software for are required. As an option, you can
use RSView Supervisory Edition software for specific applications.
Additional Resources
There are a number of resources available should you encounter difficulties
with your fieldbus application.
Publication 1757-PM002A-EN-E - June 2006
1-6 System Requirements
Web Sites
• Rockwell Automation
– External:
http://domino.automation.rockwell.com/applications/gs/region/gt
swebst.nsf/pages/Process_Solutions_Home
– Internal:
http://rain.ra.rockwell.com (select Process Solutions
from the A-Z menu)
• FOUNDATION Fieldbus:
http://www.fieldbus.org/
• Tech Support:
– For Knowledge-base information, go to the Tech support Web site:
http://support.rockwellautomation.com/ (select Knowledge
Bases)
– For telephone support call: 440-646-5800
Documents
For a list of additional support documentation that may be useful in
conjunction with this manual, see the
page P-2.
Related Documentation section on
Publication 1757-PM002A-EN-E - June 2006
Set Up A System
Chapter
2
In This Chapter
Purpose of this Chapter
For See Page
Purpose of this Chapter 2-1
Hardware Requirements 2-2
Software Requirements 2-5
Set Up A System 2-6
Physical Media 2-7
Network Basics 2-20
Things to Consider When Setting
Up a System
Additional Resources 2-27
This chapter describes the components of a typical fieldbus system and how to
set up and prepare your system for operation.
Refer to the Glossary for further explanation of fieldbus terms and concepts.
If you want to start using RSFieldbus for applications immediately, skip to
Chapter 4,
Applications.
2-27
1 Publication 1757-PM002A-EN-E - June 2006
2-2 Set Up A System
Hardware Requirements
To build a simple fieldbus system, you need:
• Power supply
• Power conditioner
• Fieldbus cable
• Field devices
• Connector blocks
• Ter minal blocks
• Ter minators
• 1757- FFLD linking device
• Personal computer
Power Supply
The following power supplies are available according to the referenced
Fieldbus Foundation Physical Layer Profile Specification:
Type 131 Non-I.S. Power supply intended for feeding and I.S. barrier. Output
voltage depends on barrier rating.
Type 132 Non-I.S. Power supply not intended for feeding and I.S. barrier.
Output voltage is 32 VDC Max.
Type 133 I.S. Power supply; complies with recommended I.S.
parameters
You can configure power supplies to provide dual redundancy as long as they
meet the IEC/ISA Physical Layer Standards requirements. It is not acceptable
for example, to merely parallel two power supplies.
A typical power supply for a small network is a SOLA SDN 5-24-100. 5A, 24
VDC output, 110 AC input. For more specifications on power supplies, see the
Power Considerations section on page 2-2.
Power Conditioner
Publication 1757-PM002A-EN-E - June 2006
A power supply impedance matching network is required for Fieldbus use.
This is referred to as a power conditioner. A power conditioner is a
Set Up A System 2-3
resistive/inductive network that is either external or built into the fieldbus
power supply.
Fieldbus Cable
The preferred fieldbus cable is specified in the IEC/ISA Physical Layer
Standard, Clause 22.7.2 for conformance testing. It is referred to as type “A”
fieldbus cable. This cable will probably be used in new installations.
Other types of cable can also be used. The alternate preferred fieldbus cable is
a multiple, twisted pair cable with an overall shield. It is referred to as Type
“B” cable. Less preferable types of cable include single or multiple twisted pair
cable without any shield, referred to as Type “C” cable, and multiple conductor
cable without twisted pairs, but with overall shield, referred to as Type “D”
cable.
The following table contains the types of cable identified by the IEC/ISA
Physical Layer Standard and their maximum length values. For information
about spur wire length, see the
page 2-9.
Spur Wire Length Calculations section on
Ty pe Cable Description Size Maximum Length
Type A Shielded, twisted
pair
Type B Multi-twisted pair
with shield
Type C Multi-twisted pair
without shield
Type D Multi-core, without
twisted pairs and
having an overall
shield
#22 AWG
(.8 mm2)
#22 AWG
(.32 mm2)
#26 AWG
(.13 mm2)
#16 AWG
(1.25 mm2)
1900 m
(6232 ft.)
1200 m
(3936 ft.)
400 m
(1312 ft.)
200 m
(656 ft.)
Devices
Fieldbus links smart field devices with automation systems. The devices
generally used in fieldbus networks are type 113 (bus powered) or type 114
(separate power). Examples of these devices are the Rosemount 3051S
pressure Transmitter and the Micro Motion 2700 Flowmeter.
Publication 1757-PM002A-EN-E - June 2006
2-4 Set Up A System
Connector Blocks
Connector blocks are optional coupling devices. They can be used to connect
wire to a fieldbus device, or to another section of wire (e.g. at a junction block).
Connector blocks are useful for installations where devices may be periodically
disconnected or moved.
Standard fieldbus connectors are specified in Annex B of the ISA Physical
Layer Standard and Annex A of the IEC Physical Layer Standard.
1757-FFLD Linking Device
The 1757-FFLD, also referred to as the linking device, bridges both
F
OUNDATION Fieldbus™ HSE and Ethernet/IP networks to FOUNDATION
fieldbus H1 device networks. Bridging these networks facilitates information
flow between a Logix system’s control layers.
Terminal Blocks
Terminal blocks typically provide multiple bus connections, so a device can be
wired to any set of bus terminals. They can be the same terminal blocks as
used for 4-20 mA.
Terminators
A terminator is an impedance matching module used at or near each end of a
transmission line. Terminators prevent distortion and signal loss, and are
typically purchased and installed as preassembled, sealed modules. Each
terminator has a value of 50 ohms.
ATTENTION
A trunk is the longest cable path between any two devices on the network. All
connections to the trunk are called spurs. Place the terminators at the ends of
You can use a maximum of two terminators per bus
segment.
Publication 1757-PM002A-EN-E - June 2006
Set Up A System 2-5
the trunk. The following illustration shows a sSimple Fieldbus network with
terminators
FFI
Trunk
Software Requirements
FFLD
Wire Pair
T
Terminator Terminator
Signals
T
Fieldbus
Digital
Field
Device
Personal Computer
You need a computer to run RSFieldbus software.
RSFieldbus and RSLogix 5000 software for are required. As an option, you can
use RSView Supervisory Edition software for specific applications.
Publication 1757-PM002A-EN-E - June 2006
2-6 Set Up A System
Set Up A System
When setting up a fieldbus system, you must first install and configure your
software and all fieldbus devices.
The following figure is a simplified diagram of a fieldbus system using
RSFieldbus.
Figure 2.1 Simplified Fieldbus Network HSE
RSFieldbus
HSE Network
FOUNDATION Fieldbus
H1
H1-1
H1
H1-2
FOUNDATIO N Fieldbus
H1
H1-3
Linking Device
H1
H1-4
STATUS
WDOG
BATT
NS 1
MODE
H1 Network
Field
Device
24V dc
Power Supply
Network
Terminator
Field
Device
Power
Supply
Power
Conditioner
Linking
Device
Network
Terminator
Note the relation of the HSE and H1 levels in the system.
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Set Up A System 2-7
Physical Media
Power Considerations
Fieldbus devices may be either powered from the segment (bus) or locally
powered, depending on the design. If at all possible, field devices should be
bus powered.
Power Supplies
Power supplies shall comply with IEC 61158-2 criteria and performance
requirements, with preferential consideration given to the low-power signal
option. We recommend using one power supply dedicated to the linking device
and any additional supplies dedicated toward the field devices.
Rockwell Automation manufactures a DIN rail mountable 1794-PS3 supply
that is Class 1, DIV2 compliant. It will supply +24VDC at 3 Amps.
Power Conditioning
If an ordinary power supply were used to power the fieldbus, the power supply
would absorb signals on the cable because it would try and maintain a constant
voltage level. For this reason, an ordinary power supply must be conditioned
for fieldbus use.
DC Power Supply
Putting an inductor between the power supply and the fieldbus wiring is a way
to isolate the fieldbus signal from the low impedance of the bulk supply. The
inductor lets in the DC power on the wiring, but it prevents signals from going
into the power supply.
One fieldbus power supply conditioner is required for each fieldbus network
segment (
Power conditioners should be redundant units that provide flawless transfer
from one unit to another. Primary and secondary sources should be
physically separated, not sharing a common backplane or AC source. Be
aware that power conditioners have limits on how much current they can
source.
Figure 2.2).
Figure 2.2 Power Supply With One Power Conditioner
Conditioner H1 Fieldbus
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2-8 Set Up A System
Additionally, power conditioners may have an internal terminator which
should be considered when placing terminators on the network.
Signal Wire Polarity
The combination signal/power wires have a plus (+) and minus (-) polarity
associated to the power conditioner outputs, which must be wired to the
appropriate terminals on the devices. Some devices are polarity insensitive,
meaning they still work if you connect the positive wire to the negative
terminal, and vice-versa.
Grounding
Follow all international, national and local codes for grounding and bonding
equipment. Above all, follow the manufacturer’s instructions and
recommendations for each device installed in a plant.
IMPORTANT
Signal wiring of the fieldbus segment cannot be grounded.
Grounding out one of the signal wires will shut down an
entire fieldbus network.
To prevent ground loops, a Fieldbus segment should only be grounded at one
point. This is usually done by grounding the cable shield at the control room
end of the segment.
Each process installation has a different requirement for grounding. Be sure
that the shield is electrically isolated from the transmitter housing and other
grounded fixtures.
Limiting Factors
Bus powered devices usually require 10-30ma of current and between 9-32
volts. The number of bus powered (two-wire) devices on a segment is limited
by the following factors:
• Output voltage of the fieldbus power supply
• Current consumption of each device
Publication 1757-PM002A-EN-E - June 2006
• Location of the device on the network/segment
• Location of the fieldbus power supply
• Resistance of each section of cable
• Minimum operating voltage of each device
Set Up A System 2-9
• Additional current consumption due to one spur short-circuit fault
(10ma)
The length of a fieldbus wiring system and the number of devices on a
network/segment are limited by the power distribution, attenuation, and signal
distortion. Refer to ISA 50.02 for the limitations on cable length.
Fieldbus Network Topologies
A network topology refers to the shape and design of a fieldbus network.
There are basically three types of network topologies supported: tree; bus with
spurs; and daisy chain. The daisy chain network, however, is not
recommended.
The two port linking device shown below in Figure 2.3 is an example of a
simple fieldbus network on each H1 port. Notice that there are two
terminators and one power conditioner per fieldbus segment. The terminators
should be placed at the ends of the trunk.
IMPORTANT
You can use a maximum of two terminators per bus
segment.
Publication 1757-PM002A-EN-E - June 2006
2-10 Set Up A System
Figure 2.3 Rockwell linking device with a Simple Two-Port
Fieldbus Network
Terminator Terminator
Wire Pair
TwoPort
Linking
Device
Power
Conditioner
Power Supply
TT
Fieldbus Device
Terminator Terminator
Wire Pair
TT
Fieldbus Device
T
Power
Conditioner
Tree Topology - Chicken Foot
This topology consists of a single fieldbus segment connected to a common
junction box to form a network. A tree topology is practical if the devices on
the same segment are well separated but in the general area of the junction
box. It allows maximum flexibility when configuring and assigning devices to
networks/segments, and it is the preferred topology for reuse of existing
wiring.
(1)
Figure 2.4 is an example of a junction box at the end of a trunk. Remember
that a trunk is the longest cable path between any two devices on the network.
Since it is at the end of the trunk, the terminator within the junction box is
activated. The spurs that are shown on the bottom of the junction box must be
taken into consideration using the maximum spur length table (
Table 2.1 on
page 13).
(1)
FF Engineering Guide (6.1.2)
Publication 1757-PM002A-EN-E - June 2006
Figure 2.4 Tree Topology (Chicken Foot)
Junction Box
Set Up A System 2-11
1 Linking
ce
T
Tru nk
Note: The ìTî is for Terminator.
T
Publication 1757-PM002A-EN-E - June 2006
2-12 Set Up A System
Figure 2.5 and Figure 2.6 are examples of chicken foot topologies using
Relcom Blocks.
Figure 2.5 Tree Topology (Chicken Foot) Using Relcom Blocks
Isolated
Terminator
Block
Expansion
Block
To H1 Linking
Device
TT
Trunk
Power
Conditioner
D/1 D/3D/2 D/4 D/5 D/6 D/7
Figure 2.6 Relcom Blocks in a Chicken Foot or Star Fieldbus
Topology
Bus With Spurs Topology
This topology consists of fieldbus devices that are connected to a multi-drop
bus segment through a length of cable called a spur. A bus with spurs topology
is technically acceptable but not generally a good economic choice.
Figure 2.7 below is an example of a bus with spurs topology. Since it is at the
end of the trunk, the junction box on the right has its internal terminator
enabled.
Publication 1757-PM002A-EN-E - June 2006
ng
e
T
Figure 2.7 Pepperl + Fuchs F4-JB-I1.CGS FieldConnex
Junction Boxes
Junction Box
Junction Box Junction Box
Spur Wire Length Calculations
Spur lengths can vary from 1 meter to 200 meters. If you have a choice about
spur length, the general rule is that the shorter the spur, the better. A spur less
than 1 meter is considered a splice.
lengths for devices.
Table 2.1 Recommended Maximum Spur Length Table m(ft)
Set Up A System 2-13
Table 2.1 below lists recommended spur
Total Devices 1 Device per Spur 2 Devices Per
Spur
25-32 1(3) 1(3) 1(3) 1(3)
19-24 30 (98) 1(3) 1(3) 1(3)
15-18 60 (197) 30 (98) 1(3) 1(3)
13-14 90 (295) 60 (197) 30 (98) 1(3)
1-12 120 (394) 90 (295) 60 (197) 30 (98)
Note: These lengths are recommended, not required
3 Devices per
Spur
4 Devices per
Spur
Shielding
For optimal performance, fieldbus cables should be shielded. Common
multi-conductor (multi-core) “instrument” cable can be used. It has one or
more twisted pairs, an overall metallized shield, and a shield wire.
The instrument shield should be terminated at the host (power conditioner)
end of the network in a marshalling cabinet and should not be connected to
ground at any other place. If a multiple home run cable goes to a fieldbus
junction box, do not attach the cable shield wires from different networks
together. This creates ground loops and noise on the network. The most
common problems with fieldbus networks are usually due to noise, which can
occur if you have the wrong wiring, improper grounding, and/or bad
connections.
A cable signal encountering a discontinuity, such as a wire open or short,
produces a reflection. The reflection is a form of noise that distorts the
original signal. A terminator is used at the ends of a fieldbus cable to prevent a
reflection.
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2-14 Set Up A System
F
F
F
Figure 2.8 Proper Shielding for a Tree Network
FFLD
T
T
All Shields
Tied Here
Signal Quality
When a fieldbus network’s signal quality is poor, it can cause intermittent loss
of communication to devices, unreasonably long downloads, and lost data. The
following components are critical to achieving good signal quality:
• Shielded two wire cable, preferably specifically designed for fieldbus.
The type of cable will determine overall length of the trunks and drops.
Publication 1757-PM002A-EN-E - June 2006
• Terminators. Terminators reduce noise on segments caused by signal
reflections at the end of an open cable. One terminator on each end of
the H1 trunk is needed for proper performance.
• Power conditioners are mandatory between a supply and the H1 trunk,
which can deliver 9-32 V DC consistently out of the conditioner when
under the appropriate load from the cable resistance and while powering
the devices. One power supply, or redundant power supplies designed
for fieldbus, can be used.
• In areas vulnerable to lightning, lightning arresters should be installed.
The four issues above along with proper shielding and grounding will ensure
proper signal qualities.
Set Up A System 2-15
Protocol Analysis
There are a number of ways in which you can verify that the network you have
set up will perform properly. A protocol analyzer is a tool that allows you to
test for the content of the message sent, what the messages mean, and what
sequence the fieldbus devices talk to each other. It should be noted, however,
that a protocol analyzer is an advanced tool with a complex range of functions.
Publication 1757-PM002A-EN-E - June 2006
2-16 Set Up A System
Fieldbus Network Testers
Other testers are used to monitor and characterize network signals. The
Relcom Fieldbus Network Monitor (FBT-3) can be used to examine the
(1)
operation of a live fieldbus network, without interfering with its operation.
The FBT-3 will verify the DC voltage on the network and check how noisy the
network is. It can also be used to measure peak noise levels, framing errors, the
number of transmitters on the wire, and what the signal level of the weakest
field transmitter is. In addition, with the FBT-3 you can see the total number of
devices up and running, and what devices are left on the network. The FBT-3
can be purchased from Relcom (
www.relcominc.com).
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FBT-3 Manual
Set Up A System 2-17
Another way of testing the signal quality of a network is to use an oscilloscope.
We recommend a hand-held battery-operated unit because of its small size and
ease of use. The Fluke 199-3 ScopeMeter is one such scope.
Figure 2.9 Fluke 199-3 200MHz ScopeMeter
Other scopes that can be used include the TPI-E1505, the Extech-381275
(
www.professionalequipment.com), and the Techtronix THS700 Series
(www.tek.com).
Signal Analysis
Oscilloscopes, whether portable or stationary, from 50MHz to 1GHz, can be
used to capture and examine the waveform. The power supply waveform
should be a +/- 0.75 VDC to +/- 1.00 VDC square wave riding on the 9 V
DC to 32 V DC steady power supply with < 0.10 V DC ripple. The sharper
the rising and falling edges of the waveform, the better the data transfer. The
physical media of a system will determine what shape the waveform takes.
The signal is a current modulated ±10mA signal on a 50 test load. This
generates a 1.0 Vpp signal. A valid signal can range from 150mVpp up to
1.0Vpp and noise must not exceed 75mvpp (
Figure 2.10).
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2-18 Set Up A System
Figure 2.10 An Ideal Fieldbus Communications Signal
75-500 mv
Max Noise
75 mv (pk-pk)
75-500 mv
Good Network Scope Display
In order to analyze a fieldbus network signal, you must know what constitutes
a good signal versus a bad one.
consisting of two terminators.
Figure 2.11 represents a normal signal
Figure 2.11 Good Network Signal
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Publication 1757-PM002A-EN-E - June 2006
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FF Engineering Guide (11.4.3)
Bad Network Scope Display
R
Bad network signals can inhibit the performance of your network. A common
reason for bad signals is the addition of one or more unnecessary terminators
in a network.
Remember, there can be only two terminators per bus segment.
WA
Figure 2.12 shows a bad signal due to only one terminator in a system, while
Figure 2.13 shows a bad signal due to one extra terminator (3 total).
Set Up A System 2-19
Figure 2.12 Bad Network Signal Due to One Terminator
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11.4.3 FF Engineering Guide
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2-20 Set Up A System
Network Basics
Figure 2.13 Bad Network Signal Due to Three Terminators
When using the linking device, there are two networks that must be
considered: the HSE network and the H1 network.
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HSE
HSE stands for High Speed Ethernet. HSE is the Fieldbus Foundation's
backbone network running Ethernet and IP. An HSE field device is a fieldbus
device connected directly to a High Speed Ethernet (HSE) fieldbus. Typical
HSE field devices include HSE linking devices, HSE field devices running
function blocks (FBs), and host computers.
IP Addresses
Every device that communicates over the Internet is assigned an IP address
that uniquely identifies the device and distinguishes it from other devices on
the Internet. An IP address consists of 32 bits, often shown as 4 octets of
numbers from 0-255 represented in decimal form instead of binary form.
For example, the IP address 168.212.226.204 in binary form is
10101000.11010100.11100010.11001100.
It is easier to remember decimals as opposed to binary numbers, so we use
decimals to represent the IP addresses when describing them. However, the
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Additional material for ëPhysical Mediaí section taken from FF Engineering
Guidelines, Relcom's Fieldbus Wiring and Test Solutions Guide
(WWW.Relcominc.com), and Foundation Fieldbus Project Implementation
Considerations (Power point Slide by John Yingst at Honeywell)
Publication 1757-PM002A-EN-E - June 2006
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