Practical steps to a successful PROFIBUS project - Richard Needham and Xiu Ji

Practical Steps to a Successful
PROFIBUS Project
Slides by Dr. Xiu Ji - MMU
Presentation today by Richard Needham – Hi-Port Controls

Outline of this presentation

Presentation objective
Introduction to PROFIBUS and associated benefits
Connection options and rules
Other cabling issues : grounding and interference
Design Considerations
Implementation issues
Essential training

Practical steps to a successful project, The PROFIBUS Group Seminars, Dr Xiu Ji

Slide 2

Introduction to PROFIBUS
Fieldbus is widely used in many automation systems.
PROFIBUS solutions for Factory Automation (FA) and
Process Automation (PA)
Applications also involving drives, instruments, servos,
robotics, functional safety, redundancy, and explosive
environments etc.
Extensive diagnostic functions available to operators and
maintenance engineers
Diagnostic tools available for engineering, commissioning,
maintenance, and fault finding
Excellent support from PROFIBUS International, regional
events and competence and training centres.


Slide 3

More Information
More adjustable settings and parameters (e.g. scaling,
linearization and calibration).
Diagnostic data to inform if measurement is valid.


Slide 4

Extensive Diagnostics
Controller

SCADA/HMI

1

2
Engineering
Station

3

PA Software

2
Analyser


Slide 5

PROFIBUS Applications

Factory
automation

Process
automation

Vehicle
manufacture
Bottling plants
Warehousing
systems
Switchgear
Hollow glass
production

Chemical
industry
Petrochemical
industry
Paper and
textile industry
Foodstuffs
Power stations
Sewage plants

Drive
technology
Machine tools
Packaging
machines
Pressing plants
Paper production


6

Safety
applications
Vehicle
assembly
Machine tool
building

Slide 6

The PROFIBUS Family
PROFIBUS DP (Decentralised Periphery)

Low cost, simple, fast for general automation applications
Within short distances, in large quantities, mainly in-door, in dry
areas, in cabinets
Parameters, options and capabilities can be defined using a
simple, text ‘GSD’ file.
Physical layer uses RS485 or fiber optic


Slide 7

The PROFIBUS Family

PROFIBUS PA (Process Automation)

Developed specifically for the process industry to replace 4-20mA
transmission
Two-wire connection carrying both power and data
Spread over long distances, in low quantities, mainly out-doors,
in wet and exposed sites
Parameters, options and capabilities are defined in additional to a
GSD file, in EDD or FDT/DTM
Large number of parameters, options and diagnostic events
Cyclic and acyclic communications
PA equipment is often used in explosive environments


Slide 8

Transmission Technologies
PROFIBUS supports different transmission technologies

HART on
PROFIBUS

LabAutomation

XY

Weighing &
Dosage

PROFIsafe, I&M, iPar-Server,
Time Stamp, Redundancy, …

Communication
Technology
Transmission
Technologies

....

PROFIBUS DP (DP-V0, -V1, -V2)

Wired

Optical

RS4 85 / RS485-IS
MBP / M BP-IS

Engineering Technologies
GS D, EDD, FDT / DTM, TCI

Common
Application
Profiles

Encoder

Ident Systems

PA Devices

Specific
Application
Profiles

PRO FIdrive

Wired, Optical, and Wireless

Glass, PC F, Plastic


Wireless

Slide 9

Connection technologies

1
0

PROFIBUS DP uses 2-core shielded and twisted RS485 wiring.
9-pin sub-D or M12 connectors extensively used.

DP can also use plastic or glass fibre optic cabling.
ST/BFOC connectors widely used

PROFIBUS PA uses “Manchester Bus Powered” (MBP) cabling
over 2 cores.
Glanded screw or M12 connection normally used


Slide 10

Optical transmission
The implementation of a fibre optic cable network involves the
use of electro optical converters (OBT and OLM):
for long distance, between buildings, and
to solve grounding problem (grounds with un-even earth
potential).

OLM (Optical Link Module)

OBT (Optical
Bus Terminal)

FO
Coupler

FO
Coupler

Fibre to Copper


Slide 11

Control System Architecture


Slide 12

From DP (RS485) to PA (MBP)

1

1

1

4
To
7
volts
0

0

PROFIBUS PA, MBP

PROFIBUS DP, RS485
Current/mA

0

1

1

0

0

+9mA

10 mA
-9mA
time


Slide 13

DP & PA Segments
One PROFIBUS network can host up to 126 stations (masters and slaves) –
capacity of a PROFIBUS DP master
Limitation of RS485 and MBP – 32 loads and total cable length per segment

Segment
1 RS485
M

Repeater

S

Segment 2
RS485
S

Segment 3
Fibre Optic

S

S

R
S

O

S

C

DP/PA
Coupler S

S

O

S
S

Segment 4
RS485

S

M

Fibre optic
links

S

Each RS485 segment are best laid
out as a “linear bus” daisy-chaining
from device to device.

Segment 5
MBP

MBP segments can be laid out in a
more flexible manner using Tee
junctions to create spur lines.

S


Slide 14

DP Segment Cable Length
When using best quality PROFIBUS RS485 (Type-A) cables, the
segment cable length is limited according to the network speed.
Baud rate

Maximum segment length

9.6 kbit/s

1 200m

19.2 kbit/s

1 200m

45.45 kbit/s

1 200m

93.75 kbit/s

1 200m

187.5 kbit/s

1 000m

500.0 kbit/s

400m

1.5 Mbit/s

200m

3.0 Mbit/s

100m

6.0 Mbit/s

100m

12.0 Mbit/s

100m


Low
speeds

Middle
speeds
High
speeds
Slide 15

PA Segment Cable Length
PA baud rate is fixed at 31.25 kbit/s.
The maximum segment cable length is 1900 meters for nonintrinsically safe applications, and….
1000 meters for intrinsically safe applications


Slide 16

Segmentation, PA
The maximum number of devices on a PA segment is the same
as the maximum on a DP segment, which is 32.
However, how many slaves can be connected to a PA segment
depends primarily on the power supplied to the segment.
Segment Coupler
V = 13.4 VDC, I = 100 mA

Maximum number of
PA slaves = 100 / 14 = 7

I actual = 5 x 14 = 70 mA
14 mA

14 mA

14 mA

#13

14 mA

14 mA
#16

T

#17

#15
#14


Slide 17

Reflections
When electrical signals travel down a cable, any electrical
discontinuity can cause reflections to occur
The end of the cable in particular is a major discontinuity, which
can cause severe reflections, particularly with fast changes
Just like an echo, the reflected signal can cause multiple signals
or corrupted telegrams to appear on the line


Slide 18

Reflections

Reflection caused by
missing terminator

missing terminator

missing terminator

Analysis of PROFIBUS system behaviour is covered in “PROFIBUS in
Practice – system engineering, troubleshooting and maintenance”.

Slide 19

Termination - Rules
To avoid reflections from ends of the cable it is essential
that each segment is terminated at both ends and
nowhere else
Both terminators in each segment must be powered at all
times
Terminator switches and resisters are normally include in
9-pin PROFIBUS connectors for this purpose, with plug-in
terminators used for M12 schemes
+5 volt power is needed for these terminators to work
properly. This is normally supplied from the connected
device


Slide 20

Termination
Standalone termination boxes are also available
for DP
and for PA

Termination on Repeaters


Slide 21

Termination
#10

#0

#1

#11
T

T

DP/PA
coupler

Power supply for PA segment
T
T

1 network with 2
segments.
#13

#15
#14


#16

#17

Slide 22

Causes of Reflections
Missing terminator
Un-powered terminator
Terminator switch - faulty
Extra terminator
Reflection can also be caused by:

Un-certified devices
Cable length between two devices is too short
Spurs are used in high speed networks
Wrong types of cables are used
Cores are sharply bent


Slide 23

Allowance of RS485 Spurs

Bit rate

Total allowable spur
capacitance

Total Spur cable
length/segment*

>1.5 Mbit/s

None

None

1.5 Mbit/s

0.2 nF One spur @ 6.7m or 6.7 m

500 kbit/s

0.6 nF 6 spurs @ 1.1m each 20 m

187.5 kbit/s

1.0 nF

33 m

93.75 kbit/s

3.0 nF

100 m

19.2 kbit/s

15 nF

500 m

It is much more flexible @ low speed.
* Calculated for PROFIBUS cable type A at 30pF/m

Slide 24

Allowance of MBP Spurs
The length of the individual spur-lines on a PA segment depends
upon the total number of spurs used:
Number of
spur-lines

Maximum spur length
non-intrinsically safe

Maximum spur length
intrinsically safe

25 to 32

1m

1m

19 to 24

30 m

30 m

15 to 18

60 m

60 m

13 to 14

90 m

60 m

1 to 12

120 m

60 m

Note that the maximum cable length of 1900m includes
cable used for spurs. E.g. 18 x 60 = 1080m spurs + 810m trunk line.

Slide 25

Interference

2
6

Interference is picked up from adjacent equipment or
connected equipment with poor Electromagnetic Compatibility
(EMC) rating.
Interference can be caused by:

Inadequate earthing of equipment,
Poor or incorrect earthing of cable shield,
Insufficient segregation of power and bus cables,
Routing cables through electrically noisy areas, and
Heavy earth currents on the cable screen.


Slide 26

Equipotential Bonding


Slide 27

Installation: Shielding and Grounding
intern

2
8

Shielding and Grounding
The recommended grounding practices:
Connect all PROFIBUS interfaces and cable shields to ground.
Use a grounding cable to go from cabinet to cabinet
in the same segment – equipotential bonding.

Types of grounding:
Direct grounding (at any connecting point)
Capacitive grounding


Slide 28

Equipotential Bonding at a Device
Connect the PROFIBUS cable shield to the equipotential
bonding at every PROFIBUS station assuming local potentials
are equal!
Connector

Shielded, twisted-pair cable

Red = +
Green = Rx

Cable shield route
to ground

Rx

Tx

Tx

Device

Device


Slide 29

Connector wiring problems
Which connectors are incorrectly wired?

A

B

C


D
Slide 30

Cable Segregation
• All channels and partitions must be properly earthed.
• Use flexible bonding links are protected against corrosion.
• Braided straps are better than solid metal.


Slide 31

Cable Segregation Distance
In general, the greater the spacing between the cables and the
shorter the paths run parallel, the lower the risks of
interference.
Recommended cable segregation distances:
20 cm

Cable
Category I

50 cm

10 cm

Cable
Category II

10 cm

Cable
Category III

50 cm

Cable
Category IV


50 cm

Slide 32

Cable Segregation ?
An example: variable frequency drives
Can you spot the error here?

Power cable route


Slide 33

Spot the errors


Slide 34

Spot the errors


Slide 35

Spot the errors


Slide 36

Standard connections – PROFIBUS DP


3
7

Slide 37

Standard connections – PROFIBUS PA

3
8

Trunk
PROFIBUS DP

Link/
Coupler

T

T

PROFIBUS PA
Spur lines

Devices

PROFIBUS DP

Link/
Coupler

T

Junction
Box

PROFIBUS PA

Junction
Box

Trunk

T

Spur lines

Devices


Slide 38

Spot the errors


Slide 39

Design considerations - details

Limitations of segment loads and total cable length
Standalone terminations for DP, redundant power supply to
terminators
Network drawings – node addresses, mark of termination
position, cable routes, cable length between connectors and
junction boxes, trunk cable and drop cable length
Piggyback connectors – spare connection into EVERY segment
for voltage measurements and troubleshooting


Slide 40

Design considerations - architecture

4
1

Which network to use – PROFIBUS, PROFINET, DP, PA, AS-i?
Designation of safe and hazardous areas
Production and functional safety systems
Cable routes – fibres, copper cables, earthing systems,
equipotential bonding cable in place?
Cabinet or field assembly
Connection of devices via remote IO or integrated fieldbus?
Use of redundancy at difference levels
Network and device access for engineering, monitoring and
maintenance


Slide 41

Installation Checklists

4
2

Checklist to determine network topology and obtain the
network drawing
Checklist for PROFIBUS DP (RS485) Grounding
Checklist for PROFIBUS PA (MBP) Grounding
Checklist for PROFIBUS DP (RS485) Cabling
All above are included in “PROFIBUS in Practice – installing
PROFIBUS devices and cables” as templates for a Factory
Acceptance Test document.


Slide 42

Practical steps to a successful PROFIBUS project

4
3

The very first step to a successful project should be

Training
PROFIBUS training courses are available for:
Installers,
System Designers,
Commissioning Engineers, and
Maintenance staff.

Many industry sectors specify that their staff, contractors and
sub contractors must be appropriately trained.
Competence Centre - Manchester Metropolitan University
Training Centre – Verwer Training and Consultancy


Slide 43

Certified PROFIBUS Installer Training

4
4

This training is widely accepted as the minimum standard of
training for anyone who is working in PROFIBUS systems at a
technical level.
Available as a one-day training course in house or on-site.
It teaches the basic principles of PROFIBUS and covers the basic
layout, installation and testing of DP and PA networks.
It is also essential basic training for system designers,
maintenance and all engineering staff.
Background details are covered in the series of “PROFIBUS in
Practice”, the orange and blue textbook.
Extra days can be added to extend the training for maintenance,
design and engineering staff.


Slide 44

PROFIBUS System Design Training

4
5

Good overall design, with good documentation and clear
specifications of required wiring, installation, testing,
commissioning and final setting-to-work practices are
recommended. Production of final ‘as installed’ drawings are
also recommended (to assist with subsequent maintenance)
Designer training will allow companies to ensure that their
designers are aware of the common design pitfalls and able to
produce systems that are cost effective, efficient and
maintainable.
Designer course at MMU is 3 days covering installation,
maintenance, and design.


Slide 45

Summary: Steps to a successfully project

4
6

1. Design staff should be trained before the design starts.
2. Everyone involved in the project at a technical level is trained to
an adequate level, at the least to the designer or installer level
3. Make sure that designers are fully aware of the methods for
diagnosing and locating faults, before start of design
4. Ensure that health checking and performance monitoring
facilities are incorporated into the network
5. Follow the extensive guidance that is available from PI and from
competency and training centres, for example, incorporating
the checklists in to your installation acceptance tests


Slide 46

Practical steps to a successful PROFIBUS project - Richard Needham and Xiu Ji

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