Practical steps to a successful PROFIBUS project - Xiu Ji of the UK's PICC

Practical Steps to a Successful
PROFIBUS Project
Dr. Xiu Ji

Outline of this presentation
Basics of PROFIBUS

Considerations at the design stage
Installation - visual checks
Summary – Steps to a successful PROFIBUS project

Practical steps for a successful project, Xiu Ji. PROFIBUS Seminar at MTC, Coventry, 2013.

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
Probably the single reason to use bus or networked devices and systems

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

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 file, GSD file.
Machines or a production line can be stopped in case of
communication problems
Physical layer uses RS485 or fiber optic


Slide 6

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 additional to a
GSD file, also in EDD or FDT/DTM.
Machines and processes cannot be stopped if there are only
communication problems
Large number of parameters, options and diagnostic events
Cyclic and acyclic communications
PA equipment is often used in explosive environments


Slide 7

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

RS485 / RS485 -IS
MBP / MBP-IS

Engineering Technologies
GSD, EDD, FDT / DTM, TCI

Common
Application
Profiles

Encoder

Ident Systems

PA Devices

Specific
Application
Profiles

PROFIdrive

Wired, Optical, and Wireless

Wireless

Glass, PC F, Plastic


Slide 8

Connection technologies

9

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 9

Fibre Optic
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)

Fibre to Copper


Slide 10

Control System Architecture


Slide 11

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 12

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
DP/PA
Coupler

C

S

S

O

S
S

Segment 4
RS485

S

M

Fibre optic
links

S
S
Segment 5
MBP

Page 23
Slide 13

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 14

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.
Just like an echo, the reflected signal can cause multiple signals
or corrupted telegrams to appear on the line.


Slide 15

Reflections


Slide 16

Termination - Rules
To avoid reflections from the ends of the cable it is
essential that each segment is terminated at the two ends
and nowhere else.
Two terminators in each segment must be powered at all
times.


Slide 17

Termination
Standalone termination boxes are available.
for DP, and
for PA.

Termination on Repeaters


Slide 18

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 19

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 bended.



Page 31

Slide 20

Interference

2
1

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 21

Equipotential Bonding


Slide 22

Installation: Shielding and Grounding
intern

2
3

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 23

Grounding of devices and shields
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 = -

Screw
terminals
Rx

Cable shield route
to ground

Rx

Tx

Tx

Device

Device


Slide 24

Wrong connectors
Which connectors are faulty?

A

B

C


C
Slide 25

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 26

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

 10 cm

 50 cm

Cable
Category II

 10 cm

Cable
Category III

 50 cm
Cable
Category IV


 50 cm

Slide 27

Cable Segregation ?
An example: frequent converters.
Can you spot the error here?

Power able route


Slide 28

Spot the errors


Slide 29

Spot the errors


Slide 30

Spot the errors


Slide 31

Use PROFIBUS connections - DP


3
2

Slide 32

Use PROFIBUS connections - PA

3
3

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 33

Spot the errors


Slide 34

Design considerations - details
Limitations of segment loads and total cable length

Standalone terminations for DP, redundant power supply to
terminators
Network drawings – node addresses, position of termination,
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 35

Design considerations - architecture
Which network to use – PROFIBUS, PROFINET, DP, PA, AS-i?

3
6

Designation of safe and explosive 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
Design documents and drawings

Slide 36

Installation Checklists

3
7

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
Page 73


Slide 37

Practical steps to a successful PROFIBUS project
The very first step to a successful project should be

3
8

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

Many industry sectors specify that their staff, contractors and
sub contractors must be appropriately trained.
PI Competence Centre - Manchester Metropolitan University,
in-house or on-site training
PI Training Centre – Verwer Training and Consultancy, on-site
training for min. 6 people


Slide 38

Summary: Steps to a successfully project

3
9

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.
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 into your installation acceptance tests.
Reference (Page 79)


Slide 39

Practical steps to a successful PROFIBUS project - Xiu Ji of the UK's PICC

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