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

Practical Steps to a SuccessfulPROFIBUS Project

Slides by Dr. Xiu Ji - MMU

Presentation today by Richard Needham – Hi-Port Controls

Practical steps to a successful project, The PROFIBUS Group Seminars, Dr Xiu Ji Slide 2

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


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 explosiveenvironments 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.


More Information

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


Extensive Diagnostics

Controller

EngineeringStation

PA Software

SCADA/HMI

12

23

Analyser


6PROFIBUS Applications

Vehicle manufactureBottling plantsWarehousing systemsSwitchgearHollow glass production

Vehicle assemblyMachine tool building

Chemical industryPetrochemical industryPaper and textile industryFoodstuffsPower stationsSewage plants

Machine toolsPackaging machinesPressing plantsPaper production

Factoryautomation

Processautomation

Drivetechnology

Safetyapplications


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


The PROFIBUS Family

PROFIBUS PA (Process Automation)Developed specifically for the process industry to replace 4-20mA transmissionTwo-wire connection carrying both power and dataSpread over long distances, in low quantities, mainly out-doors, in wet and exposed sitesParameters, options and capabilities are defined in additional to a GSD file, in EDD or FDT/DTMLarge number of parameters, options and diagnostic eventsCyclic and acyclic communicationsPA equipment is often used in explosive environments


Transmission Technologies

Communication Technology


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

Wired RS485 / RS485-IS

MBP / MBP-IS

Engi

neer

ing

Tech

nolo

gies

GS

D, E

DD,

FD

T / D

TM, T

CI

OpticalGlass, PCF, Plastic

Wireless

PRO

FIdr

ive

PA D

evice

s

Enco

der

Iden

t Sys

tem

s

Wei

ghin

g &

Dos

age

HAR

T on

PR

OFI

BUS

LabA

utom

atio

n

SpecificApplication Profiles

CommonApplication Profiles

XY . . . .

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

Communication Technology


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

Wired RS485 / RS485-IS

MBP / MBP-IS

Engi

neer

ing

Tech

nolo

gies

GS

D, E

DD,

FD

T / D

TM, T

CI

OpticalGlass, PCF, Plastic

Wireless

PRO

FIdr

ive

PA D

evice

s

Enco

der

Iden

t Sys

tem

s

Wei

ghin

g &

Dos

age

HAR

T on

PR

OFI

BUS

LabA

utom

atio

n

SpecificApplication Profiles

CommonApplication Profiles

XY . . . .

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

PROFIBUS supports different transmission technologiesWired, Optical, and Wireless


Connection technologies

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

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, andto solve grounding problem (grounds with un-even earth potential).

Fibre to Copper

OLM (Optical Link Module)OBT (OpticalBus Terminal)

FOCoupler

FOCoupler


Control System Architecture


From DP (RS485) to PA (MBP)

0

-9mA

time

Current/mA

+9mA

1 1 0 0

PROFIBUS PA, MBP

10 mA

4To7

volts

PROFIBUS DP, RS485

0 0

1 1 1


DP & PA Segments

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

M

S

S S

S

S S

S

S

M

S

S

S

SR O O

Segment 1 RS485

Segment 2 RS485

Segment 3 Fibre Optic

Segment 4 RS485

Segment 5 MBP

Repeater

Fibre optic links

C

DP/PA Coupler

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

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


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 length9.6 kbit/s 1 200m

19.2 kbit/s 1 200m45.45 kbit/s 1 200m93.75 kbit/s 1 200m187.5 kbit/s 1 000m500.0 kbit/s 400m1.5 Mbit/s 200m3.0 Mbit/s 100m6.0 Mbit/s 100m

12.0 Mbit/s 100m

Low speeds

High speeds

Middle speeds


PA Segment Cable Length

PA baud rate is fixed at 31.25 kbit/s.

The maximum segment cable length is 1900 meters for non-intrinsically safe applications, and….

1000 meters for intrinsically safe applications


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 CouplerV = 13.4 VDC, I = 100 mA

#13 #14#15

#16#17

T

14 mA 14 mA 14 mA 14 mA 14 mA

Maximum number of PA slaves = 100 / 14 = 7

I actual = 5 x 14 = 70 mA


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


Reflection caused by missing terminator



Reflections

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


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


Termination

Standalone termination boxes are also availablefor DPand for PA

Termination on Repeaters


Termination

1 network with 2 segments.

DP/PA coupler

#1#0 #10 #11

#13 #14#15

#16#17

Power supply for PA segment

TT

T

T


Causes of Reflections

Missing terminatorUn-powered terminatorTerminator switch - faultyExtra terminatorReflection can also be caused by:

Un-certified devices Cable length between two devices is too shortSpurs are used in high speed networksWrong types of cables are usedCores are sharply bent


Allowance of RS485 Spurs

Bit rateTotal allowable spur

capacitanceTotal Spur cable length/segment*

>1.5 Mbit/s None None

1.5 Mbit/s 0.2 nF 6.7 m

500 kbit/s 0.6 nF 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

* Calculated for PROFIBUS cable type A at 30pF/m

One spur @ 6.7m or

6 spurs @ 1.1m each

It is much more flexible @ low speed.


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 lengthnon-intrinsically safe

Maximum spur lengthintrinsically safe

25 to 32 1 m 1 m

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.


Interference

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, andHeavy earth currents on the cable screen.

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Equipotential Bonding


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

Installation: Shielding and Grounding 28

intern


Equipotential Bonding at a Device

Connect the PROFIBUS cable shield to the equipotential bonding at every PROFIBUS station assuming local potentials are equal!

Shielded, twisted-pair cable

Cable shield route to groundRx

Tx Tx

Rx

Connector

Device Device

Red = +Green = -


Connector wiring problems

Which connectors are incorrectly wired?

A CB D


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.


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:

Cable Category II

20 cm

10 cm 10 cm

50 cm 50 cm 50 cm

Cable Category I

Cable Category III

Cable Category IV


Cable Segregation ?

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

Power cable route


Spot the errors


Spot the errors


Spot the errors


Standard connections – PROFIBUS DP37


Standard connections – PROFIBUS PA38

TLink/Coupler

TPROFIBUS DP PROFIBUS PA

Trunk

Spur lines

Devices

Link/Coupler

TPROFIBUS DP PROFIBUS PA TJunction

Box Junction

Box

Spur lines

Trunk

Devices


Spot the errors


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


Design considerations - architecture

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

41


Installation Checklists

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.

42


Practical steps to a successful PROFIBUS project

The very first step to a successful project should be

TrainingPROFIBUS training courses are available for:

Installers,System Designers,Commissioning Engineers, andMaintenance 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

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Certified PROFIBUS Installer Training

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.

44


PROFIBUS System Design Training

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.

45


Summary: Steps to a successfully project

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

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