Profibus commissioning and maintenance - Richard Needham

PROFIBUS
Commissioning
and
Maintenance
Presented by :-
Richard
Needham
Hi-Port Controls

Agenda
Topic 1
Topic 2
Topic 3
2
PROFIBUS Commissioning and Maintenance : Richard Needham - November 2016
PROFIBUS Commissioning & Maintenance
Introduction
PROFIBUS DP essentials
Typical faults which may occur
Important preparations for fault-finding
Tools and expertise needed to tackle problems
Expected PROFIBUS network quality / performance
Examples of typical analyser screen images
Preventive maintenance
What to do when the fault alarm rings!
Commissioning issues
Use test Master in place of operational PLC
Check cable connections & waveforms
Confirm slave address settings
Get slaves into data exchange : run test data
Connect PLC and confirm overall performance

High speed serial network
Bi-directional digital communications
Multi-drop cable array linking Masters & Slaves
Transferring both plant values and control signals
What is a PROFIBUS DP Network?
Master
Slave
1
Slave
2
Slave
3
Slave
4
This is called a Network Segment
3
The Master shown above is usually a semi-autonomous network
controller within a PLC, using shared memory or similar for passing
data between the two. Each is likely to operate at different cycle times
3

Bi-directional digital communications
……but with only one device transmitting at any time…
…as directed by the Master which separately addresses each
slave, one a time, then awaits reply from that device
PROFIBUS resilience is partly derived from the fact that the
Master can cope with occasionally illegal (corrupted) or missing
replies – then asking for a second or subsequent attempt
Only when a device totally fails to reply, will it be indicated as lost
to the PLC which may then stop the operational program, but
generally the Master will continue it’s cyclic scanning of all slaves,
using a special Sync message addressed to the known missing
device in the expectation that it may be able to come back online
later
What is a PROFIBUS DP Network?
4PROFIBUS Commissioning and Maintenance : Richard Needham - November 2016
4

Typical faults which may occur
Failure of expected replies from one or more slaves is the most
common fault symptom
This is most likely to be due to connection network damage
One of the more common causes of connection damage is poor
installation work undertaken when the system was first built
Such poor workmanship may not become apparent or impact on
system reliability for several years, but might then gradually start
to reduce the overall communications quality until eventually
causing failure
Following photos show typical and frequently seen problems!
5

PROFIBUS cable installation problems
6
Wrong plug used Cable sheath not secured
Cable screen not earthed properly Poor cable preparation
Correct strip tool should be used!

What to do first when faults are noted
After seeing that a device or devices are no longer
communicating reliably, or at all, one should first check for
power supply to each, then look for cable breaks or wiring
damage and check for corrupted waveforms
To see which devices are still connected, the
communication reliability and waveform quality one needs
a PROFIBUS Analyser Tool
…..and test point(s) on the network to which it may be
attached!
7

Preparations for fault-finding
Needless to say, one also needs to know how to use any
available tools effectively and have reasonable
appreciation of PROFIBUS wiring and protocol basics!
Accurate network ‘as built’ drawings will be helpful – these
might also usefully include geographic information about
locations of each device within the site, where appropriate
(particularly in multi-level buildings or distributed networks)
And hopefully a historical bench mark report against which
you can compare currently measured performance
8

Test Points for PROFIBUS Analyser connection
We need at least one test point in each network segment
This will allow electrical waveform, voltage and full
message analysis
With usual 9-pin PROFIBUS connectors you will need (at
least) one with a rear PG test socket, as in following slide
9
Master
Slave
1
Slave
2
Slave
3
Slave
4
Test point here

9-pin PROFIBUS DP network plug
Plug for network
cable
connection to
Slave or Master
Optional female
PG rear test
connector
8

Test Points for PROFIBUS Analyser connection
M S S S s
Repeater
s s
Segment 1 – up to 32 devices
11
Test Point 1
Test Point 2
Segment 2 – up to 32 more
The left hand test point will allow a connected analyser to see messages to
and from all devices, but will only faithfully show waveforms and voltages for
devices on segment 1
Although waveforms from devices in segment 2 will be ‘visible’ at Test Point 1,
these can actually show only the waveforms and voltages from the repeater
circuits – hence Test Point 2 is needed to see true values from segment 2
devices!
9

PROFIBUS Analyser Tools
PROFIBUS Analyser Tools are available from a number of
different suppliers
But for this presentation we will show use of the Procentec
ProfiTrace tool. Broadly similar features are provided in
tools from other manufacturers
12
ProfiTrace is supplied as
a suite of computer
programs, with the test
computer connected to a
PROFIBUS network with
USB cable onto a small
ProfiCore Ultra adapter
and a short Tap Lead, as
in adjacent picture and
following slides

Connecting test kit to test point….
13

…..then start test software, and here check device
driver voltages 14

PROFIBUS Analyser connection issues
It is vital that any test equipment connected to an
operational PROFIBUS network does not interfere with
normal operations of that network
Hence use of very short connection links and high input
impedance to the attached test device
Some analysers include local front panel display to allow
performance inspection without need for separate
computer. This can be useful, but will add to the device
size and weight loading on the test point connector
ProfiTrace uses a very small, lightweight adapter, with
scope for long USB cable to computer location
15

What do we want to see on the network?
Network operating speed : bit rate ?
Details of devices connected : their addresses and type ?
What do the waveforms look like : noise, spikes, ringing ?
Is the Idle Voltage correct for 2 terminators ?
Are all connected device driver voltages OK ?
Check failure statistics for lost, repeats and syncs ?
A good network should show 1 volt idle voltage, square
waveforms and no message repeats (or losts / syncs)
Following slides show typical ProfiTrace images
16

Initial ProfiTrace Live List display
Typical Live List view after
connection to running
network
Network speed
displayed here
Slave with address 66
- here in normal data
exchange
Master with
address shown
as red number
17
Slave with extended
diagnostic errors
15

Oscilloscope waveform and voltage display
Double-click on the
device legends to see
associated waveforms
from each
Horizontal Time
Scale
Vertical Voltage
Scale
Display cursors
Note bit interpretation shown
hereSelected device
address
confirmed here
Check important idle
voltage level is at 1
volt as set by
terminators
16

12 Mbps example waveform on large network
19

More usual waveform shape, but with spikes
20

Large network bar graph example
21
This photo shows the individual driver voltages from all connected
devices as seen at test point

Topology Scan : Typical result report
Start the Topology
scan
Total cable
length
Cable length between
devices
20

Preventive Maintenance
In addition to fault-finding work, PROFIBUS Analysers, such a
ProfiTrace, should be used on a regular basis to check on
continued performance of all networks, including low level stats
This will not only help to identify any gradually degrading
network performance issues, but may also help to identify
increasing incidents of interference or device weaknesses (as
seen through increasing numbers of message repeats)
When weaknesses are identified, these may be addressed
immediately, or tracked over time to the point where they are felt
to threaten overall network reliability due to increasing numbers
Scans of this nature also help keep staff fluent and familiar with
the test tools (and network documentation) to ensure optimal
effectiveness when a major network failure occurs
23

High availability network maintenance
Networks which MUST be kept running safely and securely,
including those with personal safety or very high failure
costs may be fitted with automatic 24/7 performance
monitoring and fault reporting kit
For this requirement Procentec provides it’s ComBricks
range of modular repeaters which can be programmed (by
maintainers) to check, log and alert on typical network
performance issues such as redundant power supply
failures, message repeats, lost devices etc. Such reports are
logged to local microSD memory cards, but may also be
sent as email alerts to maintenance staff, then allowing dial-
in access to see both current real-time network status and
recorded information, using a browser program
Broadly equivalent devices are provided by other firms
24

Location of faults in distributed systems
It is worth mentioning that even with the best tools, fault-
finding in such distributed control or monitoring systems can
be very challenging!
In some cases, fault symptoms may not appear anywhere
near the fault itself
For example, failure of a terminator at the end of a segment
may lead to missing or corrupted messages from devices a
long way back down that segment, cause by reflections
Some faults may also trigger multiple different symptoms,
so it is worth realising that, with a previously reliably
network, any new failure will usually only be caused by 1
fault……….
…unlike when commissioning a new system, where multiple
faults may need to be found and sorted, one by one
25

Commissioning using ProfiTrace
ProfiTrace can be used in place of a PLC/Master on a new
network to confirm cable integrity, connected device
addresses and operation of these devices
In this case the ProfiCaptain Master software is arranged to
drive the network, scanning and reporting connected devices.
Although connected devices will not (at least initially) here be
operating in the usual Data Exchange, normal waveforms, bar
graphs, topology scan (diagramming) and message statistics
features of ProfiTrace will all work – and the addresses of any
software settable devices may be changed online
26
ProfiCore
Ultra
Slave
1
Slave
2
Slave
3
Slave
4

27
Step 1 : scan for connected devices,
showing addresses of each using
ProfiCaptain Stop mode. This checks
cables and device address settings
Step 2 : Run Class 2 Scan for device
Identifiers. Name details then taken
from associated GSD files for each
Step 3 : Filter GSD file list to those for these
devices only, select required options for each,
then bring devices online and into full Data
Exchange - may allow test data checks too

If GSD files are available for the connected devices,
ProfiCaptain may be used to Scan the network for
identification of all devices, replacing the device addresses
with better details in the Live List (& printable) reports
One may then automatically filter the available GSD file list to
isolate only those for connected devices and so help to quickly
set-up and bring each into full Data Exchange. This may then
allow automatically changing test patterns or fixed data values
to be output to these to help verify operation / setup
These procedures may be applied to individual cabinets or
sections of a network, without final PLC. This can be done
before shipping to site, as part of a factory acceptance test,
then again on-site once all other sections are connected
Once the final PLC is available ProfiTrace may be used to
confirm correct operation of the completed network!
28

Review and wrap-up
In the above slides I have attempted to highlight some of
the most important issues that need to be considered for
successful PROFIBUS DP network commissioning and
maintenance
This has been a very rapid review of a complex topic and
in no way claims to have covered all aspects. For
example, I have made no reference to PROFIBUS PA or
AS-i networks, which you may also need to understand
For more comprehensive introduction to PROFIBUS you
should look into joining a one day Certified PROFIBUS
Installer Course, which is not only intended for installers,
but also for managers, designers, bidding teams etc –
thereafter a 1 day Commissioning and Maintenance
Course is also available
For further discussions and ProfiTrace demo see our
exhibition stand here today!
29

Speaker contact details
For further information contact :-
Richard Needham -- Hi-Port Controls
Tel : 02392 552855 Mob : 07739 847277
richard@hiport.co.uk
Website : www.hiport.co.uk
30

What to do when the fault alarm rings!
Assuming this may be due to a PROFIBUS related issue,
find your test kit and any associated computer that may be
needed to run it!
Before you leave the office, check it works and you know
how to use it! – a few minutes here may well save lots of
embarrassment later
If ProfiTrace is used, connect the ProfiCore Ultra to your
computer and run the self check procedure. This will
confirm that your test software is working, that the
PROFIBUS to USB adapter is working and that you have
the correct licence files in place
It can also provide a useful reminder of how to run the
software before you reach the shop floor!
You’re now ready to go!
31

Profibus commissioning and maintenance - Richard Needham

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