profibus commissioning and maintenance - richard needham

PROFIBUS

Commissioning

and

Maintenance

Presented by :-

Richard

Needham

Hi-Port Controls

Agenda

Topic 1

Topic 2

Topic 3

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PROFIBUS Commissioning and Maintenance : Richard Needham - March 2017

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

PROFIBUS Commissioning & Maintenance : Introduction

PROFIBUS network technology can provide robust, long-lasting network reliability and resilience Special tools are needed for checking and confirming the performance quality of each new installation Contractor claims that a new network is ‘clearly working’ needs to be queried with request for proof! How well is it working? What can such tools do? What are the quality indications? New system performance reports : essential benchmark for on-going maintenance work! How can these tools be used later for ongoing preventive maintenance and fault-finding

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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

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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


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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 awaiting 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, after more than one request, 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, now sending special Sync messages addressed to the known missing device in the expectation that it may be able to come back online later Important : System may have stopped, but Master still working!

What is a PROFIBUS DP Network?

5 PROFIBUS Commissioning and Maintenance : Richard Needham - March 2017

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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!

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PROFIBUS cable installation problems 7


Wrong plug used Cable sheath not secured

Cable screen not earthed properly Poor cable preparation

Correct strip tool should be used!

PROFIBUS cable installation problems

Ideally new PROFIBUS cables should only be installed by properly Certified PROFIBUS Installers Expecting a normal electrical wiring contractor to do this special high speed data wiring job properly is unreasonable…. …only a little extra training is required, but this can make a huge difference later All new cable installations should be checked for continuity, short circuits and crossed connections before slaves are installed and powered Additionally, correct orientation of all IN and OUT wires at each new 9-pin PROFIBUS connector should be checked, as the OUT wire will be disconnected when local terminator switch is set (as may be needed later for fault location work)

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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!

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Moving on now to in-service failure response…

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

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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

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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


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Separately

marked IN and

OUT cable

locations

Test Points for PROFIBUS Analyser connection

M S S S s

Repeater

s s

Segment 1 – up to 32 devices

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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!


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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

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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…. 15


…..then start test software, and here check device

driver voltages 16


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 comfortable computer location

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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 any 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

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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

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Slave with extended

diagnostic errors


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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

here Selected device

address

confirmed here Check important idle

voltage level is at 1

volt as set by

terminators


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12 Mbps example waveform on large network 21


More usual waveform shape, but with spikes 22


Large network bar graph example 23


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


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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 frequency 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

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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

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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, caused by reflections Some faults may also trigger multiple different symptoms, so it is worth realising that, with a previously reliable network, any new failure will usually be caused by only 1 fault………. …unlike when commissioning a new system, where multiple faults may need to be found and sorted, one by one

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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

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ProfiCore

Ultra

Slave

1

Slave

2

Slave

3

Slave

4

Commissioning using ProfiTrace 29


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

Commissioning using ProfiTrace

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!

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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!

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Speaker contact details

For further information contact :- Richard Needham -- Hi-Port Controls Tel : 02392 552855 Mob : 07739 847277 [email protected] Website : www.hiport.co.uk

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mailto:[email protected]

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!

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profibus commissioning and maintenance - richard needham

Engineering