Technical White Paper Fieldbus Testing with Online Physical Layer by lindahy

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Technical White Paper Fieldbus Testing with Online Physical Layer

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									                            Technical White Paper

                            Fieldbus Testing with Online Physical Layer Diagnostics

                            The significant benefits realized by the latest fully automated fieldbus
                            construction     &   pre-commissioning   hardware,   software   and   test
                            methodology




                            Prepared by:
26/09/2006 TDOCT-1107_USA




                            Gunther Rogoll
                            Senior Manager P+F fieldbus technology

                            Ren Kitchener
                            Fieldbus Specialist P+F fieldbus technology




                                                                                                         Released EDM checkout 2006-SEP-28
Released EDM checkout 2006-SEP-28
                                                                                                         Fieldbus Testing with Online Physical Layer Diagnostics



                            1    Abstract .................................................................................................................................................... 1


                            2    Introduction.............................................................................................................................................. 1


                            3    How is Commissioning Achieved with Fieldbus Today? .......................................................................... 1
                                 3.1       AG-181 Overview .............................................................................................................................. 1


                            4    Fieldbus Testing Using Advanced Physical Layer Diagnostics................................................................ 2
                                 4.1       The New Commissioning Strategy ................................................................................................... 3
                                 4.2       The New Test Procedure .................................................................................................................. 3
                                 4.3       The Revised Test Procedure ............................................................................................................ 4
                                 4.4       Partially Constructed Sites ............................................................................................................... 5


                            5    Fault Finding & Troubleshooting Procedure............................................................................................ 5
                                 5.1       Primitive Faults ................................................................................................................................. 5
                                 5.2       The Process of Elimination............................................................................................................... 5
                                 5.3       Further Troubleshooting Using the Inline Oscilloscope .................................................................. 6
                                 5.4       Elimination Method .......................................................................................................................... 7
                                 5.5       Savings Case Study .......................................................................................................................... 8


                            6    Summary .................................................................................................................................................. 9
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                            1 Abstract                                                level, with supporting automated documentation,
                                                                                      assuring uncompromised segment quality and
                            The utilization of online advanced physical layer
                                                                                      availability for the customer.
                            diagnostic systems for automated construction
                            and pre-commission test and report generation,            3 How is Commissioning
                            up to the point of loop check-out.                          Achieved with Fieldbus Today?
                            2 Introduction                                            The Foundation Fieldbus™ Engineering Guide
                                                                                      ‘AG-181; section 11’ sets out a detailed proce-
                            Fieldbus has fully matured following its cautious
                                                                                      dure for installing and commissioning fieldbus
                            introduction back in the late 1990s: Many of the
                                                                                      segments. Whilst this guide is relevant for Field-
                            major projects are now using digital fieldbus
                                                                                      bus testing, it still maintains the need for techni-
                            technology as the preferred platform for control
                                                                                      cally advanced manual testing, using sophisti-
                            and instrumentation.      Most of the lessons
                                                                                      cated manually operated test equipment and
                            learned from the early projects have been im-
                                                                                      hand completed test sheets.
                            plemented successfully for the current projects,
                            and there is no doubt that the companies re-              3.1 AG-181 Overview
                            sponsible for commissioning are seeing a                  The guide assumes that at least one set of test
                            marked improvement in the commissioning times             equipment is made available, comprising:
                            with a resulting reduction in CAPEX.
                                                                                          1. Digital multi-meter for current, voltage
                            With the recent introduction of online Advanced                      and resistance.
                            Physical Layer Diagnostic equipment, the transi-
                                                                                          2. Advanced capacitance meter capable of
                            tion to a fully automated network test and report-
                                                                                                 independent RC measurement.
                            ing program reduces the time and cost for con-
                            struction and commissioning even further by                   3. Digital storage oscilloscope.
                            optimizing the test process and report genera-
                                                                                          4. Handheld fieldbus signal and data
                            tion.
                                                                                                 analyzer.

                            The release of the new Advanced Physical Layer                5. Set of paper test sheets, pens and
                            diagnostic equipment will of course need a re-                       screwdrivers.
                            vised, yet vastly simplified, construction and
                            commissioning      procedure   requiring   minimal        The test equipment is used to check and test one
                            technical expertise.                                      segment at a time, and provisions must be made
                                                                                      to identify the segment terminals and special
                            This paper will provide an insight into fieldbus          terminals or adaptors should be made available
                            commissioning and how it’s achieved today, with           for connection of the various meter probes.
26/09/2006 TDOCT-1107_USA




                            an overview of how significant savings can be
                            made using advanced physical layer diagnostics            Many correctly installed terminals have no ex-
                            for high speed automated construction and                 posed conductor to clip test probes to. Therefore,
                            commissioning testing with automated test re-             ‘eyelets’ should be provided for testing, then
                            port generation.                                          removed after testing as they are exposed and
                                                                                      not insulated. Alternatively, wires must be re-
                            It also provides the ‘handover’ of a system that          moved from the terminals and replaced after
                            will have been fully checked to a higher technical        testing.

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The test procedure basically covers the following         AG-181 also requires wires, which are already
test activities:                                          terminated, to be disconnected for testing and
                                                          then reconnected after testing. This can give rise
    1. Cable continuity and isolation tests.              to potential failure issues if the terminals are not
    2. Cable resistance and capacitance                   correctly re-installed.
         checks - pole to pole, pole to shield, ca-
                                                          Furthermore, hand completed paper documents
         pacitive unbalance and grounding
                                                          can be prone to errors, omissions or ultimately,
         quality.
                                                          falsification, where signoffs and handovers may
    3. Signal communication level analysis and            not be complete, particularly when under ‘time
         limits.                                          penalty’ pressures.
    4. Noise level analysis and limits.
                                                          The result is a lengthy test procedure, with poten-
    5. Oscilloscope signal capture and detailed           tial errors, which will take time and require expert
         waveform analysis.                               fieldbus knowledge, particularly if there is a de-
    6. Completion of paper documentation.                 viation from the test specification limits.

These test requirements demand far more time              4 Fieldbus Testing Using
and expertise when compared to an equivalent 4-             Advanced Physical Layer
20 mA cable, and require a high level of meas-              Diagnostics
urement accuracy using highly skilled engineers
                                                          With the introduction of Online Advanced Physi-
able to interpret the advanced information.
                                                          cal Layer Diagnostics [APLD], it is now possible to
                                                          test the entire network automatically at the
Additionally, manual testing, in accordance with
                                                          ‘touch of a button’. Furthermore, it is now possi-
AG-181, requires a degree of electronic signal
                                                          ble to test many more physical layer attributes,
analysis using oscilloscopes, and AC measur-
                                                          above that required for AG-181, with very little
ing/analyzing equipment.       Whilst oscilloscope
                                                          knowledge of the fieldbus physics, and create
data is extremely useful, to understand many of
                                                          software driven reporting with simplified result
the potential faults that can occur, or exist, would
                                                          summaries that can easily be understood.
require specialist signal analysis knowledge be-
yond that required for AG-181 implementation.
                                                          The APLD is able to test, validate and report:
In-band noise, power supply impedance prob-
lems, signal jitter errors or inverted signals would      Trunk current measurement
not normally be revealed when following the               Data Jitter measurement
guidelines within AG-181, and these unseen
                                                          Data signal amplitude and amplitude variations
failures could create problems during loop
                                                          Shield to pole capacitive and resistive unbalance as a
checkout or they may create problems much                 percentage for each pole.
further down the line.
                                                                                                                             26/09/2006 TDOCT-1107_USA




                                                          Direct pole to pole short circuit

Certainly, to perform an adequate test to reveal          Full spectral frequency analysis

all of the potential faults or unseen failures would      Trunk voltage measurement
require further lengthy analysis and calculation          ‘Signal inverted’ warning
using more sophisticated test equipment and
                                                          Digital storage oscilloscope for troubleshooting
extensive engineering knowledge.



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                            The latest generation of APLD, used for auto-               4.2 The New Test Procedure
                            matic test, is integrated within the power supply           From the maintenance or test PC, each Ethernet
                            architecture, so that wiring or electrically con-           home run will test and report 124 segments
                            necting test equipment into each segment is                 automatically, one after the other.
                            eliminated.
                                                                                        Each segment will be tested for:
                            Fig. 4-2 illustrates how the APLD module is inte-
                            grated within a fieldbus power hub, then daisy                      1. Compliance or conformance with
                            chained into other power hubs and segments,                              AG-181 section 11.
                            with a capability of monitoring and testing                         2. Compliance with IEC-61158-2
                            124 segments for each Ethernet spur. It can                              (fieldbus standard).
                            easily be seen that the interconnecting wiring for
                                                                                                3. Compliance with FF-831, power sup-
                            the test equipment is minimized, and it will be
                                                                                                     ply impedance and
                            left in place, without further connection or dis-
                                                                                                     compatibility.
                            connection for online diagnostics during the op-
                            erational lifetime of the plant.                                    4. Operation, conformance and func-
                                                                                                     tionality of cable, devices, termina-
                            4.1 The New Commissioning Strategy                                       tors, power supplies and protection
                            Today’s modern technology with rigorous test                             electronics.
                            requirements will exhibit very low failures when
                            installed. The cable installation generally reveals
                            a failure, of one type or another, of much less
                            than 2%. Based on this figure, only 2 segments
                            per 100 would be expected not to function first
                            time, therefore, 98 segments would function first
                            time without any failures. This reinforces the
                            option for complete installation and test at the
                            same time. After all, where the majority of seg-
                            ments will work first time, it would be pointless to
                            approach testing with a view that all instruments
                            and cable runs will fail.

                            In conclusion, the new strategy will adapt a
                            faster, more accurate method of testing by way of
                            fully constructing each segment and testing it
                            automatically in ‘one hit’. Thereafter, any failure
                            can be dealt with in a sequential manner.
26/09/2006 TDOCT-1107_USA




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4.3 The Revised Test Procedure
The test procedure for automated test and reporting is shown below:




Fig. 4-1




                                                                                                        26/09/2006 TDOCT-1107_USA




Fig. 4-2




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                            4.4 Partially Constructed Sites
                            Where the control system and/or supporting fieldbus power supplies are not on site or cannot be installed,
                            mobile diagnostic automatic test equipment (ATE) equipment can be considered where the mobile ATE can
                            provide the same level of automation and reporting albeit on a segment by segment test basis.

                            Fig. 4-3 illustrates the connection of a mobile diagnostic system powered by a portable reference fieldbus
                            power supply with additional integrated terminators. This system can also be used to interrogate devices
                            independent of the fieldbus network.




                              Fig. 4-3




                                                                                      5.2 The Process of Elimination
                            5 Fault Finding & Troubleshoot-
                              ing Procedure                                           It would be anticipated, but not expected, that a
                                                                                      low percentage of segments will fail, some of
                            5.1 Primitive Faults                                      which may show more than one failure. The
26/09/2006 TDOCT-1107_USA




                            If the software reports failures, troubleshooting         automated test system will provide a diagnostic
                            using a ‘process of elimination’ has to be per-           report displaying a number of possible failures.
                            formed. First, though, primitive failures, such as
                                                                                      But first, the elimination process will be by far the
                            power supply voltage loss or trunk short circuit
                                                                                      quickest method to assess the probable type and
                            need to be ruled out.
                                                                                      position of the fault.




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The flow chart Fig. 5-2 demonstrates how the              Eliminated cable and junction box disturbance

process of elimination is undertaken.                     Also, disturbance to the control room marshalling
                                                          cabinet cable network, patch bays, or having to
5.3 Further Troubleshooting Using the
                                                          open field junction boxes to connect oscillo-
    Inline Oscilloscope
                                                          scopes, can lead to additional faults. Using an
As described earlier, there will be a degree of
                                                          inbuilt online oscilloscope eliminates the need to
expected failures. Whilst assessing a faulty seg-
                                                          disturb any hardware until a specific targeted
ment, further detailed oscilloscope data can be
                                                          repair is required.
viewed for more advanced troubleshooting analy-
sis.                                                      A record also for remote use

                                                          The oscilloscope data can be recorded, in a very
The fieldbus oscilloscope bridges the gap be-
                                                          simple way, on the maintenance terminal. This
tween automatic diagnosis and manual trouble-
                                                          way, a record can be found, and the information
shooting where further in-depth information can
                                                          can also be sent to a remote expert for
be assessed by competent engineers from an
                                                          additional    troubleshooting,       again      saving
inbuilt dedicated digital storage oscilloscope with
                                                          valuable time.
a vast selection of trigger point options:

An oscilloscope is by far the best tool for trouble-
shooting unusual or complex network faults, and
integrating the oscilloscope within the diagnostic
module has many advantages:

Valuable time saving during failure tracking

Integrating an oscilloscope into the diagnostic
module can save a great deal of downtime /
troubleshooting time – time spent finding and
reading the drawings, tracking down the correct
terminals and connecting the test probes to the
terminal points in the control room marshalling            Fig. 5-1 Oscilloscope example with zoom capability,
                                                           a host of dedicated trigger point options and digital
cabinets and so on.                                        storage
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                            5.4 Elimination Method
                            See also Fig. 4-2 and Fig. 4-3
26/09/2006 TDOCT-1107_USA




                            Fig. 5-2




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5.5 Savings Case Study                                           The range seems to vary between 10 minutes per
This case study will provide an example of how                   loop (a check), and up to 2 hours per loop (a
much time can be saved when using an auto-                       check inclusive of repair work) depending on the
mated test system.                                               project   definition.   For    a   4-20 mA     system,
                                                                 30 minutes per 4-20 mA loop will result in over 2
This case study will consider:                                   ¼ months worth of qualified and experienced
                                                                 engineering based on an 8 hour shift per day,
Number of instruments         1,200
                                                                 and a full working week. This case study will con-
Number of segments            100 (12 in-                        sider a shorter time estimate.
                              struments per
                              segment)
                                                                 Pre-commissioning can be grouped with con-
Man day                       8 hours
                                                                 struction, but for simplicity, pre-commissioning is
Mean time to         repair   4 hours                            grouped with commissioning where the common
(MTTR) a fault
                                                                 aspect of control loop checking is ignored as this
Every project varies with regard to engineering                  will be the same for any hardware model.
staff levels and time schedules. Other factors
such as the process or the product to be manu-                   It is also assumed, for this case study, that
factured and the environment also play an impor-                 during construction and pre-commissioning /
tant part in overall expenditure, so the estimates               commissioning, there will be 1 ½ % failure with
are general, but they do give an overview of the                 1% attributed to cable failures and ½ % due to
vast savings potential.                                          hardware failures.

Some contractors will allow a team up to
30 minutes for construction testing, pre-commis-
sioning checks and repair per instrument loop.

                                                              MODEL
Task
                                                                                   Fieldbus without      Fieldbus    with
                                                              4-20 mA
                                                                                   diagnostics           diagnostics

Constructional checks - each cable will be checked for:
continuity, pole to pole and each pole to shield isolation    5 minutes     per    10 minutes per
                                                                                                         Not required
and a test sheet completed. Allowing for time to read the     cable                segment
drawings and locate the terminals and connect the cable
testers.
                                                              1,200 instrument
NOTE: For fieldbus, additional cable resistance and ca-                            100    segments:
                                                              cables: 1,200 x 5
pacitance checks are required. For fieldbus with diagnos-                          100 x 10 = 1,000      Not required
                                                              = 6,000 minutes
tics, the cable can be checked at the same time as pre-                            minutes or 2 days
                                                              or 12 ½ days
commissioning checks are performed.

Construction failures: anticipated percentage of cable        1%       predicted   1%       predicted
failures and the time taken to repair the fault based on a    failure = 12, 4-     failure = 1, trunk,   Not required
4 hour ‘mean time to repair’ (MTTR).                          20 mA loops          12 spurs
                                                                                                                                    26/09/2006 TDOCT-1107_USA




NOTE: Fieldbus has the same number of spur cables as
the 4-20 mA model, plus an additional trunk cable.                                 13 x 4h = 6 ½
                                                              12 x 4h = 6 days                           Not required
                                                                                   days

Pre/commissioning instrument checks
4-20 mA Analogue - each instrument should be tested           10 minutes per       60 minutes per        8 minutes per
with a loop calibrator or handheld tester to ensure correct   cable                segment               segment
device polarity, operational voltage test and loop current




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                                                                                          MODEL
                            Task
                                                                                                                 Fieldbus without     Fieldbus    with
                                                                                          4-20 mA
                                                                                                                 diagnostics          diagnostics
                            check for both analogue inputs and analogue outputs with
                            a test sheet completed.
                            Fieldbus - each network should be tested to ensure cor-       1,200 instrument
                                                                                                                 100    segments:     100 segments:
                            rect device communication, signal and noise quality, tag      cables: 1,200 x
                                                                                                                 100 x 60 = 6,000     100 x 8 = 800
                            number and address validation, power supply voltage test      10 = 12,000
                                                                                                                 minutes or 12 ½      minutes or 1.6
                            with a test sheet completed.                                  minutes or 25
                                                                                                                 days                 days
                                                                                          days
                            NOTE: The advanced diagnostic model will test many
                            more physical layer parameters in a shorter time.

                            Pre/commissioning failure: anticipated failures and the       0.5%     predicted     0.5%     predicted   1.5% predicted
                            time taken to repair the fault based on a 4 hour ‘mean        failure = 6, 4-        failure =~ 1 seg-    failure =~ 2
                            time to repair’ (MTTR)                                        20 mA loops            ment                 segments
                            NOTE: Fieldbus with diagnostics will include the predicted
                            cable failures.                                               6 x 4h = 3 days        1 x 4h = 1/2 day     2 x 4h = 1 days


                            Construction and commissioning times in man-days              46.5 days              21.5 days            2.6 days




                            6 Summary                                                         Furthermore, electronic reporting will be accurate
                            Construction and pre-commissioning / commis-                      and complete allowing project managers to as-
                            sioning time saving is a very important considera-                sess progress effectively.       From the data, the
                            tion, but it should not compromise accuracy,                      repair time as a percentage of testing time can
                            quality and reliability.                                          be    accurately     assessed     allowing   for    pre-
                                                                                              commissioning optimization. The integrated test
                            Using APLD will increase the test performance,                    equipment eliminates cable interference and its
                            reduce time and accurately report without addi-                   transition into the operational phase would be
                            tional skill sets or an increase in staffing levels.              effortless as well as extremely cost effective.
                            In fact, it is possible to reduce the skill sets and
                            staffing levels to only one on-site and/or off-site               Finally, the handover to the customer would have
                            fieldbus specialist to focus only on the antici-                  followed a thorough and accurate test sequence
                            pated or more complex failures if and when they                   that will cost effectively guarantee quality, per-
                            occur - even going as far as to say that the                      formance and reliability.
                            equipment supplier may provide expert engineers
                            to aid construction and commissioning, but only
                            during failure assessment when they are needed.

                            There is no doubt that using non-intrusive auto-
                            matic test equipment for construction and com-
26/09/2006 TDOCT-1107_USA




                            missioning will save significant time, perform
                            many more complex test measurements, and
                            automatic test and reporting can accurately and
                            reliably uncover tolerated faults that could cause
                            failure during operation or when a compound
                            failure would result in a fatal error later on during
                            the operational phase.


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