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Profibus Troubleshooting

Profibus
Troubleshooting
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Profibus Troubleshooting

Viscotherm AG
Neuhaus
8132 Hinteregg / Zürich
Switzerland

Tel.: +41 1 986 28 00

Fax: +41 1 986 28 28
Internet: www.viscotherm.ch
Email: info@viscotherm.ch

Document: AP-005e
Datum: 12.02.2002

Softwarestand: V2.0

Disclaimer of liability, copyright

The reproduction, transmission or use of this document or its contents is not permitted
without express written authority. Offenders will be liable for damages. All rights, including
rights created by patent grant or registration of a utility model or design, are reserved.

Technical data subject to change.

We have checked the contents of this manual for agreement with the hardware and
software described. Since deviation cannot be precluded entirely, we cannot guarantee
full agreement. However, the data in this manual are reviewed regularly and any
necessary corrections included in subsequent editions. Suggestions for improvement are
welcomed.

Viscotherm excludes any liability in regards to this document and the relevant software.
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Profibus Troubleshooting

1. Troubleshooting network physics

The most normal failure when the diagnostic tool reports “nonsense” is physical errors on
the network like cable connect errors, miss contact, wrong termination etc. Some simple
ways to find these errors will be mentioned here.
Data errors can occur if the PROFIBUS cable is incorrectly attached to the bus
connectors. Such basic errors can be detected and remedied with the simple test method
described below. The test method shown schematically in figure below allows you to
detect data wires which are swapped over in the connectors. During the test, the bus
connectors must not be connected to any PROFIBUS devices. In addition, all bus
terminating resistors should be removed or disabled. The tests require two 9 pin female
Sub-D test connectors. Test connector 1 is provided with a single pole changeover
switch, the moving contact of which is connected to the shield (case) of the test
connector. The two fixed contacts are connected to pin 3 (data wire B) and pin 8 (data
wire A), respectively. Test connector 2 is used to connect an Ohmmeter to the bus.
During the cable tests, the two test connectors 1 and 2 are initially plugged into the two
bus connectors at each end of the bus segment. The following test can be made by
taking measurements between the contacts 3 and 8 and the shield of test connector 2
while operating the changeover switch on test connector 1:

• Data cable swapped over

• Open circuit of one of the data cables
• Open circuit of the cable shield
• Short circuit between the data cables
• Short circuit between the data cables and the shield
• Additional bus terminating resistors inserted unintentionally
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Profibus Troubleshooting

2. Test configuration

Carrying out the tests

• Configuration A: Set switch of test connector 1 to position 3 (connects pin 3 to

screen). Connect ohmmeter to test connector 2 between pin 3
and the screen.
• Configuration B: Set switch of test connector 1 to position 8 (connects pin 8 to
screen). Connect ohmmeter to test connector 2 between pin 8
and the screen.
• Configuration C: Set switch of test connector 1 to position 3 (connects pin 3 to
screen). Connect ohmmeter to test connector 2 between pin 8
and the screen.
• Configuration D: Switch position of test connector 1 is not important. Connect
ohmmeter to test connector 2 between pin 3 and pin 8.

Warning: The measured value can be falsified if the ohmmeter connection are touched.
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Profibus Troubleshooting

3. Test 1

Start

Configuration A

R < x ohm
R = x ohm
Short circuit R = infinity
Data cable and
beween data cable
screen ok
and screen

Data cable A or or
Cable check
screen open circuit

Configuration B Configuration C

R = x ohm
R < x ohm
R = infinity
R = infinity Screen ok R = x ohm
Data cable B ok Possible short
Data cable A and
Data cable B or Data cable A open circuit between Data cable A and
B or screen open
screen open circuit circuit data cable B and B swapped over
circuit
screen

x = 110 ohm/km
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Profibus Troubleshooting

4. Test 2
Same as test 1 except configuration A and configuration B are exchanged, i.e. start with
configuration B.

5. Test 3
Too many bus terminating resistors inserted.

Start

Configuration D

R < 110 + x ohm

R = 110 + x ohm
Too many
Everything ok
terminators

x = 110 ohm/km

In order to assess the measurements you make, it is necessary to know the loop
resistance of the bus cable segment. This is dependent on the cable type used and the
installed cable length. The locaton of a fault can be determinated without opening up the
bus connectors by unplugging test connector 1 and plugging it into another bus connector
which is closer to test connector 2 while carrying out repeated Ohmmeter measurements
at test connector 2.