Transcript Application: Bus Health Test using Fluke 225C

Application
Industrial Bus Health Test
using
Fluke 225C Color ScopeMeter
Application: Bus Health Test using Fluke 225C
ProfiBus Test at the Wavin Plastics factory
• Wavin manufactures large volumes of plastic parts for
infrastructural purposes like tap- and rainwater systems, surface
heating and cooling and last-mile telecom.
• Wavin is best known for its plastic pipes, of various types and
diameters
Application: ProfiBus Test at Wavin Plastics factory
Situation:
• Factory Automation was originally based on centralized
hardware and direct control, using ‘traditional’ control
with e.g. 4-20 mA current loops and with all PLCs
installed in the control room
• Recently, conversion to Profibus control was rolled out in
another section of the factory
The conversion to Profibus allows for better control over production
equipment and offers a data link to the office’s Ethernet
environment.
Hundreds of devices are now connected to the control-room over a
single Profibus network cable.
Network installed
• After installation and start-up, the new system was
handed over to the factory maintenance crew
• The maintenance engineers set up a full verification
of the network
– As an ‘acceptance test’ of the complete network
– To collect reference data for future maintenance
– To collect ‘day one’ data for a preventive maintenance
schedule
Network verification
• A full scan of the network was carried out using a Fluke 225C
Color ScopeMeter with Bus Health Test capability.
• At each individual network
node, all signal parameters
were verified against the
Profibus signal standards….
• ….. and at each node, the
eye-pattern was recorded.
All test results were positive…..
except one.
All is fine, or…?
At one particular bus node,
ScopeMeter indicated an excessive
overshoot in the signal, exceeding the
signal requirements as defined in the
ProfiBus standards
The eyepattern confirmed that a
large overshoot was present on
the pulses, leading to severe
distortion of the bus signal
Overshoots?
On the Profibus main cable (‘the trunk’), overshoots
may be caused by:
• Incorrect cable termination
– i.c. too few or too many terminators switched on
Note: terminators need to be installed only at both physical ends of the
Profibus trunk
• Cable split (“T-split”) in the trunk
• Poor (bad) contact in the trunk
• Incorrect cable lengths between devices
– Making that too many devices are connected at almost the same spot
on to the trunk
• Gives excessive loading of the network
Profibus Standards dictates a minimum distance between device
connections of 1 meter (= 3.3 ft).
The root cause
A further research through the network revealed a cabinet in which
4 devices had been connected with very short wiring in between.
A clear
violation of the
basic Profibus
assembly
rules !
….in detail
Main signal cable
entering the cabinet
The same
sections
seen in
more
detail.
Interconnections within
this cabinet
Remedy
• The 3 cable segments were replaced by segments of 1 m each
• The extra lengths of cable were routed through the cable
support rail
New test results
(measured from the location at which originally the error was seen):
Conclusions
• Errors on an industrial network can be identified easily
using the ‘Bus Health Test’ function of the
Fluke 225C or 215C Color ScopeMeter.
• These ScopeMeters also allow you to find network errors
before the errors bring the network to a full stop.
• Even if a network appears to be working flawlessly,
errors may be in there, which are going to hurt
you – sooner or later.
Better find those sooner than later!
Fluke – Keeping your world up and running!