Industrial Bus Health Test using Fluke 225C Color ScopeMeter Application

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 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 offices 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

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. Network verification

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 The same sections seen in more detail. Main signal cable entering the cabinet 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!