Industrial fault scenarios in practice

The customer experienced that starting the machine failed intermittently. In some cases the equipment started normally, while in other cases it did not respond under the same conditions. The fault was especially hard to pinpoint because it did not occur continuously; such intermittent issues can cause significant downtime since the problem may not appear during on-site inspection. During the on-site check, an additional warning was observed: the Siemens SIMATIC S7-300 CPU313 BATF (Battery Fault) LED was blinking.

During troubleshooting, we first examined how the machine start chain works. The checks showed that the PLC always issued the start command, so the issue was not located in the control program. By checking the auxiliary relays in the control cabinet under load, we identified a relay that behaved abnormally: the control signal arrived, but the switching action did not occur in certain instances. Based on measurements, the relay’s internal contact defect caused the starting problem. In parallel, we also checked the PLC status indicators: the CPU313 BATF fault indication suggested that the PLC buffer battery had aged.

Intermittent relay faults are among the most difficult categories of industrial troubleshooting. An internal relay contact may not fail completely, but only lose proper contact under certain conditions. That is why the machine can start correctly one time and fail to start the next. The BATF indication observed during the investigation did not directly cause the starting issue, but it was an important warning: the Siemens S7-300 buffer battery maintains memory during power outages. With a depleted battery, a longer power interruption can lead to program loss or data loss, which can significantly increase downtime.

After every start attempt, the equipment remained in a locked-out state and the control system reported a safety system fault. The „FAULT” message shown on the operator interface alone did not make it clear what was blocking the start, so the machine was not operational.

During troubleshooting it quickly became clear that some element of the safety system was preventing the start. This is especially critical because safety relays and monitoring modules perform person and machine protection functions. If the system detects an irregular condition, it blocks machine start for safety reasons. The goal of the investigation was to precisely determine which part of the safety system was blocking the start.

In case of a safety system fault, a shutdown is often not caused by a defective component, but by a state that does not meet the safety conditions required by the system. After checking the safety system and identifying the root cause, the equipment returned to normal operation in a safe manner.

The equipment would not start, the motor protection repeatedly tripped, and from the operator side only the shutdown itself was visible.

A protective trip on its own does not explain the actual cause. In cases like this, the starter circuit, load side, motor side, and control signal path all need to be checked separately.

The aim was not to replace the full system, but to pinpoint the fault accurately and define the necessary corrective action.

The machine reported a fault and an alarm appeared on the display, but the reason for the shutdown was not immediately clear.

In this type of case, the displayed message, power supply, communication path, and the condition of the related sensors have to be assessed together.

Effective troubleshooting depends on interpreting the visible symptom, the information shown on the display, and the current operating condition as one complete picture.

The motor stopped after a short period of operation and would not restart afterwards. The inverter gave no clear feedback, the display was inactive, and the equipment appeared to be switched off.

With this type of symptom, checking the inverter alone is not enough. The control signals, power supply, and the condition of the related sensors and protective devices also need to be checked.

Not every inverter-related fault points to an actual hardware failure. In many cases, the cause is an interrupted signal or a protective state. The right solution comes from evaluating the full system, not just the inverter on its own.

The entire production line stopped and production could not be restarted. The system did not provide a clear fault indication, and the cause was not obvious at first glance.

During troubleshooting, the control chain was checked step by step: the power supply, starter circuit, control signals, and the related connections.

A wire had partially slipped out of a connector, so the control signal no longer reached the required point. Once the faulty connection was restored, the line could be started again immediately. It is a clear reminder that not every fault requires redesign or major intervention. Even a simple connection fault can cause a complete shutdown, and precise fault finding often leads to the faster and more cost-effective solution.