PLC Fault Evidence Worksheet and Troubleshooting Record
Build one traceable record from the physical symptom through input, logic, output and field action, then document cause testing, authorized correction and functional verification.
Beginner → Intermediate → Advanced workflow
- Beginner—define the event: record a non-confidential reference, operating mode, sequence step, exact symptom, expected response and last known normal cycle.
- Intermediate—trace every boundary: compare the physical input with the module and PLC state, follow permissives and logic, then trace the output through the interface device to field action and feedback.
- Advanced—test and verify: document the hypothesis, supporting and contradicting evidence, authorized corrective action, restored safeguards and representative post-repair test.
Prerequisites: complete the PLC Troubleshooting Guide and use the approved site/OEM method. This worksheet structures evidence; it does not authorize PLC access, electrical work, program changes or operation of equipment.
Use one row per fault event or controlled training scenario
Keep the original event intact. If the mode, sequence step, load, controller revision or test condition changes materially, preserve the earlier evidence and create a linked record. Do not overwrite the initiating alarm order after a reset or replace a pre-repair observation with the successful retest.
Use generic training-system descriptions when a record may leave the site's controlled environment. Store production asset identifiers, program revisions, screenshots, network information and work-order evidence only in authorized systems with appropriate access control.
Field groups and intended use
Event and operating context
- Machine_Mode / Sequence_Step: establish where the automatic or manual process stopped and who owned the command.
- Symptom_Observed / Expected_Response: separate what physically occurred from what the approved sequence required.
- Alarm_Event_Order / Last_Known_Normal: preserve the initiating evidence before reset, acknowledging any clock differences.
- Recent_Work_or_Change: record relevant maintenance, power, network or configuration activity without assuming it caused the fault.
Input, logic, output and field-action evidence
- Physical_Input_Condition / Input_Module_Indication / PLC_Input_Tag_State: compare each boundary rather than treating a screen indication as proof of the physical sensor.
- Permissive_or_Interlock_State / Logic_or_Sequence_Evidence: state the missing or satisfied conditions using approved cause-and-effect information. A false interlock may be correct protection.
- PLC_Output_Command_State / Output_Module_Indication / Interface_Device_State: trace the command through the output channel, remote I/O or relay boundary.
- Actuator_or_Field_Action / Feedback_Return_State: confirm both the requested movement and the feedback needed for the next sequence step.
Diagnostics, hypothesis and cause testing
- Device_or_Module_Diagnostics / Network_or_Remote_IO_Observation: record approved diagnostic observations and their timestamps, not copied proprietary configurations.
- Hypothesis_Tested / Test_Method_or_Observation: describe one safe testable explanation and how it was examined.
- Supporting_Evidence / Contradicting_Evidence: retain facts that move the hypothesis up or down; contradictory evidence prevents premature parts replacement or program edits.
- Cause_Status: distinguish suspected, supported, confirmed under the approved process and inconclusive.
Correction, safeguards and verification
- Corrective_Action / Change_Control_Reference: connect authorized work to the supported cause and controlled revision process.
- Safeguards_Restored: confirm temporary test arrangements are removed and guards, interlocks, modes and access controls are restored.
- Functional_Test_Condition / Post_Repair_Result: test the affected command, permissive, field action, feedback, alarm and safe-stop behavior under a representative approved condition.
- Recurrence_Monitoring / Follow_Up: define what will be checked, by which role and when; a cleared alarm alone is not proof of repair.
Record quality check
- Confirm the correct machine, controller or training system before recording an observation.
- Separate physical evidence, PLC indication, interpretation, suspected cause and confirmed cause.
- Preserve timestamps and state whether clocks were synchronized.
- Record the operating mode, sequence step, process state and load needed to make retest evidence comparable.
- Capture both supporting and contradicting evidence before recommending a component or software change.
- Verify the complete function and restored safeguards after authorized corrective work.
Connect the worksheet to the LMS practical logbook
After removing confidential details, summarize the engineering lesson—not the protected controller data—in the browser-local Practical Logbook. Select PLC / Automation, describe the generic symptom and reasoning, state what evidence changed your hypothesis, and record the next learning action. The logbook is an educational reflection, not a formal competency or maintenance record.
Safety, cybersecurity, privacy and engineering limitations
This worksheet is not an approved troubleshooting procedure, electrical test method, controller backup, program-change record, safety validation, work order or authorization to connect to operational technology. It intentionally provides no universal voltage, timing, network, fault-code, bypass or shutdown limits.