PLC Fault Tracer From an Operator Symptom

Prompt

I want you to act as a controls troubleshooter. An operator reported this symptom: "${Operator symptom:Conveyor 3 starts, then drops out after a few seconds}". Platform: ${Platform and version}. I am pasting the source of the blocks, routines or POUs involved, the calling order from the main task, and the I/O list.

Start from the output or fault that misbehaves, ${Tag that misbehaves:the motor run output}, and trace it backward across every block. Give a table:
Hop | Block / routine / network / line | Exact condition for this hop | Tag I must watch online to confirm it

Then:
1. List every write to each tag in the chain, in every block, including both branches of every IF and writes that happen after a block call.
2. Say which block calls which, and whether any call is conditional.
3. Rank your top 3 hypotheses for the symptom, each with one read-only check that would confirm or rule it out.
4. List what you cannot see from this code: HMI writes, network or comms partners, forces, hardware configuration, blocks I did not paste.
Do not propose a fix yet. I will send back live values for your watch list first.

=== CODE (all blocks involved) ===
${Paste block sources}

=== I/O LIST ===
${Paste I/O list}

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Context cost: ≈305 tokens when used.

Why this score

Quality checklist

• ✓ Sets a role: yes
• ✓ States a clear task: yes
• ✗ Gives context: no
• ✓ Sets constraints: yes
• ✓ Defines the output: yes
• ✓ Breaks work into steps: yes

The checklist is automatic and applies the same rules to every prompt. It checks structure, not whether the output is good. Prompt scores aren't comparable with tool scores. How we rank

Security

Scanned Nov 4, 2026 at the text shown on this page, with Cisco's open-source skill-scanner.

None of the patterns we list turned up: shell commands, network requests, reading environment variables, downloading and running code, or installing packages.

A scan lists patterns in the code. It can't prove an add-on is harmless, and it can miss things, so read what you install. How we scan

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