AI-Powered PLC Fault Diagnosis
A maintenance operator reported the shear relief staying out on a palletizer. Our AI analyzed the ladder logic and identified the root cause in seconds -- tracing through timer logic, sensor states, and downstream interlocks to deliver actionable troubleshooting steps.
A Routine Maintenance Call
During a production shift on a palletizing line, the machine operator noticed the shear relief mechanism was staying extended continuously. Under normal operation, the shear relief should only activate briefly during specific phases of the stack pushing cycle.
The maintenance technician needed to understand which part of the PLC program controlled the shear relief, what conditions were supposed to govern its operation, and what could cause it to stay activated.
Instead of spending hours tracing through hundreds of rungs of ladder logic in Studio 5000, the technician uploaded the ACD file to PLC Company and asked the AI a simple question.
“The operator reported the shear relief staying out all the time.”
-- Maintenance technician, via AI chat
From Question to Root Cause
The AI traced through the ladder logic, identified the controlling rung, and delivered a complete root cause analysis with troubleshooting steps.
Technician's Question
The operator reported the shear relief staying out all the time
AI Analysis
Root Cause Analysis
The shear relief is controlled in PNL20_Outputs Rung 3:
The shear relief timer ShearReliefTON starts timing when StckPreStopSensor is NOT active (XIO = examine if open).
Why It Is Staying Out
- StckPreStopSensor is likely stuck OFF/False -- This sensor should normally be ON when there is no stack present at the pre-stop position
- When StckPreStopSensor = False, the XIO instruction becomes TRUE, causing ShearReliefTON to continuously time
- ShearReliefTON.DN stays TRUE once the timer completes, which affects the stack pusher interlocks in PNL20_Outputs Rung 1
Impact on Stack Pusher Operation
Looking at PNL20_Outputs Rung 1:
The stack pusher stop logic requires ShearReliefTON.DN to be TRUE. If this timer is always running due to a bad sensor, it keeps the downstream interlocks permanently enabled.
Follow-up Question
What would StckPreStopSensor look like to check it?
AI Analysis
Physical Sensor Identification
Tags to Monitor in PLC/HMI
Physical Location
- Mounted on the stack pusher mechanism near the pre-stop position
- Connected to Panel 20 (PNL20) via IFM IO-Link module
- Wired to Digital Input 1.7 on the IFM module
- Likely a photoelectric beam or inductive proximity sensor
Expected Behavior
- Sensor TRUE = No stack present at pre-stop position (normal idle state)
- Sensor FALSE = Stack is present at pre-stop position
- Sensor should change state as stacks move through the system
Troubleshooting Steps
- If sensor is always FALSE: check wiring, power, sensor alignment, or sensor failure
- If sensor is always TRUE: check if sensor is detecting properly or if there is a stuck stack
- Verify sensor type: NO (Normally Open) vs NC (Normally Closed) wiring
What the AI Delivered
Root Cause in Seconds
Traced the XIO instruction through the timer done bit to identify StckPreStopSensor as the probable failed component.
Cross-Reference Analysis
Found the downstream impact: ShearReliefTON.DN feeds into stack pusher interlocks in a completely different rung.
Physical Identification
Pinpointed the exact I/O module (PNL20, DI1.7), sensor type (photoelectric/proximity), and mounting location.
No License Required
All of this from an uploaded ACD file in the browser. No Studio 5000, no Rockwell license, no VPN to the plant network.
Three Steps to Diagnosis
Upload Your PLC File
Drag and drop your ACD, L5X, or RSS file. The system parses every program, routine, rung, and tag automatically.
Ask a Question
Describe the problem in plain English. The AI has full context of your entire PLC program and understands Allen-Bradley instruction sets.
Get Expert Analysis
Receive a detailed root cause analysis with specific rung references, tag cross-references, and actionable troubleshooting steps.
Try It With Your PLC File
Upload an ACD, L5X, or RSS file and start asking questions about your program.
Common Questions
Can AI really troubleshoot PLC faults?
Yes. When you upload a PLC program file, the AI has full access to every rung of ladder logic, every tag definition, and every I/O mapping. It can trace signal paths, identify which instructions control specific outputs, and cross-reference conditions across multiple routines to pinpoint root causes. It works the same way an experienced controls engineer would, but in seconds instead of hours.
What PLC file formats are supported?
PLC Company supports Allen-Bradley ACD files (Studio 5000 native format), L5X files (Studio 5000 XML exports), and RSS files (RSLogix 500 for SLC and MicroLogix). This covers ControlLogix, CompactLogix, GuardLogix, SLC 500, MicroLogix 1000, 1100, and 1400 controllers.
How does the AI understand ladder logic?
The AI understands the structure and semantics of Allen-Bradley ladder logic instructions including XIC, XIO, OTE, OTL, OTU, TON, MOV, COP, and dozens more. It reads tag names to infer physical meaning (sensors, valves, motors), traces signal paths through branches and subroutines, and understands sequencer patterns to explain what the program does in plain English.
Do I need programming experience to use this?
No programming experience is required. You can ask questions in plain English like 'why is the shear relief staying out' or 'what controls the stack pusher'. The AI translates the technical ladder logic into clear explanations with actionable troubleshooting steps that any maintenance technician can follow.