PLCTrain learning guide / Simulation examples
The belt is clear.
Why does the photoeye say blocked?
A blocked signal does not prove there is a box in the way. It tells you what one part of the control system is reporting. Your job is to find where that report stops matching the evidence.
In Conveyor Rescue, the same stopped-belt symptom can come from a sensor issue, a wrong input mapping, or a wrong logic condition. Compare those layers before deciding which part to change.
Four things that are easy to confuse
- The actual space. Is the receiving section visibly clear or occupied? That is the physical situation, not yet a PLC diagnosis.
- The sensor signal. A photoeye uses light to detect a condition. Whether its electrical output turns on for light or darkness depends on its configuration and sensing mode.
- The PLC input and tag. An input address identifies a point on a module. A tag gives that point meaning in the program. A useful name still needs the correct mapping.
- The ladder instruction. The instruction tests the tag value. It does not independently look at the conveyor.
Banner's photoelectric sensor training explains light-operate and dark-operate behavior. Do not assume that every real sensor uses the same blocked/clear convention as this game.
What the demo's names mean
| Label | Meaning in this example |
|---|---|
I4 | The physical input used for the receiving photoeye in the demo. |
I5 | A different input. Reading it by mistake can make a good sensor appear to disagree with the program. |
PE2_Blocked | The program's receiving-photoeye tag: 1 means reported blocked; 0 means reported clear. A wrong mapping or a force can make this report misleading. |
Find the first mismatch
If the virtual receiving space is clear but the physical photoeye input reports blocked, investigate the simulated beam and sensor setup. If the physical input behaves correctly but the tag does not match it, investigate mapping and temporary forces. If the tag is correct but the rung allows the wrong behavior, investigate the condition being tested.
That is more useful than changing several things until the conveyor moves. One change followed by the same test tells you more about cause and effect.
Height and alignment are different
A beam can point toward its reflector and still sit too close to the belt. The height lesson uses a 4-5 mm beam-height target above the belt so learners can see why a simulated frayed belt edge may interrupt a low beam. The close-up window shows the adjustment.
That height is this training scenario's target, not a specification for every conveyor. Real mounting height, alignment, sensing mode, package size, and clearances must come from the equipment design and the sensor manufacturer's instructions.
Moving once is not proof
In the demo, remove temporary forces and turn forcing off before final verification. Use the repeatable checks to show both outcomes: feeding when the receiving section is clear and stopping when it is occupied. Finish the full box transfer, rather than treating the first movement as success.
Does a green contact mean the photoeye is working?
No. It means the instruction is true for the tag value it is reading. That value could be mapped incorrectly or overridden. Compare it with the physical input and machine state.
Read the source, too.
The examples above describe PLCTrain. These manufacturer references explain the underlying concepts; they are not endorsements of PLCTrain.