Challenge #4 · plc-io
The Machine Goes Blind
A part-present photo-eye should tell the PLC there's a part in the nest. The sensor's own light comes on when the part's there, but the machine acts like nothing's there and won't index.
① Run your checks
② Make the call
③ Explain your reasoning optional
A strong answer covers:
- What you did: walked the signal chain, the sensor's target LED, the voltage at its output terminal, and the voltage + LED at the PLC input.
- The reason: LED on and 24V at the sensor output means it's switching; but 0V and a dark input LED at the card means the signal dies in the run between them.
- Determined outcome: the fault is the conductor in between (open wire, backed-out ferrule, or mis-landed terminal), not the sensor and not the card; trace the wire.