Mechatronics System Integration
Mechatronics System Integration
This domain tests how mechanical, electrical, control and software subsystems are joined into one working machine: signal interfacing, earthing and shielding, communication links, I/O mapping, safety interlocks and commissioning sequence. Questions are usually practical - a fault that appears only after integration.
Core rules
- Common signal levels: 24 V DC digital, 0–10 V or 4–20 mA analogue, RS-485 for Modbus RTU, Ethernet-based protocols for higher-level integration, IO-Link for smart sensors.
- Match sensor output type to input card type: PNP (sourcing) sensor to a sinking input; NPN to a sourcing input. Check the common terminal before wiring.
- Grounding: earth the panel backplate and machine frame at one point, bond shields at one end only to avoid earth loops, and route analogue and encoder cables away from motor and VFD cables.
- Interlocks belong in both hardware and software: an emergency stop must remove power directly, not via PLC logic alone.
- Commissioning order: mechanical alignment, then power and safety checks, then I/O point-to-point test, then manual jog, then sequence test, then documentation and back-up.
Worked example
After integration, a new sensor lights up but the PLC input never turns on. Reasoning: the sensor is PNP and outputs +24 V, but the input card is also sourcing type with its common at +24 V, so no current path exists. Check the common terminal; either move the common to 0 V (sinking card) or fit an NPN sensor or interface relay. Verify with a meter: 24 V at the sensor output but 24 V also at the input terminal means no current can flow.
Traps
Blaming the program for a wiring-level mismatch; earthing both ends of a shield; relying on software for an emergency stop; skipping the point-to-point I/O test before running the sequence.