Industrial Automation
Industrial Automation tests how discrete, continuous and batch operations are mechanised and integrated. The exam expects you to select sensing and actuation, structure a control hierarchy and judge whether an automated line meets its throughput and quality targets.
Core rules and concepts
- The automation hierarchy follows ISA-95: field devices, control (PLC/DCS), supervisory (SCADA/HMI), manufacturing execution (MES) and enterprise (ERP). Data should flow upward with defined ownership; control decisions should not depend on the enterprise layer.
- Discrete automation uses relays, contactors, PLCs, sensors, solenoids and VFDs. Continuous automation uses PID loops and advanced control. Batch automation follows ISA-88 recipe, unit and equipment-module models.
- Select sensors by output type, sensing range, response time, environment and failure mode. PNP/NPN, normally open/normally closed and fail-safe wiring are common exam discriminators.
- VFDs change motor speed and torque; check harmonic distortion, cable length, EMC filters and motor insulation. Servos and motion controllers add position and velocity loops with encoder feedback.
- Overall equipment effectiveness is Availability × Performance × Quality. It is not the same as utilisation, which measures busy time rather than good output.
- Safety functions must be designed to ISO 13849 or IEC 62061 and validated; a safety-rated component alone does not make a safety function.
Worked example
A line has planned production time of 480 minutes, actual running time of 432 minutes, ideal cycle time of 30 s and 960 good parts out of 1,000 produced. Availability = 432/480 = 90%. Performance = (1,000 × 30 s)/(432 × 60 s) = 500/432 = 1.157, which is impossible, so check the data: 432 minutes can produce at most 864 parts at 30 s. Using 840 produced, performance = 840/864 = 97.2%. Quality = 960/1,000 = 96%. OEE = 0.90 × 0.972 × 0.96 = 84.0%. The reasoning matters more than the arithmetic: always check that performance cannot exceed 100%.
Traps
Confusing OEE with uptime; ignoring changeover and minor stops; choosing a sensor without checking PNP/NPN or fail-safe state; and assuming a safety-rated device satisfies the whole safety function.