Maintenance Systems, Fault Diagnosis and Condition Monitoring
What this domain tests
Maintenance strategy selection, reliability metrics, condition monitoring techniques and basic electrical checks on machine tools.
Core rules
- Strategies: breakdown (reactive), preventive (time-based), predictive (condition-based), corrective. TPM builds autonomous maintenance and 5S; RCM selects tasks by failure consequence.
- Metrics: MTBF = operating time ÷ number of failures; MTTR = repair time ÷ number of repairs; availability = MTBF ÷ (MTBF + MTTR).
- OEE = Availability × Performance × Quality, each expressed as a decimal.
- Condition monitoring: vibration (ISO 10816 zones; rising high-frequency energy indicates bearing defects), thermography for loose connections, oil analysis for wear metals, ultrasound for leaks and early bearing faults, and motor current signature analysis.
- Electrical checks: insulation resistance with a megger (a healthy 400 V motor reads well above 1 MΩ, typically hundreds of MΩ), earth continuity, correct overload relay setting, and clamping current on all phases to detect single-phasing.
- Always isolate and prove dead before electrical work.
Worked example
A machine runs 480 min in a shift with 30 min planned downtime, 20 min breakdown, produces 900 parts of which 27 are rejected. Availability = 450/480 = 0.9375; Performance = 0.95; Quality = 873/900 = 0.97. OEE = 0.9375 × 0.95 × 0.97 = 0.864, i.e. 86.4 %. OEE is a product, never an average.
Traps that cost marks
- Averaging the three OEE factors instead of multiplying them.
- Meandering an insulation test with the motor still connected to the drive.
- Confusing preventive (calendar) with predictive (condition-based).