Manufacturing Execution Systems Fundamentals
What the exam tests
This domain tests the boundary between business planning and plant-floor control: ISA-95 levels, MES functional scope, order execution, genealogy, and how MES differs from ERP and SCADA.
Core models
- ISA-95 separates Level 4 business planning, Level 3 manufacturing operations management, Level 2 monitoring/supervisory control, Level 1 control, and Level 0 physical process. MES owns work-order execution, dispatching, tracking, data collection, quality, and material genealogy.
- ISA-88 provides batch models: recipe, unit, phase, and procedural control. MES may orchestrate recipes but does not replace batch control.
- Core MES functions include resource allocation, operations scheduling, dispatching, data collection, quality management, maintenance management, product tracking, and performance analysis.
- A work order authorizes a quantity; a routing defines operation sequence; a BOM defines consumed materials.
Worked example
ERP releases 1,000 units. MES splits the order into two lots of 500 because a mixer has 500-unit capacity. At operation 20, 8 units are scrapped. MES reports 992 good units and consumes material for 1,000 starts. Reasoning: order quantity is authorization, lot size is execution granularity, and yield is good output divided by starts (992/1,000 = 99.2%), not by the original order.
Traps
- Treating MES as ERP: MES usually does not own financial costing or customer invoicing.
- Confusing SCADA with MES: SCADA supervises equipment; MES contextualizes production.
- Assuming one work order equals one lot; lot and serial granularity are configured.
- Ignoring ISA-95 boundaries when answering integration questions.