1.1 Functional Hierarchy (ISA-95)

In complex manufacturing environments,manufacturing, blurring the lines between business planning and machine control invitesis disaster.not an "agile" feature; it is a structural vulnerability. The ISA-95 standard isacts not academic theory; it isas the structural firewall that preventspreventing your ERP finance system from accidentally crashing a robotic arm. AdhereYou must adhere to this hierarchy to ensure latency-sensitive processes (Machine Control) remain mathematically isolated from high-level transactional logic.logic (Business Planning).

The Five Levels of Control

Respect the separation of concerns. Each level operates on a differentrigid time scale and data granularity.

Level 4: Business Planning (ERP)

• Role: The "Brain". Handles Finance,Manages Order Entry, Purchasing, HR, and HR.Ledger.
• Time Scale: Days/Months.Days / Weeks.
• Rule:Mandate: Level 4 asksdefines "What do we needwhat to build?"build. It must never asksask, "What is the temperaturenozzle of the ovenpressure right now?"

Level 3: Manufacturing Operations (MES)

• Role: The "Coordinator". Manages Workflow, Quality, WIP Tracking, and Genealogy.
• Time Scale: Minutes/Minutes / Seconds.
• Rule:Mandate: Level 3 converts the ERP'sERP "Order" into a specific "Job" for the floor.. It acts asis the bridge between the dollar and the sensor.

Level 2: Monitoring & Supervisory (SCADA / HMI)

• Role: The "Watchtower". Real-time visualizationVisualization and controlline-level of a specific line or area.control.
• Time Scale: Seconds/Seconds / Sub-seconds.
• Rule:Mandate: Aggregates machineraw datasignals into actionable dashboardsoperator for operators.dashboards.

Level 1: Sensing & Manipulation (PLC / CNC)

• Role: The "Muscle". Logic controllers that drivedriving motors, valves, and actuators.
• Time Scale: Milliseconds.Milliseconds (< 10ms).
• Rule:Mandate: Critical safety logic lives here. Never rely on thea cloud server to stop a conveyor.

Level 0: Physical Process

• Role: The "Reality". The actualphysical sensor, motor, or chemical reaction.

Decision Logic: The "Golden Record" Rules

Do not duplicate data ownership. Use this logic to assign the "Master" status for critical data objects.

Rule 1: Product Data (BOM & Routing)

• IF data defines Cost, Vendor, or Top-Level Structure → THEN ERP is the Golden Record.
• IF data defines Recipe Parameters, Feeder Setup, or Screw Torque → THEN MES is the Golden Record.

Rule 2: Work Orders (WO)

• IF the object represents Financial Demand or Customer Commitment → THEN ERP owns the Header.
• IF the object represents a specific Batch, Serial Number, or Split-Lot → THEN MES owns the WIP State.

Rule 3: Inventory & Genealogy

• IF the query is "What is the total value of stock?" (COGS) → THEN Query ERP.
• IF the query is "Which specific capacitor batch is in this PCB?" (Compliance) → THEN Query MES.

ISA-95 Mapping Worksheet

Use this table to map objects across your specific facility.

Data Object	Level 4: ERP Object (Planning)	Level 3: MES Object (Execution)	Level 0-2: Machine/SCADA Object (Control)
Time Horizon	Shifts / Days	Minutes / Hours	Milliseconds / Seconds
Product Definition	Item Master: SKU, Bill of Materials (BOM), Std Cost.	Process Recipe: Reflow Profile (245˚C), SMT Feeder List, AOI Inspection Criteria.	Machine Program: G-Code, PLC Tag, Setpoint Variable (SP).
Production Command	Production Order: "Make 500 units of SKU-A due Friday."	Dispatch List / WIP: "Line 1, Run Job #101. Sequence: Solder → Place → Reflow."	State Logic: Start / Stop / Hold / E-Stop.
Quality Result	Lot Disposition: Pass/Fail status for the entire order (100 units).	Unit History: "Serial #12345 passed AOI but failed ICT at Test Point 4."	Telemetry: Voltage read (5.1V), Camera Image, Torque value (2.5 Nm).
Maintenance	Asset Ledger: Depreciation schedule, Capital Expenditure (CapEx).	Maintenance Log: Cycle counts, Calibration expiry dates, Tool usage.	Alarms: Motor Over-current, Temp High Limit, Vibration Alert.

The "Demilitarized Zone" (DMZ) LogicArchitecture

Direct communication between non-adjacent levels creates security holes and dependency hell.chains that cause downtime.

Communication Rules

• L4 (ERP) ↔→ L1 (PLC): Strictly Forbidden. The ERP should never talk directly to a machine. If the office network lags, the machine crashes.must not crash.
• L4 (ERP) ↔→ L3 (MES): Permitted. ViaUse transactional APIs (REST/SOAP). for order exchange.
• L3 (MES) ↔→ L1 (PLC): Restricted. Use anLevel OPC-UA2 server or (Edge Gateway (Level 2)Gateway/OPC-UA) as a buffer. Do not let theallow MES to query thea PLC 100 times per second directly.

Pro-Tip: Design for "Headless" operation. If yourthe ERP (L4) goes down,offline, the factory (L1-L3) must continue to run. If your architecture requires the ERP to be online to print aproduce, label, youand havepack violatedgoods thefor hierarchy.at least 24 hours. Sync data when L4 returns.

Data GranularityAggregation & SummarizationFlow

Data loses granularity but gains context as it moves up the stack, but loses granularity.stack.

The Aggregation Flow

1. Level 1 (PLC): Reads temperature at 100Hz (100 samples/sec).
2. Level 2 (SCADA): Calculates the 1-second rolling average.
3. Level 3 (MES): Records the Min/Max/Avg for the specific "Unit Serial Number".
4. Level 4 (ERP): Records "Process Pass/Fail"Pass" for the Production Order.

Data Storage Logic

• If you need to debug a motor stall → Query L1/L2 Historian.
• If you need to prove regulatory compliance for a specific unit → Query L3 Database.
• If you need to calculate Cost of Goods Sold (COGS) → Query L4 Ledger.

Convergence & Edge Computing

Modern IIoT (Industrial Internet of Things) devices blur these lines. However, the logical hierarchy remains valid even if the physical hardware changes.

Smart Device Handling

Even if a smart screwdriver connects via Wi-Fi (physically skipping L1/L2 wiring), logically treat it as an L1 device managed by an L3 driver.

• Rule: Edge devices must buffer data locally. If Wi-Fi drops, the torque value must be saved and pushed later.

Final Checklist

Category	Metric / Control	ThresholdMandatory /State	Engineering RuleConsequence
Architecture	L4 ↔→ L1 Link	Strictly Forbidden	Air-gap (Airlogic Gapprevents logic)business traffic from flooding control networks.
Resilience	Decoupling	L3 runs 24h+ withoutBuffer	Production L4must connectionnot stop during ERP maintenance windows.
Safety	Logic Hosting	Critical Safety Stops must reside in L1 (PLC)	Critical stops (E-Stop, Light Curtain) must be hardwired/local.
Data	Granularity	Separated	ERP stores Financials; MES stores GenealogyGenealogy.
Latency	Control Loop	< 10ms	High-speed loops stay in L1; Loops > 1s loopscan gomove to L3L3.
Network	Segmentation	VLAN Separated	Isolate Shop Floor (OT) from Office (IT) VLANtraffic.