Control Narrative
Template (Word + Excel)

A control narrative (also called a control philosophy document or operating philosophy) is the engineering document that describes, in structured prose, how each control loop and interlock on a unit is intended to operate. It captures the control objective, the normal operating mode (auto, manual, cascade, ratio, feedforward), the setpoint source, the control action, tuning parameters, alarm limits, interlock and permissive logic, startup and shutdown sequences, operator action, and failure mode. It is the primary input to DCS configuration, operator training, and operating procedure development.

Required sections per loop: document reference and revision, unit and system description, P&ID reference, loop tag numbers per ISA 5.1, control objective, normal operating mode, setpoint source, process variable range, output range, control action (direct or reverse), tuning parameters, alarm limits (LL, L, H, HH), interlock description, permissive conditions, startup sequence, normal operation, shutdown sequence (normal and emergency), operator action required, failure mode, cross-reference to the cause and effect matrix, SIL determination, and HAZOP register. See the ISA 5.1 instrumentation standard reference.

Pathnovo, an engineering document intelligence platform, drafts control narratives by extracting every loop from the P&IDs, cross-referencing the I/O list for tag and signal data, the C&E matrix for interlock logic, and the SIL determination worksheet for safety classification. The platform assembles a structured per-loop narrative covering objective, control mode, setpoint source, alarm limits, interlock logic, and failure mode. Output is configurable to your EPC narrative format. Drafts are reviewed and approved by the control system engineer. See the P&ID extraction workflow.

The control narrative is the engineering intent: it describes what the control system must do (control objectives, modes, interlocks). The functional specification is the vendor implementation: it describes how the chosen DCS or PLC vendor's logic blocks are configured to deliver the narrative (specific function block IDs, parameter values, tag database entries). The narrative is owned by the process and control system engineers and is the input to vendor configuration. The functional specification is owned by the system integrator and is the input to DCS Factory Acceptance Test (FAT) and Site Acceptance Test (SAT).

Every interlock described in the control narrative must trace to a row on the cause and effect matrix, and every safety-instrumented row on the C&E matrix must be described in the control narrative. The narrative provides the prose context (which operating case the interlock protects against, how the operator is alerted, how the interlock is reset and the unit restarted) that the matrix cannot capture. Pathnovo cross-checks the narrative against the C&E matrix to flag interlocks described in one and missing from the other. See the cause and effect matrix template.

On a revamp project, the existing narrative is the baseline. Each loop is reviewed against the revamp scope and flagged as 'retained', 'modified', 'new', or 'removed'. Retained loops preserve existing control logic; modified loops update setpoints, tuning, or interlocks; new loops describe newly introduced control objectives; removed loops are demolished. Particularly important on brownfield revamps where DCS migration (Honeywell TDC 3000 to Experion, Yokogawa Centum CS to CENTUM VP) requires re-baselining the narrative against the new platform's function blocks before re-configuration begins.

The control narrative is the source document for the operating manual and operator training programme. Each loop section of the narrative becomes a section of the operating procedure (Standard Operating Procedure, Startup Procedure, Shutdown Procedure, Emergency Operating Procedure). Operator training cards are built one-per-loop from the narrative content. On commissioning, the narrative is also the basis for the Operator Training Simulator (OTS) scenarios. Keeping the narrative aligned with the as-built configuration is critical: drift between narrative and DCS is a common HAZOP audit finding.