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Specification

Control Narrative

CN

The control narrative explains the process in the language operators use, rather than in control system terms. It sits between the P&ID and the FDS: it says why the plant behaves as it does, which is exactly what an FDS full of tables leaves out.

Do you need this one?

Process plant, and anything with continuous control loops. On a discrete machine the FDS sequence section usually covers it, and a separate narrative is duplication you will have to keep in step.

What is in it

  1. 01Process overview
  2. 02Equipment description
  3. 03Control loops
  4. 04Normal operation
  5. 05Start-up and shutdown
  6. 06Upset conditions
  7. 07Operator responsibilities

Written by

Process engineer with the control engineer

Approved by

Process owner

Written against

  • ISA-5.1 for instrument identification
  • ISA-88 for procedural terminology

Preview

Control-Narrative.md
# Control Narrative
## {{PROJECT_NAME}}

| | |
|---|---|
| **Document title** | Control Narrative (CN) |
| **Document number** | {{DOC_NO}} |
| **Revision** | {{REV}} |
| **Date** | {{DATE}} |
| **Project** | {{PROJECT_NAME}} |
| **Client** | {{CLIENT}} |
| **Prepared by** | {{AUTHOR}}, {{COMPANY}} |

### Revision history

| Rev | Date | Description | Author | Approved |
|---|---|---|---|---|
| 0 | {{DATE}} | First issue | {{AUTHOR}} | |
| | | | | |

### Approval

| Role | Name | Signature | Date |
|---|---|---|---|
| Author | {{AUTHOR}} | | |
| Reviewer (engineering) | | | |
| Approver ({{COMPANY}}) | | | |
| Approver ({{CLIENT}}) | | | |

---

## 1. Process overview

[Describe what the plant makes, and how. Write it so a new operator could read this section
alone and understand what they are looking at on the plant floor. Avoid control system
vocabulary here entirely.]

---

## 2. Equipment description

| Tag | Equipment | Function | Rating |
|---|---|---|---|
| [P-101] | [Feed pump] | [Transfers feed from T-101 to R-201] | [m3/h, kW] |
| | | | |

---

## 3. Control loops

One subsection per loop. The measurement, the final element, the strategy, and, importantly,
what the loop is protecting against.

### 3.1 [FIC-101, feed flow control]

| Item | Detail |
|---|---|
| Measurement | [FT-101, magnetic flow meter, 0 to 50 m3/h] |
| Controller | [FIC-101, PID] |
| Final element | [FCV-101, equal percentage, air to open] |
| Normal setpoint | [value and units] |
| Setpoint source | [Operator entry / recipe / cascade from LIC-201] |
| Action | [Direct / reverse, and why] |
| Failure position | [Fail open / closed / last, and the consequence of each] |

**Description.** [Prose: what the loop does, when it is in automatic, what an operator should
expect to see, and what it means when the valve sits at 100 percent.]

**Tuning.** [Initial values, and a note on the dominant time constant.]

---

## 4. Normal operation

[The steady state. What the operator watches, what the normal ranges are, what routine
interventions are expected during a shift.]

---

## 5. Start-up and shutdown

### 5.1 Cold start
[Numbered, in order, including the checks that must pass before each stage.]

### 5.2 Normal shutdown

### 5.3 Emergency shutdown
[What trips, in what order, and what stays running. State explicitly which items remain
energised, because that is the question the maintenance team will ask first.]

---

## 6. Upset conditions

| Condition | Symptom | Cause | System response | Operator action |
|---|---|---|---|---|
| [High level in T-101] | [LAH-101 alarm] | [Outfeed blocked] | [Feed pump stops] | [Investigate outfeed] |

---

## 7. Operator responsibilities

[What the operator is expected to do, and, just as usefully, what they must not do. If there
are actions that require a permit or a second person, say so here.]

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