# Plant operating document: WaterPlant

*Generated by PlantMind on 2026-10-28 03:22:53 from the approved PLC program. Synthetic plant, advisory document.*

## Overview (written by the model from the facts below)

LT-101 and LT-301 control P-101 start/stop; P-101 must be on for P-201 start and stop; P-201 also stops if AT-201 exceeds 1.8 or is commanded off via HMI; P-301 starts when LT-301 reaches 30.0 and stops when it falls below 20.0, with interlocks enforced during HMI commands.

## Equipment and instruments

| Tag | Name | Type | Unit |
|---|---|---|---|
| LT-101 | Raw water tank level | sensor | % |
| FT-101 | Intake flow | sensor | m3/h |
| AT-201 | Chlorine residual | sensor | ppm |
| LT-301 | Treated water tank level | sensor | % |
| PT-301 | Distribution discharge pressure | sensor | bar |
| P-101 | Intake pump | pump | - |
| P-201 | Chlorine dosing pump | pump | - |
| P-301 | Distribution pump | pump | - |

## Protective interlocks

| ID | Protects | Trips when | Purpose | Program |
|---|---|---|---|---|
| IL-01 | P-101 | LT-101 is below 15.0 | Trip intake pump on raw tank low-low (dry-run protection) | line 53 |
| IL-02 | P-101 | LT-301 is above 95.0 | Trip intake pump on treated tank high-high (overflow protection) | line 55 |
| IL-03 | P-201 | P-101 is off | Trip chlorine dosing when there is no intake flow | line 68 |
| IL-04 | P-201 | AT-201 is above 4.0 | Trip chlorine dosing on chlorine overdose | line 70 |
| IL-05 | P-301 | LT-301 is below 15.0 | Trip distribution pump on treated tank low-low | line 83 |
| IL-06 | P-301 | PT-301 is above 6.0 | Trip distribution pump on overpressure | line 85 |

## What stops each pump

- P-101 (Intake pump) stops when: IL-01 (LT-101 is below 15.0); IL-02 (LT-301 is above 95.0); automatic control: P-101 auto-stops when LT-101 is below 30.0 OR LT-301 is above 90.0.
- P-201 (Chlorine dosing pump) stops when: IL-03 (P-101 is off); IL-04 (AT-201 is above 4.0); automatic control: P-201 auto-stops when P-101 is off OR AT-201 is above 1.8.
- P-301 (Distribution pump) stops when: IL-05 (LT-301 is below 15.0); IL-06 (PT-301 is above 6.0); automatic control: P-301 auto-stops when LT-301 is below 20.0.

## Automatic control

- P-101 auto-starts when LT-101 is at least 50.0 AND LT-301 is below 85.0
- P-101 auto-stops when LT-101 is below 30.0 OR LT-301 is above 90.0
- P-201 auto-starts when P-101 is on AND AT-201 is below 1.2
- P-201 auto-stops when P-101 is off OR AT-201 is above 1.8
- P-301 auto-starts when LT-301 is at least 30.0
- P-301 auto-stops when LT-301 is below 20.0

## Alarms

| ID | Warns when |
|---|---|
| AL-01 | LT-101 is below 25.0 |
| AL-02 | AT-201 is below 0.2 |
| AL-03 | PT-301 is above 5.0 |

## External command paths

- P-201 can also be commanded by an external SCADA/HMI write (P_201_HMI_CMD); interlocks still apply
- P-301 can also be commanded by an external SCADA/HMI write (P_301_HMI_CMD); interlocks still apply

## Limits of this document

- It is generated only from the PLC program text; physical piping, valves and site procedures are not included.
- It describes the APPROVED program. If the running program differs, the Change Guard reports it.
- Verify it with the responsible control engineers before relying on it.