Hydraulic Pressure Control — CODESYS 3.5

PLC control program for an industrial hydraulic system with three pressure sensors, a proportional valve, PID-based pressure regulation, and fault diagnostics.

Overview

This project demonstrates a complete control solution typical of food and meat-processing machinery (fish-processing lines, separators, press systems). It was developed as a standalone demo based on real commissioning experience.

System Description

Component	Details
Pressure sensors	3× 4–20 mA transmitters (0–250 bar)
Proportional valve	0–100% analogue output
Control strategy	PID closed-loop on working pressure
Fault handling	Overpressure, wire-break, E-stop

Project Structure

src/
  GVL.st                  — Global variable list
  FB_PressureScale.st     — 4-20mA scaling with wire-break detection
  FB_HydraulicControl.st  — Main hydraulic control FB (PID + faults)
  MAIN.st                 — Main program (entry point)

Tech Stack

• Platform: CODESYS 3.5
• Language: Structured Text (ST) — IEC 61131-3
• PID: CODESYS standard FB_PID library
• Signal: 4–20 mA scaled via 0–32767 ADC range

How It Works

1. FB_PressureScale reads raw ADC values from each sensor, scales them to bar, and flags wire-break faults if the signal drops below 3.8 mA.
2. FB_HydraulicControl runs PID control on the working pressure (P2), driving the proportional valve output.
3. Overpressure on P2 or any sensor fault triggers an immediate valve close and sets a fault code.
4. MAIN wires sensors → control FB → global outputs each scan cycle.

Author

Nikita Poliakov — Automation & Instrumentation Engineer
2+ years delivering end-to-end control systems for food and meat-processing equipment.
LinkedIn | work.nikita@bk.ru