Practical Application of Siemens PLC in Industrial Wastewater Recovery

The industrial wastewater recovery system has high automation control requirements, which directly affects the environmental compliance and economic benefits of enterprises. This article details the design and implementation of a wastewater recovery control system based on the S7-1500 PLC.

1. Hardware Configuration Plan

PLC Selection and I/O Configuration

• Main Control Unit: SIMATIC S7-1500 (CPU 1516-3 PN/DP)
• Digital Input Module: DI 32xDC24V (6ES7521-1BL00-0AB0) × 2
• Digital Output Module: DQ 32xDC24V/0.5A (6ES7522-1BL00-0AB0) × 1
• Analog Input Module: AI 8xU/I/RTD/TC (6ES7531-7KF00-0AB0) × 2
• Analog Output Module: AQ 4xU/I (6ES7532-5HD00-0AB0) × 1

I/O Point Allocation Table (Partial)

Digital Input:
%I0.0 - System Start Button
%I0.1 - System Stop Button
%I0.2 - Emergency Stop Button
%I1.0-%I1.7 - Pump Running Feedback
%I2.0-%I2.7 - Valve Limit Feedback

Analog Input:
%IW64 - pH Value Detection
%IW66 - Turbidity Detection
%IW68 - Water Level Detection
%IW70 - Pressure Detection

Peripheral Device Selection

• Frequency Converter: SINAMICS G120
• Touch Screen: SIMATIC HMI TP1200 Comfort
• Water Quality Analyzer: E+H Online pH Meter, Turbidity Meter
• Flowmeter: Siemens MAG5100W Electromagnetic Flowmeter

2. Control Program Design

Variable Definition Specification

// Global Variable Example (DB1)
STRUCT
    System_Status: INT;    // System Status
    pH_Value: REAL;       // pH Value
    Turbidity: REAL;      // Turbidity Value
    Tank_Level: REAL;     // Tank Liquid Level
END_STRUCT

Program Architecture

The main program adopts a modular design, including the following function blocks:

1. OB1 Main Loop Program

• System Status Management
• Process Flow Control
• Data Acquisition Processing

2. FB1 Water Quality Monitoring Function Block

// Water Quality Monitoring Function Block Example
FUNCTION_BLOCK "Water_Quality_Monitor"
VAR_INPUT
    Enable: BOOL;         // Enable Signal
    pH_Raw: REAL;        // pH Raw Value
    Turbidity_Raw: REAL; // Turbidity Raw Value
END_VAR
VAR_OUTPUT
    Quality_OK: BOOL;    // Water Quality OK Signal
    Alarm_Status: WORD;  // Alarm Status Word
END_VAR

Data Storage Design

// Operating Parameter Data Block (DB10)
DATA_BLOCK "Process_Parameters"
VERSION 1.0
NON_RETAIN
BEGIN
    Set_pH_Min: REAL := 6.5;     // pH Lower Limit
    Set_pH_Max: REAL := 8.5;     // pH Upper Limit
    Set_Turb_Max: REAL := 10.0;  // Turbidity Upper Limit
END_DATA_BLOCK

3. Operation Interface Design

Main Screen Layout

• Dynamic Display Area for Process Flow
• Real-time Data Display Area
• Operating Status Indicator Area
• Operation Button Area
• Alarm Information Display Area

Parameter Setting Interface

• Process Parameter Settings
• PID Parameter Adjustment
• Alarm Limit Settings
• System Configuration Options

4. System Debugging Plan

Step-by-Step Debugging Process

1. I/O Point Testing
2. Single Device Control Testing
3. Interlocking Function Testing
4. Process Parameter Tuning
5. Exception Handling Verification

Parameter Tuning Key Points

• pH Control PID Parameter Tuning
• Water Level Control PID Parameter Tuning
• Frequency Converter Parameter Configuration
• Alarm Threshold Confirmation

5. System Optimization and Maintenance

System Optimization Suggestions

1. Adopt Multi-Level PID Cascade Control Strategy
2. Implement Predictive Maintenance Function
3. Increase Data Statistical Analysis Function
4. Optimize Energy Consumption Control Algorithm

Daily Maintenance Key Points

1. Regularly Backup Programs and Parameters
2. Check Sensor Calibration Status
3. Monitor System Operating Data
4. Regularly Test Protection Functions

The wastewater recovery control system solution introduced in this article has been successfully applied in multiple projects. We welcome discussions and exchanges to jointly improve the level of industrial automation.

Complete Solution for PLC Control in Industrial Wastewater Treatment