Industrial Water Conservation Control System

The industrial water conservation control system can effectively reduce water resource consumption in enterprises, achieving precise monitoring and intelligent regulation, with the core being the PLC control strategy and system integration.

1. Hardware Configuration

The core of the industrial water conservation control system lies in a reasonable hardware configuration, which directly affects the stability and scalability of the system.

PLC and Expansion Module Selection

For small and medium-sized water conservation projects, it is recommended to use the Siemens S7-1200 series PLC, such as the CPU 1214C DC/DC/DC. This model has 14 digital input points, 10 digital output points, and 2 analog input points, which basically meet the general water conservation control needs. For scenarios with a large number of I/O points, expansion can be achieved through signal modules SM 1231 and SM 1232 to realize more analog input and output.

I/O Point Allocation Table

Digital Inputs:

%I0.0 - Pump 1 Run Feedback

%I0.1 - Pump 2 Run Feedback

%I0.2 - High Water Level in Tank

%I0.3 - Low Water Level in Tank

%I0.4 - System Fault Reset

%I0.5 - Auto/Manual Switch


Digital Outputs:

%Q0.0 - Pump 1 Start/Stop Control

%Q0.1 - Pump 2 Start/Stop Control

%Q0.2 - Inlet Solenoid Valve

%Q0.3 - System Fault Indicator


Analog Inputs:

%IW64 - Tank Level Sensor (4-20mA)

%IW66 - System Flow Meter (4-20mA)


Analog Outputs:

%QW80 - Proportional Control Valve (0-10V)

Peripheral Device Selection

Level Sensor: Use the SITRANS LH100 submersible pressure transmitter, measuring range 0-10m, accuracy ±0.3%, 4-20mA output signal, suitable for tank level monitoring.
Flow Meter: Use the electromagnetic flow meter MAG 5100W, diameter DN50, measuring range 0-100m³/h, meeting industrial water monitoring needs.
Actuator: Use the SIPART PS2 intelligent electric valve positioner with matching control valve, response time <0.2s, ensuring quick flow regulation.

2. Control Program Design

A reasonable program architecture is the foundation for the stable operation of the system, following the principles of modularity and maintainability.

Variable Definition Specification

// Global Variables (DB1)

"DB_System".bPump1_Run        // Pump 1 Run Status

"DB_System".bPump2_Run        // Pump 2 Run Status

"DB_System".rTankLevel        // Tank Level Value

"DB_System".rFlowRate         // System Flow Value

"DB_System".bAutoMode         // Automatic Mode Flag

"DB_System".bAlarm            // System Alarm Flag

"DB_System".rValvePosition    // Control Valve Opening

Program Architecture Design

The program adopts a three-layer architecture design:

OB Layer: OB1 (Main Loop), OB100 (Startup), OB82 (Diagnostic Interrupt)
FB Layer: Function Blocks, including Pump Control (FB1), Level Control (FB2), Flow Regulation (FB3), Alarm Handling (FB4)
DB Layer: Data Blocks, including System Parameters (DB1), Historical Data (DB2), Alarm Information (DB3)

Function Block Design

Taking the pump rotation control function block as an example:

// FB1: Pump Rotation Control Function Block

FUNCTION_BLOCK "FB_PumpControl"

VAR_INPUT

    bAuto : Bool;             // Automatic Mode

    bStart : Bool;            // Start Command

    bStop : Bool;             // Stop Command

    rTankLevel : Real;        // Tank Level

    rLevelHigh : Real;        // High Level Setting

    rLevelLow : Real;         // Low Level Setting

    tSwitchTime : Time;       // Switch Time

END_VAR


VAR_OUTPUT

    bPump1On : Bool;          // Pump 1 Start

    bPump2On : Bool;          // Pump 2 Start

    bAlarm : Bool;            // Alarm Output

END_VAR


VAR

    tRunTime1 : Time;         // Pump 1 Run Time

    tRunTime2 : Time;         // Pump 2 Run Time

    bPriority : Bool;         // Priority (1: Pump 1 Priority, 0: Pump 2 Priority)

    tTimer : TON;             // Timer

END_VAR


BEGIN

    // Control logic in manual mode

    IF NOT #bAuto THEN

        #bPump1On := #bStart AND NOT #bStop;

        #bPump2On := FALSE;

        RETURN;

    END_IF;
    
    // Level control in automatic mode

    IF #rTankLevel &lt;= #rLevelLow THEN

        // Low level start condition

        IF #bPriority THEN

            // Pump 1 priority

            #bPump1On := TRUE;

            #bPump2On := FALSE;

        ELSE

            // Pump 2 priority

            #bPump1On := FALSE;

            #bPump2On := TRUE;

        END_IF;

    ELSIF #rTankLevel &gt;= #rLevelHigh THEN

        // High level stop condition

        #bPump1On := FALSE;

        #bPump2On := FALSE;

    END_IF;
    
    // Rotation control logic

    #tTimer(IN := #bPump1On OR #bPump2On,
            PT := #tSwitchTime);
    
    IF #tTimer.Q THEN

        // Switch priority

        #bPriority := NOT #bPriority;

        // Reset timer

        #tTimer(IN := FALSE);

    END_IF;
    
    // Exception handling: Both pumps fault alarm

    #bAlarm := NOT (#bPump1On OR #bPump2On) AND (#rTankLevel &lt;= #rLevelLow);

END_FUNCTION_BLOCK

3. System Debugging Methods

System debugging is a key step to ensure the stability and reliability of the control system, following the principle of debugging from simple to complex, step by step.

Step-by-Step Debugging Method

Hardware Connection Testing:

Check power supply, grounding, and communication lines
I/O point wiring check
Sensor signal calibration verification

Unit Module Testing:

Individually debug each function block
Verify the correctness of logical control
Correct program bugs and document

System Integration Testing:

Module interface testing
Data interaction verification
System response time testing

Parameter Tuning Steps

For the water conservation control system, key parameter tuning includes:

Level Control Parameters:

High and low level set values
Level sensor range calibration
PID control parameters (take Kp=2.5, Ti=60s, Td=10s as initial values)

Flow Control Parameters:

Flow upper and lower limit settings
Valve opening and flow relationship calibration
Flow PID control parameters (take Kp=1.8, Ti=45s, Td=5s as initial values)

Exception Simulation Testing

Verify system response by simulating the following exceptions:

Sensor failure (disconnection, short circuit)
Actuator failure (valve stuck)
Communication interruption
Power supply anomalies (power failure, fluctuations)

For each exception, record the system response and optimize the control strategy.

4. User Interface Design

The human-machine interface is the window for user interaction with the system, and good interface design can enhance the operational experience and system maintainability.

Interface Layout Description

The water conservation control system HMI interface designed based on Siemens SIMATIC WinCC mainly includes:

Main Screen: System process flow diagram, intuitively displaying water flow direction and equipment status
Parameter Settings: System parameter configuration interface with hierarchical permission control
Trend Curves: Historical trends of key parameters such as flow and level
Alarm Page: Real-time alarms and historical alarm records
User Management: Operation permission management interface

Parameter Settings Description

The parameter settings interface includes the following key areas:

Operating Parameters:

Water pump start/stop level settings
Water pump rotation time settings
Flow upper and lower limit settings

Control Parameters:

PID parameter adjustment area
Control mode selection
Auto/Manual switch

System Parameters:

Alarm limit settings
Signal filtering parameters
Data acquisition cycle

All parameters are set with reasonable upper and lower limit constraints to prevent misoperation leading to system anomalies.

5. Fault Diagnosis and Troubleshooting

A complete fault diagnosis mechanism is an important guarantee for improving system reliability.

Common Fault Analysis

Abnormal Level Measurement:

Symptoms: Level display is unstable or fixed value
Causes: Sensor failure, wiring issues, range setting errors
Resolution: Check wiring, calibrate sensor, verify range

Water Pump Fails to Start:

Symptoms: Start command issued but pump does not run
Causes: Relay failure, fuse blown, motor protection triggered
Resolution: Check control circuit, replace components, reset protection

Flow Control Instability:

Symptoms: Large flow fluctuations, unable to reach set values
Causes: Inappropriate PID parameters, valve characteristics mismatch, unstable air source pressure
Resolution: Retune PID, check valve, stabilize air source

Diagnosis Tool Usage

Siemens STEP 7 Diagnostic Function:

Use online monitoring function to observe program execution
Utilize variable table to monitor key data
Verify output response through forced function

Fault Log Analysis:

Establish system log data block to record anomalies
Use timestamps to analyze the order of fault occurrences
Combine alarm information to locate root causes

The industrial water conservation control system maximizes water resource utilization through precise control. We welcome you to share your application experiences and optimization suggestions!