Water Tank Level Control for Agricultural

PROGRAM PLC_CONTROL_LOGIC_EXAMPLE
VAR
    // Inputs
    start_button : BOOL;
    stop_button : BOOL;
    system_ready : BOOL;
    error_detected : BOOL;

    // Outputs
    motor_run : BOOL;
    alarm_signal : BOOL;

    // Internal State
    system_state : INT := 0; // 0=Idle, 1=Running, 2=Error
    runtime_counter : INT := 0;


    // Soil & Weather Monitoring
    Soil_Moisture_Level : REAL;  // Percent volumetric water content
    Soil_Temperature : REAL;     // °C
    Ambient_Temperature : REAL;
    Rainfall_Today : REAL;       // mm
    Wind_Speed : REAL;           // m/s

    // Irrigation Control
    Irrigation_Zone_Active : ARRAY[1..8] OF BOOL;
    Zone_Runtime : ARRAY[1..8] OF TIME;
    Water_Flow_Rate : REAL;      // L/min
    Water_Total_Daily : REAL;    // Liters

    // Scheduling & Automation
    Irrigation_Schedule_Enable : BOOL;
    Scheduled_Start_Time : TIME;
    Scheduled_Duration : TIME;
    Manual_Override : BOOL;

    // ET (Evapotranspiration) Calculation
    Reference_ET : REAL;         // mm/day
    Crop_Coefficient : REAL;     // Kc value
    Crop_ET : REAL;              // Actual crop water use

    // Fertigation (Fertilizer Injection)
    Fertilizer_Injection_Active : BOOL;
    EC_Sensor : REAL;            // Electrical Conductivity (mS/cm)
    Target_EC : REAL := 2.5;
    Fertilizer_Tank_Level : REAL;

    // Freeze Protection
    Freeze_Alarm_Temp : REAL := 2.0;  // °C
    Freeze_Protection_Active : BOOL;

    // Remote Weather Station Integration
    Weather_Forecast_Rain : BOOL;
    Weather_Data_Valid : BOOL;
    Last_Weather_Update : DATE_AND_TIME;
END_VAR

// ==========================================
// BASE APPLICATION LOGIC
// ==========================================

CASE system_state OF
    0: // Idle state
        motor_run := FALSE;
        alarm_signal := FALSE;

        IF start_button AND system_ready AND NOT error_detected THEN
            system_state := 1;
        END_IF;

    1: // Running state
        motor_run := TRUE;
        alarm_signal := FALSE;
        runtime_counter := runtime_counter + 1;

        IF stop_button OR error_detected THEN
            system_state := 2;
        END_IF;

    2: // Error state
        motor_run := FALSE;
        alarm_signal := TRUE;

        IF stop_button AND NOT error_detected THEN
            system_state := 0;
            runtime_counter := 0;
        END_IF;
END_CASE;

// ==========================================
// AGRICULTURAL SPECIFIC LOGIC
// ==========================================

    // Smart Irrigation Based on Soil Moisture
    FOR i := 1 TO 8 DO
        IF Soil_Moisture_Level < Target_Moisture_Min THEN
            IF NOT Weather_Forecast_Rain THEN
                // Only irrigate if no rain forecasted
                Irrigation_Zone_Active[i] := TRUE;
            END_IF;
        ELSIF Soil_Moisture_Level > Target_Moisture_Max THEN
            // Soil saturated - stop irrigation
            Irrigation_Zone_Active[i] := FALSE;
        END_IF;
    END_FOR;

    // ET-Based Irrigation Scheduling
    // Calculate crop water requirement
    Crop_ET := Reference_ET * Crop_Coefficient;

    // Adjust irrigation runtime based on ET
    Irrigation_Runtime := (Crop_ET * Zone_Area) / (Water_Flow_Rate * 60.0);

    // Weather-Based Irrigation Adjustment
    IF Rainfall_Today > 5.0 THEN  // > 5mm rain
        // Skip irrigation - sufficient rainfall
        Irrigation_Schedule_Enable := FALSE;
    END_IF;

    IF Wind_Speed > 20.0 THEN  // High wind
        // Delay irrigation - poor uniformity in wind
        Irrigation_Zone_Active[1..8] := FALSE;
    END_IF;

    // Time-Based Scheduling with Override
    IF Manual_Override THEN
        // Operator control takes precedence
        Irrigation_Zone_Active[Current_Zone] := Manual_Start;

    ELSIF Irrigation_Schedule_Enable THEN
        IF Current_Time >= Scheduled_Start_Time THEN
            // Start scheduled irrigation
            Irrigation_Zone_Active[Current_Zone] := TRUE;
        END_IF;
    END_IF;

    // Fertigation Control - EC-Based
    IF Irrigation_Zone_Active[Current_Zone] THEN
        IF EC_Sensor < Target_EC THEN
            // Inject fertilizer to reach target EC
            Fertilizer_Injection_Active := TRUE;
        ELSIF EC_Sensor > (Target_EC * 1.1) THEN
            // Too concentrated - stop injection
            Fertilizer_Injection_Active := FALSE;
        END_IF;
    END_IF;

    // Fertilizer Tank Monitoring
    IF Fertilizer_Tank_Level < 15.0 THEN  // Below 15%
        Fertilizer_Low_Alarm := TRUE;
        Fertilizer_Injection_Active := FALSE;
    END_IF;

    // Freeze Protection System
    IF Ambient_Temperature < Freeze_Alarm_Temp THEN
        Freeze_Protection_Active := TRUE;
        // Run irrigation to create insulating ice layer
        // OR activate wind machines / heaters
        Irrigation_Zone_Active[1..8] := TRUE;
    END_IF;

    // Water Usage Totalization
    Water_Total_Daily := Water_Total_Daily + (Water_Flow_Rate * 0.1 / 60.0);

    // Daily reset at midnight
    IF Current_Time = TIME#00:00:00 THEN
        Water_Total_Daily := 0.0;
    END_IF;

// ==========================================
// AGRICULTURAL SAFETY INTERLOCKS
// ==========================================

    // Irrigation System Interlocks
    Production_Allowed := (System_Pressure > Min_Pressure)
                          AND (System_Pressure < Max_Pressure)
                          AND (Water_Source_Available)
                          AND NOT Freeze_Protection_Active
                          AND Weather_Data_Valid;

    // Prevent Over-Irrigation
    IF Soil_Moisture_Level > Saturation_Point THEN
        Irrigation_Zone_Active[1..8] := FALSE;
        // Prevent waterlogging and nutrient leaching
    END_IF;

    // Water Conservation Mode
    IF Drought_Restriction_Active THEN
        // Limit irrigation to essential zones only
        Max_Daily_Water := Restricted_Water_Limit;
    END_IF;

    // System Pressure Protection
    IF System_Pressure < Min_Pressure THEN
        // Low pressure indicates leak or pump failure
        Irrigation_Zone_Active[1..8] := FALSE;
        Low_Pressure_Alarm := TRUE;
    END_IF;