Chemical Dosing System for Food & Beverage

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;


    // FDA 21 CFR Part 11 Compliance Variables
    CleanInPlace_Active : BOOL;
    CIP_Cycle_Complete : BOOL;
    Sanitization_Timer : TON;
    Sanitization_Duration : TIME := T#15m;

    // Food Safety Monitoring
    Product_Temperature : REAL;
    Max_Safe_Temperature : REAL := 45.0;  // °C for cold chain
    Min_Cook_Temperature : REAL := 74.0;   // °C for cooking
    Temperature_Alarm : BOOL;

    // Hygiene Interlocks
    Hygiene_Check_Passed : BOOL;
    Last_Sanitation_Time : DATE_AND_TIME;
    Sanitation_Required : BOOL;

    // HACCP Critical Control Points
    CCP_Temperature_OK : BOOL;
    CCP_Time_OK : BOOL;
    CCP_Pressure_OK : BOOL;
    HACCP_Alarm : BOOL;

    // Product Contact Surface Status
    Surface_Sanitized : BOOL;
    Washdown_Mode : BOOL;
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;

// ==========================================
// FOOD & BEVERAGE SPECIFIC LOGIC
// ==========================================

    // CIP (Clean-in-Place) Sequence Enforcement
    IF CleanInPlace_Active THEN
        Production_Enable := FALSE;
        Motor_Run := FALSE;
        // Lock out all production during sanitation cycle
    END_IF;

    // Sanitization Timer Logic
    Sanitization_Timer(IN := CleanInPlace_Active, PT := Sanitization_Duration);
    CIP_Cycle_Complete := Sanitization_Timer.Q;

    // Temperature Monitoring for Food Safety (HACCP CCP)
    IF Product_Temperature > Max_Safe_Temperature THEN
        Temperature_Alarm := TRUE;
        HACCP_Alarm := TRUE;
        // Log violation for regulatory audit trail
    END_IF;

    // Periodic Sanitation Requirement Check
    // Require sanitation every 4 hours of operation
    IF Runtime_Counter > 144000 THEN  // 4 hours in 100ms cycles
        Sanitation_Required := TRUE;
        Production_Enable := FALSE;
    END_IF;

    // Washdown Mode - Water-resistant operation
    IF Washdown_Mode THEN
        // Reduce speeds during cleaning
        Target_Speed := 20.0;
        // Disable non-washdown rated equipment
    END_IF;

    // HACCP Critical Limits Monitoring
    CCP_Temperature_OK := (Product_Temperature >= Min_Cook_Temperature) AND
                          (Product_Temperature <= Max_Safe_Temperature);
    CCP_Time_OK := (Process_Timer >= Min_Process_Time);
    CCP_Pressure_OK := (System_Pressure >= Min_Safe_Pressure) AND
                       (System_Pressure <= Max_Safe_Pressure);

    IF NOT (CCP_Temperature_OK AND CCP_Time_OK AND CCP_Pressure_OK) THEN
        HACCP_Alarm := TRUE;
        // Trigger batch rejection
    END_IF;

// ==========================================
// FOOD & BEVERAGE SAFETY INTERLOCKS
// ==========================================

    // Production Allowed Only When Hygienically Safe
    Production_Allowed := NOT CleanInPlace_Active
                          AND CIP_Cycle_Complete
                          AND Hygiene_Check_Passed
                          AND Surface_Sanitized
                          AND NOT Sanitation_Required
                          AND NOT HACCP_Alarm
                          AND CCP_Temperature_OK
                          AND NOT Temperature_Alarm;

    // Emergency Stop Must Trigger CIP Before Restart
    IF Emergency_Stop THEN
        Sanitation_Required := TRUE;
        CIP_Cycle_Complete := FALSE;
    END_IF;