Chemical Dosing System for Pharmaceutical

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 & EU GMP Compliance
    Batch_Number : STRING[20];
    Batch_Start_Time : DATE_AND_TIME;
    Batch_Status : INT;  // 0=Pending, 1=Active, 2=Complete, 3=Quarantine

    // Electronic Batch Records (EBR)
    Recipe_ID : STRING[20];
    Material_Lot_Numbers : ARRAY[1..10] OF STRING[20];
    Critical_Process_Parameters_OK : BOOL;

    // Environmental Monitoring (Cleanroom)
    Room_Classification : STRING[10];  // ISO 5, ISO 7, ISO 8
    Particle_Count : REAL;
    Room_Pressure_Differential : REAL;  // Positive pressure in Pa
    Pressure_Alarm : BOOL;

    // Validation & Qualification
    Equipment_Qualified : BOOL;
    IQ_OQ_PQ_Status : INT;  // 1=IQ, 2=OQ, 3=PQ Complete
    Calibration_Due_Date : DATE;
    Calibration_Valid : BOOL;

    // Audit Trail Variables
    User_ID : STRING[20];
    Operation_Timestamp : DATE_AND_TIME;
    Change_Logged : BOOL;
    Electronic_Signature_Required : BOOL;

    // Sterility Assurance
    Sterilization_Cycle_Complete : BOOL;
    Sterility_Validated : BOOL;
    Bioburden_Acceptable : 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;

// ==========================================
// PHARMACEUTICAL SPECIFIC LOGIC
// ==========================================

    // GMP Batch Control - No production without batch record
    IF Batch_Status <> 1 THEN  // Not Active
        Production_Enable := FALSE;
    END_IF;

    // Critical Process Parameters (CPP) Validation
    Critical_Process_Parameters_OK :=
        (Temperature >= Recipe_Temp_Min AND Temperature <= Recipe_Temp_Max) AND
        (Pressure >= Recipe_Pressure_Min AND Pressure <= Recipe_Pressure_Max) AND
        (Mix_Speed >= Recipe_Speed_Min AND Mix_Speed <= Recipe_Speed_Max);

    IF NOT Critical_Process_Parameters_OK THEN
        Batch_Status := 3;  // Quarantine batch
        Production_Enable := FALSE;
        // Log deviation for quality review
    END_IF;

    // Cleanroom Environmental Monitoring
    IF Room_Pressure_Differential < Min_Pressure_Diff THEN
        Pressure_Alarm := TRUE;
        Production_Enable := FALSE;
        // Environmental excursion requires investigation
    END_IF;

    IF Particle_Count > Max_Particle_Limit THEN
        Room_Classification := 'FAIL';
        Production_Enable := FALSE;
        // Cleanroom integrity compromised
    END_IF;

    // Equipment Qualification Check
    Calibration_Valid := (Current_Date <= Calibration_Due_Date);

    IF NOT Equipment_Qualified OR NOT Calibration_Valid THEN
        Production_Enable := FALSE;
        // Equipment must be qualified and calibrated
    END_IF;

    // Audit Trail - Log all critical changes
    IF Parameter_Changed THEN
        Operation_Timestamp := CURRENT_DATETIME();
        Change_Logged := TRUE;
        Electronic_Signature_Required := TRUE;
        // Store: User_ID, Old_Value, New_Value, Reason, Timestamp
    END_IF;

    // Material Traceability
    FOR i := 1 TO 10 DO
        IF Material_Lot_Numbers[i] = '' THEN
            Material_Traceability_Complete := FALSE;
            // All materials must have lot tracking
        END_IF;
    END_FOR;

// ==========================================
// PHARMACEUTICAL SAFETY INTERLOCKS
// ==========================================

    // GMP Production Interlocks
    Production_Allowed := Equipment_Qualified
                          AND Calibration_Valid
                          AND (Batch_Status = 1)
                          AND Critical_Process_Parameters_OK
                          AND NOT Pressure_Alarm
                          AND (Particle_Count <= Max_Particle_Limit)
                          AND Sterility_Validated
                          AND Material_Traceability_Complete;

    // Batch Integrity Protection
    IF Emergency_Stop OR Critical_Alarm THEN
        Batch_Status := 3;  // Automatic quarantine
        // Batch requires quality investigation
    END_IF;

    // Cross-Contamination Prevention
    IF Previous_Product <> Current_Product THEN
        IF NOT Changeover_Cleaning_Complete THEN
            Production_Enable := FALSE;
            // Prevent cross-contamination
        END_IF;
    END_IF;