Routines to compute PID value and regulate heater controls

PROCESS_PHASE-COMPUTE_PID.ino

'------------------------------------------------------------------------------- 
'  Regulates heater controls based on phase temperature parameters 
'-------------------------------------------------------------------------------
PROCESS_PHASE:      
    GOSUB READ_TEMPERATURE
    GOSUB COMPUTE_PID

    WHILE (elapsedTime <> 0)
        IF (SecondsChanged = 1) THEN 
            elapsedTime = elapsedTime - 1

            GOSUB READ_TEMPERATURE
            GOSUB COMPUTE_PID

            TimeOn = (cycleTime * OutVal)/100

            Tvar = Tvar + 1

            IF (Tvar >= outMax) THEN Tvar = outMin

            IF (Tvar < TimeOn AND curTemp < setpoint) THEN
               PORTPIN = 1 : PINSTATE = 1 : GOSUB SET_PIN
            ELSE 
                PORTPIN = 1 : PINSTATE = 0 : GOSUB SET_PIN
            ENDIF

            GOSUB DISPLAY_STATUS

            SecondsChanged = 0
        ENDIF
    WEND     
RETURN

'-------------------------------------------------------------------------------
'  Computes the output drive from the individual PID components.
'-------------------------------------------------------------------------------
COMPUTE_PID:     
    errorCurrent = setpoint - curTemp

    pTerm = Kp * errorCurrent

    iTerm = iTerm + (Ki * errorCurrent)

    IF (iterm > outMax) THEN iTerm = outMax
    IF (iTerm < outMin) THEN iTerm = outMin

    dTerm = (curTemp - lastMeasured)

    OutVal = (pTerm + (iTerm - (Kd * dTerm)))

    lastMeasured = curTemp
RETURN