21: PID INSTRUCTION21-14 « FC4A MICRO SMART USER ’S MANUAL »Application ExampleThis application example demonstrates a PID control for a heater to keep the temperature at 200°C.In this example, when the program is started, the PID instruction first executes auto tuning according to the designated ATparameters, such as AT sampling period, AT control period, AT set point, and AT output manipulated variable, and also thetemperature data inputted to the analog input module. The control output remains on to keep the heater on until the tem-perature reaches the AT set point of 150°C. Auto tuning determines PID parameters such as proportional gain, integraltime, derivative time, and control action.When the temperature reaches 150°C, PID action starts to control the temperature to 200°C using the derived PID param-eters. The heater is turned on and off according to the output manipulated variable calculated by the PID action. When theheater temperature is higher than or equal to 250°C, an alarm light is turned on by the high alarm output.The analog input module data is also monitored to force off the heater power switch and force on the high alarm light.Operand SettingsNote 1: The output manipulated variable during auto tuning is a constant value. In this example, the AT output manipulatedvariable is set to the maximum value of 100 (100%), so the control output (S2+6) remains on during auto tuning.Note 2: When analog I/O module FC4A-L03AP1 is used for the PID instruction, select the binary data to make sure that theprocess variable takes a value of 0 through 4095.Operand Function Description Allocation No. (Value)S1+3 Operation mode AT (auto tuning) + PID action D3 (1)S1+4 Linear conversion Enable linear conversion D4 (1)S1+5 Linear conversion maximum value 1300°C D5 (13000)S1+6 Linear conversion minimum value 0°C D6 (0)S1+10 Integral start coefficient 100% D10 (0)S1+11 Input filter coefficient 70% D11 (70)S1+12 Sampling period 500 ms D12 (50)S1+13 Control period 1 sec D13 (10)S1+14 High alarm value 250°C D14 (2500)S1+15 Low alarm value 0°C D15 (0)S1+19 AT sampling period 1.5 sec D19 (150)S1+20 AT control period 3 sec D20 (30)S1+21 AT set point 150°C D21 (1500)S1+22 AT output manipulated variable 100% (Note 1) D22 (100)S2+1 Auto/manual mode Auto mode M1 (OFF)S2+2 Output manipulated variable limitenable Disable output manipulated variable limits M2 (OFF)S2+3 Integral start coefficient disable Enable integral start coefficient (S1+10) M3 (OFF)S2+4 High alarm output ON: When temperature ≥ 250°COFF: When temperature < 250°C M4S2+6 Control outputRemains on during auto tuning;Goes on and off according to the controlperiod (S1+13) and output manipulated vari-able (S1+1) during PID actionM6S3 Set point 200°C D100 (2000)S4 Process variable Analog input data of analog I/O module 1, ana-log input channel 0; stores 0 through 4095 D760Analog input operating status Stores 0 through 5 D761Analog input signal type Type K thermometer D762 (2)Analog input data type 12-bit data (0 to 4095) (Note 2) D763 (0)D1 Manipulated variable Stores PID calculation result D102PID start input Starts to execute the PID instruction I0Monitor input Starts to monitor the analog input moduledata for high alarm and operating status I1Heater power switch Turned on and off by control output M6 Q0High alarm light Turned on and off by high alarm output M4 Q1
