FP_PID

PID processing with optional PWM output

PID processing is performed to keep the process value PV as close as possible to the set point value SP. In contrast to FP_PID_BASIC, this instruction enables a PWM output (on-off output). Auto-tuning is also available to automatically calculate the PID control data Kp, Ti, and Td.

Parameters

Input

Run (BOOL): Start condition
s1_Control (PID_Control_DUT): Control data
s2_ProcessValue (INT): Process value (-30000–30000)
s3_Parameters (PID_PARAMETERS_DUT): PID control parameters

Input/output

s4_WorkArea (PID_WORK_AREA_DUT): Data table of PID parameters

NOTE
When you execute the instruction for the first time, i.e. when the execution condition specified at Run turns to TRUE, the default values are written to the DUT members 1 to 9 of DUT .

Before the second execution of FP_PID, you need to change the DUT members 1 to 9 of the DUT to the required values.

Output

PWM (BOOL): Pulse-width modulated output (optional, can be used instead of manipulated value output)

Remarks

The period (cycle) of the PWM output is the sampling time Ts (the frequency of the PWM output is 1/Ts) and the duty is the manipulated value MV in 0.01% units, e.g. MV = 10000 means a duty of 100%.
The instruction has to be executed twice. The first execution resets the values in PID_WORK_AREA_DUT, then the correct values for the DUT members 1 to 9 in PID_WORK_AREA_DUT need to be set so that the second execution of the instruction uses the correct values.

Error flags

sys_bIsOperationErrorHold (turns to TRUE and remains TRUE)

if the area specified using the index modifier exceeds the limit.
if a value specified for a parameter of PID_Parameters_DUT is outside the permissible range

sys_bIsOperationErrorNonHold (turns to TRUE for one scan)

if the area specified using the index modifier exceeds the limit.
if a value specified for a parameter of PID_Parameters_DUT is outside the permissible range

Example

POU header

All input and output variables used for programming this function have been declared in the POU header. The same POU header is used for all programming languages.

	VAR
		Automatic: BOOL:=TRUE;
		dutControl: PID_Control_DUT;
		PV: INT:=0;
		ParametersHold: PID_Parameters_DUT;
		ParametersNonHold: PID_Work_Area_DUT;
		bPWMOutput: BOOL:=FALSE;
	END_VAR

LD body

BODY
    WORKSPACE
        NETWORK_LIST_TYPE := NWTYPELD ;
        ACTIVE_NETWORK := 0 ;
    END_WORKSPACE
    NET_WORK
        NETWORK_TYPE := NWTYPELD ;
        NETWORK_LABEL :=  ;
        NETWORK_TITLE :=  ;
        NETWORK_HEIGHT := 7 ;
        NETWORK_BODY
B(B_VARIN,,dutControl,15,2,17,4,);
B(B_VARIN,,ParametersHold,15,4,17,6,);
B(B_CONTACT,,Automatic,6,1,8,3,);
B(B_VARIN,,ParametersNonHold,15,5,17,7,);
B(B_F,FP_PID!,,17,0,30,7,,?DRun?Ds1_Control?Ds2_ProcessValue?Ds3_Parameters?Ds4_WorkArea?As4_WorkArea?APWM);
B(B_VARIN,,PV,15,3,17,5,);
B(B_VAROUT,,bPWMOutput,30,1,32,3,);
L(1,2,6,2);
L(8,2,17,2);
L(1,0,1,7);
        END_NETWORK_BODY
    END_NET_WORK
END_BODY

ST body

bPWMOutput := FP_PID(Run := Automatic, 
                     s1_Control := dutControl,
                     s2_ProcessValue := PV,
                     s3_Parameters := ParametersHold,
                     s4_WorkArea := ParametersNonHold);