FB_TemperaturePID

 Function Block - Provides PID temperature control with auto tuning.

Inputs

Input	Data Type	Range	Unit	Default	Description
iEN	BOOL				Enable function.
iREFTEMP	LREAL				Reference temperature [°C].
iTEMP	LREAL				Actual temperature [°C].
iSTART	BOOL				Start PID or auto tuning.
iMODE	BOOL				FALSE-automatic. TRUE-tuning.
iKP	LREAL				PID Proportional Gain.
iKI	LREAL				PID Integral Gain.
iKD	LREAL				PID Derivative Gain.
iTC1S	BOOL				Sampling Time is 1s.
iTC5S	BOOL				Sampling Time is 5s.
iPROGCYCLE	LREAL				Execution time of the function [ms].

Outputs

Output	Data Type	Range	Unit	Description
oOK	BOOL			Function enabled.
oCHECKSTABLE	BOOL			TRUE when checking if ambient temperature is stable.
oTUNESTART	BOOL			Tuning is started.
oTUNEOK	BOOL			Tuning is completed.
oTAU	LREAL			System Time Constants.
oPWM	BOOL			PWM command for heater.
oERR	BOOL			Function error.
oERRID	INT			Function ID error (in case of oERR=TRUE).
oPOWER	LREAL			% of power requested from heater (100%=full power).
oTICK	BOOL			Pulse every sampling time.

Remarks

Figure 1: FB_TemperaturePID

Usage

Tuning Process

Figure 2: FB_TemperaturePID Usage 1

Tuning Procedure

1. Verify the ambient temperature is stable.
   The measured delta_temp=Tmax-Tmin must be lower than 0.1*Tmax.
   This step takes 10 cycles (10*iTC5s or 10*iTC1s).
   The tuning fails (oERR=TRUE, oERRID=1) if the ambient temperature is greater than 0.1*Tmax, otherwise Tamb=(Tmax+Tmin)/2.
2. Start tuning Phase1: output oPWM is kept TRUE until the final measured temperature iTEMP gets over iREFTEMP/2.
   After that, oPWM is kept LOW.
3. Start tuning Phase2.
   With oPWM kept LOW, the temperature gets down until the final value is lower than [(iREFTEMP/2-Tamb)*0.368+Tamb].

After, PID gains are calculated as:

Kp=10
Ki=0.14
delta_time = time to complete Phase2

Kd=SQRT(delta_time)*7

The tuning is completed.

• 
  

• oTAU may be useful for setting the proper sampling time (1s or 5s).

Start PID Controller

Figure 3: FB_TemperaturePID Usage 2

• When starting the PID controller:
  • The output oPWM is modulated five times within the sampling time (blue line is oTICK, green line is oPWM).
  • Each pulse length depends on output oPOWER (100%=full length).

Figure 4: FB_TemperaturePID Usage 3

FBD Language Example

FFLD Language Example

IL Language Example

Not available.

ST Language Example

//Run PID function with determined proportional, integral, and derivative gains

//send PWM output to command heater
udfbThPID( TRUE, 90, Temp_mes, TRUE, FALSE, KP, KI, KD, FALSE, TRUE, 1);
Tau_Calculated := udfbThPID.oTAU;
PWM_CMD := udfbThPID.oPWM;
Power := udfbThPID.oPOWER;
Tick := udfbThPID.oTICK;