PID_compact TIA Basic V13

Hi,

Please advise what could be a source of a problem with PID_Compact, it is called in cycled interrrupt. OB, and goes into fine-tuning (in configuration wizard), without any errors, but just don't turn on PWM output, though it have to.

I suppose some pre-requisite with configuration, just in the beginning of learning pid in Tia.

Any ideas of most probable cause of this ? 

Thanks! (due to I can only attach 1 file, another file will be in next reply to this message  )

 Hello Eam,

First to all, i'm noticing that you are use a S7-1200... PID simulation have a very annoying problem with that devide, coz for new versions of PID_Compact and PID_TEMP the output will never work...

I recommend you to change to and older version of the PID, I mean, go to Technology/PID Control/Compact PID and the click on version (it appear V5.0 - v4.0- v3.0..... and choose v3.0), It will allow you use only Compact V1.2 and 3step, but the PID_Compact v1.2 works very similiar to PID Compact V2.2.

You only have to check how to "initialize" the PID, because it has some different instructions compared with V4.0. Just play with the instruccions, and the one to control the PID mode is this:

"PID_Compact_1".sRet.i_Mode

If you have any doubt, jus post it.

Regards

---------------------

BEFORE CHECK THESE EXAMPLES, read the PID_Compact manual for V3.0, there you can check the PID modes,

An small example  of PID initializing:

"PID_Compact_1".sRet.i_Mode := 4;

"PID_Compact_1".ManualValue := 0.0;

 "PID_Compact_1"(Setpoint := "Temp Max",

                 Input := "Sim_PT1_DB".Output

 );

 "PID_Compact_1".sRet.r_Ctrl_Cycle := 1.0;

 "PID_Compact_1".sRet.i_Mode := 0;

_______

Example of running:

IF "Act PID" = FALSE THEN

        "PID_Compact_1".sRet.i_Mode := 3;

        "Act PID" := TRUE;

        "PID_Compact_1".Reset := FALSE;

    END_IF;

    IF "TUNE PID" = TRUE THEN

        "PID_Compact_1".sRet.i_Mode := 2;

        "TUNE PID" := FALSE;

    END_IF;

    "PID_Compact_1"(Setpoint:="Temp Max",

                    Input:="Sim_PT1_DB".Output

    );

    //**this is an example DB**

    "Sim_PT1_DB"(Reset:=False,

                 Calc_Param:=False,

                 Input:="PID_Compact_1".Output,

                 TM_LAG1:=10.0,

                 Cycle:=0.1,

                 Max_Out:=100.0,

                 AMB_TEM:=19.0);

    IF "PID_Compact_1".sParamCalc.i_Event_TIR = 9900 THEN

        "PID_Compact_1".Reset := TRUE;

        "Act PID" := FALSE;

    END_IF;

eam_rts

Hi,

Please advise what could be a source of a problem with PID_Compact, it is called in cycled interrrupt. OB, and goes into fine-tuning (in configuration wizard), without any errors, but just don't turn on PWM output, though it have to.

I suppose some pre-requisite with configuration, just in the beginning of learning pid in Tia.

Any ideas of most probable cause of this ? 

Thanks! (due to I can only attach 1 file, another file will be in next reply to this message

Hi eam,

one reason why output is 0.0 while input is below setpoint might be that "Invert control logic" checkbox in basic settings is activated (Config.InvertControl / sPid_Cmpt.b_InvCtrl = TRUE).

Is this the case?

This is only necessary if an increasing output should decrease the input e.g. for cooling.

If not, which values did you configure for

- Minimum ON / OFF time (Advanced settings -> PWM limtis in configuration editor)

- Sampling time of PID algorithm (Advanced settings -> PID parameters in configuration editor)

- Cyclic time of the calling OB

Cheers

Mach11

 Dear Jav, thanks much for your reply, 

I don't yet played with PID, was going to, and wanted to check if I got you right

Jav

 PID simulation have a very annoying problem with that devide, coz for new versions of PID_Compact and PID_TEMP the output will never work...

 regarding simulation - you meant working in configuration wizard? because my portal is Basic and don't have PLCSIM in it.  

Jav

 (it appear V5.0 - v4.0- v3.0..... and choose v3.0), It will allow you use only Compact V1.2 and 3step, but the PID_Compact v1.2 works very similiar to PID Compact V2.2.

 My Tia of  V13 and PLC of 2.2 put 1.2 version of PID Group in the project, and 1.2 for function block - do I have to choose again 3.0 for  PID COMPACT group and re-choose 1.2  for function block version? see attachment

 so your idea is just to try calling the block playing with parameters and don't touch Configuratoin mode (wizard or simlulation as you called it )

Dear Mach11,

Thanks much for your reply , I tried both inverted and not inverted version,

Most likely my mistake that I configured PID partially with tech. block configuration wizard, Jav in reply to my post said that this won't work on 1200 of 2.2 version., and I have to play with only FB parameters in program. 

I will have 2 PID in my application (HVAC) one for cooling with external air fans and second to control positive pressure (also fans but exhausting ) in a premise , so the processes are very slow. Now I'm going to use it like this - 

OB cycled inerrupt of 1000 ms

PID samplng time 5 seconds

MIn OFF ON time - 1 minute

Hi eam,

there is no problem with using the configuration editor for PID_Compact.

The only thing that doesn't work is simulating PID_Compact V2.x with PLCSIM 1200, but this does not concern the configuration editor and as far as I understood you don't use PLCSIM so this is no problem for you.

One problem that I see is the configuration of your PWM times:

PID sampling time is always the period time of your PWM.

So your minimum on and off times should be between PID sampling time and OB cyclic time.

But with your configuration the minimum on and off times are bigger than the PWM period time, so you should decrease your minimum time or increase your PID sampling time depending on your application.

Please also be aware if you have 1 sec OB cyclic time and 5 sec PID sampling time, that the PWM can only work in 20% steps: 0%, 20%, 40%, 60%, 80%, 100%. Depending on your application this resolution might be too rough to achieve good results

You could achieve a better resolution if you decrease the OB cyclic time or if you increase the PID sampling time e.g. with 0.5 sec OB cyclic time and 5 sec PID sampling time you get 10% steps resolution for your PWM.

Hello Eam, I saw that you are no using S7-PLCSIM, so my recommendation is not useful... that's only for Simulations...

If you are doing you process and sending the data to the PC, it may be more likely what Mach is saying. However, it can be useful if you send us a Print of your PID config, how you parameterized or configurated the PID-----> PLC_OV >Technologic Objects > PID_Compact > Configuration

Regards,

Javier

Dear Mach11,

Thanks for your guidance regarding sample time and ON/OFF time for PID_Compact. I tried it with PWM output and it worked well . 

Now I play with analog output configuration and observe big after-action saturation - i.e. it increases output till 100% then, when error is fully removed , output is relucting for long time, i.e. becomes saturated for long time  , e.g. 30% while error = 0. 

Pls see attached file . 

in addition to the previous post - more details,

I use invert logic for cooling. So when Tinside > Tsetp. PID responds, bigger error, bigger PID output, when error decrease, PID output also decreases and responds. 

But as soon as error = 0 , the PID output freezes , and just keeps some value not equal to 0.

Seems like it goes in " hidden " inactive mode, but status output = 3 (for automatic). 

In this state, if I re-trigger "PID_Compact_2".sRet.i_Mode  --> 0 --> 3 then PID wakes up again.

I attach PID tech. obj. settings - not latest version, I also tried to remove Integral time with no effect.