Dear colleagues, 

I have one system which consist S7 1200, and purpose of that system is temperature regulation. It has 3 PID blocks (PID_Compact V1.2). Problem is when we have power failure, or if we have to switch of power supply due to maintenance PID block doesn't start. For eg. when I go to commissioning window in error window we have message like "Set point outside limits", even when set point is 3, and Process value high limit is 15 (lower limit is 0). Then I start block from commissioning window and everything is ok until power  failure. 

Software has been created by using TIA V13.

If you have similar experience, or you know solution of this problem, please share it. 

Best regards, 

Ugljesa

Hi, 

Check the "Enable last mode after CPU restart" checkbox. 

See the SIMATIC S7-1200, S7-1500 PID control manual chapter "4.2.1.1 Basic settings V1" on the page 100.

Hello Ugljesa,

I'd sometimes the same problem, but not with all the PID's within the same project.

I've found that by some reason in the PID DB the "state" (output variable) and "sRet.i_mode" both went to 0. Until I have a better solution, for now I will move value 3 to these variables when this problem occurs. In addition I'm using a 10s on delay timer to detect the 0 value. So after 10s value 3 will be written. The timer will also set the "reset" bit (input variabel inside the PID DB) via a pulse bit. 

Best regards,

Alex

Hi,

First I want to thank you for your answer. I checked that and Enable last mode after CPU restart is set to TRUE. 

Hello,

Perhaps these links might help:

How do you prevent the PID Compact controller of the S7-1200 from switching off when the controller is switched off and on again and in the case of invalid process values?

How do you restart a PID controller that has been stopped because of a scan time error or switch off the scan time monitoring?

Best regards,

Wizard

This might help. 

I will try this. Thank you.