Using RETAIN - help

Hi Everyone, I´m using TIAV14SP1, RTAdvanced (PC) and S71215.

I need to retain values in case of power failure/power off.

CASE 01:

My recipe is sending data to a DB. In case of a POWER FAILURE, I need the PLC to start at the exact point where it was before the power failure.

CASE 02:

I also need to store important adjustments of the machine (offsets, PID adjustments, etc).

So, how to make this data RETAIN its values in case of POWER FAILURE? I´m testing it with the PLCSim but it´s not holding the values.

PS: I´m setting the field RETAIN in the DBs.

What am I doing wrong? Thanks.

Have a look at his example, if you have lots of data this would be specially helpful.

PLCSIM should retain the values on switching start-stop-start, is that what you're doing?

 Hello Kal.A,

I´m pressing a button to SWITCH PLC OFF and then SWITCH PLC ON again...

If I just press stop-start would it represent the same as a power failure?

Thanks.

Kal.A

Have a look at his example, if you have lots of data this would be specially helpful.

PLCSIM should retain the values on switching start-stop-start, is that what you're doing?

0_Einstein

For S7-1200/1500:

Unless the PLC power is lost, the RETAIN action does not take place.  The PLC retains the current values of everything, retained or not.

On power up, DBs are initialized to their start values unless configured as RETAIN.  In that case, the save values are restored to the DB's current values.

@Einstein
As far as I know the RETAIN function is used when transferring from STOP to RUN.

DB tag not set to retain and transition to RUN will result in the tag being reinitialized to its start value.

The attached animation for your review.

@Eduardo:
There is one issue that I do not know how to test for.

Assume the HMI/Scada is running and the PLC powers on. Is the PLC initialized from the HMI/Scada or are the PLC tag values used?

My designs have storage data area and a usage data area. On startup the usage area is seeded from the storage area. This method has worked well for me.

0_Einstein

My understanding about "RETAIN" is... On power loss, the PLC is designed to have enough power to backup all retained values to flash memory (or something like that).

On power up, data is copied from the flash memory to proper locations as you stated, during the OFF to RUN state, before launching a Startup OB.

 I am not fighting you on what "retain" means.

What I am voicing is the fact that the tags marked as "retain" does not initialize to start values when transitioning to RUN. The other tags do initialize to start values.

From a designer's perspective the value of the tag is retained when transitioning to RUN. In actual fact the retained tags are not inititalized.

Non-retained tags are overwritten to start values when the PLC goes to RUN.

This fail to initialize attribute makes it seems as though the value in the tag is retained while in actual fact it is not. Someone could in error assume it shows the retention behaviour while it is not.

EduardoFS

 Hello Kal.A,

I´m pressing a button to SWITCH PLC OFF and then SWITCH PLC ON again...

If I just press stop-start would it represent the same as a power failure?

Thanks.

Kal.A

Have a look at his example, if you have lots of data this would be specially helpful.

PLCSIM should retain the values on switching start-stop-start, is that what you're doing?

 

 That is a very good question and I don't know the answer as to what the power switch does. I am traveling and will not have be able to have look till tomorrow.

There are three modes to the CPU, RUN, START and STOP so I would assume that turning On the CPU from an Off state equates to START as far as RETAIN and NON RETAIN is concerned.  Retained values should remain  intact.

Kal.A

That is a very good question and I don't know the answer as to what the power switch does. I am traveling and will not have be able to have look till tomorrow.

There are three modes to the CPU, RUN, START and STOP so I would assume that turning On the CPU from an Off state equates to START as far as RETAIN andtNON RETAIN is concerned.  Retained values should remain in intact and no-retained will depend on start-up configuration of the CPU. If it is set for warm re-start then no menory reset will occure and no-retained will hold their value.

Safe travels to you!

My previous replies aims to go into detail of what you speak of now. The GIF animation demonstrated what the simulation delivers for power on and stop -> run.

Safe return.

Thanks qwazee. I am on my phone and not a very good network, hence didn't even try clicking on your image. I will have a look a bit later.

Cheers