Initial values

[naturephoenix]

Hi,

What do you guys do when you have situation like this:

After leaving commisioning some variables(Tags inside DBs) I want to be fixed even when PLC lose supply and starts again, but some variables I want that they have last user value.

So If I set some reference of PID and during sometime user change reference I have 2 options:

1. Once PLC lose supply and starts again reference is my original reference

2. Reference is user's last reference typed via touch panel.



How do you guys split up these variables, how do u handle this?
DO you might use OB100 for Option 1 or???

 

[cardosocea]

There is normally an area of the PLC that is non-volatile... perhaps that could be where you want to keep your variables?

 

[JesperMP]

I guess it is a Siemens S7-300 or S7-400 since you mention OB100.

You can for each DB specify if it shall be retained (the default) or non-retained.

 

[naturephoenix]

I guess it is a Siemens S7-300 or S7-400 since you mention OB100.

You can for each DB specify if it shall be retained (the default) or non-retained.

Yes its SIEMENS s7-300

Where is that option

 

[JesperMP]

Open the properties of the DB in question.
Then there is a selection to activate "non-retain".

 

[ASF]

I don't think that's quite what the OP is after. Retentive means, does it hold it's last value, or does it revert to zero when the PLC powers up. Whereas, the OP wants some values to retain the last value, and others to revert to a fixed (but not necessarily zero) value upon power up. Or have I misunderstood?

My Siemens knowledge is limited, but IIRC OB100 is a block that runs once at startup. I would put write some code to move constants into the relevant tags at startup (for those that you want to reset to "default" values), and for the ones that you want to retain the last user setting, just leave them alone and make sure that they are checked as retentive, as per the advice above.

Hopefully I've understood what you're after properly!