i am new to PLCs. 

suppose a valve is set up to Fail Close, when Power to PLC is lost it Fail Closes. but when PLC power is again back then it OPENs. requirement is that on Power Restoration the valve should REMAIN in Close state.

Should i change relevant DB initial value? Actual Value? What is difference between two? in a program how to know that a DB is Instance DB or Shared DB?

Please Help

Hello Fahad_Ali.

Have you checked the logic of the valve output?

You can see here difference between actual and intial value of DB data

And to difference Instance DB from shared, you can see it in simatic manager screen where you see all the block, see the "Type" column and there it says what kind of DB is.

...sent from App

Thank you dear for ur response..

do u think that response of valve on restoration of power has nothing to do with relevant DB actual or initial value?

and "Actual value" is not CURRENT VALUE. ???? it is a sort of initial value. ???

and after editing "actual value" do we have to put the cpu in "stop" state or what?

Hello Fahad.

As in the FAQ says, initial value only is taken in account when you create a new DB or declare a new value on an existing DB. For PLC, only actual values are relevant. When you want to initialize a DB what you do is copy the values of "Initial Value" and move them to "Actual Values" cause actual values are relevant for PLC.

Actual value is the Current value.

You can modify Actual values without the need to stop PLC. You can even do it from a Variable table.

And addressing your valve issue. Valve should be connected to an output module, so, I'd suggest you to look at the logic that is writing the value to the output signal that controls your valve.

Hi dear

when DB is in Online/Monitor state the "Actual Value" does not change. it remains constant even though parametre(analog) is changing. 

as per valve issue the logic implemented is OK in running state and even when power goes out valves changes its state to "CLOSE" even if it was in OPEN state before loss of power, (which is perfectly alright i.e according to our requirements). but when PLC Powers up again then it OPENS (requirement is that it should stay CLOSE). SO i think it has to do something with INITIAL/ACTUAL VALUE for relevant VALVE DB.

Oh, I see. Is an analog valve. Well, you can create some logic to prevent the analog output get a value after a power loss. Probably what is happening is that the last value remains after power loss. You could add some permission that if its not set, you write a safe analog outpit value, maybe writting 0 works for your system.

...sent from App

Dear it is not an analog valve, it is a digital one but it always OPENS upon RESTORATION OF POWER and always CLOSES on LOSS OF POWER. 

CLOSE ON LOSS OF POWER is normal.

OPENING at RESTORATION OF POWER is not required.

AT RESTORATION OF POWER valve MUST remain in CLOSED STATE. 

at this time i dont have access to PLC logic. 

anyways, Thanks brother

Oh, I see, I'd suggest you to add some permission to it, something that can detect a power failure.

So, you don't have access to the PLC program?

Hi

this seems really tough. let my boss deal with it, i quit.

can you kindly suggest me good read for really a starter. Manual should deal with "debugging/maintenace" of Step7 and wincc instead of focusing on "designing".

it will be a great help for me.

thank you or your time