Siemens SIMATIC STEP 7 V5.2 Getting Started page 79

8.2 Programming Functions
In this section, you will program a timer function in our example. The timer function
enables a fan to switch on as soon as an engine is switched on (see Chapter 5),
and the fan then continues running for four seconds after the engine is switched
off (off-delay).
As mentioned earlier, you must specify the input and output parameters of the
function ("in" and "out" declaration) in the variable detail view.
The LAD/STL/FBD program window is open. You work with this variable detail
view in the same way as with the detail view for the function block (see Chapter
5).
Enter the following declarations:
Programming the Timer Function in Ladder Logic
STEP 7 Getting Started
A5E00171228-01
Programming a Function
Select the current path for entering the
Ladder instruction.
Navigate in the Program Elements
catalog until you reach the element
S_OFFDT (start off-delay timer), and
select the element.
Insert a normally open contact in front
of input S.
Insert a coil after output Q.
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