One Shot in Step 7

Sorry for the silly question, but i don't get to understand what is the diference in the Siemens Step 7 in using the:

---| |------(P)------------( )

or:


---| |----- POS -----------( )


being (P): Positive RLO Edge Detection
and POS: Address Positive Edge Detection

I have to make some changes online in a running plant, and i need the one shot to act with a sensor input.

Which one should I use?
and what is the difference between them?
and... what is RLO?

thanks for the answers.

rlo is the result of logic operation

for sensor positive edge
a i0.0
fp m0.0
=m0.1


which corresponds to to (p)


i don't know what is the other for

In first, RLO is result of logic operation. For example, if you connect in series 2 NO contacts I0.0 and I0.1, RLO will be 1 only if both I are 1 and 0 in another case after this contacts executing.
I translated your (P) and POS to STL to show difference. As you can see, both operators use same STL operator FP - positive edge detection. But in case of (P) positive edge of RLO is detected (RLO = M0.0). In second case positive edge of M0.4 is detected (through RLO too, but for you it's not important). And result is 1 only if Enable input M0.3 = 1.
So, operation principle is the same - edge detection. You can use either method.

The operation of (P) and POS are not quite the same.

For (P) the edge detection is applied to the all of the logic prior to the (P) using the RLO, this means that any of the logic bits feeding the (P) will be detected as a rising edge (in effect the last bit that rises will cause the edge to be detected)

For POS, the edge detection is only applied to the one bit that you specify.

If you only use one bit, they do indeed reduce to the same, but POS shows a BLD to allow the correct ladder to display.

POS
(P)

Once again, thanks a lot. That was indeed very clarifying.

What can i say... better that Siemens documentation