Eaton easySafety Manual page 168

Wiring with easySafety
164
Assigning operands at the input of a standard
function block
The following operands can be assigned to the input of a
standard function block:
• Constants, e.g.: 42,
• Markers such as MD, MW, MB,
• All output variables of the function blocks ...QV>
h
Caution!
When assigning the parameters of a standard function
block input, ensure that these cannot be triggered with
impermissible values during operation. There is a danger
of this if you assign a variable that can assume negative
values to a standard function block input that can only
accept positive values.
If, for example, the standard function block T timing relay
is triggered with a negative time set value, it will no longer
switch in the expected way.
You should therefore take care to exclude such situations,
as the easySafety device cannot foresee these when the
parameters are assigned.
If, for example, you have assigned the QV output of the AR
arithmetic function at input I1 of the T standard function
block, you should add the CP comparator in between in
order to detect and indicate the occurrence a negative
value.
In most applications, a thorough simulation is enough to
prevent any impermissible values at the function block
input.
02/16 MN05013001Z EN