The Digital Inputs For Hardware Limit Switches 2 - 5 - Siemens SIMATIC S5 Manual

2.8.3 The Digital Inputs for Hardware Limit Switches
The hardware limit switches are evaluated regardless of the axis type. With a rotary axis, hard-
ware limit switches are generally not required, but can be used as an additional safety measure.
The polarity of the two hardware limit switches can be assigned in the machine data record. You
can select both limit switches as normally closed or both as normally open switches using the
"polarity HW limit switches" parameter.
The hardware limit switches are only detected during a traversing movement.
If the module recognizes that a hardware limit switch has tripped, the traversing movement is
stopped and the current traversing job is terminated.
Note
A hardware limit switch is only detected if the traversing movement is towards
it. If a limit switch responds, further movement in the direction of the activated
limit switch is not possible. This traversing direction is only enabled again
when the module has detected that the axis has left the hardware limit
switch in the opposite direction or
when a hardware limit switch has been tripped and is tripped again in the
opposite direction.
in this direction is blocked. This direction can be released again by starting a traversing job in
the opposite direction, tripping the hardware limit switch again and then returning it to the
neutral position.
A blocked direction is also released when the axis reaches the precontact.
has two software limit switches. These should always be assigned so that the hardware limit
switches can never be reached during operation. Since the IP247 only starts to brake when a
software limit switch is reached, the hardware limit switches should be set far enough away frolm
the software limit switches to allow for the maximum braking distances.
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