Siemens SIMATIC S5 Manual page 107

Description of the Individual Operating Modes
Special case 3
If the precontact is activated when the reference point approach starts, the drive moves im-
mediately in the reference point direction in single steps.
"1"
"o"
Limit switch
V2
o
- VI
- V2
- V3
VI: Single step (25Hz)
V2: Start-stop frequency
V3: Reference speed
Fig, 4/1 O Reference point approach with start at the BERO
If one of the two limit switches is "out of bounds", i.e. must not be reached, you must specify the
reference direction in the machine data so that the reversal of direction only occurs at the other
limit switch. If both limit switches are prohibited, the axis must be positioned in front of or on the
comes into effect.
If the axis is already on the precontact at the beginning of the reference point approach, you can
be sure that no limit switch will be tripped. There is also no reversal of direction in the reference
point approach.
If the reference point approach is abandoned, there is no reference point even if there had been
one previously. The mode must be restarted and completed.
4-14
3 0 1 2 3 0 1 2 3
Reference direction
Excitation pattern number
Limit switch s
1 ) Reference point with synchronization
2) Reference point without synchronization