Siemens SINUMERIK 840C Installation Instructions Manual page 851

12 Functional Descriptions
12.11.1 SIPOS absolute encoder up to SW 4
Case 1: NC MD 1808* bit 3 = 0
If the bit "Absolute offset valid" is not set, reference point approach is executed as for an axis
without absolute encoder. With "Reference point reached", the calculated absolute offset is
transferred to the axial NC MD 396* and NC MD 1808* bit 3 "absolute offset valid" is
automatically set for the axis relevant axis.
The absolute offset is automatically calculated according to the following equation:
Machine system = SIPOS absolute encoder value + absolute offset
Absolute offset = machine system - SIPOS absolute encoder value
Where:
• Machine system = desired absolute position = reference point value
• SIPOS absolute encoder value = displayed absolute position (actual value)
Note:
If NC MD 396* has a value other than 0, this value must be taken into account because it is
contained in the SIPOS absolute encoder system (= displayed actual value).
Suggestion: Set NC MD 396* before synchronization.
Case 2: NC MD 1808* bit 3 = 1
If bit "Absolute offset valid" is set, reference point approach is suppressed. The condition
prevails until the user resets the bit.
In the case of the function G74 "Reference point approach from part program", referencing is
not carried out for the second case and processing starts with the following block.
Note:
Reference point approach can be restarted when NC MD 1808* bit 3 has been deleted.
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SINUMERIK 840C (IA)