Siemens SINUMERIK 840C Installation Instructions Manual page 862

04.96
Type 1: NC MD 1808* bit 3, absolute offset valid, = 0
If the bit is not set, referencing is performed like on an axis without the absolute encoder using
the BERO proximity switch as the reference point encoder.
The absolute offset is calculated automatically from the formula:
Machine system = absolute encoder value + absolute offset
or
Absolute offset = machine system - absolute encoder value
Where:
• Machine system = required absolute position = reference point value
• Absolute encoder value = displayed absolute position (actual value) with "Absolute
offset invalid"
Type 2: NC MD 1808* bit 3, absolute offset valid, = 1
If the bit is set, reference point approach is suppressed. This applies until the user resets the
bit.
With the function G 74 "Reference point approach from a part program", this second type of
referencing is not performed and the next block is processed.
Reference point approach is enabled again when NC MD 1808* bit 3=0
is reset.
Limited traversing range
When the traversing range of the absolute encoder is limited due to the position controller
resolution, the alarm 1204 "Traversing range exceeded" and the alarms 148, 152* SW limit
switch plus/minus can occur when the system is started up. In this case, it might be possible
(depending on the direction) that reference point approach with Bero is not possible. For
remedy, proceed as follows:
1st step Enter the displayed position without the first digit in the NC MD 396*, absolute
offset, and set NC MD 1808*, bits 1 and 3.
2nd step POWER ON. Afterwards, the displayed actual position must be around zero
and there is no longer an alarm pending.
3rd step Reset NC-MD 1808*, bit 3.
4th step Execute reference point approach.
© Siemens AG 1992 All Rights Reserved
SINUMERIK 840C (IA)
12.11.2 ENDAT absolute encoder (SW 5.2 and higher)
6FC5197- AA50
12 Functional Descriptions
12–87