12 Functional Descriptions 04.96
12.11.2 ENDAT absolute encoder (SW 5.2 and higher)
12.11.2.5 Offset of the absolute encoder from the machine absolutesystem
On initial installation or after replacement of the absolute encoder, the offset of the measuring
system zero to the machine zero must be ascertained or set.
•Relevant machine data:
NC MD 240* Reference point value
NC MD 244* Reference point value offset
NC MD 396* Absolute offset = Offset (measuring system ZP to machine system ZP)
NC-MD 1808* Bit 0 = 1
Axis with absolute encoder
Bit 2 = 0 Absolute encoder counting method in opposite direction
1 Absolute encoder counting method in same direction
Bit 3 = 0 Absolute offset not valid
1 Absolute offset valid
Notes:
• NC MD 1808*, bit 3:
Software limit switch and the spindle pitch error compensation are enabled. The spindle
pitch errors between the reference point and the absolute position are included in the
calculation.
• Reference point approach with EnDat absolute encoders is possible only after resetting of
the NC MD 1808*, bit 3.
• The counting methods in the same direction and in the opposite direction are determined
as follows. Move the axis to any position, start the control and note down the absolute
value. If a larger absolute value is displayed after a positive traversing step and another
POWER ON, the system is in the same direction and must not be corrected. If a smaller
absolute value is displayed, NC MD 1808*, bit 2 = 1 must be set. After the next POWER
ON, the correct actual position is indicated in the display.
• When altering the mechanical traversing direction with NC MD 564*, NC MD 1808*, bit 2
must also be adjusted.
Ascertaining the offset in the ”Reference point approach” operating mode with external
reference point encoder
Like any other standard encoder, the EnDat absolute encoder has tracks A and B, but no zero
pulse. When the NC MD 1808*, bit 0, axis with absolute encoder, is set, a difference is made
between two types in the reference point approach mode.
12–86
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50
SINUMERIK 840C (IA)