Siemens SINUMERIK 840C Installation Instructions Manual page 369

6 NC Machine Data (NC MD), NC Setting Data (NC SD)
6.7.1 Axis-specific MD bits 2 (axial bits 2)
Bit 6 = 1
Bit 5 Bit 5=0 The 2nd measuring system is not distance coded.
Bit 5=1 The 2nd measuring system is distance coded (see Functional Description for
6–184
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If the absolute position is negative, one revolution is added to the rest of the
modulo calculation.
This means that after control run-up, a position between 0 and 360° is
always displayed in the basic actual value display and the service display.
The function is activated when the bit for the rotary axis (MD 564*, bit 5), the
bit for the absolute encoder (MD 1808*, bit 0) and the bit for the function
"Single-turn absolute encoder available" (MD 1808*, bit 6) are set.
General limitations when using SIPOS/Endat encoder:
A simple overflow compensation is performed in the SIPOS hardware (65536
encoder revolutions are reduced to 0 encoder revolutions) which must be
compatible with the "Workpiece revolutions" in the NC control.
Where the SIPOS/Endat absolute encoder is connected directly to the
workpiece table (load side), the overflow compensation in the hardware is
always correct (for every position control resolution).
The above does not apply when
• using a measuring gear or
• when the encoder is connected indirectly at the motor and a
motor/load gear is used.
In such cases the gear ratio is divided into the pulse/path weighting, use of
the overflow correction is limited:
If a gear is used between the encoders and workpiece side, the
absolute encoder can only be used with rotary axes/C axes if the
following calculation
65536 · 2500 · 4 · (MD368*/MD364*) · position control resolution / 360
produces an integer value,
i.e. the maximum number of 65536 absolute encoder revolutions also
corresponds to an integer number of workpiece revolutions.
The above formular can also be set to
65536 x x/y (where x/y = gear ratio encoder/workpiece)
must result in an integer!
because when the impulse weighting is correctly parameterized MD 364*
always contains the N encoder line number (2500
contains the position control resolution and the value 360 (degrees) for rotary
axes.
Single-turn absolute encoder function active.
additional machine data which have to be set for this function).
Active: After POWER ON
Applies only to feed axes.
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4) and MD 368* always
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