Siemens SINUMERIK 840D sl Function Manual page 1591

2.6.8 Enabling the measurement system
The measuring system of a machine axis is activated in the following cases:
• Power up of the control (POWER ON)
• Activation of the measuring system via interface signal (deselection of "parking"):
• Violation of the assigned encoder limit frequency (spindles):
When the measuring system is activated, the NC synchronizes the actual value system of
the machine axis with the current absolute value. Traversing is disabled during
synchronization for axes but not for spindles.
Parameterizing the encoder limit frequency (spindles)
The EQN 1325 absolute encoder made by Heidenhain has an incremental track and an
absolute track.
If a spindle is driven at a speed above the encoder limit frequency of the incremental track,
the substantially lower limit frequency of absolute track must be parameterized as the
encoder limit frequency.
MD36300 $MA_ENC_FREQ_LIMIT
Otherwise an incorrect absolute position would be read because the parameterized encoder
limit frequency is not reached when the measuring system is activated. This would cause a
position offset in the actual value system of the machine axis.
Determining the encoder limit frequency
The encoder limit frequency to be parameterized is derived from the smaller of the two
following limit speeds:
• Encoder
• NC
Basic logic functions: Reference Point Approach (R1)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
DB31, ... DBB1.5 / 1.6 (position measuring system 1/2)
DB31, ... DBB2.1 (servo enable)
MD36300 $MA_ENC_FREQ_LIMIT
The limit speed or encoder limit frequency is listed in the data sheet of the encoder (e.g.,
limit speed = 2000 [rpm])
Due to the NC-internal evaluation process, the maximum limit speed for which error-free
calculation of the absolute value by the NC is possible is 4 encoder revolutions per
interpolation cycle.
For an interpolation cycle of, for example, 12 ms: Limit speed = 4 / 12 ms = 20,000 rpm
2.6 Referencing with absolute value encoders
Detailed description
45