Siemens SINUMERIK 840D sl Function Manual page 93

Fault
Alarm 25020
If zero-mark monitoring is tripped in the active measuring system, alarm 25020 appears:
"Axis <Axis identifier> Zero-mark monitoring of active encoder"
The affected axis is stopped via the configured braking ramp in follow-up mode:
MD36610 $MA_AX_EMERGENCY_STOP_TIME
(Maximum time for braking ramp when an error occurs)
Alarm 25021
If zero-mark monitoring is tripped in the passive measuring system alarm 25021 appears:
"Axis <Axis identifier> Zero-mark monitoring of passive encoder"
There is no further alarm response.
Alarm 25022
If the absolute value transfer is interrupted, alarm 25022 appears:
"Axis <Axis identifier> Encoder <Encoder number> Warning <Error fine identification>
There is no further alarm response.
Note
In the event of a fault, the adjustment of the absolute encoder is lost and the axis is no
longer referenced. The absolute encoder must be readjusted.
References:
/FB1/Function Manual, Basic Functions; Reference Point Approach (R1);
Chapter: Referencing with absolute encoders
Notice
Errors in the incremental track that cannot be detected with amplitude monitoring can cause
position deviations in the millimeter range. The deviation depends on the lattice pitch/line
count and the traversing velocity of the axis when the error occurs.
Complete position monitoring is only possible through redundancy, i.e., through comparison
with an independent second measuring system.
Basic logic functions: Axis monitoring, protection zones (A3)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.1 Axis monitoring
27