Siemens SINUMERIK 840C - Manual (Page 869)

12 Functional Descriptions 01.99
12.11.2 ENDAT absolute encoder (SW 5.2 and higher)
12.11.3.4 Special start-up cases
Start-up after a SW update
The rough encoder position is not erased when the software is updated. The absolute encoder
does not therefore have to be reinstalled.
Foreseeable SRAM failures
Foreseeable SRAM failures occur, for example, when the NC-CPU or the CSB board is
replaced. In such cases the following procedure is necessary:
Step 1:
Save the NC-MD as an ASCII file via the MDD on the MMC. This can be performed on the
highest machine data level or on the highest NC MD level. It is at this step that the rough
encoder position is stored in NC-MD 3944*.
Step 2:
Replace the NC-CPU or the CBS board and then switch on the control. The control now
powers up in initial clear mode and the entire SRAM area is erased.
Step 3:
Load the backed up NC-MD file in initial clear mode. After the file has been loaded, CANCEL
alarm 1376*, ”Check position absolute encoder” is output. This alarm informs you that start-up
is not yet complete and remains active even after a Power Off. The alarm cannot be
acknowledged until normal mode is restored (after Step 5).
Step 4:
Set NC-MD 1808*, bit 7, to 0.
Step 5:
Terminate initial clear mode
Step 6:
The drives equipped with an absolute encoder must now enter the closed-loop control (control
e.g. via a small traversing movement). However, the limitations for movements apply in the
switched off status requiring the axis to be repositioned.
Example:
Traversing movement (JOG 1000 increments) in positive direction
Traversing movement (JOG 1000 increments) in negative direction
Then set bit 7 to 1 in MD 1808* (range extension active)
Step 7:
Initiate NCK Power On and check the position after it has powered up.
12.11.3.5 Start-up after data loss
If data loss in the SRAM occurs because of a hardware fault and it is not possible to back up
the NC-MD file, the absolute encoder must be realigned. This task can be simplified with a
visible mark on the machine from which the commissioning engineer (Siemens Customer
Service) can determine the position offset as accurately as possible.
12–94 © Siemens AG 1992 All Rights Reserved 6FC5197- AA50
SINUMERIK 840C (IA)