Siemens SINUMERIK 840D sl Function Manual page 454

K3: Compensation
5.8 Measures for hanging (suspended axes)
As alarm 2900 deactivates the axis position control, this alarm must be configured to initiate
that the mechanical brakes are closed by the PLC. Rebooting the PLC forces the PLC
outputs to change to defined zero. The brakes must be connected up in such a way that they
remain closed at zero, i.e. a 1 signal on the PLC allows the brakes to open.
Note
In terms of its reactions, the alarm is the same as the Emergency Stop alarm (3000). For
internal reasons, the reboot delay time of the NCK can be slightly increased.
Activation
The reboot delay can be activated as follows:
MD10088 $MN_REBOOT_DELAY_TIME (reboot delay) > 0
The value that has been entered supplies the reboot delay time in seconds.
Evaluation with a system variable
System variable $AN_REBOOT_DELAY_TIME can be read in a synchronized action. A
value greater than zero indicates that the reboot request has been initiated from the HMI and
how much time (in seconds) the NCK plans until reboot (POWER OFF followed by POWER
ON). In a synchronized action, the user can identify the pending reboot and appropriately
respond (e.g. with "Safe Standstill" for a Safety Integrated application).
$AN_REBOOT_DELAY_TIME is 0.0 as long as the HMI has not initiated a reboot request.
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Function Manual, 09/2009, 6FC5397-1BP20-0BA0
Extended Functions