Siemens Sinumerik 840D sl Function Manual page 537

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Difference between $VA_IS and $AA_IM
Both variable $VA_IS and variable $AA_IM can be used to read actual values.
Table 8-10
Variable
$VA_IS
$AA_IM
Reference:
System variables $A_XFAULTSI and $VA_XFAULTSI
For crosswise data comparison errors between the NCK and SINAMICS S120, the
response depends on the actual operating state:
S SBH, SG, SE, SN or n<n
error causes a transition from Stop F to Stop B -- which in turn initiates the
fastest possible braking of the axis. A Stop A is then initiated and the pulse
enable is cancelled.
S SBH, SG and n<n
already active: In this case, a Stop F due to a crosswise data comparison error
does not result in any further action -- only Alarm 27001 or 2710x is output that
provides information. Processing then continues.
This chain of responses is not altered to ensure the appropriate level of safety for
personnel.
To allow responses to a crosswise data comparison error, system variable
$A_XFAULTSI is used to display that a crosswise data comparison error has
occurred on a particular SI axis. Retraction can then be initiated as a response to
this system variable.
Further, an axis--specific system variable $VA_XFAULTSI[<axis name>] has been
introduced so that, if necessary, axis--specific responses can be applied.
The system variables are updated independent of whether SI monitoring functions
are active or inactive.
$A_XFAULTSI
Information about Stop F for a safety axis:
Bit 0 = 1:
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SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) - - 10.2015 Edition
Difference between $VA_IS and $AA_IM
Reading the actual value used by SI
For the actual value, instead of $AA_IM, variable $VA_IM should be used
/PGA/, Programming Instructions Job Planning
synchronization active: A crosswise data comparison
x
synchronization inactive and SE/SN not used or Stop C/D/E
x
In a crosswise data comparison between NCK and drive of any
particular safety axis, an actual value error was detected.
Data Description
8.7 System variables
Meaning
8-537