4 Safety Function Blocks
4 - 64
NX-series Safety Control Unit Instructions Reference Manual (Z931)
• The FB handles a mode selection switch with up to eight positions.
• You can change the mode to change the operation mode of the machine (automatic mode, manual
mode, semi-automatic mode, etc.).
• It is assumed that the machine is in safe mode when the Controller is started. The inputs to the FB
(e.g., a machine start button) change the mode to the mode that is set on the mode selection switch
when the machine is started.
• The default state after the FB is activated is the ModeChanged state. This is the safe state for the FB,
in which all S_ModeXSel outputs and the S_AnyModeSel output are FALSE.
• When the mode selection switch is changed and the FB is in the ModeChanged state:
•If AutoSetMode is FALSE: A new S_ModeX input is acknowledged by S_SetMode changing to
TRUE to produce a new S_ModeXSel output.
•If AutoSetMode is TRUE: A new S_ModeX automatically produces a new S_ModeXSel output.
• When an S_ModeX input is TRUE, only transitions such as from 8005 to 8000 are valid. As long
as S_ModeX is FALSE, the FB will retain state 8005 even if a change to TRUE is detected for
S_SetMode.
• The time is not monitored for a transition from the ModeChanged to the ModeSelected state, i.e.,
when S_SetMode is changed to TRUE by the operator.
• If the FB is in the ModeSelected state when a new S_ModeX input (high priority) and an S_Unlock
signal (low priority) change to FALSE at the same time, the FB will enter the ModeChanged state.
• You can set constants with the default FALSE state for S_ModeX inputs that are not used for mode
selection to simplify program validation.
• Set the AutoSetMode input to TRUE only when you can ensure that no hazardous state will occur as
the result of starting the Safety CPU Unit.
Precautions for Correct Use
An error will occur for this function if more than one S_ModeX input changes to TRUE at the
same time. Use a non-shorting mode selection switch.
Function
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