Allen-Bradley Logix5000 Reference Manual page 393

Arithmetic Status Flags:
Fault Conditions:
Condition
Prescan
Rung-condition-in is false.
Examine .DN bit.
.EN bit is cleared.
.ER bit is cleared.
Rung-condition-out is set
to false.
End
Rung-condition-in is true
Postscan
Array (File)/Misc. Instructions (FAL, FSC, COP, CPS, FLL, AVE, SRT, STD, SIZE)
Arithmetic status flags are affected.
A major fault will occur if
.POS < 0 or .LEN < 0
Dimension to vary does not exist for the
specified array
Execution:
Relay Ladder Action
The .EN bit is cleared.
The .DN bit is cleared.
The .ER bit is cleared.
The rung-condition-out is set to false.
.DN Bit = 0
.DN Bit = 1
The STD instruction calculates the standard deviation of the specified elements.
Internally, the instruction uses a FAL instruction to calculate the average:
Expression = standard deviation calculation
Mode = ALL
For details on how the FAL instruction executes, see
The rung-condition-out is set to false.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Fault type Fault code
4 21
4 20
page 351.
Chapter 8
393