Allen-Bradley MicroLogix 1400 Instruction Manual page 180

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178 Timer and Counter Instructions
Publication 1766-RM001A-EN-P - October 2008
Timer Accuracy
Timer accuracy refers to the length of time between the moment a timer
instruction is enabled and the moment the timed interval is complete.
Timer Accuracy
Time Base Accuracy
0.001 seconds -0.001...0.00
0.01 seconds -0.01...0.00
1.00 seconds -1.00...0.00
If your program scan can exceed 2.5 seconds, repeat the timer instruction
on a different rung (identical logic) in a different area of the ladder code
so that the rung is scanned within these limits.
Repeating Timer Instructions
Using the enable bit (EN) of a timer is an easy way to repeat its complex
conditional logic at another rung in your ladder program.
Timing could be inaccurate if Jump (JMP), Label (LBL), Jump to Subroutine
TIP
(JSR), or Subroutine (SBR) instructions skip over the rung containing a timer
instruction while the timer is timing. If the skip duration is within 2.5
seconds, no time is lost; if the skip duration exceeds 2.5 seconds, an
undetectable timing error occurs. When using subroutines, a timer must be
scanned at least every 2.5 seconds to prevent a timing error.