Publication 1766-RM001A-EN-P - October 2008
178 Timer and Counter Instructions
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.
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.
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
TIP
Timing could be inaccurate if Jump (JMP), Label (LBL), Jump to Subroutine
(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.
efesotomasyon.com - Allen Bradley,Rockwell,plc,servo,drive
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