Allen-Bradley MicroLogix 1400 User Manual

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.
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Allen-Bradley MicroLogix 1400 Specifications

General

Processor	32-bit
Expansion Modules	Up to 7 expansion I/O modules
Power Supply	24V DC or 120/240V AC
Programming Software	RSLogix 500
Communication Ports	Ethernet, RS-232/RS-485 combo port
Controller Type	Programmable Logic Controller (PLC)
Series	MicroLogix
Digital Outputs	12
Analog Inputs	6 (embedded)
Analog Outputs	2 (embedded)
High-Speed Counter	6 high-speed counters
Pulse Output	2 (embedded)
Ethernet Port	Yes