CTI 2500-C100, Инструкция по установке и эксплуатации

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CTI 2500 Installation and Operation Guide V2.8 54
If all analog tasks have been executed within the specified scan time, the controller will restart
the analog scan, executing the analog tasks in order until the scan time expires. If a task is
processing when it is time to start a new scan, it will be suspended.
If there is no work to be done, the PLC will idle until it is time to start another scan. If the total
execution time of the discrete scan and the first execution of the analog scan exceeds the fixed
time, the scan overrun flag will be set.
NOTE
To avoid scan overruns, you must set the fixed scan time greater to a value that allows all tasks to
execute at least once.
6.2.2 Variable Scan
When variable scan is selected, the controller will execute all discrete and analog scan tasks
once and then start a new scan. All discrete and analog tasks are guaranteed one execution per
scan.
6.2.3 Variable with Upper Limit
When this option is selected, the controller shall execute the discrete scan once and then begin
executing analog tasks. Each analog task will be guaranteed execution at least once during
scan. The PLC will continue executing the analog scan tasks as long as there is work to be
done or the upper time limit has been reached. When the upper time limit expires or no analog
tasks require processing, a new scan shall begin. The scan overrun bit will be set in Status
Word 1, if the total execution time for the discrete and analog scan exceeds the upper limit.
NOTE
To avoid scan overruns, you must set the upper limit time to a value that allows all tasks to execute at
least once.
6.3 Scan Modes
Normally, the execution mode of the discrete scan and analog scan are locked together. Placing
the controller in RUN mode, places the discrete scan and analog scan in run mode while placing
the controller in PROGRAM mode places both scans in program mode.
For special application needs, it is possible to set the operating mode of the discrete scan and
analog scan separately. The following sections describe the operating modes of each scan.