Chapter 5 Program Configuration and Operation Method
5- 3
5.1.3 Scan time
The processing time from program step 0 to the next step 0 is called „Scan Time‟.
(1) Scan time calculation expression
Scan time is the sum of the processing time of scan program and interrupt program prepared by the user
and PLC internal time, and is distinguished by the following formula.
(a) Scan time = Scan program processing time ＋ Interrupt program processing time ＋ PLC internal
processing time
Scan program processing time = processing time of user program except interrupt program
Interrupt program processing time = Sum of interrupt program proceeding time processed during 1 scan
PLC internal processing time = Self-diagnosis time ＋ I/O refresh time ＋ Internal data processing time
＋ Communication service processing time
(b) Scan time depends on whether to execute interrupt program and communication processing.
Expansion interface processing time
Executing
ladder
(4Kstep)
PLC internal
processing
time
Digital I/O module
(32 point, 1 unit)
Analog module
(8 channel, 1 unit)
Comm. module
(main/expansion)
(200 byte, 1 block)
The main unit executes controls along the following steps. A user can estimate the control performance of a
system that the user is to structure from the following calculation.
Scan time = ① Scan program process ＋ ② System check & Task process ＋ ③I/O data Refresh
+ ④ Network Service + ⑤ XG5000 Service + ⑥ User Task Program process
① Scan program process = no. of instruction x process speed per each instruction (refer to XGK/XGB
instruction user manual)
② System check & Task process: 600 ㎲ ~ 1.0 ms [varies depending on the usage of auxiliary functions]
③ XG5000 Service process time: 100 ㎲ at the max data monitor
④ Task Program process time: sum of task processing time that occurs within a scan; the time calculation
by task programs are as same as that of scan program.
②System check &
Task processing
Network Module
Data exchange
Expansion
Module
Interface
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