Omron CS1W-LC001 Operation Manual page 48

Configuration of Instrumentation System
28
Note Running of the Loop Control Unit is automatically stopped when the operation
cycle of all function blocks is set to two seconds, and the load rate
continuously exceeds 70% for ten times. When this happens, processing of
the function blocks must be distributed across the Loop Control Units.
Use the following formula as a general guideline for estimating the load
rate of the Loop Control Unit at the system design stage.
How to Calculate the Load Rate
Calculate the load rate based upon the following formula.
When all operation cycles are the same operation cycle, the load rate is as
shown below. This, however, is to be used only as a guideline.
Formula
Á
Load rate
operation cycle (ms) x 100 + fixed load rate (%)
Note 1 The following table shows the fixed load rates for each operation cycle:
Operation cycle
0.1 sec
0.2 sec
0.5 sec
1 sec
2 sec
Note 2 The "sum (ms) of operation execution times of each function block" is a value
obtained by discarding values less than 10 ms from the total time obtained by
adding the "operation execution time of the function blocks" to the "execution
time of the sequence commands."
Note 3 For details on the load rate, see 3-2 Description of Operations. For details on
the operation execution times for each function block and each of the
sequence commands in the Step Ladder Program block, see Appendix-4 List
of Operation Execution Times.
5. Evaluation of External I/O Refresh Cycle (dependent on CPU Unit's
cycle time)
The operating speed (operation cycle) itself of each function block on the
Loop Control Unit is not related to the CPU Unit's cycle time. However,
as the CPU Unit's I/O memory is accessed during data exchange, for
example, between Analog I/O Units and the Basic I/O Unit, the timing of
data exchange is influenced by the CPU Unit's cycle time.
The external analog I/O refresh cycle (equivalent to the I/O refresh cycle
on a general controller) when the Loop Control Unit is configured as part
of an instrumentation system is not the same as the operation cycle of
the function blocks; but is a cycle heavily dependent on the CPU Unit's
cycle time.
Sum (ms) of operation execution times of each function block
Fixed load rate
10%
5%
2%
1%
0%
Section 1-2
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