Omron CS1W-LC001 Operation Manual page 119

Description of Operation
3-2-10-1 Evaluating the load rate at the system design stage
3-2-10-2 How to calculate the load rate
The guideline load rate for function blocks on the Loop Control Unit is 60%.
At the system design stage study whether or not the load rate of each
function block is 60% or less.
Though errors caused by PID and other operations do not occur when the
load rate exceeds 60%, use the Loop Control Unit at a load rate of 60% or
lower as there is possibility that the load rate will temporarily increase due to
fluctuations in the overhead time of FINS command communications and
internal processing.
Operation cycle group
0.1 sec.
0.2 sec.
0.5 sec.
1 sec.
2 sec.
Errors in PID and other operations occur when the load rate exceeds 100%.
When the load rate of a certain operation cycle group exceeds 60%, change
the operation cycle of function blocks among function blocks within that
group, for which an increased operation cycle will not affect the application, to
a longer operation cycle (group).
If it is estimated that an operation cycle longer than this cannot be set when
the load rate exceeds 60%, add on another Loop Control Unit (up to three
Loop Control Units can be mounted on a single PC) and distribute processing
between the mounted Units.
Use the following as a guideline to estimate the load rate of the Loop Control
Unit at the system design stage.
Calculate the load rate based on the following formula. The formula is purely
a guideline, and calculated values may differ from actual measured values.
1) When all operation cycles are the same
Formula:
Note 1 The fixed load rates are as follows:
Operation cycle
0.1 sec.
0.2 sec.
0.5 sec.
1 sec.
2 sec.
Note 2 The "total operation execution time of each function block" the total of the
"operation execution time of the function blocks + the execution time of the
sequence commands." (Values less than 10ms are discarded.)
Guideline load rate
60%
Load rate = sum (ms) of operation execution times of
Á
each function block
load rate (%)
Fixed load rate
10%
5%
2%
1%
0%
Section
operation cycle (ms) x 100 + fixed
3-2
101