Conditions For Determining The Operation Cycle - Omron CS1W-LC001 Operation Manual

Description of Operation
3-2-8

Conditions for Determining the Operation Cycle

96
The following three conditions must be satisfied on the Loop Control Unit
when determining the operation cycle:
1) The load rate (ratio between actual operation execution time and set
operation time) must be 60% or less. (For details, see 3-2-10 About Load
Rate on page 100.)
2) The external I/O refresh cycle of the entire system must not be same as the
operation cycle of the function blocks. In most cases, the maximum "external
I/O refresh cycle" is as follows depending on the timing of operations:
"about five times the cycle time of the CPU Unit" + "twice the operation cycle
of the function blocks on the Loop Control Unit"
Study whether or not any problems will arise in controllability of PID control
on the target application. (For details, see 3-2-11 External I/O Refresh Cycle
on the Overall System.)
3) Due to the relationship with the cycle time of the CPU Unit, the operation
cycle of the Field Terminal, CPU Unit Terminal, Expanded CPU Unit Terminal
and Node Terminal blocks must be a certain value or more (in most cases,
about 3.3 times the cycle time). (For details, see 3-2-11-3 Restrictions on
operation cycles of function blocks used for data exchange with the CPU
Unit.)
Á
Note 1 Before changing ITEM004 (operation cycle) of each function block, set
ITEM014 (run/stop command) of the System Common block to 0 (stop).
ITEM004 cannot be changed while the Loop Control Unit is running.
Á
To send the data of the Basic PID block (Block Model 011) and Advanced
PID block (012) to CX-Process Monitor by the Block Send Terminal to
Computer blocks (Block Models 403 and 404) set the operation cycles of
the Block Send Terminal to Computer blocks to the same value or longer
than that of the Basic PID block or Advanced PID block. If the operation
cycle of the Block Send Terminal to Computer blocks is shorter, the Set
Point value momentarily becomes 0 immediately after the Loop Control
Unit is started in the cold start mode.
Note 2 The execution cycle of sequence commands in the Step Ladder Program
block depends on the operation cycle of the Step Ladder Program block
(Block Model 301) itself. So, the operation cycle is slower than the execution
cycle (cycle time) of commands on the CPU Unit. For this reason, the Step
Ladder Program block is used in combination with other function blocks.
When high-speed processing is required, use commands on the CPU Unit.
Section 3-2