Omron CS1W-LC001 Operation Manual page 125

Description of Operation
Example
3-2-11-1 Maximum external I/O refresh cycle
Data exchange of analog input, PID operation and analog output
Analog Input Unit
A/D
Log input
conversion
Analog Output
Unit
D/A
Log input
conversion
"External I/O refresh cycle on the overall system" here (simply called the
"external I/O refresh cycle" from here on) refers to the time up to when PID
operation is performed and the Analog Input/Output Unit outputs the analog
output values after the Analog Input Unit starts to read analog input values.
(This fresh cycle indicates the response of the overall system.)
Note This "external I/O refresh cycle" is equivalent to the I/O refresh cycle (or
operation cycle) on a general controller. For this reason, when designing the
system, calculate this "external I/O refresh cycle" according to the calculation
formula shown below, and study whether or not there will be any problem in
controllability on the target application. 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"
In particular, study whether or not there will be any problem in controllability
of PID control in the case of fast-response control targets such as pressure or
flowrate.
Calculate the external I/O refresh cycle by the following calculation formula:
The maximum external I/O refresh cycle is calculated as follows:
A/D conversion time + (4 x CY) + (
conversion time
where,
CY: Cycle time of the CPU Unit
Max. operation time ( Á 1)
T:
 :
Coefficient of the total number of function blocks exchanging data with
the CPU Unit ( Á 2)
à : Smallest integer satisfying formula 1( Á 3)
CPU Unit
I/O memory
Analog
input
I/O refreshing
converted
value
I/O memory
Analog
input
I/O refreshing
converted
value
Á
x CY) + (2 x T) + (
Section
Loop Control Unit
Function block
Execution
Analog Input
cycle 0.2 s
block
Operation
cycle
Execution
PID block
cycle 0.2 s
Execution
Analog output
cycle 0.2 s
block
Operation
cycle
Â
x T) + 20 + D/A
3-2
107