Omron CS1W-LC001 Operation Manual page 154

Fail-safe Countermeasure Guidelines
136
Contact output operation
Normally, the Contact Output Unit also turns OFF when the CPU Unit
changes from the RUN or MONITOR mode to the PROGRAM mode. (The
I/O Memory Hold flag is used to hold output values.)
However, when contact values are output via the Contact Output Unit by the
Loop Control Unit, contact outputs are refreshed and then output if the CPU
Unit is in the PROGRAM mode.
Implement the following fail-safe measures to hold analog outputs or contact
outputs at specific values (for example, maximum value or minimum value)
when the Loop Control Unit has stopped running even if the CPU Unit is in
the PROGRAM mode.
1) When the user uses CX-Process Monitor or CX-Process Tool to stop
running of the Loop Control Unit when the CPU Unit is in the PROGRAM
mode:
Before the Loop Control Unit is made to stop running, switch Control
blocks such as PID blocks to Manual, and use CX-Process Monitor or
CX-Process Tool to execute setting so that the MV becomes the required
value.
2) To set ITEM014 (run/stop command) of the System Common block to 0
(stop) by the ITEM Setting blocks on the Loop Control Unit:
Before writing to the ITEM Setting blocks, switch Control blocks such as
PID blocks to Manual, and create a sequence so that the MV becomes
the required value beforehand using the Step Ladder Program block.
Note 1 When the Loop Control Unit stops running due to a malfunction of the Loop
Control Unit itself when the CPU Unit is in the PROGRAM mode, analog
output or contact output cannot be held at specific values (for example,
maximum value or minimum value). This must be taken into consideration
when designing the system.
Note 2 Processing that causes the Loop Control Unit to stop running can also be
executed when the CPU Unit is in the PROGRAM mode.
In this case, enter ITEM013 (PROGRAM mode) of the System Common
block (Block Model 000) as the CPU Unit run status, and set ITEM014
(run/stop command) of the System Common block to 0 (stop) by the Step
Ladder Program block (Block Model 301) and the ITEM Setting blocks (Block
Models 171 and 172).
System Common
block
Step Ladder
Program block
013
Section
ITEM Setting System Common
block block
014 014
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