Fail-Safe Countermeasure Guidelines; Fail-Safe Countermeasure Guidelines; Measures When The Loop Control Unit Has Stopped Running - Omron CS1W-LC001 Operation Manual

Fail-safe Countermeasure Guidelines

3-5 Fail-safe Countermeasure Guidelines

3-5-1

Measures When the Loop Control Unit Has Stopped Running

3-5-1-1 Fail-safe countermeasures for adapting to stoppage of the Loop Control
Unit when the CPU Unit is in the RUN or MONITOR mode
3-5-1-2 Fail-safe countermeasures for adapting to stoppage of the Loop Control
Unit when the CPU Unit is in the PROGRAM mode
Implement fail-safe countermeasures on the Loop Control Unit according to
the following guidelines.
When the Loop Control Unit stops running, the state before the stop occurred
is held and all operations that were being executed on the Loop Control Unit
are stopped. Refreshing between the CPU Unit and the function blocks on
the Loop Control Unit is also stopped. For this reason, the values of the
allocated areas on the Analog Output Unit and the Contact Output Unit
whose refreshing cycle was changed are held at the state before the stop
occurred by the AO and DO terminals of the Field Terminal block.
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.
To hold analog outputs or contact outputs at specific values when the Loop
Control Unit has stopped running, create a Step Ladder Program on the CPU
Unit so that each of the allocated relays on the Analog Output Unit or Contact
Output Unit are set to a specific value taking the b contact of the Loop
Control Unit CPU Unit Running flag (bit 00 allocated relay n word) as the
input conditions.
Loop Control Unit running
nth word bit 00
CPU Bus Unit Error Unit Number flag
Analog output operation
When an Analog Output Unit (for example, CS1W-MAD44) is used in regular
operation (that is, operation without a Loop Control Unit), the Analog Output
Conversion Enable flag turns OFF and analog output values are output
according to the setting of the output hold function when the CPU Unit
changes from the RUN or MONITOR mode to the PROGRAM mode.
However, when analog values are output via the Analog Output Unit by the
Loop Control Unit, the Analog Output Conversion Enable flag is forcibly
turned ON by the Loop Control Unit even if the CPU Unit is in the PROGRAM
mode, and the output hold function does not work.
The analog output setting values are refreshed and then output.
Processing at stoppage of Loop
Control Unit
• Analog output setting value on
Analog Output Unit changed by
MOV instruction
• Contact state of Contact Output
Unit changed by SET/RSET
instruction
Section 3-5
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