Control Logix OTE and OTL instuction

tutu · Mar 21, 2011

Control logix CPU have a backup battery, this battery is not only backup user program, it also backup all data of All tags.

now I have a question why the tag C value does not saved in follow rung when power failure.



     TagA    TagB                                  TagC

|-----||-----|/|-----------------------------------( )--| 

|    TagC |

|-----||--|

but when change OTE to OTL like following, TagC is be saved



     TagA                                          TagC

|-----||-------------------------------------------( L )--|

|    TagB                                          TagC

|-----||-------------------------------------------( U )--|

who can explain more details about this.

bernie_carlton · Mar 21, 2011

On restart the PLC performs a 'PreScan'. During this scan all OTE instruction addresses are set to FALSE. Latched instruction addresses are not affected.

Refer to the Allen Bradley Knowledgebase article 43379

Operaghost · Mar 22, 2011

Another tip:

In RSLogix, while looking at the ladder logic, click on an OTE or OTL (or any other) instruction then press F1. Scroll down and you can read whether an insruction is affected by the prescan.

OG

Control Logix OTE and OTL instuction

tutu

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bernie_carlton

Lifetime Supporting Member + Moderator

Operaghost

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