%s0008 is ALW_OFF in PLC 90-30 CPU351

[jcp]

Hi friends;
I attached a image in which ALW_OFF is used before the MOVE INT Block. I want to ask is this block working or not?
Becuase i think its never working and programmer used it to only confuse the people.
Please i need some explanation from ur guys?
Regards

 

[Steve Bailey]

Judging by the partial rung 356, just barely visible in your screenshot, the original programmer planned to move %R02000 to %AQ0001 under some conditions and %R07229 under others. Perhaps he never got around to defining the "other" conditions. Perhaps the "other" conditions turned out to be a problem so he inserted the ALW_OFF contact as a quick method of disabling the rung.

 

[jcp]

Sir;
Yes now i understand that where ALW_OFF is used the rung disable till the programmer delete this instruction or change to ALW_ON. am i right?

 

[Steve Bailey]

You don't have to replace it with ALW_ON (%S0007). You can replace it with any valid address for a contact instruction. You are correct that as long as the ALW_OFF contact remains, the MOVE_INT function will not be performed.

 

[tomalbright]

Unfortunately, some programmers use the ALW_OFF as a programming tool. Here's an old thread I started years ago. In the attached program, ALW_OFF was used to disable multitudes of inputs individually, rather than simply deleting rungs or some other approach.

Here ya go.

I would be very very careful removing those. If your equipment is working properly, the PLC is working properly. Don't disturb it!