What wrong with this ladder logic

PLCnewbiE80

Member
P
Join Date
Apr 2010
Location
Malaysia
Posts
8
Can some one explain there is 2 answer for this question.I can get the first answer which is input 1.02 will cause the rung not function due to either one of the inputs in turn "ON". the other answer i cannot get it.Can someone teach me.Pls refer to attachment attached below.thks

question.jpg
 
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yes you are right about the 1.02.but someone told me that there is another answer relating with addressing.i suspect that 0.00 doesnt have the purpose to put in first because is already "ON" state (close contact) unless its open contact.

to mickey
yes im in the other parts of the world stuck in the same question with you:)
 
There is nothing really wrong with using the real output addresses on the contacts. My personal preference is that I would normally use internal addressing (for example "B" in AB or "C" in Automation Direct) to develop the logic instead of real output addressing. I would then use the internal relay logic to operate the real outputs. Some say this is redundant but I can re-assign the outputs easier in the event of a hardware output failure. In response to post #5, the 0.00, 0.02, and 0.04 contacts would have to be activated with other logic rungs that are not shown. Otherwise, as you said, there would be no purpose for them.
 
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Not sure what PLC series this ladder would apply to, but it's possible, based on my assumption of the addressing convention being used, that one of the bits is addressed as both an output (0.02) and an input (1.02).

Of course, this would apply to addressing where the bits can be either an input or an output.

Also, I wouldn't think you could arrange ladder rungs like that but I only have A-B experience.
 
PLCnewbiE80 said:
The other answer for this question is 0.07 is a address of an Input Card but it is used as an output card which is another fault.
Click to expand...

that's assuming a lot...there is no documentation to state what any address is, either input or output. The logic doesn't state it either.... a bit confusing since contacts on a rung can be associated with bits, outputs, inputs, etc...
 
The other answer is it's a poor design and lacking documentation :)

I don't see anything which would make it an 'illegal operation' without further documentation... just confusing because it's poorly designed!
 

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