Asigning a PLC input to a Ladder diagram location.

[John W]

Hi there

Im having a mental block learing about Allen Bradley PLCs that we have at work.

Firstly, why you introduce a input element to a ladder logic diagram, how do you assign it to a physical input on the PLC?

Secondly, last night I was looking for a fault on equipment controlled by a Micrologics PLC.

I was looking around the program, only to see there were two rows of PLC inputs, with only one physical row available, something like 12 or 18 inputs with 6 or so outputs. I can understand where or why I was seeing two rows on inputs.

Finally, is there a free onle tutirial for me to look at so I can get my head around this side of PLC work.

Thanks


John

 

[cjd1965]

Hi

Generally, a field device (say a push button) is wired to an input, say input number 1.

Now, some smaller brick plcs have pre - assingned inputs which means that input 1 is refered to in the program as %I001, I0.1 or X001 etc depending on the make of the PLC.

Larger PLC's need to be configured. Typically there will be a rack of input and output cards, and you will tell the PLC which inputs are matched to which cards.

Cheers

Look at the tutorial on this site

 

[alearon]

hello,

You intro an input element to a ladder logic diagram because the PLC needs to know that this input will be use and will refer to it's signal once the actual switch or sensor is pluged in. You can refer the wirings to the PLC manual, normally named as X for inputs and Y for outputs. the PLC is preassigned with the numberings (i think). You just need to plug it in the correct place.


for tutorials, like other, i also proposed u try the tutorial on this site.

cheers,
Al