hi,
i'm taking a class on plc and i'm trying to figure out to identify the input and output modules if they are analog or discrete.I go to a website that the teacher says to go and i cant find a clue.the literature just gives me the following: Voltage category, number of inputs or output,points per common, voltage operating,backplane current consumption and so on but it didint help.
anybody who knows or have an idea. thanks for help.

 

If you think about it, the term "programmable logic controller" pretty much defines what you're dealing with.

 

i/o (input/output) modules, as you mentioned come in both discrete and analog. the discrete boards will likely also have a label regarding sinking (receiving voltage) and sourcing (providing voltage*). since the voltages they are referring to can be 5 vdc, 24 vdc, 120 vac (etc), and often a voltage range, it is difficult to differentiate.
an analog device normally has the points labeled AO1 or AI4 for analog out and analog in. the module itself often has info lending itself to anal or discrete. i always taught my students to look up the model number in the vendor data for all the necessary information.
what manufacturer(s) are you looking at?

*realize that no i/o modules actually provide voltage, it originates in the field and is controlled on the board by a relay, scr or solid state device.