How to know if its an input or output?

I just had a thought that I dont realize when to use a input or output address. for example, I am doing this example problem seen here http://imgur.com/a/PPYh0

you can see at the IO / Assigned memory, the project statement tells you which are Inputs and which are Outputs.

and because of that, i set my IO like so, http://imgur.com/a/GhKSz (just followed along on what was I and what was O, with I on the left and O on the right.)

however, if that assigned memory for IO wasnt given, I would be lost and probably set everything as an input address and put it on the left. (except maybe the motor.)

So how do I know which gets I and which gets O address from a project?

additionally, is it correct ( For the IO portion atleast) that Input addressed logic always stay on the left with a XIC or XIO logic while an output addressed logic is always on the right with it being an OTE? what if i set up my rung 5 (on the same example) as, XIC (walnut hopper), O:0/1 with the OTE on the rung addressed B3:0/5 ?

An easy way to look at it is that outputs are action commandsfrom PLC, and inputs are information being fed into the PLC.


Hope this helps,
Bubba.

You've got the I/O correct, the program on the other hand isn't going to work as is.

Start with your motor output. What conditions are you going to need to start the motor? What conditions are required to stop it?

Jrivers010 said:

So how do I know which gets I and which gets O address from a project?

Click to expand...

Inputs are information being taken INTO the controller. Sensors, numeric information, prox, switches, anything that will change the state of your process and inform the controller that something is DIFFERENT from the last scan.

Outputs are the signals FROM the controller to change the state of the machine. Engaging motors, changing speed settings, etc.

Jrivers010 said:

additionally, is it correct ( For the IO portion atleast) that Input addressed logic always stay on the left with a XIC or XIO logic while an output addressed logic is always on the right with it being an OTE?

Click to expand...

Not exactly. There are cases where you will use output addresses as XICs/XIOs. Sometimes simple devices don't have feedback, so you use the output address being enabled to determine if the device is enabled. For example, you might use the output of a door lock being engaged to turn on a light somewhere else in the program. Without feedback from that door lock, you would use the engaging output as XIC to enable the output to the light.

Off the top of my head, I can't think of any situation where you would use an input address as an OTE. The only way to make an input address active without actually receiving a current is by using forces in the logic, and as far as I know (could be wrong, I'm still learning too), there is no way to enable a force by toggling an address. You have to do it in the programming environment manually.

Off the top of my head, I can't think of any situation where you would use an input address as an OTE.

Click to expand...

I frequently create simulations of the controlled process in a ladder logic subroutine. For example, when a solenoid valve controlling air flow to a pneumatic cylinder is energized, X seconds later, turn off the "Retracted" limit switch and Y seconds after that turn on the "Extended" limit switch. Not all PLCs allow you to use input addresses for output instructions such as OTE.

How PLC Inputs Work
http://accautomation.ca/how-plc-inputs-work/

How PLC Outputs Work
http://accautomation.ca/how-plc-outputs-work/

Understanding the PLC Program Scan
http://accautomation.ca/understanding-the-plc-program-scan/

The above posts may help you understand clearly the inputs, outputs and scan of the PLC.
Regards,

Steve, you can't use the physical input address for that though can you? You have to make a false input address with software bit I thought. I've experimented with trying to force input channels on using outputs and they would never engage iirc. Referring to AB controllers, that's all I have experience with.

The method varies with the brand of PLC. I most familiar with GE. They allow using input addresses with output instructions, so all I have to do is call the simulation subroutine at the first rung of the main program block to have my simulated input states overwrite the states obtained from the input modules.
For AB, I think you can use input addresses as the destination of either a MOV or a COP instruction.
Either that or copy the inputs from the module to internal memory and use the internal memory in the ladder logic instead of the input addresses. A lot of people do that anyway to make their ladder logic more easily adaptable to multiple situations. When you do that, if you ever need to change the address of a real-world device, you only need to modify one line of code instead of searching for multiple instances of the input address.