Allen Bradley xio

I am new to plc programming but have an issue where I program xio with a nc stop button Allen Bradley microlight 1400 however this does not work am I doing something wrong please help

If you have a N.C. pushbutton connected to an input, that input will be ON when the button is NOT pressed.


To detect the input ON, you would use an XIC (Examine If Closed) instruction, and it will highlight green while the button is NOT pressed.

This is a typical arrangement for STOP buttons, as it protects against hardware errors (wire dropped off, switch broken, etc.).

So atm I have this
[/] -----[ ] --------( o )
---------( o )

Should I change the stop to same as the start Pb. Thank you for your help

Without going into detail of what you are trying to do...

This link may assist in your learning:

http://www.contactandcoil.com/patterns-of-ladder-logic-programming/

OK thank you very much I though I was programming it wrong that is very helpful thanks

This is how a start/stop latch will work using either a N/C or N/O Stop button

Thank you so much I really appreciate it so if I was going to put in a nc overload in line that would be the same and be an xic ?

Yes, that is assuming the overload N/C contact is N/C when the overload is not tripped but in reality this is the N/O contact, The idea is that when the overload is ok you get a closed contact so that if it trips it removes the signal to the input, in actual fact it would be a N/O in it's tripped state, sounds confusing doesn't it, like relays I always assume a N/O contact is open when not energised & N/C is closed when not energised. So it depends on what you call it. overloads often have two spare aux contacts one of each I always use the N/O contact when tripped so when reset it passes a signal, this way the input to the PLC is on when healthy, this has an advantage that if the supply to the contact was lost (broken wire) then the indication to the PLC is there is a trip. if you use a N/C contact that opens when the overload is healthy then a broken wire will not show up as a fault. For the same reason an E-stop or Stop button is normally closed so that if the signal is lost it stops the process if it is pressed or if a wire comes off or the contact spring breaks (fail safe, sort of). There has been a lot of debate over AB versus other PLC types for example XIO Examine if open is not the physical contact is open but the contact is closed and XIC is the opposite so N/O & XIC is the same & N/C XIO is the same.

yes this is a little a confusing i have been trying to nut this little issue and I have wrote the program to suit this style as is the only thing that actually works in rs500 with the nc contacts and yes does make things a little confusing. I am glad that what I am doing is down the write path and I appreciate the i put given to me. Tha k you and silly Allen Bradley with xic and xio

I generally tell people, don't choose the instruction based on the type of contact on your device. Choose the instruction based on how you want the output to work. The PLC has no concept of "normal". Nor does it have any idea what the device in the field is. Pushbutton, prox, NO, NC. It can't tell this. All it knows is that it sees either a one or a zero. How that one or zero got there is irrelevant to the PLC.

• I want my output to turn/stay ON when the contacts on this device are CLOSED so I choose Examine if Closed (XIC).
• I want my output to turn/stay ON when the contacts on this device are OPEN so I choose Examine if Open (XIO).

OG