to provide continuity through the contact. For example, if a push button is connected

to an input module, and the address of connection is 10, and you program an exam if on (XIO)

instruction to represent PB1. The processor when reading the status of the field device,

will read a zero if it is not pushed because there is no voltage. A normally open contact

will remain open. If the pushbutton is pressed, then the processor will read a 1 and the normally

open contact will close thus providing continuity in the PLC ladder rung. As soon as the push

button is released, the contact will go back to open. In a PLC, you will also see the contacts

highlighted when there is power at the input module with that address. If the contact is

not highlighted it means there is no power continuity and it’s reference device is

off. For more PLC training, go to http://www.bin95.com and click on PLC training videos on the left

hand side. You can learn more about how a PLC works and PLC automation basics.