PLC Programming Tutorial by http://www.bin95.com gives a Ladder Logic Programming Tutorial for a NOT instruction (Normally Closed) using a real world application example. The NC or NOT type Ladder Logic Programming is also used in failsafe and interlock programming. This is just a small, low resolution sample from DVD 3 of the 10 DVD PLC Training Video Course Library. The actually DVDs have much better quality and details. http://www.youtube.com/watch?v=dfWQ0W4MgGA
For instructor based PLC Training, see https://www.youtube.com/watch?v=Bw-m9gT7Nh4