9.1 Briefly define the two categories of discrete process control? 9.7 What is a ladder logic diagram? 9.9 What is a programmable logic controller? 9.10 What are the advantages of using a PLC rather than convertional relays, timers, counters, and other hardwired control composents? 9.12 The typical operating eyele of the PLC, called a acan, consists of three parts: (1) input scan, (2) program scan, and (3) output scan. Briefly describe what is accomplished in each part. 9.17 What is a programmable automatica controlle?