In order for a PLC to control an automated machine or process, it must be given a set of
instructions. These instructions, or user programs, tell the PLC what inputs to monitor, how to
process the data, and how to respond to the inputs.
By the end of this course, you will be able to
• Identify the four steps a PLC performs during operation
• Define the term input scan
• Define the term program scan
• Define the term output scan
• Identify the symbols representing normally open and normally closed contact relays
• Identify the two structures used for programming