Final answer:
A PLC controls processes by reading input conditions, executing ladder logic programs to make decisions, and then updating output terminals that influence connected devices or machinery.
Step-by-step explanation:
A PLC, or Programmable Logic Controller, operates by continuously examining the conditions of its input terminals, making decisions based on the ladder logic program, and then updating the condition of its output terminals. The PLC cycle starts by checking the status of the inputs, which can include switches, sensors, or other electrical signals. Once the inputs are read, the PLC executes its program, which consists of a series of logical operations based on the ladder logic designed by the programmer. Finally, it updates the outputs, which can control machinery, alarms, lights, or other devices, based on the decisions made during the program execution.