PLCs commonly use which types of instructions to stop a machine after a certain number of parts are produced?

The correct response indicates that PLCs (Programmable Logic Controllers) utilize CTU (Count Up) and CTD (Count Down) instructions for managing the count of produced items in an automated system.

The CTU instruction is designed to increment a count each time a specified event occurs, such as the production of a part. This count continues to rise until it reaches a predetermined value, which signifies the goal number of parts produced. At that point, a corresponding output can be activated to stop the machinery or trigger another action.

Conversely, the CTD instruction is used to decrease a count from a specified starting number down to zero. This functionality is beneficial in situations where the production process needs to count down the produced items until a stop condition is met, offering the flexibility to manage cycles in various production scenarios.

Together, these instructions provide a robust framework for effectively managing production counts, ensuring machinery operates efficiently and halts as needed when a specific production target is reached.