The CTU instruction is responsible for increasing which of the following by one?

The CTU (Count Up) instruction is designed specifically for counting events or items in programmable logic controllers (PLCs). Its primary function is to increment the accumulated value by one each time the instruction is executed under the right conditions.

When the CTU instruction is used, it keeps track of how many times an event has occurred. Whenever the instruction is triggered, it evaluates whether the count condition is met and, if so, increments the accumulated value (the current count) by one. This capability allows the CTU instruction to effectively monitor and respond to counts, making it essential in applications where tracking input events is crucial.

The other options relate to different functionalities within the context of the CTU instruction. For example, the preset value is the target count that the CTU will aim to reach, the DN bit indicates that the accumulated count has hit the preset value, and the CTU instruction tag serves as an identifier for the CTU instruction itself. However, none of these elements are directly incremented by the CTU instruction; rather, they support its functionality in counting events.