Which timer will allow you to turn on an output when rung goes true and keep the output on for 15 seconds after a condition goes false?

The correct answer is TOF (Timer Off Delay). The TOF timer functions to keep an output energized for a specified time duration after the input condition that triggered it goes false. In this case, the timer will turn on the output when the rung condition becomes true, and it will maintain that output state for 15 seconds even after the rung goes false.

This timer is particularly useful in applications where a delay is needed after a condition changes, allowing for processes or systems to complete actions or transitions smoothly without immediate cut-off when the condition is no longer true. When configuring a TOF, you set the time delay, and once the condition that started the timer goes false, the timer countdown for that duration begins, ensuring the output remains active throughout that interval.

The other timer types have different functions that do not fit the scenario described. TON, for example, is designed to turn on an output when a condition becomes true and will reset when the condition goes false, meaning it won't keep the output energized after the condition changes. CTU counts occurrences of input signals, and RTO is used for retaining values based on an input condition without inherently providing a delay for deactivation.