What is the purpose of a timer in PLC programming, and name two common timer types?

• A. To measure temperature and humidity; TDR and TRM
• B. To delay actions or create time-based sequences; TON (on-delay) and TOF (off-delay)
• C. To convert analog signals to digital; A2D and D2A
• D. To manage network communication; TCP and UDP

Answer: (B)

Timers in PLC programming enable time-based control by delaying actions or creating sequences tied to a duration. A TON on-delay timer starts counting when its input goes true, and its output turns on only after the preset time has elapsed, making it ideal for starting a device a short time after a condition occurs. A TOF off-delay timer keeps its output on for the preset time after the input goes false, which is useful for letting an action finish or cool down before turning off. These two are common because timing control is a fundamental part of sequencing in automation. Other options describe functions that aren’t timers—environmental measurements, analog-to-digital conversion, or network communication—so they don’t fit as timers.