ondelay

OnDelay refers to a timing function used in control systems and automation to postpone the activation of an output after an input signal becomes true. It is commonly implemented as a timer-on-delay (TON) feature in programmable logic controllers (PLCs), relay logic, and related software libraries. The core purpose is to ensure a condition persists for a specified interval before any action is taken.

Operation of an OnDelay timer is typically straightforward. When the input condition transitions to true, the timer starts counting from zero. If the preset delay elapses before the input returns to false, the output is activated. If the input de-asserts before the delay completes, the timer resets to zero. Some implementations include variations such as retentive timers, where accumulated time is preserved under certain conditions, or latching behavior, where once activated the output remains on until explicitly reset.

Variants and implementations can be hardware-based, such as mechanical timing relays or electronic timers in relay logic, or software-based, such as function blocks in PLC programming languages or general-purpose timers in embedded software. Delays can be fixed, where the duration is constant, or adjustable, allowing runtime configuration of the delay period.

Applications of OnDelay timers include debouncing noisy signals, ensuring a condition is stable before starting a process, sequencing operations in machines, enabling safe motor startup, and implementing staggered actions in control systems. They are often contrasted with OffDelay timers, which delay deactivation after the input condition ends.

See also: timer-on-delay (TON), timer relays, debouncing, PLC programming, delay timers.