Detailed Explanation of Timer Instructions: Three Delay Types and Their Application Examples

Basic Principles of Timers

A timer instruction is essentially an output instruction. Its unique feature is that when power flow is received at the input, the output action is not immediately triggered. Instead, the output is executed after a delay. This delay function makes timers crucial in a variety of applications. Based on their timing method and output action, timers are mainly divided into three types: on-delay timers, hold-on delay timers, and off-delay timers.

Delay Types

On-delay Timer
The core function of an on-delay timer is to transfer the output to a specific variable after a specified delay after the input is connected. In contrast to an off-delay timer, an on-delay timer begins timing the moment it is connected. Timing only continues as long as power flow is maintained. Once power flow is lost, timing stops, and no output is generated. When the timer reaches the predetermined time, it is set, triggering the output. If the input power flow is lost again, the timer is reset, and the output is deactivated. Therefore, the timer's output only occurs during the period between its set and reset states. It's important to note that both the set and reset states are closely tied to changes in input power flow.

Hold-On Delay Timer
There is a hold-on delay timer, which differs from the on delay timer. In a hold-on delay timer, if input power flow is interrupted before the timer reaches the preset timer value, the timer does not clear the current timer variable. Instead, once input power flow is restored, the timer continues to increment based on the original timer variable. The timer variable is only cleared when the preset timer value is reached and input power flow is subsequently interrupted.

Off Delay Timer
During a timer's operation, once input power flow is turned off, the specified output variable is turned off after a delay. This functionality is particularly important in many situations. For example, in traffic light control, timers ensure that red lights are on during specific time periods and green lights are on during other time periods, effectively directing traffic flow. Similarly, in stage lighting control, timers are widely used to create specific lighting effects and switching timings. These examples fully demonstrate the indispensable role of timers in various application scenarios.