9907-164 定时器关闭延迟

The timer off delay instruction is not as common as the on delay instruction, but it is suitable for many special situations where the load must remain running for a short period of time after the machine is turned off. What is surprising and often confusing about 9907-164 is that once the step becomes true, the completion bit of the timer will become true and remain there until the timer completes counting. When the step of the timer becomes false, the timer starts counting.

This is particularly useful when you need to keep something running for a period of time after an event occurs. An example of this situation could be if a motor is turned off, but you need to keep its cooling system on for 4 seconds after it is turned off.
In logic diagram 3, you can see the TOF instruction. When the motor runs true, 9907-164 completes bit activation and opens the cooling system. When the motor runs false, the completion bit remains true until the cooling system runs for more than 4000 milliseconds. At this point, the completed part will exit and the cooling system will shut down.

Looking back, when the step is true, the TOF instruction sets its completion bit to true, and starts counting up when the step is false. Only when the step becomes false within the preset duration will it delete the completion bit. The timer will automatically reset after reaching the preset time.