- Counts time base intervals when the instruction is false.
- The Timer Off Delay instruction begins to count time base intervals when the rung makes a true to false transition. As long as rung conditions remain false, the timer increments its accumulated value (ACC each scans until it reaches the preset value (PRE). The accumulated value is reset when rung conditions go true regardless of whether the timer has timed out.
Example 1
Let's say we have in the field an emergency stop. Once the E-Stop is pressed we want the siren to go on for 5 seconds.
Input / Output
- E-Stop Push Button I:1.0/0
- Siren O:2.0/0
Ladder Logic Solution
When the Estop is on then TOF T4:1 is energized. When a TOF is energized then it will reset the accumulator and its done bit will be on.
When we loose the Estop TOF will be de-energized. When TOF is de-energized it will start counting until it reaches its preset value. In this example the siren will go on for 5 seconds.
Note
- When TOF is de-energized the timer will start timing till its accumulation value is equal to preset value. If during this time the timer is de-energized then the timer will reset and set the Acc value to zero.
- Watch the use of the TOF done. (T4: 1.DN)
