Timers

Use this timer to delay turning an output ON. The TD Timer Out bit turns ON when the timer has finished running.

1. The Preset Value is initially loaded into the Current Value the first time that the TD element is seen in the program scan.

2. When the input condition of a TON timer rises (positive RLO), the Timer begins to decrement.

3. When the current value of the timer reaches 0, and the timer's input condition is still ON, the Timer Out bit turns ON.
   The Timer Out bit remains ON until the input condition falls (negative RLO).

4. When the input condition of the TON timer falls (negative RLO), the Preset Value is loaded into the Current Value.

If the input condition falls while the timer is running:

• The timer stops and reloads the Preset Value.
• The current value is not retained.
• The Timer Out bit remains OFF.
• When the input condition rises (positive RLO), the Timer begins to decrement from the Preset Value.

Use this timer to delay turning an output OFF. The TOF Timer Out bit turns OFF when the timer has finished running.

When the input condition of a TOF timer rises (positive RLO):

• The Timer Out bit turns ON.
• The Timer loads: the Preset Value is loaded into the Current Value.

When the input condition falls (negative RLO):

• The Timer begins to decrement.
• The Timer Out bit remains ON while the timer runs.
• When the current value reaches 0, the Timer Out bit turns OFF.

If the timer's input condition rises while the timer is decrementing, the Timer Out bit remains ON and the timer stops running. The current value is not retained.

 

Note	The timer can be reset at any time via the Timer Reset function.

The TA timer functions like a TON timer with two differences:

• If the input condition falls while the timer is running, the timer stops counting--but the current value is retained. This means that when the input condition rises and the timer restarts, it continues to count from the point at which it stopped.
• A TA timer must be reset using the Reset Timer Function. This resets the current value and causes the Timer Out bit to turn OFF.

When the input condition of a TA timer rises (positive RLO):

• The Timer begins to decrement.
• When the current value of the timer reaches 0, and the timer's input condition is still ON, the Timer Out bit turns ON.
  The Timer Out bit remains ON regardless of the input condition.

Use this timer to generate a pulse of specific duration. The TP Timer Out bit is ON when the timer is running and OFF at all other times.

When the input condition of a TP timer rises (positive RLO):

• The Timer Out bit turns ON

• The Timer begins to decrement.

Once the timer is running, it continues regardless of the state of the input condition.

When the current value of the timer reaches 0:

• The Timer Out bit turns OFF.

When the input condition of a TP timer falls (negative RLO):

• The Timer Preset Value is loaded into the Current Value

Note	The timer can be reset (reloaded) at any time via the Timer Reset function

The TE timer functions like a TP timer with this difference:

• If the timer input condition falls, the timer continues to run. However, if the input condition rises again, the timer reloads the preset value and begins to decrement. The Timer Done bit remains ON.
• The TE timer Timer Out bit is ON when the timer is running and OFF at all other times.

When the current value of the timer reaches 0, the Timer Done value turns OFF.

 

Note	The timer can be reset (reloaded) at any time via the Timer Reset function.