akYtec Lesson 4: Master the Timers (TON/TOF)

Timers are the heartbeat of industrial logic. In this lesson, we cover TON (On-Delay) and TOF (Off-Delay).

In industrial automation, timing is everything. Whether you are delaying a motor start to prevent a power surge or keeping a safety fan running after a machine stops, you need timers. In this lesson, we will cover the two most essential timer blocks: TON and TOF.

Goal: Create a “Safety Fan” that stays on for 10 seconds after a machine stops.

• TON (Timer On): Delays the start. If you press a button, the output waits X seconds before turning on.
• TOF (Timer Off): Delays the stop. When you turn the signal off, the output stays on for X seconds.

The Practical Logic:

1. Drag a TOF block from the Library.
2. Connect your Pump Output (Q1) to the input of the TOF.
3. Connect the TOF output to Fan Output (Q2).
4. Set the PT (Preset Time) to T#10s in the properties.
5. Simulation: Notice that when Q1 goes low, Q2 stays “Hot” for exactly 10 seconds.

Understanding TON (Timer On-Delay)

The TON timer is used to delay an action. When the input signal becomes True, the timer starts counting. The output only turns True after the specified time has passed. If the input signal drops to False at any point during the countdown, the timer resets to zero.

Example use case: A lubrication pump that must run for 5 seconds before a main conveyor belt starts.

Understanding TOF (Timer Off-Delay)

The TOF timer is used to extend an action. When the input signal is True, the output is instantly True. However, when the input signal drops to False, the output stays True for a specific duration before finally turning off.

Example use case: An extraction fan that stays on for 30 seconds after a welding machine is turned off to clear the air.

📸 Screenshot 1: Locating the Timers

• Action: Hover your mouse over the “Library” pane on the right side of akYtec ALP.
• Focus: Expand the Timers folder.
• What to show: Clear view of the TON, TOF, and TP blocks in the list.
• Caption: “Locating the Timer function blocks in the ALP Library.”

📸 Screenshot 2: The Logic Wiring

• Action: Show the full canvas with the SR Flip-Flop, the TOF block, and the Outputs.
• Focus: The wire connecting the Q of the Flip-Flop to the IN of the TOF.
• What to show: How the logic “flows” from the main output into the timer.
• Caption: “Wiring the TOF (Off-Delay) timer to the pump control logic.”

📸 Screenshot 3: Setting the Time (Properties)

• Action: Click on the TOF block so it is highlighted.
• Focus: The Properties window at the bottom of the screen.
• What to show: The PT (Preset Time) field with the value T#10s typed in.
• Caption: “Configuring the delay duration using the industrial T# format.”

📸 Screenshot 4: Active Simulation (Input ON)

• Action: Press the Play button (Simulation mode) and click the Start button (I1).
• Focus: Both Q1 and Q2 lines should be red (indicating they are ON).
• What to show: The logic state while the system is running.
• Caption: “Simulation Mode: Both outputs active simultaneously.”

📸 Screenshot 5: The “Off-Delay” in Action

• Action: Turn off the start signal while in simulation.
• Focus: The TOF block itself.
• What to show: The ET (Elapsed Time) value counting up while Q1 is grey (OFF) and Q2 is still red (ON).
• Caption: “The TOF timer maintaining the fan output after the pump has stopped.”
  

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Programming the Safety Fan Logic

We will now create a project where a fan (Output Q2) stays active for 10 seconds after a pump (Output Q1) is stopped.

• Step 1: Open your akYtec ALP project from Lesson 3.
• Step 2: In the Library on the right, navigate to the Timers section.
• Step 3: Drag a TOF block onto the center of the canvas.
• Step 4: Connect the wire from your SR Flip-Flop output (which controls Q1) to the input (IN) of the TOF block.
• Step 5: Drag a new Output (Q2) from the device resources and connect it to the output (Q) of the TOF block.
• Step 6: Click on the TOF block. In the Properties pane at the bottom, find the PT (Preset Time) field. Type T#10s to set a 10-second delay.

Testing in Simulation

Run the simulation and activate Input I1. You will see both Q1 (Pump) and Q2 (Fan) turn on instantly. Now, deactivate the signal. Notice that while Q1 turns off immediately, Q2 remains active. The TOF block will begin counting down, and Q2 will only turn off once the 10-second threshold is reached.

Industrial Best Practice

When using timers in high-voltage environments, always remember that timers in software are “logical.” If the PLC loses power, the timer resets. For critical safety applications where a fan must run regardless of the PLC state, hardware-based safety relays are used. For standard automation processes, however, these software blocks are the industry standard for precision control.