Mitsubishi PLC Self Resetting Timer Programming | Ladder Logic Examples & Guide

Understanding PLC Self Resetting Timers

A PLC self resetting timer, also known as a PLC auto reset timer, is a timer that, once activated, counts up to a preset value. Upon reaching this value, instead of simply stopping, the timer resets itself and starts counting again from zero. This creates a cyclic or repeating timing sequence, eliminating the need for external reset logic in many applications. The Mitsubishi PLC timer instruction set includes functions that, when combined strategically, can achieve this self-resetting behavior. This functionality is especially useful for tasks like flashing lights, periodic machine lubrication, or any process that requires a repeating time interval.

Mitsubishi PLC Timer Instruction Set and Self-Resetting Logic

To implement a self resetting timer in PLC ladder logic using a Mitsubishi PLC, you'll typically employ the TON (Timer On Delay) instruction. The key to creating the self-resetting behavior lies in using the timer's output contact to reset itself. This creates a feedback loop where the timer's activation triggers its own reset. The Mitsubishi PLC timer instruction set provides the necessary tools, and the implementation often involves a simple ladder logic structure. Whether you are using a Mitsubishi FX PLC timer reset or a more advanced platform, the underlying principle remains the same.

Ladder Logic Example for a Self-Resetting Timer

Here's a basic example of PLC ladder logic self-resetting timer example using a Mitsubishi PLC:

// Ladder Logic for Self-Resetting Timer
// X0: Start Input
// T0: Timer (TON instruction)
// K100: Preset Value (10 seconds, assuming 100ms resolution)
// M0: Timer Done Bit

LD X0   // Load Start Input
OR M0 // OR with Timer Done Bit (to maintain timer running if already active)
OUT M0  // Set Timer Enable Bit

LD M0   // Load Timer Enable Bit
TON T0 K100  // Timer On Delay with 10 second preset

LD T0   // Load Timer Contact
RST T0  // Reset Timer

In this example, the `X0` input initiates the timer. The `M0` coil is used to maintain the timer running, even after the input `X0` is de-energized. When the timer `T0` reaches its preset value (K100, representing 10 seconds if the base time is 100ms), its contact activates, resetting the timer itself (`RST T0`). This creates a continuous cycle of timing and resetting.

Implementing a Self-Resetting Timer in GX Works2 and GX Developer

The implementation process may vary slightly depending on the Mitsubishi PLC programming software you're using. Whether you're working with self-resetting timer programming in GX Works2 or the older GX Developer, the core logic remains the same. The key is to use the timer's contact to trigger its own reset. In GX Works2, the user interface and available functions are often more streamlined, but the basic principles of ladder logic apply across both platforms. If working with GX developer plc reset timer functionality, ensure you are familiar with the specific instruction set available in that environment.

Detailed Steps in GX Works2

1. Open GX Works2 and create a new project for your Mitsubishi PLC.
2. Create a new ladder logic program.
3. Add a normally open contact for your start input (e.g., X0).
4. Add a coil (e.g., M0) and connect it to the start input. This coil will act as the timer enable bit. Add an OR contact with the timer done bit in series with the start input contact to keep the timer running when it's already active.
5. Add a TON (Timer On Delay) instruction. Specify the timer number (e.g., T0) and the preset value (e.g., K100 for 10 seconds). The input to the timer should be the timer enable bit M0.
6. Add a normally open contact using the timer number (T0).
7. Add an RST (Reset) instruction and connect it to the timer contact (T0). Specify the timer number (T0) to be reset.
8. Compile and download the program to your PLC.

This setup ensures that when the timer reaches its preset value, its contact activates the reset instruction, causing the timer to reset and begin counting again.

Applications of PLC Automatic Reset Timers

The PLC automatic reset timer circuit finds applications in a variety of industrial automation scenarios. Some common examples include:

• Flashing Lights: Controlling the on/off cycle of indicator lights or warning signals.
• Lubrication Systems: Periodically activating a lubrication pump to maintain machinery.
• Mixing Processes: Repeating a mixing cycle at regular intervals.
• Conveyor Systems: Controlling the intermittent movement of a conveyor belt.
• Cooling Systems: Cycling a cooling fan or pump to prevent overheating.

By using a plc cyclic timer function, these processes can be automated efficiently without the need for complex external control logic.

Advanced Self-Resetting Timer Techniques

While the basic self resetting timer in PLC ladder logic is effective, more complex applications may require variations. One such variation is the plc delay on off self-reset timer, which introduces a delay both when the timer is activated and when it's reset. This can be achieved by cascading timers or using more advanced PLC functions. Another scenario involves using the timer to trigger a sequence of events, where each event is timed based on the self-resetting timer's cycle. Understanding the Mitsubishi PLC timer instruction set fully is crucial for implementing these advanced techniques. A Mitsubishi PLC program example for auto reset may also include error handling and safety interlocks to ensure reliable and safe operation.