Advanced Course for Beginners in Mitsubishi PLC Learning

Recently, many friends have asked me how to get started with Mitsubishi PLCs. As an engineer with over 20 years of experience, I decided to organize my knowledge to help everyone avoid unnecessary detours.

Why Choose Mitsubishi PLC?

Mitsubishi PLCs hold a significant market share in the domestic industrial automation field. Its programming software, GX Works, is user-friendly, has a comprehensive instruction system, and is stable and reliable. For beginners, Mitsubishi is a good choice.

Basic Hardware Knowledge

Let’s briefly discuss the “organs” of a PLC:

• CPU: Equivalent to the brain, responsible for computation and control
• Input Module: Like our senses, receiving external signals
• Output Module: Similar to hands and feet, controlling external devices
• Power Supply Module: Provides power to the entire system
• Communication Module: Enables data exchange with other devices

Special Reminder: When purchasing, pay attention to the power supply voltage (AC220V or DC24V) and ensure the I/O points meet actual needs.

Software Environment Setup

1. Download the GX Works3 software (it is recommended to use the official version)
2. Install the USB driver
3. Select the correct PLC model when creating a new project

Common Issues: If the software reports an error upon opening, it is often due to compatibility settings not being changed. Right-click → Properties → Compatibility → Run as administrator.

Detailed Explanation of Basic Instructions

LD/LDI (Input Instructions)

Understand this instruction as a regular switch. LD is a normally open contact, while LDI is a normally closed contact.

OUT (Output Instruction)

Controls the relay coil action, which means it activates the device.

Let’s look at a simple example:

Copy

LD X0    ; X0 switch pressed
OUT Y0   ; Y0 light on

This is like a lighting switch at home; when the switch (X0) is pressed, the light (Y0) turns on.

SET/RST (Set/Reset Instructions)

• SET: Similar to a latching circuit, the output remains active
• RST: Releases the latching state

Practical Application Case: Simple Motor Start/Stop Control

Assuming we want to achieve the following functionality:

1. Press the START button to start the motor
2. Press the STOP button to stop the motor
3. Automatically shut down in case of overload

Example Ladder Diagram:

Copy

LD X0    ; START button
OR M0    ; Latching contact
ANI X1   ; STOP button (normally closed)
ANI X2   ; Overload protection (normally closed)
OUT M0   ; Running status storage
OUT Y0   ; Motor running

Debugging Tips

1. Check Before Powering On: Ensure wiring is correct, especially the power polarity
2. Monitoring Function: Use the online monitoring function of GX Works3 during operation to observe I/O status
3. Force ON/OFF: During debugging, you can force input/output states, but remember to cancel them in time

Common Errors and Solutions

1. Program not responding

• Check if the PLC is in running status
• Confirm if the input voltage is normal
• Check the alarm indicator light

1. Output not functioning

• Check if the external load is normal
• Confirm the output type (relay/transistor)
• Verify program logic

Practical exercise suggestions:

1. Build a simple control circuit using physical components or simulation software
2. Start with single instructions and gradually increase complexity
3. Simulate faults frequently to improve troubleshooting skills

Next time, we will delve into the use of counters and timers, which are important functions in PLC control.