Siemens/Mitsubishi PLC Programming Beginner's Guide to Setting Up Your First Project

First, the basic knowledge: PLC project in the end is what?

​The essence of a PLC project is the sophisticated collaboration of hardware and logicTake conveyor start-stop control as an example. Take the conveyor belt start-stop control as an example, PLC receives the instruction through the input module (X0=start button signal), and after the CPU parses the ladder program, it drives the output module (Y0=contactor coil) to act. The core hardware contains:

  • ​CPU moduleThe "brain" that executes the programme, Siemens S7-1200 or Mitsubishi FX3U is the preferred choice to start with.
  • ​I/O Modules: bridge to the physical world, DI point-of-connection sensors, DO point-of-control actuators
  • ​power module: Provides 24V DC, misconnection of 220V will burn out the module (common accident!)

​Why is ladder diagram the language of choice?​
Because of its direct mapping to the electrical control logic, the self-locking circuit in the figure implements "release the button and still keep the motor running":

laddermake a copy of
|--[X0]----[Y0]--|  // Start button trigger
|--[Y0]----(self-locking)-|  // Y0 normally open contact remains energised
|--[X1]----[/Y0]-|  // Stop button cut off




Scenario practice: build a motor control project from scratch


Step 1: Guide to avoiding pitfalls in software installation






brand name
programming software
a death trap
prescription






Siemens (company name)
TIA Portal V18
Installation path with Chinese
Full English Path + Disable Antivirus




Mitsubishi
GX Works2
USB driver not installed
Download the special driver from the official website




​Operational verification: Create a new project after software installation and select the corresponding PLC model (e.g. Mitsubishi FX3U-CPU).









Step 2: The Golden Three Steps of I/O Configuration


    

  1. ​Physical wiring​

      

    • Pushbutton → PLC input: normally open pushbutton connects to X0, normally closed emergency stop connects to X1 (NC contact must be used!)
      • 

    • PLC output → contactor: Y0 connected to KM coil, output type selected relay (transistor type easy to burn)
      • 

    

    2. 

  2. ​address allocation​

    pythonmake a copy of
    # Mitsubishi FX Series Configuration Example
inputs = {'X0': 'Start Button', 'X1': 'Emergency stop switch', 'X2': 'Overload protection'}
outputs = {'Y0': 'Motor contactor', 'Y1': 'Fault light'}
    

    3. 

  3. ​electrical isolation: power lines (≥2.5mm²) and control lines in separate slots, shielded twisted pair for analogue signals
    4. 



Step 3: Write the first ladder programme


​Siemens S7-1200 motor start/stop programme::


laddermake a copy of
// Network 1: Activating self-locking
|--[I0.0]----[Q0.0]--|  // I0.0 = start button
|--[Q0.0]----(self-locking)--|  
|--[I0.1]----[/Q0.0]-|  // I0.1 = Stop button


​Mitsubishi FX3U Forward and Reverse Interlocking Programme::


laddermake a copy of
|--[X0]--[X2]--[Y1NC]--(Y0)--|  // Positive start (Y1 interlock)
|--[X1]--[X2]--[Y0NC]--(Y1)--|  // Reverse start (Y0 interlock)
|--[T0 K50]-------------------|  // Switching delay 0.5 seconds to prevent short circuit




​Key TipsEmergency stop circuits must be hardwired independently of the PLC, as accidents have been caused by contactors sticking due to programmed interlocks alone.






III. Solutions: Debugging Failures and Advancement Paths


First Aid Manual for High Frequency Faults






impunity
detection point
Root and Branch Programme






PLC without power supply
Measurement of L+/L- voltage
Replacement of 24V power supply (range 22.8-25.2V)




Input signal not responding
Check COM terminal wiring
NPN sensor to 24V+, PNP to 0V




Output point burnout
Viewing Load Current
Solenoid Valve Parallel Resistive Absorption Module






Steps from Rookie to Engineer


    

  1. ​Foundation consolidation (1 month)​

      

    • Master the timer (TON instruction), counter (CTU instruction) application
      • 

    • Completion of star-delta start procedure (delayed switching of main/auxiliary contactors)
      • 

    

    2. 

  2. ​Hands-on project (3 months)​

      

    • Material Sorting System: Cylinders triggered by photoelectric sensors
      • 

    • HMI touch screen production: EasyBuilder design start-stop interface of Velantone
      • 

    

    3. 

  3. ​High salary springboard (6 months)​

      

    • PID temperature control: thermostat ± 1 ℃ precision adjustment
      • 

    • Modbus communication: PLC and inverter speed control linkage
      • 

    

    4. 





Ten years ago when I was debugging a servo system, I didn't set the home sensor causing the unit to hit a limit -The value of the first project is not in running it perfectly, but in teaching you to respect the safety circuit.. Behind every line of code today is a deep understanding of the rules that govern how the physical world works.

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