When working with touchscreens and PLCs, communication issues are common. Here are four key questions to check:
- Are the PLC parameters consistent with the project setup?
- Is the communication cable wired according to the wiring diagram?
- Is the correct COM port selected in the project when connecting to the screen?
- If everything seems okay, check the address settings in the PLC program.
Method:
Step 1: Check PLC Parameters
Use the PLC programming software to connect to the PLC and verify the current settings. Compare them with the ones in your project. If there's a mismatch, adjust accordingly.
Step 2: Online Simulation
Use your configuration software to connect the PLC directly to the computer via the communication cable. Simulate the online communication by using a numeric input or toggle component. Observe if the operation changes after the simulation ends and whether the NC (Normally Closed) status is properly reflected. Note that previous operations not recorded may cause confusion.
Step 3: Test the Wiring
Use a multimeter to test the wiring based on the pin layout from the wiring diagram. This helps identify any physical connection issues between the PLC and the touchscreen.
Step 4: Touchscreen Parameter Settings
Check the following settings on the touchscreen:
- Communication Port: Confirm whether it's set to COM1 or COM2, depending on which port the PLC is connected to.
- Device Type: This is crucial. If the protocol is not selected correctly, no other settings will matter.
- Connection Method: Ensure the communication method matches the PLC—RS485 or RS232C.
- Interface Parameters and PLC Station Number: These must align with the settings in the PLC.
Step 5: Check the Communication Cable
If the parameters are correct, the next step is to check the physical connection. Verify that the RS485 or RS232C cables are properly connected. Different PLCs may have different wiring configurations, so refer to the maintenance manual for specific guidance.
Online Simulation – Bypassing the Touchscreen
If communication still fails, some users might suspect the touchscreen or the interface. To isolate the issue, you can simulate the communication directly between the PLC and the computer.
How to Perform Online Simulation:
- Connect the PLC to the computer using an RS232 cable. Some PLCs have built-in RS232 ports, while others may require an adapter.
- Create a simple project with two components: one for displaying values and another for input. Set the addresses to match those in the PLC.
- Ensure the engineering parameters match the PLC settings exactly.
- Click on the "Online Simulation" function to see if the PLC communicates with the PC. If it works, the problem is likely not with the PLC or its settings.
This process helps eliminate potential causes step by step and ensures smooth communication between the PLC and the touchscreen system.
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