Touch screen and plc communication parameter settings and communication is not a solution - Database & Sql Blog Articles

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When it comes to touch screens and PLCs, many users face common communication issues. Here are four key questions to help identify the problem:

1. Are the PLC parameters consistent with the project settings?
2. Is the communication cable wired correctly according to the wiring diagram?
3. Is the correct COM port selected in the project when connecting to the screen?
4. If the parameters and wiring are correct, check the PLC program address.

Method:

Step 1: Check the PLC Parameters

Use the PLC programming software to connect to the PLC and verify its current settings. Compare them with the ones set in your project. This helps ensure that both systems are aligned.

Step 2: Online Simulation

Use your configuration software to connect the PLC's communication cable to the computer. Simulate the online communication by using a numeric input or switch component. Observe if the system behaves as expected before and after the simulation. If the NC (normally closed) contacts don’t respond properly, there may be an issue with the setup.

Step 3: Test the Wiring

Use a multimeter to test the wiring based on the pinout provided in the wiring diagram. This ensures that all connections are made correctly and there are no short circuits or miswired lines.

Step 4: Check the Touch Screen Settings

Review the touch screen’s parameter settings carefully. Pay attention to the following:

• Communication Port Setting: Confirm whether the touch screen is using COM1 or COM2 for communication with the PLC.
• Device Type: This is the most critical setting. If the communication protocol is not selected correctly, everything else won't work.
• Connection Method: Ensure that the connection type (RS485 or RS232C) matches the PLC's interface.
• Interface Parameters and PLC Station Number: These must match the settings in the PLC itself.

Step 5: Troubleshoot the Communication Line

If the parameters are set correctly, the next step is to check the physical connections. Make sure the RS485 or RS232C wiring is correct. Different PLC models may have different wiring configurations, so refer to the manufacturer's documentation for guidance.

Online Simulation: Bypass the Touch Screen

When communication fails, some users may suspect either the touch screen or the interface. An effective way to test this is through online simulation. This involves connecting the PLC directly to the computer, bypassing the touch screen entirely.

How to Perform Online Simulation:

1. Connect the PLC to the computer via RS232. Some PLCs have built-in RS232 ports, while others may require an adapter.
2. Create a simple project with two components: one for displaying data and another for input. Set the addresses to match those in the PLC.
3. Ensure that the engineering parameters match the PLC’s settings exactly.
4. Click on the online simulation feature to see if the PLC communicates with the PC. If it does, you can rule out issues with the PLC or its configuration.

This method is a quick and reliable way to isolate the problem and determine whether the issue lies with the touch screen, the PLC, or the communication setup.