Application of PLC in printing machinery and equipment 2

February 19, 2020

General faults and troubleshooting
The PLC control system has stable performance. Each input and output point has indicator lights. As long as you are familiar with the basic working principles and understand the program operation steps, PLC faults are easily eliminated. Many engineering technicians are unfamiliar with PLC operating points; PLC operating points are less likely to fail, and maintenance personnel ’s attention is focused on the parts that often fail, and the parts with few failures are often ignored, all of which increase It is difficult to troubleshoot the PLC.

With PLC, you don't need to know the internal circuit in detail. As long as you understand the working principle of each part, you can effectively eliminate various PLC faults.

Now there are various brands of PLCs on the market. The faults are strange and weird. Common faults: power failure, power module damage, motherboard damage, communication failure, SF light failure, I / O failure, password protection cannot enter the program, etc.

PLC troubleshooting general methods:
1. Check if the power supply (pwr) is normal? There are two types of power supply: one is AC 220V (voltage) and the other is DC + 24V (voltage). Measured with an electricity meter. If the above voltage is abnormal, the problem lies in the external power supply circuit. If the above voltage is normal, the pwr lamp does not work. On, check the fuse, or replace the entire power module.

2. Is the RUN light on? No light, check that the programmer is in the PRG or LOAD position? If the switch is in the run position, the programmer is plugged in, the RUN lamp is off, and no error code is displayed, you need to replace the CPU module.

3. Is the fault light on? Is the battery light (BATT) on? On, it means that the battery is insufficient, and the program cannot run. Replace the lithium battery. Replace the battery and let the PLC test run. If the operation fails, you need to reinstall the original program.

4. After the above faults are eliminated, check each input and output working point:
Enter the operating point and compare the status displayed by the programmer with the LED indicator of the input operating point: If they are the same, compare the operating status of the LED and the input point (button, limit switch, etc.). If the two are different, measure the input module and find that If there is a problem, replacing the input device cannot solve the problem. Replace the input module.

If the signal is a counter, reset the running program again. If the operation fails, check the logic that controls the reset.

If the internal timer fails, replace other internal timers. If all internal timers have been used up, replace the CPU module.

If the signal is Onagawa, there is no output or the status is different from Onagawa, use a programmer to check the output points and program list. Find the disconnected work point, and so on, and continue searching. For most equipment factories, due to the protection of intellectual property rights, the editing program is not open. The user cannot display the working status from the programmer, cannot find the PLC internal faults, and can only find it based on experience.