PLC(Programmable Logic Controller) is a type of control device that has been specifically designed for industrial use. It is capable of controlling processes of varying complexities, and can be programmed to perform a series of events or programs triggered by inputs such as timers or counters. When an event is triggered, the PLC can turn external devices on or off, or transmit a sequence of pulses to them. By altering the programs installed in a PLC, different functions can be performed in various control environments.

The evolution of control techniques has been ongoing for a significant amount of time. Initially, humans were responsible for controlling the master loving system. Later, electrical applications were introduced, and relay contacts were used for control. Relays enabled power to be switched without the use of mechanical switches. Relays are frequently used for creating simple logic interrupt control operations. The advent of computers brought about a new era in control, with the introduction of PLC programmable control technology.

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PLC control is increasingly being used in overhead crane control systems due to its ability to simplify circuitry and make designs safer, easier and more reliable. Traditional designs, on the other hand, rely on relays and contactors for control. The starting and speed control of the crane is achieved through AC winding and resistance series. However, this type of design has several drawbacks, such as low reliability, complex operation, high failure rate, power waste, and low efficiency.

To address these issues, thorough research was conducted, and PLC and converter technology were implemented in the overhead crane control system. The results showed that after this improvement, energy consumption was reduced, mechanical wear-out was minimized, and the starting performance was enhanced. This proves that the application of PLC in overhead crane control systems is not only beneficial in terms of performance but also in terms of energy efficiency and equipment maintenance.

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PLC troubleshooting

  • I/O modules

It is a common misconception that when a PLC malfunctions, it is usually due to internal processor issues. However, a significant percentage of problems actually arise from faulty I/O modules or malfunctioning field equipment. It is important to note that diagnosing the source of the problem is not a cause for panic, as distinguishing between issues with the I/O system and processor is relatively simple.

Each type of problem has its own unique signature that can be easily identified and examined, leading to a clear diagnosis. It is crucial to properly diagnose and fix any issues with the I/O system or field equipment to ensure the proper functioning of the entire PLC system.

  • In or out?

When the issue is traced back to a specific I/O module, it is usually due to an external problem such as wiring errors. On the other hand, internal problems can cause erratic behavior, widespread failures, or even complete failure of the entire PLC system.

Before delving into specific problems, it is crucial to check the “integrity” of the PLC. This refers to checking the electronic grounding of the PLC, rather than questioning its ethical values or financial records.

Furthermore, the power and ground wiring should be examined to determine whether there are any loose, corroded, or damaged connections. The power supply should be checked using a digital meter, and both AC and DC voltages should be zero. This will help to ensure that the power supply is functioning correctly and providing the necessary power to the PLC.

  • Interference

Electromagnetic interference (EMI) or radio frequency interference (RFI) can cause problems for the PLC. EMI and RFI can be caused by various sources such as lightning strikes, welding in the area, or handheld radio transmitters. Handheld radios used by maintenance staff, emit powerful radio frequency radiation which can disrupt and interfere with unprotected electronic equipment like the PLC. Shielding, grounding, and power conditioning can be used to improve the resistance of the PLC against EMI and RFI problems.

  • Corrupted Memory

Absolutely, having a backup copy of the program is essential to quickly recover from any issues that may occur with the PLC. It is also important to perform regular backups and store them in a safe and secure location, preferably off-site. Backups should be tested periodically to ensure that they are working correctly and that the program can be restored in the event of a failure.

In addition to EMI and RFI, other environmental factors can also affect the PLC’s memory, such as extreme temperatures, humidity, and vibrations. Proper storage and environmental conditions can help to prevent these issues from occurring.

  • Confusion

Once the internal and external status conflict is identified, the next step is to locate the cause of the issue. This may involve tracing the signal path, checking the wiring and connections, and testing the components. Troubleshooting may also require the use of diagnostic tools such as multimeters, oscilloscopes, and logic analyzers.

It is important to follow a systematic approach when troubleshooting, starting with the simplest and most obvious solutions before moving on to more complex or difficult ones. Keeping a record of the troubleshooting steps and the results of each test can also be helpful in identifying patterns or trends in the system’s behavior.

In summary, troubleshooting PLC issues involves identifying and resolving conflicts between the internal status of the PLC and the external situation. This requires a systematic approach, diagnostic tools, and record keeping to effectively locate and fix the issue

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  • Troubleshooting ground loops
  • Diagnostic PLC indicators
  • Troubleshooting PLC inputs
  • Troubleshooting PLC outputs
  • Troubleshooting the CPU

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