Hollysys PLC - Six Fault Types of PLC and Troubleshooting Methods (4-6)

Fourth, the fundamental sequence of repairing PLC.

1. Start first.

1) When repairing the PLC, do not start directly immediately, but first ask about the situation and the phenomenon of the problem before and after the problem;

2) If you repair an unfamiliar PLC, you should first understand its operating principle.

2. Clean first and then repair.

When repairing a PLC, you can turn the machine on and clean the PLC first.

3. PLC view first outside and then inside.

When repairing a PLC, look at the external phenomena and causes, and if the exterior is normal, then look inside the PLC.

4. First no electricity judgment and then power on judgment.

First of all, in the absence of electricity, first determine whether the fuse is damaged or whether it is not energized to identify the fault. If you can't tell it, then power on to check the PLC.

Fifth, the fundamental process of PLC system maintenance and fault removal.

Overall diagnosis: You can find out the general direction of the fault point according to the overall view flow chart, and then gradually refine and find out the specific problem.

1. Diagnosis of power supply problems.

If the power lamp is not lit, you need to check the power supply system and the power lamp itself.

2. Diagnosis of operation problems.

If the power supply is normal and the operation indicator light is not on, it means that the system may have stopped normal operation due to some abnormal reason.

3. Diagnosis of input and output problems.

1) The input and output is the channel for information exchange between the PLC and external equipment;

2) Whether the input and output are operating normally is not only related to the input/output unit, but also related to the condition of components such as connection wiring, terminal blocks, and fuses.

Sixth, the fundamental process of finding general PLC faults.

When repairing the PLC, plug in the programmer, turn the switch to the RUN position, and then find it according to the following process:

1) If the PLC aborts in the direction and condition (local) where some outputs are encouraged, it is generally in an intermediate state, then look for the signal that causes the next operation, and the programmer will show the ON/OFF condition of the signal;

2) If the input signal is used, the condition displayed by the programmer is compared with the LED indication of the input module, and if the results are not the same, the need to replace the input module is clarified. Before replacing the module, check whether the I/O expansion cable and related connections are normal;

3) If the input condition is the same as the LED indication of the input module, compare the condition of the LED and the input device. If the two are different, you need to measure the input module. If a problem is found, the I/O equipment, field wiring, power supply, etc., need to be replaced. Otherwise, the requirement replaces the input module;

4) If the signal is a coil, there is no output or the output is different from the condition of the coil, then the programmer needs to check the driving logic of the output, and check the program list;

5) If the signal is a timer and stops at a non-zero value less than 999.9, the CPU module needs to be replaced;

6) If the signal controls a counter, you need to check the logic of the control reset first, and then check the counter signal. Then check and identify whether the relevant components are abnormal and require replacement.

Hollysys PLC - Six Fault Types of PLC and Troubleshooting Methods (4-6)

Hollysys PLC - Six Fault Types of PLC and Troubleshooting Methods (4-6)

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