Fault Analysis of PLC Control Cabinet

Due to the increasingly powerful functions of integrated circuits, the integration of PLC internal boards is already very high, there are few discrete components, and discrete components are mostly micro-sealed devices, so the current PLC or controller maintenance methods are also mainly It is based on replacing the faulty board. The fault analysis method is as follows:

1) If the analog input signal sent to the PLC by the field meter or sensor is normal with a multimeter, and the data on the display is not normal, and the other analog input signals are normal, the input of the PLC or controller may be faulty. .

2) The field instrument or sensor sends the analog input signal of the PLC. The data on the display is not normal. The analog signal input is replaced by the standard signal generator and connected to the PLC. The data on the display is not normal. It can be determined that the input has been burned or the card is damaged, and the input card needs to be replaced.

3) If the PLC or controller program can conclude that there should be an analog output, such as an input analog signal becomes smaller (or larger), an analog output signal should be increased, and the output has no analog signal output, then It may be that the output card is faulty, the output is burned out or the card is damaged, and the output card needs to be replaced.

4) The analog output of the PLC or controller is not normal. The data input function of the display screen outputs a fixed analog signal to the analog output terminal. If the analog output terminal still outputs an abnormality, the output card may be initially determined to be faulty.

5) Switch input signal PLC, but the PLC does not respond or the display is not displayed. You can use the multimeter to measure the input. If the external input signal is normal, you can preliminarily determine that the PLC's digital input card is faulty.

6) The external switch input signal is input to the PLC. The PLC does not respond or the display is not displayed. The input terminal can be removed and the input is high or low. If the switch input signal still does not display normally, then It can be preliminarily determined that the PLC's digital input card is faulty.

7) The PLC switch quantity signal has no output. The switch can be manually triggered by the button on the display. If the switch output signal still has no output, it can be preliminarily determined that the digital output card is faulty.

8) If the program in the PLC is lost (the probability of this failure is low), it is generally the case that all signals cannot be input and output normally, and the program needs to be refilled.