What are the common fault analysis and handling measures of Siemens PLC?

What are the common faults and handling measures of Siemens PLC? What measures should be taken in the work project to solve the fault and make the equipment operate normally? There are several common faults in the operation of CNC machine tool PLC. Let's get to know them together.

 1. If the power grid fluctuates too much, the PLC will not work.

This means that the PLC has no output. First check the input signal (power signal, interference signal, command signal and feedback signal). For example, the built-in PLC of CNC lathe with SINUMERIK 3g-4b system cannot work. Using the observation method, first check the power grid voltage waveform with an oscilloscope. It is found that the power grid voltage fluctuation is too large, and the jump duration of undervoltage noise is greater than 1s. Since the machine tool is in the commissioning stage, the system fault of the unit shall be eliminated. From the internal power grid interference measures (filtering, isolation and voltage stabilization), it can be seen that the conventional power supply system has been unable to cut off or filter out the power grid undervoltage noise with a long duration, which is caused by insufficient anti power grid measures (internal causes), resulting in the failure of PLC to work normally. An AC voltage regulator is added at the power input of the system, and the PLC works normally.

 2. electromagnetic interference

  In the commissioning stage of a new machine tool, when the machine tool is shut down frequently, electromagnetic interference faults often occur, but it can work. Although parameter confusion and internal factors of components can be eliminated, the possible reason is the system instability caused by electromagnetic interference of power grid or environment, and the external reason is the frequency conversion induction interference source. This is because the capacity of the selected components is too small and the power grid interference pulse is too large, which makes the inductive components in the filter magnetically saturated and unable to filter out the high-frequency interference pulse. A 2.2mf capacitor is connected in parallel between the power input lines of the system, that is, an absorption network is added for troubleshooting.

3. Plc-md parameter failure

   The fault occurs in the commissioning stage. When returning to zero, it can only move in the negative direction of the coordinate axis. If the movement is normal, an overtravel alarm will appear. For example, in a machining center of FANUC 0m system, when the reference point return operation (zero return operation) is carried out after power on, the over travel alarm occurs after the feed shaft moves forward a certain distance, but the travel switch is not actually touched. The reset method does not eliminate the alert. Power on again after power failure, and the fault remains unchanged, indicating that the essence of the alarm is soft override. Since the machine tool is in the debugging stage, the possibility of wrong over travel caused by hardware failure can be eliminated.

  First check whether the parameter setting table is chaotic, and then use the parameter modification method. 1. Turn off the alarm soft key and return the alarm soft key to on after returning to zero; 2. Temporarily modify the soft limit parameter (143) to + 999999, and restore the original parameter value after returning to zero. Both methods can eliminate the fault after restarting the machine.

  4. PLC input board failure

   PLC input board failure often occurs in automatic machining, CRT display alarm, and the machine tool cannot work. For example, when the CNC machine tool of FANUC 3t-a system is automatically processed, the CRT displays "not ready", the machine tool cannot work normally, and the alarm display main control board, whether CNC or PLC, is good, and there is no specific alarm content. There is a suspected fault with the servo amplifier or the PLC. However, if the servo amplifier is faulty, it should alarm when starting self diagnosis. Therefore, the fault can be located as the I / O interface board of PLC, which belongs to hardware fault. The main reason should be the hardware fault of the front circuit corresponding to the output "not ready".

By analyzing the common faults of Siemens PLC and understanding the troubleshooting measures, we can make better use of Siemens PLC.