Before the small series for everyone to share about the PLC programming content, today to share a maintenance knowledge, I hope to help everyone! First, the CPU is abnormal When the CPU is abnormally alarming, check that all units of the CPU unit are connected to the internal bus. The specific method is to replace the unit that may cause the fault in turn, find the fault unit, and deal with it accordingly. Second, the memory is abnormal When the memory is abnormal, if it is a problem with the program memory, the fault will be reproduced after reprogramming. This situation may be caused by noise interference causing changes in the program, otherwise the memory should be replaced. Third, the input / output unit is abnormal, the expansion unit is abnormal When such an alarm occurs, first check the insertion status of the input/output unit and the expansion unit connector, the cable connection status, and determine the unit in which the failure occurred before replacing the unit. Fourth, do not execute the program In general, you can check according to the input---program execution---output steps. (1) The input check is identified by the input LED indicator or by an input monitor composed of a writer. When the input LED is not lit, it can be initially determined that the external input system is faulty, and then checked with the multimeter. If the output voltage is not normal, it can be determined that the input unit is faulty. When the LED is on and the internal monitor is not displayed, it can be considered as a failure of the input unit, CPU unit or expansion unit. (2) The program execution check is checked by the monitor on the writer. When the state of the contact of the ladder diagram is inconsistent with the result, it is a program error (such as dual use of the internal relay), or the operation part is faulty. (3) The output check can be identified by the output LED indicator. When the operation result is correct and the output LED indicates an error, it can be considered as a failure of the CPU unit and the 1/0 interface unit. When the output LED is lit and there is no output, it can be judged that the output unit is faulty or the external load system has failed. In addition, due to the different PLC models, 1/0 is not the same as the LED connection (some are connected to the 1/0 unit interface, and some are connected to the 1/0 unit). Therefore, the fault range judged by the LED is also different. 5. Some programs are not executed. The inspection method is the same as the previous item. However, if the input time of the counter, step controller, etc. is too short, a non-response failure will occur. At this time, it should be verified whether the input time is large enough. The verification can be based on the input time < input unit The maximum response time + the operation scan time is multiplied by two. 6. The power supply will be powered down for a short period of time, and the program content will disappear. (1) In addition to checking the battery, the following checks are also required. (2) Check by repeatedly turning on the power of the PLC itself. In order to make the microprocessor start up correctly, the PLC has a save program circuit when the reset point circuit and the power supply are disconnected. When such a circuit fails, the program cannot be saved. Therefore, the power supply can be checked on and off. (3) If the battery abnormality alarm still occurs after replacing the battery, it can be determined that the leakage current of the memory or the external circuit is abnormally increased. (4) The on/off of the power supply always occurs synchronously with the machine system, and the noise influence generated by the machine system can be checked. Because the disconnection of the power supply is a fault that often occurs simultaneously with the operation of the machine system, most of which is caused by the strong noise generated by the motor or the winding. Seven, PROM can not run First check if the PROM insertion is good, then determine if the chip needs to be replaced. 8. After the power is turned back on or reset, the action stops. This type of fault can be considered as noise interference or poor internal contact of the PLC. The cause of noise is generally caused by the small capacitance of the circuit board or the poor performance of the components. The cause of poor contact can be checked by gently tapping the PLC body. Also check the insertion status of the cables and connectors. Nine, the interference of the inverter to the PLC analog quantity In the automatic control system, the use of the frequency converter is more and more extensive, and the interference problem of the inverter to the PLC analog quantity is also highlighted. The following is an example of an inverter's analog-to-PLC interference and a solution to overcome such interference with a signal isolation module. Phenomenon: The AO point in Siemens PLC sends a 4-20mA current control signal to the Siemens inverter, which cannot control the inverter to start. Fault finding: 1. Suspected analog output board problem. Use a multimeter to measure the 4-20mA output signal. The signal is normal. 2, began to suspect that there is a problem with the input signal of the inverter control signal, and replaced the same type of inverter, the problem remains. 3. Use a hand-held signal transmitter to make a 4-20mA output signal source and output a standard current signal to the inverter. This inverter starts, so we eliminate the fault of the analog output board and the inverter. 4. It is presumed that the interference signal of the inverter is transmitted to the analog channel. 5, in order to verify, add a signal isolation module TA3012, TA3012 input terminal in the PLC analog 4-20mA output channel 6. Connect the analog output module, the output terminals 1 and 2 are connected to the inverter, and the terminal is connected to the external 24VDC power supply. The inverter starts normally. 7. According to this, the root cause of the problem is that the inverter interferes with the analog channel. I believe that many self-control engineers have encountered the problem of the inverter's interference with the PLC analog when debugging the system. Therefore, the author shares his own system debugging experience. In the automatic control system used by PLC and inverter at the same time, we should pay attention to the following matters: 1. The PLC power supply and the power system power supply (inverter power supply) are respectively configured, and the PLC power supply should select the isolation transformer; 2. The power line should be as Signal lines are separated, signal lines are to be shielded; 3. Whether analog signal input or analog signal output, analog channel always uses signal isolation module; 4. PLC software design is used for software filtering; 5. Signal ground and power ground are designed separately. . Do the above five points, the problem of the inverter's interference with the PLC analog quantity can be solved. Yuoto "Thanos (English /russia)
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