The fault diagnosis of PLC

Any PLC self-diagnosis function, when the PLC abnormal should make full use of its self diagnosis function to analyze the cause of the problem. Generally when PLC an exception occurs, first check the power supply voltage, PLC controller and I/O terminal connectors and screw loosening, and any other abnormalities. Then based on the PLC basic unit set up all kinds of LED light condition, to check whether there is any abnormal on PLC itself and the external. The FX series PLC, for example, below will show according to the LED indicator light conditions to diagnose method of PLC the cause of the problem. 1. The power indicator ( ( 权力) The LED indicator) When supply POWER to the PLC basic unit, the basic unit set on the surface of the [POWER] leds will bright lights. If the POWER supply closed but [POWER] LED light is not bright, please make sure the POWER supply wiring. In addition, if the same power drive sensors, please make sure the presence of load short circuit or over current. If it weren't for this reason, could be mixed with conductive object in PLC or other abnormal situations, make the blown fuse inside the basic unit, this time can be solved by replacing the fuse. 2. Error instructions ( [EPROR] LED flashing) When the program syntax errors ( If forget to set the timer or counter constant, etc. ) , or there are abnormal noise, electrical conductivity due to reasons such as caused by foreign bodies with the content of the program memory changes, [EPROR] LED flashes, PLC controller in the STOP state, the output at the same time all come OFF. In this case, should check whether the program is wrong, check the presence of electrical conductivity and high strength were mixed with foreign body sources. When an error occurs, 8009, 8060 ~ 8068 one of the special values are written to the data register D8004, assuming that the written D8004 content is 8064, is by looking at the D8064 can know the content of the error code. Error and the error code corresponding to the actual content see PLC controller manual error code table. 3. Error instructions ( [EPROR] LED lights) Because PLC internal electrical conductivity with foreign body or affected by external abnormal noise, caused more than 200 ms, the CPU is out of control or operation cycle is WDT error, EPROR LED lights, PLC at the STOP, output into OFF all at the same time. If power can be reset, the PLC is back to normal at this time, please check the presence of abnormal noise and placing signage at the electrical conductivity of foreign body in. In addition, please check the PLC grounding is in line with the requirements. Inspection process if there is a [EPROR] the change of the LED lights to flicker, program checks, please. If [EPROR] LED still keep the light, please make sure that the program operation cycle is too long, Monitor D8012 known maximum sweep time) 。 If after all the checks, [EPROR] LED lights status still cannot lift, PLC internal should be considered a fault happens, please contact with the manufacturer. 4. Input indicates whether the input unit of the LED lights or destroy, please check whether the input signal switch is ON or OFF state. If the input rated current of the switch capacity is too large or due to reasons such as oil intrusion, prone to poor contact. When the input switch with LED lights use resistor in parallel, even if the input switch OFF but still conducting the parallel circuit, still can be input to the PLC. If you use a light sensor, and other input devices, such as light/by light parts with dirt, cause sensitivity changes, may not fully into the 'ON' position. In the short period of time than PLC operation cycle, not to receive input ON and OFF. If the input terminals with different voltage, will damage the input circuits. 5. Output indicates whether the output unit of the LED lights or destroyed, if the load cannot be ON or OFF, is mainly due to the overload and short circuit or load capacity of the impact of the load current and so ON, the relay output contact adhesive, or contact interface leads to poor contact.
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