When the PLC failure how do we find? - - - - - -

small PLC is an industrial computer, it is a problem, first is to exclude PLC ontology or peripheral problems, if it is PLC ontology appear problem, often ERR goes on, or the red light is shining, the normal state is generally RUN RUN green light, if it is happen this kind of problem of ontology, can repair the probability of success is not high. Some PLC by keeping the data inside the battery, the battery voltage is lower than a certain threshold, there will be a battery alarm prompt the light, then need to replace the battery, and need to be charged to replace, if the battery has no electricity, or replace the battery is not charged operation, often can cause the RAM data is missing, then need to refresh the program and data, so PLC maintenance time at ordinary times, must have the habit of program and data backup, or by key time have no, only to the programming and debugging.

power failure will also accounts for a certain ratio of failure of ontology, the PLC input is generally 220 communication, there are also some thing of 24 v or 12 v input, but there's chips, need 5 VDC or 3. 3 VDC, so have a step-down switch power supply circuit, the circuit because the current is big, high temperature, high temperature in some bad or dust occasions are problematic, if the indicator is on, the PLC is commonly switch power supply is broken. Bad, switch power supply for the general level of a little electronic maintenance people, repairing it isn't particularly difficult, such as the control chip 384 x the probability of these bad or switch tube is higher, generally replaced.

if there is a fierce flash a red light or ERR lights, is often the mainboard is broken, lost cause or program, you can try to instill the program again, if not, nor is there much maintenance value, up to the watchdog IC chips and the replacement of the reset circuit, or replace the chip crystals, if still can't solve the problem, is suggested to give up, this device integration is too high, maintenance is very difficult, and the price of the motherboard is not particularly expensive, don't have much value. Bad output output point, also is the more common PLC controller ontology failure, especially the PLC relay output type, in some occasions, frequent switch action will easy to hang up relay, the service life of the relay is about 100000 times, 3 - often used 5 years, may is broken, it is easy to find this kind of problem, after all, see the output light is lit, but no contact closure or disconnect is measured with a multimeter can find problems, open it, find some domestic similar small relay replacement, generally no problem. If it is broken transistor, common is input through the high pressure, input and output is likely to be damaged, often to replace the light coupling and some amplifier transistor circuit.

if it is a peripheral problems, can according to the input and output of the logic circuit diagram to analysis, from the macro and equipment operation, also can block out some input/output interlock to separate test to find problems. If there is a PLC program more simple, because PLC controller has online diagnosis function, can perform alone, look at the execution to the point where the corresponding output state is normal, you can find the point of failure.

the hardest or some system problems, especially some problems of repaired circuits. One year, the big pendulum long lung problems, they have PLC program, equipment department also has a top industrial computer program, the outside circuit drawings are complete, and can be online diagnosis of various states, but the big pendulum operation to a logical point, automatic trip, and all the power, without any warning and prompt. They permitted for a long time can't find the problem, also found a lot of people came to see, can't get a point of failure. Then I go to help them to see that in the control room seems to be nothing special, because the others are checked, I get up to more than 10 meters high, there is a scene of small controller, there's some relay inside, because I repeatedly watched their drawings and field work logic, problem point should be in inside the box. I let them start up operations for several times, each time is running to a relay location jump with gear, but the relay is a common dc relay. I tried to tear down the relay coil line, let them operate again, the equipment running at a certain time, and stop, but there were no trip, my judgment is the relay has a problem, down to examine, discovered is relay fly-wheel diode reverse the direction, so run to a state of the relay coil charged, equivalent to 12 v dc power supply, directly to the fly-wheel diode is the wizard, is formed on 12 v power supply circuit, so power tripping the whole trip in the system, the diode reverse away, estimated at that time when someone inspect the site of the change caused by a wrong line. So this type of PLC peripheral fault, there is no any alarm prompt, all look is normal, also nothing bad, but it is not normal system operation, the fault is the most difficult to eliminate, because there are many people checked and repaired, if light see drawings and procedures, is unable to find the problem, must under the site details.

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