First, the operating environment to ensure
Because PLC is a precision electronic products, automatic control system is required for a long time without interruption, so the PLC operating environment requirements are extremely high, to dust, fire, water, high temperature, lightning, so the electrical control room are generally arranged In the double-layer glass, installed on the second floor of the water-cooled air-conditioning, electronic control room temperature is generally controlled at about 28 degrees; for dust is installed in the PLC 1M * 2.2M * 0.6M with a lock front panel In the control cabinet for the glass door, the exhaust system of the dustproof cover is installed in the upper part of the cabinet.
Second, do the daily work
1, daily preparation: the first familiar with the process, followed by a variety of PLC modules on the description of the familiar data, once again on-site layout of the understanding, and finally to ensure that their own various detection tools to be intact.
2, the daily inspection work: regular battery voltage detection of the CPU, usually under normal circumstances for the 3V, on a regular basis to constitute the PLC system related equipment inspection and maintenance, such as UPS regular maintenance, the use of downtime, the PLC control Cabinet for manual dust removal, cooling, PLC program regular manual backup and battery backup and the replacement of the relevant bad parts and so on. Third, PLC fault diagnosis
(A) the general rule:
For the PLC system fault detection method: a touch, two look, three smell, four listen, five trace trace method, six replacement method.
The CPU temperature is not high, CPU normal operating temperature does not exceed 60 ℃, because the hand can accept the temperature of the human body temperature 37 ~ 38 ℃, feel appropriate; two look, look at the board of the module lights Whether it is normal; three smell, smell there is no smell, or whether the electronic components or cable burned; four, listen to any changes, screw nail loose, relay work or not, listen to the scene staff to reflect the situation; According to the drawings and process to find the location of the fault; six parts of the uncertainty of parts replacement method to determine the fault.
(B) specific steps:
When the PLC software is not normal, the main CPU to see whether the normal state of the RUN, CPU is not normal after the re-download control program.
When the PLC hardware is not normal, the inspection is done in the following order:
1, see whether the power supply PLC power: there is power measurement voltage is +24 V within ± 5% range, there is power and normal, then the next step; power is not normal power supply module output and input If the input is not normal, if the output is not normal and the input is normal, then replace the module; if the input is not normal, then the input current counter current law to check accordingly, such as 24V AC and DC transformer input voltage AC voltage 220V ± 10% Check, normal, then replace the DC 24V transformer. No power trace trace, with the schematic + on-site layout of the total map + wiring drawings, to check the power supply to the power supply of the various components of the electrical device wiring is correct, incorrect, re-wiring; correct check the air switch with a multimeter Of the incoming and outgoing terminals whether the normal power supply, no normal power supply, to identify the outside world or their own reasons, if the outside is the lack of voltage or no voltage, or heavy load, or serious overcurrent analysis , Until the accident to exclude the normal power supply so far; if the replacement of the device itself is bad.
2, know the CPU work mode and priority: high priority STOP, HOLDUP, STARTUP (WARMRESTART, COLDRESTART); low priority are: RUN, RUN-P (PG / PC online read and write procedures). Check whether the CPU is in RUN mode, either in STOP mode, in RUN mode, or both in flash mode and in STOP mode. If only the RUN mode is the CPU and the board is normal for step 3. If it is to maintain the mode appears, may be running during the user program breakpoint and in the debugger state, or in the boot mode breakpoint appears, re-debug this program, the control program can be downloaded to the CPU again.
If it is STOP mode, visual cause of the cause of STOP analysis: A, no electricity, analysis of non-electric reasons, because the power supply sector problems, or abnormal power-down (because there are 1K3AH UPS guarantee very few abnormal situation), usually The case for the maintenance of electricity, and after the end of the manual delivery of electricity. And then use the PLC’s online function to change the working mode of the CPU from STOP to RUN; B, CPU bad, replace the new good type of the same type of CPU; C, a bad board, orderly replacement of the board. For the hardware replacement should pay attention to the use of the original device with the same product with the same type, with the version to do, otherwise it will cause the actual PLC configuration and the corresponding programming software configuration database hardware configuration is different from the user can not control the normal cycle of the program carried out.
3, the various motherboards and expansion boards on the communication cable inspection and inspection of the LED lights of each module to see if there is a bad module fault light, if the module is not normal. For the digital output module on the point of the fact that the real life of the light switch is the same function and is often open point, so online maintenance of any point of the module, as long as no wiring and the address in the control program does not give the output Signal to detect its pass through it can, if the pass, then the point is not normal, normal is normal; not normal when the hardware connection line to another point of re-work; In addition, we can also use the new module to replace , On the replacement of the module to measure the point off the state, through, then the point is bad, nowhere that the point is better. For the digital input module point when the conduction of the coil, is normally closed state, it can be online or offline detection, with a table to detect if the dead pixels, then it is unreasonable state, then for the point of re-wiring; Pass state. As long as the hardware wiring re-point after the re-use the corresponding programming software to control the software 0X or 1X address replacement work. For the analog input module is the same with the digital input module, each channel is equivalent to a wire form, that is equivalent to the normally closed point, so the method of detecting the channel is good or bad for the use of table detection function to detect , When the state is good when the state, when the bad state is bad; analog output module detection method and digital output module the same. If the bad channel on the hardware wiring need to replace the channel and at the same time replace the control program in the corresponding 3X or 4X address; the other for the analog module will have to select the check block selection, the fuse is disconnected check work. Software configuration is normal, usually voltage 1 ~ 5V or current 4 ~ 20mA, which according to the type of sensor used and intelligent converter to choose. After the hardware point or channel replacement work conditions are allowed to STOP
PLC CPU, and then re-download the program, if the conditions are not allowed to update the changes directly to download the program without stopping CPU. A good channel / good point for an unused input module is connected in series with the last used good channel / good point or specially set in software.
4, a large number of output modules on the board of the power module in the normal production state is not power off, because at this time the power, then the relay cabinet will make the normally open relay into a normally open state, prone to error, so To test this type of output module, to contact with the field operator, the part of the relevant equipment for manual operation, and then remove the digital output module power supply line after the module point measurement work.
5, the detection of various types of switches: such as relays, proximity switches, air switches and other device detection work is based on the type of switch is normally closed or normally open to distinguish between the use of the table to detect its pass and unreasonable state , Its state and the opposite good device state, then the device is broken, the replacement of the. For most of the circuit using the normally open type, they are used for manual control or automatic control of the current on and off; for the normally closed type is mainly used in the protection circuit. Which can know the switch class and protection of the normal state of the device for the normal identification of the device is good or bad.
6, communication module detection is the use of a simple new communication module with a replacement to identify the board is using the module is normal.
7, the wire measurement method: the wire is also through the detection method. You can use the known wire to detect the wire is not good or bad, the method is to connect a good wire and the unknown wire after the test off the state.
8, resistance detection: live state when the detection voltage, when not detected when the corresponding resistance.
Four, summary
Through the detection can be excluded from the work of most of the failure, and because of this work involves the exchange of single-phase power 220V and DC 24V cross-operation, work should pay attention to the accumulation of safety knowledge and common sense, as well as in the work of security precautions And gas safety procedures to ensure safe operation.

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