First, the guarantee of the operating environment Because plc is a precision electronic product, the system of automatic control is required to run for a long time, so the operating environment of the PLC is extremely high, and it must be dustproof, fireproof, waterproof, high temperature resistant, and lightning resistant. The electrical control room is generally arranged on the second floor with double-glazed water-cooled air-conditioning. The temperature of the electric control room is generally controlled at about 28 degrees. For dust-proof, the PLC is installed at 1M*2.2M*0.6. The front panel with M lock is a control cabinet with a glass door. The upper part of the cabinet is equipped with a dust extraction system for cooling the cabinet.
Second, do the daily work 1, daily preparations: the first familiar with the process, followed by the familiarity of the various modules of the PLC, the site layout, and finally ensure that their own testing tools are intact.
2, daily inspection work: Regularly carry out the voltage detection of the CPU battery, under normal circumstances is 3V, regular inspection and maintenance of the relevant equipment that constitutes the PLC system, such as UPS regular maintenance, use the shutdown timing, control each PLC The cabinet performs manual dust removal, cooling, periodic manual backup of the PLC program, battery backup and replacement of related bad components.
Third, the diagnosis of PLC faults (a) General rules:
For the fault detection method of PLC system: one touch, two look, three smell, four listen, five track trace pursuit method, six replacement method.
One touch, check the CPU temperature is not high, the CPU normal operating temperature does not exceed 60 ° C, because the hand can accept the temperature of the human body temperature 37 ~ 38 ° C, feel is appropriate; second look, look at the indicators on each board Whether it is normal; three smells, smells no smell, electronic components or cables are burned; four listen, listen to no change, loose nails, relays work normally, listen to the situation of the field staff; five failures According to the drawings and process flow to find the location of the fault; six pairs of uncertain parts to replace the part to determine the fault.
(2) Specific steps:
When the software of the PLC is not normal, it mainly depends on whether the RUN status of the CPU is normal. If it is not normal, the CPU is cleared and the control program is downloaded again.
When the PLC hardware is not normal, check the following order:
1. Check whether the PLC power supply has power: if there is electricity, the measured voltage is within ±5% of +24V. If there is power and normal, proceed to the next step; if there is power, the output and input terminals of the power module are performed. If the output is not normal and the input is normal, replace the module; if the input is not normal, perform the countercurrent rule on the input, such as ±10% of the AC voltage of the input voltage of the 24V AC/DC transformer. Check, if normal, replace the DC 24V transformer. If there is no electricity, follow the traces. With the schematic diagram + site layout master map + wiring drawing, check whether the wiring of the output terminals of the various electrical devices that supply power to the power module is correct, incorrect, and re-wired; check the air switch correctly with the multimeter. Whether there is normal power supply at the incoming end and the outgoing end, there is no normal power supply, and it is found that the external or self-cause, if it is the outside, is the voltage is insufficient or there is no voltage at all, or the load is too heavy, or serious overcurrent, etc. Until the accident is excluded from normal power supply; if it is bad for its own device, replace it.
2, understand the CPU operating mode and priority: high priority STOP, HOLDUP, STARTUP (WARMRESTART, COLDRESTART); low priority: RUN, RUN-P (PG / PC online read and write procedures). Check whether the CPU is in the RUN mode, or in the STOP mode, or the RUN mode flashing state and the STOP mode are both in the hold mode or the debug mode. If it is only in RUN mode, the CPU and each board are normally performing step 3. If the hold mode occurs, it may be that the user program has a breakpoint during the running process and is in the debugger state, or the breakpoint appears in the startup mode. In this case, re-commission the program and download the control program to the CPU again.
If it is STOP mode, the cause of STOP caused by visual analysis: A, no electricity, analysis of the lack of electricity, because the power supply department has a problem, or abnormal power failure (because there is a 1K3AH UPS to ensure that abnormalities rarely occur), usually In the case of powering up for maintenance, manual power is sent after the inspection is over. Then use the online function of the PLC to convert the working mode of the CPU from STOP to RUN; B, the CPU is bad, replace the new CPU of the same type and the same version; C, the board is broken, and the board is replaced in an orderly manner. For hardware replacement, please pay attention to using the same product and the same version as the original device. Otherwise, the actual PLC configuration and the hardware configuration in the hardware configuration database of the corresponding programming software are different, and the normal cycle of the user control program cannot be performed. carried out.
3. Check the communication cable on each motherboard and expansion board and check the LED lights of each module to see if there is a faulty module with a faulty module. If so, the module is not normal. For each point on the digital output module, it is the same function as the real life light switch and is a normally open point. Therefore, when you are online to repair any point of the module, as long as there is no wiring and the address is not output in the control program. When the signal is detected, it can be detected. If it is through, the point is not normal. If it is not normal, it will be normal. If it is not normal, the other point of the hardware connection line should be reconnected. In addition, we can replace it with a new module. If the point of the replaced module is measured and turned on, the point is broken, and the point is not good. For the point of the digital input module, when the coil is turned on, it is normally closed. It can be detected online or offline. If the meter detects that it is a bad point, it will be unreachable. Pass status. As long as the hardware wiring is re-switched and reconnected, the corresponding software should be used to replace the control software with 0X or 1X address. For the analog input module is the same as the digital input module, each channel is equivalent to a wire form, which is equivalent to the normally closed point, so the method of detecting the channel is good or bad. It is good when the state is on, and is bad when the state is off; the detection method of the analog output module is the same as that of the digital output module. If the bad channel is connected to the hardware, it is necessary to replace the channel and replace the corresponding 3X or 4X address in the control program. In addition, for the analog module, the selection of the range block should be checked, and whether the fuse is disconnected or not. Whether the software configuration is normal, generally 1 to 5V voltage or 4 to 20mA current, which is selected according to the type of sensor and smart converter used. After the hardware point or channel replacement work is allowed, the CPU of the PLC must be STOP, and the program should be re-downloaded. If the condition is not allowed, the program will be downloaded directly with the update change without stopping the CPU. A good channel/good point for unused input modules is connected in series with the last used good channel/good point or special settings in the software.
4. The power module on the board of a large number of output modules cannot be powered off during normal production. Because the power is turned off at this time, the normally open relay in the relay cabinet will become normally open, which is prone to errors. To detect such an output module, it is necessary to contact the on-site operator to perform manual operation on the relevant equipment of this part, and then remove the power supply line of the digital output module and work on the module.
5, the detection of various types of switches: such as relays, proximity switches, air switches and other devices, according to the type of switch is normally closed or normally open to distinguish, use the table to detect its pass and nowhere The state is opposite to the good device state, then the device is broken and replaced. For the majority of the circuit, the normally open type is used, which is used to manually control or automatically control the on and off of the current; for the normally closed type, it is mainly used in the protection circuit. By this, it is possible to know how the normal state of the switch and protection devices normally recognizes the device.
6. The communication module is detected by using a simple new communication module to identify whether the module being used on the board is normal.
7. Measuring method of the wire: The wire is also carried out by detecting the on-off method. It is possible to use a known wire to detect a wire that is not known to be good or bad, by connecting a good wire to an unknown wire and measuring the on-off state.
8. Resistance detection: The voltage is detected when the battery is in the power state, and the corresponding resistance is detected when the power is not charged.
Fourth, the summary can be used to eliminate most of the faults in the work. In addition, this work involves the intersection of AC single-phase electric 220V and DC 24V. Pay attention to accumulating safe electricity knowledge and common sense when working, and at work. Safety precautions and gas safety regulations to ensure safe operation.
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Transformer is a device that USES the principle of electromagnetic induction to change the ac voltage. Its main components are primary coil, secondary coil and iron core.The main functions are: voltage transformation, current transformation, impedance transformation, isolation, voltage stabilization (magnetic saturation transformer), etc.According to use can be divided into: power transformer and special transformer (electric furnace change, rectifier, power frequency transformer, voltage regulator, mining, audio transformers, intermediate frequency transformer, high frequency transformer, impact transformer, instrument transformer, electronic transformer, reactor, transformer, etc.).The circuit symbol T is often used as the beginning of the number. Examples: T01, T201, etc.
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