Regular inspection and maintenance of PLC systems - Solutions - Huaqiang Electronic Network
First, plc inspection and maintenance
Regular inspection
PLC is an industrial control device. Although many measures have been taken in terms of reliability, the working environment has a great impact on PLC. Therefore, the PLC should be regularly checked every six months. If the working conditions of the PLC do not meet the standards specified in Table 1, some emergency treatment is required to make the PLC work in the standard environment.
2. Daily maintenance
In addition to the lithium battery and relay output contacts, PLC has basically no other vulnerable components. Due to the random access memory (RAM) of the user program, the counter and the auxiliary relay with the holding function are protected by a lithium battery. The life of the lithium battery is about 5 years. When the voltage of the lithium battery is gradually reduced to a certain extent, the basic unit of the PLC The battery voltage drop indicator lights up. The user is reminded that the program supported by the lithium battery can be kept for about one week, and the battery must be replaced, which is the main content of daily maintenance.
Steps to replace the lithium battery:
1 Before disassembling, let the PLC be powered on for more than 15S (this can charge the capacitor as the backup power of the memory. After the lithium battery is disconnected, the capacitor can be temporarily powered by the PLC to protect the information in the RAM from being lost) ;
2 Disconnect the AC power of the PLC. 3 Open the battery cover of the basic unit. 4 Remove the old battery and install the new battery. 5 Cover the battery cover. Replace the battery time as short as possible. Generally, it is not allowed to exceed 3 minutes. If the time is too long, the program in RAM will disappear.
Second, fault finding
PLC has a strong self-diagnosis capability. When the PLC itself fails or the peripheral device fails, it can be diagnosed by the LED of the diagnostic indication function on the PLC.
The maintenance and fault diagnosis of programmable controllers is a problem faced by every industrial control person engaged in plc applications. You are welcome to express your opinions on this issue.
The following uses a plc as a description template, and the other types of PLCs are similar, introducing the methods of maintenance, diagnosis, and replacement of plc.
Maintenance Overview Generally, all kinds of PLCs (using a plc as a description template, and the rest of the PLCs are similar) are designed to work in a long-term uninterrupted work system. However, occasionally some places need to modify the action, it is very important to quickly find the place and modify them. It takes a lot of time to modify actions that occur outside of the PLC.
Finding the indicator light of the faulty equipment PLC and the equipment inside the machine is useful for finding faults in the entire control system of the PLC. The programmer is the main diagnostic tool that can be easily plugged into the PLC. You can observe the status of the entire control system on the programmer. When you are looking for the fault of the PLC as the core control system, as a habit, you should bring a programmer or notebook.
The basic troubleshooting sequence raises the following questions and negates them one by one based on the reasonable actions found. Replace the modules step by step until all faults are eliminated. All major corrections can be done by replacing the module. Except for a screwdriver and a multimeter, no special tools are required, no oscilloscope, advanced precision voltmeter or special test program.
1. Is the PWR (power) light on? If not, check the supply voltage at the voltage input (98-162VAC or 195-252VAC) of the AC power supply frame; for a frame that requires DC voltage, measure the DC voltage between the +24VDC and 0VDC terminals, if not appropriate AC or DC power supply, the problem occurs outside the PLC. If the AC or DC power supply voltage is normal, but the PWR light is off, check the fuse and replace the CPU frame if necessary.
2. Is the PWR (power) light on? If it is lit, check the code that shows the error, and make the corresponding correction against the code definition of the error code table.
3. Is the RUN light on? If not, check if the programmer is in the PRG or LOAD position, or if the program is faulty. If the RUN light does not illuminate and the programmer is not plugged in, or the programmer is in RUN mode and no error code is displayed, the CPU module needs to be replaced.
4. Is the BATT (battery) light on? If it is bright, you need to replace the lithium battery. Since the BATT lamp is only an alarm signal, the program may not change even if the battery voltage is too low. After replacing the battery, check the program or let the PLC test run. If the program is already wrong, reload the program recorded on the tape into the PLC after the system programming initialization is completed.
5. In a multi-frame system, if the CPU is working, the RUN` relay can be used to check the operation of several other power supplies. If the RUN relay is not closed (high impedance), check the AC or DC power supply if the AC or DC power supply is normal and the relay is disconnected as in the first step above. The frame needs to be replaced.
The general steps to find faults are related to the user's logical knowledge. The following steps are actually more general and have been modified or adjusted for specific application issues you are experiencing. The best tool for finding faults is your feelings and experience. First, plug in the programmer and turn the switch to the RUN position, then follow the steps below.
1. If the PLC stops at somewhere where the output is excited, it is usually in the intermediate state, then find the signal (input, timer, line, drum controller, etc.) that causes the next operation to occur. The programmer will display the ON/OFF status of that signal.
2. If the signal is input, compare the status displayed by the programmer with the LED indication of the input module. If the result is inconsistent, replace the input module. After discovering that there are multiple modules to be replaced on the expansion frame, check the I/O extension cable and its connections before you replace the module.
3. If the input status is consistent with the LED indication of the input module, compare the status of the LED and the input device (button, limit switch, etc.). In the difference between the two, measure the input module, if you find a problem, you need to replace the I / O device, field wiring or power; otherwise, replace the input module.
5. If the signal is a line, no output or output is different from the state of the line, you have to use the programmer to check the output drive logic and check the program list. The inspection should be carried out from the left to the left to find the first contact that is not connected. If the one that is not connected is the input, press the second and third steps to check the input point. If it is the line, press the fourth. Step and step 5 check. Be sure to make the master relay step affect the logic operation.
6. If the signal is a timer and is stopped at a non-zero value less than 999.9, replace the CPU module.
7. If the signal controls a counter, first check the logic that controls the reset, then the counter signal. Follow the 2 to 5 sections above.
Replacement of components The following is the first step to replace the system, replace the frame 1, cut off the AC power; if the programmer is installed, unplug the programmer.
2. Remove the plastic cover from the terminal block at the right end of the frame and remove the power supply wiring.
3. Unplug all I/O modules. If you have multiple working circuits during installation, don't mess with the IU/O wiring and note the location of each module in the frame so that you don't get it wrong when you plug it in again.
4. If the CPU frame, remove the CPU component and the filler module. Keep it in a safe place for future reinstallation.
5. Remove the screws of the two fixing frames at the bottom and loosen the upper two screws, but do not remove them.
6. Push the frame up and then pull the frame down and set it aside.
7. Put the new frame in from the top screw.
8. Install the bottom screw and tighten all four screws.
9. Insert the I/O module, pay attention to the position and the same as when removing.
If the module is inserted in the wrong position, it will cause dangerous or erroneous operation of the control system, but will not damage the module.
10. Insert the removed CPU and filler module.
11. Reconnect the power supply wiring to the terminal on the right side of the frame, and then cover the plastic cover of the power supply terminal.
12. Check that the power supply wiring is correct, and then turn on the power. Carefully check the operation of the entire control system to ensure that all I/O modules are in the correct position and the program has not changed.
Second, the replacement of the CPU module 1, cut off the power supply, if the programmer is inserted, unplug the programmer.
2. Squeeze the upper and lower fastening tabs of the CPU module panel to the middle to release them from the bayonet.
3. Pull the mold out vertically from the slot.
4. If the CPU is loaded with EPROM memory, unplug the EPROM and install it on the new CPU.
5. First align the printed circuit board with the bottom guide. Insert the new CPU module into the bottom guide.
6. Slightly shake the CPU module so that the CPU module is aligned with the top guide.
7. Insert the CPU module into the frame until the two elastic latches snap into the bayonet.
8. Plug in the programmer again and power it on.
9. Reload the program recorded on the tape after initializing the system programming. Check the operation of the entire system.
Third, I / O module replacement 1, cut off the power of the frame and I / O system.
2. Remove the plastic cover from the I/O module terminal. Remove the field wiring of the faulty module.
3. Remove the field wiring of the I/O terminal or remove the detachable wiring socket, depending on the type of module. Label each line or note the markings for the installation wires so that you can reconnect in the future.
4. Squeeze the upper and lower elastic latches of the I/O module to the middle to release them from the bayonet.
5. Pull out the I/O module vertically.
Suizhou simi intelligent technology development co., LTD , https://www.msmsmart.com