I. Why is maintenance needed?
1. In order to extend service life;
2. To ensure the stability of equipment operation;
3. This is also a manifestation of 5S.
II. Problems that may arise from neglecting maintenance
A dirty electrical cabinet can cause short circuits, arcing, and burn out the equipment.
A clogged fan filter in the electrical cabinet will result in poor heat dissipation and consequently, poor equipment stability.
Excessive humidity can cause equipment to short circuit;
Overheating in certain high-current locations over a prolonged period can burn out equipment.
III. Preparatory Work
Various tools: screwdrivers, wrenches, megohmmeters, multimeters, clamp meters; vacuum cleaners; heat guns, markers, files, etc.
Spare parts: fan filter, contactor auxiliary contact, relay coil, heat shrink tubing, conductive paste.
Personnel: Not only electricians but also programmers are needed. Because if programmers are involved, they can also maintain the software, preventing and eliminating many software glitches in advance.
IV. Precautions
Make a plan, develop detailed steps, and follow them step by step. Never trust an idea that comes to mind on a whim; instead, consider all aspects carefully and then proceed with the plan step by step.
1. Safety First: Disconnect the power before disassembling the equipment; please be careful.
2. When cleaning the electrical cabinet, be careful not to spread dust everywhere;
3. Mark all areas that have been modified and observe them carefully. For example, if some wires have been reconnected or some wire lugs have been re-pressed, check these areas for any problems after the equipment is put back into production.
V. Data Backup
Backing up the program is essential. If the equipment fails one day, you'll be helpless without the program. With the program, you can at most replace the controller. Therefore, this is a must-know skill for equipment maintenance personnel.
1. For data that needs to be archived for a long time (such as historical trend curve data in the military industry), the historical trend data can be backed up to an external hard drive, and then the Windows-based operating system, such as an HMI system with WinCC Intouch, can be shut down; then the main power supply can be turned off.
2. For some controllers that cannot communicate, such as soft starters, it is necessary to manually record the internal parameters in case of unforeseen circumstances.
VI. System power failure
After the data backup is complete, perform the switching operation. When de-energizing, first disconnect the following protection switches.
Then disconnect the main switch (when powering on, first turn on the main switch on the control cabinet, and then turn on each of the protection switches below in sequence).
Safety locks should be used to secure the device after a power outage to prevent accidental power restoration.
VII. Appearance and Environmental Inspection
Temperature and ambient conditions: 0~40℃
Relative humidity below 85%
Amplitude less than 0.5 mm (10~55 Hz)
Free from excessive dust, salt, and iron filings.
24VDC output voltage measurement: Is it within the normal range?
After powering off, test the system insulation using a megohmmeter to assess the equipment insulation.
8. Control cabinet cleaning
Power off the equipment, cover up electronic components with heat dissipation holes such as PLC and frequency converter, and it is best to remove the PLC module.
Only vacuum cleaners can be used; compressed air cannot be used because compressed air will blow dust into the equipment, and compressed air often contains water, which can cause a short circuit if it enters the equipment.
After vacuuming, check if the wiring is loose.
9. Cable Inspection
Is the main cable loose? If it is loose, it is very easy to burn out.
Check if the large cable joint is blackened: If so, check if the cable lugs are not tightened or if the contact current is too high.
10. Equipment grounding inspection
Profibus grounding measurement: Pay attention to whether the shielding layer is aging. An aging shielding layer will result in poor grounding, which can easily cause Profibus station loss.
Analog signal grounding measurement : The principle is the same as above.
Check the grounding wire for rust; if rust is found, repair it.
XI. Contactor Inspection
Are the mounting screws and input/output wires of the large contactor loose?
Large contactor contact condition : Check for signs of melting on the main contacts, and inspect the arc-extinguishing cover for blackening and damage.
Contactor terminal status : Are they burnt black?
Pull-in time and voltage test : Check the contactor's pull-in time and the continuity of the incoming and outgoing lines.
Check if the contactor makes a normal clicking sound. If it makes a "buzzing" sound after clicking, disassemble and check the condition of the contacts.
12. Copper busbar inspection
Check the heat shrink tubing for damage;
Check the copper busbar connections: If the copper appears discolored, it indicates that the copper busbar may be overheating. If necessary, disassemble the copper busbar, align it flat, apply conductive paste, and tighten it.
13. Relay Inspection
If the solenoid valve fails to engage or disconnect during production, follow the steps below to check.
a . Check if the LED light on the relay corresponding to the solenoid valve is lit. If it is lit, it means the solenoid valve is energized; if it is not lit, it means it is not energized.
b . Use a multimeter to measure whether there is power at pins A1 and A2 of the relay.
If the solenoid valve malfunctions during production, the following steps can be taken:
Generally, only one set of contacts will be damaged. If the relay has two sets of contacts, and one set is damaged, you can consider replacing the other set. For example, if the field wiring is for contacts 11-14, and it is damaged, you can replace it with contacts 21-24. In this case, simply loosen the wires on pins 11 and 14 and replace them with pins 21 and 24.
If replacing the contacts doesn't work, you can consider replacing the coil. Simply remove a less important relay coil from a less important circuit and replace it with the coil. Be careful not to insert it in the wrong direction.
14. Replace the filter.
Depending on the site conditions, the filter should be replaced every six months or a year.
If the filter becomes clogged, it will severely affect the heat dissipation of the equipment.
15. Inspect the fan of the frequency converter and power regulator.
Check if the inverter and power regulator fan are operating normally.
Check if the vents are blocked. If the fan blows out a cloud of dust when turned on, it means it needs to be cleaned.
XVI. Equipment Overheating Inspection
Electrical cabinet temperature
Large cable and bronze plate temperature
Cable temperature
If you have an imaging device, that would be best; otherwise, you'll have to use a temperature gun.
Regularly check the temperature inside the cabinet, the temperature of the main cables, and the temperature of the cables on site to prevent damage to cables and components due to dust accumulation or other reasons .
17. Clamp-on ammeter test
1. Under normal circumstances, one person should operate the equipment while another person supervises it. When measuring, the safe distance between the hand and the live parts should be kept at more than 10 centimeters.
2. Before measurement, first estimate the magnitude of the load current and voltage, and select the range accordingly. If it is impossible to estimate, to prevent damage to the clamp meter, start the measurement with the highest range and switch to a lower range as the reading increases.
3. Changing the range is not allowed during measurement. Because the secondary side is essentially short-circuited during measurement, switching ranges during measurement will cause a momentary open circuit in the secondary side, inducing a very high voltage, which may cause the internal insulation of the clamp meter to break down.
4. To minimize errors, the conductor being measured should be placed as centrally as possible in the clamp meter jaws during measurement. The clamp jaws should be tightly closed during measurement. If there is noise, reopen and close the clamp once. If noise persists, carefully inspect the clamp. Remove any dirt or debris before proceeding with the measurement.
5. After measurement, the range switch should be set to the highest position to prevent damage to the instrument due to negligence in not selecting the range during the next use.
6. Clamp meters are generally used to measure the current on the low-voltage side of distribution transformers or motors. They must not be used on high-voltage lines to avoid insulation breakdown and electric shock.
18. Software Maintenance - PLC Diagnostic Buffer
1. Recording and organizing equipment hardware alarms.
2. Equipment problems may not necessarily cause equipment downtime, but they are recorded in the PLC's diagnostic buffer. Therefore, regularly checking these records is of great significance for equipment maintenance.
3. Promptly identify the sites experiencing problems, find the causes, and prepare accordingly.
4. Some people may say that they can't understand this, that's okay, you can save it as a txt file and send it to someone else for help.
Critical diagnostic buffer alarms:
A. A site is lost; then it reappears shortly afterward. This is rather dangerous and needs to be checked.
The more dangerous reason is that the communication may be interfered with or the DP bus connector may be oxidized or even the shielding layer may be oxidized, resulting in poor grounding. Now it sometimes loses connection and then comes back, but who knows when the station will be completely lost.
B. If a certain analog quantity cannot be found, this also needs attention:
Possible reasons include: the analog signal may be affected by interference, but overall the problem is not serious.
C. There is another type of software problem:
Similar to example B above, except that this alarm indicates that a certain data in the DB block cannot be found, the reason being that the software pointer is faulty and points to a non-existent address.
For example, if DB80 only has 1000 bytes, and you write a pointer addressing program that points outside of DBB1000, it will throw an error. If it's just an error, it's not a big deal, but the problem is that it will directly enter an infinite loop and crash.
19. Software Maintenance - HMI Alarms
Check the device alarms, especially those that occur frequently, and eliminate the causes of these alarms:
For example, if a flow switch on the equipment frequently alarms, it can be disassembled and cleaned.
For example, if a valve frequently times out of control, it may be due to excessive wear.
20. PLC power supply battery replacement
1. Before disassembling or assembling, the PLC should be powered on for more than 15 seconds (this allows the capacitor in the backup power supply of the memory to charge; when disconnected, this capacitor can provide a brief power supply to the PLC to protect the information in the RAM from being lost).
2. Disconnect the AC power supply to 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 with the cover.
Note that battery replacement time should be kept as short as possible, generally not exceeding 3 minutes. Otherwise, the program in RAM will be lost.
21. Holiday Precautions
1. During holidays, the main power supply to the equipment can be turned off, but the power supply to the lighting and fan circuits should be left on.
2. Always turn on the control cabinet ventilation fan or air conditioner; otherwise, moisture may accumulate inside the equipment during rainy weather, causing a short circuit.
Case: Once during the Spring Festival, it rained for several days and the fan was not turned on. As a result, condensation formed inside the PLC of the equipment, and water droplets flowed down the glass of the voltmeter and ammeter. After returning to work, I used a hot air gun to blow it out for a long time.
