The following introduces the environmental conditions and countermeasures when installing PLC control cabinet (hereinafter referred to as "cabinet").
temperature
The use environment temperature of PLC is related to the use temperature of components, which should generally be within the range of 5℃ ~ 40℃. On the other hand, in the natural cooling control cabinet without forced cooling, the cabinet itself is miniaturized due to the space saving and miniaturization of equipment and systems, so the temperature inside the cabinet is sometimes higher than that outside the cabinet 10℃ ~ 15℃. Therefore, the following measures need to be taken to solve the heating problem of places and cabinets. In order to ensure that the temperature in the cabinet does not exceed the operating temperature range of the unit, sufficient temperature margin should be reserved as far as possible for use in the temperature range with margin.
High temperature (fig. 1. Reference)
(1) natural air cooling (natural ventilation depends on shutters above and below the cabinet)
When installing in the cabinet, it is best not to use cooling equipment such as fans and air conditioners. At this point, the precautions for installing PLC are as follows:
1 should not be set at the top of the hot air gathering in the cabinet.
In order to ensure ventilation space, the upper and lower parts should keep enough distance from other equipment and distribution pipes.
Don't install it in a direction other than the specified direction (such as vertical or inverted), otherwise it will cause abnormal heating inside the PLC.
4 Don't install directly above the equipment with high calorific value such as heater, transformer and large-capacity resistor.
5 Avoid direct sunlight.
(2) Forced ventilation (forced ventilation through the fan at the upper part of the cabinet)
③ Forced circulation type (forced circulation ventilation is carried out by the fan in the cabinet with closed structure)
④ The overall cooling mode of the room.
(Use air conditioner to cool the whole room where the control cabinet is placed)
notes
The relationship between environmental conditions and cooling methods is as follows.
? Set the control cabinet in a room with less dust →
? Place it in a dusty place → ③ or ④.
Countermeasures when using fans
1 Install an air filter at the air inlet of the outside air and take measures to prevent dust from entering.
The air filter should be cleaned with water regularly.
If the fan and air conditioner fail, we can install a temperature sensor near the PLC to give an alarm.
low temperature
In cold areas and other places, when the temperature is lower than 0℃ in the morning, a small-capacity space heater can be installed in the cabinet to preheat the air in the cabinet to about 5℃. In addition, because the PLC power supply will generate heat when it is energized, do not turn off the power supply.
humidity
In order to maintain the insulation characteristics of PLC, it must be used in the range of relative humidity of 35% ~ 85%. Especially in winter, the heating is turned on and off, and sometimes it will condense due to the sharp change of temperature, leading to short circuit and misoperation. When this danger occurs, it is necessary to keep the power on at night, or set a heater in the control cabinet for micro-heating. To prevent condensation. (See Figure 2)
Vibration? ridicule
PLC is tested according to sine wave vibration test method (JISC0040/IEC68-2-6) and impact test method (JIS C004 1/IEC68-2-27) in environmental test methods (electrical and electronic). Under impact, there should be no misoperation.
But don't set it to vibrate frequently? Impact, especially where such vibration and impact may directly act on PLC or control cabinet.
The methods to reduce vibration and impact are as follows.
1 ① For vibration and impact from outside, the control cabinet can be separated from its source. Or use anti-vibration glue to fix PLC and control cabinet.
2 ② Anti-vibration treatment of building structure and ground.
atmosphere
When used in the following places, it may lead to poor contact between connectors and components. Parts of corrosion, so it is necessary to take measures such as air purification.
(1) in the dust? Acid? Where there is a lot of iron powder and oil smoke. In places where organic solvents float, you can use a large cabinet with a closed structure, and the temperature inside will not rise greatly.
(2) Especially in places with corrosive gases, the air of the control cabinet should be cleaned (purified), and the external corrosive gases should be prevented from entering by slightly pressurizing the cabinet.
(3) where there is combustible gas, it may become a fire source. This place can be equipped with explosion-proof equipment or not.
working range
When setting up PLC and cabinet, we should consider the operation such as use, operability and maintenance, so please pay attention to the following contents.
① Leave space for program operation and unit replacement. Besides, consider maintenance? Safe operation, as far away from high-voltage equipment and power equipment as possible.
② The installation position of ②②PLC and I/O unit should consider the convenience of connection and operation of peripheral devices such as unloading tools.
(3) ③PLC and I/O units are often equipped with maintenance and inspection indicators, so they should be installed at a height that operators can easily see and reach.
④ In the control system using PLC, most of them should consider the future transformation and expansion, so the expansion space of 1-20% should be considered in advance.
⑤ If necessary, leave a space of about 600mm behind the cabinet as a maintenance channel.
Electrical environment of PLC control cabinet
Power supply, grounding and noise (interference) are the main electrical environments. When installing and wiring equipment, the most important thing is to prevent harm to the human body and not to let the electrical signals be affected (interfered).
Location of PLC
Considering the safety of maintenance work, it should be set separately from high-voltage equipment (above 600V) and power equipment. If necessary, try to keep it away from the set.
(See Figure 3)
Configuration and arrangement of PLC and each unit (see Figure 4)
① The units adjacent to the CPU unit are preferably special units and input units with less interference.
② The coils and contacts of electromagnetic contactors and relays of external circuits are interference sources and should be configured separately from PLC. (About above 100 mm)
Wiring of power supply system (see Figure 5)
① Separate the PLC power supply from the power supply of input and output equipment, and install a noise filter near the lead-in part of the PLC power supply.
② By adding an isolation transformer, the grounding interference can be greatly attenuated. At this time, the secondary side of the isolation transformer should not be grounded.
③ The wiring between the transformer and PLC is tightly twisted pair according to the shortest distance, which is separated from the high voltage line and power line.
Wiring of external input and output signal lines
① When the inductive load is connected to the output signal, in order to absorb noise, a surge suppressor and a diode are connected near each inductive load in the AC circuit and the DC circuit. (See Figures 6 and 7)
② Do not tie the output signal line with the high-voltage line and power line into a wire harness, and do not wire it at short distance or in parallel. When approaching, the conduit can be used to separate or wire other conduits. At this time, the catheter and the catheter must be grounded. (See Figure 8)
(3) When it is impossible to separate through the conduit, all shielded cables can be used to connect the PLC side with the grounding terminal and open the input device side.
④ It is an ideal method to use wiring without * * * direct impedance. But at this time, because of the increase of wiring, it is sometimes necessary to use loops. The loop should use thick wires with sufficient margin and connect wires with the same signal level.
⑤ When the input and output lines are long, wire the input signal line and output signal line respectively.
⑥ Indicator lamp (especially filament type) is connected with twisted pair.
⑦ It is effective to use CR surge absorber, diode and other anti-interference measures as noise sources of input equipment and output load equipment.
External wiring
Wiring method plays an important role in establishing a powerful system to resist all kinds of noise and make the system run on the basis of high reliability. Wiring operation, especially anti-interference countermeasures, often depends on experience, so it needs to be operated under a good management system based on this manual.
Prevent wrong wiring
(1) If a label is wrapped around the cable to indicate the direction, it can not only prevent wiring errors, but also facilitate inspection and maintenance after wiring.
② Wiring in different colors.
③ Put cables transmitting similar signals into the same conduit and group them.
General preventive measures
(1) Do not connect wires with butt joints between terminals.
② The terminals of multi-core cables should be properly supported and fixed to avoid tension at the wire ends.
③ When connecting movable parts such as doors, fix one end of the wire on the fixed part and the other end on the movable part, and use flexible wires to avoid damaging the wires due to the opening and closing of the doors.
(4) The terminal of the wire should be crimped. When connecting with the terminal, a torque screwdriver should be used to tighten the screw with appropriate pressure to realize the connection. Especially when connecting the terminals connected to the AC power supply unit, in order to ensure safety, it is hoped that the U-shaped crimping terminal should be used instead of the ring crimping terminal.
⑤ In the wiring process, when the dust cover is installed on the PLC unit, the dust cover shall not be removed before the wiring is completed to prevent wiring debris from entering. In addition, the dust cover must be removed after wiring, because the internal temperature will rise sharply during operation, which will lead to the decline of function.
⑥ All wiring of the power supply circuit is twisted pair.
⑦ Do not tie the primary side and the secondary side of the noise filter together, because this will reduce the effect of the noise filter.
Routing path
The following combination, due to the type of signal? Due to different attributes and levels and inductance, S/N (Signal-to-Noise Ratio) decreases. Therefore, in principle, other cables should be used and routed through other paths. In addition, the sorted wiring is also convenient for future maintenance and system replacement.
① Power cord and signal cord
② Input signal and output signal
③ Analog signals and digital signals.
④ High level signal and low level signal.
⑤ Communication cable and power cable
⑥DC signal and AC signal
⑦ High frequency equipment (frequency converter, etc.). ) and signal line (communication)
Wiring method
① When signal cables with different properties are put into the same conduit, they must be isolated.
② Try to avoid accommodating more than one power cord in the same conduit. When they must be placed together, a partition must be placed in the conduit and grounded. (See Figure 9)
(3) When wiring with conduits, don't put the wires of 1 loop in different conduits, because the conduits are hot. (see figure 10)
(4) in order to make the power cable and signal cable not interfere with each other, don't wire them in parallel.
⑤ If it is installed in a cabinet with high-voltage equipment, it will induce noise, so try to be far away from high-voltage and power system for wiring.
⑥ Install the PLC at a distance of more than 200mm from the power cord of the high-voltage line, or put the high-voltage line and power cord into a metal tube for wiring, and completely ground the metal tube in Class D (Class III grounding). (see figure 1 1)
Other preventive measures
① According to different models, the input/output module has negative and positive terminals and positive terminals. Pay attention to polarity when wiring.
② The appearance of optical cable is similar to that of general communication cable and power cable, but the inside is composed of optical fiber and protective optical fiber strain sheet, filler wire and filler, so special attention should be paid when using it. In particular, typesetting construction should be carried out in accordance with the prescribed methods and standards, and there should be no excessive impact tension, excessive bending, torsion and excessive extrusion.
disembark
Grounding purpose
Grounding has two purposes.
(1) By keeping the potential caused by leakage and induction due to faults at the ground potential level, the human body can be prevented from getting an electric shock, that is, the protective grounding for the purpose of ensuring safety.
(2) It includes anti-interference grounding to prevent noise from external invasion and noise generated by equipment and devices from causing harm to other equipment and devices, which is necessary grounding (functional grounding) to play the function of equipment or system.
As for these grounding gases, sometimes it needs to be solved by experience and experiment. Therefore, we must fully study and consider in advance before grounding.
Grounding method and matters needing attention
(1) One-point grounding principle
I hope to consider in advance that the grounding wire is a "facility to determine the potential". Under normal circumstances, there is no current flowing in the grounding wire (current is not allowed to flow back to the loop and grounding * * *).
(2) When grounding, try to use special grounding (the distance between grounding electrode and other grounding electrodes is greater than 10m).
(1) Class-D grounding is adopted in the grounding project, and it is better to use special grounding separate from other equipment grounding.
② When professional grounding cannot be used, as shown in figure 12(b), its grounding electrode is connected with the grounding electrode of other equipment to form * * * grounding.
(3) In particular, it is necessary to avoid grounding with high-power equipment such as motors/frequency converters. In order to prevent mutual influence, they should be grounded separately.
④ Avoid connecting grounding electrodes (sometimes only steel bars) to multiple devices only for the purpose of preventing electric shock.
⑤ The grounding electrode should be as close to PLC as possible to shorten the grounding wire.
(3) Grounding precautions
(1) When the signal line grounding and the shell grounding are the same grounding, it is necessary to insulate the channel substrate (metal plate in the grounding control cabinet) with insulators. (see figure 13)
② The cabinet equipped with PLC needs to be electrically insulated from other equipment. This is to prevent leakage current from other electrical equipment.
③ When there is high-frequency equipment, the cabinet equipped with PLC should be grounded at the same time.
④ When the shielded cable is used for input and output wiring, the shielded conductor near the PLC side should be connected to the grounding terminal of the housing, as shown in Figure 14. In addition, for communication cables, the shielding principle in the communication equipment manual should be observed.
(4) 4) Grounding terminal of PLC
The PLC is equipped with the following two grounding terminals.
: connected to the bottom plate of PLC, usually used to prevent electric shock and protect the grounding terminal from grounding.
: The functional grounding terminal is connected to the neutral point of the noise filter and grounded when the power supply interference causes misoperation.
If the terminal is properly thermally grounded, the interference of power supply mode will be weakened, but there are many cases where grounding picks up noise, so attention should be paid to it when using it.
(5) In the connection of AC power supply unit, when the equipment power supply is grounded in single phase, the grounding phase side must be connected to the terminal side of L2/N (or L 1/N).
refer to
① Maintenance and inspection manual of programmable controller (PLC)
② Install ②SYSMAC CS series user manual.