Weighbridge is the main weighing device for bulk cargo measurement, which brings us more convenience. But do you know? The environment will also have an effect on the weight scale anti-jamming device and have different effects in different environments. The environment can interfere with the normal use of the loadometer jammer. For example, in the rainy season and more thunderous season in summer, how to protect and protect our platform scales? The following Xiaoheng Metrology Xiaobian to everyone to answer how to reduce the impact of thunderstorms on the scales.
Since lightning is unpredictable and the cause of lightning damage is complex, there is no way to completely eliminate its effects. However, if a variety of methods are used in combination, the lightning damage can be effectively reduced, and the effects of lightning protection can achieve satisfactory results. Therefore, it is necessary to establish a sound and reliable lightning protection grounding system for the electronic truck scale to ensure the entire The electronic weighing system operates safely, reliably and stably.
Lightning prevention measures analysis
According to the destructiveness and characteristics of lightning, lightning can be divided into direct lightning and induced lightning. Direct lightning strikes sound, light, and electricity at the same time. The instantaneous current reaches hundreds of thousands of amperes. The electrical and thermal effects produced can lead to fires and melted objects. Inductive lightning (also known as secondary lightning strikes) is more frequent than direct lightning strikes. Higher and indirect losses are the most significant features of lightning disasters since the 1980s, and they are also an urgent problem to be solved in lightning protection technology. In the following, we will discuss mine protection measures in light of their respective characteristics.
1. Prevent direct lightning
Because there are many empty buildings around the electronic truck scale in the mining area, there are few high-rise buildings nearby, or they are not protected by the lightning protection system of high-rise buildings. This may cause discharge between the charged clouds in the sky and direct lightning strikes. . For this reason, reliable lightning protection measures must be taken in areas prone to lightning interference and damage, so as to avoid damage caused by lightning strikes. Therefore, according to the specific location, according to the standard set reasonable lightning rod, the tip discharge effect and the charge in the cloud, effectively protect the electronic weighing system, to avoid direct lightning.
Direct lightning strike lightning protection equipment is the role of lightning, that is, to prevent lightning directly hit the metering room and the various areas of the air-termination device within the protection of metal lines and electrical equipment. The various metal wires outside the protection range of the air-termination device and the inductive lightning caused by the direct lightning strike cannot be protected.
2. Anti-lightning electronic hanging scales, electronic platform scales, electronic desk scales, special functions electronic scales
When the lightning discharge path does not pass through the lightning protection device, a powerful transient electromagnetic field is generated in the discharge process to induce a strong electromagnetic pulse in a nearby conductor, which is called an induced lightning. Induction lightning can invade the conductor through two different induction methods: electrostatic induction and electromagnetic induction.
2.1 Anti-static induction When a lightning strikes a thunderstorm, there is no direct lightning strike between the charged clouds in the air and the outdoor weighing platform, but electrostatic coupling will cause the device to carry charges that are opposite in polarity to the cloud. When the lightning cloud discharges from the cloud with other cloud groups and suddenly disappears, a large amount of back-flow current will be generated in order to evacuate the large amount of charges accumulated on the top of the weighing platform. An electronic truck scale generally has 10 to 12 supporting points connected to the sensor. When the static induction lightning strike causes a large current to flow back, the above-mentioned bearing point is a defective part of the return flow path and electrostatic induction is formed in the circuit. For this purpose, a large-current bypass cable must be installed at the upper and lower ends of the sensor (such as a bridge load cell) or at the left and right ends (such as a cantilever-type load cell), that is, a multi-strand braided copper wire is used to bridge the cable. Make the whole sensor form the grounding equipotential state, and the base plate and the load-bearing station are connected into an equipotential body, which can prevent the accidental current from passing through the sensor and cause the damage of the sensor. In this way, there is a large current return path between the weighing platform and the electronic vehicle grounding grid. When static induction occurs, electrons can be replenished from the earth, so that it cannot be quickly evacuated after the device generates a high potential.
2.2 Anti-electromagnetic induction lightning strike In recent years, in addition to the direct lightning strikes, the electronic truck scale in the coal industry is more of a surge current that is destructive to precision electronic equipment due to electromagnetic effects of lightning.
(1) The generation of surges. Surge is an abnormally large current pulse in the order of microseconds. Its wave head time is generally 0.25 to 20 μS, and its unit energy is generally 2.5 to 10 MJ/, which can cause electronic equipment to be damaged by transient overvoltage. While lightning is the most obvious cause of power surges, when lightning strikes in the air, strong discharges occur between clouds with opposite-polarity charges. This produces electromagnetic fields with large amplitudes and very steep rising edges. This high-intensity transient electromagnetic field will cause Electromagnetic fields involve large amounts of induced electromotive force on conductors, which can damage the components of weighing instruments, computer hosts, and displays. Therefore, lightning surges generated by hitting power lines, signal lines, and lightning electromagnetic pulses can cause computers, instrumentation, and other electronic devices to be damaged by transient overvoltages. In addition, large electrical equipment, elevators, generators, air conditioners, refrigeration equipment, etc. can also cause surges. UPS can also be destroyed by power surges.
(2) The principle of surge protection. At present, the use of surge protectors has become increasingly frequent during surge protection; Surge protection devices (SPDs) are required to include at least one nonlinear voltage limiting element for limiting transient overvoltages and Shunt current device. The general surge protector uses MOV (metal oxide semiconductor varistor) technology, which is different from spark gap technology. Surge can't be stopped because it contains too much energy. It is for this reason that the strategy to protect sensitive electrical equipment from power surges is to divert power surges from the equipment. When the voltage rises to the level set at the top, the MOV immediately operates with a response time of 1 to 3 nanoseconds. The “V†in the MOV is a varistor. At the instant of the response, the resistance of the MOV is reduced from its full value to almost zero ohms. The MOV makes the transient high voltage find the path to the ground and attracts the overcurrent away from the sensitive electrical equipment. MOV Leakage of excess voltage, electrical equipment continues to operate at normal operating voltage.
According to the principle of operation surge protectors are divided into three categories, (a) Voltage SPD (Voltage switching tspdypeSPD) switch type, no surge occurs when the high impedance, when the voltage surge occurs when the mutation is low impedance. Discharge gaps, gas discharge tubes, thyratrons, and triacs are commonly used as components of such SPDs. This type of SPD is sometimes referred to as a "short-circuit switch" or "Kropa type" SPD. (b) Voltage-limiting SPD (Voltage limiting type SPD), which is high impedance when no surge occurs. As the surge current and voltage increase, the impedance continuously decreases. Varistors and suppressor diodes are commonly used as components of such SPDs. This type of SPD is sometimes referred to as a "clamp type" SPD. (c) Combinatorial type SPD (Combinatino type SPD), which is a combination of a voltage-switching type component and a voltage-limiting type component. It can be displayed as a voltage switching type or a voltage limiting type or both, depending on the applied voltage. The characteristics. According to the function of the surge protector in the electronic information system, it can be divided into power surge protector, antenna surge protector and signal surge protector.
(3) The choice of surge protector. When choosing a surge protector, a manufacturer with advanced technology should be selected. The product should have detailed specifications, technical specifications, origin, standard certificates in compliance with various aspects, and sales licenses.
1) Whether the design is user-friendly and easy to install. The ideal product should be a small, compact and can be installed in an existing space while being easy to install. Therefore, the closer you install the surge protector to the distribution box, the better it is within 15cm.
2) Reaction time. The surge protector response time must be faster than the surge. The reaction time meets the technical requirements in the nanosecond (nanosecond) level.
3) The maximum current that can be processed at one time. The maximum current, or peak current, is the ability of a surge protector to handle the maximum current.
4) The ability to absorb energy. The ability of a surge protector to absorb energy is measured in Joules. The higher the Joule value, the longer the surge protector can last.
5) Ability to clamp voltage. That is, the ability to clamp the overvoltage into the safe range that the electrical equipment can withstand.
The GAL73-1998 standard, which came into effect on June 1, 1998, states that the clamping voltage of computer lightning protection devices (surge protectors) for 220/380V power systems should be less than or equal to 2kV.
6) Meet international and national standards. International standards, including UL449, IEEE, NEMA, and IEC.
(4) Surge protection plan. In addition to incoming line power, lightning surges are mainly infiltrated into the device through the signal line, causing damage to the interface circuits of the weighing instrument and computer. Therefore, attention should be paid to surge protection and must not be held. There is luck. In view of the above, in order to further reduce the damage caused by power surges, we have formulated the following preventive measures.
The first is reasonable wiring and shielding. The low-voltage power cables entering the pound room should be buried with a cable with a metal armored shield and grounded at both ends of the shield to minimize the high voltages of lightning introduced from the various conductors.
The second is the joint grounding of equal potentials, that is, lightning protection grounding, protection grounding, and work grounding are commonly connected to the scale body grounding network. The grounding network resistance requirements are below 4. This type of grounding effectively reduces the ground resistance and allows the ground potential between devices to be equal. The entire weighing instrument system has a common grounding system.
The third is to install surge protectors. The lightning protection system of the power supply system shall adopt a three-level lightning protection system. The 220/380V power supply system in the pound room shall adopt the TN-CS type. Since the electronic devices in the pound room are close to each other, only the power supply must be installed at the lower end of the power supply. The class of composite lightning protection devices is to install the FYS-0.22kV arrester between each phase line and the neutral line to implement the first and second lightning protection of the distribution system; at the power outlets related to the measurement system, The surge protector is installed for the third level protection of the power supply. The wiring is as shown in the figure. Through multi-level lightning protection facilities, complete discharge of lightning over-current, limit over-voltage, as far as possible to prevent lightning from entering the metering system through the power line, damage the system equipment.
At the same time, the ADSL dedicated line access is used for the measurement room network connection. To avoid the possibility of the lightning of the communication cable, the technology used is to connect the signal arrester (signal SPD) before the cable is connected to the metering system and reduce the lightning strike as much as possible. Impact of system equipment.
The fourth is the lightning protection of the sensor signal cable. In the entire weighing and metering system, there is one place that can't be neglected. There is a long distance sensor signal cable from the pound room to the weighing platform. Lightning strikes through the electromagnetic induction route, can introduce the high potential on the line road, causes the weighing instrument to damage due to the lightning strike. For this reason, the signal cables, especially the signal cable shields of the pound room to the scale body and the metal conduit should be grounded reliably, blocking all the lightning electromagnetic pulses from the space invading channels, making the lightning seamlessly drillable. Eliminate the destruction of electromagnetic induction lightning strikes.
Therefore, the overvoltage and electromagnetic interference protection of the measurement room is an important technical means for ensuring normal office, electrical equipment and personal safety, and is an indispensable technical link for ensuring the normal operation of electronic equipment and information networks. The role of surge protection in daily office and business activities has also become more prominent and important.
Third, the conclusion
Since lightning is unpredictable and the cause of lightning damage is complex, there is no way to completely eliminate its effects. However, if a variety of methods are used in combination, the lightning damage can be effectively reduced, and the effects of lightning protection can achieve satisfactory results. Therefore, it is necessary to establish a sound and reliable lightning protection grounding system for the electronic truck scale to ensure the entire The electronic weighing system operates safely, reliably and stably.
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