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Among many advanced materials, 1J85 Permalloy has received special attention for its excellent magnetic properties and wide application. However, where does the particularity of this material come from? What are the unique features of its composition, performance and application fields? This article will explore 1J85 Permalloy in depth and take you to find out.   1. Composition analysis of 1J85 Permalloy   1J85 Permalloy, as a soft magnetic alloy, is mainly composed of elements such as nickel, iron, and molybdenum. This specific alloy ratio gives it unique physical and chemical properties. Specifically, 1J85 alloy contains approximately 80% nickel (Ni), 15% iron (Fe), and approximately 5% molybdenum (Mo). This unique composition configuration makes 1J85 alloy perform well in magnetic properties, mechanical properties, and electrical properties.   2. Performance advantages of 1J85 Permalloy   1. High magnetic permeability One of the biggest features of 1J85 Permalloy is its high magnetic permeability. This property enables it to effectively conduct magnetism in a magnetic field, thus playing an important role in various electromagnetic applications.   2. Low coercivity Coercivity refers to the reverse magnetic field strength required to eliminate the magnetization state of a material after it is magnetized. 1J85 alloy has a low coercivity, which means that it can be quickly magnetized and demagnetized under a small magnetic field, greatly improving the response speed and efficiency of electromagnetic equipment.   3. Good temperature stability 1J85 alloy can keep its magnetic properties basically unchanged over a wide temperature range, which makes it suitable for electronic equipment and electromagnetic systems that need to work under different temperature conditions.   IV. Expansion of application areas   1. Transformers and inductors 1J85 Permalloy is widely used in power transformers and inductors. In these applications, the high magnetic permeability and low loss characteristics of the alloy can effectively improve the energy efficiency and performance of the equipment.   2. Electromagnetic shielding Due to the high magnetic permeability of 1J85 alloy, it is also often used as an electromagnetic shielding material to reduce electromagnetic interference between electronic equipment and ensure the normal operation of the equipment.   3. Precision sensors The high sensitivity and good temperature stability of 1J85 alloy make it an ideal material for manufacturing various precision sensors, such as magnetic sensors, position sensors, etc.

Main performance of split core current transformer:   Split core current transformer mainly cooperates with relay device. When short circuit, overload and other faults occur in the line, it provides signal to relay device to cut off the fault circuit to protect the safety of power supply system. The working conditions of protective micro current transformer are completely different from those of measuring transformer. The protective transformer only starts to work when the current is several times or dozens of times larger than the normal current. Main requirements of protective transformer: 1. Reliable insulation, 2. Sufficiently large accuracy limit coefficient, 3. Sufficient thermal stability and dynamic stability.   Split core current transformer can meet the accuracy level requirements under rated load. The large primary current is called rated accurate limit primary current. The accuracy limit coefficient is the ratio of rated accurate limit primary current to rated primary current. When the primary current is large enough, the core will be saturated and cannot reflect the primary current. The accuracy limit coefficient represents this characteristic. Accuracy level of protective transformer 5P, 10P   Split core current transformer function The transformer for power system is a special transformer that transmits the information of high voltage and large current of the power grid to the metering, measuring instruments, relay protection and automatic devices on the low voltage and small current secondary side. It is a contact element between the primary system and the secondary system. Its primary winding is connected to the power grid, and the secondary winding is connected to the measuring instrument, protection device, etc. The transformer cooperates with the measuring instrument and metering device to measure the voltage, current and electric energy of the primary system; cooperates with the relay protection and automatic device to form electrical protection and automatic control of various faults in the power grid. The performance of the transformer directly affects the accuracy of the measurement and metering of the power system and the reliability of the action of the relay protection device.  

Permalloy usually refers to an iron-nickel alloy with a nickel content in the range of 30~90%. It is a widely used soft magnetic alloy.   Through appropriate processes, magnetic properties can be effectively controlled, such as an initial magnetic permeability of more than 105, a large magnetic permeability of more than 106, a coercive force as low as 2‰ Oersted, and a rectangular coefficient close to 1 or close to 0. Permalloy with a face-centered cubic crystal structure has good plasticity and can be processed into 1μm ultra-thin strips and various usage forms. Commonly used alloys include 1J50, 1J79, 1J85, etc. The saturation magnetic induction intensity of 1J50 is slightly lower than that of silicon steel, but the magnetic permeability is dozens of times higher than that of silicon steel, and the iron loss is 2~3 times lower than that of silicon steel.   It is made into a transformer with a higher frequency (400~8000Hz) and a small no-load current, which is suitable for making small high-frequency transformers below 100W. 1J79 has good comprehensive performance and is suitable for high-frequency low-voltage transformers, leakage protection switch cores, common-mode inductor cores and current transformer cores. The initial magnetic permeability of 1J85 can reach more than 100,000 105, which is suitable for low-frequency or high-frequency input and output transformers, common-mode inductors and high-precision current transformers for weak signals.

No matter what type of rod-shaped inductor coil, it is inevitable that it will heat up during use! Heating is a normal phenomenon, but if the heating is too large, it may not be a normal phenomenon.   In fact, the solution to inductor heating is essentially the same even for different inductor types. It needs to be solemnly explained: the function of the rod-shaped inductor coil is to store energy, suppress electromagnetic interference, pass DC and block AC. When the current flowing through the inductor coil is large, the coil will heat up. In severe cases, it will get hot, the inductance of the inductor will decay, and the surface temperature of the inductor body will rise. When the temperature rise current exceeds 40 degrees Celsius, the inductor will lose its inductance characteristics. In severe cases, the entire PCB board will be burned. According to the experience summary of the case, the common reasons for the heating of the rod-shaped inductor coil are mainly the following:   1. If the abnormal heating of the magnetic rod coil inductor is caused by improper use of the equipment, this only needs to adjust the use method and use it correctly according to the specifications. In fact, it can be solved.   2. If the abnormal heating is caused by the quality problem of the magnetic rod coil inductor:   The treatment method for this reason is relatively responsible, because it may involve the traceability of the magnetic rod coil inductor product itself. Any product quality problem means that there may be a large number of substandard products in the batch of magnetic bar coil inductors produced by the supplier.   The correct way to deal with it is to determine which aspect of the product causes the quality problem. Is it the poor quality of the enameled wire used, or the coil winding does not meet the requirements, or the problem with the core powder formula that causes abnormal heating? This requires our technical intervention and a comprehensive test and analysis of the product to find out the problem. As long as we can determine the problem, we can provide specific and effective solutions.

From the wire with large current, a small current can be induced in a certain proportion for measurement, and it can also provide power for relay protection and automatic devices.   Example: For example, there is a very thick cable with a very large current. If you want to measure its current, you need to disconnect the cable and connect the ammeter in series in this circuit. Because it is very thick and the current is very large, a large ammeter is needed. But in fact, there is no such large ammeter, because the specifications of the current meter are all below 5A. What should I do? At this time, you need to use a current transformer.   First select a suitable current transformer, and then pass the cable through the current transformer. At this time, the current transformer will induce current from the cable, and the magnitude of the induced current is just reduced by a certain multiple. Send the induced current to the instrument for measurement, and then multiply the measured result by a certain multiple to get the real result.   For example, now you need to measure the current magnitude of a cable. First, pass a cable through a 500/5 current transformer (500/5 is actually 100 times), then connect the current transformer to the ammeter, and the ammeter measures 4A. From this, we can calculate that the real current of the cable is 4*100=400A.   Wiring diagram: Some friends may say that a clamp meter can also achieve this goal. In fact, there is a current transformer inside the clamp meter, and the principle is similar.   Use: 1) The wiring of the current transformer should comply with the series principle: that is, the primary winding should be connected in series with the circuit to be measured, and the secondary winding should be connected in series with all instrument loads 2) According to the size of the measured current, select the appropriate change, otherwise the error will increase. At the same time, one end of the secondary side must be grounded to prevent the primary side high voltage from entering the secondary low voltage side once the insulation is damaged, causing personal and equipment accidents 3) The secondary side is absolutely not allowed to be open-circuited, because once the circuit is open, the primary side current I1 will all become magnetizing current, causing φm and E2 to increase sharply, causing the core to be over-saturated and magnetized, causing serious heat and even burning the coil; at the same time, after the magnetic circuit is over-saturated and magnetized, the error increases. When the current transformer is working normally, the secondary side is similar to a short circuit. If it is suddenly opened, the excitation electromotive force will suddenly change from a very small value to a very large value, and the magnetic flux in the core will present a severely saturated flat-top wave. Therefore, the secondary winding will induce a very high peak wave when the magnetic field passes through zero, and its value can reach thousands or even tens of thousands of volts, which will endanger the safety of the staff and the insulation performance of the instrument.In addition, the secondary side open circuit makes E2 reach hundreds of volts, which will cause electric shock accidents once touched. Therefore, the secondary side of the current transformer is equipped with a short-circuit switch to prevent the primary side from opening. As shown in Figure 1, K0, during use, once the secondary side is open, the circuit load should be removed immediately, and then the vehicle should be stopped for processing. It can be used again after everything is processed. 4) In order to meet the needs of measuring instruments, relay protection, circuit breaker failure judgment and fault recording devices, current transformers with 2 to 8 secondary windings are installed in the generator, transformer, outgoing line, busbar section circuit breaker, bus tie circuit breaker, bypass circuit breaker and other circuits. For large current grounding systems, it is generally configured in three phases; for small current grounding systems, it is configured in two or three phases according to specific requirements 5) The installation location of the protective current transformer should be set to eliminate the non-protected area of ​​the main protection device as much as possible. For example: if there are two sets of current transformers, and the position allows, they should be installed on both sides of the circuit breaker so that the circuit breaker is within the cross protection range 6) In order to prevent the flashover of the pillar current transformer bushing from causing busbar failure, the current transformer is usually arranged on the outgoing line or transformer side of the circuit breaker 7) In order to reduce the damage caused by internal faults of the generator, the current transformer used for automatic adjustment of the excitation device should be arranged on the outgoing line side of the generator stator winding. In order to facilitate analysis and find internal faults before the generator is connected to the system, the current transformer used for measuring instruments should be installed on the neutral point side of the generator.   Principle: In the power supply and electricity lines, the current and voltage vary greatly from a few amperes to tens of thousands of amperes. In order to facilitate the measurement of secondary instruments, it needs to be converted into a relatively uniform current. In addition, the voltage on the line is relatively high. If it is measured directly, it is very dangerous. The current transformer plays the role of current conversion and electrical isolation. Earlier, most of the display instruments were pointer-type current and voltage meters, so most of the secondary currents of the current transformers were ampere-level (such as 5A, etc.).   The current ratio of the primary winding current I1 to the secondary winding current I2 of the current transformer is called the actual current ratio K. The current ratio of the current transformer when working at the rated working current is called the rated current ratio of the current transformer, expressed as Kn.   Kn=I1n/I2n I. What are the common faults of the current transformer? How to judge and deal with it? What items should be checked during normal inspections. A. Common faults of current transformers are: 1. The secondary side of the current transformer is open 2. The current transformer is overheated during operation 3. Smoke or odor inside the current transformer 4. The screws of the current transformer coil are loose, and there is a short circuit between turns or layers 5. Discharge inside the current transformer, abnormal sound or discharge sparks between the lead and the shell 6. The oil-filled current transformer has serious oil leakage or the oil level is too low   B. Usually, judgment and treatment should be carried out according to the abnormal phenomenon that occurs. For example, use a temperature test wax sheet to check the heating condition, and judge whether it is open circuit according to the sound and meter indication value. Once a fault is found, it should be repaired or replaced immediately. The items of normal patrol inspection generally include:   1. Check for overheating and abnormal odor 2. Regularly check the insulation condition 3. Check whether the three-phase indication value of the ammeter is within the allowable range and whether it is overloaded 4. Whether the porcelain part is clean and complete, whether there is damage and discharge 5. Whether the oil level of the oil-filled current transformer is normal, and whether there is oil leakage 2. Why is the secondary side of the current transformer not allowed to be open circuit? What are the dangers after opening the circuit?   1. Usually, the primary current of the current transformer has nothing to do with the current of the secondary load. When the current transformer is operating normally, since the secondary side impedance is very small (close to the short circuit state), most of the magnetic lines of force generated by the primary current are compensated by the secondary current, the total magnetic flux density is not large, and the secondary side potential is not high. But when the secondary circuit is open, the secondary current is equal to zero, and the primary current completely becomes the excitation current, generating a very high potential in the secondary coil (the peak value can reach several thousand volts or even higher), which may not only damage the secondary insulation, but also threaten personal safety. In addition, excessive increase in the core magnetic flux density may also cause the core to overheat and be damaged.   III. Hazards of long-term overload of current transformer Once the current transformer is overloaded for a long time, the core magnetic flux density will reach saturation, increase the error of the current transformer, and the meter indication will be incorrect, so it is not easy to grasp the actual load or operation. In addition, due to the increase in magnetic flux density, the core and secondary coil will overheat and the insulation will be damaged.   IV. Signs and treatment of the secondary side of the current transformer open circuit: When the secondary side of the current transformer is open, it is often accompanied by the following phenomena:   1. The ammeter and power meter indicate zero, the electric meter does not rotate, and a buzzing sound is emitted. 2. The current transformer itself has a squeaking discharge sound or other abnormal sounds, and the terminal block may be burnt.   When the current transformer is open-circuited, the potential generated is related to the primary current. Therefore, when dealing with the open-circuit fault of the current transformer, it is necessary to reduce the load or make the load zero, and then use insulating tools to handle it. The corresponding protection device should be disabled during the handling.

When we choose an inductor, we need to choose different inductors for different circuit boards. At the same time, we also need to see what the role of the inductor is in the circuit. Only in this way can we pre-select the desired inductor from many inductor types. So what should we pay attention to when using a magnetic ring inductor in the circuit? Today, let's learn about the precautions for selecting a magnetic ring inductor.   We all know the importance of inductor selection to the progress of a plan. If there is a problem with the inductor selection in the plan, it will seriously delay the construction period, waste manpower, funds, etc. and cause significant losses. When selecting a magnetic ring inductor, pay attention to the following points:   1. The inner diameter of the magnetic ring inductor is often larger than its own wire diameter, so as not to cause damage to the circuit board wire.   2. When we choose a magnetic ring inductor, we must also know what its role is in the circuit, that is, what kind of clutter should be resisted in the circuit, whether it is high frequency or low frequency, because this is about the selection of its important component-the magnetic core. There are two main types of magnetic ring inductor cores: manganese core and nickel core. Nickel core anti-interference magnetic ring belongs to high-frequency anti-interference. Its magnetic permeability generally ranges from tens to one thousand. Its magnetic permeability is low, and the loss is very small under high-frequency operation. It can work in high-frequency short waves. Manganese core magnetic ring inductor is opposite to nickel core. The selection of these two magnetic cores must be made by customers according to the actual application of magnetic ring inductor.   3. There is another important factor in the selection of magnetic ring inductor-wire diameter. The size of the wire diameter should be determined according to the actual current of the magnetic ring inductor.   In short, when selecting magnetic ring inductor, if the installation space allows, try to choose a long length, large outer diameter, and inner diameter that fits the connecting wire, so that the anti-interference performance will be stronger.   If the magnetic ring inductor in the circuit is not selected correctly, or it is not installed properly during installation, the magnetic ring inductor will not play the due anti-interference role, resulting in serious consequences of equipment damage. Therefore, the magnetic ring inductor should be used accurately.

The split core current transformer is a sensor instrument that can be used for current measurement and microcomputer protection. Because of the characteristics of the split-type core that can be customized, opened and easy to install, it is widely used in the fields of AC motors, lighting equipment, air compressors, and current monitoring of heating, ventilation and air conditioning devices, power management, building self-control systems, and industrial power grid transformation.   The split core transformer core produced by Hemei Electronics can not only be customized according to customer requirements, but also have a measurement accuracy of up to 0.2S level. In terms of materials, the split-type transformer core uses high-magnetic induction high-quality silicon steel sheets with excellent characteristics such as high magnetic flux density, low iron loss and low magnetostriction; in production and processing, a high-precision slitting machine is used to slit the silicon steel sheets, and then after computer-controlled fully automatic winding and winding forming and high vacuum annealing, it is cut into the size and shape required by the customer by a precision cutting machine, which ensures the accuracy and stability of the core and can be better applied to the field of split-type transformers.   Material: silicon steel, Permalloy   Thickness: 0.23mm, 0.27mm, 0.30mm   Annealing: ultra-high vacuum annealing   Specifications: customized according to customer requirements, ring, rectangle, special shape are all available   Price: Depends on the material and shape   II. Comparison of advantages and disadvantages of open-type current transformer   1. Advantages:   This type of current transformer uses high-quality imported silicon steel sheets with high magnetic permeability as magnetic conductive materials. It has the characteristics of divisible iron core and small magnetic circuit loss. Its semi-circular iron core and secondary winding are vacuum cast in a flame-retardant plastic shell with high-quality epoxy resin, which is moisture-proof, stable in performance, and maintenance-free.   2. Disadvantages:   Since the iron core is separated, the accuracy cannot be too high. Generally, the highest accuracy is 0.5.   During installation, clamp the two semicircular rings on the phase-splitting cable and hold it tightly with a clamp. The three elastic rubber rings press against the cable and integrate it with the cable, which is harmonious and beautiful. It is applicable to 10KV and 35KV cables of 35mm-400mm.   III. Applicable occasions   Applicable occasions: general measurement and protection in power systems with strong mobility or narrow space.

Is the split core transformer good? What are the disadvantages of the split core current transformer?   What is the split core transformer? Is the split core transformer good? The split core current transformer is suitable for indoor devices with a rated voltage of 10kV and below. It is used for circuit control, measurement, line transformation measurement and protection. So what are the disadvantages of the split core current transformer? The link of the induction current in the split core transformer is disconnected, that is, the induction core is not a closed whole, and the magnetic circuit efficiency is reduced at the gap. It is difficult to make a complete fit after the opening, so there will be a certain impact on the induction effect and accuracy.   Is the split core transformer good? The split core current transformer is suitable for indoor devices with a rated voltage of 10kV and below. It is used for circuit control, measurement, line transformation measurement and protection.   Structure introduction of split core current transformer This current transformer adopts a high-strength PVC shell and a fully cast busbar structure. The transformer is directly stuck on the cable. Three elastic rubber rings are against the cable and the cable is integrated. The transformer core is made of high-quality silicon steel sheets, and the secondary wire is evenly wound on the core. The transformer is an split core structure and can be installed without cutting the cable.   Application scope of split core current transformer 1. The altitude of the installation site does not exceed 3000m; 2. Ambient temperature: -25—+40℃; 3. The outer diameter of the primary cable that can be worn: φ8—φ240mm 4. Input: 0~60KA 5. Output: 0~500mA 1A or 5A 5VDC or 4~20MA (customer-defined) There is no pollution, corrosive and explosive media in the atmosphere that seriously affect the insulation performance of the transformer.   What are the disadvantages of split core current transformers 1. The working noise is relatively loud 2. The heat is relatively large 3. The measurement error is relatively large 4. The price is high   The link of the induction current in the split core transformer is disconnected, that is, the induction core is not a closed whole, and the efficiency of the magnetic circuit is reduced at the gap. It is difficult to make it fit perfectly after opening, so it will have a certain impact on the sensing effect and accuracy.

The split core current transformer can convert high voltage into low voltage and large current into small current for measuring or protecting the system. What is its accuracy check like? The following is the editor's summary:   1. Error breakdown The split current transformer test generally uses the comparison of the measured current and the standard current, and the secondary current difference is the error. This inspection method is called the comparison method. The standard product requires two levels higher than the measured product, and the error can be ignored at this time. If the standard product is only one level higher than the measured product, the error of the test result plus the error of the standard product should be considered.   2. Calibration: In addition to the standard product and the calibrator, there should be a current booster that can provide the primary current for the split current transformer, a voltage regulator, and a load that can adjust the current of the current booster.   3. Usually, a calibrator is used to measure the quantity. Since the product calibrator measures the ratio of the current difference between the measured product and the standard product to the secondary current, the requirements for the calibrator are not high. What level of split current transformer can be checked is basically determined by the standard product.   In order to transmit electrical energy, split core current transformers often use AC voltage and high current circuits to deliver electricity to users, and this electricity cannot be directly measured by instruments.

Not necessarily.   The magnetic force F of the magnet is the product of the magnetic field magnetic induction intensity gradient deltaB and the magnetic moment m, F=deltaB*m.   The purpose of adding an iron core to the solenoid coil is to make the magnetic field generated by the solenoid magnetize the magnetic material of the iron core to increase its magnetic moment. The magnetic moment of the helix is ​​m1=NIS, the magnetic moment of the iron core is the volume component of its magnetic field intensity M m2=MV, and the magnetic field intensity M of the magnetic material is the magnetic field intensity H of the solenoid multiplied by the magnetic permeability u of the magnetic material, and the magnetic permeability is the product of the relative magnetic permeability u0 of the vacuum and the relative magnetic permeability ur of the magnetic material (i.e. u=u0*ur).   Finally, F=(m1+m2)*deltaB=(NIS+Mv)*deltaB=(NIS+uo*ur*H*v)*deltaB. The relative magnetic permeability ur of Permalloy is indeed very high. If the current in the solenoid is very small, that is, the magnetic field intensity H generated by the solenoid is very small and has not yet reached the saturation of Permalloy, its suction will indeed increase; but the saturation magnetic induction intensity of Permalloy is low, and the magnetic field generated by the solenoid reaches 7000A/m, which can basically magnetize it to saturation, and its suction will not continue to increase.   Therefore, your answer is not necessarily. When the current of the solenoid is small and has not yet saturated the magnetic core, its suction can be increased; but if the current is large and saturates it, a magnetic material with high saturation magnetic induction intensity and high relative magnetic permeability should be selected.

Classification of magnetic materials   Magnetic materials are divided into two types: soft magnetic materials and hard magnetic materials. Magnetic materials that are easily demagnetized after magnetization are called soft magnetic materials, and their coercive force is very small. Hard magnetic materials (such as magnetic steel and permanent magnetic alloys) are not easy to demagnetize.   Soft ferrite cores are an important category of magnetic materials. They are widely used, such as magnetic rods in radios, magnetic cores in tape recorders and televisions, magnetic rings of deflection coils, magnetic heads of video recorders, and high-frequency transformers in switching power supplies. Soft ferrite cores come in many varieties and shapes, and can be roughly classified as follows:   (1) Classification by shape: mainly threaded cores, ring cores (referred to as magnetic rings), tubular cores, pot cores (i.e. magnetic pots), E-shaped, sun-shaped, U-shaped, T-shaped, I-shaped, and Wang-shaped cores. In addition, there are single-hole, double-hole, and multi-hole cores.   (2) Classification by working frequency: there are low frequency, medium frequency, high frequency and very high frequency cores.   (3) Classification by material: the material grades are as follows: MXO-manganese zinc ferrite; NXO-nickel zinc ferrite; NQ-nickel lead ferrite; NGO-nickel zinc high frequency ferrite; GTO-very high frequency ferrite.

Components related to "magnetism" in circuit boards include Permalloy cores, inductors, transformers, electromagnetic relays, contactors, Hall sensors, etc. This article explains the inspection and maintenance methods of magnetic components in circuit boards.   (1) Inductor Inductor coils are wires wound around an insulating frame, which can be hollow, iron core or magnetic core. In the application of industrial control circuit boards, the most common use is for filtering or energy storage in switching power supplies. Various appearances of inductors. The unit of inductance is Henry, abbreviated as Henry, represented by the letter H. There are also millihenry (mH), microhenry (uH), and nanohenry (nH). The relationship between them is: 1H = 1000mH 1mH = 1000uH 1uH = 1000nH Inductor coils use direct marking method, 22uH, 100 represents 10uH, 4R7 represents 4.7uH, R10 represents 0.1uH, and 22n represents 22nH; some inductors use color ring marking method, and their inductance is the same as the color ring resistor, such as color ring brown, black, brown, and silver represent inductance 100uH ±10% There is a type of inductor used to absorb ultra-high frequency (above 50MHZ) interference, this type of inductor is called magnetic beads. There is another type of commonly used inductor called common mode inductor, also called common mode choke. It is a 4-terminal device led out by two identical windings wound on a ferrite core (Permalloy core). Each set of coils is connected in series in the circuit. If there is a differential mode signal, the magnetic flux generated by the signal through the two coils cancels each other, and the coil has no blocking effect on the differential mode signal. When there is a common mode signal, the magnetic flux generated by the two coils is enhanced, and the coil's blocking effect on the signal is enhanced. This blocking effect is bidirectional, which can not only prevent the front-stage interference signal from entering the rear stage, but also prevent the rear-stage interference signal from entering the front stage. In the maintenance of industrial circuit boards, inductor coils are components that are not easy to damage. Occasionally, they are broken due to corrosion, burned due to excessive current, and short circuits between coil turns. Open circuit damage can be measured with the resistance range of a multimeter. The inductance can be measured with an inductance tester. It is recommended to use a digital bridge to test the inductance. Because most power circuit energy storage inductors operate at higher frequencies, all above 10kHz, the frequency is selected at 10kHz when using a bridge test. In addition to paying attention to the inductance, the test focuses on the D value. The normal D value should be less than 0.1. If the D value is greater than 0.2, it is determined that there is a short circuit between the coil turns.   (2) Transformer The transformer is a device that uses the principle of electromagnetic induction to change the voltage. Common transformers in industrial control circuit boards are power frequency transformers using iron cores and switching transformers using ferrite cores (Permalloy cores). The basic characteristics of an ideal transformer are: the ratio of the input and output AC voltages is the same as the ratio of the number of turns of the input and output coils, so in theory, the AC voltage can be arbitrarily stepped up or down. Transformers with silicon steel sheet cores are generally used in industrial frequency applications of 50~400HZ. The magnetic flux density of the silicon steel sheet core is large. Although there is insulation paint between the stacked silicon steel sheets, there is still eddy current loss in a single silicon steel sheet. This type of core is not suitable for high-frequency applications. The resistivity of ferrite core is much greater than that of metal and alloy magnetic materials, so the eddy current loss is very small. Transformers made of ferrite core are used in relatively high-frequency occasions such as energy storage inductors and switching transformers of switching power supplies. In addition, different new transformer core materials have appeared, such as Permalloy and amorphous nanocrystalline materials, which can take into account both magnetic permeability and eddy current loss. Transformer failure detection method Common transformer damages include coil burnout or internal overheating that burns the coil insulation and causes a short circuit between coil turns. It is easier to judge the coil open circuit by measuring the resistance, while the short circuit between turns is more troublesome to judge because the coil itself has a small resistance and is not easy to distinguish through resistance testing. Generally speaking, transformers with serious internal short circuits between turns generate more heat, which will burn the covering material of the transformer coil and have more or less burnt smell. This situation can be clearly distinguished by observing the appearance of the transformer. Some transformers have internal turn-to-turn short circuits, which are not so obvious from the appearance. Friends who often repair switching power supplies may have such an experience, that is, they have tested and even replaced almost all suspected components of the switching power supply except the transformer, including the Permalloy core, but the power supply has not been repaired yet, and finally they suspect that the switching transformer is damaged. If there is a way to detect transformer damage at the beginning, wouldn’t it be easy? In fact, this is completely possible, and the instrument for detection is still a digital bridge. The method is to put the digital bridge in the 10KHZ test inductance loss D value state, and test it online without removing the transformer. The bridge signal voltage is selected as 0.3V, and the D value of the transformer main winding coil is tested. The normal transformer D value should be <0.1. If the D value is >0.2, the transformer is judged to be damaged. In addition to switching transformers, digital bridges are also applicable to determine whether other types of transformers are damaged, but it should be noted that when selecting the frequency, a frequency close to the actual operating frequency of the transformer should be used.   (3) Electromagnetic relays and contactors Electromagnetic relays and contactors are devices that use the electromagnetic force generated by electromagnetic coils in conjunction with springs and mechanical levers to control the on and off of contacts. Relays usually have a sealed packaging space to minimize the impact of external adverse environments on contacts. Relative to contactors, the contact current they control is smaller; the contact current of contactors is larger. There are also reed relays, whose principles are similar to those of electromagnetic relays, but the contact current is relatively smaller, the contacts are sealed, and are not polluted by dust, moisture and harmful gases, and the response speed and reliability are greatly improved. Common faults of relays and contactors are large contact resistance, burnt contacts, and open circuit when contacts are closed. When testing, the rated voltage can be applied to the coil to detect the conduction and closure of the contacts. Both the coil and the non-powered conditions must be tested. The ohm range of a multimeter can be used to measure the resistance of the contacts when they are on. If there is no abnormality, it is basically close to 0Ω. If it is above 10Ω, it is considered a fault. If the contacts are visible, emergency maintenance can be performed by filing off the ablated and oxidized parts of the contacts to reveal the metallic luster. The relay or contactor can be put back into use. For safety reasons, it is recommended to replace new parts. After the relay coil is energized, the energy is transmitted to the coil and the armature is attracted. After the power is cut off, if no measures are taken, the electromagnetic energy of the coil will inevitably generate a high self-induced electromotive force at both ends of the coil during the transition from power on to power off. There will be a high voltage, which may damage other components. Therefore, a diode should be connected in reverse parallel to the coil to provide a release circuit for the electromagnetic energy of the coil. When testing the quality of the relay online, a reverse coil rated voltage can be applied to the diode end according to the direction of the diode for detection without removing the relay to detect the Permalloy core. In high current occasions such as inverters and servo drives, many current detections require Hall sensors. The working principle of Hall current sensors is based on the Hall effect. A certain current is passed through a conductive sheet in the x direction, and the magnetic field in the z direction passes through the sheet vertically. Then, the electrons in the conductive sheet are acted upon by the Lorentz force in the process of moving toward the negative pole, and gather in the y+ direction, making one end in the y+ direction negatively charged and the other end in the y- direction positively charged. If the voltage VH at both ends is measured, its magnitude is proportional to the current I and the magnetic induction intensity B. If the current I is constant, then the magnitude of VH directly reflects the magnitude of the magnetic induction intensity B, so as long as VH is measured, the magnitude of B can be known. The principle of the Hall current sensor is that the through-core conductor generates a circumferential magnetic field proportional to the current. The magnetic field passes vertically through the Hall sensor in the middle of the iron core. The Hall voltage Vh induced by the sensor is proportional to the measured current of the conductor, so the current of the measured conductor can be measured contactlessly. The actual Hall sensor has three wires, two positive and negative power lines, and one current lead line. A sampling resistor is connected in series between the current lead line M and 0V. The direction and magnitude of the current flowing through the sampling resistor are proportional to the magnitude and direction of the current passing through the sensor wire. Therefore, the magnitude and positive and negative of the voltage at both ends of the sampling Permalloy core resistor reflect the magnitude and direction of the wire current. Detection method of Hall current sensor It is common for the current sensor to be damaged. The most convenient test method is to test the voltage of the output end to 0V after power is turned on. If there is no current in the core wire, the voltage at the sensor signal output end should be 0V. If the measured voltage offset is more than ±1V, it is judged that there is a problem with the Hall current sensor and the Permalloy core. Some Hall sensor Permalloy cores are connected to a single power supply. When there is no current in the corresponding core wire, the signal output voltage is half of the power supply voltage. If a 5V voltage is connected, the output voltage is 2.5V.