What is resistance?
The resistance refers to the resistance encountered in the circuit, or the ability of the object to obstacle the current
The larger the resistance, the greater the resistance of the current, the smaller the current. Conversely, the smaller the resistance, the smaller the resistance suffered by the current, and the larger the current is.
The symbol of the resistance is “R”. The unit of the resistance is Ohm, referred to as Europe, and is represented by the letter “ω”.
Any object has resistance, and the conductor is no exception. Everyone may have such an experience. When the rice cooker is cooking, the wire will be a little heated. The reason is that because the copper of the creation of the wire has a resistance. Electricity is distributed in a hot way, as shown in Figure 1-7.
So is the resistance perfect? of course not. It is because of the existence of resistance that we can control the size of the current. In order to make the current work according to people’s wishes, people have created a resistor.
The resistor is an element that limits the current. It is usually referred to as a resistor for short. It is the most fundamental and most commonly used electronic component. It is generally applied to various electronic circuits.
Common resistors are shown in Figure 21.
Due to the different manufacturing materials and structures, there are many varieties of resistors. Common carbon membrane resistors, metal membrane resistors, organic core resistors, wire wound resistors, rated tap resistors, variable resistors, slide line types, slide line types Vertencers and sheet resistors.
In electronic manufacturing, commonly used carbon membranes or metal membrane resistors. The carbon membrane resistance has the characteristics of high stability, good high -frequency characteristics, small negative temperature coefficients, stable pulse load, and low capital. The application is common. The metal membrane resistance has characteristics such as high stability, small temperature coefficient, good thermal resistance, small noise, wide operating frequency range and small volume, etc. The application is also very common.
How to identify the resistor
The text symbol of the resistor is “R”, and the graphic symbol seems to be shown in 2-2.
The model naming of the resistor consists of 4 parts, as shown in Figure 2-3.
The first part of the letter “R” represents the main name of the resistor, the second part of the letter represents the data of the resistor, the third part is used to represent the classification of the resistor with numbers or letters, and the fourth part is used to represent the serial number. See the significance of the resistor model for Table 2-1.
For example, a resistor model is RT11, which means that this is an ordinary carbon membrane resistor. The model of a resistor is RJ71, which means that this is a fine metal membrane resistor.
What are the characteristics of the resistor
The characteristics of the resistor are that the DC and communication are thick. Any current must be obstacles and restrictions through the resistor, and the current must generate voltage drops on the resistor, such as
Figure 2-4 shown.
How to understand the parameters of the resistor
The main parameters of the resistor are
(1) resistance value
The resistance value is referred to as resistance, the fundamental unit is Ohm, referred to as Oh (ω). Commonly used units include thousands of euros (KΩ) and Zhaou (MΩ). The conversion relationship between them is 1MΩ = LOOOKΩ, 1kq-1000Ω. There are two types of resistance on the resistor on the resistor.
, Directly print the PN value of the electric PN on the resistor. For example, the words “5.1” or “5R1” are printed on the 5.1Ω resistor. The resistance in the 6.8kΩ resistor is “6.8K” or “6K8”, as shown in Figure 2-5.
Color ring method
, That is, 4 or 5 color rings are printed on the resistor to indicate the resistance value. The unit of the resistance value is ω.
Regarding the 4 ring resistor, the L and 2 ring represent the two valid numbers, the third ring represents multiple multiplications, and the fourth ring represents allows bias, as shown in Figure 2-6. Regarding the 5 ring resistor, the L, 2, and 3 ring represents the three-bit effective number, the fourth ring represents multiple multiplications, and the fifth ring represents allows bias, as shown in Figure 2-7.
The color rings are generally 12 colors of black, brown, red, orange, yellow, green, blue, purple, gray, white, gold, silver, and their significance is shown in Table 2-2. For example, the 4 -color ring of a resistor is “yellow, purple, orange, and silver” in order, and its resistance value is 47kΩ and the error is ± 10%. The 5 -color ring of a resistor is “red, yellow, black, orange, and gold” in turn, and its resistance value is 240kq and the error is+5%.
In electronic manufacturing, 4 ring or 5 rings resistance can be used. In terms of frequency -frequency and bias circuits, the resistance of small errors should be selected as much as possible. If necessary, you can use the Om table to detect the selection.
(2) Rating power
The rated power is another main parameter of the resistor. The power of the common resistors is 1/8W, 1/4W,)/2W, 1W, 2W, 5W, etc. The symbols are as shown in Figure 2-8, which is more than 5W. Indicate with numbers.
In the use, a resistor with a rated power equal to or a large ten circuit should be selected. The circuit diagram does not indicate the power consumption of the resistor at the work of the resistor, but you don’t need to think about it. For example, there is no request for the power of the resistor in a large amateur electronic manufacturing. At this time, the L/8W or 1/4W resistor can be selected.
Classification of resistance
Resistance, English name Resistance, usually abbreviated as R. It is a basic nature of the conductor, which is related to the size, material, and temperature of the conductor. Ohm’s Law said, I = U/R, then R = U/i, the basic unit of resistance is Ohm, which is expressed in the Greek alphabet “ω”. There is such a definition: when the conductor is added with a volt voltage, a ampel current generates a ampel current. The corresponding resistance value. The main function of the resistance is to prevent current flow. In fact, “resistance” is a nature, and the resistance that usually referred to in electronic products refers to a component such as resistors. The master said to the apprentice: “Find a 100 -Euro resistor!” It refers to a resistor with a “resistance value” of 100 ohms, and Ohm is often referred to as Euro. The common unit of resistance values is thousands of euros (KΩ) and Zhaou (MΩ).
The resistance is the easiest component and the most widely used electronic component, which accounts for about 35%of all electronic components.
Carbon membrane resistance
The hydrocarbons are decomposed in high temperature and vacuum, deposited on porcelain sticks or porcelain tubes to form a layer of crystalline carbon membrane. Change the thickness and length of the carbon membrane can get different resistance.
Advantages: The cost of carbon membrane resistance is low.
Disadvantages: Poor stability and large errors. It is the largest resistance element in electronics, electrical appliances, and information products, and the carbon membrane resistance is darker.
The allowable errors are mainly:
± 5%, ± 10%, ± 20%mostly used for low -required circuits.
Metal membrane resistance
Heating alloys in vacuum and evaporation of alloys to form a layer of conductive metal membrane on the surface of the porcelain stick. Changing the thickness of the metal membrane can control the resistance value. Compared with this resistance compared to the carbon membrane resistor:
The volume is small, the noise is low, and the stability is good, but the cost is high. The color of the metal membrane is bright, and it can be subdivided into a variety of types such as high -frequency, high pressure, and precision.
The allowable errors are: ± 0.1%, ± 0.2%, ± 0.5%, ± 1%more applied in occasions with higher accuracy requirements.
Metal oxide film resistance (RY)
Spray the surface of the hot ceramic skeleton with a metal salt solution such as tin and 金 to the surface of the hot ceramic skeleton. This type of resistance and thermal stability are good, and the rated power range is 1/8W ~ 50KW.
Suitable for non -burning, temperature resistance, humidity resistance and other occasions.
Wire wound resistance
The resistance value of the wire wound resistor, the stable work, the temperature coefficient, the heat resistance, the heat resistance, the high power, but the resistance value is small, the distributed inductance and distributed capacitance are large, and the production cost is also higher.
Suitable for low -frequency and high accuracy requirements.
High power cable winding resistance (RX)
Use Kang copper or nickel chromium alloy wire resistance wire around the ceramic skeleton. This resistance is divided into two types: fixed and variable. It is characterized by stable work, good thermal resistance, and small error range.
Suitable for high -power occasions, the rated power is generally more than 1W.
Organic solid resistance (RS)
Organic solid solid resistors are mixed with granular conductive, filling and adhesives and other materials, and then pressed together, and then installed in a resistor composed of a plastic shell. Its lead is directly pressed in the resistor body. Due to the large cross section of this resistor conductor, it has strong overload capacity, high reliability, and low price. Its main disadvantage is low accuracy.
This kind of resistor is generally used where the load cannot be disconnected and the working load is large, such as the circuit of the audio output headset connecting the headset
The fuse resistance, also known as the fuse resistance, is a component with dual function of resistance and fuse. Most of the melting resistance is gray. Use color rings or numbers to represent the resistance value, and the rated power is determined by the resistance size. When using it normally, it has the characteristics of the electrical appliances of ordinary resistance. Once the circuit fails, it will melt it within the specified time, thereby protecting the role of other important components. At present, non -fixed (one -time) insurance wire resistance is generally used at home and abroad. Its rated power is 0.25W, 0.5W, 1W, 2W, 3W and other specifications. The resistance value can be 0.22 ~ 5.1K.
Use high -value and protected circuit components in series, and is often used in power and secondary power circuits.
Cemental resistance is also a fuse resistor. The resistance line is wrapped on the heat -resistant porcelain. The outside is fixed with heat -resistant, humidity and corrosion -resistant materials. Cemental resistance is made of the resistor into the rectangular porcelain box, and is sealed with a special non -combustible thermal cement charging. It is quickly melted when the circuit is over flow to protect the circuit.
Zero Om resistance
Plug -in: zero resistance value, no words on the resistance, there is a black line in the middle. Zero Om symbol mark
Patch: The number “0” is marked above.
When the PCB board is wiring, it is inevitable to cross the wiring. In order to prevent the wiring circles, the bridge can be used to install zero ohm resistance.
Power -type wireless resistance resistance
(Aluminum shell resistance)
The special line winding method is used to make the inductive measurement only one of the dozens of people in general lines. The metal shell is conducive to heat dissipation.
It is suitable for high -power circuits and a harsh environment of magnetic fields, so it is often called power resistance.
Network Resistor, which is a network resistor (Wire-Wound Resistor). Dipping is encapsulated together in the resistance set with exactly the same parameters and combined. One of their pins is connected together as a public pin. The rest of the pins lead normally. So if a drainage is composed of N resistors, then it has N+1 pins. Generally speaking, the leftmost one is a public pin. It is generally marked with a color point in the discharge. Dipholics have the advantages of convenient assembly and high installation density. At present, it has been widely used in television, monitors, computer motherboards, and small appliances. There is usually a public end, which is represented by a small white point on the surface of the packaging. Its color is usually black or yellow. Dipping is generally used on digital circuits, such as: as a pull -up or drop -down resistor as a parallel port. It is more convenient to use the resistance than a number of only fixed resistors.
Dipping is the abbreviation of a row of resistors, which is a thick film resistance network with a variety of ways. Dipping is generally used in digital circuits, instrument circuits and computer circuits, such as the decayer in the instrument circuit.
Classification according to the resistance body material
Metal oxide film type
Glass glazed membrane type
Synthetic carbon film
Inorganic solid type
Power -type resistor
High -voltage resistor
High -frequency resistor
Explanation according to the material of the resistance:
1. Carbon film resistor
The carbon membrane resistor is made of crystal carbon that is decomposed by vacuum temperature and heat decomposition on the cylindrical or tube -shaped ceramic skeleton. Use the thickness of the carbon membrane and the carvings to control the resistance value. The shape and structure of the carbon membrane resistor are shown in Figure 2.
Carbon membrane resistor
碳膜电阻器有良好的稳定性,负温度系数小,高频特性好,受电压和频率影响较小,噪声电动较小,脉冲负荷稳定,阻值范围宽,制作工艺简单,生产成本低, So it is widely used in various electronic products.
Metal membrane resistor
Metal membrane resistors are made of metal or alloy materials with vacuum heating on the porcelain base to form a layer of film. It is also made of high -temperature decomposition, chemical deposition, and burning. Show.
Figure 3 Metal membrane resistor
The stability and thermal resistance of the metal membrane resistor are good, the temperature coefficient is small, the operating frequency range is large, and the noise electromotivity is small. It is often used in high -frequency circuits.
Metal oxide film resistor
Metal oxide film resistors are made of metal salt solution (tin tin tin and tin oxide) such as tin and pupae to the surface of the hot ceramic skeleton in the heating furnace of about 550 ° C. The conductive membrane layer of this resistor is uniform, the membrane and the skeleton matrix are firm, and some performance is better than the metal membrane resistor. The shape of the metal oxide film resistor is shown in Figure 4. The shape of the ordinary metal oxide film resistor is basically the same as that of the metal membrane resistor. The structure is mostly cylindrical and the axial formula.
Figure 4 Metal oxide film resistor
Metal oxide film resistors have strong anti -oxidation capacity than metal membrane resistors, strong ability to resist acid and salt, and have good thermal resistance. The disadvantages of the metal oxide film resistor are due to the characteristics of the material and the limitation of the thickness of the membrane layer. The resistance range is small, and its resistance range is 1Ω to 200 kΩ; the rated power is 1/8 ~ 10 W; 25 w ~ 50 kW.
Synthetic carbon film resistor
The synthetic carbon membrane resistor is a carbon black, fillers and organic adhesives into suspension, and re -applied to the insulated skeleton, and aggregate by heating. Its resistance range is high and can reach 10 ~ 106 mΩ; the rated power is 1/4 ~ 5 W; the maximum operating voltage is 35kV. Its disadvantages are poor humidification, low voltage stability, poor frequency characteristics, and large noise. This resistor is not suitable for general resistors. This resistor is mainly suitable for high -voltage and high -resistance resistors, and is often packaged by glass shells to make vacuum -European resistors for micro -current testing. Its shape is shown in Figure 5.
Figure 5 Synthetic carbon film resistor
Organic synthetic solid resistor
Organic synthetic solid resistors are made of carbon black, graphite and other conductive substances and fillers with organic adhesives into powder, and are made into plastic shells after the hot pressure of dedicated equipment. The lead pressure plastic of the solid resistor is in the resistor body. One is an universal hat, and the other is a resistor with end caps and the end cap as the electrode. The shape and structure of organic solid resistors are shown in Figure 6.
Use high -value and protected circuit components in series, and is often used in power and secondary power circuits.
Figure 6 Organic synthetic solid resistor
This resistor has high mechanical strength, good reliability, and has strong overload capacity; small volume, low price; large inherent noise, large distribution parameters, poor voltage and temperature stability, resistance range of 4.7Ω ~ 22 mΩ; The working voltage is 250 ~ 500 V; the rated power is 1/4 ~ 2 W. This resistor is not suitable for being used in electrical circuits that require higher electrical appliances. At present, common organic synthetic solid resistors include RS11 and RS types. RS organic solid cardiac resistance is commonly used on the car instrument (oil pressure gauge).
Glass glaze resistor
The glass glaze resistor is mixed with metal silver, crickets, and crickets such as metal oxides and glass glazed adhesives into pulp. It is applied to the ceramic skeleton and sintered by high temperature. At present, the resistor is mostly made of oxide and glass glaze adhesives. Metal glass glaze resistors have ordinary and precise types. The shape and structure of the glass glaze resistor are shown in Figure 7.
This resistor is resistant to high temperature, good wet resistance, good stability, small noise, small temperature coefficient, large resistance range, and the resistance range is 4.7Ω ~ 200 mΩ L/2 W, 1 W, 2 W, high power 500 W; the maximum voltage is 15 kV.
Wire wound resistor
The wire wound resistor is a resistor made of citrus, manganese copper, or nickel chromium alloying in the ceramics skeleton with a pyrine -like resistance material. Some surfaces of this resistor are covered with a layer of glass glaze, which is often called glass glaze wire wound resistors; some surfaces are covered with layer of protective organic paint or varnish, called paint wire wound resistors; Naked line winding is called a naked wire winding resistor. In addition to the protective effect on the resistance, the surface -coated protective layer is also conducive to maintaining the stability of its resistance when changing the working environment conditions. The shape of the wire wound resistor is shown in Figure 8.
The noise of the wire wound resistor is small, or even no current noise; the temperature coefficient is small, the heat stability is good, the high temperature resistance can reach 315 ° C; MΩ; the rated power is 1/8 ~ 500 W. The disadvantage is poor high -frequency performance.
Explain according to the use of resistance:
(1) Ordinary type.
Refers to resistance that can adapt to general technical requirements. The rated power range is 0.05, √2W, and the resistance value is 1 q ~ 22mq. The allowable error is ± 5070, ± 10%, ± 20020, etc.
There are high precision and stability resistors. The power is generally not greater than 2W. The nominal value is between O.OIQ ～ 20mq. The accuracy is between ± 2020 ~ ± o.oolozo.
(3) High -frequency type.
The resistance of the resistance itself is very small, which is often called inductive resistance. For high -frequency circuit, the resistance value is less than LKQ, the power range is wide, and the maximum can reach LOOWO
(4) High -voltage type.
For the resistance in high-voltage devices, the power is between 0.5-15W, the rated voltage can reach more than 35kV, and the nominal yang value can reach LGQO
(5) High -resistant type.
The resistance value is above 10mq, and it can reach up to L014QO
(6) resistance network
(Resistance row) O comprehensive film mask, photocalism, sintering and other process techniques, make multiple parameters and performance resistance on a substrate, connect to a resistance network, also called
(7) Sensitive resistance.
Various types of sensitive resistors can be divided into two types: slow variable and mutant -type according to their information transmission relationships. They are widely used in technical fields such as detection and automation control.
1) Voltage resistance.
It is mainly Antoxytoma, silicon carbide and zinc oxide voltage resistance.
2) Wet sensitivity resistance.
Wet sensor resistance is composed of sensor wet layers, electrodes, and insulators. Lithium chloride wet -sensitive resistance increases with the increase in humidity and the resistance decreases. The disadvantage is that the test range is small, the characteristics of the characteristics are not good, and the temperature is greatly affected by the temperature. The disadvantage of carbonist resistance is low temperature sensitivity, and the resistance value is greatly affected by temperature and less used. Oxide moisture -sensitive resistance performance is superior, it can be used for a long time, and the temperature is less affected by temperature. The resistance and humidity changes are linear.
3) Optical resistance.
Most of the light -sensitive resistance is made of semiconductor material. It uses the optical conductivity of the semiconductor to make the resistance of the resistor change with the strength of the radiation light. When the radiation light is enhanced, the resistance value is significantly reduced; when the radial light is weakened, the resistance value is significantly increased
4) Qi -sensitive resistance.
Qi -sensitivity resistance uses some semiconductor to absorb some gases after an oxidation and reduction reaction. The main component is metal oxides. The main varieties are metal oxide gas -sensitive resistance, composite oxide gas -sensitive resistance, and ceramic gas -sensitive resistance.
5) Limin resistance.
Limin resistance is a resistor that changes with the change of pressure, which can make various torque meters, semiconductor microphones, and pressure sensors. The main varieties are silicone -sensitive resistors and selenium alloy alloying resistance resistors. Relatively speaking, alloy force sensitivity resistors have higher sensitivity.
The resistance value of the thermistor will show a step jump change with the changes in the body’s temperature and has semiconductor characteristics. The thermistor is divided into a positive temperature coefficient thermistor (referred to as PTC thermistor) and negative temperature coefficient thermistor (referred to as NTC thermistor) o more than a certain temperature (Curie Temperature), PTC The resistance value of thermistor resistance increases with the rise of temperature.
Under normal circumstances, organic polymer PTC thermistor is suitable for overcurrent protection, and ceramic PTC thermistor can be suitable for various purposes.
The resistance value of the NTC thermistor resistance is decreased with a step jump with the temperature. O NTC thermistor is based on metal oxides such as manganese, cobalt, nickel, and copper, and is made of ceramic technology. When the temperature is low, the number of loads of these oxide materials is small, so its resistance value is high; as the temperature increases, the number of loads increases, so the resistance value is reduced.
7) Fractive resistor.
The fuse resistor is commonly known as a felling resistor and is a dual -function element with a melting wire and the resistor. Under normal circumstances, there is a function of ordinary resistors. Once the circuit fails, the resistor will melt the route within the prescribed time due to overload, which will protect other circuits. The fuse resistor is mostly gray, and the color ring or number indicates the resistance value. The melting time of fuse electricity is generally common models of 10SO fuse resistors include RF10, RF11, RRD0910.RRD0911 and other ORF10 surfaces. Only the standard power does not bid.
Compared with the traditional fuse and other protective devices, the fuse resistor has the advantages of simple structure, convenient use, small fuse power, and short fuse time, which are widely used in electronic devices.
8) magnetic resistance.
The magnetic resistance is made of the principle of the resistance value of the resistor using magnetoelectric effects. Its resistance value changes with changes in the density of the magnetic flux through its magnetic flux. Its significant feature is that the relationship between resistance and magnetic field strength in weak magnetic fields is a square relationship, and it has high sensitivity.
What are the uses of the resistor
The main function of the resistor is
(1) Flow limit
The resistance of the resistor restricted the current in the circuit, the larger the resistance value, the smaller the current.
As shown in Figure 2-9, the RMB diode circuit, R is a current-limiting resistor. From the Om Law I = U/R, when the voltage U is certain, the current of the flowing resistor flows the resistor R is inversely proportional to its resistance R. Due to the presence of a current -limiting resistor R, the current of the light -emitting diode VD is limited to 10mA to ensure that the VD work is normal.
The working point of adjusting the transistor is an example of the resistor used as a current. As shown in Figure 2-10, the transistor amplifier circuit is shown, and the electrode current IC (working point) of the transistor collector is resolved by its baseline current IB. Change the resistance of the base resistance RB of the transistor to change the IB, that is, the IC is changed, that is, the working point of the transistor is changed.
(2) pressure reduction
When the current passes through the resistor, the voltage drop will inevitably produce. The larger the resistance value, the larger the voltage drop.
As shown in the relay circuit as shown in Figure 2-11, R is the lower voltage resistance. The size of the voltage drop is proportional to the product of the resistance R and the current I, that is, U = IR. Applying the antihypertensive effect of a resistor R can enable a higher power supply voltage to comply with the request of the work voltage of the component. As shown in the circuit in Figure 2-11, the working voltage of the relay is 6V and the working current is 60mA, and the power supply voltage is 12V. It must be connected in a 100Ω reduction resistor R before working normally.
The load resistance of the amplifier is also an example of the antihypertensive effect of the resistor. In the transistor amplifier circuit as shown in Figure 2-12, the collector resistance R, which is the load resistor. The transliteration signal UI makes the transistor of the transistor set electrode current IC change accordingly. Due to the antihypertensive effect of the RC, the amplified output voltage UO can be obtained from the VT set.
(3) Division of pressure
Based on the antihypertensive effect of the resistor, the resistor can also be used as a regulator.
As shown in Figure 2-13, the resistor R1 and R2 constitute a pressure division. Because the two resistors are connected in series, the current J’s current J is equal, and the voltage drop on the resistance is 1/3U, the upper pressure of R2 was reduced to 2/3U, and the separation pressure (the load resistance must be greater than R1, R2), and the voltage ratio was R1/R2.
The RC filter network is a special pressure division. As shown in Figure 2-14, the R and C2 can be understood as the pressure division, and the output voltage UO is taken from the voltage drop on the C2. Regarding the unlimited capacity of DC C2, the tolerance of the AC C2 is far less than R. Therefore, the DC voltage drop on the C2 is very large, and the exchange voltage drops very small, reaching the purpose of expanding the filtering.
How to choose a resistor
Commonly used resistors are carbon membrane resistors, metal membrane resistors, organic core resistors, glass glaze resistors, wire wound resistors, cement resistors, fuse resistors, etc.
(1) Carbon film resistor
The carbon membrane resistor is a more commonly used resistor-the structure is shown in Figure 2-15. It forms a layer of carbon membrane on the ceramic skeleton as the resistor body, plus the metal hat cover and the lead, the surface, the surface, the surface Apply insulating maintenance paint.
The performance characteristics of the carbon membrane resistor are good stability, the voltage is small, the negative temperature coefficient is small, the applicable frequency is wide, the noise is small, and the price is low. The resistance range of the carbon membrane resistor is usually 1 ~ LOXL060, which is very common in various electronic circuits.
(2) Metal lumbar resistor
Metal membrane resistors are one of the most commonly used resistors. The structure is shown in Figure 2-16. It forms a layer of metal or alloy film on the ceramic skeleton as the resistor body. Insulation and maintenance paint.
The performance characteristics of the metal membrane resistor are high stability, less affected by voltage, small temperature coefficients, good thermal resistance, small noise, wide operating frequency, good high -frequency characteristics, carbon film resistor with the same power than the same power than the same power Many small. The resistance range of the metal membrane resistor is usually 1 to 109Ω, which is very common.
(3) Organic core resistor
The structure of the organic core resistor is shown in Figure 2-17. The resistance body is a solid cylinder made of carbon black, graphite and other conductive substances, mixed organic adhesives. Essence
The performance characteristics of the organic core resistor is that the mechanical strength is high, the overload can be strong, the reliable is better, the volume is low, the price is low, but the noise is large and the stability is poor. The resistance range of the organic core resistor is usually 4.7-22×106Ω, which is generally used in the circuit with a high request.
(4) Glass glaze resistor
The structure of the glass glaze resistor is shown in Figure 2-18. A mixture of a layer of metal oxide and glass glaze adhesive on the ceramic skeleton is made as a resistor body and sintered by high temperature.
The performance characteristics of glass glaze resistors are high temperature resistance and high humidity resistance, good stability, small noise and temperature coefficient, and high reliability. The resistance range of glass glaze resistors is usually 4.7 to 20xl07Ω, which is commonly used in high -resistance, high pressure, high temperature and other places.
(5) Line winding resistor
The wire winding resistor is also one of the more commonly used resistors, and the structure is shown in Figure 2-19. The resistor of the wire wound resistor is the resistance wire. The resistance wire is wrapped on the ceramic skeleton, the lead is connected, and the appearance is coated with a layer of glass glaze or insulating paint to make a wire wound resistor.
The performance characteristics of the wire wound resistor are extremely noise, high temperature resistance, high power, good stability, small temperature coefficient, high fineness, but poor high -frequency characteristics. The resistance range of the wire wound resistor is usually 0.1-5×106Ω, which is especially suitable for high temperature and high-power places.
(6) Cement resistor
Cemental resistance is the habit of ceramic sealing power line winding resistor. The structure is shown in Figure 2-20. The wire windows are placed in the ceramic shell and sealed with packaging, leaving only two ends of the lead outside.
The performance characteristics of cement resistors are high power, high temperature resistance, good insulation performance, good stability and overload, and good flame retardant and explosion -proof performance. The resistance range of the cement resistor is usually 0.1-4300Ω, which is mainly used in high-power low-resistance places.
(7) Fractive resistor
The fuse resistor, also known as the insurance resistor, is a special component with both resistors and fuses. The text symbol of the fuse resistor is “RF”, and the graphic symbol is shown in Figure 2-21.
The resistance value of fuse resistors is small, and its main function is insurance. The use of fuse resistors can use only one component to play a current limit and insurance.
As shown in Figure 2-22, an example of a melting resistor should be used for the application of a high-power transistor. When the circuit is working normally, the fuse resistor RF plays the role of a current limit resistance. Once the load circuit seizures or short circuit, the fuse resistor RF is quickly fused, which plays a role in maintaining the transistor.
How to detect the resistor
The good or bad of the resistor is available
Digital multimeter resistance
(1) Poinage universal meter detection
During the detection, first transfer the generous universal meter (hereinafter referred to as a multi-purpose table) based on the resistance value of the resistor resistance value to the proper “Q” gear, as shown in Figure 2-23.
Because the multimeter obstructs the calibration of ordinary central resistance, and its scale line is non -linear, the measurement resistor should prevent the meter needle from both ends of the scale line. Ordinary measurement of “RXI” gear can be selected, 100 to 1000Ω resistors can be selected “RX10” gear, 1 to 10kΩ resistor optional “RX100” gear, 10-100kΩ, the resistor can choose “RXLK” gear, the resistor can be selected, the resistor can be selected, the “RXLK” gear can be selected. LOOKΩ, the above resistor can choose the “RXLOK” gear.
After the measurement gear is selected, the universal meter resistance is needed to stop the school zero. As shown in Figure 2-24, the two-meter table two tablets are briefly connected to each other, and the “zero” knob is rotated to the “0” bit (fullness) of the resistance scale of the resistance scale. The need for special attention is that every time the gear is changed in the measurement, the school should be stopped to stop the school zero.
The two-meter two-table pens (regardless of each other, negative) are connected with the two ends of the resistance to the resistance to the test. As shown in Figure 2-25, the needle should refer to the corresponding resistance scale. For example, if the intonation is not moved, the indication small stability or the indicator value is very different from the marker value on the resistor, it is stated that the resistor is damaged.
When measuring the resistor with a resistance of more than tens of thousands of euros, pay attention to the two-ends of the resistance of the resistor at the same time, as shown in Figure 2-26 to avoid the measuring error of connecting the human body resistance.
(2) Digital multimeter detection
Digital multimeter does not use school zero before measuring the resistor. Turn the gear knob to the appropriate “O” gear, and open the power switch to measure.
When choosing a measurement position, try to make the display screen show more effective figures. Ordinary measurement of “200Ω” gear can be selected as a “200Ω” gear, the 200-1999Ω resistor can be optional Optional “20KQ” gear, 20-199.9kΩ resistor can be optional “200KΩ” gear, 200-1999kΩ resistor can be selected “2MΩ” gear, 2 to 19.99mq resistors can choose “20MΩ” gear, 20-99 The 9MΩ resistor can choose the “200MΩ” gear. A resistors above 200MΩ cannot measure because of the highest range (take DT890B digital multimeter as an example). During the measurement, the two tabs (regardless of each other, negative) are connected to both ends of the measured resistor, and the LCD shows the resistance value of the measured resistance R, as shown in Figure 2-27. If the “000” (short -circuit), the highest level of the “1” (disconnection), or the value of the indicator is very different from the resistance value, it is stated that the resistor is damaged.
Usage of high power resistance
Different power, the resistor has different functions and applications. It is a current limit element. After connecting the resistance in the road, the resistance value of the resistor is fixed and generally two pins, which can limit the current of the branch road through it. The resistance value cannot be changed is called a fixed resistor. The resistance value is called a potentiometer or a variable resistor. The ideal resistor is linear, that is, the instantaneous current of the resistor is proportional to the external voltage. For variable resistors for separate pressure. On the exposed resistance body, one or two migrant metal contacts are pressed tightly. The contact position of the contact position determines the resistance value between one end and the contact of the resistor.
The terminal voltage and current have a determined function relationship, which reflects the transformation of electrical energy into other forms of capacity. It is expressed by the letter R. The unit is Om ω. Actual devices such as light bulbs, electric heating wires, and resistors can be represented as resistance components. Electric vortex displacement sensor Merchants product data display Display resistance element is generally related to temperature, materials, materials, length, and cross -sectional area. The physical quantity that measures the resistance that the resistance is affected by the temperature is the temperature coefficient. The percentage of changes in the resistance value. The main physical characteristics of the resistance are the substation energy as thermal energy. It can also be said that it is an energy -consuming element, and the current has internal energy. Resistance usually plays pressure and diversion in circuits. For signals, both communication and DC signals can pass the resistance.
Small -power resistors are usually composed of carbon membranes encapsulated in plastic shells, and high -power resistors are usually winding resistors, which are made of metal wires with large resistors around porcelain hearts. If the resistance value of a resistor is close to Zero EM (for example, a large cross -section wire between the two points), the resistor does not hinder the current, and the circuit of this resistor is short -circuit and the current is infinite. If a resistor has infinitely large or large resistors, the circuit of the resistor in series can be regarded as the opening, and the current is zero.
The commonly used resistors in the industry are between two extreme conditions. It has a certain resistance and can pass a certain current, but the current is not as large as the short circuit. The flow limit of the resistor is similar to the role of small diameter pipes between the two large diameter pipes to limit the water flow. Resistance, English name Resistance, usually abbreviated as R. It is a basic nature of the conductor, which is related to the size, material, and temperature of the conductor. Ohm’s Law said, I = U/R, then R = U/I, the basic unit of resistance is Ohm, which is represented by the Greek alphabet “ω”. There is such a definition: when the conductor is added with a volt voltage, the one -ampel current generates a ampel current. The corresponding resistance value. The main function of the resistance is to prevent current flow. In fact, “resistance” is a nature, and the resistance that usually referred to in electronic products refers to a component such as resistors. Om is often referred to as Europe. There are even thousands of euros (KΩ), Zhaou (MΩ), and millimeter (MΩ) that indicate the common unit of resistance values.
The process and structure of resistance
There are many types of resistors, and they can be divided into two categories according to whether the resistance can be changed:
2.1 Fixed resistance
Fixed resistance, as the name implies, is the resistance value of the resistance and immutable. Most of the time, the resistance we use is fixed. It can be roughly classified according to the different packaging.
2.1.1 Axial Leaded Resistor
The axis leading resistance is usually cylindrical. The two outer electrodes are axial wires at both ends of the cylindrical body. According to the different materials and processes, it can be divided into multiple types.
Wire Wound Resistor
The winding resistance is to wrap the nickel chromium alloy wire around the alumina ceramics base, and the control resistance size is controlled one after another. The winding resistance can be made to precision resistance, the tolerance can be 0.005%, and the temperature coefficient is very low. The disadvantage is that the parasitic inductance of the winding resistor is relatively large and cannot be used for high frequency. The volume of the winding resistance can be made very large, and then the external radiator can be used to be used as a high -power resistor.
Carbon Composition Resistor
The carbon synthesis resistance is mainly burned into a cylindrical resistor by carbon powder and adhesive. The concentration of the carbon powder determines the size of the resistance value, adds tin -plated copper leads to both ends, and finally encapsulates. The carbon synthesis resistance process is simple, and raw materials are easy to obtain, so the price is the cheapest. However, the performance of the carbon synthesis resistance is not very good, the tolerance is relatively large (that is, the precision resistance can not be done), the temperature characteristics are not good, and the noise is usually relatively large. Carbon synthetic resistance has good resistance to resistance. Because the interior can be regarded as a carbon rod, it is basically not broken and burned.
1. Applicable to high -pressure high -power applications
2. Can withstand high energy in a short time
3. No longer used in the usual scene, because the price
1. ground resistance
2. Gas circuit breaker
3. Large motor
4, perceptual heater
Carbon Film Resistor
Carbon membrane resistance is mainly formed a layer of carbon mixed film on the ceramic rod, such as directly applying a layer. The thickness of the carbon membrane and the carbon concentration can control the size of the resistance; in order to control the resistance more accurately In the spiral groove, the more the spiral resistance, the larger the resistance; the last metal lead is added, and the resin packaging is formed. The carbon membrane resistance process is more complicated and can be used for precision resistance, but due to the reasons of carbon quality, the temperature characteristics are not very good.
Carbon membrane resistors are one of the membrane resistors (Filmresistors). It uses high -temperature vacuum coating technology to closely attach carbon to the surface of the porcelain stick to form a carbon film, then add appropriate connecting cutting, and apply epoxy resin sealing on its surface. It is often coated with green paint. The thickness of the carbon membrane determines the size of the resistance value, and the thickness of the control membrane is usually used to control the resistor.
1. Stable performance, wide range of resistance, high limit voltage;
2. The surface is painted with yellow paint, and it is small to earth yellow or pink;
3. Use environmental temperature: -55 ℃ ～+125 ℃;
4. Scope of accuracy: ± 5%, ± 2%.
Metal Film Resistor
Similar to the carbon membrane resistance structure, the metal membrane resistance mainly uses vacuum deposition technology to form a layer of nickel chromium coating on the ceramic rod, and then process the spiral groove on the coating to accurately control the resistance. The metal membrane resistance can be said to be a relatively good resistance, high accuracy, can be used as the E192 series, and then the temperature characteristics are good, the noise is low, and it is more stable.
The metal membrane resistance uses nickel chromium or similar alloy vacuum plating technology. The membrane is on the surface of the white porcelain stick, and the resistance value of the final requirement is achieved to achieve the precision resistance value of the final requirement. The metal membrane resistor provides a wide range of resistance, has the characteristics of precision resistance and small tolerance range. It can also be used in metal membrane fuse resistors. The carbon membrane resistance is currently the largest use of electronics, electrical appliances, and information products. It is the carbon of organic compounds from high temperature vacuum, closely attached to the carbon membrane body on the surface of the porcelain stick, and cutting it after proper joints, and coated with epoxy resin sealing on its surface to protect. From the appearance, the metal membrane is five rings (1%), and the carbon membrane is a four -ring (5%). The metal membrane is blue, the carbon membrane is earthy or other colors.
Metal membrane resistance, stability, small error, high accuracy, small volume.
Carbon membrane resistance, otherwise.
Metal Oxide Film Resistor
Similar to the metal membrane resistance structure, the metal oxide film is mainly to form a tin oxide film in the ceramic rod. In order to increase the resistance, a layer of pyrone oxide film can be added to the tin oxide film, and then processed on the oxide film The spiral groove is used to accurately control the resistance. The biggest advantage of metal oxide film resistance is high temperature resistance.
1. Low noise
2. Good high -frequency characteristics
3. Stable work
2.1.2 chip resistance
Metal Foil Resistor
Metal foil resistance forms a nickel chromium alloy through vacuum melting, and then makes metal foil through rolling, and then metal foil is adhesive to alumina ceramics, and the shape of the metal foil is controlled by the photoresistic process to control the resistance Essence Metal foil resistance is the best resistance that can be controlled at present.
Thick Film Resistor
The screen printing method used by thick membrane resistors is to put a layer of silver electrodes on the ceramic base, and then print a layer of dioxide between the electrodes as the resistor. The resistance membrane of thick membrane resistors is usually thicker, about 100 microns. The specific process process is shown in the figure below.
The thick membrane resistance is currently the most application resistance, the price is cheap, and the container is 5%and 1%. Most of the products use 5%and 1%sheet -shaped thick membrane resistance.
Thin Film Resistor
The film resistance is the nickel chromium -t -chrome film through vacuum deposition on the base of aluminum oxide ceramic. Usually only 0.1um thick, only one thousandth of the thick membrane resistance, and then etch the film into a certain shape through the photoresal process. The Thin Film process has been mentioned many times in the articles of the capacitance and inductance before. The lithography process is very accurate and can form a complex shape. Therefore, the performance of film capacitors can be controlled well.
The film resistance and thick membrane resistance are widely used in resistance, and the appearance is extremely similar. Many users confuse them or directly treat them as the same component. So is they the same? what differences are there? And listen to Xiaobian to answer your answer.
The biggest difference between the two is: of course, the difference in thickness of the membrane, the membrane thickness of the thick membrane resistance is usually greater than 10 μm, and the film resistance is usually less than 10 μm, and most of them are less than 1 μm. It is made from the screen printing process. The film resistance uses a process method such as vacuum evaporation and magnetic sputtering. The material with a certain resistivity of a certain resistivity is placed on the surface of the insulated material to make a resistor. Then there is the general accuracy of thick membrane resistance as high as the film resistance. The common accuracy of the thick film resistance is 10%, 5%, 1%, etc., while the film resistance accuracy can reach 0.1%, 0.01%, etc.; Membrane resistance is usually large, and the temperature coefficient of the film resistance can be very low, such as 5ppm/℃, 10 ppm/℃, etc. Therefore, the resistance value of the film resistance is small and more stable and reliable with the temperature.
In summary, the film resistance has more advantages, and the price is relatively expensive. It is often used in various instruments, medical devices, power supply, power equipment, electronic digital products, etc. When selecting the resistance type, of course, the most expensive one can be blindly selected, but the appropriate one is based on actual needs. When the temperature coefficient and accuracy requirements are high, the resistance of the film process is used. of.
2.2 Variable resistance
The variable resistance is that the resistance value can be changed. There are two types of resistance: one is that the resistance of the resistance value can be adjusted manually; the other is that the resistance value can be changed according to other physical conditions.
2.2.1 adjustable resistance
When I go to middle school, I should use sliding resistors for experiments. A movement of a sliding resistor can be used. The small light bulbs can become brighter or darkened. The sliding resistor is a adjustable resistor, and the principle is the same.
The adjustable resistance is usually divided into three types:
The potentiometer or divisionometer, this is a three -terminal device. The potentiometer is divided into two resistors by the middle tap. Through the middle tap, the resistance value of the two resistors can be changed, and the voltage obtained can be changed.
The resistor is actually the potentiometer. The only difference is that the resistor only needs to use two ports, which is purely a resistor that can accurately adjust the resistance value.
Formulator is actually a potentiometer, but you do n’t need to adjust it frequently. For example, when the device is left, it can be adjusted. Generally, special tools such as screwdriver are required to adjust.
2.2.2 Sensitive resistance
Sensitive resistance is a type of sensitive element. Most of these resistors are particularly sensitive to certain physical conditions. As soon as the physical conditions change, the resistance value will change with, and it can usually be used as sensors, such as photoresistor, wet sensitivity resistance, magnetic sensitivity Resistance and so on. There should be a large number of thermistor and pressure -sensitive resistance in circuit design, which are often used as protective devices.
PTC is a positive temperature coefficient resistance. There are usually two types: one is ceramic material, called CPTC, which is suitable for high -voltage and large current occasions. The other is polymer polymer material, called PPTC, which is suitable for low -voltage small current occasions.
Ceramic PTC, its resistance material is a polycrystalline ceramic, which is a mixture of a variety of materials such as carbonate and titanium dioxide. The PTC temperature coefficient has a strong non -linearity. When the temperature exceeds a certain threshold, the resistance will become large, which is equivalent to disconnection, which can play a role in short circuit and overcurrent protection.
At the same time, there is negative temperature coefficient resistance, namely NTC.
Voltage -sensitive resistors are usually metal oxide variable resistors, that is, Metal Oxide Varistor (MOV). Its resistance materials are mixed with zinc oxide particles and ceramic particles. The characteristic of MOV is that when the voltage exceeds a certain threshold, the resistance drops rapidly and can pass through large currents, so it can be used for surge protection and overvoltage protection.
The zinc oxide ceramics uses a process similar to MLCC to make a multi -layer pressure -sensitive resistance, that is, MLV. The MLV packaging is small, usually sheets, and the rated voltage and streaming capabilities are much smaller than MOV. It is suitable for low -voltage DC occasions.
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