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resistor (Resistor), generally referred to as resistance , which generally refers to all resistance Of Electronics or electric machinery Accessories. Operation follow of resistor Ohm's law , which Resistance value Defined as Voltage And electric current Divisive Quotient 。

Resistance scale method

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Resistive resistance The standard method usually has Color ring method 、 Digital method 、 Digital method 。 Color ring method is common in general resistance.

Color ring method

The so-called color ring method means that resistance parameters are represented by different color scales. There are 4 color rings and 5 color rings in the color ring resistance. The meanings of each color ring are as follows.

colour	numerical value	Multiplicity	tolerance
black	zero	x 1	——
brown	one	x 10	Plus or minus 1%
gules	two	x 100	Plus or minus 2%
orange	three	x 1000	——
yellow	four	x 10000	——
green	five	x 100000	Plus or minus 0.5%
blue	six	x 1000000	Plus or minus 0.25%
violet	seven	x 10000000	Plus or minus 0.10%
gray	eight	——	Plus or minus 0.05%
white	nine	——	——
golden	——	x 0.1	Plus or minus 5%
silvery	——	x0.01	Plus or minus 10%
Achromatic ring	——	——	Plus or minus 20%

To read the parameters of the color ring resistance, first determine the reading direction. Generally speaking, the color ring representing tolerance is far away from other color rings and wider. After judging the direction, you can read from left to right.

For example, if the color of a 4-color ring resistor is red (2), purple (7), yellow (x10000), and silver (plus or minus 10%) from left to right, the resistance value of this resistor is 27 Ω x10000=270000 Ω, that is, 270K Ω, and the tolerance is plus or minus 10%.

For another example, the colors of a 5-color ring resistor from left to right are red (2), green (5), blue (6), red (x100), brown (plus or minus 1%), then the resistance value of this resistor is 256 Ω x100=25600 Ω, that is, 25.6K Ω, and the tolerance is plus or minus 1%.

Digital method

Since the resistance of the patch is relatively small, it is rarely marked with resistance value. Even if there is, the digital method is generally used, namely:

101 refers to 10 * 10 ^ 1 Ω, i.e. 100 Ω resistance;

102 refers to the resistance of 10 * 10 ^ 2 Ω, i.e. 1K Ω;

103 - 10 * 10 ^ 3, i.e. 10K Ω resistance;

104 -- 10 * 10 ^ 4, i.e. 100K Ω resistance;

503 represents 50 * 10 ^ 3, i.e. 50K Ω resistance;

And so on. If a resistance is marked 22 * 103, it is 220K Ω.

Digital method

Use three digits to indicate the nominal value of the element. From left to right, the first two digits represent significant digits, and the third digit represents 10n (n=0-8). When n =9 is a special case, representing 10 ^ (- 1). Plastic 103 of resistor means 10 * 10 ^ 3=10k. Sheet resistance is usually marked by digital method, for example, 512 indicates 5.1k Ω. capacitance The upper digital mark 479 is 47 * 10 ^ (- 1)=4.7pF. The resistor marked with 0 or 000 is a jumper, and the resistance value is 0 Ω. When marked by digital method, the unit of resistance is ohm, capacitance The unit is pF, inductance Generally, digital signs are not used.

The electrical performance indicators of resistors usually include Nominal resistance , error And Rated power Etc.

It forms some functional circuits together with other elements, such as RC circuit 、 RL circuit Etc.

The resistance is a Linear element 。 The reason why it is a linear element is that it is found through experiments that under certain conditions, the current flowing through a resistance is proportional to the voltage at both ends of the resistance - that is, it is in accordance with Ohm's law ：I=U/R

Common carbon film resistance or Metallic film The resistor is available when the temperature is constant and the voltage and current values are limited within the rated conditions Linear resistance To simulate. If the voltage or current exceeds the specified value, the resistor will not comply with Ohm's law due to overheating, or even be burned. The relationship between the working voltage and current of the linear resistor is shown in Figure 1. There are many kinds of resistors, which are usually divided into carbon film resistors and metal resistors, Wirewound resistance Etc.: It also includes fixed resistance and variable resistance, Photoresistor 、 Varistor 、 Thermistor 、 Humidity sensitive resistor Etc.

In general, use A multimeter It is easy to judge the resistance: adjust the multimeter to Ohmic scale The resistance value of the resistance can be read out from the multimeter by placing two probes of the multimeter on both ends of the resistance. It should be noted that the hand cannot touch the metal part of the probe when testing the resistance. However, in actual electrical maintenance, resistance damage rarely occurs. Pay attention to whether the resistance is Faulty soldering 、 Desoldering 。

Resistance element

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resistance

Resistance elements are energy consuming elements that hinder current, such as Light bulb: Electric heaters and other electrical appliances. Resistance law: R= ρ L/S

ρ ——The resistivity of the material making the resistance, International System of Units For Ommi（ Ω ·m）

L ——Wound into resistance wireway Length in meters (m)

S ——Wires wound into resistors Cross sectional area , SI unit is square meter (m2)

R ——Resistance value, in ohms (Ω) in SI unit.

ρ It is called resistivity: the resistance of a conductor made of a certain material with a length of 1 meter and a cross-sectional area of 1 square millimeter is called the resistivity of this material. It is a physical quantity describing the properties of materials. In the International System of Units, the unit of resistivity is ohm · m, and the common unit is ohm · mm2/m. And conductor length L , Cross sectional area S It has nothing to do with the material and temperature of the object. The resistivity of some materials increases with the increase of temperature, and some vice versa.

The relationship between resistance and temperature The resistance value of a resistance element is generally related to temperature. The physical quantity that measures the resistance value affected by temperature is the temperature coefficient, which is defined as the percentage of resistance value change when the temperature increases by 1 ° C. If the resistance value of any resistance element at temperature t1 is R1, and when the temperature rises to t2, the resistance value is R2, then the (average) temperature coefficient of the resistance in the temperature range t1~t2 is a>0 if R2>R1, and R is called Positive temperature coefficient Resistance, that is, the resistance value increases with the increase of temperature; If R2<R1, then a<0, and R is called Negative temperature coefficient The resistance, that is, the resistance value decreases as the temperature increases. Obviously a absolute value The greater the resistance, the greater the influence of temperature. R 2 = R 1[1 + a （ t 2－ t 1）]。

Resistance classification

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According to resistance characteristics:

Fixed resistance Adjustable resistance Special resistance（ Sensitive resistance ) .

Those that cannot be adjusted are called fixed value resistance or fixed resistance, while those that can be adjusted are called adjustable resistance. The common adjustable resistance is Sliding rheostat , for example radio The volume adjustment device is a circular sliding rheostat, which is mainly used for voltage distribution. It is called potentiometer 。

By material of manufacture:

Carbon film resistance Metal film resistance, wire wound resistance, Non inductive resistance ， Film resistance Etc.

Film resistance

use evaporation The method is to evaporate and plate a certain resistivity material on the surface of insulating material. Mainly as follows:

Carbon film resistor

Carbon film resistance

Carbon film resistance (carbon film resistance) is usually marked by the symbol RT; For the earliest and most commonly used resistor, use vacuum The spraying technology sprays a layer of carbon film on the ceramic rod, and then processes and cuts the outer layer of the carbon film into spiral stripes. The resistance value is determined according to the number of spiral stripes. The more spiral stripes, the greater the resistance value. Finally, apply on the outer layer epoxy resin It is sealed and protected. Although its resistance error is higher than that of metal film, it is cheap. Carbon film resistors are still widely used in various products. They are the most basic components of electronics, appliances, equipment and information products.

Metal film resistor

Metal film resistor, usually marked by the symbol RJ; It also uses the vacuum spraying technology to spray on the ceramic rod, only replacing the carbon film with a metal film (such as nickel chromium), making different resistance values on the spiral lines on the metal film car, and plating precious metal on both ends of the ceramic rod. Although it is more expensive than carbon film resistor, it is low noise, stable, less affected by temperature, and accurate Gao Cheng Has its advantages. Therefore, it is widely used in advanced audio equipment, computers, instruments, national defense and space equipment.

metal oxide film resistor

some instrument Or if the device needs to be operated under high temperature for a long time, the stability of the device will not be maintained with ordinary resistance. Metal can be used in this case Oxide film resistance (metal oxide thin film resistor), which uses high temperature burning It is used to burn a layer of metal oxide film (with tin and tin chemical compound Spray the solution into a constant temperature furnace at 500~500 ℃, and coat it on the rotating ceramics It is formed on the matrix. Material is also OK zinc oxide And make different resistance values for the spiral lines on the metal oxide film vehicle, and then spray non combustible paint on the outer layer. Its performance is similar to that of metal film resistor, but the resistance range is narrow. It can still maintain its stability at high temperatures. Its typical characteristics are that the metal oxide film is more firmly combined with the ceramic matrix, and the resistance film is loaded power It is also high. It has strong acid and alkali resistance and salt fog resistance, so it is suitable for working in harsh environments. It also has the advantages of low noise, stability and good high-frequency characteristics. The symbol RY is often used as a sign.

Synthetic film resistance

metal oxide film resistor

It is obtained by coating conductive composite suspension on the substrate, so it is also called paint film resistance.

Since the conductive layer is in granular structure Noise Large, low precision, mainly manufactured by others high pressure , high resistance, small resistor.

Winding resistance

Use high resistance alloy The wire is wound on the insulating skeleton and coated with heat-resistant glaze insulation layer or insulating paint.

The winding resistance has a low temperature coefficient, high resistance precision, good stability, heat resistance and corrosion resistance, and is mainly used for high precision Power resistance use, shortcoming The high frequency performance is poor, time constant Large.

wire-wound resistor

Square wire wound resistance (steel wire wound resistance), also known as cement battery, is made of nickel, chromium, iron and other alloys with high resistance Resistance wire It is wound on the non alkaline heat-resistant ceramic parts, protected by heat resistant, moisture resistant and non corrosive materials, and then put the winding resistor body into the porcelain frame, filled and sealed with special incombustible heat-resistant cement. The difference of incombustible coating wire winding resistance is that the outer coating is changed from silycon resin or incombustible coating. They have the advantages of accurate resistance, low noise, good heat dissipation and can withstand large Power consumption , mostly used for amplifier Power level part. The disadvantage is that the resistance value is small, the cost is high, and the inductance is not suitable for use in high-frequency circuits.

Solid carbon resistance

A solid resistor is made by mixing carbon granular conductive material, filler and adhesive. The wires shall be embedded during manufacturing. The resistance value depends on the proportion of toner and the thickness of carbon rod.

Features: low price, but its resistance error Noise voltage Large, poor stability, seldom used.

Metallic glass uranium resistance

Metal powder and glass uranium powder are mixed and printed on the substrate by screen printing.

Moisture resistant, high temperature, low temperature coefficient, mainly used in Thick film circuit 。

chip resistor SMT

Chip resistance (chip resistance) is a form of metallic glass uranium resistance. Its resistance body is highly reliable ruthenium series glass uranium material sintered at high temperature. It is characterized by small size, high precision, good stability and high-frequency performance, and is suitable for high-precision electronic product In the substrate. The patch resistance elimination is to reduce the resistance of multiple devices with the same value chip resistor The purpose of making a SMD resistor is to effectively limit the number of components, reduce manufacturing costs and reduce the area of the circuit board.

Non inductive resistance

Non inductive resistance It is often used as a load to absorb the use of products process Unwanted generated in Electricity , or play the role of buffering and braking, and such resistance is often called JEPSUN Braking resistor Or Jebsen Load resistance 。

By installation mode:

Plug in resistance chip resistor 。

By function:

Load resistance, sampling resistance, shunt resistance, protection resistance, etc.

main parameter

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Basic parameters:

1. Nominal resistance value: the nominal resistance value on the resistor is called the nominal value. Unit: Ω, k Ω, M Ω. The nominal value is marked according to the standard series formulated by the country, not arbitrarily calibrated by the manufacturer. Not all resistors are present.

2. Allowable error: the maximum allowable deviation range of the actual resistance value of the resistor from the nominal value is called the allowable error. Error code: F, G, J, K... (Common error range: 0.01%, 0.05%, 0.1%, 0.5%, 0.25%, 1%, 2%, 5%, etc.).

3. Rated power: at the specified ambient temperature atmosphere No flow, the allowable power consumption on the resistor under the condition of long-term continuous operation without damage or basic change of resistor performance. The common ones are 1/16W, 1/8W, 1/4W, 1/2W, 1W, 2W, 5W and 10W.

4. Temperature coefficient: ± ppm/℃, that is, the change of resistance value caused by unit temperature. Ppm (Part Per Million) means parts per million, for example, for a resistance with a nominal resistance value of 1k, the temperature coefficient is ± 100ppm/℃, which means that the temperature change is one centigrade The change of resistance value is 1k ± 0.1 Ω, the change is 100 ℃, the change of resistance value is 1k ± 10 Ω, and the precision is very high. The temperature coefficient of resistance has a precision level of tens of ppm, the common level is 200~250 ppm, and the worst level is only 500 ppm.

Marking method of resistance and error:

1. Direct marking method - the main parameters and technical performance of the resistor are directly marked on the resistor body with numbers or letters.

eg：5.1k Ω5% 5.1k ΩJ

Photoresistor

2. Character symbol method - combine the characters and numbers regularly to represent the main parameters of the resistor.

eg: 0.1Ω=Ω1=0R1, 3.3Ω=3Ω3=3R3,3K3=3.3KΩ

3． Color code Method - Use color rings of different colors to represent the resistance value and error level of the resistor. Common resistance is generally represented by four rings, Precision resistance Use 5 rings. Digital method.

Use three digits to indicate the nominal value of the element. From left to right, the first two digits represent the significant digits, and the third digit represents 10 ^ n（ n =0～8）。 When n =9 is a special case, representing 10 ^ (- 1).

0-10 Ω resistance with decimal point is expressed as XRX, RXX eg :

471=470Ω105=1M 2R2=2.2Ω

103 of plastic resistor means 10 * 10 ^ 3=10k. Sheet resistance is usually marked by digital method, for example, 512 indicates 5.1k Ω. The digital mark 479 on the capacitor is 47 * 10 ^ (- 1)=4.7pF. The resistor marked with 0 or 000 is a jumper, and the resistance value is 0 Ω. When marking with digital method, the unit of resistance is ohm, and the unit of capacitance is pF, inductance Generally, digital signs are not used.

Determination of the first ring of color ring resistance:

Identification Method of Color Ring Resistance

1. Four ring resistance

Because the color ring that represents error is only gold or silver, the gold or silver ring in the color ring must be the fourth ring.

2. Five ring resistance: this is precision resistance.

(1) Judging from the resistance range: because the general resistance range is 0-10M, if the read resistance exceeds this range, the first ring may be wrong. (2) Judging from the color of error ring: the color of error ring includes silver, gold, purple, blue, green, red and brown. If the color ring near the resistor end is not the error color, it can be determined as the first ring.

Identify the resistance value of the color ring resistance:

Color ring resistor is widely used in electronic products. Its advantage is that during assembly, debugging and repair, the color ring can be seen clearly from any angle and the resistance value can be read out without moving the components. It is convenient to use. A resistance color ring consists of 4 parts (excluding precision resistance).

The first and second rings of the four color rings respectively represent the first two digits of the resistance value; The third ring represents the power of 10; The fourth ring represents error.

Here are some key points to master this method:

(1) Remember the number represented by each color of the first and second rings. It can be remembered as follows:

Brown=1

Red=2,

Orange=3,

Yellow=4,

Green=5,

Blue=6,

Purple=7,

Grey=8,

White=9,

Black=0.

The color distribution of the rainbow: red, orange, yellow, green, blue, indigo (di à n), purple. Remove the indigo, add gray, white and black at the back, and add brown at the front, corresponding to the number 1.

In terms of order of magnitude, they can be divided into three major grades in body: gold, black and brown are ohmic; Red is a thousand Euros, orange and yellow are ten thousand Euros; Green is megaohm, and blue is 10 megaohm. This division is also good for memory. Therefore, we should first look at the third ring color (the penultimate color) to be accurate.

The error represented by the fourth ring color: 5% for gold; 10% for silver; Colorless is 20%.

For example:

Example 1: The four color rings are yellow, orange, red and gold

Reading method: the number corresponding to the first three colors is 432, gold is 5%, so the resistance value is 43X10 * 2=4300=4.3K Ω, and the error is 5%.

Select common sense

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Resistance value and error of resistor:

Resistance value selection : The principle is that the smaller the difference between the nominal resistance value of the resistor used and the required resistance value, the better.

Error selection: time constant The error of resistor required for RC circuit shall be as small as possible. Generally, it can be selected within 5%. Decoupling circuit, Feedback circuit The load circuit of the filter circuit does not require high error. 10% - 20% resistor can be selected.

Note the limit parameters of the resistor:

Rated voltage : When the actual voltage exceeds the rated voltage, even if the power requirements are met, the resistor will also be damaged by breakdown.

Rated power : The rated power of the selected resistor should be more than twice the actual power to ensure the reliability of the resistor in the circuit for long-term operation.

To prefer universal resistors:

There are many types, complete specifications, large production batch, and resistance range, appearance and shape of universal resistors volume There is a choice of size, which is convenient for purchase and maintenance.

Select according to the circuit characteristics:

High frequency circuit : The smaller the distribution parameter, the better. High frequency resistance such as metal film resistance and metal oxide film resistance shall be selected.

Low-frequency circuit : Both winding resistance and carbon film resistance are applicable.

Power amplifier circuit Bias circuit and sampling circuit: the circuit requires high stability, so the resistor with small temperature coefficient should be selected.

Decoupling circuit and filtering circuit: there is no strict requirement for resistance value change, and all kinds of resistors are applicable.

Common types

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Photoresistor

1. Thermistor: It is a kind of resistor that is very sensitive to temperature. It is divided into positive temperature coefficient resistor and negative temperature coefficient resistor. The rated power Maximum operating voltage , nominal resistance, pay more attention to the maximum operating temperature, resistance temperature coefficient and other parameters, and pay attention to the direction of resistance change.

2、 Photoresistor : CdS and other materials, with resistance light A resistor that varies in strength. Divided into visible light Photoresistor , infrared photosensitive resistance, ultraviolet photosensitive resistance. Determine the circuit spectrum characteristic.

3. Varistor: Yes Voltage variation Very sensitive Nonlinear resistance Device. When the voltage on the resistor is within the nominal value, the resistance value on the resistor is infinite state , when the voltage is slightly higher than Nominal voltage When the voltage drops below the nominal voltage, the resistance begins to increase again.

Varistors can be divided into non-polar (symmetric) and polar (asymmetric) varistors. When selected, Varistor The nominal voltage value of shall be 2-2.5 times of the voltage applied at both ends of the varistor. Pay attention to the pressure.

4. Humidity sensor: Yes humidity The resistor is very sensitive to changes and can be used in various humidity environments. It is a transducer that converts humidity into electrical signals. The selection shall be based on the different characteristics of different types and numbers as well as the precision, humidity coefficient, response speed, humidity range, etc. of the humidity sensitive resistor.

Note: The main characteristic of resistance at low frequency is resistance characteristic, but at high frequency, it not only shows resistance characteristic, but also shows Reactance Features, this is in the radio Aspects (in particular RF Circuit).

Resistance measurement

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Use a multimeter to measure the large resistance:

The maximum range of resistance gear of 31/2-digit and 41/2-digit digital multimeter is generally 20M Ω. For a 31/2-digit digital multimeter, using different resistance ranges can only measure the resistance within the range of 0.1 Ω~19.99M Ω; The 41/2-digit digital multimeter can only measure the resistance within the range of 0.01 Ω~19.999M Ω. When the measured resistance Rx ≥ 20M Ω, the instrument will display the overflow symbol "1".

The experiment proves that the range of the 20M Ω resistance scale of the 31/2-digit or 41/2-digit digital multimeter can be expanded to 100M Ω by using the following "parallel resistance method".

1. Measurement method

Prepare a resistance R1 of more than 10 megohm in advance, turn the digital multimeter to the 20M Ω gear, and then measure the resistance R1. Then connect the measured resistance Rx in parallel at both ends of R1, and then measure the total parallel resistance R.

According to the calculation formula of resistance parallel connection, it is easy to deduce.

Measurement example:

The measured resistance is a high resistance Rx with unknown mark, and the nominal resistance of 10M Ω is selected for R1. Using the 20M Ω resistance gear of DT830 digital multimeter, the measured resistance value of R1 is 10.05M Ω. After Rx and R1 are connected in parallel, DT830 is used for measurement, and the measured total resistance value R=7.70M Ω.

Therefore, the nominal value of the measured resistance should be 33M Ω.

2. Measurement precautions

1) When the resistance value of the measured resistance Rx exceeds 100M Ω, the total resistance value R after parallel connection is very close to the resistance value of the selected standard resistance R1. In addition, the digital multimeter itself has an error of ± 1 word, which will increase the measurement error. Therefore, this method is not suitable for measuring resistance values greater than 100M Ω.

2) During measurement, the measured resistance Rx and the standard resistance R1 should be connected firmly in parallel, and the two can be fixed with alligator clips if necessary.^[1]

Resistivity calculation

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Resistance (Figure 1)

Calculation formula of object resistance: R= ρ L/S , where, L Is the length of the object, S Is the cross sectional area of the object, the scale coefficient ρ It is called the resistance coefficient or resistivity of an object. It is related to the material of the object and is numerically equal to the resistance value of an object of unit length and area at 20 ℃. Therefore, resistance is related to four factors: conductor length, cross-sectional area, type (material) and temperature.

Physical meaning; It reflects the blocking effect of the material on the current, which is equal to the resistance value of the conductor made of this material with a length of 1m and a cross-sectional area of 1m ㎡.

The specific relationship between resistivity and temperature is: ρ=ρ 0（1+ α t ）， among ρ zero Is the resistivity of the conductor at zero degrees, α Is the temperature coefficient of the conductor.

R =1 /G , where G Is an object conductance The smaller the resistance of the conductor, the greater the conductivity, which is equal to the reciprocal of the resistance. The unit is Siemens, referred to as West, and the symbol is s.

Factors affecting resistance required by junior high school students:

When the length and material of conductors are the same, Cross sectional area The smaller the, the greater the resistance

When the cross-sectional area and material of conductors are the same, the longer the length, the greater the resistance

When the cross sectional area and length of conductors are the same, the materials of conductors are different and the resistance is different.

The resistance of most metals increases with temperature.

Common conductor resistivity

Resistivity of material at 20 ℃ (µ Ω· m)

Silver 0.016

Copper 0.0172

Gold 0.022

Aluminium 0.029

Zinc 0.059

Iron 0.0978

Lead 0.206

Mercury 0.958

Carbon 25

Constantan (54% Cu, 46% Ni) 0.50

Manganin (86% copper, 12% manganese, 2% nickel) 0.43

Lighting bulb (working) 100~2000

Model designation

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The model of domestic resistor consists of four parts (not applicable Sensitive resistance ）

Various types of resistance (8 sheets)

Part I: The main name, expressed in letters, represents the name of the product. For example, R represents resistance and W represents potentiometer.

Part II: Materials, represented by letters, indicate what materials the resistor is composed of: T-carbon film, H-synthetic carbon film, S-organic solid, N-inorganic solid, J-metal film, Y-nitriding film, C-deposition film, I-glass glaze film, X-wire winding.

Part III: Features, expressed by numbers or letters. 1-ordinary, 2-ordinary, 3-ultra-high frequency, 4-high resistance, 5-high temperature, 6-precision, 7-precision, 8-high voltage (potentiometer means special), 9-special, G-high power, T-adjustable, X-small, L-measuring, W-fine adjustment, D-multi turn.

Part IV: Serial number, expressed in numbers, indicates different varieties of the same kind of products, so as to distinguish the overall dimensions and performance indicators of products.

For example: R T 1 1 type ordinary carbon film resistance a1

Related parameters

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Resistance of various precision (6 sheets)

There are many types of common resistors. Some resistors are expensive, so they play a very important role in some circuits. However, some circuits do not require high accuracy, so in order to save costs, resistors with lower accuracy can be used. The most commonly used resistors are carbon film resistors and metal film resistors. Carbon film resistors are used in circuits with low precision, while metal film resistors are used in circuits with high precision. Of course, if some "special circuits" require very high accuracy of the circuit, then it requires careful selection of resistance.

Carbon film resistance: The resistance of carbon film is 5% - 10%

Metal film resistance: The high accuracy for use at ambient temperature of - 55 ℃~+125 ℃ is: ± 0.5%, ± 0.1%, ± 0.2, ± 0.01%, and generally within 1% - 5%.

Green robe resistance: This is the name of a metal film resistor that appeared in the middle and late 1980s. It is named because of its dark green appearance. It is found in MF12 and MF14 multimeters. But according to my own actual measurement, the performance is general, and the aging, deviation and temperature coefficient are quite different from Hongpao resistance.

Resistance (Figure 2)

Hongpao resistance: Code: RJJ, high stability and low temperature coefficient precision metal film, large size, good performance. After our own tests, the resistance of many years of aging rarely exceeds 0.5%, and the temperature coefficient is about 30ppm/℃. Please note that there is another kind of Hongpao resistor with ordinary precision, code RJ, with ordinary performance.

General wire winding resistance: Manganese copper or constantan resistance wire is used, which is not sealed (only painted). Because the wire diameter is generally thick, the aging index is good, but the temperature coefficient is not very good, which is generally between 15ppm/℃ and 35ppm/℃.

Precision wire winding resistance: The resistance wire is generally made of precision manganese copper, and its stability has been improved after sealing. A large number of 0.01% resistances have been tested, and most of them can still be kept within 0.02% after several years. The temperature coefficient also reaches a high level due to material selection and process, which is about 5ppm/℃ to 20ppm/℃. The price of new products is about 5 yuan/piece.

Resistance (Figure 3)

Low TC wire winding resistance: TC (temperature coefficient). It is commonly used in various old foreign precision instruments (such as Fluke). It uses nickel chromium resistance alloy. The temperature coefficient is very low, generally between 1 ppm/℃ and 5 ppm/℃. Some resistors are marked with the measured temperature coefficient. The aging is not big, basically within 20ppm/year, and the second-hand price is about 10 yuan/piece. After calibration, such resistance can be used as a general standard resistance.

Fully sealed wire winding: The resistance wire material is the same as above, but the use of metal shell seal (the lead is post welded) completely eliminates moisture and oxidation, so the stability is very high, reaching about 8ppm/year, and the temperature coefficient is mostly within 1ppm/℃, which is widely used in the old generation of high-level measuring instruments and standard resistors. The second-hand price is about 50 yuan/piece.

Resistance (Figure 4)

Plastic block resistance: Due to the use of nickel chromium resistance alloy and compensation technology, the temperature coefficient can be very low, even<1ppm/℃. However, the aging characteristic of the resistance is not very good due to poor sealing. It can only guarantee 25ppm/year, and the typical value is 12.5ppm/year. The price of new products is about 50 yuan/piece, and that of second-hand products is about 20 yuan/piece. Such resistance is also often used by audio enthusiasts, because in addition to the above characteristics, it also has ultra-low noise And non inductance.

Resistance of gold sealing block: This is the highest level resistance at present. The internal structure is the same as above, but the cermet seal is used (similar in appearance Crystal oscillator ）, completely eliminate external aging factors, and zero temperature coefficient technology makes the temperature coefficient difficult to measure. The typical aging value is 2ppm/year, and some reach below 0.5ppm/year. The price of new products is about 400 yuan/piece. Western countries have blocked China from importing for military purposes. Even the 8-and-a-half digit multimeter 3458A is only used (as an internal standard resistor).

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