Resistor models, types, and performance

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Basic Knowledge _ Resistor Models, Types, and Performance I. Method of naming resistor models: Domestic resistors have models that consist of four parts (not applicable to sensitive resistors). The first part is the main designation, represented by letters, and indicates the name of the product. Where R represents resistance, and W represents a potentiometer. Part 2: Materials, represented by letters, indicate the material from which the resistor body is made. T – carbon film, H – synthetic carbon film, S – organic solid, N – inorganic solid, J – metal film, Y – nitride film, C – deposited film, I – glass glaze film, X – wire-wound. Part Three: Classification, generally represented by numbers; certain types are indicated by letters to show what category the product belongs to. 1-Standard, 2-Standard, 3-UHF, 4-High resistance, 5-High temperature, 6-Precision, 7-Precision, 8-High voltage, 9-Special, G-High power, T-Adjustable. Part Four: Serial number, indicated by digits, used to represent different varieties within the same type of product, in order to distinguish their physical dimensions and performance characteristics. For example: RT 11 – ordinary carbon film resistor type a1. II. Classification of resistors: 1. Wire-wound resistors: general-purpose wire-wound resistors, precision wire-wound resistors, high-power wire-wound resistors, and high-frequency wire-wound resistors. 2. Film resistors: carbon film resistors, synthetic carbon film resistors, metal film resistors, metal oxide film resistors, chemically deposited film resistors, glass glaze film resistors, and metal nitride film resistors. 3. Solid resistors: inorganic synthetically made solid carbon resistors, organic synthetically made solid carbon resistors. 4. Sensitive resistors: varistors, thermistors, photorezystors, force-sensitive resistors, gas-sensitive resistors, humidity-sensitive resistors. III. Main characteristic parameters 1. Nominal resistance value: The resistance value indicated on the resistor. 2. Allowable error: The percentage of the difference between the nominal resistance value and the actual resistance value relative to the nominal value is called the resistance tolerance; it indicates the accuracy of the resistor. The relationship between allowable error and precision grade is as follows: ±0.5%–0.05, ±1%–0.1 (or 00), ±2%–0.2 (or 0), ±5%–Grade I, ±10%–Grade II, ±20%–Grade III. 3. Rated power: The maximum power that a resistor can dissipate during long-term operation under normal atmospheric pressure of 90–106.6 KPa and an ambient temperature range of –55°C to +70°C. The rated power series for wire-wound resistors is (W): 1/20, 1/8, 1/4, 1/2, 1, 2, 4, 8, 10, 16, 25, 40, 50, 75, 100, 150, 250, 500. The rated power series for non-wire-wound resistors is (W): 1/20, 1/8, 1/4, 1/2, 1, 2, 5, 10, 25, 50, 100. 4. Rated voltage: The voltage calculated from the resistance value and the rated power. 5. Maximum operating voltage: The maximum continuous operating voltage permitted. When operating at low pressure, the maximum operating voltage is lower. 6. Temperature coefficient: The relative change in resistance value for every 1°C change in temperature. The smaller the temperature coefficient, the better the stability of the resistance. A resistance value that increases as temperature rises has a positive temperature coefficient, while the opposite case has a negative temperature coefficient. 7. Aging coefficient: The percentage change in the resistance value of a resistor under long-term operation at its rated power; it is a parameter that indicates the lifespan of the resistor. 8. Voltage coefficient: The relative change in the resistor for every 1 volt change in voltage within the specified voltage range. 9. Noise: Irregular voltage fluctuations that occur in resistors, consisting of thermal noise and current noise. Thermal noise arises from the irregular free movement of electrons within a conductor, resulting in irregular changes in voltage between any two points in the conductor. IV. Methods of marking resistor resistance values 1. Direct marking method: The resistance value is indicated on the surface of the resistor using numbers and unit symbols, with the allowable tolerance expressed as a percentage; if no tolerance is specified, it is assumed to be ±20%. 2. Alphanumeric notation: The nominal resistance value is represented by a systematic combination of Arabic numerals and alphanumeric symbols, with the allowable tolerance also expressed using alphanumeric symbols. The digit before the symbol indicates the resistance value in whole numbers, while the digits following it represent the resistance value to the first decimal place and then to the second decimal place. Alphanumeric symbols indicating the allowable error: The alphanumeric symbols D, F, G, J, K, M correspond to allowable tolerances of ±0.5%, ±1%, ±2%, ±5%, ±10%, ±20%. 3. Digital method: A marking method in which the nominal value of a resistor is expressed using three digits. The digits are arranged from left to right; the first two digits represent the significant value, while the third digit indicates the exponent, that is, the number of zeros, with the unit being ohms. Deviations are usually represented by symbolic characters. 4. Color coding method: Use bands or dots of different colors on the surface of the resistor to indicate the nominal resistance value and allowable tolerance. Most resistors abroad use the color coding method. Black-0, Brown-1, Red-2, Orange-3, Yellow-4, Green-5, Blue-6, Purple-7, Gray-8, White-9, Gold-±5%, Silver-±10%, Colorless-±20%. When the resistance is expressed in four digits, the last digit must be gold or silver; the first two digits represent the significant figures, the third digit indicates the power, and the fourth digit denotes the tolerance. When the resistance is five rings, the last ring is far apart from the previous four rings. The first three digits are the significant figures, the fourth digit is the exponent, and the fifth digit is the deviation. V. Common Resistors 1. Potentiometer A potentiometer is a electromechanical component that generates an output voltage proportional to the displacement of its brush on the resistive element. 1.1 Synthetic carbon film potentiometers: The resistive element is formed by coating a substrate surface with ground materials such as carbon black, graphite, and quartz. This manufacturing process is simple, and these potentiometers are the most widely used ones at present. It is characterized by high resolution, good wear resistance, and a long service life. The disadvantages are current noise, high non-linearity, poor moisture resistance, and low stability of the resistance value. 1.2 Organic solid potentiometers: Organic solid potentiometers are a new type of potentiometer; they are created by using heat and pressure to compress organic resistive powder into the grooves of an insulator. Compared to carbon film potentiometers, organic solid potentiometers offer advantages such as better heat resistance, higher power handling capacity, greater reliability, and improved wear resistance. However, it has a large temperature coefficient, high dynamic noise, poor moisture resistance, a complex manufacturing process, and low resistance value accuracy. It is used to regulate voltage and current in compact, highly reliable, and wear-resistant electronic devices as well as in AC and DC circuits. 1.3 Metal glass uranium potentiometers are made by applying a metal glass uranium resistance paste onto a ceramic substrate in a specific pattern using screen printing, followed by high-temperature sintering. Its features include a wide range of resistance values, good heat resistance, high overload capacity, resistance to moisture and wear, making it a promising type of potentiometer. The disadvantages are high contact resistance and significant current noise. 1.4 Wound Potentiometer A wound potentiometer is made by using constantan wire or nichrome alloy wire as the resistive element, which is then wound around an insulating frame. Wire-wound potentiometers feature low contact resistance, high precision, and a small temperature coefficient. Their disadvantages include poor resolution, relatively low resistance values, and poor high-frequency performance. It is mainly used as a voltage divider, rheostat, and for zeroing and setting operating points in instruments. 1.5 Metal film potentiometers: The resistive element of a metal film potentiometer can be made of alloy films, metal oxide films, metal foils, etc. Its features include high resolution, high temperature resistance, a low temperature coefficient, low noise, and good smoothness. 1.6 Conductive plastic potentiometers: A DAP (dipropyl phthalate) resistive paste is applied to an insulating substrate using a special process, and then heated to form a resistive film; alternatively, DAP resistive powder is thermoplastically pressed into the grooves of an insulating substrate to create a solid body that serves as the resistive element. Its features include: good smoothness, excellent resolution, good wear resistance, long service life, low operational noise, high reliability, and resistance to chemical corrosion. Used in servo systems for space devices, missiles, aircraft radar antennas, etc. 1.7 Potentiometers with switches: There are rotary switch potentiometers, push-pull switch potentiometers, and push-push switch potentiometers. 1.8 Pre-set potentiometers: In a circuit, once a pre-set potentiometer has been adjusted to the desired setting, its adjustment position is sealed with wax, so it does not need to be adjusted again under normal circumstances. 1.9 Linear slide potentiometer: The resistance value is changed using a linear sliding mechanism. 1.10 Dual potentiometers: There are off-axis dual potentiometers and coaxial dual potentiometers. 1.11 Contactless potentiometers: These eliminate mechanical contacts, offering long service life and high reliability; they include photoelectric potentiometers, magnetosensitive potentiometers, etc. 2. Solid carbon resistors: These are solid resistors made by mixing carbon particles with conductive materials, fillers, and binders. Features: It is inexpensive, but it has large resistance value errors and noise voltage, as well as poor stability; therefore it is rarely used these days. 3. Wound resistors are made by winding high-resistance alloy wire around an insulating core, with a heat-resistant glaze insulating layer or insulating paint applied on the outside. Wound resistors have a low temperature coefficient, high resistance value accuracy, good stability, as well as heat and corrosion resistance; they are primarily used as precision high-power resistors. Their disadvantages are poor high-frequency performance and a large time constant. 4. Film resistors are made by evaporating a material with a specific resistivity onto the surface of an insulating material. The main points are as follows: 4.1 Carbon film resistors are made by depositing crystalline carbon on a ceramic rod framework. Carbon film resistors have low costs, stable performance, a wide range of resistance values, and low temperature and voltage coefficients, making them the most widely used resistors today. 4.2 Metal film resistors. The alloy material was evaporated and deposited on the surface of the ceramic rod framework using vacuum evaporation. Metal film resistors have higher precision than carbon film resistors, better stability, and lower noise and temperature coefficients. It is widely used in instruments and communication equipment. 4.3 Metal oxide film resistors: A layer of metal oxide is deposited on an insulating rod. Since it is an oxide in itself, it is stable at high temperatures, resistant to thermal shock, and has a high load-bearing capacity. 4.4 Synthetic film resistor: It is obtained by coating a conductive composite suspension on a substrate, and is therefore also known as a paint film resistor. Due to the granular structure of its conductive layer, it generates high noise and has low precision; it is mainly used to manufacture high-voltage, high-impedance, small-sized resistors. 5. Metal-glass uranium resistors: Metal powder and glass uranium powder are mixed and printed on a substrate using screen printing. Resistant to moisture and high temperatures, with a low temperature coefficient; mainly used in thick-film circuits. 6. SMD surface-mount resistors are a type of metal-glass resistor; their resistive element is made from highly reliable ruthenium-based glass materials that have been sintered at high temperatures, with electrodes constructed from silver-palladium alloy paste. It has a small size, high precision, and good stability; as it is a sheet-type component, it exhibits excellent high-frequency performance. 7. Sensitivity resistors: Sensitivity resistors are those whose characteristics are sensitive to factors such as temperature, voltage, humidity, light, gases, magnetic fields, and pressure. The symbol for a sensitive resistor is the ordinary resistor symbol with a slash added to it, along with an indication of the type of sensitive resistor, such as t.v., etc. 7.1 Varistors mainly include silicon carbide and zinc oxide varistors, with zinc oxide possessing more excellent properties. 7.2 Humidity sensors consist of a humidity-sensitive layer, electrodes, and an insulator. The main types of humidity sensors include lithium chloride-based humidity sensors, carbon-based humidity sensors, and oxide-based humidity sensors. Lithium chloride humidity sensors have a resistance that decreases as humidity increases; their disadvantages include a limited measurement range, poor reproducibility of their characteristics, and significant sensitivity to temperature. The disadvantages of carbon humidity sensors are low sensitivity at low temperatures, a significant influence of temperature on their resistance value, and aging issues, which result in their limited use. Oxide humidity sensors exhibit superior performance; they can be used for extended periods, are less affected by temperature, and their resistance varies linearly with humidity levels. There are materials such as tin oxide and ferronickel. 7.3. Photoresistors: A photoresistor is an electronic component whose conductivity changes in response to variations in light intensity. When a substance is exposed to light, the concentration of charge carriers increases, thereby raising the conductivity – this is known as the photoconductive effect. 7.4 Gas sensors are made by utilizing the redox reactions that occur when certain semiconductors absorb specific gases; their main component is metal oxides. The main types include metal oxide gas sensors, composite oxide gas sensors, and ceramic gas sensors. 7.5、Force-sensitive resistor: A force-sensitive resistor is a type of resistor whose resistance value changes in response to pressure; it is referred to as a piezoresistor abroad. The so-called pressure resistance effect refers to the phenomenon in which the resistivity of semiconductor materials changes in response to mechanical stress. It can be used to manufacture various torque meters, semiconductor microphones, pressure sensors, and more. The main types include force-sensitive resistors and selenium-germanium alloy force-sensitive resistors; relatively speaking, alloy resistors have higher sensitivity. This post was last edited by 771207 on 2008-2-18 20:20]