Weak current College】 【precision resistance classification and characteristics of】.

<br> What is precision resistance? <br> In fact, for not engaging in measurement of unwanted points so clear, you can generally think of high-precision, high accuracy, low-error, and so is a meaning. However, for .the word "precision", can be broken down into broken down into three elements: <br> <br> Temperature coefficient. Temperature change is the enemy of resistance, temperature coefficient general use ppm / ¡ .æ said that temperature 1 degree corresponds to a resistance change a few parts per million. 100ppm / ℃ is 0.01% / ℃. <br> Aging. The long-term stability, which may be expressed in ppm / year, and also useful% ./ year. Factory-no matter how accurate resistance, aging, then quickly changed, namely loss of high accurate meaning. <br> Initial adjustment error, this is not too important how much is the idea, as long as the deviation remains unchanged when .it doesn't matter, measurements can be made. Therefore, in this article, didn't do a not to discuss. <br> For accuracy is not too high resistance, we can not say the General accuracy of some resistance. Such as .the electrical resistance of 0.1% accuracy, that is a composite error, actually mean, at room temperature (10 ° c-35 ° c), 1 year, including all of the error, you should still be able to guarantee the resistance in 0.1 .%. <br> However, for high requirements, the specific characteristics of resistance will be tested, this is a good choice. This article will take a common high precision resistors with temperature coefficient and aging two indicators do a description. <br> Common .precision resistor has three categories: metal film resistors, wire wound resistors and block resistance. <br> <br> Metal film resistors are the most common, but better for precision metal film resistors, features a temperature coefficient of resistance is small, relatively stable .. But because of the relatively thin film comparison so fragile, spiral cutting and pressing parts easily out of the question. <br> Wire-wound resistors is also very popular, and even the once highly accurate devices of the main resistance. The resistance wire .materials now there are three: <br>-Older-constantan, heat resistant, but the temperature factor is not very good, and copper thermal electromotive force is relatively high. <br> - MN, Cu, MN, Cu, although precise .heat but the temperature is not too high but temperature coefficient is very small, and thermal electromotive force small copper, is widely used in wire-wound resistors materials. <br> - Evanohm, is translated into El Buddha GNOME is a Nickel-chromium .-aluminium copper alloy, can also be referred to as NI-CR alloy temperature coefficient of resistance, minimal, compared to hard materials, welding performance. <br> Block resistance, also called metal foil resistors, foreign manufacturers to Vishay as representative, is .in the ceramic substrate adhesion on alloy resistive layer then no photographic moment, not only uses a nickel resistance alloy materials and ceramic substrate for further temperature compensation, allowing the temperature coefficient is very small, and many can do <1ppm / ℃. Domestic models ., for poor performance RJ711. <br> The following is the precision resistance classification properties map to the underlying data is based on his years of collection, accumulation, test arrangement. The horizontal axis is the vertical temperature coefficient, the aging rate, therefore, .any resistance to this figure has a position, the more close to the lower-left corner indicates the resistance, the better. <br> <br> <br> The following are the typical resistance do a presentation. <br> <br> .Metal film resistors, the relatively small volume of General, relatively thin film resistance, temperature coefficient and high resistance to aging, besides (> 1M) and low impedance (<5), 1% can guarantee. <br> Green robe resistance .. This is on the mid 1980 'sa metal film resistors terms, because the appearance of dark green and, in view of the MF12 and MF14 multimeter. But according to own actual measurement, performance in General, aging, bias and temperature coefficient of resistance .with red considerably. <br> The Red resistance, high stability, code-named RJJ low temperature coefficient precision metal film, the volume is large, performance is very good, thanks to your own testing, years of resistance, ageing seldom exceed 0.5% ., temperature coefficient are 30ppm / ℃. Please note that the Red resistance there is also a normal accuracy, code-named RJ, performance in General. <br> General wire wound resistors, the use of copper or manganese constantan wire, unsealed (lacquer .), because the wire diameter General indicators of aging for rough comparison so good, but temperature coefficient is not too good, generally is 15ppm / ℃ to 35ppm / ¡ .æ. <br> Precision wire wound, resistance wire generally use precision sealing manganin, improved stability after the actual test large numbers of 0.01% resistance, the vast majority of a few years later still remains within the 0.02%. Temperature coefficient selection and also .because the process reaches a higher level, approximately 5ppm / ℃ to 20ppm / ¡ .æ. New price is approximately 5 Yuan / only. <br> (Also, there is a high-seal wire wound, the stability is better) <br> <br> <br> Low-TC (temperature coefficient) wire-wound .resistors, are common in older abroad (such as Fluke) a variety of precision instruments, the use of nickel resistance alloy, low temperature coefficient, generally 1ppm / ℃ to 5ppm / ¡ .æ and resistance are each only indicate the measured temperature coefficient. Aging is not large, the basic 20ppm/year, second-hand price approximately 10 Yuan / only. Such resistance for calibration, you can as a general standard resistors. <br> < .br> <br> The entire seal wire wound, resistance wire materials ibid., but using a metal shell sealed (leader is the back welding) completely eliminate the humid and oxidation stability is high, reaching 8ppm/year or so, temperature coefficient is .also mostly in 1ppm / ℃, widely used in the older generation of high level measuring instrument and standard resistance, I have a dedicated article done details. Secondhand prices approximately 50 Yuan / only. <br> <br> Plastic block resistance. Due to .the use of nickel resistance alloy and compensation technology, temperature coefficient can be very low, even <1ppm / ℃. But the resistance because the seal is not very good so aging characteristics is not very good, only guarantee 25ppm/year, typical 12.5 .ppm / year. New price is about 50 Yuan / only, second-hand about 20 Yuan / only. This resistance is also often used by audio enthusiasts, becauseIn addition to the above characteristics, but also have low noise and excellent characteristics such as non .-sense. <br> <br> <br> <br> Gold Seal block resistance, this is by far the highest levels of resistance, the internal structure of ibid. but Cermet seal (looks like a crystal oscillator), complete elimination of .external factors of ageing, while zero-temperature coefficient technology enables temperature coefficient reaches is difficult to measure it. Aging typical 2ppm/year, and some reach 0.5ppm/year. New price is approximately 400 Yuan per, Western countries on the blockade, is .strictly prohibited imports for military purposes, even the 8-bit half-multimeter 3458A also just use a (do internal standard resistance). <br> <br> <br> <br> It should be noted that even if the same class of .resistance, the different manufacturers, different times of the products, the difference is very big, just try to find a typical range. <br> <br> Report: what's the best pointer multimeter resistance? <br> Select resistance depends on the grade ., multimeter generally uses grade of 1 / 4 or 1 / 5, such as 2.5 on selected 0.5%, 1-selected 0.2% or 0.25%. <br> Wire wound is best, stability and temperature coefficient of resistance of the small, but .very difficult to be high, therefore mostly low resistance of wire-wound. Only see there is still used 5M resistance wire wound is MF35. <br> Voltage measurement stalls, and so need to 5M 3M of high resistance, generally only selected metal film .. And high precision metal film is more difficult, requires high resistance membrane (such stability may be worse), large volume. Traditional red RJJ precision metal film is very appropriate. Amateur condition if a quest for performance, you can use 6 ring 1M metal .film 0.1% resistance multiple tandem. <br> <br> <br>.