IMG_20191022_095728.jpg - TYPES Of amro TO MA RESISTANCE Since Rzo of Eq(3.8 is the resistance of the conductor at 20"C and EXAMPLE 3.8 If the

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Unformatted text preview: TYPES Of amro TO MA RESISTANCE Since Rzo of Eq. (3.8) is the resistance of the conductor at 20"C and EXAMPLE 3.8 If the resistance of a copper wire at freezing (0"C) 7 - 20'C is the change in temperature from 20"C, Eq. (3.8) can be 30 0, what is its resistance at - 40"C? written in the following form: Solution: Eq. (3.5) R = P-[1 + 020 AT] (3.9) 234 5" C+0 234.5"C -4090 30 0 RZ providing an equation for resistance in terms of all the controlling R2 = (30 02 )( 194.5 . C) 234 5" C = 24.88 0 parameters, PPM/'C EXAMPLE 3.9 If the resistance of an aluminum wire at room tempera For resistors, as for conductors, resistance changes with a change in tem- have (20'C) is 100 mall (measured by a millichrometer), at what temper. perabare. The specification is normally provided in parts per million per atacre will its resistance increase to 120 mo? Solution: Eq (35) degree Celsius (PPM/ C), providing an imn late indication of the sensi arity level of the resistor to temper For resistors, a 5000 PPM Level is 256"C + 20"C 236"C+ Iz considered high, whereas 20 PPM is quite low, A 100O PPMP'C character. re results in a change is zenis- 100 m() 120 mo istic reveals that a 19 change in rance equal to 1000 PPM, or 1009/1,0m,AND = VLOG of its nameplate and I2 = 120 mn 2560 C valve not a significant change for most applications, However, a 10" (100 m(2- 2365C change results in a change equal to 1/ICO (19) of is nameplate valve, which is becoming significant, The concern, therefore, lies not only with the PPM level, but also with the range of expected temperalive vacation, In cavallion form, the change in resistance is given by TABLE 2.A Temperature coefficient of resistance for panous //Temperature Coefficient of Resistance AR = PARINA (PPM)AT) (3,18) conduction ar KyC There is a second popular equation for calculating the resistance of a conductor at different temperatures, Defining Material Temperature and IT is the change in temperature fron the reference lord of Life. Copper (2,7) Gold EXAMPLE .10 FOR & I KEL CANON CORPORATION FORGOT WINA A PIMA as The temperature coefficient of resistance it & temperature of 20C 6,665 and his as the resistance of the sample at 20VC, We determine the resis tance Re, at a temperature , by Solution, 6.606 Contrastan (2.8, The values of an, for different materials have been evaluated, and a fewr are listed in Table 24, Ex (32) can be written in the following for # 1160 42 AT from which the site of scifi for a, we defined, 26 TYPES OF RESISTORS Since ARIAT is the slope of the sucre in Fig, 211, we can conclude that Fixed Resistors the higher the temperature coefficient of resistance for a material, the Revision are made in many forme, the all belong in side of ers more SERSHIDE IN THE resistance level in changes in temperature, Referring 16 Table 2.3, we find that copper is more sensitive to rein perature variations than to silver, gold, of aluminum, although the differ...
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  • Fall '19
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