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Part Name  Description 
N_09U00683 Datasheet(PDF) 4 Page  AVX Corporation 

4 page 3 NTC Thermistors General Characteristics 2.1.5. Further approximation of R (T) curve The description of the characteristic R (T) can be improved by using a greater number of experimental points, and by using the equation: 1 = A + B ( n R) + C ( n R)3 T The parameters A, B and C are determined by solving the set of equations obtained by using the measured resis tances at three temperatures. The solution of the above equation gives the resistance at any temperature: The precision of this description is typically 0.2°C for the range –50 to +150°C (A, B, C being determined with exper imental values at –20, +50 and 120°C) or even better if this temperature range is reduced. The ratios R(T)/R(25°C) for each of the different materials shown on pages 29 to 33 have been calculated using the above method. 2.1.6. Resistance tolerance and temperature precision An important characteristic of a thermistor is the tolerance on the resistance value at a given temperature. This uncertainty on the resistance (DR/R) may be related to the corresponding uncertainty on the temperature (DT), using the relationship: T = 100 • R • 1 R Example: consider the thermistor ND06M00152J — • R (25°C) = 1500 ohms • Made from M material • R (T) characteristic shown on page 23 gives: =  4.4%/°C at 25°C • Tolerance R/R = ±5% is equivalent to: T = 5%/4.4%/°C = ±1.14°C 2.1.7. Resistance tolerance at any temperature Any material used for NTC manufacturing always displays a dispersion for the R (T) characteristic. This dispersion depends on the type of material used and has been especially reduced for our accuracy series thermistors. Thus, the tolerance on the resistance ( R 2/R2) at a temper ature T 2 is the sum of two contributions as illustrated on Figure 1: – the tolerance R 1/R1 at a temperature T1 used as a reference. – an additional contribution due to the dispersion on the characteristic R (T) which may be called “Manufacturing tolerance” (Tf). Figure 1 Differentiating the equation R = A exp (B/T), the two contri butions on the tolerance at T can also be written: R2 = R1 + ⎪⎪ • B R2 R1 The T(f) values given with the resistance – temperature characteristics on pages 29 to 33 are based on a computer simulation using this equation and experimental values. 2.1.8. Designing the resistance tolerances Using the fact that the coefficient decreases with temper ature ( α = –B/T2), it is generally useful to define the closest tolerance of the thermistor at the maximum value of the temperature range where an accuracy in °C is required. For example, let us compare the two designs 1 and 2 hereafter: Only the Design 2 is able to meet the requirement ΔT 1°C from 25°C to 100°C. R Ω R 25 25 °C T Temperature ( °C) Graph with B Graph with B ± ΔB } ( ΔR) 25 °C } } (ΔR)25°C + TF } =(ΔR) T 1  1 T 1 T 2 TR α Design 1 Design 2 (°C) (Ω) (%/°C) R/R(%) T(°C) R/R(%) T(°C) 0 3275 5.2 3.5 0.7 5.0 1.0 25 1000 4.4 3.0 0.7 4.5 1.1 55 300 3.7 3.5 1.0 4.0 1.1 85 109 3.1 4.1 1.3 3.4 1.1 100 69.4 2.9 4.5 1.6 3.0 1.0 A 1/T C () A 1/T C () n R (T) = ] [ 27 2 1 3 B C 3 + 3 2 327 2 + 4 3 ()  3 +27 2 A 1/T C () () () + 3 2 327 2 + 4 3 A 1/T C () B C () () 
