Abstract
The NTC (negative temperature coefficient) thermistor precision is significantly increased by the calibration process. The full calibration procedure process itself is sophisticated as it requires a set of calibration points when using the Steinhart-Hart equation for the linearization of the T(R) (Temperature – Resistance) characteristics. Aging and degradation processes tend to distort the metrological characteristics of the NTC thermistors. The novel method of calibration for groups of thermistors produced by the same manufacturer using the same technology is proposed in this paper. The initial calibration data acquired from the calibration results or from the manufacturer is used for approximate computations. During the additional calibration, the approximate data for the group of thermistors is adjusted using linear transformations. The result analysis for five different types of thermistors (A, B, C, D and E) revealed that the temperature measurement errors in the temperature range from 20 0C to 80 0C can be reduced by up to 10 times using the proposed method. The aging and degradation processes were investigated using the thermocycling procedure implemented with steep transitions (100 0C ... 0 0C ... 100 0C). The thermistor R(T) characteristics were repeatedly measured after 1000, 2000 and 3000 thermocycles. The results revealed that statistically, the average error of the temperature measurement for the types C, D and E increased significantly after 3000 thermocycles, whereas the measurement error trend of the thermistors of types A and B was insignificant (p > 0.05). DOI: http://dx.doi.org/10.5755/j01.eee.20.6.7268
Highlights
Precise temperature measurement and control is important in many fields of the science and industry, including biochemical, material sciences, energy accounting, process control
The temperature measurement error using five A type sensors in the temperature range from 25 0C to 80 0C, when the Steinhart–Hart interpolation equation (1) with the coefficients A0, A1, and A3 determined by the R(T) measurement data of the 1st sensor (Fig. 1, No 1) was used for the calculations, are illustrated in the Fig. 1
The temperature measurement error using type A sensors ranged from +0.3 oC to -0.1 oC, which fall within the error value range declared by the manufacturer
Summary
Precise temperature measurement and control is important in many fields of the science and industry, including biochemical, material sciences, energy accounting, process control. Performance, throughput and resistance to the environmental impacts, various types of temperature sensors are used that operate on the base of different physical effects. Thermistor is a type of temperature sensor, that delivers a good sensitivity and a competitive price, but the non-linearity of the dependence of the R(T) curve and deterioration of the metrological. The R(T) dependencies are different and depend both on the material properties and technology applied during the manufacturing process. The scatter of the parameters is controlled by the manufacturer by grouping the R(T) characteristics. The temperature-resistance T(R) dependencies are assigned to each group by calibrating in discrete steps with intervals of 1 0C. The Steinhart-Hart equation is used for approximation of the dependencies written as
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