Enhancing linearity in thermistor signal conditioning circuit using linear numerical search

Temperature to frequency converters (TFC) have been used as thermistor signal conditioning circuit (SCC) and linearization. Many TFC have been proposed by the researchers out of which 7555 timer based SCC has been employed in several applications. The application of 7555 timer based SCC demands a method for generating the optimal circuit parameters yielding desired linearity and sensitivity for a given input temperature range. Two classical methods, namely, inflection point and three point methods have been employed by several researchers for this task. These classical methods, being simple in nature, offer moderate linearity and the residual non-linearity is normally further improved with the help of other supporting methods like software based techniques. In the present work, a linear numerical search based scheme is proposed to enhance the linearization capability of 7555 timer based SCC in TFC. The enhancement is attained by just selecting the appropriate value of a resistor in SCC application. The proposed method has been investigated in simulation on three different industrial grade thermistors for the input temperature range of 0°C-100°C for 7555 based SCC. An enhancement of linearity performances of 4.9%, 4.7% and 4.7% have been obtained over the three point method and 21.7%, 18.3% and 17.8% over the inflection point method for thermistor 1, thermistor 2 and thermistor 3, respectively. Based on these data it can be concluded that linear numerical search a promising solution for linearity enhancement of thermistors in 7555 SCC. The results presented in this work are useful to the design engineers as enhanced linearity also reduces the requirements of further processing.