Method for temperature measurement based on integration of the transient process part of the condenser discharge on a resistance thermometer

Purpose: improving the speed and accuracy of temperature measurement by a resistive sensor (RTD) with remote two-wire connection in distributed monitoring systems. Development and implementation of a temperature measurement method based on the processing of the integration results of the initial phase of the transient discharge process of a capacitor shunting a resistance thermometer, evaluation of the parameters of the integration time determination model and testing of the method on an experimental bench. Determination of errors in measuring RTD resistance by integrating the initial phase of the transition process using a linear model for determining the integration time and evaluating the effectiveness of the proposed solution in comparison with alternative methods.

Methods. The mathematical description of the method is based on the theory of electrical circuits. The effectiveness of the method was evaluated based on the results of experimental studies. When developing a linear model for determining the integration time, a linear regression model was built, and relative errors were calculated based on the average results of multiple measurements.

Results. A method for determining the resistances of resistive temperature sensors based on the processing of the integration results of the initial phase of the transient capacitor discharge process on a two-wire connection in distributed monitoring systems is proposed and investigated.

A mathematical description of the method is given, on the basis of which an algorithm for calculating the resistance of the RTD has been developed, eliminating the influence of the resistance of the connecting wires on the measurement results. The developed algorithm is based on the integration of the transient process of capacitor discharge (accumulation and summation of samples) over a limited time interval, while preserving the results in the middle (t1) and the end of the interval (t2) and calculating the resistance of the RTD based on the obtained parameters.

The parameters of the integration time adjustment model are determined, and measurement errors are estimated. The method was tested using an experimental stand based on an ATmega328 microcontroller and a P4831 resistance store with an accuracy class of 0.02.

Discussion. The results of the research and testing of the RD temperature measurement method presented in the paper demonstrate its effectiveness in reducing measurement errors caused by the influence of the resistance of connecting wires. The application of the proposed measurement methods and processing algorithms makes it possible to use two-wire sensor connections in distributed monitoring systems while maintaining measurement accuracy at the level of more complex and expensive threeand four-wire circuits, eliminating the influence of the resistance of the connecting wires. The application of the voltage integration method described in the work at the initial stage of the transient process allows not only to increase performance, but also to ensure the required level of measurement accuracy. Experimental studies have shown that the relative measurement errors of the method proposed by the authors when using the linear model for determining the integration time do not exceed 0.07% in the range of nominal resistances of 1-4 kOhm (corresponds to the temperature range measured by a platinum resistance thermometer, 0600 0C) with an artificial increase in the total resistance of the connecting wires to a value exceeding 200 ohms.

The proposed method can be applied in monitoring systems using taxiways located at a considerable distance from the measuring unit.

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