Prospects of Using a Modified Null Method for Temperature Measurement with Resistance Sensors
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THERMOPHYSICAL MEASUREMENTS PROSPECTS OF USING A MODIFIED NULL METHOD FOR TEMPERATURE MEASUREMENT WITH RESISTANCE SENSORS A. V. Filatov, K. A. Serdyukov, and A. A. Novikova
UDC .621.36
The article describes and analyzes the existing problems when using linear measuring devices for measuring temperature. When measuring temperature with resistive temperature sensors, a modified null method is proposed to use, which ensures the invariance of the meter to changes in the measuring path gain. The null balance in the measuring path is maintained automatically by synchronous pulse-amplitude and pulsewidth modulations and using of a tracking circuit for adjustment of the width signal. Once the null balance is achieved, the width modulation control pulse duration will be linearly related to the resistance of the temperature sensor. Modification of the null method simplifies the design of a thermometer with a resistive sensing element. In this proposed mechanism, two precision resistors which are passive units replace the active precision units to increase the accuracy and improve the linearity of its conversion characteristics. The work reports the errors of temperature measurements by the modified null method and describes the calibration of a manufactured digital thermometer with a miniature platinum resistance temperature sensor. The proposed modification of the null measurement method can be used to construct devices comprising a sensor with a sensing element, namely electrical resistance that is altered under the influence of a nonelectrical parameter. Keywords: temperature measurement, resistive temperature sensors, modification of the null measurement method.
Introduction. Measurement of temperature as a physical value represents a quite common and an important task. The linearity of the temperature scale necessitates the use of linear measuring devices, and their transfer characteristics can be presented as a system of equations Y B AX; (1) Y B AX, where X and Y are input and output signals, respectively; A and B are coefficients of the slope and shift of the linear transformation characteristic, respectively. According to the electrical circuit theory, the coefficients A and B determine the signal values of the two internal reference elements (sources) of the measuring device, which are adjusted by calibration. Two sources of reference signals are connected alternately to the input of the measuring device in two-point calibration. Further, the values of the reference signals applied to the input are assigned to the reference internal elements in (as) the process of adjustment. Then, these values are memorized and used as reference ones. These reference values characterize the linear transfer characteristic of the measuring device. The work [1] describes thermometers with a Wheatstone measuring bridge, one arm of which comprises a sensitive resistive element (thermal resistance), and also a differential amplifier. In these thermometers, the first reference value Tomsk State University of Control Systems and Ra
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