Monitoring of Thermal Environment in Space Using Acoustic Probe

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The propagation velocity of sound is often used to measure temperature. The sound probe has the advantage of non-contact sensing and quick response. By combining a sound probe with computerized tomography (CT) and data interpolation, an image of temperature distribution through space can be reconstructed. We have proposed methods for measuring the mean temperature and the temperature distribution in two-dimensional space using an acoustic CT (A-CT) method with a very small number of acoustic transducers. This monitoring system can be set up easily and can monitor the atmosphere any time. This system has the advantage that it can be used in such applications as indoor environment evaluation, air conditioning, and energy conservation.As a result of the foundational research over two years, next facts were proven. The thermometry using the sound probe confirmed being suitable for environmental monitoring of large-scale space of several thousand mィイD12ィエD1, life space of several mィイD12ィエD1 … More and enclosed space of several cmィイD12ィエD1. This study can also contribute to environmental problem such as the dioxin prevention. Outlines of achieved research result are as follows.(1) Temperature Measurement Using Sound Probe and its Measurement Error ィイD11,2)ィエD1A burst of sound created by the computer is connected to a transmitter via the digital-to-analog (D-A) converter, and the received signal is applied to the computer via the analog-to-digital (A-D) converter. The time of flight of the sound is measured from the correlation in time between the created burst signal data and the measured signal. The time resolution is exactly 4 μs because the sampling frequency was exactly 250 kHz. Using a short base line, the measurement of mean temperature was possible at the accuracy of 0.5゜C or less.(2) Measurement of Temperature Distribution in Rectangular Space ィイD13)ィエD1The measured object is a rectangular space of size 4,020 mm (D) × 4,200 mm (W) partitioned into a 3 × 3 grid, with 9 unit cells. By arranging a certain geometrical property of the sound propagation path, we can formulate an expression for the temperature distribution as a matrix function of the sound velocity. Twelve transducers are installed in contact with the four walls. We create a temperature gradient throughout the room using an electrical heat source. Experimental reconstruction results of the room temperature distribution were in agreement with the distributions estimated from the temperature profiles of the heat sources.(3) Measurement of Temperature Distribution in Circular Space ィイD14)ィエD1The measured object is a circular space with a radius of 1,480mm. Sixteen transducers are installed on the circular stage. Without a mechanical motion, projection data for the reconstruction is acquired by electronic scanning. We reconstruct the temperature distribution by interpolation from a small number of data set. Electrical heaters create a temperature gradient in space. The temperature profile is measured by 19 thermocouples and used for a computer simulation. Experimentally reconstructed images are in agreement with the simulated images.(4) Space Thermometry Using Delay Line Oscillator ィイD15)ィエD1Acoustic thermometry in space using a double-delay line oscillator is described. The delay line oscillator is one of the important components in the sensor systems. In this study, an adverse effect of a discontinuous oscillation was solved with the adoption of the acoustic technique, which uses multiple oscillators. An experimental result at 40 kHz shows that the error of measured room temperature is 1.5%, in a room of size 4,020 mm (D) × 4,200 mm (W) × 3,550 (H), with air conditioning. The acoustic thermometry proposed in this study has advantages over conventional methods, for such applications as atmospheric monitoring and air conditioning. Less