Measurements of air temperature and humidity with sound

V okviru naloge smo zasnovali merilnik hitrosti zvoka, s katerim posredno določimo temperaturo in relativno vlažnost zraka. Merjenje hitrosti zvoka temelji na vzpostavitvi stoječega valovanja v cevi ter določanju frekvence minimuma. Na podlagi literature smo opredelili potrebno natančnost merjenja za določitev točke rosišča zraka. S pomočjo frekvenčne in termične analize smo simulirali teoretične pogoje in vzpostavljeno stoječe valovanje v cevi. Izdelali smo programsko kodo za obdelavo zvočnega signala in izračun hitrosti zvoka. Predstavili smo rezultate merjenja hitrosti zvoka z merilnikom ter opredelili natančnost merilnega instrumenta in glavne vplivne parametre. Ugotovili smo, da lahko hitrost zvoka merjenja v stacionarnih pogojih izvedemo z ustvarjenim merilnikom, pri čemer so meritve dovolj natančne za določitev točke rosišča zraka. V zaključku smo predstavili parametrično analizo vpliva merjenih parametrov na določanje razmerja specifičnih toplot.In the scope of this master thesis, a meter for measuring the speed of sound was developed in order to indirectly determine the air temperature and relative humidity. The measurement of the speed of sound is based on the establishment of the standing waves in the pipe and the determination of the minimum frequency. Relying on literature, the necessary measurement accuracy is identified to determine the dew point of the air. Frequency and thermal analysis are used to simulate theoretical conditions and the established standing waves in the pipe. Also, a software code was created to process the sound signal and to calculate the speed of sound. The results of the measurements carried out with the meter for measuring the speed of sound are presented, along with the accuracy of the measuring instrument and influential parameters. It was found that the measurement of the speed of sound in steady-state conditions can be carried out with the meter – the measurement results are sufficiently accurate to be able to determine the dew point. The last chapter of the thesis offers a parametric analysis of the effect of measured parameters on the determination of the ratio of specific heat