WESTON INSTRUMENTS & ELECTRONICS - ACS Publications

May 18, 2012 - WESTON INSTRUMENTS & ELECTRONICS. Anal. Chem. , 1963, 35 (11), pp 130A–130A. DOI: 10.1021/ac60204a826. Publication Date: ...
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INSTRUMENTATION

AVCDisTS tube, sealed at the ends with trans­ mitter and receiver, will resonate at a frequency f0 = nc/21 where c is the velocity of sound, 1 is the length of the pipe, and η = 1, 2, 3, . . .. The velocity of sound in an ideal gas is: c = V ^ v R T / m ) where γ is the ratio of the specific heats, R is the molar gas constant, Τ is the absolute tempera­ ture, and m is the molecular weight. If this is substituted in the preceding equation, we have:

FROM WESTON

f0 = (1/21) V ( y R T / m )

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WESTON

I N S T R U M E N T S & ELECTRONICS Circle No. 133 on Readers' Service Card 130 A

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ANALYTICAL CHEMISTRY

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hence the resonant frequency is pro­ portional to -ν/Τ a r ) d is a function of the parameters of the gas. The authors have given details of a transducer of this type for the meas­ urement of temperature. In their case, the sensitivity attained (depending upon the length of the resonator) was 1 to 9 cycles per second for ° C. Actually, the general technique of such resonators, particularly when used with modern electronic counting techniques, can attain high precision and be employed, as the equations in­ dicate or imply, for such things as specific heats, the analysis of gases, liquids, or solids, or for determining elastic constants, Young's modulus, etc. Frequency measurements are easily made to 1 part in 108 or better and over a wide range of counting intervals. Once more we mention the fact that during World War I the Germans were analyzing nitrogen-hydrogen mix­ tures for use in the Haber nitrogen fixation process by blowing them through an organ pipe. For a pipe of fixed dimensions, the pitch or fre­ quency is a function of the average molecular weight of the gas mixture. The speed of sound in hydrogen is 1260 meters/second and that of nitro­ gen 337.5 m./sec. In the absence of fancy electronics at that time and to avoid the need for analysts with a sense of absolute pitch, a motor driven siren was used to match the tone to zero beat. TRANSLATIONS OF RUSSIAN INSTRUMENTATION LITERATURE

Another convenient source of current information on Soviet developments in instrumentation, measurement tech­ niques, and automatic control is Meas­ urement Techniques, a translation of Izmeritel'naya Tekhnika, a publication of the Academy of Sciences of the U.S.S.R. It is published and distrib­ uted at nominal subscription rates under a grant in aid to the Instrument Society of America from the National Science Foundation.