FI74547B - FOERFARANDE FOER FASTSTAELLANDE AV EN BINAER GASBLANDNINGS BLANDNINGSPROPORTION. - Google Patents

Description

74547

METHOD FOR DETERMINING THE MIXTURE OF A BINARY GAS MIXTURE

The present invention relates to a method for determining the mixture ratio of a binary gas mixture based on the measurement of the speed and temperature of sound. A binary mixture is also considered here to be a multi-component mixture which can be divided into two parts so that the composition of each part remains unchanged and only their relative mixture ratio varies.

A moisture meter based on the measurement of the speed of sound is described in Finnish patent No. 54977 "Drying moisture meter for the drying process". With the device 10 according to the patent publication, the measurement is performed in such a way that the measuring sensor has one sound source and two detectors. The technical solution is an accurate phase measurement of the sound transmitted at a fixed frequency. The disadvantage of this method is to achieve sufficient accuracy in high industrial noise. The speed of sound is also based on a humidity-15 meter marketed by Mahlo GMBH, where a sample stream is sucked from the atmosphere to be examined by a compressed air injector into a fluidistor oscillator, the pitch of which is determined by the sound rate in the sample gas. Recently, acoustic humidity measurement has been reviewed in Morris & Dagle, "A Fast 20 Response Sonic Hygrometer," Moisture and Humidity 1985, Proceedings of the 1985 International Symposium on Moisture and Humidity, Washington DC, April 15-18, 1985.

The method according to the invention is intended to eliminate the drawbacks present in the known solution models. The invention is characterized by the features of the claim.

In the present invention, the accurate measurement of the speed of sound propagation is based, firstly, on the use of an acoustic waveguide, the purpose of which is to form a well-defined measurement geometry and to isolate the measurement space from ambient noise. Second, the audio transmission used is wideband, which allows the transit time to be determined from the autocorrelation function of the received signal or from an appropriately formed cross-correlation fiction.

2 74547

The use of an acoustic waveguide also offers a considerable advantage in that the audio transmitter and receiver can often be placed outside the edge of the measuring atmosphere causing the problem, if necessary to be separated by a sound-transmitting membrane.

5 With an acoustic waveguide, I also do not naturally arrange two different lengths of sound from the transmitter to the receiver, the travel time difference of which depends only on the mechanical structure of the waveguide itself and the gas contained in it, not at all from the sound transmitter or receiver. In this case, the autocorrelation furiction of the audio signal 10 recorded from a single receiver shows two side peaks which are located symmetrically at the above-mentioned travel time difference from the origin (Fig. 1).

In gases, the speed of sound C is obtained from the known formula (1) C = (γΚΓ / Μ) 1/2, where 15 y is the adiabatic constant R is the general gas constant = 0.082056 [dm3 »atm / nol K] T is the temperature [k] M is average itolecular weight

By measuring the gas state and the speed of sound propagation, the average molecular weight can be calculated.

The average molecular weight, in turn, determines the mixture proportions of the binary gas mixture. For example, air can be thought of as a binary mixture of dry air and water vapor. The absolute humidity of Ky 1 inert air can be calculated from the formula

M

p · M 1 - M

25 (2) p = - ^ - [g / am3] 2 RT 1 _ \ o

Md

II

74547 3 Here p is the air pressure M. is the molecular weight of dry air 28,964 a M is the molecular weight of water 18,015

H0O

5 and 2 M average molecular weight solved from formula (1) γΚΓ (3) M =.

C2

In addition to the direct waveguide connection from the transmitter to the receiver, the required second travel path can be formed from a side branch placed in the atmosphere to be measured 10, from the end of which the sound is reflected back to the main branch. As the sound travels back and forth, the effect of the gas flow rate on the sound travel time is eliminated. The side branch can also be divided into several parallel branches of the same length. The gas in the branch must be sufficiently in contact with the atmosphere to be measured for the sensor to react quickly to changes in the atmosphere.

Since the generation of the correlation function and the calculation of the exact travel time from it clearly require more expensive electronics than the sensor itself, a more economical implementation is often achieved by connecting several sensors alternately to the same measuring electrode at the multiplexer.

When choosing a broadband transmission, it must be taken into account, first, that the simplest correlator only considers whether the signal is above or below its average (polarity correlator), but completely ignores the amplitude of the signal. Second, it must be borne in mind 25 that as sound progresses in a gas-filled acoustic waveguide, the high frequencies are attenuated clearly more than the low frequencies. The broadband transmission can be noise type or frequency scanning. High frequencies are especially important in accurately determining the travel time difference.

The method according to the application, and in particular the mixture ratio meters manufactured according to the method, can vary greatly within the scope of the patent requirements.

Claims (2)

4 CLAIM 7 4 5 4 7 A method for accurately measuring the mixture ratio of a binary gas mixture based on the accurate measurement of the speed and temperature of sound, characterized in that a broadband audio signal is transmitted in an acoustic waveguide filled with several parallel side branches of the same length connected to the same main pipe point, the sound of each of which is reflected back to the main branch and that the travel time difference τ corresponding to the difference L of the different paths is determined as the distance of the received signal autocorrelation function "side peaks" from the origin and the average of the formula γΒΤ M = - τ2 L2 where Y en the adiabatic constant R is the general gas constant 25. is the absolute temperature of the gas, or an equivalent formula calculated for a more realistic gas than the ideal gas, and I! that the partial densities Pj, and ς> 2 30 of the mixed gases (1, 2) are calculated from the formulas 5 74547 p · Mjl 1 - m / m2 Pl RT 1 - Mj / Mj p · M2 1 - M / Mj p = ---— FT 1 - M2 / M1 with a molecular weight of blend gas 1 5 M2 is the molecular weight of a blend gas 2, or that the result is represented in the desired form by deriving in a known manner from these formulas or similar formulas valid for a more realistic gas than the ideal gas. 6 7 4 5 4 7 PATENTKRAV u ^ 'In the case of a basic gas supply with a high temperature and temperature base for the purpose of bleaching and the use of a binary gas stream, the light is shown in Figure 5. varande gasen fyllt akustiskt rör längs tva skilda vägar av olika längd fran en sändare account en mottagare och 10. att den längre vägen bildas av tvä eller flera, i jämbredd med varandra och av samma längd varande si-dogrenar, fran vilkas respektek änd -Steel to the right side of the field and 15. Fig. 1 of the signaling frameworks diffuse τ, somewhat of the skill and power of the L, after which there was a strong, best relationship relationship function "standard" of the origin of the field and the figure of 20 in the case of medium-sized gas enligt form M - ifr2 L2 där γ är en adiabatkonstant 25 The total temperature of the gas constant The absolute temperature or the total temperature, the realistic formula is ideal