WO1988006291A1 - DEVICE FOR DETERMINING THE PRODUCT OF P0x$(1,3)$ FOR A GAS - Google Patents
DEVICE FOR DETERMINING THE PRODUCT OF P0x$(1,3)$ FOR A GAS Download PDFInfo
- Publication number
- WO1988006291A1 WO1988006291A1 PCT/SE1988/000066 SE8800066W WO8806291A1 WO 1988006291 A1 WO1988006291 A1 WO 1988006291A1 SE 8800066 W SE8800066 W SE 8800066W WO 8806291 A1 WO8806291 A1 WO 8806291A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- measuring
- gas
- volume
- product
- pressure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Ceased
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/02—Analysing fluids
- G01N29/036—Analysing fluids by measuring frequency or resonance of acoustic waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/32—Arrangements for suppressing undesired influences, e.g. temperature or pressure variations, compensating for signal noise
- G01N29/326—Arrangements for suppressing undesired influences, e.g. temperature or pressure variations, compensating for signal noise compensating for temperature variations
Definitions
- the present invention relates to a device for deter mining the product of p Q • ⁇ for a gas, wherein ⁇ is the ratio between the specific heat capacity of the gas at constant pressure and at constant volume, and p 0 is the static pressure in the gas.
- ⁇ is a parameter included in many formulas which are used to determine gas volumes. This is a problem, since appropriate devices for determining the parameter ⁇ have not been available so far.
- the only possibility known today of determining ⁇ is to determine the specific heat capacity at constant pressure and at constant volume separately by calorimetric methods and then to evaluate ⁇ . Values of ⁇ derived in this way for different gases can be found in scientific tables.
- ⁇ is in present-day methods, made equal to the constant value given in the tables. However, this is not quite satisfactory because ⁇ varies, inter alia, with the temperature. Furthermore, ⁇ is not well defined for all gases. Finally, ⁇ may vary from one location to another in a receptacle containing gas, if the gas forms layers.
- the volume of the gas above the petrol in the tank is determined and subtracted from the total tank volume, which yields the petrol volume.
- formulas containing ⁇ are used.
- ⁇ is not well defined for petrol vapour.
- ⁇ varies with the temperature and often from one location to another in the tank because the petrol vapour tends to form layers.
- the object of the present invention is to provide a device for determining the product of p fi • ⁇ for a gas, which solves the above-mentioned problem.
- a device that is characterised by a measuring cell adapted to be filled with the gas for which the product of pzie • ⁇ is to be determined, means for varying the volume of the measuring cell such that pressure variations arise in the gas in the measuring cell, means for measuring at least one parameter dependent on the variation of volume, and means for calculating the product of p 0 • ⁇ by means of the parameter measured by said measuring means.
- the product of p fl • ⁇ or, if a pressure gauge is added, the parameter ⁇ can be easily determined for all gases.
- the device can be used together with different types of devices for measuring gas volumes, and an accurate value of ⁇ is constantly obtainable, whereby also the accuracy of the gas volume measurement is improved.
- ⁇ does not have the same value throughout, several different devices according to the invention can be mounted.
- the device shown in the drawing comprises a cylind ⁇ rical receptacle 30 having a cylindrical wall 31 and a bottom 33.
- a membrane 34 having a mass m and an active area A is disposed in the receptacle 30.
- the membrane 34 has a central portion 35 rigidified by gluing an aluminium disc to each side of the membrane.
- the membrane 34 is fixed along its periphery to the cylindrical wall 31 of the receptacle 30 and has in the vicinity of this wall a folded or deflected portion -36 extending circularl around the membrane near the periphery thereof and re ⁇ sulting in a low spring rate k for the suspension of the membrane 34. Designed in this manner, the membrane 34 will perform a translational movement, i.e. it will move parallel to itself when caused to oscillate.
- a coil 37 is located above the membrane 34. The coil 37 is wound such that its turns lie in planes parallel to the membrane 34.
- a magnet 38 is located directly below the coil and in the central part of the membrane 34.
- the coil 37, the magnet 38 and current supply means constitute together exciting means adapted to cause the membrane 34 to oscillate.
- the membrane 34 defines together with the bottom 33 of the receptacle a measuring cell or a space 42 which has a known volume V - when the state of the measuring cell is known. This may be the case when the membrane is in a resting position in which it is not affected by the exciting means.
- the volume of the space 42 can, however, be varied by means of the membrane 34 which together with the exciting means constitutes the means for volume variation.
- the bottom 33 of the space 42 has holes 39 through which the gas to be measured can penetrate. The holes 39 are designed to block the frequencies of pressure variations generated by the membrane in the space 42.
- the frequencies normally lie in the range from 200 Hz up to some kHz.
- a microphone 41 is situated in the bottom 33. Together with means (not shown) for amplification, transformation and counting, said micro ⁇ phone forms frequency measuring means which are utilised for determining the frequency of the pressure variations generated in the space 42.
- the frequency measuring means and the current supply means are connected to control and calculation means (not shown) for determining the product of p n • ⁇ for the gas in the space 42.
- the control and calculation means may comprise a computer.
- the function of the device shown in Fig. 1 will now be described.
- the receptacle 30 is placed in e.g. a tank containing the gas on which the measurement is to be carried out, the gas penetrating into the space 42 through the holes 39.
- the membrane 34 is then caused to oscillate, leading to periodic pressure variations in the gas in the space 42. These pressure variations are recorded by the microphone 41 which converts the pressure variations into electrical signals, the fre ⁇ quency of which is determined by the frequency measuring means.
- the excitation of the membrane 34 can take place in different ways.
- the membrane 34 can be caused to oscillate by supplying a short current pulse through the coil 37.
- the system consisting of the gas in the space 42 and the membrane 34 will conse- quently perform a damped sinus oscillation with the natural frequency of the system, which is recorded by the frequency measuring means.
- a sinus- -shaped current can be supplied through the coil, the frequency of this current can be scanned, and the ampli- tude of the oscillation of the membrane 34 can be detec ⁇ ted.
- the frequency determined by the frequency measuring means equals the resonant frequency of the oscillating system consisting of the membrane 34 and the gas in the space 42. If the resonant frequency is to be deter ⁇ mined in this way, the device must be provided with means for measuring the amplitude of the membrane 34.
- Another method for detecting the moment when the system has reached the resonant frequency is to detect the instant at which a rapid phase position change occurs between the sinus wave supplied to the coil 37 and the electrical signal obtained from the microphone. This way of determining the resonant frequency requires means for comparison of phase positions.
- A is the active area of the membrane
- m is the mass of the membrane
- f is the measured frequency of the system
- k is the spring rate of the suspension of the membrane
- V ,- equals the volume of the measu ⁇ ring cell 42 when the state thereof is known.
- the membrane and the exciting means associated with the device can, for example, be designed according to a conventional loudspeaker construction including a cap membrane of aluminium. This gives the advantage of lower weight and higher resonant frequency.
- the means for varying the volume may comprise a piston instead of a membrane.
- the micro- phone 41 measuring the frequency of the pressure varia- tions generated in the gas may be replaced by means for measuring the magnitude of the pressure variation caused by the volume variation in the measuring cell. In this case, p n • ⁇ can be calculated as V f • ⁇ p/ ⁇ V.
- Other embodiments of the device according to the inven ⁇ tion are conceivable.
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Measuring Fluid Pressure (AREA)
- Acoustics & Sound (AREA)
Abstract
A device for determing the product of p0x$(1,3)$ for a gas, wherein $(1,3)$ is the ratio of the specific heat capacity of the gas at constant pressure and at constant volume, and p0 is the static pressure in the gas, includes a measuring cell (42) adapted to be filled with the gas for which the product of p0x$(1,3)$ is to be determined, means (34, 37, 38) for varying the volume of the measuring cell such that pressure variations arise in the gas in the measuring cell, means (41) for measuring at least one parameter dependent on the variation of volume, and means for calculating the product of p0x$(1,3)$ by means of the parameter measured by said measuring means. The device can be completed with a pressure gauge for measuring the static pressure p0, whereby $(1,3)$ can be determined.
Description
DEVICE FOR DETERMINING THE PRODUCT OF PQ • κ FOR A GAS
The present invention relates to a device for deter mining the product of pQ • κ for a gas, wherein κ is the ratio between the specific heat capacity of the gas at constant pressure and at constant volume, and p0 is the static pressure in the gas. κ is a parameter included in many formulas which are used to determine gas volumes. This is a problem, since appropriate devices for determining the parameter κ have not been available so far. The only possibility known today of determining κ is to determine the specific heat capacity at constant pressure and at constant volume separately by calorimetric methods and then to evaluate κ. Values of κ derived in this way for different gases can be found in scientific tables. When volumes are determined by using gas formulas where κ is included, κ is in present-day methods, made equal to the constant value given in the tables. However, this is not quite satisfactory because κ varies, inter alia, with the temperature. Furthermore, κ is not well defined for all gases. Finally, κ may vary from one location to another in a receptacle containing gas, if the gas forms layers.
A practical case where the above-mentioned problem with κ arises, is the measuring of the petrol volume in vehicle tanks. In order to keep the volume measurement unaffected by the fact that the surface of the petrol tilts when driving up and down hills and through curves, the volume of the gas above the petrol in the tank is determined and subtracted from the total tank volume, which yields the petrol volume. When the gas volume is determined, formulas containing κ are used. However, κ is not well defined for petrol vapour. Furthermore, κ varies with the temperature and often from one location
to another in the tank because the petrol vapour tends to form layers. To be able to determine the volume of the petrol vapour, one then must either assume some kind of average value for κ or carry out several ea- surements so that κ can be eliminated. The drawback of the first solution is that the value of the petrol volume will be inaccurate, while the drawback of the second solution is that more than one measurement has to be carried out, and that special steps must be taken to change any measuring parameter between measurements. The object of the present invention is to provide a device for determining the product of pfi • κ for a gas, which solves the above-mentioned problem.
This object is achieved by means of a device that is characterised by a measuring cell adapted to be filled with the gas for which the product of p„ • κ is to be determined, means for varying the volume of the measuring cell such that pressure variations arise in the gas in the measuring cell, means for measuring at least one parameter dependent on the variation of volume, and means for calculating the product of p0 • κ by means of the parameter measured by said measuring means.
By this device, the product of pfl • κ or, if a pressure gauge is added, the parameter κ can be easily determined for all gases. The device can be used together with different types of devices for measuring gas volumes, and an accurate value of κ is constantly obtainable, whereby also the accuracy of the gas volume measurement is improved. In a receptacle where κ does not have the same value throughout, several different devices according to the invention can be mounted.
An example of the present invention will now be described with reference to the accompanying drawing which illustrates an embodiment of a device according to the invention for determining the product of pn • κ.
The device shown in the drawing comprises a cylind¬ rical receptacle 30 having a cylindrical wall 31 and a bottom 33. A membrane 34 having a mass m and an active area A is disposed in the receptacle 30. The membrane 34 has a central portion 35 rigidified by gluing an aluminium disc to each side of the membrane. The membrane 34 is fixed along its periphery to the cylindrical wall 31 of the receptacle 30 and has in the vicinity of this wall a folded or deflected portion -36 extending circularl around the membrane near the periphery thereof and re¬ sulting in a low spring rate k for the suspension of the membrane 34. Designed in this manner, the membrane 34 will perform a translational movement, i.e. it will move parallel to itself when caused to oscillate. A coil 37 is located above the membrane 34. The coil 37 is wound such that its turns lie in planes parallel to the membrane 34. A magnet 38 is located directly below the coil and in the central part of the membrane 34. The coil 37, the magnet 38 and current supply means (not shown) constitute together exciting means adapted to cause the membrane 34 to oscillate. The membrane 34 defines together with the bottom 33 of the receptacle a measuring cell or a space 42 which has a known volume V - when the state of the measuring cell is known. This may be the case when the membrane is in a resting position in which it is not affected by the exciting means. The volume of the space 42 can, however, be varied by means of the membrane 34 which together with the exciting means constitutes the means for volume variation. Furthermore, the bottom 33 of the space 42 has holes 39 through which the gas to be measured can penetrate. The holes 39 are designed to block the frequencies of pressure variations generated by the membrane in the space 42. The frequencies normally lie in the range from 200 Hz up to some kHz. A microphone 41 is situated
in the bottom 33. Together with means (not shown) for amplification, transformation and counting, said micro¬ phone forms frequency measuring means which are utilised for determining the frequency of the pressure variations generated in the space 42. The frequency measuring means and the current supply means are connected to control and calculation means (not shown) for determining the product of pn • κ for the gas in the space 42. The control and calculation means may comprise a computer. The function of the device shown in Fig. 1 will now be described. The receptacle 30 is placed in e.g. a tank containing the gas on which the measurement is to be carried out, the gas penetrating into the space 42 through the holes 39. The membrane 34 is then caused to oscillate, leading to periodic pressure variations in the gas in the space 42. These pressure variations are recorded by the microphone 41 which converts the pressure variations into electrical signals, the fre¬ quency of which is determined by the frequency measuring means. The excitation of the membrane 34 can take place in different ways. For example, the membrane 34 can be caused to oscillate by supplying a short current pulse through the coil 37. The system consisting of the gas in the space 42 and the membrane 34 will conse- quently perform a damped sinus oscillation with the natural frequency of the system, which is recorded by the frequency measuring means. Alternatively, a sinus- -shaped current can be supplied through the coil, the frequency of this current can be scanned, and the ampli- tude of the oscillation of the membrane 34 can be detec¬ ted. When the membrane 34 oscillates at maximum amplitude, the frequency determined by the frequency measuring means equals the resonant frequency of the oscillating system consisting of the membrane 34 and the gas in the space 42. If the resonant frequency is to be deter¬ mined in this way, the device must be provided with
means for measuring the amplitude of the membrane 34. Another method for detecting the moment when the system has reached the resonant frequency is to detect the instant at which a rapid phase position change occurs between the sinus wave supplied to the coil 37 and the electrical signal obtained from the microphone. This way of determining the resonant frequency requires means for comparison of phase positions.
Once the frequency has been determined by any of the techniques described above, the product of p. • n can be calculated in the calculation means by using the formula
An example of an embodiment of the device accor- ding to the invention has been described above. Many ways to modify the device within the scope of the appen¬ ded claims are evident to those skilled in the art. The membrane and the exciting means associated with the device can, for example, be designed according to a conventional loudspeaker construction including a cap membrane of aluminium. This gives the advantage of lower weight and higher resonant frequency. Further¬ more, the means for varying the volume may comprise a piston instead of a membrane. Moreover, the micro- phone 41 measuring the frequency of the pressure varia-
tions generated in the gas may be replaced by means for measuring the magnitude of the pressure variation caused by the volume variation in the measuring cell. In this case, pn • κ can be calculated as V f • Δp/ΔV. Other embodiments of the device according to the inven¬ tion are conceivable.
Claims
1. Device for determining the product of pQ • κ for a gas, wherein κ is the ratio between the specific heat capacity of the gas at constant pressure and at constant volume, and p~ is the static pressure in the gas, c h a r a c t e r i s e d by a measuring cell (42) adapted to be filled with the gas for which the product of pQ • κ is to be determined, means (34, 37, 38) for varying the volume of the measuring cell such that pressure variations arise in the gas in the measuri cell, means (41) for measuring at least one parameter dependent on the variation of volume, and means for calculating the product of pQ • κ by means of the para¬ meter measured by said measuring means.
2. Device according to claim 1, c h a r a c t e - r i s e d in that the measuring means (41) include means for measuring the frequency f of the pressure variations generated in the gas.
3. Device according to claim 1 or 2, c h a r a c ¬ t e r i s e d in that the means for varying the volume of the measuring cell include a membrane (34) having an active area A, a mass m, and a spring rate k for the suspension, and exciting means (37, 38) adapted to cause the membrane to oscillate.
4. Device according to claim 3, c h a r a c t e - r i s e d in that the calculation means are adapted to calculate the product of pQ • κ according to
P„ • H = Vref ' m ' {-2jπf )2 ~ Vref ' km
wherein Vret ~ is the volume of the measuring cell (42) when the state thereof is known.
5. Device according to claim 1, c h a r a c t e ¬ r i s e d in that the measuring means include means for measuring the magnitude of the volume variation ΔV in the measuring cell, and means for measuring the size of the pressure variation Δp; and that the calcu¬ lation means are adapted to calculate the product of p_ • κ according to
V - Δp Pn ' H = re£ * υ ΔV wherein V .- is the volume of the measuring cell (42) when the state therof is known.
6. Device according to any one of the preceding claims, c h a r c t e r i s e d by a pressure gauge for measuring the static pressure pQ in the gas, whereby κ can be calculated according to
κ = Pθ ' κ .
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8700662A SE8700662D0 (en) | 1987-02-18 | 1987-02-18 | SET AND DEVICE FOR VOLUME SAFETY AND DEVICE FOR DETERMINING A PI DEPENDENT VALUE |
| SE8700662-3 | 1987-02-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO1988006291A1 true WO1988006291A1 (en) | 1988-08-25 |
Family
ID=20367573
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/SE1988/000066 Ceased WO1988006291A1 (en) | 1987-02-18 | 1988-02-17 | DEVICE FOR DETERMINING THE PRODUCT OF P0x$(1,3)$ FOR A GAS |
Country Status (2)
| Country | Link |
|---|---|
| SE (1) | SE8700662D0 (en) |
| WO (1) | WO1988006291A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5237852A (en) * | 1992-03-23 | 1993-08-24 | Atlantic Richfield Company | Measurement of gas properties |
| EP0607458A4 (en) * | 1992-08-13 | 1994-08-31 | Nauchno-Proizvodstvennoe Predpriyatie Biotekhinvest | |
| CN102798496A (en) * | 2012-07-25 | 2012-11-28 | 北京航空航天大学 | Method for measuring pressure in rotating state |
| US10048217B2 (en) | 2016-03-11 | 2018-08-14 | Southwest Research Institute | Calibrated volume displacement apparatus and method for direct measurement of specific heat of a gas |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2521634A (en) * | 1947-03-04 | 1950-09-05 | William H Janssen | Acoustic chamber for analysis of gaseous mixtures |
| US3411351A (en) * | 1965-10-23 | 1968-11-19 | Simmouds Prec Products Inc | Fluid measuring system |
| US3596510A (en) * | 1970-02-04 | 1971-08-03 | Nasa | Resonant infrasonic gauging apparatus |
| DE2211611A1 (en) * | 1972-03-10 | 1973-09-20 | Maihak Ag | METHOD AND DEVICE FOR DETERMINING THE CONCENTRATION OF GAS MIXTURES |
| GB1580282A (en) * | 1977-04-26 | 1980-12-03 | Elf Aquitaine | Measurement of ratios of spcific heats |
| US4535627A (en) * | 1982-04-01 | 1985-08-20 | Battelle Memorial Institute | Method of and apparatus for determining the level of liquid in a vessel |
| WO1986003834A1 (en) * | 1984-12-21 | 1986-07-03 | Enpece Ab | Method and apparatus for volume measurement |
-
1987
- 1987-02-18 SE SE8700662A patent/SE8700662D0/en unknown
-
1988
- 1988-02-17 WO PCT/SE1988/000066 patent/WO1988006291A1/en not_active Ceased
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2521634A (en) * | 1947-03-04 | 1950-09-05 | William H Janssen | Acoustic chamber for analysis of gaseous mixtures |
| US3411351A (en) * | 1965-10-23 | 1968-11-19 | Simmouds Prec Products Inc | Fluid measuring system |
| US3596510A (en) * | 1970-02-04 | 1971-08-03 | Nasa | Resonant infrasonic gauging apparatus |
| DE2211611A1 (en) * | 1972-03-10 | 1973-09-20 | Maihak Ag | METHOD AND DEVICE FOR DETERMINING THE CONCENTRATION OF GAS MIXTURES |
| GB1580282A (en) * | 1977-04-26 | 1980-12-03 | Elf Aquitaine | Measurement of ratios of spcific heats |
| US4535627A (en) * | 1982-04-01 | 1985-08-20 | Battelle Memorial Institute | Method of and apparatus for determining the level of liquid in a vessel |
| WO1986003834A1 (en) * | 1984-12-21 | 1986-07-03 | Enpece Ab | Method and apparatus for volume measurement |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5237852A (en) * | 1992-03-23 | 1993-08-24 | Atlantic Richfield Company | Measurement of gas properties |
| EP0607458A4 (en) * | 1992-08-13 | 1994-08-31 | Nauchno-Proizvodstvennoe Predpriyatie Biotekhinvest | |
| CN102798496A (en) * | 2012-07-25 | 2012-11-28 | 北京航空航天大学 | Method for measuring pressure in rotating state |
| US10048217B2 (en) | 2016-03-11 | 2018-08-14 | Southwest Research Institute | Calibrated volume displacement apparatus and method for direct measurement of specific heat of a gas |
Also Published As
| Publication number | Publication date |
|---|---|
| SE8700662D0 (en) | 1987-02-18 |
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