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
  • G01N29/024—Analysing fluids by measuring propagation velocity or propagation time of acoustic waves

Definitions

• the present invention relates to device for measuring oxygen concentration in gas mixtures containing helium and / or hydrogen, especially for underwater breathing apparatus.
• electro-galvanic fuel cells and thermo-paramagnetic sensors are used.
• Electro-galvanic fuel cells consist of a lead anode and a gold-plated cathode, with an aqueous electrolyte solution of potassium hydroxide between them.
• the electrolyte is saturated with oxygen from the environment and the cell produces a current that is proportional to the oxygen concentration in the electrolyte.
• the material of the electrodes is consumed, which reduces the cell lifespan. If the lifespan has elapsed or if the cell characteristic is significantly degraded, the component has to be replaced.
• the electrochemical cell changes its properties during its lifespan and must be therefore frequently calibrated. During the calibration, the device or a part thereof that is intended for measuring the oxygen concentration should be shut down and filled with air or with other gas with defined oxygen content.
• thermo-paramagnetic sensors use the paramagnetic properties of oxygen which is drawn into the magnetic field generated by a permanent magnet with pole pieces. As the magnetic susceptibility of oxygen is much stronger than this of nitrogen, helium, argon and other gases contained in air mixtures, the impact of the magnetic field to oxygen is selective.
• the space between the pole pieces is asymmetrically heated by a resistance wire. Magnetic susceptibility of oxygen decreases with temperature and therefore, the heated oxygen is pushed out by new cool oxygen coming from the measured environment. In this way, a gas flow occurs which speed rate increases with increasing oxygen content.
• the gas flow velocity is detected by the rate of cooling of the heating wire resistor and, derived from this quantity, the content of oxygen is calculated based on the calibration curve.
• the thermo-paramagnetic sensors have unlimited life, but feature a high consumption of electricity, which parameter usually appears as a disadvantage for mobile diving devices powered by battery.
• the device for measuring oxygen concentration in gas mixtures containing helium and / or hydrogen especially for underwater breathing apparatus that are based on the fact that the oxygen content in the gas mixture contained in the breathing apparatus varies whereas the mutual ratio of the content of unbreathable gases remains constant and that consequently, it is not necessary to use sensor specifically calibrated to detect oxygen, because the oxygen content in gas mixture can be determined indirectly by measuring the speed of sound in the gas mixture with the consequent calculation based on the concentration of helium and hydrogen, and by knowing their proportion in the unbreathable gas mixture
• the substance of the invention is based on the fact that it contains a sensor which consists of a measuring tube provided with an inlet opening allowing filling of breathing gas mixture to be analyzed and with an outlet orifice for excess gas mixture, and further equipped with the first extension and with the second and third extensions that are located in a certain distance, wherein the first extension is equipped with a sound pulse transmitter dt the inlet opening, while the second extension and the third extension are equipped ith "
• the digital block is completed by a correction temperature sensor that is arranged close to the outlet orifice of the measuring tube of the sensor.
• the measuring tube of the sensor is calibrated and that its partial dimensions, particularly the length of its extensions as well as their mutual spacing is precisely determined, whereby the acoustic pulses emitted by the transmitter feature a wavelength exceeding the diameter of the measuring tube, typically at a frequency of 2 kHz at pulse duration of 20 ms.
• the device for measuring oxygen concentration in gas mixtures containing helium and / or hydrogen, especially for underwater breathing apparatus is based on the finding that the concentration of helium and hydrogen can be measured by the speed of sound in the gaseous breathing mixture. Considering the significantly different propagation speeds of the sound in helium (973 m/s at 273.15 K) and hydrogen (1261 m/s at 273.15 K) compared with the speed of sound in oxygen (315 m/s at 273.15 K), the concentration of helium and hydrogen dan be determined with sufficient accuracy.
• the speed of sound is measured directly by sending a sound pulse in the measuring tube I of the sensor 100 that is filled with the gas mixture to be analyzed and the said pulse is received by two different receivers such as the microphones 3, 4 that are built into the measuring tubeI at a known mutual distance.
• the oxygen concentration is then determined as the product of the equation calculated from the speed of sound in gases: where c is the speed of sound [ms- 1 ]
• Cp is the specific heat at constant pressure [J -1] (as a weighted average of the heat of individual components of mixture)
• Cv is the specific heat at constant volume [JK-1] (as a weighted average of the heat of individual components of gas mixture)
• R is the universal gas constant (8.3145 Jmol-lK-1)
• T is the thermodynamic temperature of the mixture [K]
• the sensor 100 which consists of the measuring tube i equipped with three extensions 10, 11 and 12.
• the measuring: tube 1 s calibrated and its dimensions, particularly the length and the distance of the first extension ⁇ . and this of the second extension 12 are accurately measured.
• the measuring tube 1 is filled with the analysed breathing gas mixture through the inlet opening 8 in the way that the measured mixture fills the entire space of the measuring tube 1 including all extensions 10 ⁇ H and 12.
• the surplus of the gas mixture flows out from the measuring tube 1 of the sensor 100 through the outlet orifice 9.
• the measuring tube 1 On its first extension 10, the measuring tube 1 is provided with the sound pulse transmitter 2 consisting of a speaker.
• the transmitter 2 transmits repeatedly sound pulses of an appropriate frequency.
• the frequency is set so that the wavelength of sound waves exceeds the diameter of the measuring tube 1.
• the suitable diameter of the measuring tube is 5 mm and the frequency is 2 kHz with pulse duration of 20 ms.
• the sound pulses travel through the measuring tube 1 at the speed of sound, which depends on the composition of the measured gas mixture.
• Each transmitted pulse is primarily received by the receiving microphone 3 located at the second extension H and then by the receiving microphone 4 located at the third extension 12.
• the electrical signals from both microphones 3 and 4 are directed to the circuit 5 for measuring the time difference.
• the measured time difference is transferred from the circuit 5 for measuring the time difference into the digital block 6.
• the temperature sensor 13 In the measuring tube I is located the temperature sensor 13, represented for example by a monolithic integrated circuit.
• the temperature sensor 13 detects the temperature of the analyzed gas mixture. The temperature affects the speed of sound and must be taken into account in subsequent calculations.
• the digital block 6 calculates, based on the known distance of the second extension 1_1 and the third extension 12 and on the time difference between received pulses, the speed of sound in the measured gas mixture as: where c is the speed of sound [ms-1]
• ⁇ is the time difference between the sound pulses received by microphones 3 and 4 [s] I
• the invention is usable in some special applications, such as medical devices, etc.

Landscapes

• Physics & Mathematics (AREA)
• Acoustics & Sound (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)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=46052491

Family Applications (1)

Country Status (2)

Cited By (3)

Citations (5)

Family Cites Families (5)

• 2011
  • 2011-04-01 CZ CZ20110184A patent/CZ2011184A3/cs not_active IP Right Cessation
• 2012
  • 2012-03-21 WO PCT/CZ2012/000027 patent/WO2012130194A1/en active Application Filing

Patent Citations (5)

Also Published As

Similar Documents

Legal Events