WO2007065476A1 - Appareil et procede de mesure d'un ecoulement de gaz - Google Patents

Appareil et procede de mesure d'un ecoulement de gaz Download PDF

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Publication number
WO2007065476A1
WO2007065476A1 PCT/EP2005/056539 EP2005056539W WO2007065476A1 WO 2007065476 A1 WO2007065476 A1 WO 2007065476A1 EP 2005056539 W EP2005056539 W EP 2005056539W WO 2007065476 A1 WO2007065476 A1 WO 2007065476A1
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WIPO (PCT)
Prior art keywords
gas
tof
flow
actual
flight
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Application number
PCT/EP2005/056539
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English (en)
Inventor
Magnus HALLBÄCK
Original Assignee
Maquet Critical Care Ab
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Maquet Critical Care Ab filed Critical Maquet Critical Care Ab
Priority to PCT/EP2005/056539 priority Critical patent/WO2007065476A1/fr
Publication of WO2007065476A1 publication Critical patent/WO2007065476A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
    • G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters

Definitions

  • the present invention relates to an apparatus for measuring a gas flow as defined in the preamble of claim 1. It also relates to a method of measuring a gas flow as defined in the preamble of claim 14.
  • the volumetric flow is not relevant. Instead there may be a desire to measure the mass flow. If temperature, pressure and composition of the gas are all constant, the volumetric flow could be used to calculate the mass flow. This is also possible if the variations are slow, so that they can be measured by available pressure, temperature and gas concentration sensors. If the variations are faster sensors having sufficiently low time constants may not be available. In particular it is difficult to find temperature sensors that have a sufficiently low time constant, that is, that will react fast enough to changes in the temperature. The same is valid for the composition of the gas. Gas concentration sensors that will react fast enough are generally not available. US 6 199 423 discloses a method of measuring the mass flow of a gas using ultrasound sensors.
  • Time-of-flight signals are obtained from the ultrasound sensors in the way common in the art and are used together with the pressure and the temperature of the gas flow to calculate the mass flow.
  • the method is adapted to non-ideal gas mixtures of complex components. Some of the adaptations made according to US 6 199 423 make this method unsuitable for measuring a flow of breathing gas in a ventilator.
  • an apparatus for measuring a gas flow ⁇ through gas flow channel comprising at least one ultrasound transducer arranged to emit and receive at least a first ultrasound signal through the gas flow in the channel to obtain at least a first time-of-flight signal, a pressure sensor P, and means for determining a volumetric gas flow through the gas flow channel, said apparatus being characterized in that it comprises calculating means arranged to calculate a mass flow of gas by the following steps:
  • the object is also achieved by a method of calculating a mass flow of gas using ul- trasound sensors, said method comprising the following steps:
  • the apparatus and method of the invention are particularly useful in ventilation of patients.
  • the gas is substantially comprised of oxygen and nitrogen in varying concentrations.
  • the expiration gas levels of up to 5% CO2 and H2O may be present, but the variations in these levels are limited and the thermal properties of such a gas mixture are close to those of pure two-atomic gas mixtures, and vary mainly due to variations in the O2-N2-composition .
  • gas flow measurements during ventilation it is a problem that both pressure and temperature may vary quickly during the respiratory cycle. Therefore, measuring a momentary volumetric gas flow will not be meaningful. In this case, a mass flow will be more relevant.
  • the calculating means is arranged to calculate the instantaneous volumetric flow ⁇ actuai according to
  • tof up and tof dO are the time-of- flight upstream and downstream and k t is a first calibration constant.
  • the calculating means is preferably arranged to calculate the sound velocity Cactuai for the gas according to tof up + tof do
  • an ultrasonic sensor may be placed orthogonal to the gas flow to obtain one time-of-flight signal.
  • the calculating means may be arranged to calculate the mass flow W(t) according to
  • Yo may be selected such that ⁇ o is a good approximation of ⁇ (t).
  • the calculating means is further arranged to calculate a volumetric flow of gas. This is particularly useful in applications where both the volumetric flow and the mass flow are needed, since it enables the calculation of both the volumetric and the mass flow with only one flow sensor.
  • the apparatus according to the invention is particularly well suited for measuring a gas flow in a gas tube of a ventilator, said gas tube being arranged to transport breathing gas to a patient or expiratory air from the patient.
  • Figure 1 shows, schematically, an arrangement for measuring the gas flow in a channel, known per se.
  • Figure 2 is an overall flow chart of the method according to the invention.
  • Figure 3 illustrates a measurement arrangement for measuring the washout of O2 in which the inventive arrangement shown in Figure 1 may be used.
  • FIG. 4 illustrates a second embodiment of the invention. Detailed Description of Embodiments
  • a gas flow ⁇ passes through a gas flow channel.
  • a first and a second ultrasound transducer, Tl, resp. T2 are arranged to measure the gas flow in the channel, according to the prior art.
  • a pressure sensor P is also included.
  • both transducers Tl, T2 act as both transmitter and receiver.
  • a pulse train is transmitted from the first transducer Tl and received by the second transducer T2, that is, in essentially the same direction as the gas flow. The time of flight downstream tof do is measured. Then a pulse train is transmitted in the opposite direction, from T2 to Tl, and the time of flight upstream tof up is measured.
  • the time of flight upstream and the time of flight downstream will differ and can be used to indicate the gas flow volume.
  • the skilled person is familiar with such methods.
  • the relative positions of the transducers Tl, T2, and the pressure sensor P can be varied, as is well known in the art.
  • the time of flight values tof up and tof do can be used, together with the pressure value, to determine the mass flow of gas, according to the following:
  • the time of flight signals obtained from the ultrasound transducers are used to calculate two values:
  • Ic 1 and k 2 are calibration constants dependant on the distance between the transducers.
  • Ic 1 is dependent on the cross-sectional area of the channel and the distribution of the flow across it.
  • the ultrasound measurements are performed fast, typically in a tenth of a millisecond, and therefore gives essentially instantaneous values for ⁇ actua i and c actUa i-
  • the subscript "actual" indicates that the flow and the sound velocity values obtained represent the flow and sound velocity at the present state of the gas, that is, the present pressure and temperature.
  • a separate sensor is used to determine the volumetric flow.
  • the time-of-flight signal is obtained from an ultrasonic sensor placed orthogonal to the gas flow.
  • equation 1 is not needed, and equation 2 above can be modified to
  • the velocity of sound in the gas depends on the molecular weight (M) and the absolute temperature (T) according to equation (3)
  • the volumetric flow can be used to calculate a reference state according to the following:
  • ⁇ ref is the volumetric flow at a (theoretical) reference state [m 3 /s]
  • P ref is the density of the gas at the reference state [kg/m 3 ]
  • ⁇ actua i is the volumetric flow at the current state [m 3 /s]
  • P actua i is the density of the gas at the current state [kg/m 3 ]
  • the density, p is determined from the ideal gas law:
  • Equation (6) may be used to calculate the flow in a reference state defined by the selected pair ⁇ p ref ,T ref ⁇ , based on the volumetric flow for the current state.
  • equation (9) may be rewritten as
  • the instantaneous mass flow through the sensor can be obtained, provided that the factor ⁇ 0 is selected correctly. This is valid as long as ⁇ (t) is substantially constant, which is known to be the case for mixtures of two-atomic gases at moderate temperatures.
  • Step Sl Obtain the time of flight signals for the upstream and downstream
  • Step S2 Calculate the instantaneous volumetric flow and sound velocity for the gas (equations (1) and (2))
  • Step S3 measure the pressure in the gas flow.
  • Step S4 calculate a relationship between the actual volumetric flow, the actual sound velocity, the actual pressure and a constant ⁇ o according to equation (11), which can be interpreted as the instantaneous mass flow through the ultrasonic sensor.
  • step S3 can be performed at any point in the procedure before step S4. As discussed briefly above, only one time-of-flight signal is needed if a separate flow sensor is used, which may be obtained by one or two ultrasonic sensors placed orthogonal to the gas flow in step Sl.
  • FIG. 3 illustrates the use of the inventive apparatus in the ventilation of a patient, represented by a pair of lungs 51.
  • the patient is ventilated using a ventilator 53 which is connected to the patient through a Y piece 55 which interconnects a first tube 57 for breathing gas provided by the ventilator and a second tube 59 for remov- ing expired air from the patient, with the patient's lungs in the way common in the art.
  • the breathing gas will normally comprise an appropriate mixture of air and O2.
  • the expired air is output to the surroundings from the ventilator at a gas outlet 61, for example through a valve 63.
  • the gas flow may be measured at the gas outlet 61 or the valve 63.
  • an ultrasonic flow sensor 65 as shown in Figure 1 is provided near the valve 63, upstream or downstream of the valve 63.
  • the ventilator itself, as well as the flow sensor 65 are controlled by one or more control units, which are represented in Figure 3 by one control unit 69.
  • the sensor 65 as well as the control unit 69 may be located externally or may be integral parts of the ventila- tor 53.
  • the control unit 69 is also used for performing the calculations discussed in connection with Figure 2. These calculations may of course be performed in a separate calculation unit of the ventilator, or in an external unit.
  • Figure 4 illustrates an alternative embodiment, which is similar to that shown in Figure 3, except that a separate flow sensor 67 is used to obtain the volumetric flow.
  • the sensor may be placed upstream or downstream of the valve 63 and may, for example, be one of the following:
  • the time-of flight signals upstream and downstream are not needed.
  • the velocity of sound is preferably measured orthogonal to the flow.
  • only one ultrasonic transducer Tl is needed, instead of two as shown in Fig. 1, since the signal will be reflected by an object such as a wall placed opposite of the transducer Tl.
  • two ultrasonic transducers may be used, placed on opposite sides orthogonal to the flow.
  • the relative positions of the transducer/s, and the pressure sensor P, can be varied, as is well known in the art.

Abstract

Le débit massique d'un gaz peut être calculé au moyen de capteurs ultrasonores et des étapes suivantes: on obtient les signaux de temps de vol pour la partie amont et la partie aval, on mesure la pression du gaz dans l'écoulement, on calcule le flux volumétrique instantané et la vitesse du son pour le gaz et on calcule le débit massique à partir d'une relation existant entre le flux volumétrique véritable, la vitesse du son véritable et la pression véritable et une constante ?0.
PCT/EP2005/056539 2005-12-06 2005-12-06 Appareil et procede de mesure d'un ecoulement de gaz WO2007065476A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2005/056539 WO2007065476A1 (fr) 2005-12-06 2005-12-06 Appareil et procede de mesure d'un ecoulement de gaz

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2005/056539 WO2007065476A1 (fr) 2005-12-06 2005-12-06 Appareil et procede de mesure d'un ecoulement de gaz

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010122117A1 (fr) 2009-04-22 2010-10-28 Syddansk Universitet Système de ventilation comprenant une mesure du flux par ultrasons
WO2010130290A1 (fr) * 2009-05-13 2010-11-18 Maquet Critical Care Ab Appareil respiratoire anesthesique dote d'une unite reflecteur volumique a penetration reglable
US9347932B2 (en) 2010-10-04 2016-05-24 Arizona Board Of Regents, A Body Corporate Of The State Of Arizona Acting For And On Behalf Of Arizona State University Device and method for breath analysis using acoustic resonance flow rate

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5152174A (en) * 1990-09-24 1992-10-06 Labudde Edward V Mass flow rate sensor and method
WO1995018958A1 (fr) * 1994-01-10 1995-07-13 Siemens Aktiengesellschaft Procede pour la determination du debit volumetrique d'un gaz dans un tube de mesure

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5152174A (en) * 1990-09-24 1992-10-06 Labudde Edward V Mass flow rate sensor and method
WO1995018958A1 (fr) * 1994-01-10 1995-07-13 Siemens Aktiengesellschaft Procede pour la determination du debit volumetrique d'un gaz dans un tube de mesure

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010122117A1 (fr) 2009-04-22 2010-10-28 Syddansk Universitet Système de ventilation comprenant une mesure du flux par ultrasons
WO2010130290A1 (fr) * 2009-05-13 2010-11-18 Maquet Critical Care Ab Appareil respiratoire anesthesique dote d'une unite reflecteur volumique a penetration reglable
EP2767302A3 (fr) * 2009-05-13 2014-09-24 Maquet Critical Care AB Appareil respiratoire anesthésique doté d'une unité réflecteur volumique avec pénétration réglable
US9149590B2 (en) 2009-05-13 2015-10-06 Mapquet Critical Care AB Anesthetic breathing apparatus having volume reflector unit with controllable penetration
US11266805B2 (en) 2009-05-13 2022-03-08 Maquet Critical Care Ab Anesthetic breathing apparatus having volume reflector unit with controllable penetration
US9347932B2 (en) 2010-10-04 2016-05-24 Arizona Board Of Regents, A Body Corporate Of The State Of Arizona Acting For And On Behalf Of Arizona State University Device and method for breath analysis using acoustic resonance flow rate

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