Oxygen concentration system for generating oxygen-enriched gas
Abstract
An ultrasonic apparatus for measuring the concentration and flow rate of a sample gas, comprising: a conduit for the flow of the sample gas; a first ultrasonic transmission-reception device mounted inside the duct; a second ultrasonic transmission-reception device mounted inside the conduit so as to face the first ultrasonic transmission-reception device; a transmission-reception switch to switch the operating mode of the first and second transmission-reception ultrasonic devices between a transmission mode to transmit ultrasonic waves and a reception method to receive ultrasonic waves; a temperature sensor, located inside the conduit, to measure the temperature of the sample gas flowing through the conduit; generating the first ultrasonic transmission-reception device, when in the transmission mode, ultrasonic waves traveling forward with respect to the flow direction of the sample gas, and generating said device, when in the reception mode , a waveform that travels backwards based on the received ultrasonic waves that were generated by the second ultrasonic transmission-reception device; generating the second ultrasonic transmission-reception device, when it is in the transmission mode, ultrasonic waves that travel backwards with respect to the flow direction of the sample gas, and generating said device, when it is in the reception mode , a waveform that travels forward on the basis of the received ultrasonic waves that were generated by the first ultrasonic transmission-reception device; means for generating trigger signals when the waveforms that travel forward and those that travel backward exceed a predetermined level; means for generating zero-forward and backward signals when the waveforms that travel forward and those that travel backward exceed a zero level; propagation time calculation means, coupled to the temperature sensor, the means for generating trip signals and the means for generating zero-crossing signals, to (1) calculate a possible range of propagation times on the basis of the gas temperature detected by the temperature sensor, (2) determine whether the phases in which the first two firing signals, generated respectively on the basis of the waveforms that travel forward and those that travel backward, coincide or not with one another, (3) process the zero-crossing signals so that the phases coincide with one with the other if they did not do it before, (4) obtain instant time of zero reference time by calculating the average value of the instants of zero crossing time in the forward direction and in the backward direction, (5) obtain an ultrasonic reception point by subtracting an integer multiple from the cycle of the ultrasonic waves so that the subtraction results fall within the possible range of propagation times and (6) estimate the ultrasonic propagation time on the basis of the ultrasonic reception point.
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18 claims: 3 independent, 15 dependent
- 1ES 2 565 635 T3 REIVINDICACIONES 1. Un aparato ultrasónico para medir la concentración y el caudal de un gas de muestra, que comprende:un conducto para que fluya el gas de muestra;un primer dispositivo ultrasónico de transmisión-recepción montado en el interior del conducto;un segundo dispositivo ultrasónico de transmisión-recepción montado en el interior del conducto de forma que quede enfrentado con el primer dispositivo ultrasónico de transmisión-recepción;un conmutador de transmisión-recepción para conmutar el modo de funcionamiento de los dispositivos ultrasónicos de transmisión-recepción primero y segundo entre un modo de transmisión para transmitir ondas ultrasónicas y un modo de recepción para recibir ondas ultrasónicas;un sensor de temperatura, situado dentro del conducto, para medir la temperatura del gas de muestra que fluye a través del conducto;generando el primer dispositivo ultrasónico de transmisión-recepción, cuando se encuentra en el modo de transmisión, ondas ultrasónicas que viajan hacia adelante con respecto a la dirección de flujo del gas de muestra, y generando dicho dispositivo, cuando se encuentra en el modo de recepción, forma de onda que viaja hacia atrás sobre la base de las ondas ultrasónicas recibidas que fueron generadas por el segundo dispositivo ultrasónico de transmisión-recepción;generando el segundo dispositivo ultrasónico de transmisión-recepción, cuando se encuentra en el modo de transmisión, ondas ultrasónicas que viajan hacia atrás con respecto a la dirección de flujo del gas de muestra, y generando dicho dispositivo, cuando se encuentra en el modo de recepción, forma de onda que viaja hacia adelante sobre la base de las ondas ultrasónicas recibidas que fueron generadas por el primer dispositivo ultrasónico de transmisión-recepción;medios para generación de señales de disparo cuando las formas de onda que viajan hacia adelante y las que viajan hacia atrás superan un nivel predeterminado;medios para generación de señales de paso por cero hacia adelante y hacia atrás cuando las formas de onda que viajan hacia adelante y las que viajan hacia atrás superan un nivel cero;medios de cálculo del tiempo de propagación, acoplados al sensor de temperatura, a los medios para generación de señales de disparo y a los medios para generación de señales de paso por cero, para (1) calcular un posible rango de tiempos de propagación sobre la base de la temperatura del gas detectada por el sensor de temperatura, (2) determinar si las fases en las cuales dos primeras señales de disparo, generadas respectivamente sobre la base de las formas de onda que viajan hacia adelante y de las que viajan hacia atrás, coinciden o no la una con la otra, (3) procesar las señales de paso por cero de tal manera que las fases coincidan la una con la otra si no lo hacían antes, (4) obtener instante de tiempo de paso por cero de referencia por cálculo del valor medio de los instantes de tiempo de paso por cero en dirección hacia adelante y en dirección hacia atrás, (5) obtener un punto de recepción ultrasónico restando un múltiplo entero del ciclo de las ondas ultrasónicas de tal manera que los resultados de la resta caigan dentro del posible rango de tiempos de propagación y (6) estimar el tiempo de propagación ultrasónica sobre la base de el punto de recepción ultrasónico.
- 2Un aparato ultrasónico de acuerdo con la reivindicación 1, en el cual la distancia a lo largo del conducto entre dispositivos ultrasónicos de transmisión-recepción primero y segundo se selecciona de tal manera que sólo un resultado de la resta caiga dentro del posible rango de tiempos de propagación determinado en las posibles condiciones de trabajo del aparato ultrasónico.
- 3Un aparato ultrasónico de acuerdo con la reivindicación 2, en el cual la distancia a lo largo del conducto entre dispositivos ultrasónicos de transmisión-recepción primero y segundo se selecciona para que cumpla la siguiente relación. (L s /C min (T min ) - L s /C max (T min )) < 1/f donde:Ls: longitud de propagación (m) f: frecuencia de las ondas ultrasónicas en el gas de muestra (Hz) Cmin(Tmin): el límite inferior de la velocidad ultrasónica (m/s) a través del gas de muestra a la temperatura mínima de trabajo Tmin (grados Celsius) Cmax(Tmin): el límite superior de la velocidad ultrasónica (m/s) a través del gas de muestra a la temperatura mínima de trabajo Tmin (grados Celsius)
- 4Un aparato ultrasónico de acuerdo con la reivindicación 1, en el cual el radio interior del conducto se selecciona de tal manera que la diferencia entre el tiempo de propagación hacia adelante y hacia atrás es menor que el ciclo de las ondas ultrasónicas bajo la condición de trabajo del gas de muestra. ES 2 565 635 T3
- 5Un aparato ultrasónico de acuerdo con la reivindicación 1, en el cual el radio interior del conducto se selecciona para que cumpla la siguiente relación Ls(Cmin(Tmin) - Qmax/(60000ftr )) — Ls(Cmin(Tmin) + Qmax/(60000ftr )) < 1/f donde:Ls: longitud de propagación (m) y r: radio interior del conducto (m) f: frecuencia de las ondas ultrasónicas en el gas de muestra (Hz) Cmin(Tmin): el límite inferior de la velocidad ultrasónica (m/s) a través del gas de muestra a la temperatura mínima de trabajo Tmin (grados Celsius) Qmax: el límite superior del caudal del gas de muestra (litros/min)
- 6Un aparato ultrasónico de acuerdo con la reivindicación 1, en el cual el conducto incluye una porción recta y porciones perpendiculares conectadas perpendicularmente a los extremos de la porción recta; los dispositivos ultrasónicos de transmisión-recepción primero y segundo están situados en las porciones perpendiculares de forma que queden enfrentados con los extremos de la porción recta; y la distancia entre los dispositivos ultrasónicos de transmisión-recepción primero y segundo y los respectivos extremos de la porción recta del conducto cumplen la siguiente relación 0<D<fxr 2 /C D:la distancia (m) entre los dispositivos ultrasónicos de transmisión-recepción primero y segundo y los respectivos extremos de la porción recta f: frecuencia de las ondas ultrasónicas en el gas de muestra (Hz) r: radio interior del conducto (m) C: velocidad de las ondas ultrasónicas (m/s)
- 7Un método para medir la concentración de gas de muestra que fluye a través de un conducto, que comprende los pasos de:generar ondas ultrasónicas que viajan hacia adelante con respecto a la dirección del flujo del gas de muestra;generar ondas ultrasónicas que viajan hacia atrás con respecto a la dirección del flujo del gas de muestra;medir la temperatura del gas de muestra que fluye a través del conducto;generar señales de disparo cuando las formas de onda que viajan hacia adelante y las que viajan hacia atrás superen un nivel predeterminado;generar señales de paso por cero hacia adelante y hacia atrás cuando las formas de onda que viajan hacia adelante y las que viajan hacia atrás superen un nivel cero;calcular un posible rango de tiempos de propagación sobre la base de la temperatura del gas detectada por el sensor de temperatura;determinar si las fases en las cuales dos primeras señales de disparo, generadas respectivamente sobre la base de las formas de onda que viajan hacia adelante y de las que viajan hacia atrás, coinciden la una con la otra;procesar las señales de paso por cero de tal manera que las fases coincidan la una con la otra si no lo hacían antes;obtener instante de tiempo de paso por cero de referencia calculando valor medio de los instantes de tiempo de paso por cero en dirección hacia adelante y en dirección hacia atrás;obtener un punto de recepción ultrasónico restando un múltiplo entero del ciclo de las ondas ultrasónicas de tal manera que los resultados de la resta caigan dentro del posible rango de tiempos de propagación;y estimar el tiempo de propagación ultrasónica/o sobre la base del punto de recepción ultrasónico.
- 8Un método de acuerdo con la reivindicación 7, en el cual las ondas ultrasónicas que viajan hacia adelante y las que viajan hacia atrás son transmitidas y recibidas por dispositivos ultrasónicos de transmisión-recepción primero y segundo que están situados dentro del conducto, seleccionándose la distancia a lo largo del conducto entre los dispositivos ultrasónicos de transmisión-recepción primero y segundo de tal manera que sólo un resultado de la resta caiga dentro del posible rango de tiempos de propagación en las posibles condiciones de trabajo del aparato ultrasónico. ES 2 565 635 T3
- 9Un método de acuerdo con la reivindicación 8, en el cual la la distancia a lo largo del conducto entre los dispositivos ultrasónicos de transmisión-recepción primero y segundo se selecciona para que cumpla la siguiente relación (— s /C min (T min ) - l-s/ C max( T min)) < 1/f donde:f: frecuencia de las ondas ultrasónicas en el gas de muestra (Hz) Cmin(Tmin): el límite inferior de la velocidad ultrasónica (m/s) a través del gas de muestra a la temperatura mínima de trabajo Tmin (grados Celsius) Cmax(Tmin): el límite superior de la velocidad ultrasónica (m/s) a través del gas de muestra a la temperatura mínima de trabajo Tmin (grados Celsius)
- 10Un método de acuerdo con la reivindicación 7, en el cual el radio interior del conducto se selecciona de tal manera que la diferencia entre el tiempo de propagación hacia adelante y hacia atrás sea menor que el ciclo de las ondas ultrasónicas bajo la condición de trabajo del gas de muestra.
- 11Un método de acuerdo con la reivindicación 7, en el cual el radio interior del conducto se selecciona para que cumpla la siguiente relación -s(Cmin (Tmin) - Qmax/(60000Kr 2 )) - -s(Cmin(Tmin) - Qmax/(60000Kr 2 )) < 1/f donde:-s: longitud de propagación (m) r: radio interior del conducto (m) f: frecuencia de las ondas ultrasónicas en el gas de muestra (Hz) Cmin(Tmin): el límite inferior de la velocidad ultrasónica (m/s) a través del gas de muestra a la temperatura mínima de trabajo Tmin (grados Celsius) Qmax: el límite superior del caudal del gas de muestra (litros/min)
- 12Un sistema de concentración de oxígeno para generar un gas enriquecido en oxígeno, que comprende un aparato de concentración de oxígeno para generar un gas enriquecido en oxígeno por adsorción de nitrógeno para extraer el nitrógeno del aire; y un aparato ultrasónico para medir la concentración de oxígeno en el gas enriquecido en oxígeno y el caudal del gas enriquecido en oxígeno, comprendiendo el aparato ultrasónico:un conducto para recibir y hacer fluir el gas enriquecido en oxígeno;un primer dispositivo ultrasónico de transmisión-recepción montado en el interior del conducto;un segundo dispositivo ultrasónico de transmisión-recepción montado en el interior del conducto de forma que quede enfrentado con el primer dispositivo ultrasónico de transmisión-recepción;un conmutador de transmisión-recepción para conmutar el modo de funcionamiento de los dispositivos ultrasónicos de transmisión-recepción primero y segundo entre un modo de transmisión para transmitir ondas ultrasónicas y un modo de recepción para recibir ondas ultrasónicas;un sensor de temperatura, situado dentro del conducto, para medir la temperatura del gas enriquecido en oxígeno que fluye a través del conducto;generando el primer dispositivo ultrasónico de transmisión-recepción, cuando se encuentra en el modo de transmisión, ondas ultrasónicas que viajan hacia adelante con respecto a la dirección de flujo del gas enriquecido en oxígeno, y generando dicho dispositivo, cuando se encuentra en el modo de recepción, forma de onda que viaja hacia atrás sobre la base de las ondas ultrasónicas recibidas que fueron generadas por el segundo dispositivo ultrasónico de transmisión-recepción;generando el segundo dispositivo ultrasónico de transmisión-recepción, cuando se encuentra en el modo de transmisión, ondas ultrasónicas que viajan hacia atrás con respecto a la dirección de flujo del gas enriquecido en oxígeno, y generando dicho dispositivo, cuando se encuentra en el modo de recepción, forma de onda que viaja hacia adelante sobre la base de las ondas ultrasónicas recibidas que fueron generadas por el primer dispositivo ultrasónico de transmisión-recepción;medios para generación de señales de disparo cuando las formas de onda que viajan hacia adelante y las que viajan hacia atrás superan un nivel predeterminado;ES 2 565 635 T3 medios para generación de señales de paso por cero hacia adelante y hacia atrás cuando las formas de onda que viajan hacia adelante y las que viajan hacia atrás superan un nivel cero;medios de cálculo del tiempo de propagación, acoplados al sensor de temperatura, a los medios para generación de señales de disparo y a los medios para generación de señales de paso por cero, para (1) calcular un posible rango de tiempos de propagación sobre la base de (sobre la base de) la temperatura del gas detectada por el sensor de temperatura, (2) determinar si las fases en las cuales dos primeras señales de disparo, generadas respectivamente sobre la base de las formas de onda que viajan hacia adelante y de las que viajan hacia atrás, coinciden o no la una con la otra, (3) procesar las señales de paso por cero de tal manera que las fases coincidan la una con la otra si no lo hacían antes, (4) obtener instante de tiempo de paso por cero de referencia por cálculo del valor medio de los instantes de tiempo de paso por cero en dirección hacia adelante y en dirección hacia atrás, (5) obtener un punto de recepción ultrasónico restando un múltiplo entero del ciclo de las ondas ultrasónicas de tal manera que los resultados de la resta caigan dentro del posible rango de tiempos de propagación y (6) estimar el tiempo de propagación ultrasónica sobre la base de el punto de recepción ultrasónico.
- 13Un sistema de concentración de oxígeno de acuerdo con la reivindicación 12, en el cual la distancia a lo largo del conducto entre dispositivos ultrasónico de transmisión-recepción primero y segundo se selecciona de tal manera que sólo un resultado de la resta caiga dentro del posible rango de tiempos de propagación determinado en las posibles condiciones de trabajo del aparato ultrasónico.
- 14Un sistema de concentración de oxígeno de acuerdo con la reivindicación 12, en el cual la distancia a lo largo del conducto entre los dispositivos ultrasónicos de transmisión-recepción primero y segundo se selecciona para que (se) cumpla la siguente relación ( l-S/Omin ( Tmin ) - (-s/C max (Tmin)) < 1/f donde:-s: longitud de propagación (m) f: frecuencia de las ondas ultrasónicas en el gas de muestra (Hz) Cmin(Tmin): el límite inferior de la velocidad ultrasónica (m/s) a través del gas de muestra a la temperatura mínima de trabajo Tmin (grados Celsius) Cmax(Tmin): el límite superior de la velocidad ultrasónica (m/s) a través del gas de muestra a la temperatura mínima de trabajo Tmin (grados Celsius)
- 15Un sistema de concentración de oxígeno de acuerdo con la reivindicación 12, en el cual el radio interior del conducto se selecciona de tal manera que la diferencia entre el tiempo de propagación hacia adelante y hacia atrás es menor que el ciclo de las ondas ultrasónicas bajo la condición de trabajo del gas enriquecido en oxígeno.
- 16Un sistema de concentración de oxígeno de acuerdo con la reivindicación 12, en el cual el radio interior del conducto se selecciona para que cumpla la siguiente relación -s(Cmin (Tmin) — Qmax/60000^r )) — -s(Cmin(Tmin) + Qmax/60000ftr )) < 1/f donde:-s: longitud de propagación (m) r: radio interior del conducto (m) f: frecuencia de las ondas ultrasónicas en el gas de muestra (Hz) Cmin(Tmin): el límite inferior de la velocidad ultrasónica (m/s) a través del gas de muestra a la temperatura mínima de trabajo Tmin (grados Celsius) Qmax: el límite superior del caudal del gas de muestra (litros/min)
- 17Un sistema de concentración de oxígeno de acuerdo con la reivindicación 12, en el cual el conducto incluye una porción recta y porciones perpendiculares conectadas perpendicularmente a los extremos de la porción recta; los dispositivos ultrasónicos de transmisión-recepción primero y segundo están situados en las porciones perpendiculares de forma que queden enfrentados con los extremos de la porción recta; y la distancia entre los dispositivos ultrasónicos de transmisión-recepción primero y segundo y los respectivos extremos de la porción recta del conducto que cumple la siguiente relación. 0<D<fxr 2 /C D:la distancia (m) entre los dispositivos ultrasónicos de transmisión-recepción primero y segundo y los respectivos extremos de la porción recta f: frecuencia de las ondas ultrasónicas en el gas de muestra (Hz) r: radio interior del conducto (m) ES 2 565 635 T3 C: velocidad de las ondas ultrasónicas (m/s)
- 18Un sistema de concentración de oxígeno de acuerdo con la reivindicación 12, en el cual el conducto está unido al aparato de concentración de oxígeno en un punto para permitir que el conducto se expanda térmicamente en la dirección longitudinal de la porción recta libremente por fuerza externa que se puede generar cuando el conducto se 5 deforma térmicamente.
Independent claims18
177 paragraphs in 5 sections, as filed
ES 2 565 635 T3
DESCRIPTION
Ultrasonic apparatus and method for measuring gas flow and concentration
Technical Field
The invention relates to an ultrasonic apparatus and a method for measuring the concentration of oxygen gas in a sample gas and the flow rate of the sample gas, which is supplied from an oxygen concentrator used for medical purposes.
Previous Technique
It is well known that the speed of propagation of ultrasonic waves through a sample gas is presented by a function of the concentration and temperature of the sample gas. The velocity C (m / s) of the ultrasonic waves propagating through a stationary gas is presented by the flow equation (1) with average molecular weight M and the temperature T (K)
C = (KRT / M)<sup>1/2</sup>... (1)
Where:
K: ratio of molecular specific heat at constant volume and molecular specific heat at constant pressure
R: gas constant
Therefore, the measurement of the velocity C (m / s) of the ultrasonic waves propagating through a sample gas will provide the average molecular weight M of the sample gas through a calculation. For example, the average molecular weight M of a sample gas containing an oxygen-nitrogen gas mixture with a mixing ratio P: (1-P) (0 <P <1) will be calculated by the following equation (2) .
M = M02P + Mn2 (1-P) ... (2)
Where:
M02: Molecular Weight of oxygen gas
Mn2: Molecular Weight of Nitrogen Gas
Therefore, the oxygen concentration P will be obtained by means of a calculation based on the measurement of the average molecular weight M. When the sample gas is an oxygen-nitrogen mixture, a value of K = 1.4 is reasonable over a wide range of oxygen-nitrogen mixing ratios.
When the velocity of the ultrasonic waves propagating through a sample gas is C (m / s) and the flow velocity of the sample gas is V (m / s), the velocity C1 (m / s) of ultrasonic waves propagating in the forward direction with respect to the sample gas flow is Ci = C + V, and the velocity C2 (m / s) of ultrasonic waves propagating in the backward direction with respect to the flow of the sample gas sample gas is C2 = CV. Therefore, the velocity V (m / s) of the sample gas flow is calculated by the following equation (3).
V = (C1-C2) / 2. (3)
The flow (m<sup>3</sup>/ s) of the sample gas is obtained by multiplying the flow rate of the sample gas by the area (m<sup>2</sup>) of the section of the conduit through which the sample gas flows.
Methods and apparatus have been developed to measure the concentration of a certain gas or the flow rate of a sample gas, using the above principle, on the basis of the propagation speed or the propagation time of the ultrasonic waves through the sample gas. For example, Japanese Unexamined Patent Publication (Kokai) No. 6-213877 describes an apparatus for measuring the concentration and flow rate of a sample gas by measuring the propagation time of ultrasonic waves propagating between two ultrasonic transducers positioned one opposite each other within a conduit through which the sample gas flows. Furthermore, Japanese Unexamined Patent Publications (Kokai) No. 7-209265 and No. 8-233718 describe an apparatus for measuring the concentration of a certain gas contained in a sample gas by measuring the propagation speed or the propagation time. of ultrasonic waves propagating through a volume with a reflective type apparatus including an ultrasonic transducer and a reflector located in front of it.
In such a method and apparatus for measuring concentration and flow rate using the propagation speed of ultrasonic waves, it is necessary to accurately measure the propagation time of the ultrasonic waves. However, the signal generated on the basis of the received ultrasonic waves always includes a noise component, which makes it difficult to determine when the ultrasonic waves are received by the ultrasonic transducer. Therefore, the propagation time of ultrasonic waves is estimated indirectly by means of a complex signal processing procedure or complex hardware. For example, Japanese Unexamined Patent Publication (Kokai) No. 9-318644 describes a method for measuring a propagation time of ultrasonic waves in which the waveform of received ultrasonic waves is integrated. After the results of the waveform integration reach a predetermined value, the first zero crossing time instant is determined as the propagation time of the waves 2
ES 2 565 635 T3 ultrasonic for flow measurement. According to the method, the rate of generation of the zero crossing signal does not fluctuate even though the amplitude of the received waves fluctuates to some extent. Therefore, the zero crossing time instant obtained is relatively close to the moment when they actually arrive. the ultrasonic waves . However, the zero crossing time instant obtained is not the actual propagation time of the ultrasonic waves. In particular, when concentration is measured, the measurement error is greatly affected by the difference between the actual propagation time and the zero crossing time.
Furthermore, Japanese Unexamined Patent Publication (Kokai) No. 60-138422 describes a flow measurement device in which an envelope curve is calculated based on the waveform of received ultrasonic waves. The rise time of the envelope curve is calculated using an approximate equation to estimate the ultrasonic propagation time. However, to sample the received ultrasonic waves, hardware is required and to calculate the envelope curve based on the sampled waveform, complex signal processing is required. Therefore, according to the invention of JPP '422, it is difficult to provide a compact device with low cost.
Description of the Invention
The object of the invention is to provide an ultrasonic apparatus and a method for measuring gas concentration and flow rate, which enables the concentration and flow rate of a sample gas to be accurately measured without complex signal processing and without additional hardware.
In accordance with the present invention, there is provided an ultrasonic apparatus for measuring the concentration and flow rate of a sample gas, comprising:
a conduit for the sample gas to flow;
a first ultrasonic transmission-reception device mounted inside the conduit;
a second ultrasonic transmission-reception device mounted outside the conduit so that it faces the first ultrasonic transmission-reception device;
a transmit-receive switch for switching the mode of operation of the first and second ultrasonic transmit-receive devices between a transmit mode for transmitting ultrasonic waves and a receive mode for receiving ultrasonic waves;
a temperature sensor, located within the conduit, to measure the temperature of the sample gas flowing through the conduit;
generating the first ultrasonic transmitting-receiving device, when it is in the transmitting mode, ultrasonic waves traveling forward with respect to the flow direction of the sample gas, and generating said device, when it is in the receiving mode , waveform traveling backward based on the received ultrasonic waves that were generated by the second transmit-receive ultrasonic device;
generating the second transmitting-receiving ultrasonic device, when it is in the transmitting mode, ultrasonic waves traveling backward with respect to the flow direction of the sample gas, and generating said device, when it is in the receiving mode , waveform traveling forward based on the received ultrasonic waves that were generated by the first transmit-receive ultrasonic device;
means for generating trigger signals when the waveforms traveling forward and those traveling backward exceed a zero level;
means for generating forward and backward zero crossing signals when forward traveling and backward traveling waveforms exceed a zero level;
propagation time calculation means, coupled to the temperature sensor, the trigger signal generation means and the zero crossing signal generation means, to (1) calculate a possible range of propagation times based on of the gas temperature detected by the temperature sensor, (2) determine if the phases in which the first two trigger signals, generated respectively on the basis of the waveforms traveling forward and backward, coincide or not with each other, (3) process the zero-crossing signals in such a way that the phases coincide with each other if they did not do it before, (4) obtain a reference zero crossing time instant by calculating the mean value of the zero crossing time instants in the forward direction and in the backward direction, (5) obtain an ultrasonic reception point by subtracting an integer multiple from the cycle of the ultrasonic waves in such a way that the results of the subtraction fall within the possible range of propagation times and (6) estimate the ultrasonic propagation time on the basis of the ultrasonic receiving point.
Furthermore, according to another feature of the invention, a method of measuring the concentration of sample gas flowing through a conduit is provided, comprising the steps of:
generating ultrasonic waves traveling forward relative to the flow direction of the sample gas;
ES 2 565 635 T3 generating ultrasonic waves traveling backward relative to the flow direction of the sample gas;
measuring the temperature of the sample gas flowing through the conduit;
generating trigger signals when the waveforms traveling forward and those traveling backward exceed a predetermined level;
generating zero crossing signals in the forward direction and in the backward direction when the waveforms traveling forward and those traveling backward exceed a zero level;
calculating a possible range of propagation times based on the gas temperature detected by the temperature sensor;
determining whether the phases in which the first two trigger signals, respectively generated on the basis of the waveforms traveling forward and those traveling backward, coincide with each other;
processing the zero crossing signals in such a way that the phases coincide with each other if they did not do so before;
obtaining the reference zero crossing time instant by calculating the mean value of the zero crossing time instants in the forward direction and in the backward direction;
obtaining an ultrasonic reception point by subtracting an integer multiple from the cycle of the ultrasonic waves in such a way that the results of the subtraction fall within the possible range of propagation times; and estimating the ultrasonic propagation time based on the ultrasonic reception point.
Furthermore, according to another feature of the invention, there is provided an oxygen concentration system for generating an oxygen-enriched gas, comprising an oxygen concentration apparatus for generating an oxygen-enriched gas by nitrogen adsorption to extract nitrogen. from air; and an ultrasonic apparatus for measuring the oxygen concentration in the oxygen-enriched gas and the flow rate of the oxygen-enriched gas, the ultrasonic apparatus comprising:
a conduit for receiving and letting the oxygen-enriched gas flow;
a first ultrasonic transmission-reception device mounted inside the conduit;
a second ultrasonic transmission-reception device mounted inside the conduit so that it faces the first ultrasonic transmission-reception device;
a transmit-receive switch for switching the mode of operation of the first and second ultrasonic transmit-receive devices between a transmit mode for transmitting ultrasonic waves and a receive mode for receiving ultrasonic waves;
a temperature sensor, located within the conduit, to measure the temperature of the oxygen-enriched gas flowing through the conduit;
generating the first ultrasonic transmission-receiving device, when it is in the transmission mode, ultrasonic waves traveling forward with respect to the flow direction of the oxygen-enriched gas, and generating said first device, when it is in the mode reception, waveform that travels backward on the basis of the ultrasonic waves that were generated by the second transmit-receive ultrasonic device;
generating the second ultrasonic transmission-receiving device, when it is in the transmission mode, ultrasonic waves traveling backward with respect to the flow direction of the oxygen-enriched gas, and generating said second device, when it is in the mode reception, waveform that travels forward based on the received ultrasonic waves that were generated by the first transmit-receive ultrasonic device;
means for generating trigger signals when the waveforms traveling forward and those traveling backward exceed a predetermined level;
means for generating forward and backward zero crossing signals when forward traveling and backward traveling waveforms exceed a zero level;
propagation time calculation means, coupled to the temperature sensor, the trigger signal generation means and the zero crossing signal generation means, to (1) calculate a possible range of propagation times based on of the gas temperature detected by the temperature sensor, (2) determine if the phases in which the first two trigger signals, generated respectively on the basis of the waveforms traveling forward and those traveling backward, coincide with each other, (3) process the zero-crossing signals in such a way that the phases coincide with each other. another if they did not do it before, (4) obtain the reference zero crossing time by calculating the average value of the zero crossing time instants in the forward direction and in the backward direction, (5) get a reception point 4
ES 2 565 635 T3 ultrasonic subtracting an integer multiple of the cycle of the ultrasonic waves in such a way that the results of the subtraction fall within the possible range of propagation times and (6) estimating the ultrasonic propagation time based on the point of ultrasonic reception.
Furthermore, according to another feature of the invention, there is provided an oxygen concentration system for generating an oxygen-enriched gas, comprising:
an oxygen concentrating apparatus for generating an oxygen-enriched gas by nitrogen adsorption to extract nitrogen from the air; and an ultrasonic apparatus for measuring the oxygen concentration in the oxygen-enriched gas and the flow rate of the oxygen-enriched gas, the ultrasonic apparatus comprising:
a conduit for flowing a target gas, the concentration of which is to be measured;
a first ultrasonic transmission-reception device mounted inside the conduit;
a second ultrasonic transmission-reception device mounted inside the conduit so that it faces the first ultrasonic transmission-reception device;
the conduit includes a straight portion and perpendicular portions connected perpendicularly to the ends of the straight portion;
the first and second ultrasonic transmission-reception devices are located in the perpendicular portions so that they are facing the ends of the straight portion; and the distance between the first and second ultrasonic transmission-reception devices and the respective ends of the straight portion of the conduit fulfilling the following relationship.
0 <D <fxr<sup>2</sup>/ C where:
D: the distance (m) between the first and second ultrasonic transmit-receive devices and the respective ends of the straight portion f: frequency of the ultrasonic waves in the sample gas (Hz) r: inner radius of the duct (m)
C: speed of ultrasonic waves (m / s)
Brief Description of Drawings
Figure 1 is a schematic diagram of an oxygen concentration apparatus according to the invention;
Figure 2 is a schematic diagram of an ultrasonic apparatus of the invention;
Figure 3A is a waveform based on received ultrasonic waves;
Figure 3B is an enlarged illustration of a portion of the waveform shown in Figure 3A;
Figure 4 is an illustration showing the ultrasonic waveform with trigger signals and zero crossing signals;
Figure 5 is a graph showing the relationship between the speed of the ultrasonic waves and the temperature;
Figure 6 is an illustration showing forward traveling and backward traveling ultrasonic waveforms in the case where the phases, in which the trigger signals are generated, coincide with each other;
Figure 7 is an illustration similar to that of Figure 6 in the case where the phases do not coincide with each other;
Figure 8 is an illustration similar to that of Figure 6 in the case where the phases do not coincide with each other;
Figure 9 is an explanatory illustration for explaining how to obtain the zero crossing time point with the assumption that the sample gas is in a steady state;
Figure 10 is an explanatory illustration to explain how to obtain the ultrasonic receiving point;
Figure 11 is a section of the ultrasonic apparatus according to another embodiment of the invention;
Figure 12 is an explanatory illustration to explain the acoustic field formed at the front of an ultrasonic transducer;
Figure 13 shows experimental results of ultrasonic waveforms that were obtained by an apparatus of Figure 11;
ES 2 565 635 T3
Figure 14 shows experimental results of ultrasonic waveforms that were obtained by an apparatus of Figure 11; Y
Figure 15 shows experimental results of ultrasonic waveforms that were obtained by an apparatus of Figure 11;
Best Mode of Carrying Out the Invention
Next, a preferred embodiment of the present invention will be described. In the embodiment described below, a sample gas is composed of a mixture of oxygen and nitrogen. However, the sample gas that can be measured is not limited to a sample gas of oxygen and nitrogen, and the present invention can be supplied in a mixture that includes another gas.
Figure 1 shows a schematic diagram of an oxygen concentration system having an ultrasonic gas concentration and flow rate measuring apparatus in accordance with a preferred embodiment of the present invention.
Apparatus 100 includes an oxygen concentration apparatus 102 that produces an oxygen-enriched gas by extracting nitrogen from the air supplied by a compressor 104 from outside the system through a filter 106. Oxygen-enriched gas produced by apparatus 102 from Oxygen concentration is supplied to an ultrasonic apparatus 200 of the present invention through a flow adjusting device 108, such as for example a pressure reducing valve. The produced oxygen-enriched gas is then delivered to a user or patient through a production filter 110.
The oxygen concentrating apparatus includes a plurality of columns (not shown) to house nitrogen adsorbent such as a zeolite, a piping system (not shown) that includes conduits for directing compressed air from compressor 104 to each of the columns of the plurality of them and to direct the oxygen-enriched gas produced from the columns to the flow adjusting device 108, and valves (not shown) located in the piping system to selectively open and close the conduits, such that the adsorbent contained in one of the columns adsorbs nitrogen to produce the oxygen-enriched gas and the adsorbent contained in the others. columns let out the adsorbed nitrogen for regeneration of the adsorbent.
Referring to Figure 2, the ultrasonic apparatus 200 of the present invention for measuring the concentration and flow rate of a sample gas will now be described.
The concentration and flow rate measurement apparatus 200 includes a conduit 202 for flowing a sample gas or oxygen-enriched gas produced by the oxygen concentration apparatus 102. Conduit 202 has a straight portion 208 and perpendicular portions 204 and 206 connected to the ends of the straight portion. The straight portion 208 comprises a conduit element having a circular section, the diameter of which does not change along the longitudinal axis. A first ultrasonic transducer 218, providing a first ultrasonic transmitting-receiving device, is fixedly provided at one end of the interior of the straight portion, and a second ultrasonic transducer 222, providing a second ultrasonic transmitting-receiving device, it is fixedly mounted at the other end of the interior of the straight portion 208 so that it faces the first ultrasonic transducer 218. In this embodiment, the distance between the first 218 and second 222 ultrasonic transducers is called the propagation length Ls.
The perpendicular portion, located on the upstream side with respect to the direction of gas flow through conduit 202, has an inlet port 204a. The oxygen concentration apparatus 102 is connected, through a supply conduit 210, to the inlet port 204a as a source 212 of sample gas.
The perpendicular portion 206, located on the downstream side with respect to the direction of gas flow through the conduit 202, has an outlet port 206a to which the production filter 110 is connected.
A transmit-receive switch 224 is connected to the first 218 and second 222 ultrasonic transducers. The transmit-receive switch 224 independently switches the mode of operation of the first 218 and second 222 ultrasonic transducers between a transmission mode in which the first 218 and second 222 ultrasonic transducers transmit ultrasonic waves and a receive mode in the that the first 218 and second 222 ultrasonic transducers receive the ultrasonic waves. The transmit-receive switch 224 is connected to a microcomputer 226 such that the switching operation of the transmit-receive switch 224 is controlled by the microcomputer 226.
Temperature sensors 216 and 220, for measuring the temperature of the gas flowing through conduit 202, are preferably located in perpendicular portions 204 and 206 such that they do not disturb flow in straight portion 208. The temperature sensors 216 and 220 are connected to the microcomputer 226. In this connection, if the changes in the temperature of the sample gas are small, only one of the temperature sensors 216 and 220 can be placed.
A driver 228 is connected to microcomputer 226 to drive the ultrasonic transducers first.
218 and second 222, a zero crossing detection circuit 230 for detecting
ES 2 565 635 T3 zero of the signals from the first 218 and second 222 ultrasonic transducers, a display unit 234 to indicate, for example, the operating condition of the device 200 and the measurement results and a memory 232 that includes a non-volatile memory device or a disk device for storing the operating system for the microcomputer 226 and various parameters.
The operation of the ultrasonic apparatus 200 for concentration and flow measurement of the present embodiment will now be described.
A sample gas, for example an oxygen-nitrogen gas mixture whose mixing ratio is P: (1-P) (0 <P <1), is supplied to the conduit 202. At that time, the sample gas temperatures are measured by the temperature sensors 216 and 220 and the average value thereof is stored in memory 232 as the reference temperature Tü (K). According to the embodiment, the operating temperature range of the system 100 is preferably selected, for example, between 5-35 degrees Celsius.
During the delivery of the sample gas, pulses are transmitted from the microcomputer 226 to the driver 228 to generate the ultrasonic waves. The first ultrasonic transducer 218 is supplied with a voltage pulse from the driver 228 through the transmit-receive switch 224. The first ultrasonic transducer 218 generates ultrasonic waves corresponding to the voltage pulse. The ultrasonic waves generated by the first ultrasonic transducer 218 propagate through the sample gas flowing through the straight portion 208 of the conduit 202 and are received by the second ultrasonic transducer 222. The second ultrasonic transducer 222 generates an electrical signal corresponding to the received ultrasonic waves and sends it to the microcomputer 226 through the transmit-receive switch 224 and the zero-crossing detection circuit 230. The microcomputer 226 calculates the forward propagation time ts1 (s) based on the instant of time that the transmitted pulses are generated and sent to the driver 228 and the instant that the electrical signal from the second ultrasonic transducer 222 is received.
Next, the transmit-receive switch 224 switches the mode of operation of the first ultrasonic transducer 218 from the transmit mode to the receive mode just after the electrical signal from the second ultrasonic transducer 222 is received and also switches the mode of operation. of the second ultrasonic transducer 222 from the receive mode to the transmit mode. After this, pulses are transmitted from microcomputer 226 to driver 228 to generate the ultrasonic waves. The second ultrasonic transducer 222 is supplied with a voltage pulse from the driver 228 through the transmit-receive switch 224. The second ultrasonic transducer 222 generates ultrasonic waves corresponding to the voltage pulse. The ultrasonic waves are received by the first ultrasonic transducer 218. The first ultrasonic transducer 218 generates an electrical signal corresponding to the received ultrasonic waves and sends it to the microcomputer 226 through the transmit-receive switch 224 and the zero-crossing detection circuit 230. The microcomputer 226 calculates the backward propagation time ts2 (s) based on the instant of time that the transmitted pulses are generated and sent to the driver 228 and the instant that the electrical signal from the first ultrasonic transducer 218 is received.
Obtaining the average value of ts1 and ts2, it is possible to eliminate the affectation of the flow of the sample gas in the conduit 202. The ultrasonic propagation time ts in the stationary sample gas is defined by the following equation (4):
ts = (ts1 + ts2) / 2 ... (4)
The microcomputer 226 then calculates the speed Cs (m / s) of ultrasonic propagation through the stationary sample gas using the flow equation (5).
Cs = Ls / ts ... (5)
The oxygen concentration Ps is obtained by the following equation (6) on the basis of equations (1) and (2).
Ps = (KRTs / Cs<sup>2</sup> - Mn2) / (M02-Mn2). (6)
Furthermore, the oxygen concentration in the sample can be obtained as a ratio of the ultrasonic propagation velocity in the sample gas and the ultrasonic propagation velocities in 100% oxygen gas and in 100% nitrogen gas. That is, using equation (1), the ultrasonic propagation velocity C02 (m / s) at temperature Ts (K) through 100% oxygen gas and the ultrasonic propagation velocity Cn2 (m / s) can be easily obtained. at temperature Ts (K) through 100% nitrogen gas. In this way, Ps can be calculated by the following equation (7) with the ultrasonic propagation speed Cs (m / s) through the sample gas.
Ps = (1 / Cs<sup>2</sup> - 1 / Cn2<sup>2</sup>) / (1 / C02<sup>2</sup> - 1 / Cn2<sup>2</sup>) . (7)
These calculations are performed by the microcomputer 226, and the results are indicated by the display unit 234.
Next, the explanation will go to a method of obtaining ts1 and ts2. In this connection, in the present application, at the time when the first ultrasonic transducer 218 or the second 222 transmits the ultrasonic waves
ES 2 565 635 T3 is called the emission time and the moment in which the first ultrasonic transducer 218 or the second 222 receives the ultrasonic waves is called the ultrasonic reception point.
Figure 3A shows a typical ultrasonic waveform received by microcomputer 226 and Figure 3B is an enlargement of a portion of the waveform shown by circle 3B. As Figures 3A and 3B show, the waveform includes various noise components, which makes it difficult to detect the ultrasonic reception point of the ultrasonic waves propagating through the sample gas. Therefore, according to the present invention, the ultrasonic reception point is estimated based on the zero crossing time instant of the waveform that is detected after the amplitude of the waveform increases sufficiently to certain point. For this, the zero crossing detection circuit 230 includes a zero crossing comparator and a trigger comparator.
Referring to Figure 4, the trigger comparator sends a trigger signal Sti to microcomputer 226 when the waveform rises above a predetermined level. The zero crossing comparator sends a zero crossing signal Zci to the microcomputer 226 when the waveform rises above the zero level. The microcomputer 226 determines each of the zero crossing signals Zci as a zero crossing time instant after the first trigger signal Sti is received by the microcomputer 226. Preferably, the microcomputer 226 determines three first signals Zc1, Zc2 and Zc3 of zero crossing as first to third zero crossing time instants.
The interval between each of the zero crossing time instants theoretically corresponds to the cycle of the ultrasonic waves. Therefore, the ultrasonic reception point can be estimated by tracing backward from the first zero crossing time instant Zc1 along the time axis by an integer multiple of the cycle of the ultrasonic waves and therefore the Propagation time can be estimated by subtracting the emission time and an integer multiple of the ultrasonic wave cycle from the ultrasonic reception point.
As described above, the speed C (m / s) of ultrasonic waves propagating through a stationary gas is presented by equation (1). For example, the speed of ultrasonic waves through a pure nitrogen gas at 20 degrees Celsius is 349.1 m / s, and the speed of ultrasonic waves through a pure oxygen gas at 20 degrees Celsius is 326.6 m / s. Therefore, at 20 degrees Celsius, the speed of ultrasonic waves through an oxygen-nitrogen gas mixture falls within the range of 326.6 to 49.1 m / s. Figure 5 is a graph showing the relationship between ultrasonic wave velocity and gas temperature, in which the upper and lower limits of ultrasonic velocity through an oxygen-nitrogen gas mixture are indicated by Cmax (T ) and Cmin (T). The range of possible propagation times is from Ls / Cmax (T) to Ls / Cmin (T).
Therefore, if the propagation length Ls is selected so that the following relation (8) is satisfied, only an integer can be selected, which allows the ultrasonic reception point to fall within the range of possible propagation times .
(Ls / Cmin (T) - Ls / C max (T)) <1 / f ... (8) where:
f: frequency of the ultrasonic waves in the sample gas
The temperature T of the gas that provides the maximum value of (Ls / Cmax (T) - Ls / Cmin (T)) is the lower limit of the working temperature. If the working temperature is 5 degrees Celsius, and the frequency of the ultrasonic waves is 40 kHz, the propagation length Ls that satisfies the relation (8) is calculated as follows.
Ls <12.3 cm. (9)
According to the embodiment, Ls = 0.1 is used as an example.
To obtain the ultrasonic propagation time ts, the forward and backward propagation times ts1 and ts2 are previously measured. Referring to Figure 6, trigger signals are generated when the second waves in the two waveforms, the one traveling forward and the one traveling back, exceed the trigger level. In this case, the trigger signals are generated with the same cadence or phase with respect to the waveforms and the difference in the zero crossing time instants between the waves traveling forward and those traveling backward, A = ZcBi - ZcFi, is substantially equal to the difference td of the propagation times ts1 and ts2 between the waves traveling forward and those traveling backwards (Zcfí: the zero crossing time instants of the forward traveling waveform, Zcbí: the zero crossing time instants of the backward traveling waveform, i = 1, 2, 3. (wave number )).
However, Sti trigger signals are often generated in different phases of the waveforms between waves traveling forward and those traveling backward, even if the same trigger level is used. Referring to Figure 7, for waves traveling forward, the trigger signal is generated when the third wave exceeds the trigger level, and for waves traveling backward, the trigger signal is generated when the second wave exceeds the trigger level. Therefore, the trigger signal for waves traveling backward is generated one cycle before the trigger signal for waves traveling forward. In this case, the difference in zero crossing time instants between the waves traveling forward and those traveling backward, A = ZcBi - ZcFi, gives a negative value. If the sample gas flows through line 202, A = ZcBi - ZcFi does not
ES 2 565 635 T3 must be made negative. Therefore, if Zob, - ZcFi gives a negative value, it is evident that the trigger signal for waves traveling backward is generated before the trigger signal for waves traveling forward.
On the other hand, referring to Figure 8, for waves traveling forward, the trigger signal is generated when the second wave exceeds the trigger level, and for waves traveling backward, the trigger signal is generated when the third wave exceeds the trigger level. In this case, the difference in the zero crossing time instants between the waves traveling forward and those traveling backward, A = Zcb¡ - Zcf¡, is greater than one cycle of the ultrasonic waves, which indicates that the trigger signal for waves traveling forward is generated before the trigger signal for waves traveling backward.
In accordance with the embodiment of the invention, conduit 202 is designed in such a way that the propagation time difference td between waves traveling forward and those traveling backward always falls within one cycle of the ultrasonic waves. This feature allows the microcomputer 226 to distinguish the cases shown in Figures 7 and 8 from each other and to calculate the difference td in propagation times. That is, if A = Zcb¡ - Zcf¡ is negative, the case is as shown in Figure 7, and if A = Zcb¡ - Zcf¡ is greater than one cycle of the ultrasonic waves, the case is as shown in Figure 8.
Thus, the configuration of the conduit 202 having the above feature will be described below.
The possible range of the sample gas flow velocity V (m / s) is presented by the following inequality (10).
<V <Ο / (60000πη ... (10) where:
Q: sample gas flow rate (liters / min) r: inside radius of duct (m)
As described above, the velocity of the ultrasonic waves propagating in the forward direction with respect to the sample gas flow is C1 = C + V, and the velocity of the ultrasonic waves propagating in the backward direction with respect to the sample gas flow is C2 = CV.
Where:
C: the speed of the ultrasonic waves propagating through a stationary sample gas (m / s)
C1: the speed of the ultrasonic waves propagating in the forward direction with respect to the sample gas flow (m / s)
C2: the speed of the ultrasonic waves propagating in the backward direction with respect to the sample gas flow (m / s)
V: flow velocity (m / s)
The propagation time difference td is calculated by the following equation.
td = Ls / C2 - Ls / C1 = Ls / (CV) - Ls / (C + V). (11)
Therefore, if the inner radius of the conduit 202 fulfills the following relation (12), the difference td of propagation times becomes smaller than the cycle of the ultrasonic waves.
Ls / (C - Q / (60000πr<sup>2</sup>)) - Ls / (C + Q / (60000πr<sup>2</sup>)) <1 / f. (12)
The term on the left of the inequality (12) is maximized when the speed of the ultrasonic waves through conduit 202 is minimum (C = Cmn (5 degrees Celsius) = 318.1 m / s). Therefore, for example, if the frequency of the ultrasonic waves through conduit 202 is 40 (kHz), the flow rate Q = 10 (liters / min) and the length of conduit 202 is 10 (cm), then the radius inside r (mm) of conduit 202 is r> 2.05 (mm). According to the embodiment, r = 2.5 (mm) is selected as an example.
Next, the method for measuring the concentration and flow rate of a sample gas will be described in detail.
In the first place, in the case shown in Figure 6, the difference td in propagation times between the waves traveling forward and those traveling backward is obtained by A = Zcb¡ - Zcf¡, because, as described above, the difference td of propagation times is substantially equal to the difference A = Zcb¡ - Zcf¡. In the case shown in Figure 7, the difference td of propagation times is obtained by means of B = Zcb¡ + 1 - Zcf¡. Furthermore, in the case shown in Figure 8, the propagation time difference td is obtained by B = Zcb¡ - ZcFi + 1. Preferably, a plurality of the A or B values are obtained to calculate the arithmetic mean.
Next, the velocity of the ultrasonic waves through the sample gas is estimated with the assumption that the sample gas is in a steady state. To do this, the phase difference at the outputs of the trigger signals is previously determined on the basis of the value of A. If there is no phase difference, as shown in the
ES 2 565 635 T3
Figure 6, the mean value Zc_ave of the first zero crossing time instants of the waveforms traveling forward and backward is calculated by the following equation.
<sup>Z</sup>c_ave = (ZcFl + ZcBl) / 2. „(13)
In the case shown in Figure 7, the mean value Zc_ave of the first zero crossing time instants of the waveforms traveling back and forth is calculated by the following equation.
<sup>Z</sup>c_ave = (Zcfi + ZcB2) / 2 ... (14)
In the case shown in Figure 8, the mean value Zc_ave of the first zero crossing time instants of the waveforms traveling back and forth is calculated by the following equation.
<sup>Z</sup>c_ave = (ZcF2<sup>+</sup> ZcB1) / 2. (15)
The mean value Zc_ave can be considered as the first zero crossing time instant that is obtained with the assumption that the ultrasonic waves pass through the sample gas. In the present application, the value Zc_ave is called the reference zero crossing time point.
As described above, the length of conduit 102 is designed such that only an integer is selected, allowing the ultrasonic reception point to fall within the possible range of propagation times (Figure 9). Therefore, the ultrasonic propagation time ts is estimated by tracing back from the first zero crossing time Zc_ave along the time axis by an integer multiple of the ultrasonic wave cycle until the ultrasonic reception point falls within the possible range.
The velocity Cs of the ultrasonic waves through the stationary sample gas is estimated by the following equation (16).
Cs = Ls / ts. (16)
The oxygen concentration Ps is obtained by means of equation (6) or (7) with the calculated Cs.
The times ts1 and ts2 of propagation back and forth through the sample gas flowing through conduit 202 are estimated by the following equations ts1 = ts-td / 2. (17) ts1 = ts + td / 2. (18)
The forward speeds C1 and backward C2 of the ultrasonic waves through the sample gas flowing through conduit 202 are estimated by the following equations (19) and (20).
C1 = Ls / ts1. (19)
C2 = Ls / ts2. (20)
Next, the flow rate V of the sample gas through conduit 202 is obtained from equations (3), (19), and (20). Furthermore, the flow rate Q of the sample gas is calculated by the following equation (21).
Q = 6000πΓν. (21)
Now, referring to Figures 11 to 15, a preferred embodiment of the ultrasonic concentration and flow rate measurement apparatus will be described below.
The ultrasonic concentration and flow measurement apparatus 10 includes a conduit 27 that provides conduit 202 of the embodiment of Figure 2. Housings 25 and 26, to contain the first and 21 second ultrasonic transducers, attached to the ends of the conduit 27 by portions 41 and 42 welded. Housings 25 and 26 include holes 28 and 29 that extend perpendicular to conduit 27 to provide inlet and outlet portions 204a and 206a of the embodiment of Figure 2. Conduit 27 and housings 25 and 26 are preferably manufactured therefrom. metallic material, such as for example aluminum alloy.
Conduit 27 and housings 25 and 26 are attached at one point to substrate 30 or a housing of the oxygen concentration apparatus by a screw 45. This configuration allows longitudinal deformation of conduit 27 freely by external force that can be generated when the Conduit 27 is thermally deformed.
Covers 23 and 24 are fixed to the housings 25 and 26 to close the end openings of the housings by means of screws 43 and 44, trapping O-rings 39 and 40 between the housings 25 and 26 and the covers 23 and 24. The ultrasonic transducers first 20 and second 21 are attached to the interior surfaces of caps 23 and 24. The first 20 and second 21 ultrasonic transducers generate 40 kHz of ultrasonic waves.
In addition, temperature sensors 37 and 38 for detecting the gas temperature are attached to the inner surfaces of the caps 23 and 24. The first 20 and second 21 ultrasonic transducers and the temperature sensors 37 and 38 are coupled to the microcomputer 226 through of connectors 31 and 34 fixed to the outer surfaces of the covers 23 and 24, cables 33 and 36 and connectors 32 and 35 mounted on the substrate 30.
ES 2 565 635 T3
The distance D between the end faces of the first 20 and second 21 ultrasonic transducers and the respective ends of the conduit 27 is a significant design factor. Generally, the acoustic field formed by the ultrasonic waves from an ultrasonic transducer includes near and far acoustic fields, as shown in Figure 12. Ultrasonic waves propagate linearly through the near acoustic field and, on the other hand, in the far acoustic field, they propagate in the form of spherical waves. Therefore, if the ends of the conduit 27 are outside the near acoustic field, the ultrasonic energy transmitted within the conduit 27 is reduced compared to conduits that have the ends located within the near acoustic field and therefore the sound ratio / signal noise from the transducers is reduced.
It is known that the boundary between the near and far acoustic fields occurs at a point Z0 whose distance D to the end face of an ultrasonic transducer along the center line of the transducer is defined by the following equation (22).
D = fxr<sup>2</sup>/ C ... (22)
Where:
f: frequency of the ultrasonic waves in the sample gas (Hz) r: inner radius of the duct (m)
C: speed of ultrasonic waves (m / s)
As described above, the velocity C through a sample gas is defined by equation (1). Therefore, the higher the gas temperature and the lower the molecular weight, the higher the velocity C becomes. According to the embodiment, the condition that maximizes Zo is, for example, that the sample gas is air at 35 degrees Celsius and so Zo is about 1.4mm.
Figures 13-15 show experimental results of ultrasonic waveforms that were obtained by an apparatus of Figure 11 with the distance d of 0.3 mm, 1.0 mm and 1.8 mm. The experimental results suggest that the ultrasonic energy received by the ultrasonic transducer is significantly reduced when the distance d is 1.8 mm compared to the cases of the distance d of 0.3 mm and 1.0 mm.
Contents5
50 members in 14 offices
Priority claims7
| Document | Office | Kind | Date |
|---|---|---|---|
| 2003115333 | Japan | A | |
| 2003115333 | Japan | – | |
| 2003168911 | Japan | A | |
| 2003168911 | Japan | – | |
| 2003271779 | Japan | A | |
| 2003271779 | Japan | – | |
| 2004005590 | Japan | W |
Members50
| Document | Office | Kind | |
|---|---|---|---|
| AU2004233273A1 | Australia | A1 | |
| AU2004233273A2 | Australia | A2 | |
| CA2520563A1 | Canada | A1 | |
| CA2776083A1 | Canada | A1 | |
| WO2004094960A2 | World Intellectual Property Organization (WIPO) | A2 | |
| JP2004317459A | Japan | A | |
| TW200426365A | Taiwan Province of China | A | |
| JP2005001956A | Japan | A | |
| JP2005030954A | Japan | A | |
| WO2004094960A3 | World Intellectual Property Organization (WIPO) | A3 | |
| KR20060003022A | Republic of Korea | A | |
| EP1616153A2 | European Patent Office (EPO) | A2 | |
| CN1777791A | China | A | |
| HK1083364A1 | Hong Kong, China | A1 | |
| US2006185443A1 | United States of America | A1 | |
| HK1089813A1 | Hong Kong, China | A1 | |
| TWI280363B | Taiwan Province of China | B | |
| US7213468B2 | United States of America | B2 | |
| CN100374826C | China | C | |
| AU2004233273B2 | Australia | B2 | |
| AU2004233273C1 | Australia | C1 | |
| WO2009050553A1 | World Intellectual Property Organization (WIPO) | A1 | |
| CA2675527A1 | Canada | A1 | |
| JP2009113797A | Japan | A | |
| JP4271979B2 | Japan | B2 | |
| JP4275466B2 | Japan | B2 | |
| KR20090094092A | Republic of Korea | A | |
| CN101568461A | China | A | |
| US2010052367A1 | United States of America | A1 | |
| JP4473535B2 | Japan | B2 | |
| EP2214949A1 | European Patent Office (EPO) | A1 | |
| MY142630A | Malaysia | A | |
| CN101568461B | China | B | |
| CA2675527C | Canada | C | |
| KR20110036872A | Republic of Korea | A | |
| EP2214949B1 | European Patent Office (EPO) | B1 | |
| AT518729T | Austria | T | |
| ATE518729T1 | Austria | T1 | |
| BRPI0805842A2 | Brazil | A2 | |
| KR101060541B1 | Republic of Korea | B1 | |
| EP2366981A1 | European Patent Office (EPO) | A1 | |
| KR101118945B1 | Republic of Korea | B1 | |
| KR101118949B1 | Republic of Korea | B1 | |
| US8141938B2 | United States of America | B2 | |
| CA2520563C | Canada | C | |
| CA2776083C | Canada | C | |
| EP1616153B1 | European Patent Office (EPO) | B1 | |
| ES2565635T3This record | Spain | T3 | |
| EP2366981B1 | European Patent Office (EPO) | B1 | |
| ES2600525T3 | Spain | T3 |
Numbers
- Publication
- 2565635
- Application
- 4728397
Titles2
- Spanish
- Aparato ultrasónico y método para medir la concentración y el caudal de gas
- English
- Ultrasonic device and method for measuring gas concentration and flow
Classification
- CPC, 10
- C21D7/00
- G01F1/66
- G01F1/668
- G01N29/07
- G01N29/222
- G01N2291/02809
- G01N2291/02836
- G01N2291/02881
- G01N2291/105
- G01N29/036
- IPC, 3
- G01F1 66
- G01N29 07
- G01N29 22