JP2003135601A - Oxygen-concentrating system for medical treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen-concentrating system which can accurately measure an oxygen concentration even when argon exists in addition to oxygen and nitrogen in a sample gas. SOLUTION: This oxygen-concentrating system is equipped with an oxygen- concentrating means, an ultrasonic oscillator and a reflecting plate, and a temperature sensor. In this case, the oxygen-concentrating means separates oxygen from air. The ultrasonic oscillator and the reflecting plate are arranged in a manner to be confronted with each other in piping on the downstream side of the oxygen-concentrating means, and transmit/receive an ultrasonic wave. Such an oxygen-concentrating system is equipped with a correction coefficient table for an oxygen-argon ratio in an oxygen-concentrated air based on a set flow rate of the oxygen-concentrated air which is fed to a user. Also, a concentration-computing means which computes the oxygen concentration of the oxygen-concentrated air based on the correction coefficient value is provided for this oxygen-concentrating system for medical treatment.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxygen concentrator for separating and concentrating oxygen from the air. More specifically,
The present invention relates to a medical oxygen concentrator equipped with means for measuring the oxygen concentration of oxygen enriched air sent from an oxygen concentrator used for medical purposes.

[0002]

It is widely known that the propagation velocity of ultrasonic waves propagating in a sample gas is expressed as a function of the concentration and temperature of the sample gas. When the average molecular weight of the sample gas is M and the temperature is T [K], the ultrasonic wave propagation velocity C [m / sec] in the sample gas is expressed by the following equation (1).

[0003]

[Equation 1]

Here, k and R are constants (k: ratio of constant volume molar specific heat and constant pressure molar specific heat, R: gas constant). That is,
If the ultrasonic propagation velocity C [m / sec] in the sample gas and the temperature T [K] of the sample gas can be measured, the average molecular weight M of the sample gas can be determined. It is known that if the sample gas is a gas composed of two molecules of oxygen and nitrogen, then k = 1.4. The average molecular weight M of the sample gas is, for example, oxygen 100 × P [%] (0 ≦ P ≦ 1) and nitrogen 100 × (1-P) [%, where the molecular weight of oxygen is M _O2 and the molecular weight of nitrogen is M _N2. In the case of], it can be described as M = M _O2 P + M _N2 (1-P) ---------- Equation (2), and the oxygen concentration P is determined from the measured average molecular weight M. it can.

As a feature of the ultrasonic reflection type gas concentration measuring device, it is possible to measure the concentration of the sample gas regardless of the flow rate of the sample gas. That is, the ultrasonic wave propagation velocity in the sample gas when the flow velocity of the sample gas is 0 is C [m / s
ec], when the flow velocity of the sample gas in the direction from the ultrasonic transducer to the reflector is V [m / sec], the ultrasonic propagation velocity from the ultrasonic transducer to the reflector is C + V Therefore, the ultrasonic wave propagation velocity in the direction in which the ultrasonic wave reflected by the reflecting plate returns to the ultrasonic transducer becomes CV. Since the propagation velocity of the ultrasonic wave measured by the ultrasonic reflection type device becomes the average velocity of the reciprocating ultrasonic wave, the flow velocity V of the sample gas is canceled and the flow velocity of the sample gas is 0 in the sample gas. The ultrasonic propagation velocity C of is to be measured.

Various proposals have been made regarding the method and apparatus for measuring the concentration and flow rate of the sample gas from the propagation velocity or propagation time of the ultrasonic wave propagating in the sample gas by utilizing the principle. For example, in Japanese Unexamined Patent Publication No. 6-213877, two ultrasonic transducers are arranged to face each other in a pipe through which a sample gas passes, and the propagation time of ultrasonic waves propagating between the ultrasonic transducers is measured to measure the sample. An apparatus for measuring gas concentration and flow rate is described. Further, for example, US Patent No. 5060506 describes a device for measuring the concentration of a sample gas composed of two kinds of molecules by measuring the change in sound velocity of ultrasonic waves.

[0007]

The oxygen concentration in the oxygen-enriched air generated from the oxygen concentrator is measured by using the method for accurately measuring the concentration of the sample gas by using the propagation velocity of ultrasonic waves. In this case, only the concentrations of oxygen and nitrogen change, and when molecules other than oxygen and nitrogen are present in the sample gas, the concentration of molecules other than oxygen and nitrogen is always constant, or Molecules other than nitrogen had to be always present in a constant ratio with the concentration of oxygen or nitrogen. That is, as is clear from the equation (1), the variable that can be derived when the temperature T of the sample gas and the sound velocity C can be measured is the average molecular weight M of the sample gas.
Therefore, in order to obtain the concentration of the sample gas from the average molecular weight M, the average molecular weight had to be expressed by a single variable.

However, the sample gas actually output from the oxygen concentrator contains argon in addition to oxygen and nitrogen. Further, since the concentration of argon is not always constant and changes with the set flow rate of the oxygen concentrator, there is a problem that the conventional ultrasonic oxygen concentration measuring means cannot accurately measure the oxygen concentration.

The present invention provides an oxygen concentrator equipped with ultrasonic type oxygen concentration measuring means for deriving a coefficient for correcting the argon concentration according to the flow rate of a sample gas and accurately measuring the oxygen concentration at each flow rate. Is intended.

[0010]

DISCLOSURE OF THE INVENTION As a result of earnest studies for achieving the above object, the inventors of the present invention have found that oxygen contained in a sample gas output from the same type of oxygen concentrator /
The ratio of the argon concentration is almost the same at the same sample gas flow rate, and the oxygen concentration can be accurately measured even in the presence of argon by deriving the correction coefficient of the argon concentration from the sample gas flow rate and feeding it back. Is found.

That is, according to the present invention, there are provided an oxygen concentrating means for separating oxygen from the air, an ultrasonic transducer for transmitting and receiving ultrasonic waves arranged opposite to each other in a pipe downstream of the oxygen concentrating means, a reflector, and a temperature sensor. In the provided oxygen concentrator, a correction coefficient table for oxygen and argon ratios in the oxygen-enriched air with respect to the set flow rate of the oxygen-enriched air supplied to the user is provided, and the oxygen concentration of the oxygen-enriched air is determined based on the correction coefficient value. The present invention provides a medical oxygen concentrating device comprising a concentration calculating means for calculating.

Further, according to the present invention, the concentration calculating means detects the propagation velocity until the ultrasonic wave transmitted from the ultrasonic transducer is reflected by the reflecting plate and received by the ultrasonic transducer. , A means for calculating the oxygen concentration from the ultrasonic wave propagation velocity and the gas temperature, and in particular, the concentration calculating means introduces a mixed gas of oxygen and nitrogen of a predetermined concentration into the pipe. At the time, the ultrasonic wave transmitted from the ultrasonic transducer has a function of calculating the propagation time until the ultrasonic wave is reflected by the reflector and received by the ultrasonic transducer. The present invention provides a medical oxygen concentrator, comprising: a calculating unit that calculates a reference length of a pipe that connects the reflection plate and a storage unit that stores a result of the calculated reference length.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The oxygen / argon concentration ratio output from an oxygen concentrator changes depending on the flow rate of a sample gas output from the oxygen concentrator, and the oxygen / argon concentration ratio is the sample gas. It can be expressed as a function of flow rate.

The present invention is an ultrasonic oxygen concentration measuring means suitable for mounting on an oxygen concentrating device for outputting a sample gas composed of oxygen, nitrogen and argon, and a correction coefficient for the argon concentration is calculated from the flow rate of the sample gas. It is intended to provide a medical oxygen concentrator which can be accurately derived and used to accurately measure the oxygen concentration of a sample gas.

Examples will be shown below. As shown in the schematic flow chart of FIG. 2, the oxygen concentrator of the present invention comprises two adsorption cylinders filled with high-performance Li-X zeolite as an adsorbent that selectively adsorbs nitrogen rather than oxygen, and pressurization. A compressor for supplying air to the adsorption cylinder, an oxygen supply means for supplying oxygen-enriched air generated from the adsorption cylinder to the user, and an ultrasonic oxygen concentration measuring means on the downstream side of the adsorption tower are provided.

The structure of the ultrasonic type oxygen concentration measuring means is as shown in FIG. 1, and is provided with an ultrasonic vibrator, a reflector and a temperature sensor which are arranged so as to face the pipe.

Piping 1 connecting the ultrasonic transducer 2 and the reflector 20
When calibrating the reference length L ₀ , prepare a gas with a gas concentration of 100 × P [%] and nitrogen of 100 × (1-P) [%] as a calibration gas, and use a gas flowmeter, etc. Flow rate Q ₀ [m ³ / sec]
To pipe 1. At this time, the temperature T ₀ [K] obtained by averaging the outputs of the two temperature sensors 3 is measured and stored in the nonvolatile memory 9 as the reference temperature. The temperature T ₀ [K] at this time may be any value [K] as long as it does not deviate from the temperature set as the operating temperature range of the device.

While the calibration gas is being supplied, a transmission pulse of ultrasonic waves is sent from the microcomputer 7 to the driver 5, a pulse voltage is applied to the ultrasonic transducer 2 through the transmission / reception switch 4, and ultrasonic waves are transmitted. After transmitting the ultrasonic wave, the transmission / reception switch 4 sets the ultrasonic transducer 2 in a receivable state so that the ultrasonic wave reflected by the reflector 20 can be received by the ultrasonic transducer 2. After that, the reflector 2
The ultrasonic wave reflected at 0 and received by the ultrasonic transducer 2 is input to the microcomputer 7 via the transmission / reception switch 4 and the receiver 6, and the ultrasonic wave propagation time t ₀ [se
c] is measured.

Oxygen concentration 100 x P [%], nitrogen 100 x (1-P)
Ultrasonic propagation velocity C ₀ [m / sec] in gas at [%] and temperature T ₀ [K]
Is as follows using the above equation (1).

[0020]

[Equation 2]

Since the ultrasonic wave propagation time measured when the calibration gas was introduced was t ₀ [sec], the standard of the pipe 1 connecting the ultrasonic transducer and the reflector at the standard temperature T ₀ [K] Length
Given that L ₀ [m], the following relation holds.

[0022]

[Equation 3]

That is, the reference length L ₀ [m] at the reference temperature T ₀ [K] can be obtained by the following equation.

[0024]

[Equation 4]

The above calculation is carried out in the microcomputer 7, and the reference length L ₀ [m] obtained here is stored in the non-volatile memory 9.

By introducing one kind of calibration gas having a known concentration into the apparatus by the above method, the reference length L of the pipe 1 connecting the ultrasonic transducer 2 and the reflection plate 20 at the temperature T ₀ [K]
Can calibrate ₀ [m]. The method can be realized by pushing the button equipped on the device once while the calibration gas is being supplied to the device, and the calculation itself is simple, so that the calibration can be finished in an instant. Further, even when the positional relationship between the ultrasonic transducer 2 and the reflection plate 20 is changed due to aged deterioration of the device and the propagation distance of the ultrasonic wave is changed, the device can be easily recalibrated, The reference temperature and the reference length stored in the non-volatile memory 9 can be updated.

Table 1 shows the results of gas component analysis performed at each flow rate of the sample gas output from the oxygen concentrator. The gas component analysis was performed by gas chromatography.

[0028]

[Table 1]

As shown in Table 1, it was revealed that the ratio of oxygen and argon was different depending on the flow rate. Table 1 shows the results measured by one of the oxygen concentrators, but even in the same type of oxygen concentrator, although there are some variations in the output oxygen concentration, the oxygen / argon concentration Have the same ratio. On the other hand, the type and amount of adsorbent,
The oxygen / argon ratio varies depending on the type of machine base such as the shape of the adsorption cylinder.

From the results of Table 1, a method of deriving a correction coefficient for the argon concentration depending on the flow rate of the sample gas and accurately measuring the oxygen concentration will be described below. There are various methods for correcting the argon concentration due to the change in the flow rate. For example, from Table 1, a method of directly describing the average molecular weight M in the formula (1) using the abundance ratio of oxygen and argon can be considered. That is, the molecular weights of oxygen, nitrogen, and argon are 32 and 2 respectively.
If the oxygen concentration is expressed as 100 × P [%] and the output flow rate from the oxygen concentrator is 1.00 L / min, the average molecular weight M can be expressed by the following equation (6). It will be possible.

M = 32P + 40 * (6.4 / 93.5) P + 28 (1-P- (6.4 / 93.5) P) ----- Equation (6) Furthermore, regarding the specific heat ratio k, the diatomic molecule ( Specific heat ratio of oxygen and nitrogen is 1.4, specific heat ratio of atomic molecule (argon) is 1.6
Using 7, it can be expressed as

K = 1.4 * (1- (6.4 / 93.5) P) + 1.67 * (6.4 / 93.5) P ----- Equation (7) Therefore, if the sound velocity in the sample gas and the temperature can be measured, From (1), (6), and (7), the only unknown number is P, and the oxygen concentration of 100 × P [%] can be obtained.

In the above example, the sample gas flow rate is 1.00 L / mi.
In the case of n, and at other flow rates, the oxygen / argon existence ratio set to (6.4 / 93.5) in equations (6) and (7) may be replaced with the oxygen / argon existence ratio at other flow rates. In this case, the oxygen / argon existence ratio itself becomes the correction coefficient of the argon concentration, and the argon concentration correction coefficient is referred to from the table based on the sample gas flow rate, or the relationship of the ratio of the oxygen / argon concentration to the flow rate measured in advance is approximated. If the argon concentration correction coefficient is derived as a function of the flow rate, the accurate oxygen concentration can be measured.

Alternatively, the following method may be considered in order to simplify the calculation. That is, assuming that the components of the sample gas are composed of only oxygen and nitrogen,
To calculate the oxygen concentration. Since the oxygen concentration obtained here is a value that ignores the presence of argon, it becomes a value different from the actual oxygen concentration. However, since the abundance ratio of oxygen and argon at a specific flow rate is known, it is possible to approximate the accurate oxygen concentration by multiplying the once calculated oxygen concentration value by a specific coefficient. In this case, the specific coefficient serves as a correction coefficient for the argon concentration.

For example, the flow rate of the sample gas is 1.00 L / min
In the case of, when the oxygen concentration is calculated by using the formula (2) and ignoring the presence of argon with the specific heat ratio k = 1.4, the oxygen concentration is 10
It is calculated as 2.8 [%]. However, if it is known in advance that the actual oxygen concentration is 93.5 [%], it is calculated as (93.5%) as the argon concentration correction coefficient at 1.00 L / min.
/102.8) can be obtained and the sample gas flow rate is 1.00L.
When / min, the oxygen concentration can be accurately measured by multiplying the oxygen concentration obtained by the equation (2) by the argon concentration correction coefficient (93.5 / 102.8).

Similarly, if the argon concentration correction coefficient is obtained in advance at a time other than 1.00 L / min, the argon concentration correction coefficient is referred to from the table based on the sample gas flow rate.
Alternatively, if the argon concentration correction coefficient for the flow rate is obtained by an approximate expression, the argon concentration correction coefficient at each flow rate can be determined, and the accurate oxygen concentration can be measured.

FIG. 1 is a schematic diagram showing the structure of the apparatus. The pipe 1 at the portion connecting the ultrasonic transducer 2 and the reflection plate 20 has a cylindrical shape, and the ultrasonic transducer 2 and the reflection plate 20 are arranged to face each other in the pipe 1 through which the sample gas flows. Two temperature sensors 3 are arranged near the inlet and outlet of the sample gas so as not to disturb the gas flow on the ultrasonic wave propagation path. By arranging the two temperature sensors 3 at the entrance and exit of the pipe 1, the average temperature of the sample gas flowing through the pipe 1 can be measured. When the temperature change of the sample gas is not large, the number of temperature sensors 3 may be one. The ultrasonic transducer 2 can transmit and receive ultrasonic waves, and switching between transmission and reception is performed by the transmission / reception switch 4. The nonvolatile memory 9 stores the above-described flow rate vs. argon concentration correction coefficient table. The display 8 displays the measured oxygen concentration of the sample gas.

The flow rate of the sample gas is measured by the flow rate measuring device 21, and the flow rate measurement value is obtained by the microcomputer 7.
Entered in.

Sound velocity C _s [m / sec] of sample gas, temperature T
_{If the} argon concentration correction coefficient is known from _s [° C.] and the flow rate of the sample gas, it is possible to accurately determine the oxygen concentration using any of the methods described above.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of ultrasonic oxygen concentration measuring means of a medical oxygen concentrator of the present invention.

FIG. 2 is a schematic configuration diagram of a medical oxygen concentrator of the present invention.

[Explanation of symbols]

1 piping 2 Ultrasonic transducer 3 Temperature sensor 4 send / receive switch 5 drivers 6 receiver 7 microcomputer 8 display 9 Non-volatile memory 10 Medical oxygen concentrator 11 adsorption cylinder 12 compressor 13 filters 14 Switching valve 15 Check valve 16 product tanks 17 Regulator 18 Ultrasonic oxygen concentration measuring means 19 Product Filter 20 Reflector 21 Flowmeter

Claims (3)

[Claims] 1. Oxygen comprising an oxygen concentrating means for separating oxygen from the air, an ultrasonic transducer for transmitting and receiving ultrasonic waves arranged opposite to each other in a pipe downstream of the oxygen concentrating means, a reflector, and a temperature sensor. The concentrator is provided with a correction coefficient table for the oxygen / argon ratio in the oxygen-enriched air with respect to the set flow rate of the oxygen-enriched air supplied to the user, and the concentration for calculating the oxygen concentration of the oxygen-enriched air based on the correction coefficient value. A medical oxygen concentrator, comprising a calculation means. 2. The concentration calculating means detects a propagation velocity until ultrasonic waves transmitted from the ultrasonic transducer are reflected by a reflecting plate and received by the ultrasonic transducer, 2. The medical oxygen concentrator according to claim 1, which is a means for calculating the oxygen concentration from the propagation velocity and the gas temperature. 3. The ultrasonic wave transmitted from the ultrasonic transducer when the concentration calculating means introduces a mixed gas of oxygen and nitrogen having a predetermined concentration into the pipe is reflected by a reflecting plate, Equipped with a function to calculate the propagation time until it is received by the ultrasonic transducer, the calculation means to calculate the reference length of the pipe connecting the ultrasonic transducer and the reflector from the result, the result of the calculated reference length 3. The medical oxygen concentrating device according to claim 1, further comprising a storage unit for storing.