JP7651326B2 - Propagation measurement method, gas flow rate measurement method, propagation measurement program, gas flow rate measurement program, gas flow rate measurement device, and oxygen concentrator - Google Patents

Description

The present invention relates to a propagation measurement method for measuring the propagation state of ultrasonic waves emitted from an ultrasonic sensor, and a gas flow velocity measurement method including the propagation measurement method.

Conventionally, there is known an ultrasonic gas concentration flow rate measuring device that measures the flow rate and concentration of gas by arranging ultrasonic transmitters opposite each other in the measurement flow path inside a measurement pipe through which gas flows (see, for example, Patent Document 1).

Such gas concentration flow rate measuring devices are also used in oxygen concentrators. As shown in Patent Document 2, an oxygen concentrator is a device that, for example, compresses air and then removes nitrogen from the air to produce highly concentrated oxygen. Note that oxygen concentrators are devices used to supply oxygen to patients who must receive oxygen supplements at home due to reasons such as respiratory failure.

Patent No. 6305209 Patent No. 5499265

In an ultrasonic gas concentration flow rate measuring device, the gas flow rate is first calculated based on the difference between the speed at which ultrasonic waves emitted from the ultrasonic sensor on the upstream side of the gas flow in the measurement flow path propagate and the speed at which ultrasonic waves emitted from the ultrasonic sensor on the downstream side propagate, and the gas flow rate and concentration are calculated and measured based on this flow rate. Therefore, in order to measure the gas flow rate and concentration more accurately, it is necessary to correctly grasp the propagation conditions of ultrasonic waves in the measurement flow path.

Therefore, the present invention provides a propagation measurement method that can accurately measure the propagation time of ultrasonic waves by accurately grasping the propagation conditions of the ultrasonic waves.

The propagation measurement method according to one aspect of the present invention is a propagation measurement method for measuring the propagation status in a measurement flow path of ultrasonic waves transmitted from a pair of ultrasonic sensors arranged on the upstream and downstream sides of the measurement flow path through which gas can flow, and includes the steps of transmitting a pulse group of ultrasonic waves including a plurality of pulses alternately in a forward direction from the upstream ultrasonic sensor toward the downstream ultrasonic sensor and in a reverse direction from the downstream ultrasonic sensor toward the upstream ultrasonic sensor to transmit the ultrasonic waves in the measurement flow path, setting an initial measurement waiting time value that is the time from when a reference pulse in the pulse group is transmitted from one ultrasonic sensor to when a leading pulse in the pulse group that is forward in the propagation direction than the reference pulse is estimated to be received by the other ultrasonic sensor, detecting a reference pulse reception time from when the leading pulse is estimated to be received by the other ultrasonic sensor to when the reference pulse is received by the other ultrasonic sensor, and calculating the propagation time of the pulse in the measurement flow path from the sum of the initial measurement waiting time value and the reference pulse reception time.

The above propagation measurement method further includes a step of calculating an updated measurement waiting time by subtracting a predetermined waiting time calculation adjustment value from the propagation time, and a step of replacing the measurement waiting time initial value with the updated measurement waiting time, and a step of detecting the reference pulse reception time using the updated measurement waiting time and a step of calculating the propagation time are executed again.

The above propagation measurement method may further include a step of determining whether the post-update measurement waiting time is within a predetermined range after calculating the post-update measurement waiting time, and a step of correcting the post-update measurement waiting time by adding a predetermined waiting time correction value to the post-update measurement waiting time only if the post-update measurement waiting time is outside the predetermined range.

In the above propagation measurement method, the steps of calculating the propagation time, calculating the post-update measurement waiting time, and correcting the post-update measurement waiting time may be repeated until the post-update measurement waiting time becomes a value within a predetermined range.

In the above propagation measurement method, in the step of determining whether the post-update measurement waiting time is within a predetermined range, the determination may be made based on the molecular weight of the gas calculated based on the sound speed in the measurement flow path obtained from the propagation time of the pulse in the forward direction and the propagation time of the pulse in the reverse direction.

In the above propagation measurement method, in the step of correcting the post-update measurement waiting time, a waiting time correction value may be added to the post-update measurement waiting time such that the post-update measurement waiting time becomes longer in each of the forward direction and the reverse direction when the molecular weight of the gas becomes smaller than a predetermined minimum threshold, or a waiting time correction value may be added to the post-update measurement waiting time such that the post-update measurement waiting time becomes shorter in each of the forward direction and the reverse direction when the molecular weight of the gas becomes larger than a predetermined maximum threshold.

In the above propagation measurement method, in the step of determining whether the post-update measurement waiting time is within a predetermined range, the determination may be made based on whether the difference between the propagation time of the pulse in the forward direction and the propagation time in the reverse direction is greater than a predetermined maximum value.

In the above propagation measurement method, in the step of correcting the post-update measurement waiting time, the post-update measurement waiting time for the pulse in the reverse direction may be made to coincide with the post-update measurement waiting time for the pulse in the forward direction, or the waiting time correction value may be added to the post-update measurement waiting time for the pulse in the forward direction so as to coincide with the post-update measurement waiting time for the pulse in the reverse direction.

In the above propagation measurement method, in the step of determining whether the post-update measurement waiting time is within a predetermined range, the step of calculating the propagation time may be executed again, and then the determination may be made based on whether the amount of change in the propagation time is greater than a predetermined maximum amount of change.

In the above propagation measurement method, when the waiting time calculation adjustment value is t _{inv_ost} , the reference pulse is the _N1th pulse of the pulse group, the leading pulse is the _N2th pulse of the pulse group, and a period of the pulse is X, the waiting time calculation adjustment value may satisfy the following formula (1): 0<t _{inv_ost} <(N ₁ -N ₂ )×X (1)

In the above propagation measurement method, the step of detecting the reference pulse reception time and the step of calculating the propagation time are performed multiple times using the same initial measurement wait time value and the same post-update measurement wait time, and when a group of multiple values obtained by performing the step of calculating the propagation time multiple times using the same initial measurement wait time value and the same post-update measurement wait time is taken as a group of sample values under the same conditions for the same initial measurement wait time value and the same post-update measurement wait time, the step of calculating the propagation time may use an average value obtained by excluding at least a portion of the group of sample values under the same conditions other than the median value from the group of sample values under the same conditions as the propagation time.

A gas flow rate measurement method according to one aspect of the present invention includes a step of blocking the inflow of gas into the measurement flow path, a step of performing the above-mentioned propagation measurement method while blocking the inflow of gas into the measurement flow path, a step of flowing gas into the measurement flow path after performing the propagation measurement method, a step of measuring a gas inflow propagation time, which is the time it takes for the pulse to propagate in the measurement flow path while gas is flowing into the measurement flow path, and a flow rate calculation step of calculating the flow rate of gas in the measurement flow path based on the gas inflow propagation time in the forward direction and the gas inflow propagation time in the reverse direction, and the step of measuring the gas inflow propagation time includes a step of detecting the preceding pulse with the other ultrasonic sensor. The method includes the steps of detecting the gas inflow reference pulse reception time from the time when it is estimated that the pulse will be received to the time when the reference pulse is received by the other ultrasonic sensor, calculating the gas inflow propagation time of the pulse in the measurement flow path from the sum of the post-update measurement wait time and the gas inflow reference pulse reception time, calculating the gas inflow post-update measurement wait time by subtracting the wait time calculation adjustment value from the gas inflow propagation time, and replacing the post-update measurement wait time with the gas inflow post-update measurement wait time, and re-executing the steps of detecting the gas inflow reference pulse reception time using the gas inflow post-update measurement wait time and calculating the gas inflow propagation time.

In the above gas flow velocity measurement method, in the step of setting the measurement waiting time initial value, the sound speed in the measurement flow path may be calculated from the gas temperature and the molecular weight of the gas, and the measurement waiting time initial value may be calculated by dividing the length of the measurement flow path in the propagation direction by the sound speed.

In one aspect of the present invention, a propagation measurement program causes a computer to function as: a sensor operating means for alternately transmitting a group of ultrasonic pulses including a plurality of pulses in a forward direction from the upstream ultrasonic sensor to the downstream ultrasonic sensor and in a reverse direction from the downstream ultrasonic sensor to the upstream ultrasonic sensor, so as to propagate the group of ultrasonic pulses through the measurement flow path, in order to measure the propagation status of the ultrasonic waves transmitted from a pair of ultrasonic sensors arranged on the upstream and downstream sides of a measurement flow path through which gas can flow; a waiting time initial value setting means for setting a measurement waiting time initial value, which is the time from when a reference pulse of the group of pulses is transmitted from one ultrasonic sensor to when a leading pulse of the group of pulses that is forward in the propagation direction of the reference pulse is estimated to be received by the other ultrasonic sensor; a pulse detection means for detecting a reference pulse reception time from when the leading pulse is estimated to be received by the other ultrasonic sensor to when the reference pulse is received by the other ultrasonic sensor; and a propagation time calculation means for calculating the propagation time of the pulse in the measurement flow path from the sum of the measurement waiting time initial value and the reference pulse reception time.

In the above propagation measurement program, the computer may further function as an updated waiting time calculation means for calculating an updated measurement waiting time by subtracting a predetermined waiting time calculation adjustment value from the propagation time, and as a waiting time update means for replacing the measurement waiting time initial value with the updated measurement waiting time, and the computer may function again as the pulse detection means and the propagation time calculation means using the updated measurement waiting time.

A gas flow velocity measurement program according to one aspect of the present invention causes the computer to function as a gas blocking means for blocking the inflow of gas into the measurement flow path, a gas blocking propagation measurement means for executing the above-mentioned propagation measurement program while the inflow of gas into the measurement flow path is blocked, a gas inflow means for flowing gas into the measurement flow path after the propagation measurement program is executed, a gas inflow propagation measurement means for measuring a gas inflow propagation time, which is the time it takes for the pulse to propagate in the measurement flow path while gas is flowing into the measurement flow path, and a flow velocity calculation means for calculating the flow velocity of gas in the measurement flow path based on the gas inflow propagation time in the forward direction and the gas inflow propagation time in the reverse direction, and the gas inflow propagation measurement means receives the preceding pulse at the other ultrasonic sensor. The apparatus includes a gas inflow pulse detection means for detecting a gas inflow reference pulse reception time from the time when the gas inflow is estimated to be received to the time when the reference pulse is received by the other ultrasonic sensor, a gas inflow propagation time calculation means for calculating a gas inflow propagation time of the pulse in the measurement flow path from the sum of the updated measurement waiting time and the gas inflow reference pulse reception time, a gas inflow post-update waiting time calculation means for calculating a gas inflow post-update measurement waiting time by subtracting the waiting time calculation adjustment value from the gas inflow propagation time, and a waiting time replacement means for replacing the updated measurement waiting time with the gas inflow post-update measurement waiting time, and causes the computer to function again as the gas inflow pulse detection means and the gas inflow propagation time calculation means using the gas inflow post-update measurement waiting time.

A gas flow velocity measuring device according to one aspect of the present invention comprises a measuring section forming a measurement flow path through which gas flows, a valve that adjusts the inflow of gas into the measurement flow path, a pair of ultrasonic sensors arranged on the upstream and downstream sides of the measurement flow path, a temperature sensor that measures the temperature of the gas, and a calculation device that calculates the flow velocity of the gas based on the time it takes for an ultrasonic wave emitted from one of the ultrasonic sensors to propagate through the measurement flow path and the time it takes for an ultrasonic wave emitted from the other ultrasonic sensor to propagate through the measurement flow path. The calculation device includes an opening/closing operation section that adjusts the opening degree of the valve, and a valve that alternately transmits a group of ultrasonic pulses including a plurality of pulses in a forward direction from the upstream ultrasonic sensor to the downstream ultrasonic sensor and in a reverse direction from the downstream ultrasonic sensor to the upstream ultrasonic sensor when the valve is in a closed state in which the inflow of gas into the measurement flow path is blocked. a sensor operation unit that propagates the pulse through a measurement flow path; a latency initial value setting unit that sets a measurement latency initial value, which is a time from when a reference pulse of the pulse group is transmitted from one of the ultrasonic sensors to when a leading pulse that is further forward in the propagation direction than the reference pulse of the pulse group is estimated to be received by the other ultrasonic sensor in the closed state; a pulse detection unit that detects a reference pulse reception time from when it is estimated that the leading pulse is received by the other ultrasonic sensor to when the reference pulse is received by the other ultrasonic sensor in the closed state; a propagation time calculation unit that calculates a propagation time of the pulse through the measurement flow path from the sum of the measurement latency initial value and the reference pulse reception time in the closed state; and an update unit that calculates an updated measurement latency by subtracting a predetermined latency calculation adjustment value from the propagation time in the closed state. the pulse detection unit detects the reference pulse reception time again using the updated measurement waiting time, and the propagation time calculation unit calculates the propagation time again using the updated measurement waiting time; and the arithmetic device includes a gas inflow pulse detection unit that detects a gas inflow reference pulse reception time from a time when the leading pulse transmitted from one of the ultrasonic sensors is estimated to be received by the other of the ultrasonic sensors to a time when the reference pulse transmitted from one of the ultrasonic sensors is received by the other of the ultrasonic sensors in an open state in which the valve is allowing gas to flow into the measurement flow path, and a propagation time update unit that calculates a propagation time of the reference pulse transmitted from the one of the ultrasonic sensors in the open state from a sum of the updated measurement waiting time and the gas inflow reference pulse reception time. The gas inflow propagation time calculation unit calculates a gas inflow propagation time, which is the time it takes for a pulse to propagate; a gas inflow post-update waiting time calculation unit calculates a gas inflow post-update measurement waiting time by subtracting the waiting time calculation adjustment value from the gas inflow propagation time in the open state; and a gas inflow waiting time update unit replaces the post-update measurement waiting time with the gas inflow post-update measurement waiting time in the open state. The gas inflow pulse detection unit detects the gas inflow reference pulse reception time again using the gas inflow post-update measurement waiting time, and the gas inflow propagation time calculation unit calculates the gas inflow propagation time again using the gas inflow post-update measurement waiting time. The arithmetic device further includes a flow velocity calculation unit that calculates the gas flow velocity in the measurement flow path based on the gas inflow propagation time in the forward direction and the gas inflow propagation time in the reverse direction.

An oxygen concentrator according to one aspect of the present invention includes the above-mentioned gas flow rate measurement device that calculates the flow rate of the oxygen-containing gas, and a concentrator main body provided with the gas flow rate measurement device, and the arithmetic device further includes a flow rate concentration calculation unit that calculates the flow rate of the oxygen-containing gas and the oxygen concentration in the oxygen-containing gas based on the flow rate of the oxygen-containing gas.

The above-mentioned propagation measurement methods make it possible to accurately grasp the propagation conditions of ultrasonic waves and accurately measure the propagation time of ultrasonic waves.

1 is an overall view of an oxygen concentrator according to an embodiment of the present invention; FIG. 2 is a block diagram showing a configuration of the oxygen concentrator. FIG. 2 is a block diagram of a gas flow rate measuring device in the oxygen concentrator. 3A and 3B are diagrams showing ultrasonic waves emitted from an ultrasonic sensor of the gas flow velocity measuring device. FIG. 2 is a functional block diagram of a calculation unit of the gas flow velocity measuring device. 11 is a flowchart of a flow velocity measurement program executed in the computing device, showing the state while the inflow of gas into the measurement flow path is blocked. FIG. 11 is a flowchart of a flow velocity measurement program executed in the arithmetic device, illustrating the state during which gas flows into the measurement flow path. FIG.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
(Overall composition)
1 and 2, the oxygen concentrator 1 of this embodiment is a device that supplies oxygen to a patient, concentrating air GA taken in from the outside to generate a high-concentration (e.g., about 90%) oxygen-containing gas G. Specifically, the oxygen concentrator 1 includes a concentrator main body 100 having an intake filter 11, a compressor 12, a nitrogen adsorption mechanism 13, a tank 14, and a housing 120 (see FIG. 1), and a gas flow rate measuring device 15 incorporated in the concentrator main body 100.

In the oxygen concentrator 1, air GA taken in from the outside through an intake filter 11 provided on the back of the housing 120 is compressed by a compressor 12, and the nitrogen contained in the compressed air GA is adsorbed by a catalyst (not shown) by a nitrogen adsorption mechanism 13 to generate an oxygen-containing gas (gas containing oxygen and nitrogen) G containing a high concentration of oxygen, which can be supplied to the patient. Hereinafter, the oxygen-containing gas G will be simply referred to as "gas G."

As shown in FIG. 2, the nitrogen adsorption mechanism 13 includes a pair of adsorption towers 13a and 13b. A catalyst such as zeolite is filled inside the pair of adsorption towers 13a and 13b. One of the adsorption towers 13a and 13b is pressurized to adsorb nitrogen to the catalyst, and the other is depressurized to release the nitrogen adsorbed to the catalyst and prepare for the next pressurization. In this way, in the nitrogen adsorption mechanism 13, the pair of adsorption towers 13a and 13b are alternately pressurized and depressurized to generate high-concentration oxygen. The high-concentration oxygen generated by the nitrogen adsorption mechanism 13 is stored in the tank 14. The oxygen stored in the tank 14 is supplied to the patient as gas G after passing through a gas flow rate measuring device 15. That is, the oxygen concentrator 1 of this embodiment employs a PSA (Pressure Swing Adsorption) method.

Here, each component part of the oxygen concentrator 1 is centrally controlled by a control unit (not shown). The control unit is composed of a CPU, RAM, ROM, etc., and executes various controls. The CPU is a so-called central processing unit, and executes various programs to realize various functions. The RAM is used as a working area for the CPU. The ROM stores programs executed by the CPU (for example, a propagation measurement program and a gas flow velocity measurement program, which will be described later).

As shown in FIG. 1, the housing 120 has a substantially rectangular parallelepiped shape. The housing 120 is provided with an operation button 121, a display 122, and a discharge tube (e.g., a rubber tube) 123 that is connected to the gas flow rate measuring device 15 and discharges the gas G.

(Gas flow rate measuring device)
Next, the gas flow rate measuring device 15 will be described in detail.
The gas flow rate measuring device 15 is incorporated in a housing 120. As shown in Fig. 2, the gas flow rate measuring device 15 is provided downstream of the tank 14 to measure the flow rate of the gas G, and is capable of calculating (measuring) the concentration and flow rate of oxygen in the gas G based on this flow rate. More specifically, as shown in Fig. 3, the gas flow rate measuring device 15 is an ultrasonic measuring device, and includes a measuring unit 20, a temperature sensor 30, a computing device 40, an ultrasonic sensor 60, a pressure sensor 70, and a proportional valve 80.

(Temperature Sensor)
The temperature sensor 30 is provided on the surface of the device substrate 50. The temperature sensor 30 is capable of measuring the temperature of a gas G flowing through a measurement flow path F, which will be described later, for example, on the downstream side of the measurement flow path F.

(Pressure Sensor)
The pressure sensor 70 is provided on the surface of the device substrate 50, similar to the temperature sensor 30. The pressure sensor 70 is capable of measuring the pressure of gas G flowing through a measurement flow path F, which will be described later, for example, on the upstream side of the measurement flow path F. The pressure of gas G measured by the pressure sensor 70 is used, for example, in calculations in the calculation device 40, which will be described later, when determining a constant that may vary depending on pressure.

(Measuring unit)
The measurement unit 20 is provided on the surface of the device substrate 50, similar to the temperature sensor 30 and the pressure sensor 70. The measurement unit 20 is cylindrical and has a measurement flow path F formed therein through which gas G flows from the tank 14 (see FIG. 3). In addition, an inlet flow path 24 for introducing gas G into the measurement flow path F is formed at the upstream end of the measurement flow path F in the measurement unit 20, and an outlet flow path 25 for guiding gas G from the measurement flow path F is formed at the downstream end of the measurement flow path F. The inlet flow path 24 and the outlet flow path 25 extend along the surface of the device substrate 50 in a direction perpendicular to the direction in which the measurement flow path F extends. The measurement unit 20 is formed of a resin material, such as ABS resin.

(Proportional valve)
The proportional valve 80 is disposed on the surface of the device substrate 50 and is provided further upstream of the inlet flow path 24. The proportional valve 80 controls the flow rate of the gas G flowing through the measurement flow path F by being opened and closed based on a value designated by an operation button 121 (see FIG. 1 ) of the concentrating device main body 100.

(Ultrasonic sensor)
A pair of ultrasonic sensors 60 are provided, one on the upstream side and one on the downstream side of the measurement flow path F. The ultrasonic sensors 60 are arranged facing each other in the direction in which the measurement flow path F extends. Each ultrasonic sensor 60 has an ultrasonic element (not shown) that is a transmitter/receiver capable of transmitting and receiving ultrasonic waves. The ultrasonic wave transmitted from the ultrasonic sensor 60A on the upstream side of the measurement flow path F can be received by the ultrasonic sensor 60B on the downstream side of the measurement flow path F. On the other hand, the ultrasonic wave transmitted from the ultrasonic sensor 60B on the downstream side of the measurement flow path F can be received by the ultrasonic sensor 60A on the upstream side of the measurement flow path F. A comparator circuit (not shown) is connected to each ultrasonic sensor 60, and the received ultrasonic wave is converted into a square wave.

As shown in FIG. 4, the ultrasonic sensor 60 emits a pulse group PG of ultrasonic waves that includes a plurality of pulses PU. The pulse group PG is emitted alternately from the upstream ultrasonic sensor 60A and the downstream ultrasonic sensor 60B. In this embodiment, the pulse group PG includes, for example, five or more pulses PU.

Hereinafter, the propagation direction of the pulse group PG emitted from the upstream ultrasonic sensor 60A toward the downstream side is referred to as the forward direction, and the propagation direction of the pulse group PG emitted from the downstream ultrasonic sensor 60B toward the upstream side is referred to as the reverse direction. The propagation direction of the pulse group PG coincides with the direction in which the measurement flow path F extends, i.e., the longitudinal direction of the measurement unit 20. Note that the propagation direction of the pulse group PG may intersect with the longitudinal direction of the measurement unit 20, as long as the pulse group PG has at least a component that travels from the upstream side (downstream side) to the downstream side (upstream side) of the measurement flow path F.

In addition, the _N1 -th pulse PU in the pulse group PG is called a reference pulse PU1, and the _N2- th pulse PU, which is a pulse PU ahead of the reference pulse PU1 in the propagation direction, is called a leading pulse PU2. In this embodiment, as an example, a case where _N1 = 5 and _N2 = 4 will be described. That is, the reference pulse PU1 indicates the fifth pulse PU in the pulse group PG, and the leading pulse PU2 indicates the fourth pulse PU in the pulse group PG.

(Calculation device)
The arithmetic device 40 is a computer and is composed of a CPU, RAM, ROM, etc. The CPU is a so-called central processing unit, which executes various programs to realize various functions. The RAM is used as a working area for the CPU. The ROM stores the programs executed by the CPU. The arithmetic device 40 is electrically connected, for example, to the back surface of the device substrate 50, which is opposite to the front surface (see FIG. 3).

As shown in FIG. 5, the calculation device 40 has an opening/closing operation unit 200, a sensor operation unit 201, a waiting time initial value setting unit 202, an initial pulse detection unit 203, an initial propagation time calculation unit 204, an initial updated waiting time calculation unit 205, an initial waiting time determination unit 206, an initial waiting time correction unit 207, an initial waiting time update unit 208, a gas inflow pulse detection unit 220, a gas inflow propagation time calculation unit 221, a gas inflow updated waiting time calculation unit 222, a gas inflow waiting time determination unit 223, a gas inflow waiting time correction unit 224, a gas inflow waiting time update unit 225, a flow velocity calculation unit 226, and a flow concentration calculation unit 227.

The opening/closing operation unit 200 adjusts the opening degree of the proportional valve 80 to change the amount of gas G flowing into the measurement flow path F.
The initial sensor operation unit 201 operates the ultrasonic sensor 60 to transmit the pulse group PG alternately in the forward and reverse directions as described above, and propagate the pulse group PG through the measurement flow path F.

<Initial operation>
The latency initial value setting unit 202 sets a measurement latency initial value t1inv, which is the time from when the reference pulse PU1 is emitted from one ultrasonic sensor 60 until when the leading pulse PU2 is estimated to be received by the other ultrasonic sensor, when the proportional valve 80 blocks the inflow of gas G into the measurement flow path F (hereinafter referred to as the closed state ₎ . The measurement latency initial value _t1inv is set for both the forward and reverse pulse groups PG.

本実施形態では例えば、上記閉状態においては測定流路Ｆ中のガスＧが空気であるとして、分子量Ｍを空気の平均分子量である２８．９とし、比熱比ｋを１．４とする。 In this embodiment, the measurement waiting time initial value t _1inv [μs] is calculated and set by the following formulas (1) and (2) when the temperature of gas G measured by temperature sensor 30 is T _gas [° C.], the molecular weight of gas G is M [g/mol], the specific heat ratio of gas G is k, the gas constant is R, the absolute zero is T ₀ [° C.], the sound speed in measurement flow path F is c [m/s], and the length L [m] of the measurement flow path F in the propagation direction of ultrasonic waves. Note that constants such as the molecular weight M, the specific heat ratio k, the gas constant R, the absolute zero is T ₀ , and the length L of measurement flow path F are stored in advance in the calculation device 40.

In this embodiment, for example, in the closed state, the gas G in the measurement flow path F is air, the molecular weight M is 28.9 which is the average molecular weight of air, and the specific heat ratio k is 1.4.

In the above-mentioned closed state, the initial pulse detection unit 203 detects the reference pulse reception time t2 _[μs] from the time when it is estimated that the leading pulse PU2 is received by the other ultrasonic sensor 60, that is, from the time when the measurement waiting time initial value t1inv has elapsed, to the time when the reference pulse _PU1 is received by the other ultrasonic sensor 60, by using an external interrupt. The external interrupt starts when it is estimated that the leading pulse PU2 is received by the other ultrasonic sensor 60, that is, while the amplitude of the leading pulse PU2 is at its maximum. After the external interrupt starts, the reference pulse PU1 is detected at the timing when the amplitude of the reference pulse PU1 changes from the minimum to the maximum (reference pulse PU1 detection timing). The reference pulse reception time _t2 from the start of the external interrupt to the reference pulse PU1 detection timing is detected for both the forward and reverse pulse groups PG.
In this embodiment, the initial pulse detection unit 203 detects a reference pulse PU1 for each of a plurality of (for example, 10) pulse groups PG. That is, the detection of the reference pulse PU1 is executed a plurality of times using the same measurement wait time initial value _t1inv .

In the closed state, the initial propagation time calculation unit 204 calculates the propagation time _t3 [μs] of the pulse PU in the measurement flow path F from the sum of the measurement waiting time initial value _t1inv and the reference pulse reception time _t2 . The propagation time _t3 is calculated for both the forward and reverse pulse groups PG. Hereinafter, the propagation time of the forward pulse PU is defined as t3 _(f) , and the propagation time of the reverse pulse PU is defined as t3 _(b) .

そして、同じ測定待ち時間初期値ｔ_１ｉｎｖを用いて得られた複数の値ｔ_３ｍｓｒ〔μｓ〕のグループを同一条件下サンプル値群としたとき、同一条件下サンプル値群から中央値以外の少なくとも一部を除いた残りの値ｔ_３ｍｓｒの平均値を伝搬時間ｔ_３とする。例えば、値ｔ_３ｍｓｒを１０個のうちの大きい側の値２個と、小さい側の値２個を除き、残りの６個の値ｔ_３ｍｓｒの平均値を伝搬時間ｔ_３とする。なお各々の値ｔ_３ｍｓｒから事前に設定された測定誤差を除いた状態で、平均値を算出してもよい。 In this embodiment, the initial propagation time calculation unit 204 calculates the sum of the measurement wait time initial value _t1inv and the reference pulse reception time _t2 for each of a plurality of (e.g., 10) pulse groups PG. That is, using the same measurement wait time initial value _t1inv , the calculation of the value _t3msr , which is the sum of the measurement wait time initial value _t1inv and the reference pulse reception time _t2 , is executed multiple times as shown in the following formula (3).

When a group of multiple values _t3msr [μs] obtained using the same measurement wait time initial value _t1inv is taken as a group of sample values under the same conditions, the average value of the remaining values _t3msr obtained by removing at least a portion other than the median value from the group of sample values under the same conditions is taken as the propagation time _t3 . For example, the two largest values and the two smallest values out of the ten values _t3msr are removed, and the average value of the remaining six values _t3msr is taken as the propagation time _t3 . Note that the average value may be calculated in a state where a measurement error set in advance is removed from each value _t3msr .

In the above-mentioned closed state, the initial post-update waiting time calculation unit 205 calculates a post-update measurement waiting time _t1 by subtracting a predetermined waiting time calculation adjustment value t _{inv_ost} [μs] from the propagation time _t3 according to the following formula (4). The post-update measurement waiting time _t1 is calculated for each of the forward and reverse pulse groups PG.

上記の通り本実施形態ではＮ_１＝５、Ｎ_２＝４であり、例えば周期Ｘ＝２５〔μｓ〕であれば、待ち時間算出用調整値ｔ_{ｉｎｖ_ｏｓｔ}＝１２．５〔μｓ〕となる。よって待ち時間算出用調整値ｔ_{ｉｎｖ_ｏｓｔ}は、基準パルスＰＵ１の振幅が最初に最大となったタイミングから１／２周期分戻った時（先行パルスＰＵ２の振幅が最大から最小に転じるタイミング）を、一方の超音波センサ６０から発信された先行パルスＰＵ２が他方の超音波センサ６０で受信されたと推定される時にするような値である。例えばＮ_１＝１０、Ｎ_２＝５として基準パルスＰＵ１から５パルス後を先行パルスＰＵ２とした場合でも、上記の式（５）を用いて待ち時間算出用調整値ｔ_{ｉｎｖ_ｏｓｔ}を算出することもできる。
なお先行パルスＰＵ２が他方の超音波センサ６０で受信されたと推定される時は、少なくとも先行パルスＰＵ２の振幅が最大となっている範囲内であればよいので、例えば待ち時間算出用調整値ｔ_{ｉｎｖ_ｏｓｔ}は、以下の式（６）を満たす数値であればよい。 Here, as described above, when the reference pulse PU1 is the _N1th pulse PU of the pulse group PG and the leading pulse PU2 is the _N2th pulse of the pulse group PG, when the period of the pulse PU is X, the waiting time calculation adjustment value t _{inv_ost} is calculated by the following equation (5).

As described above, in this embodiment, _N1 =5, _N2 =4, and for example, when the period X=25 [μs], the waiting time calculation adjustment value t _{inv_ost} is 12.5 [μs]. Therefore, the waiting time calculation adjustment value t _{inv_ost} is a value that is set so that the time when the amplitude of the reference pulse PU1 returns by 1/2 period from the timing when the amplitude of the leading pulse PU2 changes from maximum to minimum is the time when the leading pulse PU2 transmitted from one ultrasonic sensor 60 is estimated to be received by the other ultrasonic sensor 60. For example, even when _N1 =10, _N2 =5 and the leading pulse PU2 is five pulses after the reference pulse PU1, the waiting time calculation adjustment value t _{inv_ost} can also be calculated using the above formula (5).
When it is estimated that the leading pulse PU2 has been received by the other ultrasonic sensor 60, it is sufficient that the amplitude of the leading pulse PU2 is at least within the range where it is maximum, so for example, the adjustment value t _{inv_ost} for calculating the waiting time is a number that satisfies the following equation (6).

ここで上記式（６）において待ち時間算出用調整値ｔ_{ｉｎｖ_ｏｓｔ}の下限値がゼロ、すなわちｔ_{ｉｎｖ_ｏｓｔ}＞０を満足するようにしてもよい。この場合、先行パルスＰＵ２が他方の超音波センサ６０で受信されたと推定される時が、基準パルスＰＵ１の振幅が最大となる手前のタイミングとなる。先行パルスＰＵ２が他方の超音波センサ６０で受信されたと推定される時が先行パルスＰＵ２の振幅が最大となっている範囲内でなくとも、基準パルスＰＵ１の振幅が最大となる手前のタイミングであれば基準パルスＰＵ１を検知可能であるため、ｔ_{ｉｎｖ_ｏｓｔ}＞０としてもよい。

Here, in the above formula (6), the lower limit value of the waiting time calculation adjustment value t _{inv_ost} may be set to zero, i.e., t _{inv_ost} > 0 may be satisfied. In this case, the time when it is estimated that the leading pulse PU2 has been received by the other ultrasonic sensor 60 is the timing just before the amplitude of the reference pulse PU1 becomes maximum. Even if the time when it is estimated that the leading pulse PU2 has been received by the other ultrasonic sensor 60 is not within the range in which the amplitude of the leading pulse PU2 is maximum, the reference pulse PU1 can be detected as long as it is the timing just before the amplitude of the reference pulse PU1 becomes maximum, so t _{inv_ost} > 0 may be satisfied.

The initial waiting time determination unit 206 determines whether the post-update measurement waiting time _t1 is within a predetermined range in the above-mentioned closed state, because the post-update measurement waiting time _t1 should fall within a predetermined range to some extent in a situation where there is no flow of the gas G.

In the closed state, only when the updated measurement waiting time _t1 is outside a predetermined range, the initial waiting time correction unit 207 corrects the updated measurement waiting time _t1 by adding a predetermined waiting time correction value _{tc_ost} to the updated measurement waiting time _t1 . The waiting time correction value _{tc_ost} may be either a positive value or a negative value.

Then, when the difference between the forward propagation time t3 _(f) of the pulse PU and the reverse propagation time t3 _(b) of the pulse PU is greater than a predetermined maximum value, the initial waiting time correction unit 207 first adds a waiting time correction value tc_ost to the updated measurement waiting time t1 _(b) of the reverse pulse PU so as to make the updated measurement waiting time t1 _(b) of the pulse PU in the forward direction coincide with the updated measurement waiting time t1(f _{) of the pulse PU in the forward direction, or to make the updated measurement waiting time t1(f)} of the pulse _PU in the forward direction coincide with the updated measurement waiting time t1 _(b) of the pulse PU in the _reverse direction. Here, the maximum value of the difference between the forward propagation time t3 _(f) of the pulse PU in the forward direction and the propagation time t3 _(b) of the pulse PU in the reverse direction is a value determined based on the specifications of the oxygen concentrator 1, and is a value determined by the maximum value of the flow rate of the gas G flowing through the measurement flow path F, the length L of the measurement flow path F, etc.

この分子量Ｍ_１が予め定められた最小分子量（最小閾値）よりも小さくなる場合に順方向および逆方向の各々において、更新後測定待ち時間ｔ_１が長くなるような待ち時間補正値ｔ_{ｃ_ｏｓｔ}を更新後測定待ち時間ｔ_１に加算する。また、分子量Ｍ_１が予め定められた最大分子量（最大閾値）よりも大きくなる場合には、順方向および逆方向の各々において、更新後測定待ち時間ｔ_１が短くなるような待ち時間補正値ｔ_{ｃ_ｏｓｔ}を更新後測定待ち時間ｔ_１に加算する。ここで最小分子量および最大分子量は、酸素濃縮装置１の仕様に基づいて定まる値であって、測定流路Ｆを流れるガスＧの酸素濃度の最大値および最小値によって定まる値である。
そしてこのような分子量に基づく待ち時間補正値ｔ_{ｃ_ｏｓｔ}は、パルスＰＵの周期をＸとしたとき、例えば以下の式（９）によって算出される。

Next, the initial waiting time correction unit 207 calculates the sound speed _c1 in the measurement flow path F, which is found from the forward propagation time t3 _(f) of the pulse PU and the reverse propagation time t3 _(b) of the pulse PU calculated by the initial propagation time calculation unit ₂₀₄ using the updated measurement waiting time t1, using the following equation (7), and also calculates the molecular weight _M1 of the gas G using the following equation (8).

When the molecular weight _M1 becomes smaller than a predetermined minimum molecular weight (minimum threshold), a waiting time correction value _{tc_ost} is added to the updated measurement waiting time _t1 in each of the forward and reverse directions so that the updated measurement waiting time _t1 becomes longer. When the molecular weight _M1 becomes larger than a predetermined maximum molecular weight (maximum threshold), a waiting time correction value _{tc_ost} is added to the updated measurement waiting time _t1 in each of the forward and reverse directions so that the updated measurement waiting time _t1 becomes shorter. Here, the minimum molecular weight and the maximum molecular weight are values determined based on the specifications of the oxygen concentrator 1, and are values determined by the maximum and minimum values of the oxygen concentration of the gas G flowing through the measurement flow path F.
Such a waiting time correction value t _{c_ost} based on the molecular weight is calculated, for example, by the following formula (9), where X is the period of the pulse PU.

In the closed state, the initial waiting time updating unit 208 replaces the measurement waiting time initial value t _1inv with the updated measurement waiting time t ₁ .

<Initial operation>
The gas inflow pulse detection unit 220 detects the gas inflow reference pulse reception time t2X from the time when the leading pulse PU2 is estimated to be received by the other ultrasonic sensor 60 to the time when the reference pulse PU1 is received by the other ultrasonic sensor 60 when the proportional valve 80 is in a state where the gas G is flowing into the measurement flow path F (hereinafter referred to as an open state ₎ by an external interrupt. The external interrupt starts when the leading pulse PU2 is estimated to be received by the other ultrasonic sensor 60, that is, while the amplitude of the leading pulse PU2 is at its maximum. The reference pulse PU1 is detected at the timing when the amplitude of the reference pulse PU1 changes from the minimum to the maximum. The gas inflow reference pulse reception time _t2X is detected for both the forward and reverse pulse groups PG.
In this embodiment, the gas inflow pulse detection unit 220 detects the reference pulse PU1 for each of a plurality of (for example, 10) pulse groups PG. That is, the detection of the reference pulse PU1 is performed a plurality of times using the same post-update measurement waiting time _t1 .

In the above open state, the gas inflow propagation time calculation unit 221 calculates a gas inflow propagation time _t3X , which is the time it takes for a pulse PU to propagate through the measurement flow path F, from the sum of the updated measurement waiting time t1 and the gas inflow reference pulse reception time _t2X using the following formula ( ₁₀ ). The gas inflow propagation time _t3X is calculated for both the forward and reverse pulse groups PG. Hereinafter, the gas inflow propagation time of the forward pulse PU is defined as t3X _(f) , and the gas inflow propagation time of the reverse pulse PU is defined as t3X _(b) .

そして、同じ更新後測定待ち時間ｔ_１を用いて得られた複数の値ｔ_{３Ｘｍｓｒ}のグループを同一条件下サンプル値群としたとき、同一条件下サンプル値群から中央値以外の少なくとも一部を除いた残りの値ｔ_{３Ｘｍｓｒ}の平均値を伝搬時間ｔ_３Ｘとする。値ｔ_{３Ｘｍｓｒ}の平均値は例えば上記の通り、値ｔ_３ｍｓｒの平均値と同様の手法によって算出することができる。 In this embodiment, the gas inflow propagation time calculation unit 221 calculates the sum of the updated measurement waiting time _t1 and the gas inflow reference pulse reception time _t2X for each of a plurality of (e.g., 10) pulse groups PG. That is, using the same updated measurement waiting time _t1 , calculation of the value _t3Xmsr , which is the sum of the updated measurement waiting time _t1 and the reference pulse reception time _t2X, is performed multiple times according to the following formula (10).

Then, when a group of multiple values _t3Xmsr obtained using the same post-update measurement waiting time _t1 is taken as a group of sample values under the same conditions, the average value of the remaining values _t3Xmsr obtained by removing at least a portion other than the median value from the group of sample values under the same conditions is taken as the propagation time _t3X . The average value of the values _t3Xmsr can be calculated, for example, as described above, by the same method as the average value of the values _t3msr .

In the open state, the gas inflow post-update waiting time calculation unit 222 calculates the gas inflow post-update measurement waiting time _t1X by subtracting the waiting time calculation adjustment value t _{inv_ost} from the gas inflow propagation time t3X according to the following formula ( ₁₁₎ . The gas inflow post-update measurement waiting time _t1X is calculated for both the forward and reverse pulse groups PG.

The gas inflow waiting time determination unit 223 determines whether or not the gas inflow post-update measurement waiting time t _1X is within a predetermined range in the above-mentioned open state.

In the above-mentioned open state, the gas inflow waiting time correction unit 224 corrects the measurement waiting time after update at gas inflow t _1X by adding the above-mentioned waiting time correction value t _{c_ost} to the measurement waiting time after update at gas inflow t _1X only when the measurement waiting time after update at gas inflow t _1X is a value outside a predetermined range.
Then, similarly to the initial latency correction unit 207, when the difference between the gas inflow propagation time t3X _(f) of the forward pulse PU and the gas inflow propagation time t3X _{(b) of the reverse pulse PU becomes larger than a predetermined maximum value, the gas inflow latency correction unit 224 first adds a latency correction value tc_ost to the updated measurement latency t1X so as to match the post-update measurement latency t1X( b)} at gas inflow for the reverse pulse PU with the post-update measurement latency t1X _(f) at gas inflow for the forward pulse PU, or to match the post-update measurement latency t1X _(f) for the forward pulse PU with the post-update measurement latency t1X _(b) for the reverse pulse _PU , to the updated measurement latency _t1X .

この分子量Ｍ_１Ｘが予め定められた最小分子量（最小閾値）よりも小さくなる場合に順方向および逆方向の各々において、ガス流入時更新後測定待ち時間ｔ_１Ｘが長くなるような上記の待ち時間補正値ｔ_{ｃ_ｏｓｔ}をガス流入時更新後測定待ち時間ｔ_１Ｘに加算する。また、分子量Ｍ_１Ｘが予め定められた最大分子量（最大閾値）よりも大きくなる場合には、順方向および逆方向の各々において、ガス流入時更新後測定待ち時間ｔ_１Ｘが短くなるような上記の待ち時間補正値ｔ_{ｃ_ｏｓｔ}をガス流入時更新後測定待ち時間ｔ_１Ｘに加算する。 Next, the gas inflow waiting time correction unit 224 calculates the sound speed c _1X in the measurement flow path F, which is obtained from the gas inflow propagation time t 3X _(f) of the forward pulse PU and the gas inflow propagation time t _3X(b) of the reverse pulse PU calculated by the gas inflow propagation time calculation unit 221 using the gas inflow updated measurement waiting time t _1X , using the following formula (12), and also calculates the molecular weight M _1X of the gas G using the following formula (13).

When the molecular weight M _1X is smaller than a predetermined minimum molecular weight (minimum threshold), the wait time correction value t _{c_ost} is added to the measurement wait time t _1X after update at gas inflow in both the forward and reverse directions so that the measurement wait time t _1X after update at gas inflow becomes longer. When the molecular weight M _1X is larger than a predetermined maximum molecular weight (maximum threshold), the wait time correction value t _{c_ost} is added to the measurement wait time t _1X after update at gas inflow in both the forward and reverse directions so that the measurement wait time t _1X after update at gas inflow becomes shorter.

In the open state, the gas inflow waiting time updating unit 225 replaces the updated measurement waiting time t ₁ with a gas inflow updated measurement waiting time t _1X .

The flow velocity calculation unit 226 calculates the gas flow velocity v [m/s] in the measurement flow path F based on the forward gas inflow propagation time t3X _(f) and the reverse gas inflow propagation time t3X _(b) using the following equation (14).

The flow concentration calculation unit 227 calculates the flow rate Q [ ^m3 /s] of the gas G based on the flow velocity of the gas G calculated by the flow velocity calculation unit 226 using the following formula (15). The flow path cross-sectional area of the measurement flow path F is A [ ^m2 ]. The proportional valve 80 is controlled by the control unit so that the calculated flow rate Q becomes a preset flow rate.

Further, the flow concentration calculation unit 227 calculates the oxygen concentration P _O2 [%] in the gas G based on the above molecular weight M _1X by the following formula (16). Note that M _O2 [g/mol] is the molecular weight of oxygen, and M _N2 [g/mol] is the molecular weight of nitrogen. M _O2 = 32, M _N2 = 28. The oxygen/nitrogen adsorption mechanism 13 is controlled by the above control unit so that the calculated oxygen concentration becomes a preset value.

Next, a procedure for executing the gas flow rate measurement program (gas flow rate measurement method) will be described with reference to FIGS.
6, first, the inflow of gas G into the measurement flow path F is blocked. That is, the proportional valve 80 is closed by the opening/closing operation unit (gas blocking means) 200 (step S1).
Next, the propagation measurement program (propagation measurement method) is executed in a state where the inflow of gas G into the measurement flow path F is blocked (step S2).

In step S2, first, the above-mentioned measurement waiting time initial value _t1inv is set by the waiting time initial value setting unit 202 (step S21). Then, after a predetermined time has elapsed since execution of step S1, the sensor operation unit operates the ultrasonic sensor 60 to transmit pulse groups PG alternately in the forward and reverse directions, the initial pulse detection unit 203 detects the reference pulse reception time _t2 , and the initial propagation time calculation unit 204 calculates the propagation time _t3 of the pulse PU in the measurement flow path F (step S22).

Furthermore, in step S2, the initial post-update waiting time calculation unit 205 calculates the post-update measurement waiting time _t1 , and the initial waiting time determination unit 206 determines whether the post-update measurement waiting time _t1 is within a predetermined range. If the post-update measurement waiting time _t1 is outside the predetermined range, the initial waiting time correction unit 207 corrects the post-update measurement waiting time _t1 .

Specifically, in determining the post-update measurement waiting time _t1 , first, it is determined whether the difference between the forward pulse PU propagation time t3 _(f) and the reverse pulse PU propagation time t3 _(b) is greater than a predetermined maximum value (step S23). If it is determined in step S23 that the difference between the propagation time t3 _(f) and the propagation time t3 _(b) is greater than a predetermined maximum value, the post-update measurement waiting time _t1 is corrected (step S24). On the other hand, if it is determined in step S24 that the difference between the propagation time t3 _(f) and the propagation time t3 _(b) is equal to or less than a predetermined maximum value, it is determined whether the molecular weight _M1 is greater than a predetermined maximum molecular weight and whether the molecular weight _M1 is smaller than a predetermined minimum molecular weight (step S25). If the molecular weight _M1 is greater than the predetermined maximum molecular weight or if the molecular weight _M1 is smaller than the predetermined minimum molecular weight, the post-update measurement waiting time _t1 is corrected (step S26). After correcting the post-update measurement waiting time _t1 in steps S24 and S26, the process returns to step S22 to calculate the propagation time _t3 and again determines whether or not to correct the post-update measurement waiting time _t1 . Steps S22 to S26 are repeated until the post-update measurement waiting time _t1 becomes a value within a predetermined range.

Furthermore, if the updated measurement waiting time _t1 is within a predetermined range in step S2, the initial waiting time update unit 208 replaces the measurement waiting time initial value _t1inv with the updated measurement waiting time _t1 (step S27). After step S27, the propagation time _t3 is calculated again (step S28), and the propagation measurement program (step S2) is terminated.

After the propagation measurement program (step S2) is executed, gas G is caused to flow into the measurement flow path F as shown in FIG. 7. That is, the proportional valve 80 is opened by the opening/closing operation unit (gas shutoff means) 200 (step S3). At this time, the proportional valve 80 is held at a predetermined opening degree, and gas G is flowing into the measurement flow path F at a predetermined flow rate.

Next, the ultrasonic sensor 60 is operated by the sensor operation unit 201 to emit pulse groups PG alternately in the forward and reverse directions, the gas inflow pulse detection unit 220 detects the gas inflow reference pulse reception time _t2X , and the gas inflow propagation time calculation unit 221 calculates the gas inflow propagation time _t3X of the pulse PU in the measurement flow path F (step S4).

Thereafter, the gas inflow post-update waiting time calculation unit 222 calculates the gas inflow post-update measurement waiting time t _1X , and the gas inflow waiting time determination unit 223 determines whether the gas inflow post-update measurement waiting time t _1X is within a predetermined range. If the gas inflow post-update measurement waiting time t _1X is outside the predetermined range, the gas inflow waiting time correction unit 224 corrects the gas inflow post-update measurement waiting time t _X.

Specifically, in determining the measurement waiting time _t1X after gas inflow update, first, it is determined whether the difference between the gas inflow propagation time t3X _(f) of the forward pulse PU and the gas inflow propagation time t3X _(b) of the reverse pulse PU is greater than a predetermined maximum value (step S5). If it is determined in step S5 that the difference between the gas inflow propagation time t3 _(f) and the gas inflow propagation time t3 _(b) is greater than a predetermined maximum value, the measurement waiting time _t1X after gas inflow update is corrected (step S6). On the other hand, if it is determined in step S6 that the difference between the gas inflow propagation time t3 _(f) and the gas inflow propagation time t3 _(b) is equal to or less than a predetermined maximum value, it is determined whether the molecular weight _M1X is greater than a predetermined maximum molecular weight and whether the molecular weight _M1X is smaller than a predetermined minimum molecular weight (step S7). When the molecular weight M _1X is larger than a predetermined maximum molecular weight or smaller than a predetermined minimum molecular weight, the measurement waiting time _{t 1X after} updating at the time of gas inflow is corrected (step S8). After the measurement waiting time t _1X after updating at the time of gas inflow is corrected in steps S6 and S8, the flow returns to step S4 again to calculate the gas inflow propagation time t _3X , and again it is determined whether or not the measurement waiting time t _1X after updating at the time of gas inflow needs to be corrected. Steps S4 to S8 are repeated until the measurement waiting time t _1X after updating at the time of gas inflow becomes a value within a predetermined range.

Furthermore, if the measurement waiting time t _1X after updating at the time of gas inflow is within a predetermined range, the gas inflow waiting time update unit 225 replaces the measurement waiting time t ₁ after updating with the measurement waiting time t _1X after updating at the time of gas inflow (step S9). After step S9, the flow velocity calculation unit 226 calculates the flow velocity of the gas G in the measurement flow path F based on the forward gas inflow propagation time t _3X(f) and the reverse gas inflow propagation time t _3X(b) (step S10), and the flow concentration calculation unit 227 calculates the flow rate of the gas G and the oxygen concentration in the gas G (step S11). Note that steps S10 and S11 may be performed before step S9.

After step S11, the process returns to step S4 to continuously repeat the calculation of the gas inflow propagation time _t3X . The gas flow rate measurement program can be executed while changing the opening of the proportional valve 80. The opening and closing control of the proportional valve 80 is executed while avoiding abrupt changes in the flow rate of the gas G within a range in which no error occurs in the gas flow rate measurement program (within an applicable range).

In the oxygen concentrator 1 of the present embodiment described above, after first setting the measurement waiting time initial value _t1inv , the measurement waiting time initial value _t1inv is replaced with the updated measurement waiting time _t1 based on the propagation time _t3 calculated from the sum of the measurement waiting time initial value _t1inv and the reference pulse reception time _t2 , and the propagation time _t3 is calculated. In the same manner, the propagation time t3 and the gas inflow propagation time _t3X are calculated while repeatedly updating and replacing the updated measurement waiting time _t1 from the calculated propagation time _t3 . Therefore, the propagation time _{t3 and} the gas inflow propagation time _t3X can be calculated more accurately in accordance with the actual propagation situation of the pulse PU at all times. Therefore, the propagation situation of the ultrasonic wave can be accurately grasped from the propagation time _t3 and the gas inflow propagation time _t3X , and the propagation time of the ultrasonic wave can be accurately measured, and as a result, the measurement accuracy of the flow rate, flow rate, and concentration of the gas G can be improved.

Furthermore, until the measurement wait time initial value _t1inv , the updated measurement wait time _t1 , and the post-update measurement wait time _t1X at gas inflow are within a predetermined range, these values are corrected and then the propagation time _t3 and the gas inflow propagation time _t3X are calculated again, so that the measurement accuracy of the propagation time _t3 and the gas inflow propagation time _t3X can be further improved. Furthermore, in this embodiment, these corrections are repeated until the post-update measurement wait time _t1 and the post-update measurement wait time _t1X at gas inflow are within a predetermined range, so that the measurement accuracy of the propagation time _t3 and the gas inflow propagation time _t3X can be further improved.

The determination of whether or not to correct the measurement wait time initial value _t1inv , the post-update measurement wait time _t1 , and the post-update measurement wait time _t1X at gas inflow is made in two stages, by first determining based on the difference between the propagation times _t3 of the forward and reverse pulses PU (propagation time at gas inflow _t3X ), and then determining based on the molecular weights _M1 , _M1X of the gas G. This makes it possible to improve the accuracy of the determination of whether or not to correct the post-update measurement wait time _t1 and the post-update measurement wait time _t1X at gas inflow.

For example, the oxygen concentration of the gas G in the tank 14 is high immediately after the operation of the oxygen concentrator 1 is stopped. As time passes after the operation of the oxygen concentrator 1 is stopped, the oxygen concentration of the gas G in the measurement flow path F decreases and becomes approximately the same as that of the atmosphere. When the operation of the oxygen concentrator 1 is started in this state, the gas G with a high oxygen concentration in the tank 14 flows into the measurement flow path F all at once. Then, the measured propagation time _t3 becomes shorter than the actual value, and the molecular weight _M1 calculated from this propagation time _t3 may be smaller than the minimum molecular weight. Therefore, it is necessary to correct the measurement waiting time _t1 after updating as described above.

Furthermore, for example, when high temperature, high humidity, and low pressure air is present in the measurement flow path F after the operation of the oxygen concentrator 1 is stopped, the molecular weight of the gas G in the measurement flow path F becomes smaller than the average molecular weight of air, 28.9, so the actual measurement wait time initial value becomes smaller than the measurement wait time initial value _t1inv set as described above. In this case, the measured propagation time _t3 becomes longer than the actual value, so the molecular weight _M1 calculated from this propagation time _t3 may become larger than the maximum molecular weight described above. Therefore, it is necessary to correct the measurement wait time _t1 after updating as described above.

Therefore, by determining whether to correct the measurement waiting time initial value t _1inv , the updated measurement waiting time t ₁ , and the updated measurement waiting time t _1X at gas inflow based on molecular weight, the measurement waiting time initial value t _1inv , the updated measurement waiting time t 1, and the updated measurement waiting time t _1X at gas inflow, which fluctuate depending on the state within the measurement flow path F as described above, can be corrected to more accurate values _{and the propagation time t 3 (} propagation time at gas inflow t _3X ) can be calculated and measured.

Further, the waiting time calculation adjustment value t _{inv_ost} is calculated by the above formula (5). That is, in this embodiment, the waiting time calculation adjustment value t _{inv_ost} is 1/2 the period of the pulse PU (12.5 [μs]). Therefore, the time when the amplitude of the leading pulse PU2 is maximum can be set as the end of the post-update measurement waiting time t ₁ and the post-update measurement waiting time t _1X during gas inflow. Therefore, the post-update measurement waiting time t ₁ and the post-update measurement waiting time t _1X during gas inflow can be set accurately.

Furthermore, the propagation time _t3 and the gas inflow propagation time _t3X are set to the average value obtained by removing at least a part of the values other than the median value from the group of values sampled under the same conditions as described above. This makes it possible to eliminate noise when calculating the propagation time _t3 and the gas inflow propagation time _t3X , thereby further improving the accuracy of the propagation time _t3 and the gas inflow propagation time _t3X .

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit and scope of the present invention.
For example, there is no particular limitation as to which of the pulse group G the reference pulse PU1 and the leading pulse PU2 are set to. For example, the reference pulse PU1 may be the fifth pulse PU, and the leading pulse PU2 may be the third pulse PU. Also, if the intensity of the first or second pulse PU of the pulse group PG is sufficient, the first or second pulse PU may be the leading pulse PU2 or the reference pulse PU1.

Furthermore, in the step of determining whether the post-update measurement waiting time t ₁ (post-update measurement waiting time t _1X at gas inflow) is within a predetermined range, the determination may be made only based on the difference between the propagation time t ₃ (propagation time t _3X at gas inflow) in the forward and reverse directions, or only based on the molecular weight, or a determination based on the molecular weight and then a determination based on the difference in propagation time t ₃ (propagation time t _3X at gas inflow) may be made. Even when a determination based on molecular weight is made, the post-update measurement waiting time t _1(f) in the forward direction (post-update measurement waiting time t _1X(f) at gas inflow) and the post-update measurement waiting time t _1(b) in the reverse direction (post-update measurement waiting time t _1X(b) at gas inflow) may be made to match.

In addition, in the step of determining whether the updated measurement waiting time _t1 (the updated measurement waiting time _t1X during gas inflow) is within a predetermined range, the step of calculating the propagation time _t3 (the propagation time _t3X during gas inflow) may be executed again, and then a determination may be made as to whether the change in the propagation time _t3 (the propagation time _t3X during gas inflow) is greater than a predetermined maximum change. That is, when the change in the propagation time _t3 (the propagation time _t3X during gas inflow) is greater than the predetermined maximum change, the wait time correction value _{tc_ost} is added to the updated measurement waiting time _t1 (the measurement waiting time _t1X during gas inflow). In this case, the maximum change in the propagation time _t3 (the propagation time _t3X during gas inflow) is 1/2 the period X of the pulse PU, that is, 12.5 [μs] in the above embodiment.

The above propagation measurement program may also be executed before calculating the updated measurement waiting time _t1 , that is, up to the step of calculating the propagation time _t3 using the waiting time initial value _t1inv .

The gas flow rate measuring device 15 can also be used in devices other than the oxygen concentrator 1. The oxygen concentrator 1 is not limited to a PSA type device, but may be a device using other methods such as a membrane separation type.

The propagation measurement method of the present invention makes it possible to accurately measure the propagation time of ultrasonic waves by accurately grasping the propagation conditions of the ultrasonic waves.

1 Oxygen concentrator 15 Gas flow rate measuring device 20 Measurement unit 30 Temperature sensor 40 Calculation unit 60 (60A, 60B) Ultrasonic sensor 70 Pressure sensor 80 Proportional valve 100 Concentrator main body 200 Opening/closing operation unit 201 Sensor operation unit 202 Waiting time initial value setting unit 203 Initial pulse detection unit 204 Initial propagation time calculation unit 205 Initial updated waiting time calculation unit 206 Initial waiting time judgment unit 207 Initial waiting time correction unit 208 Initial waiting time update unit 220 Gas inflow pulse detection unit 221 Gas inflow propagation time calculation unit 222 Gas inflow updated waiting time calculation unit 223 Gas inflow waiting time judgment unit 224 Gas inflow waiting time correction unit 225 Gas inflow waiting time update unit 226 Flow rate calculation unit 227 Flow rate concentration calculation unit F Measurement flow path G Oxygen-containing gas PG Pulse group PU Pulse PU1 Reference pulse PU2 Leading pulse

Claims (18)

A propagation measurement method for measuring a propagation state in a measurement flow path through which a gas can flow, the propagation state being measured by a pair of ultrasonic sensors respectively disposed on an upstream side and a downstream side of the measurement flow path, the method comprising:
a step of alternately transmitting a group of ultrasonic pulses including a plurality of pulses in a forward direction from the ultrasonic sensor on the upstream side toward the ultrasonic sensor on the downstream side and in a reverse direction from the ultrasonic sensor on the downstream side toward the ultrasonic sensor on the upstream side, and propagating the group of ultrasonic pulses through the measurement flow path;
setting an initial value of a measurement waiting time, which is a time from when a reference pulse of the pulse group is transmitted from one of the ultrasonic sensors until when a leading pulse of the pulse group that is forward in a propagation direction of the reference pulse is estimated to be received by the other ultrasonic sensor;
detecting a reference pulse reception time from a time when the leading pulse is estimated to be received by the other ultrasonic sensor to a time when the reference pulse is received by the other ultrasonic sensor;
calculating a propagation time of the pulse in the measurement flow path from a sum of the measurement wait time initial value and the reference pulse reception time;
A propagation measurement method comprising: calculating an updated measured latency time by subtracting a predetermined latency time calculation adjustment value from the propagation time;
replacing the measurement wait time initial value with the updated measurement wait time;
Further comprising:
2. The propagation measurement method according to claim 1, further comprising the steps of: detecting the reference pulse reception time using the updated measurement waiting time; and calculating the propagation time. determining whether the post-update measurement waiting time is within a predetermined range after calculating the post-update measurement waiting time;
correcting the updated measurement waiting time by adding a predetermined waiting time correction value to the updated measurement waiting time only when the updated measurement waiting time is outside a predetermined range;
The propagation measurement method of claim 2 further comprising: 4. The propagation measurement method according to claim 3, further comprising repeating the steps of calculating the propagation time, calculating the post-update measurement waiting time, and correcting the post-update measurement waiting time until the post-update measurement waiting time becomes a value within a predetermined range. In the step of determining whether the post-update measurement waiting time is within a predetermined range,
The propagation measurement method according to claim 3 or 4, wherein the judgment is based on the molecular weight of the gas calculated based on the sound speed in the measurement flow path obtained from the propagation time of the pulse in the forward direction and the propagation time of the pulse in the reverse direction. In the step of correcting the updated measurement waiting time,
adding the latency correction value to the updated measurement latency in each of the forward direction and the reverse direction such that the updated measurement latency is increased when the molecular weight of the gas becomes smaller than a predetermined minimum threshold value;
or
6. The propagation measurement method according to claim 5, further comprising adding a latency correction value to the updated measurement latency in each of the forward direction and the reverse direction such that the updated measurement latency becomes shorter when the latency correction value exceeds a predetermined maximum threshold. In the step of determining whether the post-update measurement waiting time is within a predetermined range,
7. The propagation measurement method according to claim 3, wherein the determination is made based on whether or not a difference between the propagation time of the pulse in the forward direction and the propagation time of the pulse in the reverse direction is greater than a predetermined maximum value. In the step of correcting the updated measurement waiting time,
8. The propagation measurement method according to claim 3, further comprising: adding the latency correction value to the post-update measurement latency such that the post-update measurement latency for the pulse in the reverse direction coincides with the post-update measurement latency for the pulse in the forward direction, or the post-update measurement latency for the pulse in the forward direction coincides with the post-update measurement latency for the pulse in the reverse direction. In the step of determining whether the post-update measurement waiting time is within a predetermined range,
9. The propagation measurement method according to claim 3, further comprising the step of: calculating the propagation time again, and then making a determination based on whether or not a change in the propagation time is greater than a predetermined maximum change. 10. The propagation measurement method according to claim 2, wherein the waiting time calculation adjustment value satisfies the following formula (1): t _{inv_ost} , the reference pulse is the _N1th pulse of the pulse group, the leading pulse is the _N2th pulse of the pulse group, and a period of the pulse is X.
0<t _{inv_ost} <(N ₁ - N ₂ )×X...(1) the step of detecting the reference pulse reception time and the step of calculating the propagation time are performed a plurality of times using the same measurement wait time initial value and using the same updated measurement wait time;
When a group of a plurality of values obtained by performing the step of calculating the propagation time using the same measurement wait time initial value and the same updated measurement wait time a plurality of times is defined as a group of sample values under the same conditions for the same measurement wait time initial value and the same updated measurement wait time,
11. The propagation measurement method according to claim 2, wherein in the step of calculating the propagation time, the propagation time is determined to be an average value obtained by removing at least a portion of the group of sample values under the same conditions other than the median value of the group of sample values under the same conditions from the group of sample values under the same conditions. A step of blocking the flow of gas into the measurement flow path;
12. The propagation measurement method according to claim 2, wherein the propagation measurement method is performed in a state where an inflow of gas into the measurement flow path is blocked;
flowing a gas into the measurement flow path after performing the propagation measurement method;
measuring a gas inflow propagation time, which is a time it takes for the pulse to propagate through the measurement flow path while gas is flowing into the measurement flow path;
a flow velocity calculation step of calculating a flow velocity of the gas in the measurement flow path based on the forward gas inflow propagation time and the reverse gas inflow propagation time;
Including,
The step of measuring the gas inflow propagation time includes:
detecting a gas inflow reference pulse reception time from a time when the preceding pulse is estimated to be received by the other ultrasonic sensor to a time when the reference pulse is received by the other ultrasonic sensor;
calculating a gas inflow-time propagation time of the pulse in the measurement flow path from a sum of the updated measurement waiting time and the gas inflow-time reference pulse reception time;
calculating a post-gas inflow updated measurement waiting time by subtracting the waiting time calculation adjustment value from the gas inflow propagation time;
replacing the post-update measurement waiting time with the post-update measurement waiting time during gas inflow;
Including,
The gas flow velocity measuring method further comprises the steps of: detecting the gas inflow reference pulse reception time using the post-gas inflow update measurement waiting time; and calculating the gas inflow propagation time. The gas flow velocity measurement method according to claim 12, wherein in the step of setting the measurement waiting time initial value, the sound speed in the measurement flow path is calculated from the gas temperature and the molecular weight of the gas, and the measurement waiting time initial value is calculated by dividing the length of the measurement flow path in the propagation direction by the sound speed. A computer is provided to measure a propagation state of ultrasonic waves in a measurement flow path through which a gas can flow, the ultrasonic waves being transmitted from a pair of ultrasonic sensors disposed on the upstream side and the downstream side of the measurement flow path, respectively.
a sensor operation means for alternately transmitting a group of ultrasonic pulses including a plurality of pulses in a forward direction from the ultrasonic sensor on the upstream side to the ultrasonic sensor on the downstream side and in a reverse direction from the ultrasonic sensor on the downstream side to the ultrasonic sensor on the upstream side, thereby propagating the group of ultrasonic pulses through the measurement flow path;
a waiting time initial value setting means for setting an initial value of a measurement waiting time, which is a time from when a reference pulse of the pulse group is transmitted from one of the ultrasonic sensors until when a leading pulse of the pulse group that is located forward in a propagation direction of the reference pulse is estimated to be received by the other ultrasonic sensor;
a pulse detection means for detecting a reference pulse reception time from a time when the preceding pulse is estimated to be received by the other ultrasonic sensor to a time when the reference pulse is received by the other ultrasonic sensor; and a propagation time calculation means for calculating a propagation time of the pulse in the measurement flow path from a sum of the measurement wait time initial value and the reference pulse reception time.
Propagation measurement program to function as. The computer,
an updated waiting time calculation means for calculating an updated measurement waiting time by subtracting a predetermined waiting time calculation adjustment value from the propagation time; and
a wait time update means for replacing the measurement wait time initial value with the updated measurement wait time;
It also functions as
15. The propagation measurement program according to claim 14, for causing the computer to function again as the pulse detection means and the propagation time calculation means by using the updated measurement waiting time. The computer,
a gas blocking means for blocking the inflow of gas into the measurement flow path;
a gas interruption time propagation measurement means for executing the propagation measurement program according to claim 15 in a state where the inflow of gas into the measurement flow path is interrupted;
a gas inflow means for injecting a gas into the measurement flow path after execution of the propagation measurement program;
a gas inflow propagation measuring means for measuring a gas inflow propagation time, which is a time taken for the pulse to propagate through the measurement flow path while the gas is flowing into the measurement flow path; and
a flow velocity calculation means for calculating a flow velocity of the gas in the measurement flow path based on the forward gas inflow propagation time and the reverse gas inflow propagation time;
Function as a
The gas inflow propagation measurement means includes:
a gas inflow time pulse detection means for detecting a gas inflow time reference pulse reception time from a time when the preceding pulse is estimated to be received by the other ultrasonic sensor to a time when the reference pulse is received by the other ultrasonic sensor;
a gas inflow propagation time calculation means for calculating a gas inflow propagation time of the pulse in the measurement flow path from the sum of the updated measurement waiting time and the gas inflow reference pulse reception time;
a gas inflow time post-update waiting time calculation means for calculating a gas inflow time post-update measurement waiting time by subtracting the waiting time calculation adjustment value from the gas inflow time propagation time;
a waiting time replacement means for replacing the post-update measurement waiting time with the post-update measurement waiting time at the time of gas inflow;
Including,
a gas flow velocity measurement program for causing the computer to function again as the gas flow-time pulse detection means and the gas flow-time propagation time calculation means by using the gas flow-time updated measurement waiting time; a measurement section that forms a measurement flow path through which a gas flows;
a valve for adjusting the inflow of gas into the measurement flow path;
a pair of ultrasonic sensors disposed on the upstream side and the downstream side of the measurement flow path, respectively;
a temperature sensor for measuring the temperature of the gas;
a calculation device that calculates a flow velocity of the gas based on a time taken for an ultrasonic wave emitted from one of the ultrasonic sensors to propagate through the measurement flow path and a time taken for an ultrasonic wave emitted from the other ultrasonic sensor to propagate through the measurement flow path;
Equipped with
The computing device includes:
an opening/closing operation unit for adjusting the opening degree of the valve;
a sensor operation unit that, when the valve is in a closed state in which gas is prevented from flowing into the measurement flow path, alternately transmits a group of ultrasonic pulses including a plurality of pulses in a forward direction from the upstream ultrasonic sensor to the downstream ultrasonic sensor and in a reverse direction from the downstream ultrasonic sensor to the upstream ultrasonic sensor, thereby propagating the group of ultrasonic pulses through the measurement flow path;
a waiting time initial value setting unit that sets a measurement waiting time initial value, which is a time from when a reference pulse of the pulse group is transmitted from one of the ultrasonic sensors until when a leading pulse of the pulse group that is forward in a propagation direction of the reference pulse is estimated to be received by the other ultrasonic sensor in the closed state;
a pulse detection unit that detects a reference pulse reception time from a time when the leading pulse is estimated to be received by the other ultrasonic sensor to a time when the reference pulse is received by the other ultrasonic sensor in the closed state;
a propagation time calculation unit that calculates a propagation time of the pulse in the measurement flow path from a sum of the measurement wait time initial value and the reference pulse reception time in the closed state;
an updated waiting time calculation unit that calculates an updated measurement waiting time by subtracting a predetermined waiting time calculation adjustment value from the propagation time in the closed state;
a wait time update unit that replaces the measurement wait time initial value with the updated measurement wait time in the closed state;
having
the pulse detection unit detects the reference pulse reception time again using the updated measurement waiting time, and the propagation time calculation unit calculates the propagation time again using the updated measurement waiting time;
The computing device includes:
a gas inflow pulse detection unit that detects a gas inflow reference pulse reception time from a time when the leading pulse transmitted from one of the ultrasonic sensors is estimated to be received by the other of the ultrasonic sensors to a time when the reference pulse transmitted from one of the ultrasonic sensors is received by the other of the ultrasonic sensors in an open state in which the valve is allowing gas to flow into the measurement flow path;
a gas inflow propagation time calculation unit that calculates a gas inflow propagation time, which is a time for the pulse to propagate through the measurement flow path, from the sum of the updated measurement waiting time and the gas inflow reference pulse reception time in the open state;
a gas inflow post-update waiting time calculation unit that calculates a gas inflow post-update measurement waiting time by subtracting the waiting time calculation adjustment value from the gas inflow propagation time in the open state;
a gas inflow waiting time update unit that replaces the post-update measurement waiting time with the gas inflow post-update measurement waiting time in the open state;
and
the gas inflow pulse detection unit detects the gas inflow reference pulse reception time again using the gas inflow update measurement waiting time, and the gas inflow propagation time calculation unit calculates the gas inflow propagation time again using the gas inflow update measurement waiting time,
The gas flow velocity measuring device, wherein the calculation device further includes a flow velocity calculation unit that calculates the flow velocity of gas in the measurement flow path based on the gas inflow propagation time in the forward direction and the gas inflow propagation time in the reverse direction. The gas flow rate measuring device according to claim 17, which calculates a flow rate of an oxygen-containing gas;
A concentrator body provided with the gas flow rate measuring device;
Equipped with
The computing device further includes a flow rate concentration calculation unit that calculates a flow rate of the oxygen-containing gas and an oxygen concentration in the oxygen-containing gas based on a flow velocity of the oxygen-containing gas.

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