JPH0961415A - Metal component analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the analytical efficiency in a metal ion elution process by supplying an eluate at flow velocity higher than reference flow velocity when metal ions are detected by a measuring means. SOLUTION: The flow velocity of the eluate flowing through an eluate supply pipe 7 is adjusted by a control circuit C. Until first metal ions are detected by a measuring means 33 in a metal ion elution process, a command is issued to a pressure pump 35 so as to supply the eluate to a pressure pump 35 at flow velocity higher than reference flow velocity and, on condition that first metal ions are detected by the measuring means 33, the flow velocity of the eluate is reduced to issue a command to the pressure pump 35 so that the eluate is supplied at the velocity coinciding with reference flow velocity. By this constitution, the time from the start of the supply of the eluate to the detection of first metal ions by the measuring means 33 can be shortened to a large extent.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a nuclear power plant,
The present invention relates to a metal component analyzer for analyzing a trace amount of metal components in ultrapure water used in semiconductor manufacturing equipment and the like.

[0002]

2. Description of the Related Art Conventionally, a metal component analyzer of this type is known, for example, as shown in FIG. The configuration of this metal component analyzer will be described below along with the operation. First,
The sample liquid to be measured flows in a mother pipe 50 (for example, to a nuclear power plant or a semiconductor manufacturing apparatus) located outside the analyzer 100, and a sampling pipe 51 connected to the mother pipe 50. Through the metal component analyzer 10
1 is supplied to the sampling valve 1. The sampling valve 1 includes a plurality of sample liquid inflow pipes 1A to 1H.
One of which is connected to the sampling tube 51,
These sample liquid inflow pipes 1A to 1H are connected to the sample liquid supply pipe 30a.

On the other hand, the sample liquid supply pipe 30a is provided with a liquid feed pump 2 (P1), and the liquid feed pump 2 (P1) is driven so that the sample liquid flowing in the mother pipe 50 is sampled by the sampling pipe 51. Is sent to the reactor 3 via the sampling valve 1 and the sample liquid supply pipes 30a and 30b. Connected upstream of the reactor 3 is a reaction solution storage section 4 in which a reaction solution composed of hydrochloric acid, nitric acid or a mixed acidic solution of these is stored, and a reaction solution supply pipe 6 provided with a solution sending pump 5 (P2). The reaction solution supply pipe 6 adds a reaction solution for ionizing the metal in the sample solution to the sample solution. Then, the sample solution added with this reaction solution is heated to a predetermined temperature in the reactor 3, and as a result, the metal in the sample solution is ionized. In addition, the sample liquid supply pipe 30 passing through the reactor 3
A part of c is formed in a coil shape, and a cooling fan 7 for cooling the sample liquid is provided in the coil portion 30c 'formed in the coil shape.

In the middle of the sample liquid supply pipe 30c, p
The H adjustment unit 9 is sequentially provided. The pH adjusting unit 9 has a structure in which an ion exchange membrane is provided inside a hollow container, and the ion exchange membrane forms two space portions inside the container. Then, the sample solution to which the reaction solution (acidic solution) has been added is supplied to one side of these two space portions, and the neutralization liquid of alkaline is used as a neutralizing solution for pH adjustment in the other space portion. A liquid, for example, a 0.1 to 1N tetramethylammonium hydroxide solution or a potassium hydroxide aqueous solution is supplied, and chlorine ions (from hydrochloric acid in the reaction liquid to hydrochloric acid in the reaction liquid are passed from the sample liquid to the neutralization liquid through the ion exchange membrane. (Which was contained) migrates, and hydroxide ions also migrate from the neutralization solution into the sample solution. That is, ion exchange is performed between the two, the hydrogen ion concentration in the sample solution decreases, the pH increases, and the pH approaches neutral. In addition,
The supply and discharge of the neutralizing liquid to and from the pH adjusting unit 9 are performed through the neutralizing liquid supply pipe 11 and the neutralizing liquid outflow pipe 12, respectively.
The neutralization liquid supply pipe 11 is configured to suck up the neutralization liquid from the neutralization liquid storage section 13 by a liquid feed pump 14 (P4), and the neutralization liquid after the ion exchange flows out of the neutralization liquid. It is adapted to be guided to the discharge pipe 15 via the pipe 12.

The oxidant supply pipe 17 and the sample liquid supply pipe 30
A pH sensor 19 is provided downstream of the confluence with c, and the control means C controls the feed amount of the neutralizing liquid by the feed pump 14 (P4) based on the detection signal from the pH sensor 19. To do.

The sample liquid that has passed through the pH sensor 19 reaches the three-way automatic switching valve 20. The three-way automatic switching valve 20 guides a part of the sample liquid flowing through the sample liquid supply pipe 30c to the discharge pipe 15 through the pipe 21. That is, when the sampling valve 1 was switched and another sample liquid was supplied, first, the flow path was switched to the pipe 21 side, and the sample valve 1 and the three-way automatic switching valve 20 remained. Rinse off the previous sample solution completely. Then, after this, the flow path is switched to flow the sample liquid toward the sample liquid supply pipe 30d.

The sampling valve 1 selects the sample liquid inflow pipes 1A to 1H and the three-way automatic switching valve 20.
Is switched on the basis of a signal output from the control means C. A check valve 22 is provided in the middle of a pipe 21 leading to the discharge pipe 15 of the three-way automatic switching valve 20. The check valve 22 is opened by the pressure of the sample liquid, which prevents all the sample liquid in the pipe 21 from flowing to the drain pipe 15 leading to the drain due to the siphon phenomenon.

The sample liquid that has passed through the three-way automatic switching valve 20 is
It is supplied to the pressurizing pump 23 (P5) through the sample liquid supply pipe 30d and further pressurized by the pressurizing pump 23 (P5). When the sample liquid is pressurized by the pressurizing pump 23 (P5) to a predetermined pressure or more, the pressure sensor 24 causes the control means C to stop the operation of the pressurizing pump 23 (P5). The detection signal of is output. The sample liquid pressurized by the pressure pump 23 (P5) passes through the first concentration column 27 or the second concentration column 28 by the first four-way automatic switching valve 25 and the second four-way automatic switching valve 26. Pipes 27a and 27b, pipe 28a
・ Supplied to 28b respectively.

The first four-way automatic switching valve 25 and the second four-way automatic switching valve 26 allow the sample solution supplied from the sample solution supply pipe 30d to pass through the concentration column 27 or 28, and then through the pipe 29. The flow path of the metal ion concentration step leading to the discharge pipe 15 and the reservoir 3 supplied from the eluent supply pipe 31
After passing the eluent in 2 through the concentration column 28 or 27, the flow path of the metal ion elution step leading to the pipe 34 of the measuring means 33 is alternately formed for the concentration columns 27, 28. . That is, in the metal ion concentration step, when the sample liquid passes through the concentration column 27 or 28, the metal ions in the sample liquid are concentrated column 27 or 2.
In the metal ion elution step, the metal ions adsorbed on the concentration column 27 or 28 are
The eluent supplied from the eluent supply pipe 31 by the pressurizing pump 35 (P6) is eluted from the concentration columns 27, 28 and carried to the measuring means 33, and to such concentration columns 27, 28. Adsorption of metal ions in the sample solution (metal ion concentration step), elution (metal ion elution step)
Are alternated.

Sample liquids of different types are alternately supplied to the concentration columns 27 and 28, and the metal ions in the sample liquid are adsorbed (concentrated) and eluted (to the concentration columns 27 and 28). The four-way automatic switching valves 25 and 26 for alternately performing (analysis) are switched from the control means C when the flow rate value of the sample liquid passing through the pipe 29 measured by the flow meter 36 reaches a preset set value. It is performed by the signal emitted. When the pressure pump 35 (P6) pressurizes the eluent to a predetermined pressure or more, the pressure sensor 37 instructs the control means C to pressurize the pump 35 (P6).
A detection signal for stopping the operation of is output.

The measuring means 33 has a separation column 38 and an absorptiometer 39, and the separation column 3
After the respective metal components are separated from the eluent supplied to 8, the respective concentrations are measured by the absorptiometer 39. The separation column 38 has a characteristic that, when an eluent containing a metal component is supplied, the metal ions in the eluent are retained for a predetermined time (separation time) and then discharged, and the separation time is Different for each type of metal ion. A coloring liquid supply pipe 40 is connected in the middle of the pipe 34 between the separation column 38 and the absorptiometer 39. This coloring liquid supply pipe 40 is
Upon measuring the absorbance with the absorptiometer 39, it is for supplying a coloring liquid for coloring the metal ions, and is supplied from the coloring liquid reservoir 42 by driving the liquid feeding pump 41 (P7). Has become.

[0012]

In the metal component analyzer configured as described above, the metal ions adsorbed on the concentration column 27 or 28 are supplied through the eluent supply pipe 31 in the metal ion elution step. The absorptiometer 3 in the measuring means 33 is eluted by the generated eluent.
However, at this time, in the absorptiometer 39, it is necessary to slow down the flow rate of the eluent in order to prevent the peaks of the detected metal ions from overlapping with each other. As a result, the analysis time in the absorptiometer 39 becomes long and the analysis efficiency deteriorates.

The present invention has been made in view of the above circumstances, and it is possible to improve the analysis efficiency by shortening the analysis time of the metal ions analyzed in the metal ion elution step. The purpose is to provide an analyzer.

[0014]

In order to achieve the above object, in the first invention, the metal component contained in the sample liquid is ionized and adsorbed on the concentration column, and then the metal ion is eluted in the concentration column. A metal component analyzer for analyzing a metal component in a sample liquid by sequentially supplying metal eluent contained in the eluent to a measuring means by supplying an eluent for The eluent is supplied to the concentration column at a reference flow rate at which the ion peak is separated, and the eluent supply means is capable of varying the flow rate of the eluent with respect to the reference flow rate, and is output from the measuring means. Control means for outputting an instruction to change the flow rate of the eluent to the eluent supply means based on the detection signal;
The control means outputs an instruction to supply the eluent at a flow rate higher than a reference flow rate to the eluent supply means when the measuring means does not detect metal ions. And In the second invention,
The control means outputs an instruction to supply the eluent at a flow rate higher than the reference flow rate to the eluent supply means until the measurement means detects the first metal ion, and the measurement means outputs the first metal ion. On the condition that ions are detected, an instruction to supply the eluent to the eluent supply means so as to match the reference flow velocity is output. Further, in the third invention, the control means supplies the eluent at a flow rate higher than the reference flow rate until the eluent is supplied to the eluent supply means until a preset time is measured. It is characterized in that an instruction to supply the eluent is output so that the eluent is supplied so as to match the reference flow velocity on condition that the set time is measured.

The metal component analyzer configured as described above can achieve the following actions. That is, in the metal component analyzer according to the first aspect of the present invention, the eluent is supplied at a flow rate higher than the reference flow rate when the metal ion is not detected by the measuring means. The measurement time can be significantly shortened as compared with the conventional metal component analyzer.
In the second invention, the eluent is supplied at a flow rate higher than the reference flow rate until the first metal ion is detected by the measuring means,
On condition that the first metal ion was detected by the measuring means, the flow rate of the eluent was decreased so that the eluent was supplied so as to match the reference flow rate. Therefore, like the first invention, In the metal ion elution step, the time from the start of the supply of the eluent to the detection of the first metal ion by the measuring means can be significantly shortened as compared with the conventional metal component analyzer. In the third invention, the eluent is supplied at a flow rate higher than the reference flow rate from the start of the supply of the eluent until the preset set time is measured, and the set flow time is measured. Since the eluent is supplied so as to correspond to
Similar to the second invention, in the metal ion elution step, the time from the start of the supply of the eluent to the detection of the first metal ion by the measuring means is significantly larger than that of the conventional metal component analyzer. Can be shortened to

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIG.
This will be described with reference to FIG. Note that the metal component analyzer shown in the embodiment of the present invention has the same basic configuration as the metal component analyzer shown in FIG. 3, and therefore only the points different from the conventional one will be described in detail below.

First, the pressurizing pump indicated by reference numeral 35 (P6) in FIG. 3 is constructed so that the supply amount of the eluent per unit time, that is, the flow rate of the eluent flowing through the eluent supply pipe 31 can be varied. And the flow velocity is
It is adjusted by the control signal supplied from the control means C. Specifically, this pressurizing pump 35 (P6) is used when the metal ion is detected by the absorptiometer 39.
When the eluent is supplied to the concentration column 27 or the concentration column 28 at the reference flow rate at which the peak of the metal ion is separated, and the metal ion is not detected by the absorptiometer 39, the reference flow rate is obtained. On the other hand, the flow rate of the eluent is increased, for example, about twice. Also, FIG.
The liquid feed pump denoted by reference numeral 41 (P7) is configured so that the supply amount of the color forming liquid per unit time, that is, the flow rate of the color forming liquid flowing in the color forming liquid supply pipe 40 can be changed. , Its flow velocity is adjusted by a control signal supplied from the control means C. Specifically, the liquid feed pump 41 (P7) is interlocked with the flow rate of the eluent supplied by the pressurizing pump 35 (P6), and thereby supplies a certain proportion of the color developing liquid to the eluent. And
When the flow rate of the eluent is increased, the flow rate of the color developing solution is increased accordingly, and when the flow rate of the eluent is decreased, the flow rate of the color developing solution is reduced accordingly.

Next, the control content (control content in the metal ion elution step) for the pressurizing pump 35 (P6) executed by the control means C will be described with reference to the flowchart of FIG. The flowchart of FIG. 1 starts to be executed under the following conditions. That is, in the metal ion concentration step, when the sample liquid is supplied to the concentration column 27 or the concentration column 28 and the flow rate value of the sample liquid measured by the flow meter 36 reaches a set value (for example, 20 ml), the four-way automatic By switching the switching valves 25 and 26 together, as shown in steps 1 to 6 below, the eluent is supplied to the concentration columns 27 and 28 (one of the concentration columns) to which the sample liquid has been supplied, The metal ion elution step of eluting the metal ions adsorbed on the concentration columns 27 and 28 is started. Further, a treatment for adsorbing metal ions in the sample liquid to the concentration columns 27, 28 (metal ion concentration step), a treatment for eluting the metal ions adsorbed in the concentration columns 27, 28 with an eluent (metal ion elution step) )
As described above, by simultaneously switching the four-way automatic switching valves 25 and 26, the two concentration columns 27 and 28 are
I'm trying to alternate with each other.

<< Step 1 >> The pressurizing pump 35 (P6) is instructed to supply the eluent at a flow rate twice the reference flow rate (about 1.2 ml / min), whereby metal ions are adsorbed. Concentrating column 27 or concentrating column 28
Thus, the adsorbed metal ions are eluted at high speed.
In conjunction with this, the supply speed of the color-developing liquid by the liquid-sending pump 41 (P7) is twice the reference flow velocity (about 0.8 ml / min).
, And the ratio of the color-developing solution added to the eluent is kept constant.

<Step 2> It is judged whether or not 4 minutes have passed since the processing according to this flowchart was started, and NO.
In this case, the process of step 1 is continued and Y
In case of ES, proceed to the next step 3. Step 2
The set time of 4 minutes measured at
It is set to less than half of the time when the first metal ion (Cu ⁺² ) is detected when the coloring liquid is supplied,
As the set time, an average value obtained by conducting a plurality of experiments in advance is adopted. Also, the set time of 4 minutes is
As described above, if it is less than half the time when the first metal ion (Cu ⁺² ) is detected when the eluent / color-developing liquid is supplied at the standard speed, it takes 2 minutes even if it is 3 minutes. However, the operator can arbitrarily select it.

<< Step 3 >> The pressurizing pump 35 (P6) is instructed to reduce the flow rate of the eluent until it matches the reference flow rate (about 0.6 ml / min). In conjunction with this, the liquid feed pump 41 (P7) is instructed to reduce the supply speed of the color-developing liquid until it matches the reference flow rate (about 0.4 ml / min), and the color-developing liquid to be added to the eluent. Keep the ratio of. << Step 4 >> It is judged whether or not the output voltage output from the absorptiometer 39 is less than or equal to the voltage fluctuation width (100 μV) at which the metal ion is not detected, and N
If it is O, the process of the previous step 3 is continued, and if YES, the process proceeds to the next step 5. << Step 5 >> As in step 1, the pressurizing pump 35
(P6) twice the standard flow rate (1.2 ml / min
To supply the eluent at the same time, and at the same time, to supply the color-developing liquid to the liquid feed pump 41 (P7) at a flow rate twice as high as the reference flow rate (about 0.8 ml / min). To do. That is, in these Steps 4 to 5, the flow rates of the eluent and the color developing solution are increased again in a situation where the first metal ion is not detected yet after 4 minutes have elapsed from the start of the measurement (YES in Step 4). →
Step 5), which prevents the measurement time from being wasted.

<Step 6> The elapsed time from the start of the process according to this flowchart is the set time from the start of the supply of the eluent / coloring liquid to the detection of the last metal ion peak by the absorptiometer 39 ( (10 minutes in this embodiment)
It is determined whether or not the time has reached the set time, and if the set time has not reached NO, the processes of the above step 3 to step 5 are repeated, and if the set time matches YES, the last metal ion The flow chart is terminated by regarding the absorbance as the detection. The set time set in step 6 is the same as that of the pressurizing pump 35 (P
6) When the eluent / coloring liquid is supplied at twice the reference flow rate for 4 minutes by the liquid feed pump 41 (P7) and then the eluent / coloring liquid is supplied at the reference flow rate, the eluent / coloring liquid is generated. It shows the average value (10 minutes in the present embodiment) of the time from the start of supplying the liquid to the time when the last peak of the metal ion (Fe ²⁺ ) is completely detected by the absorptiometer 39. . The set time is shortened by the amount of the eluent / color-developing liquid being supplied at twice the reference flow rate for 4 minutes, compared to the case where the eluent / color-developing liquid is supplied at the reference speed. ing.

By going through the above steps 1 to 6, a chromatogram as shown in FIG. 2 can be obtained. In this chromatogram, after calculating the peak area of each metal ion, The concentration of the metal component contained in the sample solution can be calculated from this peak area and the relational expression (calibration curve) between the peak area detected in advance and the concentration of the metal component.

As described in detail above, according to the metal component analyzer of the above-described embodiment, the pressurizing pump 35 (P6) is used until the first metal ion is detected by the measuring means 33 in the metal ion elution step. ) Is instructed to supply the eluent at a flow rate higher than the reference flow rate (steps 1 and 5), and the first metal ion is detected by the measuring means 33 (NO in step 4).
Since the pressure pump 35 (P6) was instructed to decrease the flow rate of the eluent and supply the eluent so as to match the reference flow rate (step 3), the supply of the eluent was started. After that, the time from the measurement means 33 to the detection of the first metal ion can be significantly shortened as compared with the conventional metal component analyzer, which shortens the total analysis time of metal components. As a result, it is possible to improve the analysis efficiency of metal components.

In the above-described embodiment, the flow rate of the color-developing liquid is increased in response to the increase of the flow rate of the eluent. Ions develop color, or absorptiometer 39
It is not always necessary to increase the flow rate of the color-developing solution as long as it does not affect the measurement of the absorbance. In the metal ion elution step, the eluent at a flow rate twice as high as the reference flow rate with respect to the pressure pump 35 (P6) and the liquid feed pump 41 (P7) until the first metal ion is detected by the measuring means 33. Although it is instructed to supply the color forming liquid, this magnification can be arbitrarily selected. Further, in the above embodiment, in the metal ion elution step, the pressurizing pump 35 (P6) and the liquid feed pump 41 (P
Instruct 7) to supply the eluent and color-developing liquid at a flow rate twice the reference flow rate (step 1 and step 2),
After that, after the flow velocity is reduced to the reference flow velocity (step 3), these pressurizing pumps 35 (P6) and liquid feed pumps 41 (P) until the first metal ions are detected by the measuring means 33.
7) was instructed to supply the eluent and the color-developing solution at a flow rate twice the reference flow rate (step 4 to step 6). Of these steps, the latter half step 3 to step 6
Is not essential and may be omitted as appropriate. That is, in the above-described embodiment, the pressure pump 35 (P
6) Only by instructing the liquid feed pump 41 (P7) to supply the eluent and the color developing liquid at a flow rate twice as high as the reference flow rate (steps 1 and 2), the entire metal ion elution process is performed. The measurement time can be shortened as compared with the conventional metal component analyzer, and the metal component analysis efficiency can be improved. Further, in the above embodiment, the eluent and the color developing liquid are supplied to the pressurizing pump 35 (P6) and the liquid sending pump 41 (P7) at a flow rate twice as high as the reference flow rate for 4 minutes from the start of the eluent supply. (Step 1 and Step 2), and then the flow velocity is reduced to the reference flow velocity (Step 3), but the present invention is not limited to such a process, and for example, from the start of measurement to the measurement means 33. Pressurizing pump 35 until the first metal ion is detected at
(P6), the liquid feed pump 41 (P7) is continuously instructed to supply the eluent and the color developing liquid at a flow rate twice the reference flow rate, and the measuring means 33 detects the first metal ion. At this point (corresponding to step 4), the pressurizing pump 35 (P
6) Alternatively, the flow chart may be such that an instruction to supply the eluent and the color-developing liquid at the reference flow rate is output to the liquid feed pump 41 (P7). Further, the above-described embodiment and the constituent elements in the claims have the following relationship. That is, the eluent supply pipe 31, the reservoir 32, and the pressure pump 35.
(P6) claims "eluent supply means"
Further, the control means C constitutes "control means" in the claims.

[0026]

As described above in detail, in the metal component analyzer shown in the first invention, the eluent is supplied at a flow rate higher than the reference flow rate when the measuring means does not detect metal ions. Therefore, in the metal ion elution step, the entire measurement time can be significantly shortened as compared with the conventional metal component analyzer, and the metal component analysis efficiency can be improved. In the second invention, the eluent is supplied at a flow rate higher than the reference flow rate until the first metal ion is detected by the measuring means, and the first metal ion is detected by the measuring means on condition that the eluent flow rate. Since the eluent is supplied so as to match with the reference flow rate, the measurement means first starts the supply of the eluent in the metal ion elution step as in the first invention. It is possible to significantly reduce the time until the detection of the metal ion of (3) as compared with the conventional metal component analyzer, and to improve the analysis efficiency of the metal component. In the third invention, the eluent is supplied at a flow rate higher than the reference flow rate until the preset time is measured after the supply of the eluent is started,
On condition that the set time is measured, the eluent is supplied so as to match the reference flow velocity. Therefore, as in the first and second inventions, the eluent is supplied in the metal ion elution step. The time from the start to the detection of the first metal ion by the measuring means can be significantly shortened as compared with the conventional metal component analyzer, and the metal component analysis efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a control means C of a metal component analyzer according to the present invention.
6 is a flowchart showing the control contents in FIG.

FIG. 2 is a diagram showing a chromatogram of metal ions.

FIG. 3 is a schematic configuration diagram of a metal component analyzer according to the present invention and the related art.

[Explanation of symbols]

 27 Concentration column 28 Concentration column 31 Eluent supply pipe (eluent supply means) 32 Reservoir (eluent supply means) 33 Measuring means 35 Pressurizing pump (eluent supply means) 38 Separation column 39 Absorptiometer 41 Liquid transfer pump C control means

Claims (3)

[Claims] 1. A metal component contained in a sample solution is ionized and adsorbed on a concentration column, and then an eluent for eluting metal ions is supplied into the concentration column, and the elution liquid is measured by a measuring means. A metal component analyzer designed to analyze the metal components in a sample solution by sequentially detecting the metal ions contained in, and supplying the eluent to the concentration column at a reference flow rate at which the peaks of metal ions are separated. In addition, the eluent supply means capable of changing the flow rate of the eluent with respect to the reference flow rate, and the eluent supply means for the eluent supply means based on the detection signal output from the measuring means. And a control means for outputting an instruction to change the flow velocity, wherein the control means is greater than a reference flow velocity with respect to the eluent supply means when the measuring means does not detect metal ions. A metal component analyzer, which outputs an instruction to supply an eluent at a high flow rate. 2. The control means outputs an instruction to supply the eluent at a flow rate higher than a reference flow rate to the eluent supply means until the measuring means detects the first metal ion, and the measuring means. 2. The metal component according to claim 1, wherein an instruction to supply the eluent to the eluent supply means is output to the eluent supply means on condition that the first metal ion is detected in step 1. Analysis equipment. 3. The control means instructs the eluent supply means to supply the eluent at a flow rate higher than a reference flow rate from the start of the supply of the eluent until a preset set time is measured. 2. The metal component analyzer according to claim 1, wherein an instruction to supply the eluent so as to match the reference flow velocity is output on condition that the set time is measured.