JP2021135154A - Cause determination device and cause determination method - Google Patents

Abstract

To facilitate identification of a cause of zero point drift on a thermal flow sensor.SOLUTION: A cause determination device comprises: a target flow measured value acquiring part 20 for acquiring a flow measured value from a thermal flow sensor 201 for measuring a flow of fluid flowing through a pipeline 200; a zero point drift detecting part 27 for, on the basis of the flow measured value, determining presence of zero point drift on the thermal flow sensor 201, and detecting an amount of zero point drift; a pressure operation instruction part 23 for, if it is determined that there is zero point drift on the thermal flow sensor 201, outputting an instruction signal for varying supply pressure of the fluid, to a pressure adjusting unit 203 provided on the pipeline 200; and a drift cause determining part 24 for, on the basis of the zero point drift amount detected by the zero point drift detecting part 27 before and after the change of the supply pressure, determining a cause of the zero point drift on the thermal flow sensor 201.SELECTED DRAWING: Figure 1

Description

The present invention relates to a cause determination device and a cause determination method capable of estimating the cause of zero point drift of a thermal flow sensor.

A thermal flow sensor for measuring the flow rate of a fluid has been put into practical use (see, for example, Patent Document 1). FIG. 9 is a schematic cross-sectional view of the thermal flow sensor disclosed in Patent Document 1. The thermal flow sensor is a measurement piping unit that is arranged inside the housing 1 and the housing 1 and is fixed to the housing 1 via the telescopic members 2A and 2B, and has lower thermal elasticity than the housing 1. 3 and a sensor chip 8 for detecting the flow rate of the fluid flowing in the measurement piping unit 3.

The fluid flowing through the tube 6A flows through the through hole of the body portion 51A of the joint 5A connected to the tube 6A and flows through the measurement piping portion 3 connected to the body portion 51A of the joint 5A. It flows through the tube 6B connected to the body portion 51B of the joint 5B through the through hole of the body portion 51B of the joint 5B connected to the joint 5B. Such a thermal flow sensor is characterized in that the sensor chip 8 is fixed to the measurement piping unit 3 so as to be exposed to the fluid.

When the thermal flow sensor shown in FIG. 9 is used, for example, in a semiconductor manufacturing apparatus or a heat treatment furnace (internal atmosphere control), a wide variety of gases and liquids different from harmless gases such as air and steam handled in a building are generated. It becomes a flow measurement target.

Needless to say, it is important to maintain accuracy so that accurate flow rate measurement can be performed, for example, when targeting a manufacturing process of an ultrafine structure of a semiconductor manufacturing apparatus. Needless to say, the importance of maintaining accuracy is not limited to semiconductor manufacturing equipment. Improvements are constantly required to maintain the accuracy of flow measurement.

For example, managing the zero point of the flow rate measurement is known as one of the methods for confirming that the accuracy of the flow rate measurement is maintained. Is difficult to identify and there is room for improvement.

Japanese Unexamined Patent Publication No. 2017-09348

The present invention has been made to solve the above problems, and it is possible to simplify the identification of the cause of the zero point drift of the thermal flow sensor and improve the efficiency of the process for maintaining the accuracy of the flow rate measurement. It is an object of the present invention to provide a cause determination device and a cause determination method that can be used.

The cause determination device of the present invention has a first acquisition unit configured to acquire a flow rate measurement value from a thermal flow sensor that measures the flow rate of a fluid flowing through a pipe, and the heat based on the flow rate measurement value. When it is determined that the thermal flow sensor has a zero point drift and the zero point drift detection unit configured to determine the presence or absence of the zero point drift of the type flow sensor and detect the amount of the zero point drift. A pressure operation instruction unit configured to output an instruction signal for changing the supply pressure of the fluid to the pressure adjusting device arranged in the pipe, and the zero point before and after the change in the supply pressure. It is characterized by including a drift cause determination unit configured to determine the cause of the zero point drift of the thermal flow sensor based on the zero point drift amount detected by the drift detection unit.

Further, in one configuration example of the cause determination device of the present invention, the zero point drift detection unit outputs an instruction signal for making the flow rate of the fluid zero to the flow rate adjusting device arranged in the pipe. Based on the zero operation instruction unit configured to perform the above and the flow rate measurement value when the flow rate of the fluid becomes zero, the presence or absence of zero point drift of the thermal flow sensor and the zero point drift amount are determined. It is characterized in that it is composed of a drift evaluation unit configured to perform detection.
Further, in one configuration example of the cause determination device of the present invention, the zero point drift detection unit is configured to acquire a reference flow rate measurement value from a flow rate measuring device for calibration arranged in the pipe. Based on the acquisition unit, the flow rate measurement value acquired by the first acquisition unit, and the reference flow rate measurement value acquired by the second acquisition unit, the presence or absence of zero point drift of the thermal flow sensor. It is characterized in that it is composed of a drift evaluation unit configured to perform determination and detection of a zero point drift amount.
Further, in one configuration example of the cause determination device of the present invention, the drift evaluation unit is the first of the flow rate measurement values simultaneously acquired by the first and second acquisition units before the supply pressure of the fluid changes. The error between the value of 1 and the first value of the reference flow rate measurement value, and the second value of the flow rate measurement value simultaneously acquired by the first and second acquisition units before the supply pressure of the fluid changes. Based on the error between the value of The error between the third value of the flow rate measurement value and the third value of the reference flow rate measurement value simultaneously acquired by the first and second acquisition units after the change and the supply pressure of the fluid change. Based on the error between the fourth value of the flow rate measurement value and the fourth value of the reference flow rate measurement value simultaneously acquired by the first and second acquisition units, the thermal flow sensor is zero. It is characterized by determining the presence or absence of point drift and detecting the amount of zero point drift.

Further, in one configuration example of the cause determination device of the present invention, the drift cause determination unit is used when the zero point drift amount decreases after the supply pressure of the fluid is reduced by the pressure adjusting device, or when the fluid. If the zero point drift amount increases after the supply pressure is increased, the cause of the zero point drift is determined to be a non-sensor characteristic change system factor, and the zero point drift amount increases before and after the change in the supply pressure. When it has not changed, the cause of the zero point drift is determined to be a sensor characteristic change system factor.
Further, in one configuration example of the cause determination device of the present invention, the non-sensor characteristic changing factor is convection or leakage of the fluid, and the sensor characteristic changing factor is the thermal flow sensor exposed to the fluid. It is an attack phenomenon caused by dirt on the core portion of the above or the fluid.

Further, the cause determination method of the present invention is based on the first step of acquiring the flow rate measurement value from the thermal flow sensor for measuring the flow rate of the fluid flowing through the pipe and the flow rate measurement value acquired in the first step. , The second step of determining the presence or absence of zero point drift of the thermal flow sensor and detecting the amount of zero point drift, and when it is determined that the thermal flow sensor has zero point drift, the fluid After the third step of outputting an instruction signal for changing the supply pressure to the pressure adjusting device arranged in the pipe and the pressure adjusting by the pressure adjusting device, the flow rate measurement value is acquired from the thermal flow sensor. Based on the fourth step and the flow rate measurement value acquired in the fourth step, the fifth step of determining the presence or absence of the zero point drift of the thermal flow sensor and detecting the zero point drift amount. It is characterized by including a sixth step of determining the cause of the zero point drift of the thermal flow sensor based on the zero point drift amount detected in the second and fifth steps.

Further, in one configuration example of the cause determination method of the present invention, before the first step, an instruction signal for making the flow rate of the fluid zero is sent to the flow rate adjusting device arranged in the pipe. The second and fifth steps further include a seventh step of output, and the presence or absence of zero point drift of the thermal flow sensor based on the flow rate measurement value when the flow rate of the fluid becomes zero. It is characterized by including a step of determining the above and detecting the zero point drift amount.
Further, in one configuration example of the cause determination method of the present invention, the first and fourth steps include a step of acquiring a reference flow rate measurement value from a flow rate measuring device for calibration arranged in the pipe, respectively. In the second step, the presence or absence of zero point drift and the detection of the zero point drift amount of the thermal flow sensor are determined based on the flow rate measurement value and the reference flow rate measurement value acquired in the first step. In the fifth step, the presence or absence of zero point drift of the thermal flow sensor is determined based on the flow rate measurement value and the reference flow rate measurement value acquired in the fourth step. It is characterized by including a step of detecting the zero point drift amount and the zero point drift amount.
Further, in one configuration example of the cause determination method of the present invention, the second step is the first value of the flow rate measurement value and the first value of the reference flow rate measurement value simultaneously acquired in the first step. Based on the error between the above and the error between the second value of the flow rate measurement value and the second value of the reference flow rate measurement value simultaneously acquired in the first step, the zero point drift of the thermal flow sensor. The fifth step includes the third value of the flow rate measurement value and the reference flow rate measurement value simultaneously acquired in the fourth step, including a step of determining the presence or absence of the flow rate and detecting the zero point drift amount. The thermal flow sensor is based on the error between the third value and the error between the fourth value of the flow rate measurement value and the fourth value of the reference flow rate measurement value acquired at the same time in the fourth step. It is characterized by including a step of determining the presence / absence of zero point drift and detecting the amount of zero point drift.

Further, in one configuration example of the cause determination method of the present invention, the sixth step is when the zero point drift amount decreases after the supply pressure of the fluid is reduced by the pressure adjusting device, or when the fluid. If the zero point drift amount increases after the supply pressure is increased, the cause of the zero point drift is determined to be a non-sensor characteristic change system factor, and the zero point drift amount before and after the change in the supply pressure is determined. When it has not changed, it is characterized by including a step of determining the cause of the zero point drift as a sensor characteristic change system factor.

According to the present invention, by providing the first acquisition unit, the zero point drift detection unit, the pressure operation instruction unit, and the drift cause determination unit, the thermal flow sensor is zeroed at the site where the thermal flow sensor is installed. The cause of point drift can be easily estimated. As a result, in the present invention, the efficiency of the process for maintaining the accuracy of the flow rate measurement can be improved.

Further, in the present invention, by providing a zero operation indicating unit and a drift evaluation unit as the zero point drift detecting unit, the flow rate of the fluid is set to zero and the zero point drift amount of the thermal flow sensor is directly detected. be able to.

Further, in the present invention, by providing the second acquisition unit and the drift evaluation unit as the zero point drift detection unit, the reference flow rate measurement value obtained by the flow rate measuring device for calibration is used, and the thermal flow sensor is used. Identify whether the zero-point drift of the thermal flow sensor is due to a change in the characteristics of the sensor itself or a cause other than the sensor, without stopping the operation of the semiconductor manufacturing equipment or heat treatment furnace in which the sensor is used. be able to.

FIG. 1 is a block diagram showing a configuration of a cause determination device according to a first embodiment of the present invention. FIG. 2 is a plan view and a cross-sectional view showing the structure of the sensor chip of the thermal flow sensor. FIG. 3 is a flowchart illustrating the operation of the cause determination device according to the first embodiment of the present invention. FIG. 4 is a block diagram showing a configuration of a cause determination device according to a second embodiment of the present invention. FIG. 5 is a flowchart illustrating the operation of the cause determination device according to the second embodiment of the present invention. FIG. 6 is a flowchart illustrating a method for evaluating a zero point drift amount according to a second embodiment of the present invention. FIG. 7 is a flowchart illustrating a method for evaluating a zero point drift amount according to a second embodiment of the present invention. FIG. 8 is a block diagram showing a configuration example of a computer that realizes the cause determination device according to the first and second embodiments of the present invention. FIG. 9 is a schematic cross-sectional view of a conventional thermal flow sensor.

[Principle of invention]
The inventor has focused on the fact that the zero point drift in which the flow rate display does not become zero even though the actual flow rate is zero can be roughly divided into two causes (sensor characteristic change and non-sensor characteristic change).

For example, when various reaction gases of semiconductor manufacturing equipment are targeted for flow rate measurement, due to sensor characteristic change factors such as dirt around the sensor chip of the thermal flow sensor (flow rate measurement core part) and attack phenomenon due to the fluid to be measured. Zero point drift may occur at a non-negligible level.
However, in the case of the zero-point drift of the thermal flow sensor, there is room for improvement in that the work efficiency for dealing with defects is poor because there are causes other than the sensor characteristic change factors such as dirt on the core portion.

Then, the inventor described the non-sensor characteristic change system of "convection of fluid due to vertical piping installation" and "leakage of fluid from the downstream side of the flow meter", which are other main causes of zero point drift of the thermal flow sensor. We have found that the supply pressure of the fluid is reduced or pressurized as a method for easily discriminating between the factor and the factor of the sensor characteristic change system.

Specifically, for example, when the supply pressure of the fluid is reduced, the zero point drift amount decreases when the cause is convection or leakage of the fluid, but the zero point drift when the cause is dirt on the core part of the sensor chip. The amount does not decrease. Similarly, when the fluid supply pressure is increased, the zero point drift amount increases if the fluid convection or leak is the cause, but the zero point drift amount increases if the sensor chip core is dirty. Does not increase. By applying such a principle, it is possible to simplify the identification of the cause of the zero point drift of the thermal flow sensor, and thus it is possible to improve the efficiency of the process for maintaining the accuracy of the flow rate measurement.

[First Example]
Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a cause determination device according to a first embodiment of the present invention.
This embodiment is premised on a configuration in which the flow rate of the fluid can be surely set to zero and the zero point drift amount of the thermal flow sensor can be directly confirmed. Specifically, in addition to the thermal flow sensor 201, the pipe 200 is provided with a flow rate adjusting device 202 capable of adjusting the flow rate of the fluid flowing through the pipe 200 and a pressure adjusting device 203 capable of adjusting the supply pressure of the fluid. It is assumed that it has been done.

The cause determination device of this embodiment sets the target flow measurement value acquisition unit 20 (first acquisition unit) for acquiring the flow measurement value from the thermal flow sensor 201 to be the cause determination and the fluid flow rate to zero. A thermal flow sensor based on the zero operation instruction unit 21 that outputs an instruction signal to the flow rate adjusting device 202 arranged in the pipe 200 and the flow rate measurement value when the flow rate of the fluid becomes zero. The fluid supply pressure is changed when it is determined that the thermal flow sensor 201 has a zero point drift and the drift evaluation unit 22 that determines the presence or absence of the zero point drift of 201 and detects the zero point drift amount. Based on the pressure operation instruction unit 23 that outputs the instruction signal to the pressure adjusting device 203 arranged in the pipe 200 and the zero point drift amount detected by the drift evaluation unit 22 before and after the change in the supply pressure. A drift cause determination unit 24 for determining the cause of the zero point drift of the thermal flow sensor 201 and a determination result presentation unit 25 for presenting the determination result are provided.
The zero operation instruction unit 21 and the drift evaluation unit 22 constitute a zero point drift detection unit 27.

FIG. 2 (A) is a plan view showing the structure of the sensor chip 8 which is a core portion of the thermal flow sensor 201, and FIG. 2 (B) is a sectional view taken along line AA of the sensor chip 8 of FIG. 2 (A). .. In FIGS. 2 (A) and 2 (B), 100 is a base silicon chip, 101 is a thin-walled diaphragm formed by providing a space 102 on the upper surface of the silicon chip 100, and 103 is a diaphragm made of, for example, silicon nitride. A heater made of a metal thin film formed on the diaphragm 101, 104 is a temperature sensor made of a metal thin film heat-sensitive resistor formed on the upstream side of the heater 103 on the diaphragm 101, and 105 is a downstream of the heater 103 on the diaphragm 101. A temperature sensor made of a metal thin film heat-sensitive resistor formed on the side, 106 is an ambient temperature sensor made of a metal thin film heat-sensitive resistor, and 107 is a slit penetrating the diaphragm 101.

The heater 103 and the temperature sensors 104 to 106 are covered with, for example, a thin film insulating layer 108 made of silicon nitride. The ambient temperature sensor 106 is arranged in a place where the temperature of the fluid can be detected without being affected by the heat from the heater 103. The sensor chip 8 is mounted on the pipe 200 (measurement piping unit 3 in FIG. 9) so that the surface shown in FIG. 2 (A) is exposed to the measurement fluid.
The heater 103 generates heat so that its temperature is always higher than its ambient temperature by a constant temperature.

When the fluid in the pipe 200 is stationary, the heat applied by the heater 103 diffuses symmetrically in the upstream direction and the downstream direction. Therefore, the temperatures of the temperature sensor 104 and the temperature sensor 105 become equal, and the electrical resistances of the temperature sensor 104 and the temperature sensor 105 become equal. On the other hand, when the fluid in the pipe 200 flows from the upstream to the downstream, the heat applied by the heater 103 is carried in the downstream direction. Therefore, the temperature of the temperature sensor 105 is higher than the temperature of the temperature sensor 104. Therefore, there is a difference between the electric resistance of the temperature sensor 104 and the electric resistance of the temperature sensor 105.

The difference between the electrical resistance of the temperature sensor 105 and the electrical resistance of the temperature sensor 104 correlates with the flow velocity of the fluid in the pipe 200. Therefore, the flow rate of the fluid flowing through the pipe 200 can be obtained from the difference between the electric resistance of the temperature sensor 105 and the electric resistance of the temperature sensor 104. The thermal flow sensor 201 as described above is disclosed in Patent Document 1.

FIG. 3 is a flowchart illustrating the operation of the cause determination device of this embodiment. The zero operation instruction unit 21 outputs an instruction signal for reducing the flow rate to zero to the flow rate adjusting device 202 (valve in this embodiment) arranged in the pipe 200, thereby causing the fluid flowing through the pipe 200 to flow. The flow rate is set to zero (step S100 in FIG. 3). In this embodiment, for example, the opening degree of the valve arranged on the downstream side of the thermal flow sensor 201 is fully closed.

The target flow rate measurement value acquisition unit 20 acquires the flow rate measurement value Q from the thermal flow sensor 201 after the flow rate is adjusted by the flow rate adjusting device 202 (step S101 in FIG. 3).

The drift evaluation unit 22 evaluates the zero point drift amount D1 of the thermal flow sensor 201 based on the flow rate measurement value Q acquired by the process of step S101 (FIG. 3, step S102).

Specifically, the drift evaluation unit 22 compares a predetermined threshold value TH with the set value of the flow rate measurement value Q based on the measurement signal noise level, and the set value of the flow rate measurement value Q is equal to or less than the threshold value TH. In this case, it is determined that the flow rate measurement value Q is zero and there is no zero point drift in the thermal flow sensor 201, and the zero point drift amount D1 is set to zero. Further, when the set value of the flow rate measurement value Q exceeds the threshold value TH, the drift evaluation unit 22 determines that the thermal flow sensor 201 has a zero point drift, and determines the set value of the flow rate measurement value Q. Let the zero point drift amount be D1.

Next, when the drift evaluation unit 22 confirms that the thermal flow sensor 201 has a zero point drift (YES in step S103 of FIG. 3), the pressure operation instruction unit 23 applies pressure to the pressure adjusting device 203. By outputting the instruction signal to be changed, the supply pressure of the fluid is changed (step S104 in FIG. 3).

The pressure adjusting device 203 includes, for example, an electropneumatic regulator that receives an instruction signal from the pressure operation instruction unit 23, and a valve that is operated by the air pressure supplied from the electropneumatic regulator. When the fluid to be measured by the thermal flow sensor 201 is a gas, the electropneumatic regulator alone may be used as the pressure adjusting device 203.

When the pressure adjusting device 203 is a manual pressure adjusting device such as a regulator or a governor, the pressure operation instruction unit 23 presents the pressure instruction value to the operator who performs the pressure adjustment work, and the operator sets the pressure instruction value according to the pressure instruction value. You will operate the regulator and governor.
In principle, the change in the fluid supply pressure may be depressurized or increased, but decompression is preferable from the viewpoint of general safety.

The target flow rate measurement value acquisition unit 20 acquires the flow rate measurement value Q from the thermal flow sensor 201 after the pressure is adjusted by the pressure adjusting device 203 (step S105 in FIG. 3).

The drift evaluation unit 22 evaluates the zero point drift amount D2 of the thermal flow sensor 201 based on the flow rate measurement value Q acquired by the process of step S105 (FIG. 3, step S106). The evaluation method of the zero point drift amount D2 is the same as the evaluation method of the zero point drift amount D1 in step S102.

The drift cause determination unit 24 determines the cause of the zero point drift of the thermal flow sensor 201 based on the zero point drift amount D1 evaluated in step S102 and the zero point drift amount D2 evaluated in step S106 ( FIG. 3 step S107).

When the zero-point drift amount D2 does not change with respect to the zero-point drift amount D1, the drift cause determination unit 24 determines the cause of the zero-point drift as a sensor characteristic change factor (for example, an attack phenomenon due to dirt on the sensor chip or fluid). Is determined. When the zero point drift amounts D1 and D2 substantially match, the drift cause determination unit 24 determines that the zero point drift amount has not changed. The substantially coincidence of the zero point drift amounts D1 and D2 means that the zero point drift amount D2 is within a predetermined range (D1 ± α) centered on the zero point drift amount D1. α is a threshold value and is determined based on the measured signal noise level.

Further, the drift cause determination unit 24 causes the zero point drift when the zero point drift amount D2 evaluated after the fluid supply pressure is reduced by the pressure adjusting device 203 decreases with respect to the zero point drift amount D1. Is determined to be a non-sensor characteristic change factor (for example, fluid convection or fluid leakage). Similarly, the drift cause determination unit 24 does not detect the cause of the zero point drift when the zero point drift amount D2 evaluated after the fluid supply pressure is increased with respect to the zero point drift amount D1. Judged as a characteristic change factor. As described above, when the zero point drift amount D2 is within a predetermined range (D1 ± α), it is not determined to decrease or increase, and the zero point drift amount D2 changes with respect to the zero point drift amount D1. It is determined that it has not been done.

The determination result presenting unit 25 presents the determination result of the drift cause determination unit 24 (step S108 in FIG. 3). In this embodiment, since the offline processing for reducing the flow rate to zero is performed, the determination result presenting unit 25 displays the determination result on, for example, a monitor that can be confirmed by the operator. When the drift evaluation unit 22 confirms that the thermal flow sensor 201 has no zero point drift (NO in step S103), the determination result presenting unit 25 displays the determination result that there is no zero point drift.

As described above, in this embodiment, the cause of the zero point drift of the thermal flow sensor 201 can be estimated at the site where the thermal flow sensor 201 is installed. In this embodiment, even if the thermal flow sensor 201 is not sent to the manufacturer or the calibrator, is the zero point drift of the thermal flow sensor 201 due to a change in the characteristics of the sensor itself or a cause other than the sensor? Can be identified. As a result, in this embodiment, the efficiency of the process for maintaining the accuracy of the flow rate measurement can be improved.

[Second Example]
Next, a second embodiment of the present invention will be described. FIG. 4 is a block diagram showing a configuration of a cause determination device according to a second embodiment of the present invention.
In this embodiment, in a situation where the flow rate of the fluid cannot be reduced to zero (for example, during continuous operation of a manufacturing apparatus using the thermal flow sensor 201), the pipe 200 in which the thermal flow sensor 201 is arranged is connected to the pipe 200. It is assumed that the flow rate measuring device 205 for calibration is inserted in series. Specifically, as shown in FIG. 4, a sub-pipe 204 that branches from the pipe 200 at a portion in front of the thermal flow sensor 201 and joins the pipe 200 in front of the thermal flow sensor 201, and a sub-pipe 204. A flow rate measuring device 205 for measuring the flow rate of the fluid flowing through the auxiliary pipe 204 and a pipe switching unit 206 are provided. The flow rate measuring device 205 includes, for example, a mass flow meter.

The cause determination device of this embodiment includes a target flow rate measurement value acquisition unit 20 (first acquisition unit) that acquires a flow rate measurement value from a thermal flow sensor 201 that is a cause determination target, and a flow rate measurement device 205 for calibration. The reference flow rate measurement value acquisition unit 26 (second acquisition unit) that acquires the reference flow rate measurement value from, and the flow rate measurement value and the reference flow rate measurement value acquisition unit 26 acquired by the target flow rate measurement value acquisition unit 20. If the drift evaluation unit 22a that determines the presence or absence of zero point drift of the thermal flow sensor 201 and detects the amount of zero point drift based on the reference flow rate measurement value, and the thermal flow sensor 201 has zero point drift. A pressure operation instruction unit 23 that outputs an instruction signal for changing the supply pressure of the fluid to the pressure adjusting device 203 arranged in the pipe 200 when the determination is made, and a drift evaluation unit before and after the change in the supply pressure. A drift cause determination unit 24 for determining the cause of the zero point drift of the thermal flow sensor 201 based on the zero point drift amount detected by 22 and a determination result output unit 25a for outputting the determination result are provided.
The reference flow rate measurement value acquisition unit 26 and the drift evaluation unit 22a constitute a zero point drift detection unit 27a.

FIG. 5 is a flowchart illustrating the operation of the cause determination device of this embodiment. First, the pipe switching unit 206 switches the pipes so that all the fluid flows into the sub-pipe 204 before flowing into the thermal flow sensor 201, then returns to the pipe 200 and flows into the thermal flow sensor 201 (step 5). S200). As is clear from FIG. 4, the sub-pipe 204 is arranged so as to branch from the pipe 200, pass through the flow rate measuring device 205, and then join the pipe 200, and the pipe switching portion 206 is the pipe 200 and the sub-pipe 204. It is arranged at the branch. With such a structure, the above-mentioned pipe switching can be realized.

The pipe switching unit 206 may automatically switch the pipe in response to receiving an instruction signal from the operator instructing the cause determination of the zero point drift of the thermal flow sensor 201.

The target flow rate measurement value acquisition unit 20 acquires the flow rate measurement value Q from the thermal flow sensor 201 (step S201 in FIG. 5).
The reference flow rate measurement value acquisition unit 26 acquires the flow rate measurement value (reference flow rate measurement value) QRef from the flow rate measuring device 205 (step S202 in FIG. 5).

The drift evaluation unit 22a zeros the thermal flow sensor 201 based on the flow rate measurement value Q acquired by the target flow rate measurement value acquisition unit 20 and the reference flow rate measurement value Qref acquired by the reference flow rate measurement value acquisition unit 26. The point drift amount D1 is evaluated (step S203 in FIG. 5). FIG. 6 is a flowchart illustrating a method for evaluating the zero point drift amount D1.

First, the drift evaluation unit 22a has an error E1 between the set value of the flow rate measurement value Q (referred to as Q1) and the set value of the reference flow rate measurement value Qref when the flow rate measurement value Q1 is obtained (referred to as Qref1). Is evaluated (FIG. 6, step S300).

Specifically, when the set value Q1 of the flow rate measurement value Q and the set value Qref1 of the reference flow rate measurement value Qref are obtained, the drift evaluation unit 22a determines that the set value Q1 is centered on the set value Qref1. If it is within the range (Qref1 ± TH), the error E1 is set to zero. Further, when the settling value Q1 exceeds a predetermined range (Qref1 ± TH) centered on the settling value Qref1, the drift evaluation unit 22a makes an error of the difference Q1-Qref1 between the settling value Q1 and the settling value Qref1. Let it be E1. As described above, the threshold TH is predetermined based on the measurement signal noise level.

Next, the drift evaluation unit 22a sets a set value (referred to as Q2) of the flow rate measurement value Q different from the flow rate measurement value Q1 and a set value (Qref2) of the reference flow rate measurement value Qref when the flow rate measurement value Q2 is obtained. E2 is evaluated (step S301 in FIG. 6).

Specifically, when the set value Q2 of the flow rate measurement value Q and the set value Qref2 of the reference flow rate measurement value Qref are obtained, the drift evaluation unit 22a determines that the set value Q2 is centered on the set value Qref2. If it is within the range (Qref2 ± TH), the error E2 is set to zero. Further, when the settling value Q2 exceeds a predetermined range (Qref2 ± TH) centered on the settling value Qref2, the drift evaluation unit 22a makes an error of the difference Q2-Qref2 between the settling value Q2 and the settling value Qref2. Let it be E2.

When the errors E1 and E2 are substantially the same (YES in step S302 in FIG. 6), the drift evaluation unit 22a sets the error E1 or the error E2 as the zero point drift amount D1 (step S303 in FIG. 6). Which of the errors E1 and E2 is adopted is predetermined. The substantially coincidence of the errors E1 and E2 means that the error E2 is within a predetermined range (E1 ± β) centered on the error E1. β is a threshold value and is determined based on the measured signal noise level. When the errors E1 and E2 are both zero, the drift evaluation unit 22a determines that the thermal flow sensor 201 has no zero-point drift, and sets the zero-point drift amount D1 to zero.

When the errors E1 and E2 do not match (NO in step S302), the drift evaluation unit 22a determines that the thermal flow sensor 201 has a defect other than the zero point drift (FIG. 6, step S304).
As described above, the drift evaluation unit 22a can evaluate the zero point drift amount D1.

Similar to the first embodiment, the pressure operation indicating unit 23 is a pressure adjusting device when it is confirmed by the drift evaluation unit 22a that the thermal flow sensor 201 has a zero point drift (YES in step S204 of FIG. 5). By outputting an instruction signal for changing the pressure with respect to 203, the supply pressure of the fluid is changed (step S205 in FIG. 5).
In principle, the change in supply pressure may be depressurized or increased, but decompression is preferable from the viewpoint of general safety.

The target flow rate measurement value acquisition unit 20 acquires the flow rate measurement value Q from the thermal flow sensor 201 after the pressure is adjusted by the pressure adjusting device 203 (step S206 in FIG. 5).
The reference flow rate measurement value acquisition unit 26 acquires the reference flow rate measurement value Quref from the flow rate measuring device 205 after the pressure is adjusted by the pressure adjusting device 203 (step S207 in FIG. 5).

The drift evaluation unit 22a zeros the thermal flow sensor 201 based on the flow rate measurement value Q acquired by the target flow rate measurement value acquisition unit 20 and the reference flow rate measurement value Qref acquired by the reference flow rate measurement value acquisition unit 26. The point drift amount D2 is evaluated (step S208 in FIG. 5). FIG. 7 is a flowchart illustrating a method for evaluating the zero point drift amount D2.

First, the drift evaluation unit 22a has an error E3 between the set value of the flow rate measurement value Q (referred to as Q3) and the set value of the reference flow rate measurement value Qref when the flow rate measurement value Q3 is obtained (referred to as Qref3). Is evaluated (FIG. 7, step S400).

Specifically, when the set value Q3 of the flow rate measurement value Q and the set value Qref3 of the reference flow rate measurement value Qref are obtained, the drift evaluation unit 22a determines that the set value Q3 is centered on the set value Qref3. If it is within the range (Qref3 ± TH), the error E3 is set to zero. Further, when the settling value Q3 exceeds a predetermined range (Qref3 ± TH) centered on the settling value Qref3, the drift evaluation unit 22a makes an error of the difference Q3-Qref3 between the settling value Q3 and the settling value Qref3. Let it be E3.

Next, the drift evaluation unit 22a sets a set value (referred to as Q4) of the flow rate measurement value Q different from the flow rate measurement value Q3 and a set value (Qref4) of the reference flow rate measurement value Qref when the flow rate measurement value Q4 is obtained. E4 is evaluated (FIG. 7, step S401).

Specifically, when the set value Q4 of the flow rate measurement value Q and the set value Qref4 of the reference flow rate measurement value Qref are obtained, the drift evaluation unit 22a determines that the set value Q4 is centered on the set value Qref4. If it is within the range (Qref4 ± TH), the error E4 is set to zero. Further, when the settling value Q4 exceeds a predetermined range (Qref4 ± TH) centered on the settling value Qref4, the drift evaluation unit 22a makes an error of the difference Q4-Qref4 between the settling value Q4 and the settling value Qref4. Let it be E4.

When the errors E3 and E4 substantially match (YES in step S402 in FIG. 7), the drift evaluation unit 22a sets the error E3 or error E4 as the zero point drift amount D2 (step S403 in FIG. 7). Which of the errors E3 and E4 is adopted is predetermined. The substantially coincidence of the errors E3 and E4 means that the error E4 is within a predetermined range (E3 ± β) centered on the error E3. When the errors E3 and E4 are both zero, the drift evaluation unit 22a determines that the thermal flow sensor 201 has no zero point drift, and sets the zero point drift amount D2 to zero.

When the errors E3 and E4 do not match (NO in step S402), the drift evaluation unit 22a determines that the thermal flow sensor 201 has a defect other than the zero point drift (FIG. 7, step S404).
As described above, the drift evaluation unit 22a can evaluate the zero point drift amount D2.

The flow rate measurement value Q3 may be a value different from the flow rate measurement values Q1 and Q2, or may be the same value as either of the flow rate measurement values Q1 and Q2. Further, the flow rate measurement value Q4 is a value different from the flow rate measurement value Q3, but may be a value different from the flow rate measurement values Q1 and Q2, or may be the same value as either of the flow rate measurement values Q1 and Q2.

Similar to the first embodiment, the drift cause determination unit 24 of the thermal flow sensor 201 is based on the zero point drift amount D1 evaluated in step S203 and the zero point drift amount D2 evaluated in step S208. The cause of the zero point drift is determined (FIG. 5, step S209).

Specifically, the drift cause determination unit 24 determines that the cause of the zero point drift is a sensor characteristic change system factor when the zero point drift amount D2 does not change with respect to the zero point drift amount D1. Further, the drift cause determination unit 24 causes the zero point drift when the zero point drift amount D2 evaluated after the fluid supply pressure is reduced by the pressure adjusting device 203 decreases with respect to the zero point drift amount D1. Is determined to be a non-sensor characteristic change factor. Similarly, the drift cause determination unit 24 does not detect the cause of the zero point drift when the zero point drift amount D2 evaluated after the fluid supply pressure is increased with respect to the zero point drift amount D1. Judged as a characteristic change factor.

The determination result output unit 25a outputs the determination result of the drift cause determination unit 24 (step S210 in FIG. 5). Similar to the first embodiment, the determination result may be displayed on the monitor, but in this embodiment, since the online processing that does not make the flow rate zero is performed, the determination result output unit 25a is the thermal flow sensor 201. Information indicating that there is a possibility of zero point drift (for example, the cause of zero point drift and the amount of zero point drift D1, D2) In addition to, it is sent to the data storage device on the upper side. As a result, it becomes easy to select data suitable for use in machine learning and data unsuitable for machine learning on the upper side.

Next, the pipe switching unit 206 releases the switching of the pipe in step S200 after the completion of the cause determination process of the zero point drift, and all the fluid flows into the thermal flow sensor 201 without flowing into the sub pipe 204. The piping is returned to the state before the determination process (step S211 in FIG. 5).

The pipe switching unit 206 may automatically switch the pipe in response to the reception of the end instruction signal from the operator instructing the end of the cause determination process of the zero point drift.

As described above, in the present embodiment, the cause of the zero point drift of the thermal flow sensor 201 can be estimated without making the flow rate of the fluid zero at the site where the thermal flow sensor 201 is installed. Therefore, without stopping the operation of the semiconductor manufacturing equipment or heat treatment furnace in which the thermal flow sensor 201 is used, whether the zero point drift of the thermal flow sensor 201 is due to a change in the characteristics of the sensor itself is a cause other than the sensor. It is possible to identify whether there is something.

Further, in this embodiment, since the flow rate measuring device 205 can be removed during the operation of the flow rate measuring system using the thermal flow sensor 201, a semiconductor manufacturing apparatus or a heat treatment furnace in which the thermal flow sensor 201 is used can be removed. The calibration work of the flow rate measuring device 205 can be performed without stopping the operation of.

The cause determination device described in the first and second embodiments can be realized by a computer including a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. A configuration example of this computer is shown in FIG.

The computer includes a CPU 300, a storage device 301, and an interface device (I / F) 302. For example, a thermal flow sensor 201, a flow rate adjusting device 202, a pressure adjusting device 203, a flow rate measuring device 205, and the like are connected to the I / F 302. In such a computer, a program for realizing the cause determination method of the first and second embodiments is stored in the storage device 301. The CPU 300 executes the processes described in the first and second embodiments according to the program stored in the storage device 301.

The present invention can be applied to a flow rate measuring system using a thermal flow sensor.

20 ... Target flow rate measurement value acquisition unit, 21 ... Zero operation instruction unit, 22, 22a ... Drift evaluation unit, 23 ... Pressure operation instruction unit, 24 ... Drift cause determination unit, 25 ... Judgment result presentation unit, 25a ... Judgment result output Unit, 26 ... Reference flow rate measurement value acquisition unit, 27, 27a ... Zero point drift detection unit, 200 ... Piping, 201 ... Thermal flow sensor, 202 ... Flow rate adjusting device, 203 ... Pressure adjusting device, 204 ... Sub piping, 205 … Flow measuring device, 206… Piping switching part.

Claims (12)

A first acquisition unit configured to acquire the flow rate measurement value from a thermal flow sensor that measures the flow rate of the fluid flowing through the pipe, and
A zero-point drift detection unit configured to determine the presence or absence of zero-point drift and detect the amount of zero-point drift of the thermal flow sensor based on the flow rate measurement value.
When it is determined that the thermal flow sensor has a zero point drift, an instruction signal for changing the supply pressure of the fluid is output to the pressure adjusting device arranged in the piping. Pressure operation indicator and
A drift cause determination unit configured to determine the cause of the zero point drift of the thermal flow sensor based on the zero point drift amount detected by the zero point drift detection unit before and after the change in the supply pressure. A cause determination device comprising. In the cause determination device according to claim 1,
The zero point drift detection unit
A zero operation instruction unit configured to output an instruction signal for making the flow rate of the fluid zero to the flow rate adjusting device arranged in the pipe, and a zero operation instruction unit.
A drift evaluation unit configured to determine the presence or absence of zero point drift and detect the amount of zero point drift of the thermal flow sensor based on the flow rate measurement value when the flow rate of the fluid becomes zero. A cause determination device characterized by being composed of and. In the cause determination device according to claim 1,
The zero point drift detection unit
A second acquisition unit configured to acquire a reference flow rate measurement value from a calibration flow rate measuring device arranged in the pipe, and a second acquisition unit.
Based on the flow rate measurement value acquired by the first acquisition unit and the reference flow rate measurement value acquired by the second acquisition unit, it is determined whether or not there is a zero point drift of the thermal flow sensor and the zero point drift. A cause determination device including a drift evaluation unit configured to detect a quantity. In the cause determination device according to claim 3,
The drift evaluation unit has a first value of the flow rate measurement value and a first value of the reference flow rate measurement value simultaneously acquired by the first and second acquisition units before the supply pressure of the fluid changes. And the second value of the flow rate measurement value and the second value of the reference flow rate measurement value simultaneously acquired by the first and second acquisition units before the supply pressure of the fluid changes. Based on the error of, the presence or absence of zero point drift of the thermal flow sensor and the detection of the zero point drift amount are performed, and after the supply pressure of the fluid changes, the first and second acquisition units The error between the third value of the flow rate measurement value and the third value of the reference flow rate measurement value acquired at the same time and the simultaneous acquisition by the first and second acquisition units after the supply pressure of the fluid changes. Based on the error between the fourth value of the flow rate measurement value and the fourth value of the reference flow rate measurement value, the presence or absence of zero point drift of the thermal flow sensor and the detection of the zero point drift amount are performed. A cause determination device, characterized in that In the cause determination device according to any one of claims 1 to 4,
The drift cause determination unit determines that the zero point drift amount is reduced when the zero point drift amount is reduced after the fluid supply pressure is reduced by the pressure adjusting device, or after the zero point drift amount is increased after the fluid supply pressure is increased. If it increases, the cause of the zero point drift is determined to be a non-sensor characteristic change system factor, and if the zero point drift amount does not change before and after the change in the supply pressure, the cause of the zero point drift is determined. A cause determination device characterized in that it is determined to be a sensor characteristic change system factor. In the cause determination device according to claim 5,
The non-sensor characteristic change system factor is the convection or leak of the fluid.
The cause determination device, characterized in that the sensor characteristic change system factor is a stain on the core portion of the thermal flow sensor exposed to the fluid or an attack phenomenon due to the fluid. The first step of acquiring the flow rate measurement value from the thermal flow sensor that measures the flow rate of the fluid flowing through the pipe,
Based on the flow rate measurement value acquired in the first step, the second step of determining the presence or absence of the zero point drift of the thermal flow sensor and detecting the zero point drift amount, and
A third step of outputting an instruction signal for changing the supply pressure of the fluid to the pressure adjusting device arranged in the pipe when it is determined that the thermal flow sensor has a zero point drift.
After adjusting the pressure by the pressure adjusting device, the fourth step of acquiring the flow rate measurement value from the thermal flow sensor, and
Based on the flow rate measurement value acquired in the fourth step, the fifth step of determining the presence or absence of the zero point drift of the thermal flow sensor and detecting the zero point drift amount, and the fifth step.
A cause determination method comprising a sixth step of determining the cause of the zero point drift of the thermal flow sensor based on the zero point drift amount detected in the second and fifth steps. In the cause determination method according to claim 7,
Prior to the first step, a seventh step of outputting an instruction signal for zeroing the flow rate of the fluid to the flow rate adjusting device arranged in the pipe is further included.
In the second and fifth steps, the presence or absence of zero point drift and the detection of the zero point drift amount of the thermal flow sensor are determined based on the flow rate measurement value when the flow rate of the fluid becomes zero. A cause determination method including a step of performing the above. In the cause determination method according to claim 7,
The first and fourth steps include a step of acquiring a reference flow rate measurement value from a calibration flow rate measuring device arranged in the pipe, respectively.
In the second step, the presence or absence of zero point drift and the detection of the zero point drift amount of the thermal flow sensor are determined based on the flow rate measurement value and the reference flow rate measurement value acquired in the first step. Including the steps to do
In the fifth step, the presence or absence of zero point drift and the detection of the zero point drift amount of the thermal flow sensor are determined based on the flow rate measurement value and the reference flow rate measurement value acquired in the fourth step. A cause determination method including a step of performing and. In the cause determination method according to claim 9,
In the second step, the error between the first value of the flow rate measurement value and the first value of the reference flow rate measurement value simultaneously acquired in the first step and the error obtained in the first step are simultaneously acquired. Based on the error between the second value of the flow rate measurement value and the second value of the reference flow rate measurement value, the presence or absence of zero point drift of the thermal flow sensor and the detection of the zero point drift amount are performed. Including steps
In the fifth step, the error between the third value of the flow rate measurement value and the third value of the reference flow rate measurement value acquired at the same time in the fourth step and the error between the third value and the reference flow rate measurement value were acquired at the same time in the fourth step. Based on the error between the fourth value of the flow rate measurement value and the fourth value of the reference flow rate measurement value, the presence or absence of zero point drift of the thermal flow sensor and the detection of the zero point drift amount are performed. A cause determination method including steps. In the cause determination method according to any one of claims 7 to 10,
In the sixth step, when the zero point drift amount decreases after the supply pressure of the fluid is reduced by the pressure regulator, or after the supply pressure of the fluid is increased, the zero point drift amount increases. If it increases, the cause of the zero point drift is determined to be a non-sensor characteristic change system factor, and if the zero point drift amount does not change before and after the change in the supply pressure, the cause of the zero point drift is determined. A cause determination method including a step of determining a sensor characteristic change system factor. In the cause determination method according to claim 11,
The non-sensor characteristic change system factor is the convection or leak of the fluid.
The cause determination method, wherein the sensor characteristic change system factor is a stain on the core portion of the thermal flow sensor exposed to the fluid or an attack phenomenon due to the fluid.

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