KR20180097456A - Apparatus for estimating maintenance decision indicator, flow rate controlling apparatus, and method for estimating maintenance decision indicator - Google Patents

Abstract

An objective of the present invention is to estimate an indicator deciding whether maintenance on a flow rate controlling apparatus and related equipment is required during operation of an apparatus. An apparatus for estimating a maintenance decision indicator comprises: a valve opening degree obtaining unit (3) obtaining an opening degree of a valve when a flow rate of a fluid is maintained at a predetermined target flow rate during flow rate control using the valve to control the flow rate of the fluid; and a flow rate upper limit estimating unit (4) estimating a flow rate upper limit value as a maintenance decision indicator of a flow rate controlling apparatus when it is assumed that the opening degree of the valve reaches an upper limit at the time of acquisition based on a function approximating a relationship between the opening degree of the valve and the flow rate of the fluid and the opening degree of the valve obtained by the valve opening degree obtaining unit (3).

Description

TECHNICAL FIELD [0001] The present invention relates to a maintenance determination indicator estimation apparatus, a flow rate control apparatus, and a maintenance determination indicator estimation method.

TECHNICAL FIELD The present invention relates to a technique for estimating an index of whether or not maintenance is required for a flow control device such as a mass flow controller and related devices such as a filter.

In a semiconductor manufacturing apparatus or the like, a flow rate control device such as a mass flow controller as shown in Fig. 6 is employed to introduce a material gas into the vacuum chamber at a constant flow rate (see Patent Document 1). In Fig. 6, reference numeral 100 denotes a main body block, 101 denotes a sensor package, 102 denotes a head portion of the sensor package 101, 103 denotes a fluid sensor mounted on the head portion 102, 104 Reference numeral 105 denotes an opening at the inlet side of the flow path 105, and reference numeral 107 denotes an opening at the outlet side of the flow path 105. As shown in Fig.

Fluid flows from the opening 106 into the flow path 105 and through the valve 104 and out of the opening 107. The fluid sensor 103 measures the flow rate of the fluid flowing through the flow path 105. A control circuit (not shown) of the mass flow controller drives the valve 104 so that the flow rate of the fluid measured by the fluid sensor 103 coincides with the set value.

While continuing to control the flow rate of the material gas by the mass flow controller, it is possible to prevent dust from adhering to the mass flow controller itself or related equipment such as a filter provided in the flow path of the material gas due to influence of components included in the material gas Or the like may occur.

Therefore, there has been proposed an apparatus for correcting the valve opening degree by manipulating the valve opening so that a flow error or a pressure error does not occur only within the allowable accuracy range over the entire measurement range of the fluid sensor incorporated in the mass flow controller (see Patent Document 2) . However, in the diagnostic apparatus disclosed in Patent Document 2, it can be diagnosed whether or not the error between the measured value of the fluid sensor and the actual flow rate is within a tolerable range in the accurate drawing. However, It is necessary to keep the valve in the fully closed state or to change the valve from the fully closed state to the open state and it is difficult to perform the diagnosis during operation of the apparatus. When the mass flow controller is installed in, for example, a semiconductor manufacturing apparatus, it is difficult to stop the entire semiconductor manufacturing apparatus to diagnose the mass flow controller.

Further, in the diagnostic apparatus disclosed in Patent Document 2, when the mass flow controller is diagnosed at the operation stop timing of the semiconductor manufacturing apparatus, the fluid is introduced into the flow path of the mass flow controller during the operation stop and then the valve is changed to the fully closed state And there is a problem that labor is required for the diagnostic work. In a semiconductor manufacturing apparatus or the like, when it is possible to determine the necessity of maintenance during operation of the apparatus, it is easy to perform the operation management, and therefore, improvement is demanded.

Japanese Patent Application Laid-Open No. 2008-039588 Japanese Patent No. 5931668

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a maintenance judgment index estimating apparatus, a flow rate control apparatus, and a maintenance judgment apparatus capable of estimating an index of whether or not maintenance of a flow rate control apparatus and its related equipment is necessary, And to provide an indicator estimation method.

The maintenance determination criterion estimating device of the present invention is a device for estimating a maintenance judgment index of a fluid flowing through a valve opening configured to acquire the opening degree of the valve when the flow rate of the fluid is maintained at a predetermined target flow rate during flow control, Based on a function approximating the relationship between the opening of the valve and the flow rate of the fluid and the opening degree of the valve acquired by the valve opening degree acquisition section, And a flow rate upper limit estimation unit configured to estimate the flow rate upper limit value when it is assumed that the upper limit is reached as a maintenance determination index of the flow rate control apparatus.

In the configuration of the maintenance judgment index estimating device of the present invention, the flow rate upper limit estimating section may set the upper limit of the degree of opening of the valve corresponding to the flow rate upper limit value to 100%.

Further, in one configuration example of the maintenance judgment index estimating apparatus of the present invention, the function is defined by at least a term relating to the degree of opening of the valve and a gain which is a numerical value multiplied by the term, Wherein the flow rate upper limit value is estimated based on a formula obtained from the function and an opening degree of the valve acquired by the valve opening degree acquisition section when it is assumed that the gain decreases with time .

Further, in one configuration example of the maintenance judgment index estimating device of the present invention, the function is a function approximating a nonlinear relationship between the opening of the valve and the flow rate of the fluid, and the term relating to the opening degree of the valve is expressed as an exponential function .

 Further, in one configuration example of the maintenance judgment index estimating device of the present invention, the function is a function approximating a nonlinear relationship between the opening of the valve and the flow rate of the fluid, and the term relating to the degree of opening of the valve is expressed by a fraction function .

Further, in an example of the configuration of the maintenance judgment index estimating apparatus of the present invention, the flow rate upper limit estimating section may calculate the flow rate upper limit value based on the opening degree of the valve acquired by the valve opening degree acquiring section at the present time point, A gain calculating section for calculating the present gain at the present time and a flow rate upper limit calculating section for calculating the flow rate upper limit value based on the gain calculated by the gain calculating section.

Further, an example of the construction of the maintenance judgment index estimating device of the present invention is characterized by further comprising: an estimation result outputting section for numerically displaying the flow rate upper limit value estimated by the flow upper limit estimating section.

Further, an example of the configuration of the maintenance judgment index estimating apparatus of the present invention is characterized by further comprising an estimation result outputting section for issuing an alarm when the flow rate upper limit value estimated by the flow rate upper limit estimating section becomes less than a predetermined threshold value .

The flow rate control device of the present invention further includes a flow rate measuring section for measuring a flow rate of the fluid flowing through the flow path, a valve provided in the flow path, and a valve control section for controlling the flow rate of the fluid, And a maintenance determination criterion estimating device, wherein the valve opening degree obtaining section of the maintenance determination criterion estimating device obtains the degree of opening of the valve provided in the flow path.

The maintenance determination index estimation method of the present invention is a method for estimating a maintenance determination index of a fluid by controlling a flow rate of the fluid by using a valve, The opening degree of the valve reaches the upper limit based on the first step and the function approximating the relationship between the opening of the valve and the flow rate of the fluid and the opening degree of the valve acquired in the first step And a second step of estimating a flow rate upper limit value in the case where the flow rate control apparatus is assumed as a maintenance determination index of the flow rate control apparatus.

According to the present invention, it is possible to estimate the determination index (flow upper limit value) as to whether maintenance of the flow control device and its related equipment is necessary during operation of the apparatus. As a result, on the operator side, it becomes easy to operate and manage the semiconductor manufacturing apparatus and the like equipped with the flow rate control device. Further, in the present invention, it is possible to greatly reduce the labor required for judging whether maintenance is required or not.

1 is a diagram showing an example of a relationship between an opening of a valve provided in a mass flow controller and a flow rate of a fluid.
2 is a view showing another example of the relationship between the opening of the valve provided in the mass flow controller and the flow rate of the fluid.
3 is a block diagram showing the configuration of a flow rate control apparatus according to an embodiment of the present invention.
4 is a flow chart for explaining the flow control operation of the flow control device according to the embodiment of the present invention.
5 is a flowchart illustrating a maintenance determination index estimation operation of the flow rate control apparatus according to an embodiment of the present invention.
6 is a cross-sectional view of the mass flow controller.

[Principle of the invention]

The use of the mass flow controller is in many cases to stably maintain the flow rate of the fluid at the target flow rate determined in advance. Therefore, assuming such a use, the influence of the clogging of the filter can be estimated to be a highly reliable detection condition. More specifically, a state in which the target flow rate is stably maintained is detected, and the valve opening degree indicating signal in the condition is obtained.

Considering the case where the filter installed upstream of the mass flow controller is clogged, the flow rate which can be reached at the state in which the valve opening degree is saturated at 100% at that point is the upper limit value of the controllable flow rate at that point, , It is effective to estimate whether or not the maintenance is to be performed by estimating the upper limit value. Therefore, the inventors of the present invention have been able to obtain information on the valve opening degree with high reliability based on the use conditions peculiar to the mass flow controller, and to provide an upper limit value of the flow rate estimated therefrom (for example, an estimated flow rate at 100% It is reasonable to make a judgment index as to whether or not it is necessary.

[Example]

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Patent Document 2 shows that when the opening degree of the valve provided in the mass flow controller is changed linearly with time, the flow volume of the fluid flowing through the flow path becomes smaller toward the hinge opening side. As described above, it is known that the valve opening degree MV and the flow amount PV have a nonlinear relationship, and the amount of change in the flow rate PV decreases with respect to the variation amount of the opening degree MV as the side closer to the hinge plane. An overview of the characteristics of such a mass flow controller is shown in Fig. On the other hand, in the example of Fig. 1, the flow rate (PV) is normalized to a value of 0 to 100%. Since the characteristic shown in Fig. 1 is a nonlinear convergence phenomenon, it can be expressed by an exponential function of the following equation.

PV = K {1.0-exp (-MV / A)} ... (One)

The function approximating the relationship between the valve opening degree MV and the flow rate PV is defined as a function of the constant term 1.0 and the term relating to the valve opening degree MV and the gain K, Lt; / RTI > A in Equation (1) is a coefficient giving a nonlinear convergence state. Curve cur1 in Fig. 1 shows the initial characteristics of the mass flow controller. It is assumed that the flow rate (PV) becomes the maximum value 100% at the valve opening degree (MV) = 100% and the curve cur1 is set to the coefficient value Can be expressed as an exponential function of.

 PV = 104.0 {1.0-exp (-MV / 30.0)} ... (2)

K = 104.0 and A = 30.0 in equation (2) are examples of these values. In the case of the clogging of the filter installed in the flow path, it can be assumed that the nonlinearity, which is the characteristic of the valve itself of the mass flow controller downstream of the filter, does not change, so that the coefficient A can be regarded as being constant. Therefore, it is assumed that only the gain K decreases due to clogging of the filter or the like.

In determining whether maintenance of the mass flow controller or related equipment of the mass flow controller is necessary, it is presumed that some factor influences the operation time of the mass flow controller. However, It is reasonable to assume that the gain (K) decreases with a constant gentle pace to the extent that there is no rapid deterioration.

Here, it is assumed that the predetermined target flow rate PVx is PVx = 60.0%. In other words, SPx = 60.0% is the most standard value given as the flow set value SP of the mass flow controller. When the valve opening degree in the initial state of the mass flow controller for correcting (setting) the fluid flow rate to PVx = 60.0% is MV1, MV1 = 25.8% by curve cur1. Since the coefficient A of the nonlinear characteristic A = 30.0 has been previously grasped, the initial state gain K1 can be inversely calculated based on PVx = 60.0% and MV1 = 25.8%. On the other hand, in this initial state, the flow rate (upper flow rate limit PVh) at 100% of the valve opening degree is PVh = 100% as described above.

K1 = PVx / {1.0-exp (-MV1 / A)}

  = 60.0 / {1.0-exp (-25.8 / 30.0)} = 104.0 ... (3)

Next, the valve opening degree (MV) for maintaining the target flow rate (PVx) at the time when the operation time of the mass flow controller has elapsed to such an extent that clogging of the filter occurs is acquired. At this time, the target flow rate PVx may be a value different from the target flow rate PVx in the initial state. Here, the target flow rate PVx = 40.0%. For example, it is assumed that MV2 = 16.2% is detected as the valve opening degree (MV) for maintaining the target flow rate PVx = 40.0% at 72 hours from the start of operation. This value indicates that the valve opening degree (MV) for maintaining the target flow amount PVx = 40.0% is set to MV2 = 16.2% because the pressure at the point at which the fluid flows into the mass flow controller is lowered due to the clogging of the filter It means that you should not have to.

The gain K2 at 72 hours from the start of operation can be inversely calculated according to the following equation based on PVx = 40.0% and MV2 = 16.2%.

K2 = PVx / {1.0-exp (-MV2 / A)}

  = 40.0 / {1.0-exp (-16.2 / 30.0)} = 96.0 (4)

Therefore, it is estimated that the gain K decreased from 8.0 in the initial state, K1 = 104.0 to K2 = 96.0, by 8.0 in 72 hours. In this case, the characteristics of the mass flow controller are as shown by the curve cur2 in Fig. Then, in the state of cur2, the flow rate (upper flow rate limit PVh) at the valve opening degree of 100% can be calculated by the following equation.

PVh = 96.0 {1.0-exp (-100.0 / 30.0)} = 96.6 ... (5)

Thus, it can be judged that PVh = 96.6% is the upper limit value of the controllable flow rate in the state of cur2, which is not so serious. That is, the maintenance of the mass flow controller becomes a judgment index that it is not necessary yet.

Since it is assumed that the gain K decreases at a constant pace roughly in proportion to the running time of the mass flow controller, when the time elapses from the state of cur2 for about 72 hours, the gain K is possibly decreased by about 8.0, It can be assumed that the characteristic of the mass flow controller is like the curve cur3 (K3 = 88.0) in Fig. In the state of cur3, the flow rate (upper flow rate limit value PVh) at the valve opening degree of 100% can be calculated by the following equation. However, only when the gain K decreases at a constant pace.

PVh = 88.0 {1.0-exp (-100.0 / 30.0)} = 84.9 ... (6)

The above is summarized as follows. In the initial state (cur1), PVh = 100.0% can be estimated from the results of PVx = 60.0% and MV1 = 25.8%. In the state (cur2) after 72 hours from the start of operation, PVh = 96.6% can be estimated from the results of PVx = 40.0% and MV2 = 16.2%. In the state (cur3) after 72 hours have elapsed, PVh = 84.9% can be estimated.

Next, it is assumed that the valve opening degree (MV) for holding the target flow rate PVx is acquired at a time point of time elapses. At this time, it is assumed that the target flow rate PVx is set to 30.0% and MV4 = 19.8% is detected as the valve opening degree MV for maintaining the target flow rate PVx = 30.0%. In this case, based on PVx = 30.0% and MV4 = 19.8%, the gain K4 can be inversely calculated as shown in the following equation.

K4 = PVx / {1.0-exp (-MV4 / A)}

  = 30.0 / {1.0-exp (-19.8 / 30.0)} = 62.0 (7)

In this case, the characteristics of the mass flow controller are as shown by the curve cur4 in Fig. In this state of cur4, the flow rate (upper flow rate limit PVh) at the valve opening degree of 100% can be calculated by the following equation.

PVh = 62.0 {1.0-exp (-100.0 / 30.0)} = 59.8 ... (8)

Thus, PVh = 59.8% is the upper limit of the controllable flow rate in the state of cur4. As a result of the past, there is a case where the target flow rate PVx is set to 60.0%, and PVh = 59.8% is less than the past target flow rate PVx. That is, it becomes a determination index that maintenance of the mass flow controller is required.

From the above, the order of obtaining the index of the necessity of maintenance of the mass flow controller and its related equipment can be summarized as follows (I) and (II). According to this embodiment, it is possible to obtain a proper judgment index even when it appears that there is a margin in the valve opening degree because the low flow rate and low opening degree (the valve opening degree is sufficiently away from the upper limit) are controlled.

(I) A valve opening (MV) for maintaining the flow rate of the fluid at an arbitrary target flow rate (PVx) was obtained. Based on the valve opening degree MV, the gain K is calculated. However, the nonlinearity coefficient A is prescribed in advance.

K = PVx / {1.0-exp (-MV / A)} ... (9)

(II) The flow rate when the valve opening degree MV becomes the upper limit 100% is calculated as the controllable flow rate upper limit value PVh, and the flow rate upper limit value PVh is calculated as the flow rate upper limit value PVh, As the judgment index of whether or not

PVh = K {1.0-exp (-100.0 / A)} ... (10)

On the other hand, if the nonlinearity of Fig. 1 can be approximated, the same method can be applied in addition to the exponential function. For example, if the following function is a fractional function, the valve opening and the nonlinearity of the flow rate can be described only by arithmetic operation.

PV = K [{- A / (MV + B)} + C]

  = 1.0 [{- 3130.0 / (MV + 25.0)} + 125.2] ... (11)

K = PVx / [{- A / (MV + B)} + C] ... (12)

PVh = K [{- A / (100.0 + B)} + C] ... (13)

Similarly to the equation (1), the function of the equation (11) is defined by the terms relating to the constant term (C = 125.2) and the valve opening degree (MV) and the gain (K) According to the equations (11) to (13), the characteristics of the mass flow controller can be represented by the same Fig. 2 as in Fig. The gain K1 in the state of the curve cur1 in FIG. 2 is 1.0, the gain K2 in the state of the curve cur2 is 0.923, the gain K3 in the state of the curve cur3 is 0.846, And the gain K4 in this case is 0.596. That is, as in the example of Fig. 1, the gain K decreases at a constant pace in proportion to the operating time.

Next, the configuration of the flow control device (mass flow controller) of the present embodiment will be described. As shown in FIG. 3, the flow rate control apparatus of the present embodiment is provided with a flow rate measuring section 1 for measuring a flow rate of a fluid flowing in a flow path, a flow rate measuring section 1 for measuring a flow rate, A valve opening degree obtaining section 3 for obtaining a valve opening degree MV when the flow rate of the fluid is maintained at a predetermined target flow rate PVx during the flow rate control, And a flow rate upper limit estimating section 4 for estimating the flow rate upper limit value PVh when the valve opening degree reaches the upper limit (for example, 100%) at the time of acquisition of the valve opening degree MV as a maintenance determination index , And an estimation result output section (5) for outputting information on the estimation result of the flow upper limit estimation section (4).

Next, the operation of the flow rate control apparatus of this embodiment will be described with reference to Figs. 4 and 5. Fig. FIG. 4 is a flowchart for explaining the flow control operation, and FIG. 5 is a flowchart for explaining the operation of the maintenance determination indicator.

The flow rate measuring section 1 continuously measures the flow rate of the fluid flowing through the flow path (flow path 105 in Fig. 6) (step S100 in Fig. 4). The flow rate measuring section 1 corresponds to the fluid sensor 103 in Fig. 6, and has a well-known configuration provided in the mass flow controller.

The flow control unit 2 continuously operates the valve (the valve 104 in Fig. 6) so that the flow rate of the fluid measured by the flow rate measuring unit 1 matches the target flow rate PVx set by the operator, for example (Step S101). This flow control unit 2 also has a well-known configuration provided in the mass flow controller.

In this manner, for example, the processes of steps S100 and S101 are repeatedly executed at prescribed intervals (for example, 50 msec) until the operator instructs the end of operation of the apparatus (YES in step S102 in Fig. 4).

On the other hand, the valve opening degree acquisition section 3 acquires the valve opening degree MV (target holding valve opening degree) when the flow rate of the fluid is maintained at the target flow rate PVx (step S200 in Fig. 5 ). Specifically, the valve opening degree acquisition section 3 acquires the valve opening degree acquisition section 3 in such a manner that the absolute value of the deviation between the flow rate measured by the flow rate measurement section 1 and the target flow rate PVx continues to fall within the specified value , It is determined that the flow rate of the fluid is maintained at the target flow rate (PVx), and the current valve opening degree (MV) is acquired. The value of the constant time t is set in the valve opening degree acquisition section 3 as a prescribed value.

On the other hand, although the valve opening degree itself may be detected, the actual valve opening degree is not detected, and a signal (for example, valve opening degree indicating signal or valve driving current) output to the valve from the flow rate control section 2 is acquired , The valve opening degree may be determined based on this signal.

Next, based on the valve opening degree MV (target holding valve opening degree) acquired by the valve opening degree acquisition section 3, the flow rate upper limit estimation section 4 calculates the upper limit value (For example, 100%) is estimated as a determination index called a controllable flow rate. 3, the flow rate upper limit estimating section 4 includes a gain calculating section 40 for calculating the gain K and a flow rate upper limit calculating section 41 for calculating the flow rate upper limit value PVh .

The gain calculating section 40 of the flow upper limit estimating section 4 calculates the gain K at the present point in time to calculate the flow upper limit value PVh by using the equation 9 at step S201 in FIG. The coefficient A in the equation (9) is set in the flow rate upper limit estimation section 4 as a prescribed value. In order to grasp the coefficient A, for example, a flow rate test of the flow rate control device may be performed in advance to check the value of the coefficient A. [

The flow upper limit calculating section 41 of the flow upper limit estimating section 4 calculates the flow upper limit value PVh based on the gain K calculated by the gain calculating section 40 (Step S202 in Fig. 5). Thus, the process of the flow rate upper limit estimation unit 4 is ended.

The estimation result output unit 5 outputs the estimation result of the flow upper limit estimation unit 4 (step S203 in Fig. 5). Examples of the output method of the estimation result are numerical display of the flow upper limit value PVh, alarm output based on the flow upper limit value PVh, transmission of the estimation result information to the outside, and the like. In the case of the alarm output, when the flow rate upper limit value PVh becomes less than a predetermined threshold value (for example, less than 60%), the LED for notifying the alarm can be turned on.

The valve opening degree acquisition section 3, the flow rate upper limit estimation section 4 and the estimation result output section 5 wait until the operation end of the apparatus is instructed by the operator (YES in step S204 in Fig. 5) The processes of steps S200 to S203 are repeatedly executed every predetermined period DELTA T (for example, 24 hours).

As described above, in the present embodiment, it is possible to estimate the determination index (flow upper limit value PVh) as to whether or not maintenance is required for the flow control device and its related equipment (filter installed in the flow path, etc.) during operation of the apparatus . The operator can judge whether or not a serious situation requiring maintenance is reached based on the estimation result of the flow rate control device, so that the operator can easily manage the semiconductor manufacturing apparatus and the like. In addition, in the present embodiment, since it is not necessary to carry out the operation of introducing the fluid into the flow path of the mass flow controller during the shutdown of the semiconductor manufacturing apparatus, it is possible to greatly reduce the labor required for judging whether maintenance is required or not.

On the other hand, when the valve opening degree acquisition section 3 determines that the flow rate of the fluid is not maintained at the target flow rate PVx, the valve opening degree MV can not be obtained. In this case, Can not be calculated.

The present embodiment can also be applied to the case where the target flow rate PVx is changed on the way, but it is also possible to determine whether or not the flow rate of the fluid is maintained at the target flow rate PVx During the period of time t (t <? T), the target flow rate PVx needs to be maintained at the same value. When the target flow amount PVx is changed during the period of the constant time t, the valve opening degree MV can not be obtained.

The flow rate upper limit estimating unit 4 may calculate the gain K and the flow rate upper limit value PVh using the equations (12) and (13) instead of the equations (9) . The coefficients A, B, and C in the equations (12) and (13) are set in the flow rate upper limit estimating unit 4 as prescribed values. In order to grasp the coefficients A, B, and C, for example, a flow rate test of the flow rate control device may be performed in advance.

In the present embodiment, all of the components shown in Fig. 3 are provided in the flow control device (mass flow controller), but the present invention is not limited to this. The valve opening degree acquisition section 3, the flow upper limit level estimation section 4 and the estimation result output section 5 are installed in a host device (for example, a programmable logic controller (PLC)) as a maintenance determination index estimation device, 1 and the flow rate control section 2 may be used in combination with a general micro flow controller.

The flow rate control device described in this embodiment can be realized by a computer having a CPU (Central Processing Unit), a storage device and an interface, and a program for controlling these hardware resources. Likewise, the maintenance determination index estimation device including the valve opening degree acquisition section 3, the flow upper limit level estimation section 4, and the estimation result output section 5 can be realized by a computer and a program. The CPU of each apparatus executes the processing described in this embodiment in accordance with the program stored in each storage device. Thus, the maintenance determination index estimation method of the present embodiment can be realized.

The present invention can be applied to a technique for managing a flow control device and its related devices.

1: Flow measuring part 2: Flow control part
3: valve opening degree acquisition unit 4: flow rate upper limit estimation unit
5: estimation result output unit 40: gain calculation unit
41: Flow rate upper limit calculating section

Claims (10)

A valve opening degree acquiring section configured to acquire an opening degree of the valve when the flow rate of the fluid is maintained at a predetermined target flow rate during flow rate control for controlling the flow rate of the fluid using a valve;
Based on a function approximating the relationship between the opening of the valve and the flow rate of the fluid and the opening degree of the valve acquired by the valve opening degree acquiring section, assuming that the opening degree of the valve has reached the upper limit at the time of acquisition A flow rate upper limit estimating section configured to estimate the flow rate upper limit value in one case as a maintenance judgment index of the flow rate control device,
Wherein the maintenance estimating index estimating apparatus comprises: The maintenance evaluation index estimating apparatus according to claim 1, wherein the flow rate upper limit estimating section sets the upper limit of the degree of opening of the valve corresponding to the flow rate upper limit value as 100%. 3. The method according to claim 1 or 2, wherein the function is defined by at least a term relating to the degree of opening of the valve and a gain which is a numerical value multiplied by this term,
The flow rate upper limit estimating section may estimate the flow rate upper limit value based on a formula obtained from the function and an opening degree of the valve acquired by the valve opening degree acquisition section on the assumption that the gain decreases with passage of time, Wherein the maintenance determination index estimating unit estimates the maintenance determination index. 4. The maintenance determination indicator estimating apparatus according to claim 3, wherein the function is a function approximating a nonlinear relationship between the opening of the valve and the flow rate of the fluid, and the term relating to the degree of opening of the valve is expressed by an exponential function. 4. The maintenance determination indicator estimating apparatus according to claim 3, wherein the function is a function approximating a nonlinear relationship between the opening of the valve and the flow rate of the fluid, and the term relating to the degree of opening of the valve is expressed by a fraction function. 4. The apparatus according to claim 3, wherein the flow-
A gain calculating section for calculating the present gain at the present time based on the opening of the valve and the target flow rate acquired by the valve opening degree acquiring section at the present time for estimating the flow rate upper limit value;
Based on the gain calculated by the gain calculating section, a flow rate upper limit calculating section
Wherein the maintenance estimating index estimating unit is configured to estimate the maintenance index. 3. The maintenance determination indicator estimating apparatus according to claim 1 or 2, further comprising an estimation result outputting section for numerically displaying the flow rate upper limit value estimated by the flow upper limit estimating section. 3. The apparatus according to claim 1 or 2, further comprising: an estimation result output unit for generating an alarm when the flow rate upper limit value estimated by the flow upper limit estimation unit becomes less than a predetermined threshold value Device. A flow rate measuring section for measuring a flow rate of the fluid flowing through the flow path,
A valve provided in the flow path,
A flow rate control unit operable to operate the valve so that the flow rate measured by the flow rate measurement unit matches a predetermined target flow rate,
The maintenance determination index estimating apparatus according to claim 1 or 2,
And,
Wherein the valve opening degree acquiring section of the maintenance determination criterion estimating device acquires an opening degree of the valve installed in the flow path. A first step of acquiring an opening degree of the valve when the flow rate of the fluid is maintained at a predetermined target flow rate during flow rate control for controlling the flow rate of the fluid using a valve;
A function of approximating the relationship between the opening of the valve and the flow rate of the fluid and the opening degree of the valve acquired in the first step and assuming that the opening degree of the valve has reached the upper limit at the time of acquisition A second step of estimating the flow rate upper limit value as a maintenance determination index of the flow rate control device
Wherein the maintenance estimating index is estimated by the estimating means.

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