JP7833866B2 - Control unit, fluid control device, valve diagnostic program, and valve diagnostic method - Google Patents

Description

This invention relates to a control unit, a fluid control device, a valve diagnostic program, and a valve diagnostic method.

For example, if a malfunction occurs in a fluid control valve during a process, the process can become inefficient, resulting in significant losses. Furthermore, changes in valve opening over time can worsen controllability, including response speed. For these reasons, there is a growing demand for a function that can self-diagnose the condition of fluid control valves and predict failures or malfunctions in advance.

In this context, prior art (1) discloses a system for inspecting the Cv value of a fluid control valve while it is integrated into a system such as semiconductor manufacturing equipment, because the Cv value changes when the valve seat of the fluid control valve wears or deforms.

To explain in more detail, in this system, the fluid control valve is fully opened to allow fluid to flow, and the regulator is controlled to bring the differential pressure value of the differential pressure gauge to a predetermined value. The Cv value is then calculated using the flow rate value from the flow sensor under these conditions, and it is determined whether this calculated Cv value is within the appropriate range.

However, this method requires fully opening the fluid control valve or adjusting the differential pressure of the differential pressure gauge to a predetermined value. Therefore, to know the state of the fluid control valve via the Cv value, the process must be stopped. Conversely, this means that it's impossible to predict during the process whether a malfunction or abnormality has occurred in the fluid control valve.

Japanese Patent Publication No. 2021-56806

Therefore, this invention was made to solve the above-mentioned problems, and aims to enable the diagnosis of the fluid control valve's condition during the process.

In other words, the control unit according to the present invention is characterized by comprising: a correlation data storage unit that stores Cv value-voltage correlation data showing the correlation between the Cv value of the fluid control valve under normal conditions or a reference Cv value (a value related thereto) and the valve voltage; an actual Cv value calculation unit that calculates the actual Cv value (a value related thereto) at a predetermined timing during actual flow rate control; a reference Cv value acquisition unit that acquires the reference Cv value corresponding to the valve voltage of the fluid control valve at the predetermined timing based on the Cv value-voltage correlation data; and a valve diagnostic unit that compares the reference Cv value and the actual Cv value.

With the control unit configured in this way, the actual Cv value calculated at a predetermined timing during actual flow rate control is compared with a reference Cv value corresponding to the valve voltage at that predetermined timing. Therefore, the state of the fluid control valve can be diagnosed during the process of actual flow rate control.

Incidentally, since the type of gas controlled by the fluid control valve can change from process to process, it is desirable that the diagnosis of the state of the fluid control valve described above be performed appropriately according to the various types of gas.
Therefore, the inventors of this application experimentally determined the above-mentioned Cv value-voltage correlation data for various gas types and found that the Cv value of a fluid control valve under normal conditions differs depending on the gas type, even when the valve voltage is the same. It should be noted that the Cv value is often used as an indicator of the flowability of an ON/OFF valve, and in this technical field, it is common technical practice to use the same Cv value regardless of the gas type.

In light of the new findings described above, storing various Cv value-voltage correlation data for various gas types in the correlation data storage unit allows for appropriate diagnosis of whether a fluid control valve is malfunctioning, depending on the gas type. However, this requires considerable effort and time, as the number of gas types that can be used in the process increases, so does the amount of Cv value-voltage correlation data that must be obtained experimentally beforehand.

Therefore, it is preferable that the actual Cv value is a value obtained by correcting the Cv value at the predetermined timing using physical properties determined according to the type of gas controlled by the fluid control valve.
With this configuration, by pre-determining a reference gas type (hereinafter referred to as the reference gas), when the gas type used in the process (hereinafter referred to as the controlled gas) differs from the reference gas, the physical properties determined according to these controlled gases are used for correction. Therefore, the calculated actual Cv value is calculated as the Cv value if the controlled gas were the reference gas.
This allows the Cv value-voltage correlation data for a reference gas species to be experimentally determined and then used for various gas species used in the process. In other words, the Cv value-voltage correlation data can be unified (standardized).
As a result, it becomes possible to appropriately diagnose the condition of fluid control valves according to various gas types without requiring much time or effort.

A more specific embodiment is one in which the actual Cv value is a value obtained by correcting the Cv value at the predetermined timing using the molecular weight of the gas controlled by the fluid control valve.

It is preferable that the correlation data storage unit stores a calculation formula for calculating the reference Cv value, which includes the valve voltage as a variable, as the Cv value-voltage correlation data.
This allows for a reduction in the memory capacity required for the correlation data storage unit.

Furthermore, it is preferable to store the diagnostic results from the valve diagnostic unit in internal or external memory.
This allows for retrospective analysis of the causes of abnormalities that occur in fluid control valves.

Preferably, the valve diagnostic unit further includes an abnormality notification unit that compares the actual Cv value and the reference Cv value during actual flow rate control to diagnose whether or not an abnormality has occurred in the fluid control valve, and outputs an abnormality signal indicating that an abnormality has occurred in the fluid control valve during actual flow rate control.
With this configuration, if a malfunction occurs in the fluid control valve, it can be detected in real time during the process, allowing for appropriate action to be taken.

Incidentally, in transient states such as those after a set flow rate has been input to a fluid control valve, the fluid flow rate is not stable. If a diagnosis is made using an actual Cv value calculated under such conditions, it is difficult to obtain a reliable diagnostic result.
Therefore, it is preferable to further include a state determination unit that determines whether or not the flow rate of the fluid controlled by the fluid control valve is stable, and after the state determination unit determines that the flow rate is stable, the valve diagnostic unit starts comparing the actual Cv value and the reference Cv value.
With this configuration, the valve diagnostic unit starts the diagnosis only after the state determination unit has determined that the flow rate is stable, thus enabling the acquisition of highly reliable diagnostic results.

A fluid control device equipped with the control unit described above is also one of the present inventions, and such a fluid control device can achieve the same effects as the control unit described above.

Furthermore, the valve diagnostic program according to the present invention is characterized by comprising: a correlation data storage unit that stores Cv value-voltage correlation data showing the correlation between the Cv value or a related value (reference Cv value) of a fluid control valve under normal conditions and the valve voltage; an actual Cv value calculation unit that calculates the actual Cv value or a related value (actual Cv value) at a predetermined timing during actual flow rate control; a reference Cv value acquisition unit that acquires the reference Cv value corresponding to the valve voltage of the fluid control valve at the predetermined timing based on the Cv value-voltage correlation data; and a valve diagnostic unit that causes a computer to perform the function of comparing the reference Cv value and the actual Cv value.

Furthermore, the valve diagnostic method according to the present invention is characterized by comprising: a correlation data storage step for storing Cv value-voltage correlation data showing the correlation between the Cv value or a related value (reference Cv value) of a fluid control valve under normal conditions and the valve voltage; an actual Cv value calculation step for calculating the actual Cv value or a related value (actual Cv value) at a predetermined timing during actual flow rate control; a reference Cv value acquisition step for acquiring the reference Cv value corresponding to the valve voltage of the fluid control valve at the predetermined timing based on the Cv value-voltage correlation data; and a valve diagnostic step for comparing the reference Cv value and the actual Cv value.

The valve diagnostic program and valve diagnostic method described above can achieve the same effects as the fluid control device described above.

According to the present invention described above, the state of the fluid control valve can be diagnosed during the process. This allows for self-diagnosis of the fluid control valve's state, such as changes in valve opening over time, without requiring a separate process for diagnosing the fluid control valve, and enables the prediction of malfunctions or abnormalities in advance.

A schematic diagram showing the configuration of a fluid control device according to one embodiment of the present invention. A functional block diagram showing the functions of the control unit in the same embodiment. A graph showing the correlation between the Cv value and valve voltage in the same embodiment. A graph showing the correlation between the corrected Cv value and the valve voltage in the same embodiment. A flowchart illustrating the operation of the control unit in this embodiment. A functional block diagram showing the functions of the control unit in another embodiment.

A fluid control device according to one embodiment of the present invention will be described below with reference to the drawings.

This fluid control device 100 controls the flow rate of fluids used, for example, in semiconductor manufacturing processes. As shown in Figure 1, it is a mass flow controller comprising a metal (e.g., stainless steel) block B with an internal fluid channel X (hereinafter also referred to as the main channel X) formed within it, a flow sensor S and a fluid control valve V provided in the block B, and a control unit Z that controls the opening degree of the fluid control valve V. The fluid control device 100 here further includes a temperature sensor (not shown) for detecting ambient temperature.

In this embodiment, the flow sensor S is a thermal type, and a pressure sensor P is provided upstream of this thermal flow sensor S. However, the flow sensor S may also be a pressure type.

The control unit Z is a so-called computer equipped with a CPU, memory, A/D converter, D/A converter, and various input/output devices. As shown in Figure 1, it includes at least two functions: a flow rate calculation unit Z1 that calculates the mass flow rate of gas flowing through the main flow path X based on the output signal from the flow rate sensor S, and a valve control unit Z2 that controls the valve voltage applied to the fluid control valve V so that the calculated flow rate calculated by the flow rate calculation unit Z1 approaches the set flow rate.

Therefore, this control unit Z executes the valve diagnostic program stored in the memory, and, through the cooperation of the CPU and peripheral devices, further provides the functions of a correlation data storage unit Z3, an actual Cv value calculation unit Z4, a reference Cv value acquisition unit Z5, and a valve diagnostic unit Z6, as shown in Figure 2.

Before explaining each part, let's discuss the Cv value.

The Cv value is an indicator of how easily fluid flows through a fluid control valve V. A higher Cv value indicates that the fluid flows more easily through the fluid control valve V. This Cv value is calculated using a predetermined formula, specifically using the following formula (1).
Qg is the flow rate of the fluid flowing through the fluid control valve V, P1 is the differential pressure between the upstream and downstream sides of the fluid control valve V, Gg is the specific gravity of the fluid flowing through the fluid control valve V, and T is the ambient temperature of the fluid control valve V.

In this embodiment, Qg is the set flow rate set in the fluid control valve V, P1 is the detected pressure detected by the pressure sensor P described above, Gg is the specific gravity of the fluid when the specific gravity of air is set to 1, and T is the detected temperature detected by the temperature sensor (not shown) mounted on the fluid control device 100.

Thus, the Cv value is caused by the differential pressure between the upstream and downstream sides of the fluid control valve V, and is a value that fluctuates according to the valve opening of the fluid control valve V, i.e., the valve voltage applied to the fluid control valve V.

The graph shown in Figure 3 experimentally determines the correlation between the Cv value and valve voltage under normal operating conditions for the fluid control valve V. Specifically, it plots the Cv value when the valve voltage is varied under normal operating conditions for the fluid control valve V.

From Figure 3, a linear correlation exists between the Cv value and the valve voltage. In other words, the Cv value can be approximately expressed by a linear equation with the valve voltage as the variable.

On the other hand, Figure 3 shows that the correlation between the Cv value and valve voltage differs depending on the type of gas. That is, the Cv value of the fluid control valve V under normal conditions will differ depending on the type of gas, even if the valve voltage is the same. Specifically, the slope of the linear correlation between the Cv value and valve voltage differs depending on the type of gas.

In response to these differing correlations depending on the gas type, the inventors of this invention have found that by correcting the Cv value of the fluid control valve V under normal conditions using a physical property value determined according to the gas type, the correlation between the corrected Cv value and the valve voltage can be unified (see Figure 4).

To explain in more detail, if, for example, the molecular weight of the gas is used as the physical property value mentioned above, the Cv value of the fluid control valve V under normal conditions, which was obtained experimentally, is first corrected using the following correction formula (2) to calculate the corrected Cv value.
In this case, M is the molecular weight of the controlled gas flowing through the fluid control valve V, and the term (M/28.01) represents the ratio of the molecular weight of the controlled gas to the molecular weight of a pre-selected reference gas. The reference gas in this case is _N2 gas with a molecular weight of 28.01.

Furthermore, when this corrected Cv value is plotted in relation to the valve voltage, the correlation between the corrected Cv value and the valve voltage, as shown in Figure 4, appears.

As can be seen from Figure 4, the correlation between the Cv value and valve voltage is standardized (unified) across various gas types. That is, the corrected Cv value of the fluid control valve V under normal conditions will be approximately the same regardless of the gas type, provided the valve voltage is the same. Specifically, the slope of the linear correlation between the Cv value and valve voltage will be approximately the same regardless of the gas type.

Next, the functions and operations of each part performed by the control unit Z will be explained with reference to Figures 2 and 5.

The correlation data storage unit Z3 is set in a predetermined area of the memory and stores Cv value-voltage correlation data showing the correlation between the Cv value of the fluid control valve V under normal conditions or a reference Cv value related thereto, and the valve voltage.

This Cv value-voltage correlation data is pre-entered via input means, for example, during product shipment or maintenance. Specifically, as explained in Figure 4, it shows correlations common to multiple gas types.

In this embodiment, the calculation formula for calculating the reference Cv value, which includes the valve voltage as a variable, is stored in the correlation data storage unit Z3 as Cv value-voltage correlation data. More specifically, the Cv-voltage correlation data here is, for example, a linear formula for calculating the reference Cv value from the valve voltage. Note that the Cv value-voltage correlation data is not necessarily limited to a linear formula; various functional formulas may be used, or a lookup table may be used.

Here, under normal operation of the fluid control valve V, the Cv value obtained using the aforementioned reference gas is calculated as the reference Cv value, and data showing the correlation between this reference Cv value and the valve voltage is used as the Cv value-voltage correlation data (see Figure 4). In this embodiment, the reference gas is _N2 gas as described above, but it is not limited to this, and various gases may be used.

The actual Cv value calculation unit Z4 calculates the actual Cv value, which is the Cv value or a related value, at a predetermined timing during actual flow rate control, i.e., when the fluid control valve V is controlled and at a predetermined timing during actual flow rate measurement by Z1 (S1).

In this embodiment, the actual Cv value calculation unit Z4 corrects the Cv value at a predetermined timing while the flow rate calculation unit Z1 is measuring the actual flow rate, using a physical property value determined according to the type of gas controlled by the fluid control valve V, and calculates the corrected Cv value as the actual Cv value. In this embodiment, the molecular weight of the gas is used as the physical property value.

More specifically, the actual Cv value calculation unit Z4, during actual flow rate control, acquires the output values of the flow sensor S, pressure sensor P, and temperature sensor, along with a preset flow rate and the specific gravity of the gas that has been pre-inputted. By substituting these values into the calculation formula (1) described above, it calculates the Cv value at a predetermined timing during actual flow rate control in real time. Then, by acquiring the molecular weight of the gas that has been pre-inputted and substituting this calculated Cv value into the correction formula (2) described above, it calculates the corrected Cv value as the actual Cv value in real time.

The reference Cv value acquisition unit Z5 acquires the reference Cv value corresponding to the valve voltage of the fluid control valve V at a predetermined timing during actual flow rate control, based on the Cv value-voltage correlation data (S2). Note that the predetermined timing here is not limited to a specific point in time during flow rate measurement, but rather encompasses a certain time range. That is, the timing at which the actual Cv value calculation unit Z4 calculates the actual Cv value and the timing at which the reference Cv value acquisition unit Z5 acquires the reference Cv value may be exactly the same, or there may be a certain time difference.

The reference Cv value acquisition unit Z5 acquires the reference Cv value in real time, similar to the calculation performed by the actual Cv value calculation unit Z4 described above. Specifically, at predetermined timings during actual flow rate control, it acquires the magnitude of the valve voltage applied to the fluid control valve V in real time, and sequentially acquires the reference Cv value by substituting the valve voltage into the calculation formula stored as Cv value-voltage correlation data.

The valve diagnostic unit Z6 compares the actual Cv value calculated by the actual Cv value calculation unit Z4 with the reference Cv value acquired by the reference Cv value acquisition unit Z5 (S3).

The valve diagnostic unit Z6 in this embodiment is configured to diagnose the state of the fluid control valve V based on a comparison result obtained by comparing the actual Cv value and the reference Cv value. More specifically, by sequentially comparing the actual Cv value calculated in real time with the reference Cv value acquired in real time, it diagnoses in real time whether or not an abnormality has occurred in the fluid control valve V during actual flow rate control (S4).

Specific embodiments of this valve diagnostic unit Z6 include, for example, an embodiment that diagnoses an abnormality in the fluid control valve V when the difference or ratio between the actual Cv value and the reference Cv value exceeds a predetermined threshold.

Furthermore, by setting the aforementioned thresholds in stages, the valve diagnostic unit Z6 may be configured to, for example, diagnose that maintenance is necessary, even though there is no abnormality in the fluid control valve V, when the difference or ratio between the actual Cv value and the reference Cv value exceeds the first threshold, and to diagnose that there is an abnormality in the fluid control valve V when the difference or ratio between the actual Cv value and the reference Cv value exceeds the second threshold.

The control unit Z may be configured to store, for example, an internal or external memory, the information obtained when the valve diagnostic unit Z6 described above diagnoses an abnormality in the fluid control valve V. Furthermore, as shown in Figure 2, it may also include an abnormality notification unit Z7 that outputs an abnormality signal indicating that an abnormality has been detected during actual flow rate control.

The abnormality notification unit Z7 can, for example, notify the system of an abnormality in the fluid control valve V based on the diagnosis results from the valve diagnosis unit Z6, by displaying the information on a screen or by using sound or light (S5).

<Effects of this embodiment>
With the fluid control device 100 configured in this way, the actual Cv value at a predetermined timing during actual flow rate control is compared with a reference Cv value corresponding to the valve voltage at that predetermined timing. This allows the state of the fluid control valve V to be diagnosed during the process of actual flow rate control. As a result, the state of the fluid control valve, such as changes in valve opening over time, can be self-diagnosed without the need for a separate process to diagnose the fluid control valve V, and malfunctions and abnormalities can be predicted in advance.
Furthermore, since the output values of various sensors mounted on the fluid control device 100 are used to calculate the actual Cv value, there is no need to separately install a dedicated sensor to calculate the actual Cv value, and real-time diagnosis of the fluid control valve V can be performed while maintaining the configuration of the existing fluid control device 100.

Furthermore, as the actual Cv value, the Cv value during actual flow rate control is corrected using physical properties determined according to the type of gas controlled by the fluid control valve V. Therefore, as shown in Figure 4, the Cv value-voltage correlation data can be unified (standardized) or approached to be unified (standardized).
This allows the Cv value-voltage correlation data of the reference gas to be used for various other gas types as well, making it possible to appropriately diagnose the state of the fluid control valve V according to various gas types without requiring much time or effort.

Furthermore, if the abnormality notification unit Z7 diagnoses an abnormality in the fluid control valve V, it outputs an abnormality signal during actual flow rate control. This allows for real-time detection of the abnormality during the process, enabling appropriate countermeasures to be taken.

<Other Embodiments>
For example, the control unit Z may further include a state determination unit Z8 that determines whether or not the flow rate of the fluid controlled by the fluid control valve V is stable, as shown in Figure 6. After the state determination unit Z8 determines that the flow rate is stable, the valve diagnostic unit Z6 may be configured to start comparing the actual Cv value and the reference Cv value.
Specifically, the state determination unit Z8 can be configured to determine, for example, that the flow rate has stabilized after a predetermined time has elapsed since a target flow rate was set.
In addition, other embodiments of the state determination unit Z8 may determine that the fluid flow rate is stable when the valve voltage applied to the fluid control valve V falls within a predetermined range, or when the calculated flow rate calculated by the flow rate calculation unit Z1 falls within a predetermined range.
With this configuration, the valve diagnostic unit Z6 starts the diagnosis only after the state determination unit Z8 determines that the flow rate is stable, thus enabling the acquisition of highly reliable diagnostic results.

Furthermore, while molecular weight was given as an example of a physical property value determined by the type of gas in the above embodiment, it could also be, for example, the density, viscosity, or Reynolds number of the gas, or a value obtained by combining (operating on) several of these physical properties.

Furthermore, in the above embodiment, Cv value-voltage correlation data for a reference gas was used in common for various types of gases. However, multiple Cv value-voltage correlation data obtained in advance for various gases, not just the reference gas, may be stored in the correlation data storage unit Z3.
In this case, the actual Cv value calculation unit Z4 does not need to make corrections based on physical properties determined according to the type of gas, but rather calculates the Cv value at a predetermined timing during actual flow rate control based on calculation formula (1) as the actual Cv value.
On the other hand, the reference Cv value acquisition unit Z5 can acquire a reference Cv value corresponding to the valve voltage of the fluid control valve V at a predetermined timing, based on the Cv value-voltage correlation data stored in relation to the controlled gas.
The valve diagnostic unit Z6 can then diagnose whether or not there is an abnormality in the fluid control valve V by comparing these actual Cv values with reference Cv values.

In addition, while the Cv value of the fluid control valve V under normal conditions was used as the reference Cv value in the above embodiment, a value related to the Cv value of the fluid control valve V under normal conditions, such as a value obtained by multiplying the Cv value of the fluid control valve V under normal conditions by a predetermined coefficient, may also be used as the reference Cv value.

Furthermore, in the above embodiment, the Cv value at a predetermined timing during actual flow rate control was used as the actual Cv value. However, the actual Cv value may also be a value related to the Cv value at a predetermined timing during actual flow rate control, such as a value obtained by multiplying the Cv value at a predetermined timing during actual flow rate control by a predetermined coefficient.

Furthermore, some or all of the functions of the correlation data storage unit Z3, the actual Cv value calculation unit Z4, the reference Cv value acquisition unit Z5, and the valve diagnostic unit Z6 may be provided in a separate computer from the flow rate calculation unit Z1.

Furthermore, various modifications and combinations of the embodiments are permitted, as long as they do not contradict the spirit of the present invention.

100... Fluid control device X... Main flow path (internal flow path)
B...Block S...Flow sensor V...Fluid control valve Z...Control unit Z1...Flow calculation unit Z2...Valve control unit Z3...Correlation data storage unit Z4...Actual Cv value calculation unit Z5...Reference Cv value acquisition unit Z6...Valve diagnostic unit Z7...Anomaly notification unit Z8...Status determination unit

Claims (10)

A correlation data storage unit stores Cv value-voltage correlation data that shows the correlation between the Cv value of a fluid control valve under normal conditions or a reference Cv value which is a related value, and the valve voltage.
A real Cv value calculation unit calculates the actual Cv value, which is the Cv value or a related value at a predetermined timing during actual flow rate control.
A reference Cv value acquisition unit that acquires the reference Cv value corresponding to the valve voltage of the fluid control valve at the predetermined timing based on the Cv value-voltage correlation data,
A control unit comprising a valve diagnostic unit that compares the reference Cv value with the actual Cv value. The control unit according to claim 1, wherein the actual Cv value is a value obtained by correcting the Cv value calculated at the predetermined timing using a physical property value determined according to the type of gas controlled by the fluid control valve. The control unit according to claim 2, wherein the actual Cv value is a value obtained by correcting the Cv value calculated at the predetermined timing using the molecular weight of the gas controlled by the fluid control valve. The control unit according to any one of claims 1 to 3, wherein the correlation data storage unit stores a calculation formula for calculating the reference Cv value, which includes the valve voltage as a variable, as the Cv value-voltage correlation data. The control unit according to any one of claims 1 to 4, wherein the diagnostic results from the valve diagnostic unit are stored in internal memory or external memory. The valve diagnostic unit compares the actual Cv value and the reference Cv value during actual flow rate control to diagnose whether or not there is an abnormality in the fluid control valve.
The control unit according to any one of claims 1 to 5, further comprising an abnormality notification unit that outputs an abnormality signal indicating that an abnormality has occurred in the fluid control valve when it is diagnosed to have occurred, during actual flow rate control. The system further includes a state determination unit that determines whether or not the flow rate of the fluid controlled by the fluid control valve is stable.
The control unit according to any one of claims 1 to 6, wherein, after the state determination unit determines that the flow rate is stable, the valve diagnostic unit starts comparing the actual Cv value and the reference Cv value. A fluid control device comprising a control unit according to any one of claims 1 to 7. A correlation data storage unit stores Cv value-voltage correlation data that shows the correlation between the Cv value of a fluid control valve under normal conditions or a reference Cv value which is a related value, and the valve voltage.
A real Cv value calculation unit calculates the actual Cv value, which is the Cv value or a related value at a predetermined timing during actual flow rate control.
A reference Cv value acquisition unit that acquires the reference Cv value corresponding to the valve voltage of the fluid control valve at the predetermined timing based on the Cv value-voltage correlation data,
A valve diagnostic program that causes a computer to perform the function of a valve diagnostic unit that compares the aforementioned reference Cv value and the aforementioned actual Cv value. A correlation data storage step that stores Cv value-voltage correlation data showing the correlation between the Cv value of a fluid control valve under normal conditions or a reference Cv value which is a related value and the valve voltage,
A step to calculate the actual Cv value, which is the Cv value or a related value at a predetermined timing during actual flow rate control,
A reference Cv value acquisition step in which the reference Cv value corresponding to the valve voltage of the fluid control valve at the predetermined timing is acquired based on the Cv value-voltage correlation data,
A valve diagnostic method comprising a valve diagnostic step of comparing the aforementioned reference Cv value with the aforementioned actual Cv value.