A method for calibrating the mass flow of a gas for a thermal mass flow controller

Abstract

The disclosure provides a gas mass flow calibration method for a thermal mass flow controller, comprising: controlling the mass flow of a certain to-be-processed gas based on a standard mass flow control value, the to-be-processed gas being different from a standard gas of the thermal mass flow controller; obtaining a measured value of the mass flow of the to-be-processed gas by using a volume flow meter; obtaining a mass flow calibration model based on the standard mass flow control value and the measured value of the to-be-processed gas; calibrating a target mass flow control value of the to-be-processed gas by using the mass flow calibration model to obtain an actual mass flow control value of the to-be-processed gas, and controlling the mass flow of the to-be-processed gas based on the actual mass flow control value. Through the method provided by the disclosure, the problem that the thermal mass flow controller in the prior art can only control the mass flow of a single gas is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas flow control, in particular to a gas mass flow calibration method for a thermal mass flow controller. BACKGROUND

[0002] In order to ensure accuracy, gas analysis instruments must calibrate and test their sensors, which requires standard gases of different concentrations as reference standards. However, due to different analysis instrument scenarios and different sensor ranges, the required standard gas concentrations and types are also diverse. If various concentrations of standard gases are purchased or prepared, the cost is high and the process is complex. In recent years, dynamic gas preparation instruments have been widely used. The principle is to use high-precision flow controllers to control the flow rates of dilution gas and high-concentration standard gas, adjust the flow ratio, and obtain the target low-concentration gas.

[0003] A thermal mass flow controller is a small, precise, stable, and fast flow controller, which is very suitable for gas preparation equipment. The thermal mass flow controller is calibrated with a certain standard gas when it leaves the factory. The heat loss per unit mass flow of the calibration gas is a constant, so the thermal mass flow controller can control the mass flow of the calibration gas according to the detected heat during operation. However, for other gases of different types or different concentrations of the same type, the heat loss per unit mass flow is different from the calibration gas, so the same thermal mass flow controller cannot be used to control the mass flow of other gases. SUMMARY

[0004] Therefore, the present application provides a gas mass flow calibration method for a thermal mass flow controller, which can effectively solve the defect that the thermal mass flow controller in the prior art can only control the mass flow of a single gas.

[0005] According to a first aspect of the present application, a gas mass flow calibration method for a thermal mass flow controller is provided, comprising:

[0006] inputting a standard mass flow control value to the thermal mass flow controller to control the mass flow of a certain to-be-processed gas, the to-be-processed gas being different from the calibration gas of the thermal mass flow controller;

[0007] obtaining a mass flow measured value of the to-be-processed gas at the output end of the thermal mass flow controller;

[0008] obtaining a mass flow calibration model based on the standard mass flow control value and the mass flow measured value of the to-be-processed gas;

[0009] The target mass flow control value of the to-be-processed gas is calibrated by using the mass flow calibration model to obtain an actual mass flow control value of the to-be-processed gas, and the mass flow of the to-be-processed gas is controlled based on the actual mass flow control value.

[0010] In some embodiments, the standard mass flow control value input to the thermal mass flow controller can be one or more.

[0011] Further, the multiple standard mass flow control values input to the thermal mass flow controller are respectively 20%, 50% and 80% of the range value of the thermal mass flow controller.

[0012] In some embodiments, the to-be-processed gas and the calibration gas of the thermal mass flow controller are different kinds or different concentrations of the same kind.

[0013] In some embodiments, the mass flow measured value of the to-be-processed gas at the output end of the thermal mass flow controller is obtained by using a volume flow meter.

[0014] Further, the mass flow measured value of the to-be-processed gas at the output end of the thermal mass flow controller is obtained by using a volume flow meter, including:

[0015] Under standard conditions, the mass flow measured value of the to-be-processed gas is the reading of the volume flow meter;

[0016] Under non-standard conditions, the mass flow measured value of the to-be-processed gas is calculated based on the reading of the volume flow meter by the following formula:

[0017]

[0018] Wherein, Q 实测 is the mass flow measured value of the to-be-processed gas, P1 is the gas pressure under standard conditions, T1 is the gas temperature under standard conditions, P2 is the gas pressure under non-standard conditions, T2 is the gas temperature under non-standard conditions, and Q2 is the reading of the volume flow meter under non-standard conditions.

[0019] In some embodiments, the standard mass flow control value and the mass flow measured value of the to-be-processed gas are linearly fitted to obtain a mass flow calibration model y=kx, where k is a constant.

[0020] Further, the target mass flow control value of the to-be-processed gas is calibrated by using the mass flow calibration model to obtain an actual mass flow control value of the to-be-processed gas, including:

[0021] The target mass flow control value of the gas to be treated is substituted into the mass flow calibration model y=kx to obtain the actual mass flow control value of the gas to be treated.

[0022] The present disclosure obtains a mass flow calibration model based on the standard mass flow control value and the mass flow measured value of the gas to be treated, calibrates the target mass flow control value of the gas to be treated to obtain an actual mass flow control value, and controls the mass flow of the gas to be treated based on the actual mass flow control value, effectively solving the problem that the thermal mass flow controller in the prior art can only control the mass flow of a single gas. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings. The above and other objects, features and advantages of the present application will be more apparent through the drawings shown. The same reference numerals in all the drawings indicate the same parts. The drawings are not necessarily drawn to scale, and the emphasis is on illustrating the main principles of the present application.

[0024] Figure 1 A flow chart of a gas mass flow calibration method for a thermal mass flow controller according to an embodiment of the present disclosure;

[0025] Figure 2 A schematic diagram of a mass flow calibration model according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0027] It is to be noted that like reference numerals and letters refer to like items throughout the accompanying drawings, and once an item is defined in one drawing, it is not necessary to further define and explain it in subsequent drawings. Also, the terms such as "first", "second", and the like in the description of the present application are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between such entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the phrase "including a" does not exclude the presence of additional identical elements in the process, method, article or device including the element.

[0028] The exemplary embodiments of the present disclosure will be described hereinafter with reference to the accompanying drawings. In the description, all the features of the practical embodiments are not described for the sake of clarity and conciseness. However, it should be appreciated that many embodiment-specific decisions can be made in the process of developing any such practical embodiment in order to achieve the specific goals of the developer, and these decisions can vary from embodiment to embodiment.

[0029] It is also noted herein that, in order to avoid obscuring the present disclosure due to unnecessary details, only the device structures closely related to the scheme according to the present disclosure are shown in the accompanying drawings, and other details not closely related to the present disclosure are omitted.

[0030] It should be understood that the present disclosure is not limited to the described embodiments only due to the description below with reference to the accompanying drawings. In this context, the embodiments can be combined with each other, features of different embodiments can be replaced or borrowed, and one or more features can be omitted in one embodiment, if possible.

[0031] Figure 1 A flow chart of a gas mass flow calibration method 100 for a thermal mass flow controller according to an embodiment of the present disclosure is shown, which specifically includes the following steps:

[0032] In step 110, a standard mass flow control value is input to the thermal mass flow controller to control the mass flow of a certain to-be-processed gas, which is different from the calibration gas of the thermal mass flow controller.

[0033] In the embodiment of the present disclosure, the standard mass flow control value input to the thermal mass flow controller can be one or more.

[0034] To ensure that the calibration method provided by the present disclosure has good calibration effect in the entire range of the thermal mass flow controller, the standard mass flow control values can be selected at the front, middle and rear sections of the range of the thermal mass flow controller. Preferably, in the embodiments of the present disclosure, the plurality of standard mass flow control values input to the thermal mass flow controller can be 20%, 50% and 80% of the range value of the thermal mass flow controller. For example, when the range value of the thermal mass flow controller is 2L / min under standard conditions, 0.4L / min, 1L / min and 1.8L / min are selected as the standard mass flow control values input to the thermal mass flow controller.

[0035] It is worth noting that the above method for determining the standard mass flow control value of the thermal mass flow controller is only an example, and other methods for determining the standard mass flow control value of the thermal mass flow controller are within the protection scope of the present disclosure.

[0036] In the embodiments of the present disclosure, the to-be-processed gas and the calibration gas of the thermal mass flow controller are different types or different concentrations of the same type. For example, when the calibration gas of the thermal mass flow controller is 99.9% concentration nitrogen, the to-be-processed gas can be sulfur dioxide or 60% concentration nitrogen.

[0037] Step 120: obtaining the mass flow measured value of the to-be-processed gas at the output end of the thermal mass flow controller.

[0038] In the embodiments of the present disclosure, a volume flow meter can be connected to the output end of the thermal mass flow controller, and the mass flow measured value of the to-be-processed gas can be obtained based on the reading of the volume flow meter.

[0039] Under standard conditions, the volume flow of the gas is equal to the mass flow, and the measurement principle of the volume flow meter is not related to the type and concentration of the gas. Therefore, in the embodiments of the present disclosure, the reading of the volume flow meter can be directly used as the mass flow measured value of the to-be-processed gas.

[0040] Under non-standard conditions, the volume flow of the gas is not equal to the mass flow. According to the ideal gas condition equation wherein P1 is the gas pressure under standard conditions, V1 is the gas volume under standard conditions, T1 is the gas temperature under standard conditions, P2 is the gas pressure under non-standard conditions, V2 is the gas volume under non-standard conditions, and T2 is the gas temperature under non-standard conditions; and the volume flow is the gas volume passing through the flow section per unit time, and under the condition that the flow section is the same: wherein Q1 is the volume flow of the gas under standard conditions, Q2 is the volume flow of the gas under non-standard conditions, and it can be obtained that: That is, the volume flow rate of the gas under non-standard conditions read by the volume flow meter can be converted into the volume flow rate under standard conditions by the above formula, and the volume flow rate of the gas under standard conditions is equal to the mass flow rate, so that the measured value of the mass flow rate of the gas to be treated can be obtained:

[0041]

[0042] Q = k * (P1 / T1) * (P2 / T2) * (Q1 / Q2) 实测 Q is the measured value of the mass flow rate of the gas to be treated, P1 is the gas pressure under standard conditions, T1 is the gas temperature under standard conditions, P2 is the gas pressure under non-standard conditions, T2 is the gas temperature under non-standard conditions, Q1 is the volume flow rate under standard conditions, and Q2 is the volume flow rate of the gas under non-standard conditions, that is, the reading of the volume flow meter under non-standard conditions.

[0043] In the embodiment of the present disclosure, the gas pressure P1 under standard conditions is 101.325 KPa, and the gas temperature T1 is 273 K (Kelvin temperature).

[0044] In step 130, a mass flow rate calibration model is obtained based on the standard mass flow rate control value and the measured value of the mass flow rate of the gas to be treated.

[0045] In the embodiment of the present disclosure, linear fitting can be performed on the obtained one or more sets of standard mass flow rate control values and measured values of the mass flow rate of the gas to be treated to obtain the mass flow rate calibration model y=kx, where k is a constant. For example, when 0.4 L / min, 1 L / min and 1.8 L / min are selected as the standard mass flow rate control values input to the thermal mass flow controller, the obtained measured values of the mass flow rate are 0.416 L / min, 1.034 L / min and 1.859 L / min, respectively. Linear fitting is performed on the above three sets of data to obtain the mass flow rate calibration model y=1.033x, where x is the target mass flow rate control value of the gas to be treated, and y is the actual mass flow rate control value of the gas to be treated. Figure 2 A schematic diagram of the mass flow rate calibration model provided by the embodiment of the present disclosure is shown.

[0046] In step 140, the target mass flow rate control value of the gas to be treated is calibrated by using the mass flow rate calibration model to obtain the actual mass flow rate control value of the gas to be treated, and the mass flow rate of the gas to be treated is controlled based on the actual mass flow rate control value.

[0047] In the embodiment of the present disclosure, calibrating the target mass flow rate control value of the gas to be treated by using the mass flow rate calibration model to obtain the actual mass flow rate control value of the gas to be treated comprises:

[0048] The target mass flow control value of the to-be-processed gas is substituted into the mass flow calibration model y=kx to obtain an actual mass flow control value of the to-be-processed gas. For example, assuming that the target mass flow control value of the to-be-processed gas is 1.2 L / min, and the mass flow calibration model y=1.0333x is obtained, substituting x=1.2 into y=1.0333x can obtain the actual mass flow control value of the to-be-processed gas as 1.23996 L / min.

[0049] In the embodiments of the present disclosure, after obtaining the actual mass flow control value of the to-be-processed gas, the mass flow of the to-be-processed gas is controlled based on the actual mass flow control value. Since the to-be-processed gas is different from the calibration gas of the thermal mass flow controller, when the thermal mass flow controller is used to control the mass flow of the to-be-processed gas, the output mass flow of the thermal mass flow controller is difficult to reach the target mass flow control value after the target mass flow control value is input into the thermal mass flow controller. However, by using the mass flow calibration model provided in the embodiments of the present disclosure to calibrate the target mass flow control value to obtain the actual mass flow control value, and then inputting the actual mass flow control value into the thermal mass flow controller to control the mass flow of the to-be-processed gas, the actual output mass flow value of the thermal mass flow controller can be close to the target mass flow, so that the same thermal mass flow controller is used to control the mass flow of different gases.

[0050] The above-described embodiments are merely specific implementations of the present disclosure, and are used to illustrate the technical solutions of the present disclosure, rather than limit the same. The protection scope of the present disclosure is not limited thereto. Although the present disclosure is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can make modifications or easily think of changes to the technical solutions described in the foregoing embodiments, or make equivalent replacements to some technical features thereof, within the technical scope disclosed by the present disclosure. Such modifications, changes or replacements do not cause the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure, and should be covered within the protection scope of the present disclosure.

Claims

1. A method for gas mass flow calibration of a thermal mass flow controller, characterized by, The method comprises the following steps: inputting standard mass flow control values of a thermal mass flow controller, the standard mass flow control values being used for controlling mass flow of a to-be-processed gas, the number of the standard mass flow control values being multiple; the to-be-processed gas being different from a calibration gas of the thermal mass flow controller; connecting a volume flow meter at an output end of the thermal mass flow controller, obtaining a volume flow measured value of the to-be-processed gas through the connected volume flow meter, and converting the volume flow measured value into a mass flow measured value; linearly fitting the standard mass flow control values of the multiple to-be-processed gases and corresponding mass flow measured values to obtain a mass flow calibration model; inputting a target mass flow control value of the to-be-processed gas into the mass flow calibration model for calibration to obtain an actual mass flow control value of the to-be-processed gas, and controlling mass flow of the to-be-processed gas based on the actual mass flow control value; the conversion of the volume flow measured value into the mass flow measured value comprises: under standard conditions, the mass flow measured value of the to-be-processed gas is a reading of the volume flow meter; under non-standard conditions, the mass flow measured value of the to-be-processed gas is calculated based on the reading of the volume flow meter through the following formula: ， wherein, is the measured value of the mass flow rate of the gas to be treated, is the pressure of the gas at standard conditions, is the temperature of the gas at standard conditions, is the pressure of the gas at non-standard conditions, is the temperature of the gas at non-standard conditions, is the reading of the volumetric flow meter at non-standard conditions.

2. The method for gas mass flow calibration for a thermal mass flow controller of claim 1, wherein, the standard mass flow control values are 20%, 50% and 80% of a range value of the thermal mass flow controller respectively.

3. The method for gas mass flow calibration for a thermal mass flow controller of claim 1, wherein, the to-be-processed gas is different from the calibration gas of the thermal mass flow controller in kind or in concentration.

4. The method for gas mass flow calibration for a thermal mass flow controller of claim 1, wherein, The standard mass flow control value and the measured value of the mass flow of the gas to be treated are linearly fitted to obtain a mass flow calibration model wherein is a constant.

5. The method for gas mass flow calibration of a thermal mass flow controller of claim 4, wherein, the calibration of the target mass flow control value of the to-be-processed gas by using the mass flow calibration model to obtain the actual mass flow control value of the to-be-processed gas comprises: The target mass flow control value of the gas to be treated is taken as Substitute the mass flow calibration model The actual mass flow control value of the gas to be treated is obtained.

Images