CN111307865B - Method for improving relative humidity measurement precision - Google Patents

Abstract

The invention discloses a method for improving relative humidity measurement accuracy, comprising: selecting an initial state point, accurately measuring the dry bulb temperature and relative humidity of the initial state point, and calculating the moisture content of the initial state point; starting from the initial state point to implement In the process of temperature rise and other moisture content, the first relative humidity at each temperature point is calculated in real time, and the second relative humidity corresponding to the first relative humidity is obtained by using the wet and dry bulb method simultaneously; the first relative humidity and the second relative humidity are used to Corrected wet and dry bulb measurements. The invention can effectively improve the accuracy of relative humidity measurement by dry-wet bulb method.

Description

A Method of Improving the Measurement Accuracy of Relative Humidity

technical field

The invention belongs to the technical field of relative humidity measurement, and in particular relates to a method for improving relative humidity measurement accuracy.

Background technique

The physical definition of relative humidity is very simple and clear, but the accurate measurement of relative humidity is one of the famous problems in the field of metrology in the world. Common humidity measurement methods are: dynamic method (dual pressure method, dual temperature method, shunt method), static method (saturated salt method, sulfuric acid method), dew point method, wet and dry bulb method and electronic sensor method. In the environmental reliability test, the wet and dry bulb method is a commonly used humidity measurement method. Although this method is simple and feasible, the measurement accuracy is low and unstable. It is difficult to accurately measure the relative humidity with the wet and dry ball method. There are three factors: the first is subjective factors. When making the dry and wet ball device, the cotton yarn is not properly wound. The distance to the water surface is too long or too short; the second is objective factors, the ambient wind speed has a direct impact on the wet bulb temperature, the ambient wind speed is between 2.5m/s and 4.5m/s, and the wet and dry bulb coefficient remains basically constant ; The third is the system factor, the measurement accuracy of dry and wet bulb method is related to the measurement accuracy of dry and wet bulb temperature.

Contents of the invention

The purpose of the present invention is to provide a method for improving relative humidity measurement accuracy, so as to solve the problem of low accuracy of relative humidity measurement by wet and dry bulb method in the prior art.

In order to achieve the above object, an embodiment of the present invention provides a method for improving relative humidity measurement accuracy, including: selecting an initial state point, accurately measuring the dry bulb temperature and relative humidity of the initial state point, and calculating the moisture content of the initial state point; Starting from the initial state point, implement the moisture content process such as temperature rise, calculate the first relative humidity at each temperature point in real time, and simultaneously use the wet and dry bulb method to measure the second relative humidity corresponding to the first relative humidity; use the first relative humidity and a second relative humidity to correct the psychrometer measurements.

Preferably, the synchronous measurement of the second relative humidity corresponding to the first relative humidity by using the dry-wet bulb method includes: sequentially sampling within the specified interval of the first relative humidity, and reading the measured humidity using the dry-wet bulb method The second relative humidity of each sampling point obtained by the method.

Preferably, using the first relative humidity and the second relative humidity to correct the measured value of the dry-wet bulb method includes: correcting the measured value of the dry-wet bulb method as follows:

When y _i+1 ≧Φy≧y _i , Φ _c ＝xi ₊ [(xi _{+1 -xi} )(Φ _y -y _i )]/(y _i+1 -y _i )

Among them, Φ _c represents the measured value of the wet and dry bulb method after correction, i represents the i-th sampling point, n≧i≧1, n is the number of sampling points, x _i represents the first relative humidity of the sampling point, Φ _y represents the measured value of dry-wet bulb method, and y _i represents the second relative humidity of the sampling point.

Preferably, the specified interval is 90%-20% relative humidity, one sampling point is taken at every interval of 5%, n=16.

Preferably, when Φ _y >90% or Φ _y <20%, Φ _c =Φ _y .

Preferably, the implementation of the moisture content process such as temperature rise includes: setting the temperature and humidity of the environmental test chamber corresponding to the dry bulb temperature and relative humidity at the initial state point; maintaining the humidity of the space in the environmental test chamber The temperature remains unchanged, starting from the initial state point to heat up.

Preferably, heating and heating are carried out by heating the electric heating wire provided in the environmental test chamber.

Preferably, the heating speed is controlled to carry out uniform and slow heating and temperature rise, and the wind speed in the environmental test chamber is controlled to be ≤3m/s.

Preferably, a platinum resistance temperature sensor is used to accurately measure the dry bulb temperature at the initial state point.

Preferably, the relative humidity at the initial state point is accurately measured using a standard humidity generator based on the dual-pressure method.

Using the method for improving relative humidity measurement accuracy in the embodiment of the present invention can effectively improve the accuracy of relative humidity measurement by wet and dry bulb method.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings on the premise of not paying creative work:

Fig. 1 is the flow chart of the method for improving relative humidity measurement precision provided by the embodiment of the present invention;

Fig. 2 is the schematic diagram of the psychrometric diagram used in the method of the embodiment of the present invention;

Fig. 3 is a schematic diagram of the equal moisture content process implemented in the method of the embodiment of the present invention.

Detailed ways

The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The embodiment of the present invention provides a method for improving the measurement accuracy of relative humidity in order to solve the problem of relatively low measurement accuracy of relative humidity by the wet and dry bulb method in the prior art. Fig. 1 is a flowchart of a method for improving relative humidity measurement accuracy provided by an embodiment of the present invention. As shown in Figure 1, the method of the embodiment of the present invention includes steps S1-S3:

Step S1: Select an initial state point, accurately measure the dry bulb temperature and relative humidity of the initial state point, and calculate the moisture content of the initial state point;

Step S2: Starting from the initial state point, carry out the temperature rise and other moisture content processes, calculate the first relative humidity at each temperature point in real time, and simultaneously use the wet and dry bulb method to measure and obtain the second relative humidity corresponding to the first relative humidity;

Step S3: Using the first relative humidity and the second relative humidity to correct the measured value of the dry-wet bulb method.

That is, in the embodiment of the present invention, first select an appropriate initial state point, accurately measure the dry bulb temperature and relative humidity of the initial state point, and calculate the moisture content of the initial state point, according to the calculated initial state point Moisture content, implement the moisture content process such as temperature rise, and use the calculated relative humidity and the relative humidity measured by the dry and wet bulb method to correct the measured value of the dry and wet bulb method.

The method of the embodiment of the present invention will be described in detail below with reference to FIG. 2 and FIG. 3 . Fig. 2 is a schematic diagram of a psychrometric chart used in the method of the embodiment of the present invention. Fig. 3 is a schematic diagram of the equal moisture content process implemented in the method of the embodiment of the present invention. The psychrometric chart in Figure 2 is an example of a psychrometric chart commonly used in thermal engineering. For the sake of illustration, the isotherm, isenthalpy, isohumidity and relative humidity are drawn in the figure. The family of vertical parallel lines in the psychrometric chart is the family of isomoisture lines.

There are four parameters in the psychrometric chart: enthalpy (specific enthalpy), expressed in h, and the unit is kJ/kg; moisture content, that is, the ratio of water vapor mass to dry air mass, expressed in d, and the unit is g/kg; The dry bulb temperature is represented by t in °C; the relative humidity is represented by Φ. If any two parameters are known, the state of humid air can be determined (that is, there is a certain point on the psychrometric chart), and the remaining two parameters can be derived from two known parameters. For example, as described below, if the dry bulb temperature t and the relative humidity Φ are known, the moisture content d can be calculated; if the dry bulb temperature t and the moisture content d are known, the relative humidity Φ can be calculated.

In the case of known dry bulb temperature t and relative humidity Φ, the calculation formula of moisture content d is as follows:

d＝0.622p _qb (t)Φ/[p－p _qb (t)Φ]...(1)

Among them, p _qb (t) is the partial pressure of saturated water vapor, p is the ambient pressure, and a standard atmosphere is taken here. The pressure saturated water vapor partial pressure p _qb (t) is a function of the dry bulb temperature t, calculated as follows:

lnp _qb ＝C ₁ T ^-1 +C ₂ T ⁰ +C ₃ T ¹ +C ₄ T ² +C ₅ T ³ +C ₆ T ⁴ +C ₇ lnT

In the formula, C ₁ ~ C ₇ are Hyland-Wexler formula constants. T is Kelvin temperature scale, unit K, pay attention to conversion when calculating, T=t+273.15, t is Celsius temperature scale, unit ℃.

Conversely, if the dry bulb temperature t and the moisture content d are known, the relative humidity Φ can be calculated as follows:

Φ＝(dp)/[(0.622+d)p _qb (t)]...(2)

As mentioned above, p _qb (t) is the pressure saturation water vapor partial pressure, which is a function of the dry bulb temperature t. p is the ambient pressure, where a standard atmosphere is taken.

In the method of the embodiment of the present invention, an appropriate initial state point can be selected in the psychrometric diagram in step S1, and the moisture content process such as temperature rise can be implemented from this point in step S2. As shown in Figure 2, the vertical lines therein are all lines of equal moisture content, for example, that vertical line with moisture content d=20g/kg in Figure 2 is exactly an equal moisture content line. On the humidity line, the moisture content is the same, and the temperature along the iso-humidity line from low to high is a process of heating and equal moisture content.

As shown in Figure 3, line AC is an isohumidity line. Both B and B' are points on the line AC. T _dry represents the dry bulb temperature, t _wet represents the wet bulb temperature, and t _dew represents the dew point temperature. If point B is selected as the initial state point, start from point B, heat up along the isohumidity line AC, and reach point B'. As long as the initial state of point B is known, by measuring the dry bulb temperature t of point B', Then other state parameters of point B' can be determined, including relative humidity Φ. As mentioned above, by accurately measuring the dry bulb temperature and relative humidity of the initial state point B in step S1, the moisture content of point B can be calculated by the above formula (1). Since it is a process of equal moisture content, B' The moisture content of point is equal to the moisture content of point B, and then by measuring the dry bulb temperature of point B', the relative humidity of point B' can be calculated by the above formula (2).

Dry bulb temperature is a physical quantity that is relatively easy to measure, and the measurement accuracy is relatively easy to guarantee. Therefore, as long as the initial state of point B is accurately known, and the process of equal moisture content is accurately maintained, the measurement accuracy of the relative humidity at point B' can be guaranteed .

To accurately obtain the initial state value of point B, the dry bulb temperature t of point B is a physical quantity that is relatively easy to measure. Generally speaking, the PT100 platinum resistance temperature sensor can meet the accuracy requirements. The relative humidity Φ at point B can be measured with a standard humidity generator, choose a standard humidity generator based on the double pressure method, and within the humidity range of 15% to 90%, the error of the standard humidity generator is less than ±1.5%.

The temperature rising and other moisture content processes implemented in the method of the embodiment of the present invention are described below. As an example, an iso-moisture process can be achieved in a climate chamber. For example, set the initial value of temperature and humidity in the environmental test chamber (that is, the initial state point): the temperature is 16°C, the relative humidity is 92%, and the moisture content is calculated according to the above formula (1). From the point of initial state, heating increases the temperature. Preferably, an electric heating wire can be installed in the environmental test chamber, and the electric heating wire is heated by electricity instead of sending hot air from the outside, so as to ensure that the moisture content in the space inside the chamber remains unchanged. Control the heating speed not to be too fast, use 30 minutes to uniformly and slowly heat up to about 50°C, keep the gas flow in the test chamber, and control the wind speed at ≤3m/s to ensure that the water vapor is evenly distributed, and simultaneously use the wet and dry bulb method to measure the relative humidity. The ambient wind speed of 3m/s is also the best measurement environment for wet and dry bulb method. The environmental test chamber is not a closed system (the small hole equipped with a balance valve communicates with the outside world). The heating process is an isobaric process. According to the ideal gas state equation, the gas in the environmental test chamber expands when heated, and part of the gas leaks to the outside. The air in the test chamber flows and the water vapor is evenly distributed, so the moisture content of the humid air in the chamber remains unchanged.

As shown in Figure 2 and Figure 3, starting from the initial state point, as the temperature increases, the relative humidity gradually decreases, and the dry bulb temperature t is continuously read, and the first relative humidity Φx is calculated in real time using the above formula (2). During the process of performing equal moisture content, the second relative humidity Φ _y is measured simultaneously by using the wet and dry bulb method. In the process of temperature rise and other moisture content, the relative humidity gradually decreases from large to small. In the range of relative humidity from 90% to 20%, a sampling point is taken at an interval of 5%. There are 16 points in total, using x16, x15, x14, ..., x1 represents the value of 16 points, that is to say, when Φx is equal to 90%, 85%, 80%, ..., 20% respectively, read the value of relative humidity Φy obtained by dry-wet bulb measurement method at the same time , use y16, y15, y14, ..., y1 to represent the values of 16 corresponding points of Φy, repeat the above process of temperature rise and other moisture content for 3 to 5 times and record the experimental data, calculate y16, y15, y14, ..., y1 The average value of y16, y15, y14, ..., y1 is recorded in Table 1 below.

Table 1

Φ_x x16=90% x15=85% x14=80%  … x1=20% Φ_y y16 y15 y14  … y1

In step S3, the second relative humidity measured by the dry-wet bulb method is corrected by using the calculated first relative humidity. For example, software can be used to correct the dry and wet bulb measurements. In one example, the segmented linear correction method is used to calibrate the measured value of the dry-wet bulb method, and Φ _c is used to represent the corrected measured value of the dry-wet bulb method, as follows:

When Φ _y >90%, or Φ _y <20%, Φ _c = Φ _y (the relative humidity is too large or too small, the calibration effect may not be good, therefore, mainly for the range of relative humidity from 90% to 20% calibration).

When y2≧Φ _y ≧y1, Φ _c ＝x1+[(x2-x1)(Φ _y -y1)]/(y2-y1)

When y3≧Φ _y ≧y2, Φ _c ＝x2+[(x3-x2)(Φ _y -y2)]/(y3-y2)

 …

When y _i+1 ≧Φ _y ≧y _i , Φ _c ＝x _i +[(xi _{+1 -xi} )(Φ _y -y _i )]/(y _i+1 -y _i )

Wherein, i is the i-th sampling point, n≧i≧1, n is the number of sampling points, in this example, n=16.

After the calibration work is completed, the relative humidity can be measured by using the wet and dry bulb method corrected by the software, which can achieve the purpose of improving the relative humidity measurement accuracy. Regular calibration can effectively improve the relative humidity measurement accuracy. This kind of calibration is very simple and can be carried out when the instrument is idle, which is very practical and effective. Generally speaking, the relative humidity is measured by the dry-wet bulb method, and the measurement error is greater than or equal to ±3%. Using the method of the embodiment of the present invention, the relative humidity of the dry-wet bulb method can be made under the condition that the error of the standard humidity generator is less than ±1.5%. Humidity measurement error reaches ±2%.

Certain exemplary embodiments of the present invention have been described above only by way of illustration, and it goes without saying that those skilled in the art can use various methods without departing from the spirit and scope of the present invention. The described embodiments are modified. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the protection scope of the claims of the present invention.

Claims (3)

1. A method for improving relative humidity measurement accuracy, characterized in that, comprising: Select the initial state point, accurately measure the dry bulb temperature and relative humidity of the initial state point, and calculate the moisture content of the initial state point. Among them, the platinum resistance temperature sensor is used to accurately measure the dry bulb temperature of the initial state point. The standard humidity generator accurately measures the relative humidity at the initial state point; Starting from the initial state point, implement the moisture content process such as temperature rise, calculate the first relative humidity at each temperature point in real time, and simultaneously use the wet and dry bulb method to measure the second relative humidity corresponding to the first relative humidity; Using the first relative humidity and the second relative humidity to correct the psychrometer measurements, The synchronous measurement of wet and dry bulb method to obtain the second relative humidity corresponding to the first relative humidity, including: Sampling is carried out sequentially within the specified interval of the first relative humidity, and the second relative humidity of each sampling point obtained by using the dry-wet bulb measurement method is read, The use of the first relative humidity and the second relative humidity to correct the measured value of the dry-wet bulb method includes: correcting the measured value of the dry-wet bulb method as follows: When y _i+1 ≧Φy≧y _i , Φ _c =xi ₊ [(xi _{+1 -xi} )(Φ _y -y _i )]/(y _i+1 -y _i ) Among them, Φ _c represents the measured value of the wet and dry bulb method after correction, i represents the i-th sampling point, n≧i≧1, n is the number of sampling points, x _i represents the first relative humidity of the sampling point, Φ _y represents the measured value of dry-wet bulb method, y _i represents the second relative humidity of the sampling point, Described implementation of moisture content processes such as heating up includes: Setting the temperature and humidity of the environmental test chamber corresponding to the dry bulb temperature and relative humidity of the initial state point; Keep the moisture content in the space in the environmental test chamber constant, and start heating up from the initial state point, Among them, the heating is carried out by heating the electric heating wire installed in the environmental test chamber, Control the heating speed to heat up evenly and slowly, and control the wind speed in the environmental test chamber to ≤3m/s. 2. The method of claim 1, wherein, The prescribed range is 90% to 20% relative humidity, and a sampling point is taken at every interval of 5%. 3. The method of claim 2, wherein, When Φ _y >90% or Φ _y <20%, Φ _c =Φ _y .

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