Resistance-capacitance frequency modulation type ethanol water content measuring device and method

Abstract

The invention discloses a resistance-capacitance frequency modulation type ethanol water content measuring device and method, is applied to the technical field of sensors, and aims to solve the problems of complicated measuring circuit and unstable measuring result in the existing ethanol water content measurement. The detection electrode and the quartz crystal resonator are connected in series, the change of equivalent capacitance and equivalent resistance of the detection electrode and a solution system caused by the change of water content in ethanol can be further converted into the output frequency change of the device by utilizing the high-sensitivity resistance-capacitance frequency modulation characteristic of the quartz crystal resonator, and the resonant frequency is collected by the digital frequency meter. The method comprises the following steps: establishing a water content-frequency mathematical relationship expression by collecting frequency response data of a measuring device on ethanol solutions with different water contents; based on the expression, frequency information measured in real time can be converted into water content information of the ethanol solution, and online measurement of the water content of ethanol is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to an ethanol water content measuring device and technology. Background Art

[0002] Water and ethanol are completely miscible, and water is often inevitably included in the ethanol production process. Therefore, accurate detection of ethanol's moisture content is crucial for quality control of medical ethanol and biofuels. Advanced detection technologies can accurately measure ethanol's moisture content, thereby optimizing its performance. Currently, numerous devices and methods exist for measuring ethanol's moisture content. Karl Fischer titration requires chemical reagents, is relatively complex to operate, and lacks real-time monitoring capabilities. Fluorescence analysis has high instrumentation and environmental requirements, and the stability and selectivity of fluorescent dyes can affect measurement results. Conductivity analysis is highly temperature-dependent, making its results susceptible to ambient temperature fluctuations and typically requiring a temperature compensation module or thermostat, which increases system complexity and cost. Nuclear magnetic resonance (NMR) testing, however, is expensive and complex, making it unsuitable for on-site testing. Therefore, a detection technology solution with a simple circuit structure, stable measurement results, suitability for online monitoring, and low manufacturing cost is urgently needed in this field. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention proposes a device and method for measuring the water content of ethanol by using a resistance-capacitance frequency modulation method. The detection electrode is connected in series with a quartz crystal resonator. The frequency f output by the frequency meter is the equivalent resistance R between the detection electrode and the ethanol solution. s and equivalent capacitance C s The function is based on the frequency values ​​obtained by measuring ethanol solutions with different known water contents, and the mathematical relationship expression of water content-frequency is fitted to realize the online measurement of ethanol water content.

[0004] One of the technical solutions adopted by the present invention is: a resistance-capacitance frequency modulation type ethanol water content measuring device, comprising: a detection electrode, a quartz crystal resonator, an oscillator, a frequency counter, a computer, a detection cell, an input port, and an output port; the first end of the detection electrode is connected to the first end of the quartz crystal resonator, the second end of the quartz crystal resonator is connected to the first end of the oscillator, the second end of the oscillator is connected to the second end of the detection electrode, the output end of the oscillator is connected to the input end of the frequency counter, and the output end of the frequency counter is connected to the computer; the detection cell is used to hold an ethanol solution, and the detection electrode is placed in the ethanol solution in the detection cell; the input port and the output port are connected to both ends of the detection cell for inputting and outputting the ethanol solution;

[0005] According to the equivalent circuit model of the detection electrode and the quartz crystal resonator in series, the frequency f output by the quartz crystal resonator is the equivalent resistance R of the detection electrode and the ethanol solution as a whole. s and the equivalent capacitance C of the detection electrode and the ethanol solution as a whole s function.

[0006] The second technical solution adopted by the present invention is: a resistance-capacitance frequency modulation method for measuring the water content of ethanol, comprising:

[0007] S1. Prepare ethanol solutions with different water contents;

[0008] S2. The prepared ethanol solution is input into the detection cell through the input port. After the measurement is completed, the ethanol solution is output through the output port.

[0009] S3. Record the output frequencies of the quartz crystal resonator corresponding to ethanol solutions with different water contents respectively; and obtain a mathematical expression of the water content-frequency relationship by fitting;

[0010] S4. Input the ethanol solution with unknown water content to be measured into the detection cell from the input port, record the frequency output by the quartz crystal resonator corresponding to the measurement, input the frequency into the mathematical relationship expression of water content-frequency fitted in step S3, and thus output the water content corresponding to the ethanol solution with unknown water content to be measured.

[0011] The beneficial effects of the present invention are as follows: compared with the traditional method of measuring the water content of ethanol by measuring capacitance or resistance, the present invention uses frequency domain measurement to solve the problems of temperature drift and electrode polarization; in addition, the device and method proposed in the present invention can perform online measurement and output the measurement results online in real time, which is significantly different from many existing technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a circuit diagram of a resistance-capacitance frequency modulation type ethanol water content measuring device provided by the present invention.

[0013] Figure 2 This is a schematic diagram of a detection electrode according to an embodiment of the present invention;

[0014] in, Figure 2 (a) is a top view; Figure 2 (b) is a cross-sectional view.

[0015] Figure 3 This is an equivalent circuit model diagram of the interdigital electrodes connected in series with the quartz crystal resonator according to an embodiment of the present invention.

[0016] Figure 4 This is a graph showing the relationship between the resonant frequency of an example of the present invention and ethanol solutions with different water contents.

[0017] Explanation of the accompanying symbols: 1—detection electrode, 2—quartz crystal resonator, 3—oscillator, 4—frequency counter, 5—computer, 6—detection cell, 7—input port, 8—output port. DETAILED DESCRIPTION

[0018] To facilitate those skilled in the art to understand the technical content of the present invention, the present invention is further explained below with reference to the accompanying drawings.

[0019] like Figure 1 As shown, the present invention provides a resistance-capacitance frequency modulation type ethanol water content measuring device, comprising: a detection electrode 1, a quartz crystal resonator 2, an oscillator 3, a frequency counter 4, a computer 5, a detection cell 6, an input port 7, and an output port 8; the first end of the detection electrode 1 is connected to the first end of the quartz crystal resonator 2, the second end of the quartz crystal resonator 2 is connected to the first end of the oscillator 3, and the second end of the oscillator 3 is connected to the second end of the detection electrode 1. The detection electrode 1, the quartz crystal resonator 2, and the oscillator 3 form a series circuit, the resonant frequency of which is collected by the frequency counter 4 and transmitted to the computer 5 for processing.

[0020] The detection electrode 1 is placed in the detection cell 6, and the input port 7 and the output port 8 are connected to both ends of the detection cell.

[0021] like Figure 2 As shown, the detection electrode 1 comprises, from bottom to top, a substrate 9 and interdigital electrodes 10 fabricated on the substrate. The substrate can be any of FR-4, silicon, ceramic, or polymer flexible substrates. In this embodiment, an FR-4 substrate is used. The structural parameters of interdigital electrodes 10 are a 0.254mm spacing between adjacent fingers, a 5.08mm finger length, a 0.254mm finger width, and two pairs of fingers.

[0022] The quartz crystal resonator 2 is metal packaged and has a nominal frequency of 1-40 MHz. In the embodiment of the present invention, the nominal frequency of the quartz crystal resonator 2 is 10 MHz.

[0023] The oscillator 3 is an oscillator of the type of Pierce oscillator or phase-locked loop oscillator, etc. In the embodiment of the present invention, the oscillator 3 is a Pierce oscillator.

[0024] The equivalent circuit model of the detection electrode 1 and the quartz crystal resonator 2 in series in the ethanol solution in the detection cell is as follows: Figure 3 As shown, according to the equivalent circuit model, the resonant frequency f of the RC frequency modulation ethanol water content measuring device can be deduced as:

[0025]

[0026] in C q , Lq are the dynamic capacitance and dynamic inductance of the quartz crystal, C s and R s is the equivalent capacitance and equivalent resistance of the detection electrode 1 and the solution system. Figure 3 Middle R q is the dynamic resistance of the quartz crystal resonator, and C0 is the static capacitance of the quartz crystal resonator.

[0027] From formula (1), we can know that the equivalent resistance R of the detection electrode 1 and the solution system is s and equivalent capacitance C s When changes occur, the output frequency f of the RC frequency modulation ethanol water content measuring device will change.

[0028] During operation, the device is connected to a pipe containing an ethanol solution. When the ethanol solution contacts the detection electrode 1, the resistance and capacitance parameters of the detection electrode 1 change accordingly, following the functional relationship described in formula (1). This ultimately causes the output frequency of the RC-FM ethanol water content measurement device to change. The output frequency is counted by a frequency counter 4 and then processed by a computer 5. Based on the fitted mathematical expression, the ethanol water content is measured.

[0029] The present invention also provides a method for measuring the water content of ethanol using a resistance-capacitance frequency modulation method, the method comprising the following steps:

[0030] (1) Take a certain amount of anhydrous ethanol and distilled water and prepare them into ethanol solutions with water contents of 0%, 3%, 5%, 7%, 20%, 40%, 60%, 80%, and 100%, respectively. The ethanol solution with a water content of 0.3% is regarded as pure ethanol with a water content of 0%.

[0031] (2) Connect the input port of the device of the present invention to a pipe filled with ethanol solution.

[0032] (3) The prepared ethanol solutions were measured in order of water content from low to high using the device of the present invention, and the resonant frequencies at different water contents were recorded. By measuring the frequency response data of ethanol solutions with different water contents, the mathematical relationship expression of water content-frequency was obtained by fitting:

[0033] y=ax 2 +bx+c (2)

[0034] Where x is the frequency, y is the ethanol water content conversion result corresponding to the current frequency, and a, b, and c are correlation coefficients.

[0035] In the embodiment of the present invention, the fitted mathematical expression of the water content-frequency relationship is:

[0036] y=693.57x2 -1811.4x+10 7 (3)

[0037] (4) The ethanol solution to be tested is measured using the device of the present invention, and its water content data is displayed on a computer.

[0038] Figure 4 The resonance frequencies corresponding to different water contents in ethanol are shown, and the line connecting the scatter plots represents the best polynomial curve fit. When the present invention is working, the resonance frequency data measured by the frequency meter is transmitted to the computer, and the computer calculates the resonance frequency by Figure 4 Connect the scatter plot and find the corresponding ethanol water content data based on the frequency transmitted by the frequency counter.

[0039] Those skilled in the art will appreciate that the embodiments described herein are intended to aid the reader in understanding the principles of the present invention, and it should be understood that the scope of the present invention is not limited to such specific descriptions and embodiments. Various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, improvements, and the like made within the spirit and principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A resistance-capacitance frequency modulation type ethanol water content measuring device, characterized in that: include: Detection electrodes, quartz crystal resonator, oscillator, frequency counter, computer, detection cell, input port and output port; The first end of the detection electrode is connected to the first end of the quartz crystal resonator, the second end of the quartz crystal resonator is connected to the first end of the oscillator, the second end of the oscillator is connected to the second end of the detection electrode, the output end of the oscillator is connected to the input end of the frequency counter, and the output end of the frequency counter is connected to a computer; the detection cell is used to hold an ethanol solution, and the detection electrode is placed in the ethanol solution in the detection cell; The input port and the output port are connected to both ends of the detection cell and are used for inputting and outputting ethanol solution; According to the equivalent circuit model of the detection electrode and the quartz crystal resonator in series, the frequency f output by the quartz crystal resonator is the equivalent resistance R of the detection electrode and the ethanol solution as a whole. s and the equivalent capacitance C of the detection electrode and the ethanol solution as a whole s function.

2. The RC frequency modulation type ethanol water content measuring device according to claim 1, characterized in that: The equivalent circuit model specifically includes: the equivalent resistance R of the detection electrode and the ethanol solution as a whole s , the equivalent capacitance C of the detection electrode and the ethanol solution as a whole s , the dynamic inductance L of the quartz crystal resonator q , the dynamic capacitance C of the quartz crystal resonator q , the dynamic resistance R of the quartz crystal resonator q And the static capacitance C0 of the quartz crystal resonator; The equivalent resistance R of the detection electrode and the ethanol solution s The equivalent capacitance C between the first end, the detection electrode and the ethanol solution s The first end is connected to the equivalent resistance R of the detection electrode and the ethanol solution as a whole s The equivalent capacitance C between the second end, the detection electrode and the ethanol solution s The second end is connected; The dynamic inductance L of the quartz crystal resonator q The first terminal and the dynamic capacitance C of the quartz crystal resonator q The first terminal is connected to the dynamic capacitance C of the quartz crystal resonator. q The second terminal is connected to the dynamic resistance R of the quartz crystal resonator. q The first end is connected to the dynamic inductance L of the quartz crystal resonator. q The first end is also connected to the first end of the static capacitor C0 of the quartz crystal resonator, and the second end of the static capacitor C0 of the quartz crystal resonator is connected to the dynamic resistance R q The second end is connected; The dynamic resistance R of the quartz crystal resonator q The second end is also connected to the equivalent resistance R of the detection electrode and the ethanol solution as a whole. s First end connection.

3. The RC frequency modulation type ethanol water content measuring device according to claim 2, characterized in that: The frequency f output by the quartz crystal resonator is the equivalent resistance R of the detection electrode and the ethanol solution as a whole. s and the equivalent capacitance C of the detection electrode and the ethanol solution as a whole s The function of this function is: in, 4. The RC frequency modulation type ethanol water content measuring device according to claim 3, characterized in that: The detection electrodes are interdigitated electrodes.

5. The RC frequency modulation type ethanol water content measuring device according to claim 4, characterized in that: The structural parameters of the interdigital electrodes are as follows: a distance between adjacent fingers of 0.252-0.256 mm, a length of 5.06-5.10 mm, a width of 0.252-0.256 mm, and a number of pairs of interdigits of 1 to 10.

6. The device for measuring the water content of ethanol using a resistance-capacitance frequency modulation method according to claim 5, characterized in that: The substrate of the detection electrode is any one of an FR-4 substrate, a silicon substrate, a ceramic substrate, and a polymer flexible substrate.

7. The RC frequency modulation type ethanol water content measuring device according to claim 6, characterized in that: The quartz crystal resonator is packaged in metal and has a nominal frequency of 1-40 MHz.

8. A method for measuring the water content of ethanol using a resistance-capacitance frequency modulation method, characterized in that: include: S1. Prepare ethanol solutions with different water contents; S2. The prepared ethanol solution is input into the detection cell through the input port. After the measurement is completed, the ethanol solution is output through the output port. S3. Record the output frequencies of the quartz crystal resonator corresponding to ethanol solutions with different water contents; The mathematical expression of the water content-frequency relationship is obtained by fitting; S4. Input the ethanol solution with unknown water content to be measured into the detection cell from the input port, record the frequency output by the quartz crystal resonator corresponding to the measurement, input the frequency into the mathematical relationship expression of water content-frequency fitted in step S3, and thus output the water content corresponding to the ethanol solution with unknown water content to be measured.

9. The method for measuring the water content of ethanol using a resistance-capacitance frequency modulation method according to claim 8, wherein: The mathematical expression of the water content-frequency fitted in step S4 is: y=ax 2 +bx+c Where x is the frequency, y is the ethanol water content conversion result corresponding to the current frequency, and a, b, and c are correlation coefficients.

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