A fixed-frequency humidity measurement system and method and a readable storage medium

Abstract

The present invention provides a fixed-frequency humidity measurement system. The system measures the humidity-sensitive capacitor using a fixed measurement frequency by changing the structure and control timing of the capacitance measurement circuit, thereby solving the measurement error caused by the frequency change in the traditional oscillation circuit measurement process. At the same time, the integrator also has the ability to suppress the distributed capacitance to the ground, which is particularly suitable for the working environment where the distributed capacitance of the sensor bracket is large during the sounding process. The humidity measurement system provided by the present invention has small static and dynamic measurement errors and can meet the humidity observation requirements.

Description

Technical Field

[0001] The present invention relates to the field of meteorological detection technology, and in particular to a fixed-frequency humidity measurement system, a fixed-frequency humidity measurement system method, and a readable storage medium. Background Art

[0002] Meteorological detection is an important means of obtaining meteorological elements. It is usually used to observe the vertical distribution data of temperature, humidity, wind speed, wind direction, and air pressure from the ground to tens of kilometers. Among the many elements of meteorological detection, humidity plays an indispensable role in weather forecasting and climate monitoring. Unlike stationary ground humidity observation equipment, the fixed-frequency humidity measurement system is a special humidity measurement system installed on a sounding balloon, powered by a battery, and will fail when the sounding balloon ruptures. It has extremely high requirements for the system's volume, weight, power consumption, and cost. At the same time, the working environment of the humidity sensor will change rapidly as the sounding instrument is launched, and there are also extremely high requirements for the response speed and measurement accuracy of the humidity measurement. Therefore, it is necessary to design the fixed-frequency humidity measurement system in a targeted manner.

[0003] Humidity sensitive components are key components of fixed-frequency humidity measurement systems, usually humidity-sensitive capacitors or humidity-sensitive resistors. Because humidity-sensitive capacitors are more accurate than humidity-sensitive resistors, have a larger measurement range, and a shorter response time, they have received widespread attention in the engineering and academic fields and are currently the mainstream humidity-sensitive components in the industry. How to efficiently and accurately measure the capacitance of humidity-sensitive capacitors and thus determine humidity is an important topic in current meteorological detection. Summary of the invention

[0004] In view of the above technical problems, embodiments of the present invention provide a fixed-frequency humidity measurement system, a fixed-frequency humidity measurement system method, and a readable storage medium.

[0005] According to a first aspect, the present invention provides a fixed-frequency humidity measurement system, characterized in that the system comprises:

[0006] A logic control module, used for outputting a timing control signal;

[0007] A fixed-frequency integration module, connected to the logic control module, used to measure the capacitance of the humidity-sensitive capacitor at a fixed frequency according to the timing control signal output by the logic control module, and obtain an integrated waveform diagram of the humidity-sensitive capacitor;

[0008] a capacitance conversion module, connected to the fixed-frequency integration module and the logic control module, for converting the humidity-sensitive capacitor integration waveform output by the fixed-frequency integration module into a square wave signal having a duty cycle related to the capacitance of the humidity-sensitive capacitor, and outputting the square wave signal to the logic control module;

[0009] The logic control module calculates the capacitance of the humidity-sensitive capacitor according to the square wave signal output by the capacitance conversion module, and further measures the humidity according to the capacitance of the humidity-sensitive capacitor.

[0010] In one embodiment of the present invention, the system further comprises:

[0011] A temperature compensation module, used for measuring a direct current signal representing the ambient temperature of the humidity-sensitive capacitor;

[0012] An analog-to-digital conversion module is connected to the temperature compensation module and the logic control module, and is used to convert the electrical signal output by the temperature compensation module into a corresponding digital signal, and provide it to the logic control module, so that the logic control module can perform temperature compensation when calculating the capacitance of the humidity-sensitive capacitor according to the square wave signal output by the capacitance conversion module, and then calculate the humidity according to the capacitance of the humidity-sensitive capacitor after compensation.

[0013] In one embodiment of the present invention, the humidity-sensitive capacitance integral waveform is a periodic triangular waveform with a constant frequency and a varying amplitude.

[0014] In one embodiment of the present invention, the frequency of the square wave signal is constant, and the duty cycle varies linearly with the capacitance of the humidity sensitive capacitor.

[0015] In one embodiment of the present invention, the above-mentioned fixed-frequency integration module includes: a first four-channel analog switch and a second four-channel analog switch, a first operational amplifier and a second operational amplifier, an integration resistor and a humidity-sensitive capacitor;

[0016] The channel control terminals of the first four-channel analog switch and the second four-channel analog switch are respectively used as the input terminals of the fixed-frequency integration module and connected to the timing control signal output terminal of the logic control module. The first and second input terminals of the first four-channel analog switch receive a positive reference voltage and a negative reference voltage respectively. The third and fourth input terminals of the first four-channel analog switch are respectively grounded. The output terminal of the first four-channel analog switch is connected to the non-inverting input terminal of the first operational amplifier, and the inverting input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier. The output terminal of the first operational amplifier is connected to the inverting input terminal of the second operational amplifier through the integration resistor. The non-inverting input terminal of the second operational amplifier is grounded. The output terminal of the second operational amplifier is connected to the output terminal of the second four-channel analog switch. The first and second input terminals of the second four-channel analog switch are suspended. The third and fourth input terminals of the second four-channel analog switch are connected to the output terminal of the first operational amplifier. The humidity-sensitive capacitor is connected between the inverting input terminal and the output terminal of the second operational amplifier. The output terminal of the second operational amplifier is used as the output terminal of the fixed-frequency integration module and connected to the input terminal of the capacitance conversion module.

[0017] In one embodiment of the present invention, the system may further include a reference voltage module connected to the fixed-frequency integration module and the capacitance conversion module, and configured to provide a reference voltage satisfying preset conditions for the fixed-frequency integration module and the capacitance conversion module.

[0018] In one embodiment of the present invention, the above-mentioned preset condition includes: within the working cycle of the fixed-frequency integration module, the temperature drift of the reference voltage module is less than a given threshold.

[0019] In one embodiment of the present invention, the capacitance conversion module includes a comparator circuit, which includes a PWM voltage divider and a comparator; wherein the first input end of the comparator serves as the input end of the capacitance conversion module and is connected to the output end of the fixed-frequency integration module, the second input end of the comparator is connected to the output end of the PWM voltage divider, the input end of the PWM voltage divider is connected to the output end of the reference voltage module, and the output end of the comparator serves as the output end of the capacitance conversion module and is connected to the input end of the logic control module.

[0020] In one embodiment of the present invention, the PWM voltage divider includes a MOS transistor and a third operational amplifier, the drain of the MOS transistor is connected to the output end of the reference voltage module, the gate is connected to the PWM signal output end of the logic control module, and the source is connected to the non-inverting end of the third operational amplifier through three series resistors, wherein the node between the two resistors close to the MOS transistor is grounded through a first intermediate capacitor, the non-inverting end of the third operational amplifier is grounded through a second intermediate capacitor, and the inverting end of the third operational amplifier is connected to the node between the two resistors close to the third operational amplifier through a third intermediate capacitor; the output end of the third operational amplifier is connected to the inverting end, and is connected to the non-inverting end of the operational amplifier as the comparator as the output end of the PWM voltage divider, the inverting end of the operational amplifier is connected to the output end of the fixed-frequency integration module, and the output end of the operational amplifier is used as the output end of the capacitance conversion module and connected to the input end of the logic control module.

[0021] In one embodiment of the present invention, a capacity-temperature-humidity standard table is pre-stored in the above-mentioned logic control circuit, so that the logic control circuit can calculate the humidity according to the received digital signal by looking up the capacity-temperature-humidity standard table and linear interpolation calculation.

[0022] In a second aspect, the present invention further provides a method for performing fixed-frequency humidity measurement using the above system, the method comprising the following steps:

[0023] The working cycle of the fixed-frequency integration module is determined according to the measured capacitance of the humidity-sensitive capacitor; in specific implementation, for example, the working cycle of the fixed-frequency integration module is determined according to the value recommended by the humidity-sensitive capacitor data sheet.

[0024] The control logic control module outputs a corresponding timing control signal to the fixed frequency integration module in each working cycle, so that the fixed frequency integration module completes the charging and discharging of the humidity sensitive capacitor in each working cycle, so as to realize the periodic measurement of the humidity sensitive capacitor and obtain the humidity sensitive capacitor integral waveform diagram;

[0025] Calculating humidity according to the humidity-sensitive capacitor integral waveform diagram;

[0026] The humidity is measured by converting the humidity-sensitive capacitor integral waveform into a square wave signal whose duty cycle is related to the capacitance of the humidity-sensitive capacitor.

[0027] In one embodiment of the present invention, the control logic control module outputs a corresponding timing control signal to the fixed frequency integration module in each working cycle, so that the fixed frequency integration module completes the charging and discharging of the humidity sensitive capacitor in each working cycle, including the following steps:

[0028] Each working cycle is divided into four time segments of equal length. The control logic control module outputs corresponding timing control signals to the fixed-frequency integration module in the four time segments in turn, so that the fixed-frequency integration module completes the positive phase charging, reverse charging, primary discharge and secondary discharge of the humidity sensitive capacitor in the four time segments respectively.

[0029] According to a third aspect, the present invention further provides a readable storage medium storing a computer program, characterized in that when the computer program is executed by a processor, the steps of the fixed-frequency humidity measurement method as described above are implemented.

[0030] Compared with the prior art, the embodiments of the present invention have at least the following advantages:

[0031] The humidity measurement system provided by the present invention is a humidity measurement system based on a fixed-frequency integrator. The system cleverly applies the programmable integrator to the humidity measurement field by changing the structure and control timing of the capacitance measurement circuit, and uses a fixed measurement frequency to measure the humidity-sensitive capacitor, which fundamentally solves the measurement error caused by the frequency change in the traditional oscillation circuit measurement process. At the same time, the integrator also has the ability to suppress the distributed capacitance to the ground, which is particularly suitable for the working environment where the distributed capacitance of the sensor bracket is large during the sounding process. In addition, by establishing a more complete calibration data table, such as a capacity-temperature-humidity standard table, the measurement accuracy of the humidity measurement system can be further improved, and it can be applied to humidity observation fields such as the ground that require higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0033] Figure 1 It is a schematic diagram of the composition of the fixed-frequency humidity measurement system according to the first embodiment of the present invention;

[0034] Figure 2 It is a schematic diagram of the composition of a fixed-frequency humidity measurement system according to the second embodiment of the present invention;

[0035] Figure 3 for Figure 2 The fixed frequency integrator circuit schematic diagram of the fixed frequency humidity measurement system;

[0036] Figure 4 for Figure 2 The fixed frequency integrator signal timing diagram of the fixed frequency humidity measurement system;

[0037] Figure 5 for Figure 2 The reference voltage circuit schematic diagram of the fixed frequency humidity measurement system;

[0038] Figure 6 for Figure 2 The comparator circuit schematic of the fixed-frequency humidity measurement system. DETAILED DESCRIPTION

[0039] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0040] Humidity-sensitive capacitors are not ideal capacitors. In an environment with constant temperature and humidity, the capacitance of humidity-sensitive capacitors has a clear correlation with the measurement frequency. This characteristic causes the variable-frequency humidity measurement system based on the RC oscillation circuit to introduce certain test errors in the capacitance measurement process.

[0041] To this end, the present invention proposes a humidity measurement system with a constant measurement frequency to eliminate the fluctuation of the humidity-sensitive capacitor value caused by frequency changes and suppress the interference of the distributed capacitance of the bracket on the humidity measurement, thereby significantly improving the accuracy of humidity measurement during the sounding process.

[0042] Embodiment 1

[0043] like Figure 1 As shown, the fixed-frequency humidity measurement system of this embodiment is a program-controlled integral measurement system designed around a humidity-sensitive capacitor. The system includes:

[0044] The logic control module 100 is used to output a timing control signal;

[0045] A fixed-frequency integration module 200, connected to the logic control module 100, is used to measure the capacitance of the humidity-sensitive capacitor at a fixed frequency according to the timing control signal output by the logic control module to obtain a humidity-sensitive capacitor integration waveform diagram;

[0046] The capacitance conversion module 300 is connected to the fixed-frequency integration module 200 and the logic control module 100, and is used to convert the humidity-sensitive capacitor integration waveform output by the fixed-frequency integration module 200 into a square wave signal whose duty cycle is related to the capacitance of the humidity-sensitive capacitor, and provide the square wave signal to the logic control module 100;

[0047] The temperature compensation module 400 is used to measure a DC signal representing the ambient temperature of the humidity-sensitive capacitor;

[0048] The analog-to-digital conversion module 500 is connected to the temperature compensation module 400 and the logic control module 100, and is used to convert the DC signal output by the temperature compensation module 400 into a corresponding digital signal, and output it to the logic control module;

[0049] Among them, the logic control module 100 calculates the capacitance of the humidity-sensitive capacitor according to the square wave signal output by the capacitance conversion module 300, and performs temperature compensation when calculating the capacitance of the humidity-sensitive capacitor according to the square wave signal output by the capacitance conversion module 300, and finally calculates the humidity according to the capacitance of the humidity-sensitive capacitor after compensation.

[0050] In addition, the system further comprises a reference voltage module 600 connected to the fixed-frequency integration module 200 and the capacitance conversion module 300, and configured to provide a reference voltage satisfying preset conditions for the fixed-frequency integration module 200 and the capacitance conversion module 300.

[0051] The above system cleverly applies the programmable integrator to the humidity measurement field by changing the structure and control timing of the capacitance measurement circuit, and uses a fixed measurement frequency to measure the humidity-sensitive capacitor, which fundamentally solves the measurement error caused by frequency change in the traditional oscillation circuit measurement process.

[0052] Embodiment 2

[0053] In this embodiment, the system of the first embodiment can be composed of general devices such as a microcontroller, an analog switch, an operational amplifier, an analog-to-digital converter, etc., and its structural block diagram can be seen in the attached figure. Figure 2 .

[0054] exist Figure 2 In the invention, the microcontroller is responsible for the functions of integrator timing control, reading the register value of the external analog-to-digital converter, compensation operation, calibration, communication, etc. Under the control of the microcontroller, the integrator composed of a 4:1 analog switch (also called a four-channel analog switch) and an operational amplifier converts the capacity of the humidity-sensitive capacitor into a triangular wave waveform with a constant frequency and a variable amplitude. The comparator circuit located at the rear stage of the integrator converts the triangular wave into a square wave signal with a constant frequency and a duty cycle that varies with the capacitance of the humidity-sensitive capacitor, and provides the square wave signal to the microcontroller, so that the microcontroller can measure the capacitance of the humidity-sensitive capacitor through the duty cycle. At the same time, the analog-to-digital converter is connected to the platinum resistor to convert the electrical signal representing the ambient temperature of the humidity-sensitive capacitor into a corresponding digital signal and provide it to the microcontroller, so that the microcontroller can perform corresponding temperature compensation when calculating the capacitance of the humidity-sensitive capacitor.

[0055] The core of the above measurement system is the program-controlled fixed-frequency integrator, and its circuit schematic is shown in the figure below. Figure 3 As shown, the signal timing diagram is as follows Figure 4 shown.

[0056] Depend on Figure 3It can be seen that the programmable fixed-frequency integrator is mainly composed of a dual 4:1 analog switch U1 and an operational amplifier U2. The operational amplifier U2A is used as a voltage follower to eliminate the influence of the internal resistance of the analog switch on the circuit; the operational amplifier U2B is connected to the integral resistor R1 and the integral capacitor C (i.e., the humidity-sensitive capacitor) to form an integrator circuit, which can realize the function of converting the capacitance to the AC voltage on the one hand, and suppress the interference of the distributed capacitance on both sides of the capacitor C to the ground on the measurement result on the other hand. The control timing of the programmable fixed-frequency integrator is stored in the data cache of the microcontroller, and the data cache is written to the control pins A and B of the analog switches U1A and U1B at high speed through the timer-controlled DMA-driven GPIO.

[0057] Depend on Figure 4 It can be seen that each working cycle of the programmable fixed-frequency integrator is 200uS in total, which is equally divided into four 50uS time segments. The timing control signal output by the microcontroller selects channels 1 to 4 of the analog switch in turn. The four inputs of the analog switch U1A are the positive reference voltage Ref+, the negative reference voltage Ref- and two power grounds. The output of the analog switch U1A serves as the input of the integrator U2A. At 0-50uS, the positive reference voltage Ref+ charges the humidity-sensitive capacitor C through the integration resistor R1 and performs positive phase integration. Since the voltage at the reverse input terminal of the operational amplifier U2B is equal to the voltage at the non-inverting input terminal, the humidity-sensitive capacitor charging current can be expressed by formula (2):

[0058]

[0059] In the formula, I charge is the current flowing through resistor R1.

[0060] The voltage at the other end of the humidity sensitive capacitor is U cap , that is, the output voltage of the operational amplifier U2B, can be expressed by formula (3):

[0061]

[0062] Where C is the humidity-sensitive capacitor and t is the integration time.

[0063] When the positive phase integration is finished, the voltage of the humidity-sensitive capacitor C reaches its peak value, and then the analog switch disconnects Ref+ and selects Ref-. At 50-100uS, the analog switch connects the negative reference voltage Ref- to the integrator to reversely integrate the humidity-sensitive capacitor. The positive reference voltage Ref+ and the negative reference voltage Ref- are a set of reference voltages with the same absolute value and opposite polarity, so at the end of the reverse integration, the theoretical voltage of the humidity-sensitive capacitor should return to zero. Since the operational amplifier is not an ideal amplifier, there is still a trace amount of residual charge on the capacitor after the reverse integration is completed. This residual charge will gradually form a certain DC potential at both ends of the humidity-sensitive capacitor, which will have a serious impact on the measurement.

[0064] Therefore, at 100-200uS, the analog switch U1B short-circuits the integral resistor and the integral capacitor to form a capacitor discharge loop, and clears the integrator to eliminate residual charge and avoid charge accumulation.

[0065] After the integrator is cleared, the analog switch will select channel 1 again and enter a new integration cycle, which will be repeated to achieve continuous measurement of the humidity-sensitive capacitor.

[0066] like Figure 5 The figure shows the reference voltage circuit of the measurement system. In the present embodiment, the core of the reference voltage circuit is a micro-power shunt voltage reference. Since the working environment of the humidity measurement system is harsh and the working temperature may vary by up to 100°C, the temperature drift of the reference device is bound to have a significant impact on the measurement accuracy of the system. Usually, the solution to this problem is to replace the reference device with a lower temperature drift, but this will have an adverse effect on the system cost. In this regard, the present invention proposes that the reference voltage Ref+ can be preferably connected to one end of the comparator via a PWM voltage divider, which can greatly reduce the performance requirements of the reference device.

[0067] The duty cycle of the comparator output square wave can be expressed by equation (4):

[0068]

[0069] Where t comp is the effective time of the comparator, U comp is the reference voltage for the comparator.

[0070] By reshaping the above formula (3), we can get:

[0071]

[0072] The two input voltages of the comparator are obtained by dividing the positive reference voltage Ref+, which can be expressed as:

[0073] U comp = k Ref + (5)

[0074] Where k is a constant partial pressure coefficient. Substituting equations (5) and (6) into equation (4), we can obtain:

[0075]

[0076] In this embodiment, the single measurement cycle of the program-controlled fixed-frequency integrator is 200uS. It can be considered that the temperature of the reference voltage does not change significantly during this time, and the error caused by temperature drift can be ignored. Under this assumption, the capacitance can be expressed by formula (7). The humidity measurement designed according to the concept of the present invention can effectively reduce the error caused by the reference voltage drift on the measurement result.

[0077] In this embodiment, the output of the programmable fixed-frequency integrator is a triangular wave signal, which is not conducive to direct acquisition by a low-speed analog-to-digital converter. It is necessary to add some circuits to convert the output signal of the programmable fixed-frequency integrator into a square wave signal with a constant frequency but a duty cycle that changes linearly with the capacitance of the humidity-sensitive capacitor.

[0078] This embodiment uses a comparator circuit as an intermediate stage between the program-controlled fixed-frequency integrator and the analog-to-digital converter. Figure 6 shown.

[0079] In this embodiment, the comparator circuit is as follows Figure 6 As shown in the figure, it is mainly composed of a PWM voltage divider composed of a MOS tube Q1, an operational amplifier U3A, and a comparator U5. Unlike the resistor voltage divider, the stability of the PWM voltage divider method is mainly affected by the stability of the PWM signal, that is, it is mainly affected by the external crystal oscillator of the microcontroller. The stability of the crystal oscillator is far better than that of ordinary metal film resistors, so the influence of temperature on the accuracy of the voltage divider can be ignored. Figure 6 It can be seen that the drain of the MOS tube is connected to the reference voltage Ref+, and the gate receives the PWM output signal of the microcontroller to realize the PWM voltage division of the reference voltage Ref+. The output of the PWM voltage divider is a square wave signal. After passing through the third-order Butterworth low-pass filter composed of the operational amplifier U3A and the peripheral resistor and capacitor components, the square wave signal becomes a stable DC signal, which is used as the reference voltage of the comparator U5. The inverting end of the comparator U5 is directly connected to the output end of the program-controlled fixed-frequency integrator, and the in-phase end is connected to the output end of the third-order Butterworth low-pass filter. When the voltage output by the program-controlled fixed-frequency integrator is equal to the reference voltage of the comparator U5, the output level of the comparator U5 is reversed, realizing the conversion of the triangle wave to the square wave, and completing the conversion process of the capacity of the humidity-sensitive capacitor to the duty cycle of the square wave signal.

[0080] System calibration

[0081] It should be noted that when the humidity measurement accuracy is required to be high, it is generally believed that the capacity-temperature-humidity characteristic curve of the humidity-sensitive capacitor is nonlinear, and this curve is difficult to describe using a simple function. In order to improve the accuracy of the measurement system, the microcontroller of the measurement system of the present embodiment pre-stores a typical capacity-temperature-humidity standard table determined by multiple experiments to solve this nonlinear problem. Since the humidity-sensitive capacitor has a certain discreteness, there is a certain deviation between its static capacity and the typical capacity capacitor, so the typical capacitance-temperature-humidity standard table cannot be directly used for data conversion. In the present embodiment, the calibration process is an important bridge connecting the humidity-sensitive capacitor actually assembled by the measurement system and the typical capacitance-temperature-humidity standard table. Through calibration, the ratio and offset of the actual assembled humidity-sensitive capacitor and the typical capacitor can be calculated and written into the memory of the measurement system, and then in the actual measurement, only the table lookup and linear interpolation calculation are required to achieve accurate temperature compensation and humidity measurement.

[0082] Embodiment 3

[0083] This embodiment provides a storage medium storing a computer program. When the computer program is executed by a processor, the steps of the fixed-frequency humidity measurement system described above are implemented.

[0084] These program codes can also be loaded onto a computer or other programmable data processing device so that a series of operation steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions executed on the computer or other programmable device for implementing the process. Figure 1 The steps of a specified function in a process or multiple processes.

[0085] Storage media include permanent and non-permanent, removable and non-removable media, and can be implemented by any method or technology to store information. Information can be computer-readable instructions, data structures, modules of programs or other data. Examples of storage media can include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic disk storage or other magnetic storage devices or any other non-transmission medium that can be used to store information that can be accessed by a computing device.

[0086] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. When the terms "include" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0087] It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or described herein.

[0088] It should be understood that the exemplary embodiments in this specification can be implemented in a variety of different forms and should not be interpreted as being limited to the embodiments described herein. These embodiments are provided to make the disclosure of this application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art, and should not be interpreted as limiting the present invention.

Claims

1. A constant frequency humidity measurement system, characterized in that: The system comprises: A logic control module, used for outputting a timing control signal; A fixed-frequency integration module, connected to the logic control module, used to measure the capacitance of the humidity-sensitive capacitor at a fixed frequency according to the timing control signal output by the logic control module, and obtain an integrated waveform diagram of the humidity-sensitive capacitor; a capacitance conversion module, connected to the fixed-frequency integration module and the logic control module, for converting the humidity-sensitive capacitor integration waveform output by the fixed-frequency integration module into a square wave signal with a duty cycle related to the capacitance of the humidity-sensitive capacitor, and outputting the square wave signal to the logic control module; the capacitance conversion module includes a comparator circuit; Wherein, the logic control module calculates the capacitance of the humidity-sensitive capacitor according to the square wave signal output by the capacitance conversion module, and measures the high-altitude humidity according to the capacitance of the humidity-sensitive capacitor; The fixed-frequency integration module includes: a first four-channel analog switch and a second four-channel analog switch, a first operational amplifier and a second operational amplifier, an integration resistor and a humidity-sensitive capacitor; The channel control terminals of the first four-channel analog switch and the second four-channel analog switch are respectively used as the input terminals of the fixed-frequency integration module and connected to the timing control signal output terminal of the logic control module. The first and second input terminals of the first four-channel analog switch receive a positive reference voltage and a negative reference voltage respectively. The third and fourth input terminals of the first four-channel analog switch are respectively grounded. The output terminal of the first four-channel analog switch is connected to the non-inverting input terminal of the first operational amplifier, and the inverting input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier. The output terminal of the first operational amplifier is connected to the inverting input terminal of the second operational amplifier through the integration resistor. The non-inverting input terminal of the second operational amplifier is grounded. The output terminal of the second operational amplifier is connected to the output terminal of the second four-channel analog switch. The first and second input terminals of the second four-channel analog switch are suspended. The third and fourth input terminals of the second four-channel analog switch are connected to the output terminal of the first operational amplifier. The humidity-sensitive capacitor is connected between the inverting input terminal and the output terminal of the second operational amplifier. The output terminal of the second operational amplifier is used as the output terminal of the fixed-frequency integration module and connected to the input terminal of the capacitance conversion module.

2. The constant frequency humidity measurement system according to claim 1, characterized in that: The system further comprises: A temperature compensation module, used to measure a direct current signal representing the ambient temperature of the humidity-sensitive capacitor; An analog-to-digital conversion module is connected to the temperature compensation module and the logic control module, and is used to convert the electrical signal output by the temperature compensation module into a corresponding digital signal, and provide it to the logic control module, so that the logic control module can perform temperature compensation when calculating the capacitance of the humidity-sensitive capacitor according to the square wave signal output by the capacitance conversion module, and then calculate the humidity according to the capacitance of the humidity-sensitive capacitor after compensation.

3. The fixed-frequency humidity measurement system according to claim 1 or 2, characterized in that: The humidity-sensitive capacitance integral waveform is a periodic triangular waveform with constant frequency and variable amplitude; The frequency of the square wave signal is constant, and the duty cycle changes linearly with the capacitance of the humidity sensitive capacitor.

4. The fixed-frequency humidity measurement system according to claim 1 or 2, characterized in that: The system further comprises: A reference voltage module, connected to the fixed-frequency integration module and the capacitance conversion module, and used to provide a reference voltage that meets preset conditions for the fixed-frequency integration module and the capacitance conversion module; Wherein, the preset condition includes: within the working cycle of the fixed-frequency integration module, the temperature drift of the reference voltage module is less than a given threshold.

5. The constant frequency humidity measurement system according to claim 4, characterized in that: The capacitance conversion module includes a comparator circuit, and the comparator circuit includes a PWM voltage divider and a comparator; Among them, the first input end of the comparator serves as the input end of the capacitance conversion module, connected to the output end of the fixed-frequency integration module, the second input end of the comparator is connected to the output end of the PWM voltage divider, the first input end of the PWM voltage divider is connected to the output end of the reference voltage module, the second input end of the PWM voltage divider is connected to the PWM signal output end of the logic control module, and the output end of the comparator serves as the output end of the capacitance conversion module, connected to the input end of the logic control module.

6. The constant frequency humidity measurement system according to claim 5, characterized in that: The PWM voltage divider includes a MOS transistor and a third operational amplifier, wherein the drain of the MOS transistor is connected to the output end of the reference voltage module, the gate is connected to the PWM signal output end of the logic control module, and the source is connected to the non-inverting end of the third operational amplifier through three series resistors, wherein the node between the two resistors close to the MOS transistor is grounded through a first intermediate capacitor, the non-inverting end of the third operational amplifier is grounded through a second intermediate capacitor, and the inverting end of the third operational amplifier is connected to the node between the two resistors close to the third operational amplifier through a third intermediate capacitor; the output end of the third operational amplifier is connected to the inverting end, and is connected to the non-inverting end of the operational amplifier as the comparator as the output end of the PWM voltage divider, the inverting end of the operational amplifier is connected to the output end of the fixed-frequency integration module, and the output end of the operational amplifier is used as the output end of the capacitance conversion module and connected to the input end of the logic control module.

7. The constant frequency humidity measurement system according to claim 2, characterized in that: The logic control module has a capacity-temperature-humidity standard table pre-stored therein, so that the logic control module can calculate the humidity according to the received digital signal by searching the capacity-temperature-humidity standard table and performing linear interpolation calculation.

8. A fixed-frequency humidity measurement method based on the system according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: Determine the working cycle of the fixed frequency integration module according to the fixed frequency of measuring the capacitance of the humidity sensitive capacitor; The control logic control module outputs a corresponding timing control signal to the fixed frequency integration module in each working cycle, so that the fixed frequency integration module completes the charging and discharging of the humidity sensitive capacitor in each working cycle, so as to realize the periodic measurement of the humidity sensitive capacitor and obtain the humidity sensitive capacitor integral waveform diagram; Calculating humidity using the humidity-sensitive capacitor integrated waveform diagram; The humidity is measured by converting the humidity-sensitive capacitor integral waveform into a square wave signal whose duty cycle is related to the capacitance of the humidity-sensitive capacitor.

9. The constant-frequency humidity measurement method according to claim 8, characterized in that: The control logic control module outputs a corresponding timing control signal to the fixed frequency integration module in each working cycle, so that the fixed frequency integration module completes the charging and discharging of the humidity sensitive capacitor in each working cycle, including the following steps: Each working cycle is divided into four time segments of equal length. The control logic control module outputs corresponding timing control signals to the fixed-frequency integration module in the four time segments in turn, so that the fixed-frequency integration module completes the positive phase charging, reverse charging, primary discharge and secondary discharge of the humidity sensitive capacitor in the four time segments respectively.

10. A readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the fixed-frequency humidity measurement method according to claim 8 or 9 are implemented.

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