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 of the humidity-sensitive capacitor;

[0008] a capacitance conversion module, connected to the fixed-frequency integration module, and used for converting the humidity-sensitive capacitor integration waveform output by the fixed-frequency integration module into a first direct current signal having an amplitude related to the capacitance of the humidity-sensitive capacitor;

[0009] An analog-to-digital conversion module is connected to the capacitance conversion module and the logic control module, and is used to convert the first DC signal output by the capacitance conversion module into a corresponding digital signal, and output it to the logic control module, so that the logic control module can calculate the capacitance of the humidity-sensitive capacitor according to the first DC signal output by the capacitance conversion module, and then measure 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 second direct current signal representing the ambient temperature of the humidity-sensitive capacitor;

[0012] The analog-to-digital conversion module is also connected to the temperature compensation module and the logic control module, and is used to convert the second DC signal output by the temperature compensation module into a corresponding digital signal, and output 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 first DC signal, and then calculate the humidity according to the capacitance of the humidity-sensitive capacitor after compensation. In one embodiment of the present invention, the above-mentioned humidity-sensitive capacitor integral waveform is a periodic triangular waveform with constant frequency and variable amplitude.

[0013] In one embodiment of the present invention, the first DC signal and the second DC signal are both DC voltage signals.

[0014] 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;

[0015] 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.

[0016] In one embodiment of the present invention, the capacitance conversion module is an average value conversion circuit.

[0017] The average value conversion circuit includes a rectifier and a low-pass filter, wherein the input end of the rectifier serves as the input end of the capacitance conversion module and is connected to the output end of the fixed-frequency integration module, the output end of the rectifier is connected to the input end of the low-pass filter, and the output end of the low-pass filter is the output end of the capacitance conversion module and is connected to the input end of the analog-to-digital conversion module.

[0018] In another embodiment of the present invention, the capacitance conversion module may also be a sample-and-hold circuit;

[0019] The sampling and holding circuit includes a sampling analog switch, a sampling and holding capacitor and a sampling operational amplifier, wherein one end of the sampling analog switch is connected to the output end of the fixed-frequency integration module, and the other end is connected to the non-inverting end of the sampling operational amplifier through a sampling resistor, the non-inverting end of the sampling operational amplifier is also connected to one end of the sampling and holding capacitor, and the other end of the sampling and holding capacitor is grounded, the inverting end of the sampling operational amplifier is connected to the output end of the sampling operational amplifier through an RC parallel circuit module, and the output end of the sampling operational amplifier is the output end of the capacitance conversion module, which is connected to the input end of the analog-to-digital conversion module.

[0020] 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 analog-to-digital conversion module, and configured to provide a reference voltage satisfying a preset condition for the fixed-frequency integration module and the analog-to-digital conversion module;

[0021] 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.

[0022] In one embodiment of the present invention, the temperature compensation module comprises a platinum resistance circuit.

[0023] 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.

[0024] 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:

[0025] 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.

[0026] 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;

[0027] Calculating humidity according to the humidity-sensitive capacitor integral waveform diagram;

[0028] The humidity-sensitive capacitor integral waveform is converted into a first direct current signal whose amplitude is related to the capacitance of the humidity-sensitive capacitor to measure humidity.

[0029] 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:

[0030] 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.

[0031] 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.

[0032] Compared with the prior art, the embodiments of the present invention have at least the following advantages:

[0033] 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

[0034] The accompanying drawings, which constitute 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.

[0035] In the figure:

[0036] 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;

[0037] 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;

[0038] Figure 3 for Figure 2 The fixed frequency integrator circuit schematic diagram of the fixed frequency humidity measurement system;

[0039] Figure 4 for Figure 2 The fixed frequency integrator signal timing diagram of the fixed frequency humidity measurement system;

[0040] Figure 5 for Figure 2 The reference voltage circuit schematic diagram of the fixed frequency humidity measurement system;

[0041] Figure 6 for Figure 2 The average value converter circuit schematic diagram of the fixed frequency humidity measurement system;

[0042] Figure 7Schematic diagram of the composition of a fixed-frequency humidity measurement system according to Embodiment 3 of the present invention;

[0043] Figure 8 for Figure 7 The schematic diagram of the sample-and-hold circuit of the fixed-frequency humidity measurement system;

[0044] Fig. 9 for Figure 7 Signal timing diagram of the fixed-frequency integrator of the fixed-frequency humidity measurement system. DETAILED DESCRIPTION

[0045] 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.

[0046] 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.

[0047] 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.

[0048] Embodiment 1

[0049] 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:

[0050] The logic control module 100 is used to output a timing control signal;

[0051] 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;

[0052] A capacitance conversion module 300, connected to the fixed-frequency integration module 200, for converting the humidity-sensitive capacitor integral waveform output by the fixed-frequency integration module into a first direct current signal having an amplitude related to the capacitance of the humidity-sensitive capacitor;

[0053] The temperature compensation module 400 is used to measure a second direct current signal representing the ambient temperature of the humidity-sensitive capacitor;

[0054] The analog-to-digital conversion module 500 is connected to the capacitance conversion module 300, the temperature compensation module 400 and the logic control module 100, and is used to convert the first DC signal output by the capacitance conversion module 300 and the second DC signal output by the temperature compensation module 400 into corresponding digital signals, and output them to the logic control module 100, so that the logic control module 100 can measure humidity;

[0055] The reference voltage module 600 is connected to the fixed-frequency integration module 200 and the analog-to-digital conversion module 500, and is used to provide a reference voltage that meets preset conditions for the fixed-frequency integration module 200 and the analog-to-digital conversion module 500.

[0056] 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.

[0057] Embodiment 2

[0058] 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 .

[0059] exist Figure 2 In the process, the microcontroller is responsible for integrator timing control, reading external analog-to-digital converter register values, compensation operations, calibration, communication and other functions. 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 varying amplitude. The rectifier circuit and low-pass filter circuit located at the back of the integrator constitute an average converter, which is used to convert the triangular wave into a DC voltage signal, and finally the analog-to-digital converter converts the DC voltage signal into a corresponding digital signal for the microcontroller to read. At the same time, the analog-to-digital converter is connected to a platinum resistor to measure the ambient temperature of the humidity-sensitive capacitor for temperature compensation in the humidity measurement process.

[0060] 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.

[0061] Depend on Figure 3 It 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 and the integral resistor R 1, integrating capacitor C (i.e. humidity-sensitive capacitor) are connected to form an integrator circuit, which can realize the function of converting capacitance to AC voltage on one hand, and suppress the interference of distributed capacitance on both sides of capacitor C to the ground on the measurement result on the other hand. The control timing of the programmable integrator and fixed frequency divider 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 driver GPIO.

[0062] Depend on Figure 4 It can be seen that each working cycle of the programmable fixed-frequency integrator is 200uS, which is equally divided into four 50uS time segments. The timing control signals output by the microcontroller select 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+ passes through the integral resistor R 1 The humidity-sensitive capacitor C is charged and positive-phase integration is performed. 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):

[0063]

[0064] In the formula, I charge is the current flowing through the resistor R 1 of current.

[0065] 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):

[0066]

[0067] Where C is the humidity-sensitive capacitor and t is the integration time.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] like Figure 5 The reference voltage circuit of the measurement system is shown. In this 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 it will have an adverse impact on the system cost. In this regard, the present invention proposes that the reference voltage Ref+ can be preferably connected to the external reference voltage input port of the analog-to-digital converter to greatly reduce the performance requirements of the reference device.

[0072] In this case, the voltage U collected by the analog-to-digital converter adc It can be expressed by formula (4):

[0073]

[0074] Where CODE is the data register reading of the analog-to-digital converter, and FULL SCALE is the maximum range of the analog-to-digital converter.

[0075] By reshaping the above formula (2), we can get:

[0076]

[0077] For a triangle wave, the crest factor is The averaging circuit consisting of a rectifier and a low-pass filter can provide a linear conversion of the triangle wave to DC, which can be expressed as:

[0078] U adc = k·U cap (5)

[0079] Where k is a constant average coefficient. Substituting equations (4) and (5) into equation (3), we can obtain:

[0080]

[0081] 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 (6). 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.

[0082] In this embodiment, the output of the program-controlled 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 program-controlled fixed-frequency integrator into a DC signal. This embodiment uses an average value conversion circuit as an intermediate stage between the program-controlled fixed-frequency integrator and the analog-to-digital converter. Its circuit diagram is shown in FIG. Figure 6 shown.

[0083] In this embodiment, the average value conversion circuit includes a full-wave rectifier, which is an enhanced circuit of a half-wave rectifier, and is composed of an operational amplifier U3, diodes D1, D2, and 7 peripheral resistors. 3 =R 5 , so that the gain of the half-wave rectifier part is 1; R 4 =2R 6 , so that the gain of the half-wave rectifier relative to the input signal is 2. When the capacitor C 1 When it does not exist, for the positive half-cycle signal, the output of U3B is the sum of the input signal and the reference signal (power ground); for the negative half-cycle signal, the output of U3B is the sum of the reverse wave (gain is 2) output by the half-wave rectifier and the input signal. In this way, for a complete positive and negative half-cycle signal, a full-wave rectified signal is obtained at the output of U3B. Capacitor C 1 The addition of can make the adder part of the full-wave rectifier form a first-order low-pass filter, and its cut-off frequency F can be expressed as:

[0084]

[0085] The appropriate corner frequency can strike a balance between filtering effect and delay. 7 =20KΩ, C 1 =820nF, the filter cut-off frequency is about 10Hz. For an input voltage of 5V, the delay is about 0.08S, which is much smaller than the response time of the humidity-sensitive capacitor and can meet the needs of the humidity detection system.

[0086] Embodiment 3

[0087] Of course, the present invention is not limited to the technical solution of the second embodiment in practical application. Figure 7In the system shown, a sample-and-hold device is used as the intermediate stage between the program-controlled fixed-frequency integrator and the analog-to-digital converter. The sample-and-hold device is controlled by a microcontroller to hold the peak voltage of the triangular wave output by the program-controlled fixed-frequency integrator for a certain period of time, so that the input voltage of the analog-to-digital converter is equal to the peak voltage of the program-controlled fixed-frequency integrator during this certain period of time, that is:

[0088] U adc =U cap .

[0089] like Figure 8 As shown, the sampler and holder is mainly composed of a sampling analog switch U5A, a sampling and holding capacitor C1, and a sampling operational amplifier U3A. The sampling analog switch U5A is closed when the forward integration process of the programmable fixed frequency integrator is about to end, and the sampling and holding capacitor C1 is charged by the operational amplifier U2B through the resistor R3. The sampling analog switch U5A is disconnected during the reverse integration and zeroing process of the programmable fixed frequency integrator to prevent the programmable fixed frequency integrator from discharging the sampler and holder, so that the voltage across the sampling and holding capacitor C1 does not change, and the output voltage of the sampler and holder is equal to the peak voltage of the programmable fixed frequency integrator. In this embodiment, the accuracy of the sampler and holder is related to the charge discharge speed of the sampling and holding capacitor C1. It is not appropriate for the sampling and holding capacitor C1 to directly drive the analog-to-digital converter. Therefore, the sampling operational amplifier U3A is used here as the input buffer of the analog-to-digital converter to reduce the power loss caused by the leakage current of the input circuit of the analog-to-digital converter to the sampling and holding capacitor C1, which helps to improve the holding accuracy of the sampler and holder. The holding accuracy of the sampler and holder can be expressed by the following formula:

[0090]

[0091] Where ΔV H is the voltage drop of the sample holder during the sample-and-hold process, C H is the capacity of the sampling and holding capacitor, Q is the charge discharged by the capacitor during the sampling and holding process, and t H is the maximum hold time, I H is the leakage current caused by the sampling analog switch and the sampling operational amplifier.

[0092] Fig. 9 for Figure 7 Signal timing diagram of the programmable fixed-frequency integrator of the system shown.

[0093] System calibration

[0094] 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 above embodiment is pre-stored with a typical capacity-temperature-humidity standard table determined by multiple experiments to solve this nonlinear problem. Because 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 above 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. Then, in actual measurement, only the table lookup and linear interpolation calculation are required to achieve accurate temperature compensation and humidity measurement.

[0095] Embodiment 4

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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 fixed 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, used to convert the humidity-sensitive capacitor integration waveform output by the fixed-frequency integration module into a first direct current signal whose amplitude is related to the capacitance of the humidity-sensitive capacitor; the capacitance conversion module includes an average value conversion circuit or a sample-and-hold circuit; an analog-to-digital conversion module, connected to the capacitance conversion module and the logic control module, for converting the first DC signal output by the capacitance conversion module into a corresponding digital signal, and outputting the digital signal to the logic control module, so that the logic control module can calculate the capacitance of the humidity-sensitive capacitor according to the first DC signal output by the capacitance conversion module, and further calculate 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 for measuring a second direct current signal representing the ambient temperature of the humidity-sensitive capacitor; The analog-to-digital conversion module is also connected to the temperature compensation module and the logic control module, and is used to convert the second DC signal output by the temperature compensation module into a corresponding digital signal, and output 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 first DC signal, and then calculate the humidity according to the capacitance of the humidity-sensitive capacitor after compensation.

3. The constant frequency humidity measurement system according to claim 2, characterized in that: The humidity-sensitive capacitance integral waveform is a periodic triangular waveform with constant frequency and variable amplitude; The first direct current signal and the second direct current signal are both direct current voltage signals.

4. The constant frequency humidity measurement system according to claim 1, characterized in that: The capacitance conversion module is an average value conversion circuit; Among them, the average value conversion circuit includes a rectifier and a low-pass filter, wherein the input end of the rectifier serves as the input end of the capacitance conversion module, connected to the output end of the fixed-frequency integration module, the output end of the rectifier is connected to the input end of the low-pass filter, and the output end of the low-pass filter is the output end of the capacitance conversion module, connected to the input end of the analog-to-digital conversion module.

5. The constant frequency humidity measurement system according to claim 1, characterized in that: The capacitance conversion module is a sample-and-hold circuit; The sampling and holding circuit includes a sampling analog switch, a sampling and holding capacitor and a sampling operational amplifier, wherein one end of the sampling analog switch is connected to the output end of the fixed-frequency integration module, and the other end is connected to the non-inverting end of the sampling operational amplifier through a sampling resistor, the non-inverting end of the sampling operational amplifier is also connected to one end of the sampling and holding capacitor, and the other end of the sampling and holding capacitor is grounded, the inverting end of the sampling operational amplifier is connected to the output end of the sampling operational amplifier through an RC parallel circuit module, and the output end of the sampling operational amplifier is connected to the input end of the analog-to-digital conversion module.

6. 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 analog-to-digital conversion module, and used to provide a reference voltage that meets preset conditions for the fixed-frequency integration module and the analog-to-digital 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.

7. The fixed-frequency humidity measurement system according to claim 1 or 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-sensitive capacitor integral waveform is converted into a first direct current signal whose amplitude is related to the capacitance of the humidity-sensitive capacitor to measure humidity.

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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