CN113625368A - Fixed-frequency humidity measurement system and method and readable storage medium - Google Patents

Fixed-frequency humidity measurement system and method and readable storage medium Download PDF

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CN113625368A
CN113625368A CN202111020814.8A CN202111020814A CN113625368A CN 113625368 A CN113625368 A CN 113625368A CN 202111020814 A CN202111020814 A CN 202111020814A CN 113625368 A CN113625368 A CN 113625368A
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humidity
module
frequency
constant
operational amplifier
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李哲
周强
任海富
包坤
刘钧
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Huayun Sounding Beijing Meteorological Technology Corp
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Huayun Sounding Beijing Meteorological Technology Corp
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Abstract

The invention provides a constant-frequency humidity measuring system. The system measures the humidity-sensitive capacitor by changing the structure and the control time sequence of the capacitance measuring circuit and using the fixed measuring frequency, solves the measuring error caused by the change of the frequency in the traditional oscillation circuit measuring process, simultaneously has the capacity of inhibiting the capacitance distributed to the ground, and is particularly suitable for the working environment with larger distributed capacitance of the sensor support in the sounding process. The humidity measuring system provided by the invention has small static and dynamic measuring errors and can meet the humidity observation requirement.

Description

Fixed-frequency humidity measurement system and method and readable storage medium
Technical Field
The invention relates to the technical field of meteorological detection, in particular to a constant-frequency humidity measuring system, a constant-frequency humidity measuring system method and a readable storage medium.
Background
Meteorological detection is an important means for acquiring meteorological elements, and is generally used to observe vertical distribution data of temperature, humidity, wind speed, wind direction, and air pressure on the ground to several tens of kilometers. Among many elements of weather detection, humidity plays an important role in weather forecast, weather monitoring and the like, and occupies an indispensable position in the field of weather detection. Different from static ground humidity observation equipment, the fixed-frequency humidity measurement system is a special humidity measurement system which is arranged on an air sounding balloon, is driven by battery power supply and can fail along with the breakage of the air sounding balloon, and has extremely high requirements on the volume, the weight, the power consumption and the cost of the system. Meanwhile, the working environment of the humidity sensor can change rapidly along with the rising of the sonde, and the requirements on the response speed and the measurement accuracy of humidity measurement are very high, so that a specific design needs to be carried out on a constant-frequency humidity measurement system.
The humidity sensitive element is a key component of the constant frequency humidity measurement system, and is generally a humidity sensitive capacitor or a humidity sensitive resistor. Because the humidity sensitive capacitor has higher accuracy, larger measurement range and shorter response time than the humidity sensitive resistor, the humidity sensitive capacitor has received wide attention from engineering and academic fields and is the mainstream humidity sensitive element in the industry at present. How to measure the capacitance value of the humidity-sensitive capacitor efficiently and accurately so as to measure the humidity is an important subject of the current meteorological detection.
Disclosure of Invention
In view of the above technical problems, embodiments of the present invention provide a constant frequency humidity measurement system, a constant frequency humidity measurement system method, and a readable storage medium.
According to a first aspect, the present invention provides a constant frequency humidity measurement system, characterized in that the system comprises:
the logic control module is used for outputting a time sequence control signal;
the constant-frequency integration module is connected with the logic control module and is used for measuring the capacitance value of the humidity-sensitive capacitor at a fixed frequency according to the time sequence control signal output by the logic control module to obtain a humidity-sensitive capacitor integration oscillogram;
the capacitance value conversion module is connected with the constant-frequency integration module and the logic control module and is used for converting the humidity-sensitive capacitor integration oscillogram output by the constant-frequency integration module into a square wave signal of which the duty ratio is related to the capacitance value of the humidity-sensitive capacitor and outputting the square wave signal to the logic control module;
the logic control module calculates the capacitance value of the humidity-sensitive capacitor according to the square wave signal output by the capacitance value conversion module, and then calculates the humidity according to the capacitance value of the humidity-sensitive capacitor.
In an embodiment of the present invention, the system further includes:
the temperature compensation module is used for measuring a direct current signal representing the environment temperature of the humidity sensitive capacitor;
and the analog-to-digital conversion module is connected with the temperature compensation module and the logic control module and is used for converting the electric signal output by the temperature compensation module into a corresponding digital signal and providing the digital signal to the logic control module so that the logic control module can carry out temperature compensation when calculating the capacitance value of the humidity-sensitive capacitor according to the square wave signal output by the capacitance value conversion module and then measure and calculate humidity according to the compensated capacitance value of the humidity-sensitive capacitor.
In one embodiment of the present invention, the integrated waveform of the humidity-sensitive capacitor is a periodic triangular waveform with constant frequency and varying amplitude.
In one embodiment of the invention, the frequency of the square wave signal is constant, and the duty ratio of the square wave signal is linearly changed along with the capacitance value of the humidity-sensitive capacitor.
In an embodiment of the invention, the fixed-frequency integrating module includes: the device comprises a first four-channel analog switch, a second four-channel analog switch, a first operational amplifier, a second operational amplifier, an integrating resistor and a humidity-sensitive capacitor;
the respective channel control ends of the first four-channel analog switch and the second four-channel analog switch are used as the input ends of the constant frequency integration module and are connected with the time sequence control signal output end of the logic control module, the first input end and the second input end of the first four-channel analog switch respectively receive a positive reference voltage and a negative reference voltage, the third input end and the fourth input end of the first four-channel analog switch are respectively grounded, the output end of the first four-channel analog switch is connected with the non-inverting input end of the first operational amplifier, and the inverting input end of the first operational amplifier is connected with the output end of the first operational amplifier; the output end of the first operational amplifier is connected with the inverting input end of the second operational amplifier through the integrating resistor, the non-inverting input end of the second operational amplifier is grounded, the output end of the second operational amplifier is connected with the output end of the second four-channel analog switch, the first input end and the second input end of the second four-channel analog switch are suspended, the third input end and the fourth input end of the second four-channel analog switch are connected with the output end of the first operational amplifier, and the humidity-sensitive capacitor is bridged between the inverting input end and the output end of the second operational amplifier; and the output end of the second operational amplifier is used as the output end of the constant frequency integration module and is connected with the input end of the capacity value conversion module.
In an embodiment of the present invention, the system may further include a reference voltage module, connected to the constant-frequency integrating module and the capacitance value converting module, for providing a reference voltage meeting a preset condition for the constant-frequency integrating module and the capacitance value converting module.
In an embodiment of the present invention, the preset conditions include: and in the working period of the constant-frequency integration module, the temperature drift of the reference voltage module is smaller than a given threshold value.
In an embodiment of the present invention, the capacitance-value converting module includes a comparator circuit, where the comparator circuit includes a PWM voltage divider and a comparator; the first input end of the comparator is used as the input end of the capacitance value conversion module and connected with the output end of the constant-frequency integration module, the second input end of the comparator is connected with the output end of the PWM voltage divider, the input end of the PWM voltage divider is connected with the output end of the reference voltage module, and the output end of the comparator is used as the output end of the capacitance value conversion module and connected with the input end of the logic control module.
In an embodiment of the present invention, the PWM voltage divider includes a Mos transistor and a third operational amplifier, a drain of the Mos transistor is connected to the output terminal of the reference voltage module, a gate of the Mos transistor is connected to the PWM signal output terminal of the logic control module, and a source of the Mos transistor is connected to a non-inverting terminal of the third operational amplifier through three resistors connected in series, wherein a node between two resistors close to the Mos transistor is grounded through a first intermediate capacitor, a non-inverting terminal of the third operational amplifier is grounded through a second intermediate capacitor, and an inverting terminal of the third operational amplifier is connected to a node between two resistors close to the third operational amplifier through a third intermediate capacitor; the output end of the third operational amplifier is connected with the inverting end, the output end of the third operational amplifier serving as the PWM voltage divider is connected to the inverting end of the operational amplifier serving as the comparator, the inverting end of the operational amplifier is connected with the output end of the constant-frequency integrating module, and the output end of the operational amplifier serving as the output end of the capacitance value conversion module is connected with the input end of the logic control module.
In an embodiment of the present invention, a capacity-temperature-humidity standard table is pre-stored in the logic control circuit, so that the logic control circuit finds the capacity-temperature-humidity standard table and linear interpolation calculation according to the received digital signal to measure the humidity.
In a second aspect, the present invention further provides a method for performing constant frequency humidity measurement by using the above system, the method comprising the following steps:
determining the working period of the constant-frequency integrating module according to the capacitance value of the measured humidity-sensitive capacitor; in particular implementations, the duty cycle of the constant frequency integration module is determined, for example, based on values recommended by a humidity sensitive capacitance data table.
The control logic control module outputs a corresponding time sequence control signal to the fixed-frequency integrating module in each working period, so that the fixed-frequency integrating module completes charging and discharging of the humidity-sensitive capacitor in each working period, periodic measurement of the humidity-sensitive capacitor is realized, and a humidity-sensitive capacitor integral oscillogram is obtained;
measuring and calculating humidity according to the humidity-sensitive capacitance integral oscillogram;
and measuring and calculating humidity by converting the humidity-sensitive capacitor integration oscillogram into a square wave signal of which the duty ratio is related to the capacitance value of the humidity-sensitive capacitor.
In an embodiment of the present invention, the control logic control module outputs a corresponding timing control signal to the fixed-frequency integrating module in each working cycle, so that the fixed-frequency integrating module completes 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 with equal length, and the control logic control module sequentially outputs corresponding time sequence control signals to the fixed-frequency integration module in the four time segments, so that the fixed-frequency integration module respectively completes normal phase charging, reverse charging, primary discharging and secondary discharging of the humidity sensitive capacitor in the four time segments.
According to a third aspect, the present invention also provides a readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the steps of the constant frequency humidity measurement method as described above.
Compared with the prior art, the embodiment of the invention at least has the following advantages:
the humidity measuring system provided by the invention is a humidity measuring system based on a fixed frequency integrator, the system skillfully applies a program-controlled integrator to the humidity measuring field by changing the structure and the control time sequence of a capacitance measuring circuit, and the humidity sensitive capacitor is measured by using fixed measuring frequency, so that the measuring error caused by the frequency change in the traditional oscillating circuit measuring process is fundamentally solved, and meanwhile, the integrator also has the capacity of inhibiting the capacitance distributed to the ground, and is particularly suitable for the working environment with larger distributed capacitance of a sensor support in 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 the method can be applied to the humidity observation field such as the ground and the like with higher requirement on accuracy.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention, in which:
FIG. 1 is a schematic diagram of a constant frequency humidity measurement system according to a first embodiment of the present invention;
FIG. 2 is a schematic diagram of a constant frequency humidity measurement system according to a second embodiment of the present invention;
FIG. 3 is a schematic diagram of a constant frequency integrator circuit of the constant frequency humidity measurement system of FIG. 2;
FIG. 4 is a timing diagram of the constant frequency integrator signal of the constant frequency humidity measurement system of FIG. 2;
FIG. 5 is a schematic diagram of a reference voltage circuit of the constant frequency humidity measurement system of FIG. 2;
FIG. 6 is a schematic diagram of a comparator circuit of the constant frequency humidity measurement system of FIG. 2.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
The humidity-sensitive capacitor is not an ideal capacitor, and under the environment of constant temperature and humidity, the capacity of the humidity-sensitive capacitor has obvious correlation with the measurement frequency, and the characteristic causes a certain test error to be introduced in the capacitance measurement process of the variable-frequency humidity measurement system based on the RC oscillating circuit.
Therefore, the invention provides a humidity measuring system with constant measuring frequency, which is used for eliminating the fluctuation of the humidity sensitive capacitance value caused by the frequency change and inhibiting the interference of the distributed capacitance of the bracket on the humidity measurement, thereby obviously improving the accuracy of the humidity measurement in the sounding process.
Example one
As shown in FIG. 1, the constant frequency humidity measurement system of the present embodiment is a set of programmable integration measurement systems designed around humidity sensitive capacitors. The system comprises:
a logic control module 100 for outputting a timing control signal;
the constant-frequency integration module 200 is connected to the logic control module 100, and is configured to measure a capacitance value of the humidity-sensitive capacitor at a fixed frequency according to the timing control signal output by the logic control module, so as to obtain a humidity-sensitive capacitor integration oscillogram;
a capacitance value conversion module 300, connected to the constant-frequency integration module 200 and the logic control module 100, configured to convert the humidity-sensitive capacitor integration waveform diagram output by the constant-frequency integration module 200 into a square wave signal whose duty ratio is related to a capacitance value of the humidity-sensitive capacitor, and provide the square wave signal to the logic control module 100;
the temperature compensation module 400 is used for measuring a direct current signal representing the environment temperature of the humidity-sensitive capacitor;
an analog-to-digital conversion module 500, connected to the temperature compensation module 400 and the logic control module 100, for converting the dc electrical signal output by the temperature compensation module 400 into a corresponding digital signal and outputting the digital signal to the logic control module;
the logic control module 100 calculates the capacitance value of the humidity-sensitive capacitor according to the square wave signal output by the capacitance value conversion module 300, performs temperature compensation when calculating the capacitance value of the humidity-sensitive capacitor according to the square wave signal output by the capacitance value conversion module 300, and calculates humidity according to the compensated capacitance value of the humidity-sensitive capacitor.
In addition, the system further includes a reference voltage module 600, connected to the constant-frequency integrating module 200 and the capacitance-value converting module 300, for providing a reference voltage meeting a preset condition for the constant-frequency integrating module 200 and the capacitance-value converting module 300.
The system skillfully applies the program-controlled integrator to the humidity measurement field by changing the structure and the control time sequence of the capacitance measurement circuit and measures the humidity sensitive capacitor by using fixed measurement frequency, thereby fundamentally solving the measurement error caused by the frequency change in the traditional oscillation circuit measurement process,
example two
In this embodiment, the system of the first embodiment may be composed of general devices such as a microcontroller, an analog switch, an operational amplifier, and an analog-to-digital converter, and a block diagram of the structure of the system may be shown in fig. 2.
In fig. 2, the microcontroller is responsible for integrator timing control, reading external adc register values, compensation calculation, calibration, communication, and other functions. An integrator consisting 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 waveform diagram with constant frequency and variable amplitude under the control of a microcontroller. And a comparator circuit positioned at the rear stage of the integrator converts the triangular wave into a square wave signal with constant frequency and duty ratio changing along with the capacitance value of the humidity-sensitive capacitor, and provides the square wave signal to the microcontroller so that the microcontroller can measure the capacitance value of the humidity-sensitive capacitor through the duty ratio. Meanwhile, the analog-to-digital converter is connected with the platinum resistor and used for converting the electric signal representing the environmental temperature of the humidity-sensitive capacitor into a corresponding digital signal and providing the digital signal to the microcontroller so that the microcontroller can perform corresponding temperature compensation when calculating the capacitance value of the humidity-sensitive capacitor.
The core of the measurement system is a programmed fixed-frequency integrator, a schematic circuit diagram of which is shown in fig. 3, and a timing diagram of signals of which is shown in fig. 4.
As can be seen from fig. 3, the program-controlled constant-frequency integrator mainly consists of two 4:1 analog switch U1 and operational amplifier U2. The operational amplifier U2A is used as a voltage follower and is used for eliminating the influence of the internal resistance of the analog switch on the circuit; operational amplifier U2B and integrating resistor R1And an integrating capacitor C (namely a humidity sensitive capacitor) are connected to form an integrator circuit, so that the function of converting the capacitance capacity to alternating voltage can be realized, and the interference of distributed capacitance to the ground at two sides of the capacitor C on a measurement result can be inhibited. The control timing sequence of the program control integration frequency divider is stored in a data cache of the microcontroller, and the DMA drive GPIO is controlled by the timer to write the data cache into the control pins A and B of the analog switches U1A and U1B respectively.
As can be seen from fig. 4, each duty cycle of the program-controlled fixed frequency integrator is 200uS, and is equally divided into 4 time segments of 50uS, which are sequentially gated from channel 1 to channel 4 of the analog switch by a timing control signal output by the microcontroller. DieThe four inputs of the analog switch U1A are a positive reference voltage Ref + and a negative reference voltage Ref-respectively, and a two-way power ground, with the output of the analog switch U1A serving as the input to the integrator U2A. At 0-50uS, the positive reference voltage Ref + passes through the integrating resistor R1The humidity-sensitive capacitor C is charged, and positive phase integration is performed, and since the voltage at the inverting 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 equation (2):
Figure BDA0003241891130000071
in the formula IchargeTo flow through a resistor R1The current of (2).
The other end of the humidity sensitive capacitor is connected with the voltage UcapI.e., the output voltage of operational amplifier U2B, can be represented by equation (3):
Figure BDA0003241891130000072
wherein C is a humidity sensitive capacitor, and t is an integration time.
When the positive phase integration is over, the voltage of the humidity sensitive capacitor C peaks and then the analog switch opens Ref +, strobes Ref-. At 50-100uS, the analog switch connects the negative reference voltage Ref-into the integrator to perform inverse integration on 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 polarities, so that the theoretical voltage of the humidity sensitive capacitor returns to zero at the end of the reverse integration. Because the operational amplifier is not an ideal amplifier, a small amount of residual charge still exists on the capacitor after the inverse integration is finished, and the residual charge can gradually form a certain direct current potential at two ends of the humidity sensitive capacitor, thereby bringing about a serious influence on the measurement.
Therefore, at 100-.
After the integrator is cleared, the analog switch strobes the channel 1 again, enters a new integration period, and continuously measures the humidity-sensitive capacitor in cycles.
Fig. 5 shows a reference voltage circuit of the measuring system. In this embodiment, the core of the reference voltage circuit is a micro-power shunt voltage reference. Because the working environment of the humidity measurement system is severe, the working temperature may change up to 100 ℃, and therefore, the temperature drift of the reference device will inevitably cause a significant influence on the measurement accuracy of the system. Generally, the solution to this problem is to replace the reference device with a lower temperature drift, but this will have a negative impact on the system cost. In this regard, the present invention proposes that the reference voltage Ref + is preferably connected to one end of the comparator through the PWM divider, which may greatly reduce the performance requirements of the reference device.
The Duty cycle Duty of the comparator output square wave can be represented by equation (4):
Figure BDA0003241891130000081
in the formula tcompIs the effective time of the comparator, UcompIs the reference voltage of the comparator.
By shaping the above equation (3), we can obtain:
Figure BDA0003241891130000082
the two paths of input voltages of the comparator are obtained by dividing the positive reference voltage Ref +, and can be expressed as:
Ucomp＝k·Ref+ (5)
where k is a constant partial pressure coefficient. The compounds represented by the formulae (5) and (6) can be obtained by substituting the compounds represented by the formula (4):
Figure BDA0003241891130000083
in the embodiment, a single measurement period of the program-controlled constant-frequency integrator is 200uS, and it can be considered that the temperature of the reference voltage does not change significantly in this time, and the error caused by the temperature drift is negligible. Under the assumption that the capacitance can be expressed by equation (7), the humidity measurement designed according to the concept of the present invention can effectively reduce the error of the reference voltage drift to the measurement result.
In this embodiment, the output of the program-controlled constant-frequency integrator is a triangular wave signal, which is not beneficial to direct acquisition by a low-speed analog-to-digital converter, and a part of circuits need to be added to convert the output signal of the program-controlled constant-frequency integrator into a square wave signal with constant frequency but with a duty ratio linearly changing with the capacitance value of the humidity-sensitive capacitor.
In the present embodiment, a comparator circuit is used as an intermediate stage between the programmable constant frequency integrator and the analog-to-digital converter, and a circuit diagram thereof is shown in fig. 6.
In the present embodiment, as shown in fig. 6, the comparator circuit mainly includes a Mos transistor Q1, a PWM voltage divider composed of an operational amplifier U3A, and a comparator U5. Unlike resistive voltage division, the PWM voltage division method stability is mainly affected by the PWM signal stability, i.e., mainly by the external crystal oscillator of the microcontroller. The stability of the crystal oscillator is far superior to that of the common metal film resistor, so that the influence of temperature on the accuracy of the voltage divider can be ignored. As can be seen from fig. 6, the drain of the Mos transistor is connected to the reference voltage Ref +, and the gate receives the PWM output signal of the microcontroller to implement PWM voltage division on the reference voltage Ref +. The PWM voltage divider outputs a square wave signal, which is converted to a stable dc signal after passing through a three-stage butterworth low pass filter composed of an operational amplifier U3A and peripheral resistive-capacitive elements, and used as a reference voltage for the comparator U5. The inverting terminal of the comparator U5 is directly connected with the output terminal of the program-controlled fixed-frequency integrator, the non-inverting terminal is connected with the output terminal of the three-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, the conversion of triangular wave to square wave is realized, and the conversion process of the capacity of the humidity-sensitive capacitor to the duty ratio of the square wave signal is completed.
System calibration
It should be noted that when the humidity measurement accuracy is required to be high, the capacity-temperature-humidity characteristic curve of the humidity sensitive capacitor is generally considered to be non-linear, and this curve is difficult to describe using a simple function. In order to improve the accuracy of the measuring system, a typical capacity-temperature-humidity standard table determined through multiple experiments is stored in advance in the microcontroller of the measuring system of the embodiment to solve the non-linear problem. Because the humidity-sensitive capacitor has certain discreteness, and the static capacity of the humidity-sensitive capacitor has certain deviation from the typical capacity capacitor, the typical capacitance-temperature-humidity standard table cannot be directly used for data conversion. In this embodiment, the calibration process is an important bridge connecting the moisture sensitive capacitor actually assembled by the measurement system with the typical capacitance-temperature-humidity standard meter. Through calibration, the proportion and offset of the actually assembled humidity-sensitive capacitor and the typical capacitor can be calculated and written into a memory of a measuring system, and then accurate temperature compensation and humidity measurement can be realized only by looking up a table and performing linear interpolation calculation during actual measurement.
EXAMPLE III
The present embodiment provides a storage medium storing a computer program which, when executed by a processor, performs the steps of the constant frequency humidity measurement system as described above.
The program code can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows.
Storage media includes permanent and non-permanent, removable and non-removable media implemented in any method or technology for storage of information. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of storage media may 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 disc read only memory (CD-ROM), Digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that may be used to store information that may be accessed by a computing device.
It is noted that the terms used herein are merely for describing particular embodiments and are not intended to limit exemplary embodiments according to the present application, and when the terms "include" and/or "comprise" are used in this specification, they specify the presence of features, steps, operations, devices, components, and/or combinations thereof.
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 otherwise described herein.
It should be understood that the exemplary embodiments herein may be embodied in many different forms and should not be construed as limited to only the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of these exemplary embodiments to those skilled in the art, and should not be construed as limiting the present invention.

Claims (11)

1. A constant frequency humidity measurement system, the system comprising:
the logic control module is used for outputting a time sequence control signal;
the constant-frequency integration module is connected with the logic control module and is used for measuring the capacitance value of the humidity-sensitive capacitor at a fixed frequency according to the time sequence control signal output by the logic control module to obtain a humidity-sensitive capacitor integration oscillogram;
the capacitance value conversion module is connected with the constant-frequency integration module and the logic control module and is used for converting the humidity-sensitive capacitor integration oscillogram output by the constant-frequency integration module into a square wave signal of which the duty ratio is related to the capacitance value of the humidity-sensitive capacitor and outputting the square wave signal to the logic control module;
the logic control module calculates the capacitance value of the humidity-sensitive capacitor according to the square wave signal output by the capacitance value conversion module, and calculates the high altitude humidity according to the capacitance value of the humidity-sensitive capacitor.
2. The constant frequency humidity measurement system of claim 1, further comprising:
the temperature compensation module is used for measuring a direct current signal representing the environment temperature of the humidity sensitive capacitor;
and the analog-to-digital conversion module is connected with the temperature compensation module and the logic control module and is used for converting the electric signal output by the temperature compensation module into a corresponding digital signal and providing the digital signal to the logic control module so that the logic control module can carry out temperature compensation when calculating the capacitance value of the humidity-sensitive capacitor according to the square wave signal output by the capacitance value conversion module and then measure and calculate humidity according to the compensated capacitance value of the humidity-sensitive capacitor.
3. The constant frequency humidity measurement system according to claim 1 or 2,
the humidity-sensitive capacitance integral oscillogram is a periodic triangular oscillogram with constant frequency and variable amplitude;
the frequency of the square wave signal is constant, and the duty ratio of the square wave signal changes linearly with the capacitance value of the humidity sensitive capacitor.
4. The constant frequency humidity measurement system of claim 1,
the fixed-frequency integration module comprises: the device comprises a first four-channel analog switch, a second four-channel analog switch, a first operational amplifier, a second operational amplifier, an integrating resistor and a humidity-sensitive capacitor;
the respective channel control ends of the first four-channel analog switch and the second four-channel analog switch are used as the input ends of the constant frequency integration module and are connected with the time sequence control signal output end of the logic control module, the first input end and the second input end of the first four-channel analog switch respectively receive a positive reference voltage and a negative reference voltage, the third input end and the fourth input end of the first four-channel analog switch are respectively grounded, the output end of the first four-channel analog switch is connected with the non-inverting input end of the first operational amplifier, and the inverting input end of the first operational amplifier is connected with the output end of the first operational amplifier; the output end of the first operational amplifier is connected with the inverting input end of the second operational amplifier through the integrating resistor, the non-inverting input end of the second operational amplifier is grounded, the output end of the second operational amplifier is connected with the output end of the second four-channel analog switch, the first input end and the second input end of the second four-channel analog switch are suspended, the third input end and the fourth input end of the second four-channel analog switch are connected with the output end of the first operational amplifier, and the humidity-sensitive capacitor is bridged between the inverting input end and the output end of the second operational amplifier; and the output end of the second operational amplifier is used as the output end of the constant frequency integration module and is connected with the input end of the capacity value conversion module.
5. The constant frequency humidity measurement system according to claim 1 or 2, wherein the system further comprises:
the reference voltage module is connected with the constant-frequency integration module and the capacity value conversion module and is used for providing reference voltages meeting preset conditions for the constant-frequency integration module and the capacity value conversion module;
wherein the preset conditions include: and in the working period of the constant-frequency integration module, the temperature drift of the reference voltage module is smaller than a given threshold value.
6. The constant frequency humidity measurement system of claim 5, wherein the capacitance-to-value conversion module includes a comparator circuit comprising a PWM voltage divider and a comparator;
the first input end of the comparator is used as the input end of the capacitance value conversion module and connected with the output end of the constant-frequency integration module, the second input end of the comparator is connected with the output end of the PWM voltage divider, the first input end of the PWM voltage divider is connected with the output end of the reference voltage module, the second input end of the PWM voltage divider is connected with the PWM signal output end of the logic control module, and the output end of the comparator is used as the output end of the capacitance value conversion module and connected with the input end of the logic control module.
7. The constant-frequency humidity measuring system according to claim 5, wherein the PWM voltage divider comprises a Mos transistor and a third operational amplifier, a drain of the Mos transistor is connected to the output terminal of the reference voltage module, a gate of the Mos transistor is connected to the PWM signal output terminal of the logic control module, a source of the Mos transistor is connected to a non-inverting terminal of the third operational amplifier through three resistors connected in series, a node between two resistors close to the Mos transistor is grounded through a first intermediate capacitor, a non-inverting terminal of the third operational amplifier is grounded through a second intermediate capacitor, and an inverting terminal of the third operational amplifier is connected to a node between two resistors close to the third operational amplifier through a third intermediate capacitor; the output end of the third operational amplifier is connected with the inverting end, the output end of the third operational amplifier serving as the PWM voltage divider is connected to the inverting end of the operational amplifier serving as the comparator, the inverting end of the operational amplifier is connected with the output end of the constant-frequency integrating module, and the output end of the operational amplifier serving as the output end of the capacitance value conversion module is connected with the input end of the logic control module.
8. The constant frequency humidity measurement system according to claim 1 or 2,
and a capacity-temperature-humidity standard table is prestored in the logic control circuit, so that the logic control circuit can measure and calculate the humidity by searching the capacity-temperature-humidity standard table and linear interpolation calculation according to the received digital signals.
9. A method of constant frequency humidity measurement based on the system of any one of claims 1 to 8, wherein the method comprises the steps of:
determining the working period of the constant-frequency integration module according to the fixed frequency of the capacitance value of the humidity-sensitive capacitor;
the control logic control module outputs a corresponding time sequence control signal to the fixed-frequency integrating module in each working period, so that the fixed-frequency integrating module completes charging and discharging of the humidity-sensitive capacitor in each working period, periodic measurement of the humidity-sensitive capacitor is realized, and a humidity-sensitive capacitor integral oscillogram is obtained;
measuring and calculating humidity by using the humidity-sensitive capacitance integral oscillogram;
and measuring and calculating humidity by converting the humidity-sensitive capacitor integration oscillogram into a square wave signal of which the duty ratio is related to the capacitance value of the humidity-sensitive capacitor.
10. The method as claimed in claim 9, wherein the control logic control module outputs a corresponding timing control signal to the constant-frequency integrating module in each duty cycle, so that the constant-frequency integrating module completes the charging and discharging of the humidity-sensitive capacitor in each duty cycle, comprising the steps of:
each working cycle is divided into four time segments with equal length, and the control logic control module sequentially outputs corresponding time sequence control signals to the fixed-frequency integration module in the four time segments, so that the fixed-frequency integration module respectively completes normal phase charging, reverse charging, primary discharging and secondary discharging of the humidity sensitive capacitor in the four time segments.
11. A readable storage medium storing a computer program which, when executed by a processor, performs the steps of the method of constant frequency humidity measurement according to claim 9 or 10.
CN202111020814.8A 2021-09-01 2021-09-01 Fixed-frequency humidity measurement system and method and readable storage medium Pending CN113625368A (en)

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