CN218675339U - Constant-frequency humidity measuring system - Google Patents
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- CN218675339U CN218675339U CN202122101930.4U CN202122101930U CN218675339U CN 218675339 U CN218675339 U CN 218675339U CN 202122101930 U CN202122101930 U CN 202122101930U CN 218675339 U CN218675339 U CN 218675339U
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Abstract
The utility model provides a decide humidity measurement system frequently. 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 used for converting the humidity-sensitive capacitor integration oscillogram output by the constant-frequency integration module into a first direct current signal of which the amplitude value is related to the capacitance value of the humidity-sensitive capacitor; and the analog-to-digital conversion module is connected with the capacitance value conversion module and the logic control module and is used for converting the first direct current signal output by the capacitance value conversion module into a corresponding digital signal and outputting the digital signal to the logic control module so that the logic control module can measure and calculate the humidity. The problem of measuring error caused by frequency change in the traditional oscillation circuit measuring process is solved.
Description
Technical Field
The utility model relates to a meteorological detection technical field especially relates to a decide humidity measurement system frequently.
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 extremely high requirements are also placed on the response speed and the measurement accuracy of humidity measurement, so that a fixed-frequency humidity measurement system needs to be designed in a targeted manner.
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.
SUMMERY OF THE UTILITY MODEL
To the technical problem, the embodiment of the utility model provides a decide humidity measurement system frequently.
According to a first aspect, the present invention provides a humidity measurement system with a fixed frequency, which is characterized in that:
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 used for converting the humidity-sensitive capacitor integration oscillogram output by the constant-frequency integration module into a first direct current signal of which the amplitude value is related to the capacitance value of the humidity-sensitive capacitor;
the analog-to-digital conversion module is connected with the capacitance value conversion module and the logic control module and is used for converting the first direct current signal output by the capacitance value 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 value of the humidity-sensitive capacitor according to the first direct current signal output by the capacitance value conversion module and further measure and calculate 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 second direct current signal representing the environment temperature of the humidity sensitive capacitor;
the analog-to-digital conversion module is further connected with the temperature compensation module and the logic control module, and is used for converting the second direct current signal output by the temperature compensation module into a corresponding digital signal and outputting the digital signal to the logic control module, so that the logic control module can perform temperature compensation when calculating the capacitance value of the humidity-sensitive capacitor according to the first direct current signal, and then measure and calculate humidity according to the compensated capacitance value of the humidity-sensitive capacitor.
In an embodiment of the present invention, the humidity-sensitive capacitance integral oscillogram is a periodic triangular oscillogram with constant frequency and varying amplitude.
In an embodiment of the present invention, the first dc signal and the second dc signal are dc voltage signals.
In an embodiment of the present invention, the fixed-frequency integration 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 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 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 capacitance value converting module is an average value converting circuit.
The average value conversion circuit comprises a rectifier and a low-pass filter, wherein the input end of the rectifier is used as the input end of the capacitance value conversion module and is connected with the output end of the constant frequency integration module, the output end of the rectifier is connected with the input end of the low-pass filter, and the output end of the low-pass filter is used as the output end of the capacitance value conversion module and is connected with the input end of the analog-to-digital conversion module.
In an embodiment of the present invention, the rectifier is a full-wave rectifier.
In another embodiment of the present invention, the capacitance value converting module is a sample-and-hold circuit.
The utility model discloses a further embodiment, the sample hold circuit includes sampling analog switch, sample hold capacitor and sampling operational amplifier, wherein, the one end of sampling analog switch is connected the output of fixed frequency integral module, the other end pass through sampling resistance and connect the homophase end of sampling operational amplifier, the homophase end of sampling operational amplifier still connects the one end of sample hold capacitor, the other end ground connection of sample hold capacitor, the inverting terminal of sampling operational amplifier pass through RC parallel circuit module with the output of sampling operational amplifier is connected, the output of sampling operational amplifier does the output of capacitance value conversion module is connected the input of analog-to-digital 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 analog-to-digital conversion module, for providing a reference voltage meeting a preset condition for the constant-frequency integrating module and the analog-to-digital conversion module;
in an embodiment of the present invention, the preset condition includes: 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 temperature compensation module includes a platinum resistor circuit.
In an embodiment of the present invention, the logic control circuit has a capacity-temperature-humidity standard table pre-stored therein, so that the logic control circuit calculates the humidity by looking up the capacity-temperature-humidity standard table and linear interpolation according to the received digital signal.
Compared with the prior art, the embodiment of the utility model has the following advantage at least:
the utility model provides a humidity measurement system is a humidity measurement system based on constant frequency integrator, this system is through changing electric capacity measuring circuit's structure and control chronogenesis, be applied to humidity measurement field with programme-controlled integrator ingeniously, use fixed measuring frequency to measure humidity sensitive capacitor, fundamentally has solved the measuring error who produces because of the frequency change in traditional oscillation circuit measurement process, the integrator still has the ability of restraining the distributed capacitance to ground simultaneously, especially, be fit for exploring the great operational environment of in-process sensor support distributed capacitance. 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 form a part of the present application, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention without undue limitation of the invention:
fig. 1 is a schematic diagram illustrating a constant frequency humidity measurement system according to a first embodiment of the present invention;
fig. 2 is a schematic diagram illustrating 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 an average value converter circuit of the constant frequency humidity measurement system of FIG. 2;
FIG. 7 is a schematic diagram of a constant frequency humidity measurement system according to a third embodiment of the present invention;
FIG. 8 is a schematic circuit diagram of a sample holder of the constant frequency humidity measurement system of FIG. 7;
FIG. 9 is a timing diagram of the signals of the constant frequency integrator of the constant frequency humidity measurement system of FIG. 7.
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 accompanying drawings in conjunction with embodiments.
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 utility model provides a invariable measuring frequency's humidity measurement system to eliminate the humidity sensitive capacitance numerical value fluctuation that frequency variation arouses, and restrain the interference of support distribution electric capacity to humidity measurement, show the degree of accuracy that promotes sounding in-process humidity measurement from this.
Example one
As shown in FIG. 1, the constant-frequency humidity measuring system of the present embodiment is a set of programmable integration measuring systems designed around a humidity sensitive capacitor. 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, for converting the humidity-sensitive capacitor integration oscillogram output by the constant-frequency integration module into a first direct current signal whose amplitude is related to the capacitance value of the humidity-sensitive capacitor;
the temperature compensation module 400 is used for measuring a second direct current signal representing the environment temperature of the humidity-sensitive capacitor;
an analog-to-digital conversion module 500, connected to the capacitance value conversion module 300, the temperature compensation module 400 and the logic control module 100, for respectively converting the first dc signal output by the capacitance value conversion module 300 and the second dc signal output by the temperature compensation module 400 into corresponding digital signals, and outputting the digital signals to the logic control module 100, so that the logic control module 100 can measure and calculate humidity;
and a reference voltage module 600 connected to the constant frequency integration module 200 and the analog-to-digital conversion module 500, and configured to provide reference voltages meeting preset conditions for the constant frequency integration module 200 and the analog-to-digital conversion module 500.
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. Under the control of a microcontroller, 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 wave waveform diagram with constant frequency and variable amplitude. The rectification circuit and the low-pass filter circuit which are positioned at the rear stage of the integrator form an average value converter which is used for converting the triangular wave into a direct current voltage signal, and finally, the direct current voltage signal is converted into a corresponding digital signal by an analog-to-digital converter for being read by the microcontroller. Meanwhile, the analog-to-digital converter is connected with the platinum resistor and used for measuring the ambient temperature of the humidity sensitive capacitor so as to compensate the temperature in the humidity measuring process.
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.
From FIG. 3As known, 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 integral resistor R 1 And 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 time sequence of the program control integration frequency divider is stored in a data cache of the microcontroller, and the DMA is controlled by the timer to drive the GPIO to write the data cache into control pins A and B of the analog switches U1A and U1B at a high speed.
As can be seen from fig. 4, each working cycle of the program-controlled constant-frequency integrator is 200uS, and is equally divided into 4 time slices of 50uS, which are sequentially gated from channel 1 to channel 4 of the analog switch by the timing control signal output by the microcontroller. The four inputs of the analog switch U1A are a positive reference voltage Ref + and a negative reference voltage Ref-respectively, and two power grounds, and the output of the analog switch U1A is used as the input of the integrator U2A. At 0-50uS, the positive reference voltage Ref + passes through the integrating resistor R 1 The humidity-sensitive capacitor C is charged and subjected to forward integration, and since the voltage at the inverting input end of the operational amplifier U2B is equal to the voltage at the non-inverting input end, the charging current of the humidity-sensitive capacitor can be expressed by the formula (2):
in the formula I charge To flow through a resistor R 1 The current of (2).
The other end of the humidity sensitive capacitor is connected with a voltage U cap That is, the output voltage of the operational amplifier U2B, can be represented by equation (3):
wherein C is a humidity sensitive capacitor, and t is an integration time.
When the forward 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 100-200uS, the analog switch U1B short-circuits the integrating resistor and the integrating capacitor to form a capacitor discharging loop, and the integrator is cleared to eliminate residual charges so as to avoid the situation of charge accumulation.
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 adversely affect the cost of the system. To this end, the present invention provides that the reference voltage Ref + can be preferably connected to the external reference voltage input port of the analog-to-digital converter to substantially reduce the performance requirements of the reference device.
In this case, the voltage U acquired for the analog-to-digital converter adc May be represented by formula (4):
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.
By shaping the above equation (2), we can obtain:
for a triangular wave, the crest factor is
The averaging circuit consisting of a rectifier and a low-pass filter is capable of providing a linear conversion of a triangular wave to dc, which can be expressed as:
U adc ＝k·U cap (5)
where k is a constant mean coefficient. The compounds of formulae (4) and (5) can be substituted for formula (3):
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 this assumption, the capacitance capacity can be represented by equation (6), according to the utility model discloses a humidity measurement of design can effectively reduce the error that reference voltage drifts and cause the measuring result.
In this embodiment, the output of the program-controlled constant-frequency integrator is a triangular wave signal, which is not beneficial for the low-speed analog-to-digital converter to directly collect, and a part of circuits need to be added to convert the output signal of the program-controlled constant-frequency integrator into a direct current signal. In the embodiment, an average value conversion 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, the average value conversion circuit includes a full-wave rectifier, which is an enhancement circuit of a half-wave rectifier, and is composed of an operational amplifier U3, diodes D1, D2, and 7 peripheral resistors. In the circuit R 3 ＝R 5 Make the half-wave rectifierThe partial gain is 1; r 4 ＝2R 6 The gain of the half-wave rectifier with respect to the input signal is made to be 2. When the capacitance C 1 In the absence, for a positive half cycle signal, the U3B output is the input signal summed with the reference signal (power ground); for negative half cycle signals, the inverse wave (gain of 2) whose U3B output is the half-wave rectifier output is summed with the input signal. Thus, 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 adder part of the full-wave rectifier can form a first-order low-pass filter, and the cutoff frequency F can be expressed as:
the proper turning frequency can balance between the filtering effect and the time delay when R is 7 ＝20KΩ，C 1 When the frequency of the filter is about 10Hz and the delay time is about 0.08S for 5V input voltage, which is far shorter than the response time of the humidity sensitive capacitor, the requirement of the humidity detection system can be met when the frequency of the filter is about 820 nF.
EXAMPLE III
Of course, the present invention is not limited to this. For example, a sample holder may be used in the system shown in fig. 7 as an intermediate stage between the programmable constant frequency integrator and the analog-to-digital converter, and the microcontroller controls to hold the peak voltage of the triangular wave output by the programmable constant frequency integrator for a certain time, so that the input voltage of the analog-to-digital converter is equal to the peak voltage of the programmable constant frequency integrator within the certain time, that is:
U adc ＝U cap
as shown in fig. 8, the sample-and-hold unit 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 program-controlled fixed-frequency integrator is about to end, and the sampling holding capacitor C1 is charged by the operational amplifier U2B through the resistor R3. The sampling analog switch U5A is disconnected in the reverse integration and zero clearing process of the program-controlled fixed-frequency integrator, the program-controlled fixed-frequency integrator is prevented from discharging the sampling holder, the voltage at two ends of the sampling holding capacitor C1 is enabled not to change, and the output voltage of the sampling holder is equal to the peak voltage of the program-controlled fixed-frequency integrator. In this embodiment, the precision of the sample-and-hold device is related to the charge discharging speed of the sample-and-hold capacitor C1, and it is not suitable for the sample-and-hold capacitor C1 to directly drive the analog-to-digital converter, so the sampling operational amplifier U3A is adopted 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 sample-and-hold capacitor C1, which is helpful to improve the holding precision of the sample-and-hold device. The holding accuracy of the sample holder can be expressed by the following equation:
in the formula, Δ V H For the voltage drop of the sample holder during sample-and-hold, C H For the capacity of the sample-and-hold capacitor, Q is the charge and capacity released by the capacitor during the sample-and-hold process, t H For maximum retention time, I H Is the leakage current caused by the sampling analog switch and the sampling operational amplifier.
Fig. 9 is a timing diagram of signals for a programmed fixed frequency integrator when a sample-holder is employed.
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 four
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 (10)
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 used for converting the humidity-sensitive capacitor integration oscillogram output by the constant-frequency integration module into a first direct current signal of which the amplitude value is related to the capacitance value of the humidity-sensitive capacitor;
and the analog-to-digital conversion module is connected with the capacitance value conversion module and the logic control module and is used for converting the first direct current signal output by the capacitance value conversion module into a corresponding digital signal and outputting the digital signal to the logic control module so that the logic control module can measure and calculate the humidity.
2. The constant frequency humidity measurement system of claim 1, further comprising:
the temperature compensation module is used for measuring a second direct current signal representing the environment temperature of the humidity sensitive capacitor;
the analog-to-digital conversion module is also connected with the temperature compensation module and the logic control module, and is used for converting the second direct current signal output by the temperature compensation module into a corresponding digital signal, outputting the digital signal to the logic control module so as to enable the logic control module to carry out temperature compensation, and then measuring and calculating 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 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 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 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.
4. The constant-frequency humidity measurement system according to claim 1 or 2, wherein the capacitance value conversion module is an average value conversion circuit.
5. The constant-frequency humidity measuring system according to claim 4, wherein the average value converting circuit comprises a rectifier and a low-pass filter, wherein an input terminal of the rectifier is connected to an output terminal of the constant-frequency integrating module as an input terminal of the capacitance value converting module, an output terminal of the rectifier is connected to an input terminal of the low-pass filter, and an output terminal of the low-pass filter is connected to an input terminal of the analog-to-digital converting module as an output terminal of the capacitance value converting module.
6. The constant frequency humidity measurement system of claim 5, wherein said rectifier is a full wave rectifier.
7. The constant frequency humidity measurement system according to claim 1 or 2, wherein the capacitance value conversion module is a sample-and-hold circuit.
8. The constant-frequency humidity measuring system according to claim 7, wherein the sample-and-hold circuit comprises a sample analog switch, a sample-and-hold capacitor and a sample operational amplifier, wherein one end of the sample analog switch is connected to the output end of the constant-frequency integrating module, the other end of the sample analog switch is connected to the non-inverting end of the sample operational amplifier through a sample resistor, the non-inverting end of the sample operational amplifier is further connected to one end of the sample-and-hold capacitor, the other end of the sample-and-hold capacitor is grounded, the inverting end of the sample operational amplifier is connected to the output end of the sample operational amplifier through an RC parallel circuit module, and the output end of the sample operational amplifier is connected to the input end of the analog-to-digital conversion module.
9. The constant frequency humidity measurement system of claim 1, further comprising:
and the reference voltage module is connected with the fixed-frequency integration module and the analog-to-digital conversion module and is used for providing reference voltages meeting preset conditions for the fixed-frequency integration module and the analog-to-digital conversion module.
10. The constant frequency humidity measurement system of claim 2,
the temperature compensation module includes a platinum resistance circuit.
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| CN202122101930.4U CN218675339U (en) | 2021-09-01 | 2021-09-01 | Constant-frequency humidity measuring system |
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