CN106770507B - Humidity detection device and method based on capacitor - Google Patents
Humidity detection device and method based on capacitor Download PDFInfo
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- CN106770507B CN106770507B CN201710028420.4A CN201710028420A CN106770507B CN 106770507 B CN106770507 B CN 106770507B CN 201710028420 A CN201710028420 A CN 201710028420A CN 106770507 B CN106770507 B CN 106770507B
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- 239000003990 capacitor Substances 0.000 title claims abstract description 53
- 238000001514 detection method Methods 0.000 title claims abstract description 19
- 238000000034 method Methods 0.000 title claims abstract description 16
- 238000005259 measurement Methods 0.000 claims description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 13
- 230000003321 amplification Effects 0.000 claims description 12
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 12
- 229910052751 metal Inorganic materials 0.000 claims description 11
- 239000002184 metal Substances 0.000 claims description 11
- 238000004364 calculation method Methods 0.000 claims description 3
- 230000010287 polarization Effects 0.000 claims description 3
- 230000001105 regulatory effect Effects 0.000 claims description 3
- 238000012360 testing method Methods 0.000 claims description 3
- 230000035945 sensitivity Effects 0.000 abstract description 5
- 239000007789 gas Substances 0.000 description 6
- 230000000694 effects Effects 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 101000872083 Danio rerio Delta-like protein C Proteins 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000003723 Smelting Methods 0.000 description 1
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- 229910052782 aluminium Inorganic materials 0.000 description 1
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
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- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
- G01N27/221—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance by investigating the dielectric properties
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Abstract
The invention discloses a humidity detection device and method based on a capacitor, comprising a radio frequency transmitting module, a radio frequency receiving module, an amplifying circuit, an LC oscillating circuit and a humidity detection capacitor C 2 And a resistor R, wherein the radio frequency transmitting module and the radio frequency receiving module are in wireless connection through a wireless antenna, and are putThe large circuit is connected with the radio frequency receiving module and used for amplifying the received radio frequency signals, one end of the LC oscillating circuit is connected with the amplifying circuit, the other end of the LC oscillating circuit is connected with one end of the resistor R, the other end of the resistor R is grounded, and the humidity measuring capacitor C 2 Capacitance C with LC oscillating circuit 1 Parallel and capacitance C 1 Is an adjustable capacitor with an indication. The invention ensures the high sensitivity and precision of the capacitance hygrometer, does not need high-precision instrument for assistance, greatly reduces the cost of the capacitance hygrometer, and is convenient for application and popularization.
Description
Technical Field
The present invention relates to a humidity detecting device and method, and more particularly, to a capacitance-based humidity detecting device and method.
Background
The hygrometer is a physical property analyzer for measuring the humidity of gas. Humidity refers to the water vapor content of the gas, and there are two methods of absolute humidity and relative humidity. Absolute humidity refers to the absolute content of water vapor in a gas, most commonly in grams/meter 3. At a certain temperature and pressure, the water vapor content in unit volume has a certain limit, which is called saturated water vapor content. Relative humidity refers to the ratio of the absolute content of water vapor in a gas to the saturated water vapor content in the same volume of gas at the same temperature and pressure, commonly referred to as%r.h. Hygrometers are widely used, for example, in the production of ultra-pure metal smelting, textile processing, paper and printing, and in food storage and weather measurement, it is often necessary to use a hygrometer to measure or control the humidity of air or industrial process gases.
Current commercial hygrometers generally contain a total of three. Respectively a lithium chloride hygrometer, an alumina hygrometer and a wet and dry bulb hygrometer. However, since the above hygrometers react to humidity by changing material properties and temperature differences, the present hygrometers suffer from a number of disadvantages, including insufficient sensitivity of the hygrometers, slow reaction rates, proper temperature conditions and loss of multiple measurements. In many fields, humidity detection is particularly important, for example, the chemical industry has a particularly high requirement on the humidity measurement accuracy of the environment, and some chemical products can react with the humidity of the environment rapidly, so that the requirement on the sensitivity of the detection device is also high.
Capacitance humidity measurement is one of the important methods of new hygrometers today. Unlike the material method, the capacitance method humidity measurement device has many advantages such as high measurement sensitivity, small loss, and the like. However, the humidity measurement by the capacitance method needs to measure small capacitance change, so many capacitance methods today use many precise instruments for measuring the humidity. The manufacturing process of the precise instrument is complex and the cost is high, so that the capacitance humidity measuring device is high in price and difficult to popularize and apply effectively.
Disclosure of Invention
The invention aims to solve the technical problem of providing a humidity detection device and a humidity detection method based on a capacitor, which do not need a compact instrument, thereby reducing the humidity detection cost of the capacitor and being convenient for popularization and application.
In order to solve the technical problems, the invention adopts the following technical scheme:
humidity detection device based on electric capacity, its characterized in that: comprises a radio frequency transmitting module, a radio frequency receiving module, an amplifying circuit, an LC oscillating circuit and a humidity measuring capacitor C 2 And the resistor R is in wireless connection with the radio frequency receiving module through a wireless antenna, the amplifying circuit is connected with the radio frequency receiving module and used for amplifying received radio frequency signals, one end of the LC oscillating circuit is connected with the amplifying circuit, the other end of the LC oscillating circuit is connected with one end of the resistor R, the other end of the resistor R is grounded, and the humidity measuring capacitor C is used for measuring humidity 2 Capacitance C with LC oscillating circuit 1 Parallel and capacitance C 1 Is an adjustable capacitor with an indication.
Further, the radio frequency transmitting module and the radio frequency receiving module adopt an FM transmitting module and an FM receiving module.
Further, the FM receiving module adopts an SP7021FM receiving module.
Further, the humidity measurement capacitor C 2 Two ends are connected with an oscilloscope in parallel.
Further, the humidity measurement capacitor C 2 The capacitor is a flat capacitor and is composed of two parallel square metal plates.
The humidity detection method based on the capacitor is characterized by comprising the following steps of:
step one: calibrating in a humidity-known environment, wherein the humidity is recorded as RH1, and the frequency F emitted by the radio frequency emitting module 0 At a constant value, capacitor C 1 And a humidity measurement capacitor C 2 Parallel capacitance value C of (2) 0 For a fixed value, adjust the capacitance C 1 Make amplification circuit amplification maximum, measure humidity electric capacity C 2 ＝C 0 -C 1 Recording the capacitance value of the humidity measurement at this time as C 2 1；
Step two: testing air humidity, recording the tested air humidity as RH2, and regulating capacitance C 1 The amplification factor of the amplifying circuit is maximized, and the capacitance value of the humidity measurement at the moment is recorded as C 2 2；
Step three: calculating the capacitance difference DeltaC=C of the measured humidity 2 2-C 2 1, humidity difference Δrh=rh2-RH 1, and the value of the measured air humidity RH2 is calculated according to the formula Δrh=γ·Δc, where γ is a constant.
Further, in the first step, the adjustment of C1 makes the amplification factor of the amplifying circuit be maximally adjusted through observation of an oscilloscope.
Further, the calculation process of the formula Δrh=γ·Δc is as follows:
humidity of air
wherein ,
is biased by water in air>
Is the saturation bias of air at a certain temperature;
the relative permittivity and the air composition bias are related by
wherein ,αi The polarization intensity of each component;
bias of water vapor
Is obtained from (1) (2) (3)
When E shaped r With little variation, equation (4) can be approximated as:
is available in the form of
From dielectric constant e= e r ∈x (7)
Is available in the form of
Order the
Obtainable Δrh=μ·Δe (10)
The capacitance determination formula for an infinite uniformly charged two parallel plates is known:
wherein C is the capacitance of the capacitor, E 0 For vacuum dielectric constant, E r E is the dielectric constant of the medium in the capacitor, d is the spacing between the two parallel plates;
the capacitance is defined as:
C＝Q/U (12)
q is the amount of charge in one end of the capacitor and U is the potential difference across the capacitor;
the theoretical value of the capacitance C is
Since there is no so-called infinite metal parallel plate in reality, the metal plates at both ends will not be charged uniformly, so it is approximated as:
C＝C 0 +Δ∈·k (14)
ΔC＝Δ∈·k (15)
Δ∈＝ΔC/k (16)
wherein C0 To know a certain capacitance value, k is the capacitance change rate around this point;
thereby can be obtained
And (3) making:
then:
ΔRH＝γ·ΔC (19)。
compared with the prior art, the invention has the following advantages and effects: the invention ensures the high sensitivity and precision of the capacitance hygrometer, does not need high-precision instrument for assistance, greatly reduces the cost of the capacitance hygrometer, and is convenient for application and popularization.
Drawings
Fig. 1 is a schematic diagram of a capacitance-based humidity detection apparatus of the present invention.
Fig. 2 is a graph of signal amplitude versus capacitance for an FM receive module of the invention.
FIG. 3 is a graph of experimental data of the present invention.
Detailed Description
The present invention will be described in further detail by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and not limited to the following examples.
As shown in the figure, the humidity detection device based on the capacitor of the invention comprises a radio frequency transmitting module 1, a radio frequency receiving module 2, an amplifying circuit 3, an LC oscillating circuit and a humidity detection capacitor C 2 And a resistor R, a radio frequency transmitting module 1 and a radio frequency receiving moduleThe module 2 is connected with the radio frequency receiving module 2 by a wireless antenna in a wireless way, the amplifying circuit 3 is connected with the radio frequency receiving module 2 for amplifying the received radio frequency signal, one end of the LC oscillating circuit is connected with the amplifying circuit, the other end of the LC oscillating circuit is connected with one end of the resistor R, the other end of the resistor R is grounded, and the humidity measuring capacitor C is used for measuring the humidity 2 Capacitance C with LC oscillating circuit 1 Parallel and capacitance C 1 Is an adjustable capacitor with an indication.
The radio frequency transmitting module and the radio frequency receiving module adopt an FM transmitting module and an FM receiving module. The FM receiving module adopts an SP7021FM receiving module. Capacitance C for measuring humidity 2 Two ends of the capacitor are connected with an oscilloscope in parallel, and the humidity measurement capacitor C can be observed through the oscilloscope 2 Is a waveform signal of (a). Capacitance C for measuring humidity 2 The capacitor is a flat capacitor and is composed of two square metal plates which are parallel to each other and have a side length of 2 cm.
Capacitance C for measuring humidity 2 Based on the amplifying effect of the resonant circuit, the FM receiving module is configured to receive a carrier signal with a high frequency, pick out a certain frequency by the resonant circuit, and then demodulate the carrier signal into a useful signal. The FM receiving module is used because a resonant circuit with a high frequency can amplify the variation of a small capacitance. Unlike a standard RLC resonant circuit, the circuit employs LC parallel resonance. The resonant circuit means that when the frequency of the circuit changes, the signal intensity in the circuit changes, and when the frequency in the circuit reaches the resonant frequency of the circuit, the signal intensity is maximum, and a resonance phenomenon occurs. If the capacitance in the circuit changes at this time, the resonance phenomenon disappears and the signal intensity immediately becomes small. The resonant circuit is thus able to react to small changes in capacitance. The FM receiving module we use is an SP7021FM receiving module that receives a fixed mixed signal wave through a resonance port, and then separates the useful signal by demodulation.
A capacitance-based humidity detection method, comprising the steps of:
the humidity is referred to herein as relative humidity.
Step one: calibrating in a humidity-known environment, wherein the humidity is recorded as RH1, and the frequency F emitted by the radio frequency emitting module 0 At a constant value, capacitor C 1 And measuringHumidity capacitor C 2 Parallel capacitance value C of (2) 0 For a fixed value, adjust the capacitance C 1 Make amplification circuit amplification maximum, measure humidity electric capacity C 2 ＝C 0 -C 1 Recording the capacitance value of the humidity measurement at this time as C 2 1；
Step two: testing air humidity, recording the tested air humidity as RH2, and regulating capacitance C 1 The amplification factor of the amplifying circuit is maximized, and the capacitance value of the humidity measurement at the moment is recorded as C 2 2；
Step three: calculating the capacitance difference DeltaC=C of the measured humidity 2 2-C 2 1, humidity difference Δrh=rh2-RH 1, and the value of the measured air humidity RH2 is calculated according to the formula Δrh=γ·Δc, where γ is a constant.
In the first step, the amplification factor of the amplifying circuit is adjusted by adjusting C1 to be maximum through observation of an oscilloscope.
The calculation process of the formula Δrh=γ·Δc is:
the relative humidity RH of air is a measure of how much moisture is contained in the air, and its formula is,
humidity of air
wherein ,
is biased by water in air>
Is the saturation bias of air at a certain temperature (as a function of temperature);
the relative permittivity and the air composition bias are related by
wherein ,αi The polarization intensity of each component;
while we only concern the bias of the water vapor
Analysis from (1) (2) (3)
and ∈r Can be obtained by the relation of (2)
When E shaped r With little variation, equation (4) can be approximated as:
is available in the form of
From dielectric constant e= e r ∈ 0 (7)
Is available in the form of
Order the
It can be seen that mu is a constant
Thus, ΔRH=μ.Δε (10)
From equation (10) we get the law of relative humidity variation with dielectric constant.
For air, the relative permittivity E of air r Depending on temperature, humidity, pressure, and also the composition of the air, etc. Changes in air humidity cause e r The main reason for the minor change is that the air contains moisture and water moleculesIs of a polarity such that its concentration changes more greatly than the relative permittivity of other molecules with respect to air. Since it causes E r A slight change in air humidity can also cause a slight change in capacitance. The relationship between capacitance and dielectric constant is deduced as follows:
the capacitance determination formula for an infinite uniformly charged two parallel plates is known:
wherein C is the capacitance of the capacitor, E 0 For vacuum dielectric constant, E r E is the dielectric constant of the medium in the capacitor, d is the spacing between the two parallel plates;
the capacitance is defined as:
C＝Q/U (12)
q is the amount of charge in one end of the capacitor and U is the potential difference across the capacitor;
in reality, there is no so-called infinite metal parallel plate, and the metal plates at both ends are not uniformly charged. It is very difficult to find a decision formula for the actual capacitance. Two metal discs are used in the experiment, and two ends are connected through a power supply. At this time its capacitance formula is not being followed
Theoretical value of capacitance C
The last formula is just an approximation. If we assume C is a function C (E) about E, but if C 0 When the change delta epsilon at the capacitor is very small, the method can be used for processing by an approximation method:
C＝C 0 +Δ∈·k (14)
ΔC＝Δ∈·k (15)
Δ∈＝ΔC/k (16)
wherein C0 (unknown measurable) is given a certain capacitance value, k (unknown measurable) is the electricity in the vicinity of this pointRate of change of volume;
thereby can be obtained
And (3) making:
then:
ΔRH＝γ·ΔC (19)
the amount of change in humidity is proportional to the amount of change in capacitance.
The humidity effect of the invention is further verified by a specific experimental method:
the invention loads a signal frequency of 1KHz to a carrier signal of 89.1M through an FM transmitting module, and then receives the signal through an FM receiving module and demodulates the signal into a useful signal of 1 KHz. The useful signal was input into an oscilloscope and the signal intensity was observed. The other part of experimental device is the capacitor where air is located, we use two square metal aluminum sheets with side length of 2cm parallel to each other as a capacitor (induction capacitor), and connect the capacitor in parallel to an adjustable capacitor on a circuit board through a wire, so as to change the adjustable capacitor, and make the circuit reach a sensitive range, as shown in fig. 2, the relation between the signal amplitude and the capacitance value of the FM receiving module. The sensing capacitor is placed in a closed box, moisture is introduced into the box, the internal humidity is gradually increased, and at the moment, the signal intensity in the oscilloscope is compared with a commercial hygrometer in the box to obtain relevant data, as shown in fig. 3.
After analysis of the data by measurement with the experimental apparatus, it was found that the commercial hygrometer was changed in proportion to the change in signal measured by the apparatus by a relative humidity rise of 1% and a change in signal intensity of about 20 mV. The device can thus measure the amount of change in the relative humidity of the air.
The foregoing description of the invention is merely exemplary of the invention. Various modifications or additions to the described embodiments may be made by those skilled in the art to which the invention pertains or in a similar manner, without departing from the spirit of the invention or beyond the scope of the invention as defined in the appended claims.
Claims (3)
1. A humidity detection method based on capacitance comprises a radio frequency transmitting module, a radio frequency receiving module, an amplifying circuit, an LC oscillating circuit and a humidity detection capacitor C 2 And the resistor R is in wireless connection with the radio frequency receiving module through a wireless antenna, the amplifying circuit is connected with the radio frequency receiving module and used for amplifying received radio frequency signals, one end of the LC oscillating circuit is connected with the amplifying circuit, the other end of the LC oscillating circuit is connected with one end of the resistor R, the other end of the resistor R is grounded, and the humidity measuring capacitor C is used for measuring humidity 2 Capacitance C with LC oscillating circuit 1 Parallel and capacitance C 1 The adjustable capacitor with the indication is characterized by comprising the following steps:
step one: calibrating in a humidity-known environment, wherein the humidity is recorded as RH1, and the frequency F emitted by the radio frequency emitting module 0 At a constant value, capacitor C 1 And a humidity measurement capacitor C 2 Parallel capacitance value C of (2) 0 For a fixed value, adjust the capacitance C 1 Make amplification circuit amplification maximum, measure humidity electric capacity C 2 ＝C 0 -C 1 Recording the capacitance value of the humidity measurement at this time as C 2 1；
Step two: testing air humidity, recording the tested air humidity as RH2, and regulating capacitance C 1 The amplification factor of the amplifying circuit is maximized, and the capacitance value of the humidity measurement at the moment is recorded as C 2 2；
Step three: calculating the measured humidity capacitance difference Δc=c 2 2-C 2 1, humidity difference Δrh=rh2-RH 1, and the value of the measured air humidity RH2 is calculated according to the formula Δrh=γ·Δc, where γ is a constant.
2. A capacitance-based humidity detection method according to claim 1, wherein: and in the first step, the C1 is adjusted to ensure that the amplification factor of the amplifying circuit is maximally adjusted through observation of an oscilloscope.
3. A capacitance-based humidity detection method according to claim 1, wherein: the calculation process of the formula Δrh=γ·Δc is as follows:
humidity of air
wherein ,
is biased by water in air>
Is the saturation bias of air at a certain temperature;
the relative permittivity and the air composition bias are related by
wherein ,αi The polarization intensity of each component;
bias of water vapor
Is obtained from (1) (2) (3)
When E shaped r With little variation, equation (4) can be approximated as:
is available in the form of
From dielectric constant e= e r ∈ 0 (7)
Is available in the form of
Order the
Obtainable Δrh=μ·Δe (10)
The capacitance determination formula for an infinite uniformly charged two parallel plates is known:
wherein C is the capacitance of the capacitor, E 0 For vacuum dielectric constant, E r E is the dielectric constant of the medium in the capacitor, d is the spacing between the two parallel plates;
the capacitance is defined as:
C＝Q/U (12)
q is the amount of charge in one end of the capacitor and U is the potential difference across the capacitor;
the theoretical value of the capacitance C is
Since there is no so-called infinite metal parallel plate in reality, the metal plates at both ends will not be charged uniformly, so it is approximated as:
C＝C 0 +Δ∈·k (14)
ΔC＝Δ∈·k (15)
Δ∈＝ΔC/k (16)
wherein C0 To know a certain capacitance value, k is the capacitance change rate around this point;
thereby can be obtained
And (3) making:
then:
ΔRH＝γ·ΔC (19)。
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| RU61037U1 (en) * | 2006-10-30 | 2007-02-10 | Федеральное Государственное Образовательное Учреждение Высшего Профессионального Образования "Московская Государственная Академия Ветеринарной Медицины И Биотехнологии Имени К.И. Скрябина" | DEVICE FOR MEASURING THE HUMIDITY OF LEATHER RAW MATERIALS |
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