CN101571495B - Method for detecting moisture content of fabric on line by microwaves - Google Patents

Abstract

The invention discloses a method for detecting moisture content of fabric on line by microwaves, which adopts a device for detecting the moisture content of the fabric on line by the microwaves. The device comprises a microwave circuit unit and a data processing unit, wherein the microwave circuit unit comprises a microwave signal source, an isolator, a variable attenuator, a transmitting antenna,a receiving antenna, a detector and a DC amplifier module which are connected in turn through wireless signals; and the data processing unit comprises a data acquisition card and an LabVIEW developme nt platform which are connected through the wireless signals. The method adopts the microwave circuit unit and the data processing unit to perform transmission treatment on microwave signals, and calculates to obtain the moisture content of the fabric by detecting voltage values of changed microwave attenuation. The detection method has high measuring accuracy, does not damage or pollute the fabric, and has wide measuring range.

Description

Utilize microwave to the moisture content of fabric on-line detection method

Technical field

The invention belongs to technical field of textile printing, be specifically related to a kind of microwave that utilizes the moisture content of fabric on-line detection method.

Background technology

The water percentage of fabric is the key in the key index in the dyeing and finishing technology process, and it is not only weighing the quality of product, also helps energy savings, therefore, realizes the measurement of moisture content of fabric is absolutely necessary in dyeing and finishing technology.Along with the application of modern physics measuring technology, the measuring method of water percentage is diversified, and total is divided into directly and indirect two big classes.The most representative in the direct method is Oven Method.Yet using maximum at present is the indirect method of measurement, and the so-called indirect method of measurement is to utilize certain to cause physical quantity, records water percentage as the relation indirect between the absorption of resistance, dielectric coefficient, external radiation etc. and material water percentage.It to be needn't driving moisture in the material out of for its feature, being its characteristics fast.Mainly contain electric-resistivity method, capacitance method, infrared method etc., but also have its limitation.

(1) Oven Method: it is the air that utilizes in the resistance wire heating cabinet, makes hydrone obtain enough vaporization energies, thereby breaks away from fiber, so should be higher than the boiling point of water from temperature.Reduce the interior relative humidity of case at the same time to improve drying efficiency.Big with oven method measuring water percentage power consumption, the time is long, and damages sample easily; Simultaneously, owing to the volatilization of more intrastitial greases or other materials, influence the authenticity of measurement result; Be again under the intensification situation, claim that the weighing apparatus condition is bad, also often cause error, and can not carry out on-line measurement, can't carry out On-line Control product quality to moisture.

(2) electric-resistivity method: resistance (leading) method is the moisture electric measuring method of using the earliest, is to utilize the direct current resistance of object or electricity to lead principle design that the difference with its water cut changes.Electric conductivity was very low when fabric was done, and moisture is bigger to the influence of material resistance, and in low moisture district scope, the moisture of these moisture absorption materials and resistance are logarithmic relationship, and when water cut increased, resistance value reduced, and this is the measuring principle of electric-resistivity method.Adopt two electrode handle measured mediums to clamp, two electrodes are inserted in the media, the resistance value by detecting medium and then draw the media water-bearing amount.Utilize the method, the accompaniment in the material, impurity, finish, slurry etc. and electrostatic accumulation all exert an influence to test findings.Be again, to different fibers, different instruments has certain scope of application, even differ bigger with a kind of fiber such as quality, also has certain error.

(3) capacitance method: this method of capacitance method as dielectric, is measured its water cut to fabric by the specific inductive capacity of measuring fabric.Owing to when measuring electric capacity, also have the electricity of a parallel connection to lead composition, total variation therefore is to be reflected by the ratio that electric capacity and electricity are led, as long as therefore measure the content that corresponding value promptly can be measured moisture at the electric capacity two ends with capacitance type sensor.This instrument test result's influence factor and resistance moisture apparatus are basic identical, and just it can not contact sample, but this instrument, textural than resistance moisture apparatus complexity, stability is also poor.

(4) infrared method: infrared method claims infrared absorption again, this method is to utilize principle testing moisture that material becomes with water cut the uptake of infrared ray characteristic absorption spectrum, also be to utilize water that the different wavelength of infrared ray is had different absorptivities, and moisture relevant in uptake and the material, strong absorption band appears in water on some wave band of infrared region.The characteristics of infrared absorption are not contact with tested fabric, response speed is very fast, can survey conductive material, but remain at present in weak point, show that its stability also is subjected to the influence of some other factor, for example the material shape size of the temperature of sample, density, container, surrounding environment and other test conditions etc.

At top 4 kinds of method exposed problems, we have proposed a kind of microwave that utilizes moisture content of fabric have been carried out on-line detection method.

Summary of the invention

The purpose of this invention is to provide a kind of microwave that utilizes to the moisture content of fabric on-line detection method, it is long to have solved the Measuring Time that exists in the prior art; Damage sample easily; Can not onlinely detect; Error is big, complex structure; The problem of poor stability.

The technical solution adopted in the present invention is, a kind of microwave that utilizes is to the moisture content of fabric on-line detection method, adopt a kind of device that utilizes microwave to the online detection of moisture content of fabric, this device comprises microwave circuit unit and data processing unit, the microwave circuit unit comprises the microwave signal source that connects successively by wireless signal, isolator, variable attenuator, emitting antenna, receiving antenna, wave detector and direct current amplification module, data processing unit comprises data collecting card and the LabVIEW development platform that is connected by wireless signal

This method is implemented according to following steps:

Step 1: connect the microwave signal source current, microwave signal source sends microwave, microwave signal by behind the isolator, variable attenuator by transmission antennas transmit, receiving antenna is detected by wave detector after receiving microwave signal, convert microwave signal to the normalized current signal by the direct current amplification module again, obtain not having between emitting antenna and the receiving antenna magnitude of voltage V when measuring material ₁, the magnitude of voltage V when will not have the measurement material by data collecting card ₁Be input in the computing machine;

Step 2: tested fabric is placed between emitting antenna and the receiving antenna, keep emitting antenna and receiving antenna stationkeeping, and the axle center of emitting antenna and receiving antenna point-blank;

Step 3: connect the microwave signal source current, microwave signal source sends microwave, microwave signal by behind the isolator, variable attenuator by transmission antennas transmit, through the signal that obtains decaying behind the tested fabric, detect by wave detector behind the signal of receiving antenna receiving attenuation, convert it to the normalized current signal by the direct current amplification module again, the magnitude of voltage V when measuring material is arranged between emitting antenna after obtaining decaying and the receiving antenna ₂, the magnitude of voltage V after will decaying by data collecting card ₂Be input in the computing machine, utilize the LabVIEW platform that data are further handled, concrete treatment step is as follows:

A. set up the relation of effective dielectric constant and water percentage

$M=\frac{1}{1+\frac{{\mathrm{\ρ}}_m}{{\mathrm{\ρ}}_w}\·\frac{1}{k}}$

In the formula, M is the water percentage of fabric, ρ _wBe the density of water, ρ _mBe the density of tested fabric, $k={\left(\frac{{\mathrm{\ϵ}}_{\mathrm{rm}}}{{\mathrm{\ϵ}}_{r1}}\right)}^{\frac{1}{3}},$ ε _R1Be the relative dielectric constant of water, ε _RmEffective dielectric constant for potpourri;

B. set up the relation of effective dielectric constant and attenuation coefficient

${\mathrm{\ϵ}}_{\mathrm{rm}}={(\mathrm{\α}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}})}^2$

In the formula, ε _RmBe the effective dielectric constant of potpourri, α is an attenuation coefficient, λ ₀Be microwave wavelength in a vacuum, δ is a dielectric loss angle;

C. set up the relation of measuring voltage value and attenuation coefficient

$e^{-\mathrm{\αx}}={\left(\frac{V_1}{V_2}\right)}^2$

In the formula, x is the thickness of medium, and α is an attenuation coefficient, V ₁, V ₂Be respectively when not having the material of measurement between emitting antenna and the receiving antenna and the material of measurement being arranged the magnitude of voltage that modular terminal is shown;

D. set up the relation of water percentage and measuring voltage value

$M=\frac{1}{1+\frac{{\mathrm{\ρ}}_m}{{\mathrm{\ρ}}_w}\·{\left(\frac{{\mathrm{\ϵ}}_{r1}\·s^2{d}^2}{4\·{(\ln \frac{V_1}{V_2}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}}\·s_1)}^2}\right)}^{\frac{1}{5}}}$

In the formula, ρ _wBe the density of water, ρ _mBe the density of measured object, the area of fabric to be measured is s, and thickness is d, ε _R1Be the relative dielectric constant of water, δ is a dielectric loss angle, s ₁Be the area that antenna covered, λ ₀Be microwave wavelength in a vacuum, V ₁, V ₂Be respectively when not having the material of measurement between emitting antenna and the receiving antenna and the material of measurement being arranged the magnitude of voltage that modular terminal is shown;

Step 4: do not have the magnitude of voltage V when measuring material between emitting antenna that step 1 is obtained and the receiving antenna ₁, the magnitude of voltage V when measuring material arranged between the emitting antenna that obtains of step 3 and the receiving antenna ₂Be updated in the relational expression of step 3 water percentage and measuring voltage value, calculate the water percentage of tested fabric.

The invention has the beneficial effects as follows, adopt microwave circuit unit and data processing unit to carry out the transmission process of microwave signal, by measuring the magnitude of voltage of microwave attenuation quantitative changeization, calculate the water percentage of fabric, realize the online detection of moisture content of fabric, the measuring accuracy height can not damage or pollute fabric, and measurement range is wide.

Description of drawings

Fig. 1 is the structural representation of the pick-up unit of detection method employing of the present invention.

Among the figure, 1. microwave signal source, 2. isolator, 3. variable attenuator, 4. emitting antenna, 5. receiving antenna, 6. wave detector, 7. direct current amplification module, 8. data collecting card, 9.LabVIEW development platform.

Embodiment

The present invention is described in detail below in conjunction with embodiment.

Microwave refers to that frequency is the electromagnetic wave of 300MHz～300GHz, promptly wavelength at 1m to the electromagnetic wave between the 1mm.When microwave is propagated in wet stock, because hydrone is strong polar dipoles, the effect that hydrone is subjected to microwave electric field will produce very strong orientation polarization, and the energy loss of microwave mainly shows as the orientation polarization loss of dipole, and how much relevant the size of energy loss is with hydrone.So can calculate the relation between energy attenuation value and the detected value to a kind of tolerance of the pad value of energy, finally determine the corresponding relation of water percentage and detected value as water percentage.

Moisture on the fabric has various states, roughly can be divided into the free water two big classes on fiber absorption water and the fabric.What of moisture generally are referred to as water percentage (%) with the percent of the ratio of its moisture heavy and fiber wet weight and represent that its computing formula is as follows:

$M=\frac{G-G_m}{G}\×100\%---\left(1\right)$

In the formula: the weight in wet base of G-fabric; G _mThe dry weight of-fabric; The M-water percentage.

The present invention utilizes microwave that moisture content of fabric is carried out on-line detection method, adopts a kind of device that utilizes microwave to the online detection of moisture content of fabric, comprises microwave circuit unit and data processing unit,

The microwave circuit unit comprises microwave signal source 1, isolator 2, variable attenuator 3, emitting antenna 4, receiving antenna 5, wave detector 6 and the direct current amplification module 7 that connects successively by wireless signal.

Data processing unit comprises data collecting card 8 and the LabVIEW development platform 9 that is connected by wireless signal.

The microwave signal source 1 that adopts is solid-state signal source, and this solid-state signal source adopts GaAs body effect tube and high Q resonant cavity, is used to produce microwave signal, and this microwave signal sent into isolator 2, under the additional power source effect, produce 3 centimeter wave signals, centre frequency is 10GHz, and output power is 34mw.

Microwave remote sensor on emitting antenna 4 and the receiving antenna 5 transmits and carries the microwave signal that comprises water percentage information, and its major function is that the microwave that microwave signal source 1 is launched is become the microwave of propagating in free space and the dielectric material.According to the transmitting-receiving reciprocity principle of antenna system, receiving antenna 5 and emitting antenna 4 can be antenna of the same race.Emitting antenna 4 is used for microwave signal is arrived receiving antenna 5 by the sensor emission on the antenna; Receiving antenna 5 is used to receive the microwave signal of emitting antenna 4 emissions; It is 100LHA100 type lens antenna that the microwave that uses in the inventive method transmits and receives element, and this antenna is mainly used in superhigh frequency band.The frequency of operation f=10GHz of lens antenna, bore D=100mm, gain maximum G=20.6dB.

The power that microwave signal source 1 produces causes reflection owing to load does not match, when these power that reflect arrive unmatched signal source, will produce reflective power for the second time, is superimposed upon on the microwave signal of the direct generation of signal source to transmit to load together.In order to reduce the influence of this reflective power, just isolator 2 must be set.Isolator 2 is used to reduce the influence of the reflective power of microwave signal source 1 generation to the microwave signal of transmission; Microwave moisture measurement is the miniwatt transmission, uses field displacement isolator.Requirement to isolator 2 is that the forward decay is little, requires little 0.5dB usually; It is big that reverse attenuation is wanted, and requires usually greater than 20dB; It is big that isolation ratio is wanted, i.e. the ratio of reverse attenuation and forward decay greatly better; Standing-wave ratio (SWR) heals better little; Working band is wide, and general relative bandwidth can reach about 10%.

Variable attenuator 3 is equivalent to the low-frequency resistance device, is used for regulating the size of power level in the transmission system.In waveguide, put the attenuator that scribbles microwave absorbing material, just can constitute the absorptive attenuator of waveguide type structure, use this attenuator more in the microwave moisture measurement.

Wave detector 6 is the indicators that are used for detecting faint microwave signal relative power, is used to detect the microwave signal that receiving antenna 5 receives.It is made up of detecting transistor and detection joint, and its principle all is that the characteristic of having utilized diode reverse to end is carried out detection, extracts useful signal.The key technical indexes of wave detector 6 has tangent sensitivity, frequency response, standing wave ratio of input voltage etc.

The microwave signal that direct current amplification module 7 is used for receiving converts the 4mA～20mA current signal of standard to.

Data processing unit has comprised hardware configurations such as data collecting card and PC.Data collecting card 8 is used for gathering the data of the microwave signal after the conversion, and enter data in the computing machine, adopting USB-6009 type data collecting card, its interface shape is a USB interface, be USB (universal serial bus), it is the personal computer peripheral device bus transfer interface that develops in recent years.This interface connects simple, can connect under the situation of not cutting off the power supply, and just can use, and has the function of ' plug and play ' at once.The NIUSB-6009 data acquisition equipment has been realized multifunctional data acquiring by 8 passages, 12 analog inputs, 2 simulation outputs, 12 DIO lines and 1 timer, by the USB interface power supply, without any need for external power supply.Comprise that being used for direct signal connects detachable screw terminal, is used to support external unit and 1 plate of sensor to carry reference voltage, provide low noise high-precision 4 layer circuit boards, and up to the analog input overvoltage protection of ± 35v.

LabVIEW development platform 9 is used for handling the data of the microwave signal that collects, and obtains moisture content of fabric.The voltage signal that collects in the system is floating earth signal, and the metering system of employing is the difference test macro, and this systematic survey can suppress common mode voltage.The software development of native system is carried out under virtual instrument software through pictures development platform LabVIEW7.1.According to requirements of actual production, system not only can provide real-time Presentation Function, and the hold function of data and form can also be provided.

The present invention utilizes microwave to the moisture content of fabric on-line detection method, specifically implements according to following steps:

Step 1: connect microwave signal source 1 power supply, microwave signal source 1 sends microwave, microwave signal is launched by emitting antenna 4 by isolator 2, variable attenuator 3 backs, receiving antenna 5 is detected by wave detector 6 after receiving microwave signal, convert microwave signal to the normalized current signal by direct current amplification module 7 again, obtain not having between emitting antenna (4) and the receiving antenna (5) the magnitude of voltage V when measuring material ₁, by data collecting card 8 with magnitude of voltage V ₁Be input in the computing machine;

Step 2: the distance between emitting antenna 4 and the receiving antenna 5 is set to 40cm, with tested fabric is the center, emitting antenna 4 and receiving antenna 5 are positioned over the fabric both sides, keep emitting antenna 4 and receiving antenna 5 stationkeeping, calibrate before each test, and keep the dual-mode antenna face parallel, and the axle center of dual-mode antenna point-blank with fabric, connect microwave signal source 1 power supply, make output microwave signal power stability;

Step 3: microwave signal source 1 sends microwave, microwave signal is launched by emitting antenna 4 by isolator 2 and variable attenuator 3, microwave signal is transmitted along sensor orientation, pass through moisture tested fabric rear section energy by the moisture absorption in the fabric, the microwave energy decay, microwave signal after the energy attenuation receives by receiving antenna 5, detect faint signal by wave detector 6, convert it the 4mA～20mA current signal of standard to by direct current amplification module 7 again, obtain having between emitting antenna (4) and the receiving antenna (5) the magnitude of voltage V when measuring material ₂, the magnitude of voltage V after will decaying by data collecting card 8 ₂Be input in the computing machine, utilize 9 pairs of data of LabVIEW platform further to handle, concrete treatment step is as follows:

(a) set up the relation of effective dielectric constant and water percentage

According to the cubic root addition law of mixture dielectric constant, the effective dielectric constant of potpourri is:

${\mathrm{\ϵ}}_{\mathrm{rm}}={\left(\frac{1}{v}\underset{i}{\mathrm{\Σ}}{\mathrm{\ϵ}}_i^{\frac{1}{3}}{v}_i\right)}^3---\left(2\right)$

For the potpourri of being made up of water and fabric, its effective dielectric constant should be:

${\mathrm{\ϵ}}_{\mathrm{rm}}={\left[\frac{1}{v}({{\mathrm{\ϵ}}_{r1}}^{\frac{1}{3}}\·v_{r1}+{{\mathrm{\ϵ}}_{r2}}^{\frac{1}{3}}\·v_{r2})\right]}^3---\left(3\right)$

ε in the formula _R1Be the specific inductive capacity of water, ε _R2Be the specific inductive capacity of dry fabric, v is the cumulative volume of wet fabric, v _R1Be the volume of water in the wet fabric, v _R2Volume for fabric.

Because the research object of this method is textile material and water, at its optimum measurement frequency band, the loss of the microwave energy that is caused by moisture is far longer than the loss that dry fabric causes, how much water cut is the key factor of decision compounding substances specific inductive capacity in the fabric, so can ignore the DIELECTRIC CONSTANT of mixing fabric in the specific inductive capacity _R2After considering that fabric and water mix, the cumulative volume v of potpourri is approximately equal to the volume v of fabric _R2So formula (3) can be written as again:

${\mathrm{\ϵ}}_{\mathrm{rm}}={\left(\frac{v_{r1}}{v}\right)}^3\·{\mathrm{\ϵ}}_{r1}---\left(4\right)$

Order $k=\frac{v_{r1}}{v},$ So formula (4) can be rewritten as:

ε _rm＝ε _r1·k ³ (5)

Then:

$k={\left(\frac{{\mathrm{\ϵ}}_{\mathrm{rm}}}{{\mathrm{\ϵ}}_{r1}}\right)}^{\frac{1}{3}}---\left(6\right)$

By formula (1) as can be known, the weight G of water in the fabric _w=G-G _m, and G=mg=ρ vg, so the water percentage of tested material is:

$M=\frac{G_w}{G}=\frac{G_w}{G_w+G_m}=\frac{{\mathrm{\ρ}}_w{v}_{r1}}{{\mathrm{\ρ}}_w{v}_{r1}+{\mathrm{\ρ}}_{m}v}=\frac{{\mathrm{\ρ}}_w}{{\mathrm{\ρ}}_w+{\mathrm{\ρ}}_m\·\frac{1}{k}}$

$=\frac{1}{1+\frac{{\mathrm{\ρ}}_m}{{\mathrm{\ρ}}_w}\·\frac{1}{k}}---\left(7\right)$

(b) set up the relation of effective dielectric constant and attenuation coefficient

Propagate on the x direction with plane wave when microwave electric field, electromagnetic wave vertically penetrates uniform dielectric, and then the formulation of electric-field strength is:

E(x，t)＝E ₀e ^-αx.e ^i(βx-αt)＝E ₀cos(kx-ωt) (8)

By Electromagnetic theory as can be known:

$\mathrm{\α}=\mathrm{\ω}\sqrt{\mathrm{\μ\ϵ}}{\left[\frac{1}{2}(\sqrt{1+{\left(\frac{\mathrm{\σ}}{\mathrm{\ϵ\ω}}\right)}^2}-1)\right]}^{\frac{1}{2}}---\left(9\right)$

In formula (8), the formula (9): α is an attenuation coefficient; ω is the electromagnetic wave angular frequency; K is a circular wavenumber; ε is a dielectric constant; μ is a magnetic permeability; σ is a conductivity.

Because the medium of the approximate poor conductor of fabric, $\frac{\mathrm{\σ}}{\mathrm{\ϵ\ω}}\≤1,$ And $1+{\left(\frac{\mathrm{\σ}}{\mathrm{\ϵ\ω}}\right)}^2>0,$ So can with

Be launched into binomial series:

$\sqrt{1+{\left(\frac{\mathrm{\σ}}{\mathrm{\ϵ}\mathrm{\ω}}\right)}^2}=1+\frac{1}{2}{\left(\frac{\mathrm{\σ}}{\mathrm{\ϵ\ω}}\right)}^2-\frac{1}{8}{\left(\frac{\mathrm{\σ}}{\mathrm{\ϵ\ω}}\right)}^4+......---\left(10\right)$

Because

Above is very little, thus can do to ignore approximate, only get following formula preceding two substitution formulas (9) must: $\mathrm{\α}=\frac{\mathrm{\σ}}{2}\sqrt{\frac{\mathrm{\μ}}{\mathrm{\ϵ}}}---\left(11\right)$

By the Electromagnetic Fields ﹠ Magnetic Waves theory as can be known:

$\mathrm{\α}=\frac{\mathrm{\σ}}{2}\sqrt{\frac{\mathrm{\μ}}{\mathrm{\ϵ}}}=\frac{\mathrm{\π\λ}}{{{\mathrm{\λ}}_0}^2}{\mathrm{\ϵ}}_r\mathrm{tg\δ}---\left(12\right)$

In the formula:; λ is the wavelength of microwave in medium; ε _rBe relative dielectric constant; δ is a dielectric loss angle.

In the following formula $\mathrm{\λ}=\frac{{\mathrm{\λ}}_0}{\sqrt{{\mathrm{\ϵ}}_r}},$ Then (12) can change into:

$\mathrm{\α}=\frac{\mathrm{\π}}{{\mathrm{\λ}}_0}\sqrt{{\mathrm{\ϵ}}_r}\mathrm{tg\δ}---\left(13\right)$

By following formula as can be known, the DIELECTRIC CONSTANT of wet fabric _RmWith the pass of attenuation coefficient be:

${\mathrm{\ϵ}}_{\mathrm{rm}}={(\mathrm{\α}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}})}^2---\left(14\right)$

(c) set up the relation of measuring voltage value and attenuation coefficient

When microwave entered lossy medium, microwave input power was exponential damping with attenuation constant:

P ₂＝P ₁e ^-αx (15)

In the formula: P ₂Be the microwave power (mw) after the decay; P ₁Be input microwave power (mw); α is an attenuation coefficient; X is the thickness (cm) of medium.After medium is when containing the fabric of moisture, and microwave passes through medium, damping capacity:

$A=10\lg \frac{p_2}{p_1}---\left(16\right)$

Formula (15) substitution (16) is got:

$A=10\lg \frac{p_1{e}^{-\mathrm{\αx}}}{p_1}=10\lg e^{-\mathrm{\αx}}---\left(17\right)$

This method adopts the direct current amplification module, in modular terminal indicator display voltage value, therefore need change into magnitude of voltage to microwave power:

$P=\frac{\left|V^2\right|}{Z}---\left(18\right)$

In the formula: P is a microwave power; V is an instructed voltage; Z is a line characteristic impedance.

In actual applications, generally characteristic impedance is considered as constant, i.e. z ' ≈ z ", then as can be known by formula (16) and formula (18):

$A=10\lg {\left(\frac{V_1\sqrt{Z^{\′\′}}}{V_2\sqrt{Z^{\′}}}\right)}^2\≈20\lg \frac{V_1}{V_2}---\left(19\right)$

V in the formula ₁, V ₂Be respectively when not having the material of measurement between emitting antenna and the receiving antenna and the material of measurement being arranged the magnitude of voltage that modular terminal is shown.

By formula (17), (19) as can be known:

$e^{-\mathrm{\αx}}={\left(\frac{V_1}{V_2}\right)}^2---\left(20\right)$

(d) set up the relation of water percentage and measuring voltage value

Taken the logarithm in formula (20) both sides:

$\ln e^{-\mathrm{\αx}}=\ln {\left(\frac{V_1}{V_2}\right)}^2---\left(21\right)$

:

$\mathrm{\α}=-\frac{1}{x}\ln {\left(\frac{V_1}{V_2}\right)}^2---\left(22\right)$

Following formula substitution formula (14) is got:

${\mathrm{\ϵ}}_{\mathrm{rm}}={(-\frac{1}{x}\·\ln {\left(\frac{V_1}{V_2}\right)}^2\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}})}^2---\left(23\right)$

Get by following formula: ${\mathrm{\ϵ}}_{\mathrm{rm}}={(\frac{2}{x}\·\ln \frac{V_1}{V_2}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}})}^2---\left(24\right)$

In the following formula, x is the thickness (cm) of the medium of microwave penetrating, because the decay of the microwave that fabric causes is far smaller than the decay that water causes microwave, therefore can ignore the influence of fabric to microwave attenuation, in this case, x in the following formula can convert in the area that covers at lens antenna, the thickness of the water that microwave saw through, that is:

$x=\frac{v_{r1}}{s_1}---\left(25\right)$

s ₁The expression area that antenna covered, and above order $k=\frac{v_{r1}}{v},$ So v _R1=kv, more as can be known by formula (6):

$x=\frac{{\left(\frac{{\mathrm{\ϵ}}_{\mathrm{rm}}}{{\mathrm{\ϵ}}_{r1}}\right)}^{\frac{1}{3}}\·v}{s_1}---\left(26\right)$

If the area s of fabric to be measured, thickness are d, then the volume of fabric can be expressed as v=sd, and formula (26) is converted into:

$x=\frac{{\left(\frac{{\mathrm{\ϵ}}_{\mathrm{rm}}}{{\mathrm{\ϵ}}_{r1}}\right)}^{\frac{1}{3}}\·s\·d}{s_1}---\left(27\right)$

Get by following formula: ${\mathrm{\ϵ}}_{\mathrm{rm}}=4\·{\left[\frac{s_1}{({\left(\frac{{\mathrm{\ϵ}}_{\mathrm{rm}}}{{\mathrm{\ϵ}}_{r1}}\right)}^{\frac{1}{3}}\·s\·d)}\right]}^2\·{(\ln \frac{V_1}{V_2}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}})}^2---\left(28\right)$

Following formula substitution formula (6) is got:

$k={\left[\frac{4\·{(\ln \frac{V_1}{V_2}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}}\·s_1)}^2}{{\mathrm{\ϵ}}_{r1}\·s^2{d}^2}\right]}^{\frac{1}{5}}---\left(29\right)$

So $\frac{1}{k}={\left(\frac{{\mathrm{\ϵ}}_{r1}\·s^2{d}^2}{4\·{(\ln \frac{V_1}{V_2}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}}\·s_1)}^2}\right)}^{\frac{1}{5}}---\left(30\right)$

The relational expression that following formula substitution formula (7) is got between water percentage and measured value is:

$M=\frac{1}{1+\frac{{\mathrm{\ρ}}_m}{{\mathrm{\ρ}}_w}\·{\left(\frac{{\mathrm{\ϵ}}_{r1}\·s^2{d}^2}{4\·{(\ln \frac{V_1}{V_2}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}}\·s_1)}^2}\right)}^{\frac{1}{5}}}---\left(31\right)$

In the formula, ρ _wBe the density of water, ρ _mBe the density of measured object, the area of fabric to be measured is s, and thickness is d, ε _R1Be the relative dielectric constant of water, δ is a dielectric loss angle, s ₁The expression area that antenna covered, λ ₀Be microwave wavelength in a vacuum, V ₁, V ₂Be respectively when not having the material of measurement between emitting antenna and the receiving antenna and the material of measurement being arranged the magnitude of voltage that modular terminal is shown.

Step 4: do not have the magnitude of voltage V when measuring material between emitting antenna 4 that step 1 is obtained and the receiving antenna 5 ₁, the magnitude of voltage V when measuring material arranged between the emitting antenna 4 that obtains of step 3 and the receiving antenna 5 ₂Be updated in the relational expression of step 3 water percentage and measuring voltage value, calculate the water percentage of tested fabric.

The present invention utilizes microwave to the moisture content of fabric on-line detection method, utilize microwave attenuation to measure moisture content of fabric, in measuring process, do not need to measure concrete dielectric constant values, only need measure the magnitude of voltage that characterizes the microwave attenuation quantitative changeization, again the magnitude of voltage that records is updated in the functional relation of the moisture content of fabric set up and magnitude of voltage, through calculating the water percentage that then can know fabric.

Claims (1)

1. one kind is utilized microwave to tested moisture content of fabric on-line detection method, it is characterized in that, adopt a kind of device that utilizes microwave to the online detection of tested moisture content of fabric, this device comprises microwave circuit unit and data processing unit, described microwave circuit unit comprises the microwave signal source (1) that connects successively by wireless signal, isolator (2), variable attenuator (3), emitting antenna (4), receiving antenna (5), wave detector (6) and direct current amplification module (7), described data processing unit comprises data collecting card (8) and the LabVIEW development platform (9) that is connected by wireless signal

This method is implemented according to following steps:

Step 1: connect microwave signal source (1) power supply, microwave signal source (1) sends microwave, microwave signal is launched by emitting antenna (4) by isolator (2), variable attenuator (3) back, receiving antenna (5) is detected by wave detector (6) after receiving microwave signal, convert microwave signal to the normalized current signal by direct current amplification module (7) again, obtain not having between emitting antenna (4) and the receiving antenna (5) the magnitude of voltage V when measuring material ₁, the magnitude of voltage V when will not have the measurement material by data collecting card (8) ₁Be input in the computing machine;

Step 2: tested fabric is placed between emitting antenna (4) and the receiving antenna (5), keep emitting antenna (4) and receiving antenna (5) stationkeeping, and the axle center of emitting antenna (4) and receiving antenna (5) point-blank;

Step 3: connect microwave signal source (1) power supply, microwave signal source (1) sends microwave, microwave signal is launched by emitting antenna (4) by isolator (2), variable attenuator (3) back, through the signal that obtains decaying behind the tested fabric, detect by wave detector (6) behind the signal of receiving antenna (5) receiving attenuation, convert it to the normalized current signal by direct current amplification module (7) again, the magnitude of voltage V when measuring material is arranged between emitting antenna (4) after obtaining decaying and the receiving antenna (5) ₂, the magnitude of voltage V after will decaying by data collecting card (8) ₂Be input in the computing machine, utilize LabVIEW platform (9) that data are further handled, concrete treatment step is as follows:

A. set up the relation of effective dielectric constant and water percentage

$M=\frac{1}{1+\frac{{\mathrm{\ρ}}_m}{{\mathrm{\ρ}}_w}\·\frac{1}{k}}$

In the formula, M is the water percentage of tested fabric, ρ _wBe the density of water, ρ _mBe the density of dry fabric,

ε _R1Be the relative dielectric constant of water, ε _RmEffective dielectric constant for tested fabric;

B. set up the relation of effective dielectric constant and attenuation coefficient

${\mathrm{\ϵ}}_{\mathrm{rm}}={(\mathrm{\α}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}})}^2$

In the formula, ε _RmBe the effective dielectric constant of tested fabric, α is an attenuation coefficient, λ ₀Be microwave wavelength in a vacuum, δ is a dielectric loss angle;

C. set up the relation of measuring voltage value and attenuation coefficient

$e^{-\mathrm{\αx}}={\left(\frac{V_1}{V_2}\right)}^2$

In the formula, x is the thickness of tested fabric, and α is an attenuation coefficient, V ₁, V ₂Be respectively when not having the material of measurement between emitting antenna and the receiving antenna and the material of measurement being arranged the magnitude of voltage that modular terminal is shown;

D. set up the relation of water percentage and measuring voltage value

$M=\frac{1}{1+\frac{{\mathrm{\ρ}}_m}{{\mathrm{\ρ}}_w}\·{\left(\frac{{\mathrm{\ϵ}}_{r1}\·s^2{d}^2}{4\·{(\ln \frac{V_1}{V_2}\·\frac{{\mathrm{\λ}}_0}{\mathrm{\π}}\·\frac{1}{\mathrm{tg\δ}}\·s_1)}^2}\right)}^{\frac{1}{5}}}$

In the formula, ρ _wBe the density of water, ρ _mBe the density of dry fabric, the area of tested fabric is s, and thickness is d, ε _R1Be the relative dielectric constant of water, δ is a dielectric loss angle, s ₁Be the area that antenna covered, λ ₀Be microwave wavelength in a vacuum, V ₁, V ₂Be respectively when not having the material of measurement between emitting antenna and the receiving antenna and the material of measurement being arranged the magnitude of voltage that modular terminal is shown;

Step 4: do not have the magnitude of voltage V when measuring material between emitting antenna (4) that step 1 is obtained and the receiving antenna (5) ₁, the magnitude of voltage V when measuring material arranged between the emitting antenna (4) that obtains of step 3 and the receiving antenna (5) ₂Be updated in the relational expression of step 3 water percentage and measuring voltage value, calculate the water percentage of tested fabric.

Images