CN103207189A - Designing of circuit for measurement of wood moisture content by using microwave technology - Google Patents

Abstract

The invention relates to designing of a circuit for microwave measurement of wood moisture content and discloses a fast, non-contact, nondestructive and high-precision circuit for microwave measurement of wood moisture content, belonging to the technical field of electronic science. The circuit is designed based on xx principles and comprises a microwave signal generation circuit part, a sensor measurement circuit part, a modulation microwave signal circuit part and a narrow-band filtering and amplification circuit part. The invention has the following advantages: microwaves can penetrate wood, and microwave measurement results reflect moisture content in the wood and are free of influence by factors like the color and the structure of the wood; and a final measured value of the circuit is calculated according to a standing-wave ratio and phase shift obtained through narrow-band filtering and amplification of a deamplification signal of electromagnetic waves and a measurement signal of a sensor, so the process of measurement is fast and precision and a measurement scope can be adjusted according to actual conditions. With such advantages, the circuit is applicable to real-time rapid on-line measurement of wood moisture content.

Description

A kind of microwave technology is measured the circuit design of timber humidity

Technical field

The present invention relates to a kind of measurement timber humidity circuit, belong to electronic technology field, be specifically related to a kind of circuit design with microwave measurement timber humidity.Main realize a kind of fast, the circuit of the higher microwave measurement timber humidity of noncontact, not damaged and precision.

Background technology

The humidity of timber is an important index in the evaluation of timber transportation, storage, processing and material.Begin to finally spraying paint from buying log, in whole timber-work, know that moisture content is very necessary.It is the reference method that generally acknowledge in unique whole world that weight method (weight reduces before and after the drying process) is accurately measured water percentage, but this method is too unactual, add time-consumingly, it is expensive again to require great effort, thus easier use, fast, instrument that invasive is little becomes the main flow on the current market.Instrument on the market mainly is divided into two kinds now:

1) contact instrument (by producing the timber of electric field measurement certain depth).The degree of depth that it reads is based on the feature of instrument, the density of material and its water percentage, and the value that obtains is to measure the mean value of water percentage, and along with the increase that fathoms, its sensitivity reduces thereupon.When the water cut of measuring material be higher than 20%～30% or moisture be not when being evenly distributed in the plank, its measurement accuracy rate can reduce greatly.

2) needle-inserted instrument (measuring two interelectrode electrical impedance).The degree of depth that two electrodes insert forms the space, and the pin type instrument only is that this space of root obtains reading.Measured value is that innermost maximum water percentage is arrived on the surface between this two electrode.When the water percentage of measuring material is lower than 8%～10%, the accuracy of measured value will reduce greatly, and its destroys wood surface easily, and measuring speed is slow, can't read a lot of data in the short time.

Summary of the invention

Purpose of the present invention is exactly at the deficiencies in the prior art, and a kind of design of microwave measurement timber humidity circuit is provided.Microwave method is electrical measuring method recent development in recent years.This be a kind of fast, noncontact, undamaged measuring method, and precision is higher.Because microwave can penetrate timber, so its measurement result has reflected the moisture of timber inside, be not subjected to the influence of factors such as wood color, structure simultaneously.To be attenuation of Electromagnetic signal and sensor measurement signal by narrow-band filtering amplify final measured value obtains standing-wave ratio (SWR) and phase shift is tried to achieve, and this makes measuring process rapidly and can adjust precision and measurement range according to actual conditions.These advantages make microwave method be suitable for very much the real-time measurement of timber humidity.

The present invention includes microwave signal and produce circuit part, modulated microwave signal circuit part, sensor measuring circuit part and narrow-band filtering amplification circuits.

The microwave signal of telling produces circuit part and comprises microwave source, dual operational amplifier U1A, photoelectrical coupler U2, resistance R 1, R2, R3, R4, R5, Rc.Wherein resistance R 1, R2, R3 and dual operational amplifier U1A, photoelectrical coupler U2 forms photoisolator.Resistance R 4, R5, Rc form bridge T type attenuator.

The modulated microwave signal circuit part of telling comprises dual operational amplifier U5A, photoelectrical coupler U4, code switch S1, S2, resistance R 10, R11, R12, R13, R14, R15, R16, R17, R18.Resistance R 16, R17, R18, dual operational amplifier U5A, photoelectrical coupler U4 forms photoisolator.Code switch S1, S2, resistance R 10, R11, R12, R13, R14, R15 form adjustable bridge T type attenuator.

The sensor measuring circuit of telling partly comprises dual operational amplifier U1B, U5B, photoelectrical coupler U3, U6, loudspeaker horn LS1, LS2, resistance R 7, R8, R9, R19, R20, R21, capacitor C 1, C2, C3.Resistance R 7, R8, R9, dual operational amplifier U1B, photoelectrical coupler U3 and resistance R 19, R20, R21, dual operational amplifier U5B, photoelectrical coupler U6 forms photoisolator respectively.Loudspeaker horn LS1, LS2 and capacitor C 2, C3 form Sensor section.

The narrow-band filtering amplification circuits of telling comprises transformer T1, NPN transistor Q1, adjustable inductance L1, I.F.T. (being commonly called as middle week) T2, quartz crystal Y1, resistance R 22, R23, R24, R25, capacitor C 4, C5, C6, C7, C9, adjustable capacitor C 8.Transistor Q1 is put level in being; Resistance R 22, R23, R24 and capacitor C 4, C5 form dc bias circuit; Resistance R 25 is formed isolation circuit with capacitor C 6.Quartz crystal Y1, adjustable capacitor C 8 are formed filtering circuit with adjustable inductance L1.

Description of drawings

Fig. 1 is circuit connection diagram of the present invention

Fig. 2 is general structure frame figure of the present invention

Fig. 3 is the principle schematic of bridge T type attenuator and adjustable bridge T type attenuator

Fig. 4 is the equivalent electric bridge principle schematic of narrow-band filtering amplifier

Embodiment

The invention will be further described below in conjunction with drawings and Examples.

As shown in Figure 1, the circuit of microwave technology measurement timber humidity comprises that microwave signal produces circuit part (1), modulated microwave signal circuit part (2), sensor measuring circuit part (3) (4) and narrow-band filtering amplification circuits (5).

Microwave signal produces circuit part (1) and mainly is made up of photoisolator and bridge T type attenuator.Photoisolator has the effect that the input and output of making are isolated mutually, so the electric signal transmission has unidirectional characteristics.The diode D1 of U2 is in by in the feedback network of being made up of dual operational amplifier U1A in the photoelectrical coupler, and the voltage V strictness that the emitter of the electric current of the light emitting diode D1 that flows through and the phototriode Q in the photoelectrical coupler produces is linear.Fig. 3 is the principle schematic of bridge T type attenuator and adjustable bridge T type attenuator.Bridge T type attenuator has following computing formula:

R ₁＝R _C*(N-1) (1)

R ₂=R _C/ (N-1) (2) so $N=\sqrt{\frac{R_1}{R_2}}+1,$ R ₁R ₂＝R _c ²

Wherein N is attenuation multiple, R _CValue for characteristic impedance.

Modulated microwave signal circuit part (2) mainly comprises photoisolator and adjustable bridge T type attenuator.As shown in Figure 3, the attenuation multiple of adjustable bridge T type attenuator can be selected the attenuation multiple of signal by the gear that switch S 1, S2 are selected, its attenuation multiple can for:

N ₁＝1 (3)

${\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HSA00000848356100011.png,HSA00000848356100041.png"\; state="\{\{state\}\}">N</figure-callout>}}_2=\sqrt{\frac{R_{11}}{R_{21}+R_{22}}}+1,R_{11}(R_{21}+R_{22})={R_c}^2---\left(4\right)$

${\mathrm{<figure-callout\; id="3"\; label="N"\; filenames="HSA00000848356100011.png"\; state="\{\{state\}\}">N</figure-callout>}}_3=\sqrt{\frac{R_{11}}{R_{22}}}+1,R_{11}{R}_{22}={R_c}^2---\left(5\right)$

${\mathrm{<figure-callout\; id="4"\; label="N"\; filenames="HSA00000848356100011.png"\; state="\{\{state\}\}">N</figure-callout>}}_4=\sqrt{\frac{R_{11}+R_{12}}{R_{21}+R_{22}}}+1,(R_{11}+R_{12})(R_{21}+R_{22})={R_c}^2---\left(6\right)$

${\mathrm{<figure-callout\; id="5"\; label="N"\; filenames="HSA00000848356100011.png"\; state="\{\{state\}\}">N</figure-callout>}}_5=\sqrt{\frac{R_{11}+R_{12}}{R_{12}}}+1,(R_{11}+R_{12})R_{22}={R_c}^2---\left(7\right)$

Can make this road microwave signal keep equating with the wave amplitude of following road microwave signal to the selection of code switch.

Sensor measuring circuit part (3) (4) mainly comprise photoisolator and Sensor section.Place timber to be measured between loudspeaker horn LS1, the LS2 in the Sensor section.Loudspeaker horn LS1, LS2 send sound wave and receive sound wave from timber to timber respectively.Receive acoustic signals from the end output of photoisolator.

Narrow-band filtering amplification circuits (5) mainly is made up of transformer T1, NPN transistor Q1, adjustable inductance L1, I.F.T. T2, quartz crystal Y1 etc.Shown in figure four, two sections Ln and the Lm of adjustable inductance L1 are the symmetric coil of resonant tank.I.F.T. T2 forms second resonant tank, and it plays a part impedance matching on the one hand, but also appropriate change passband on the other hand influences the value of equivalent quality factor q by it.The output of amplifier also is subjected to the influence of the series resonance characteristic of quartz crystal Y1, make C8=Co (Co is the static capacity of quartz crystal Y1) when regulating adjustable capacitor C 8, the effect of Co is balanced, and the series resonance characteristic of quartz crystal and the passband width in the circuit are depended in the output of amplifier.When C8＞Co, inevitablely be lower than ω _qCertain frequency on the capacitive reactance that presents of crystal equal the capacitive reactance of C8, this is bridge balance, no-output; When C8＜Co, inevitablely be higher than ω _pCertain frequency on the capacitive reactance that presents of crystal equal the capacitive reactance of C8, bridge balance at this moment, no-output.Therefore, regulate C8 and can change passband width, also can make bridge balance point aim at the undesired signal frequency, like this, electric bridge is just maximum to the undesired signal decay, the waveform that two paths of signals can obtain exporting by the narrow-band filtering amplifying circuit.

As shown in Figure 2, overall work mode for circuit of the present invention, microwave source passes through photoisolator earlier, make between input and output and isolate mutually, then by 10 times of bridge T type attenuator decay, the benchmark microwave signal through isolating decay is divided into two-way then: the one road earlier through adjustable bridge T type attenuator, by regulating bridge T type attenuator, the two way microwave signals wave amplitude equates about making, and arrives an end of narrow-band filtering amplifier then through photoisolator; Another road through photoisolator then the emission loudspeaker by the left side send sound wave and arrive tested timber, then the reception loudspeaker on right side receive through the other end that arrives the arrowband frequency-selecting amplifier behind the acoustic signals of timber by photoisolator.Two paths of signals passes through the signal receiving port 1,2 of narrow-band filtering amplifier respectively, by the final ripple signal of narrow-band filtering amplifier output, again relatively the wave number of output wave signal and benchmark microwave signal than and phase differential, can table look-up and record the water percentage of timber by both standing-wave ratio (SWR) and phase shift at last.

Claims (1)

1. the circuit of a microwave technology measurement timber humidity comprises that microwave signal produces circuit part, modulated microwave signal circuit part, sensor measuring circuit part and narrow-band filtering amplification circuits:

The microwave signal of wherein telling produces circuit part and comprises microwave source, dual operational amplifier U1A, photoelectrical coupler U2, resistance R 1, R2, R3, R4, R5, Rc, resistance R 1, R2, R3, dual operational amplifier U1A, photoelectrical coupler U2 forms photoisolator, and resistance R 4, R5, Rc form bridge T type attenuator;

The modulated microwave signal circuit part of telling comprises dual operational amplifier U5A, photoelectrical coupler U4, code switch S1, S2, resistance R 10, R11, R12, R13, R14, R15, R16, R17, R18.Resistance R 16, R17, R18, dual operational amplifier U5A, photoelectrical coupler U4 forms photoisolator, and code switch S1, S2, resistance R 10, R11, R12, R13, R14, R15 form adjustable bridge T type attenuator;

The sensor measuring circuit of telling partly comprises dual operational amplifier U1B, U5B, photoelectrical coupler U3, U6, loudspeaker horn LS1, LS2, resistance R 7, R8, R9, R19, R20, R21, capacitor C 1, C2, C3, resistance R 7, R8, R9, dual operational amplifier U1B, photoelectrical coupler U3 and resistance R 19, R20, R21, LM358D dual operational amplifier U5B, photoelectrical coupler U6 forms photoisolator respectively, and loudspeaker horn LS1, LS2 and capacitor C 2, C3 form Sensor section;

The narrow-band filtering amplification circuits of telling comprises transformer T1, NPN transistor Q1, adjustable inductance L1, I.F.T. T2, quartz crystal Y1, resistance R 22, R23, R24, R25, capacitor C 4, C5, C6, C7, C9, adjustable capacitor C 8, transistor Q1 is put level in being, resistance R 22, R23, R24 and capacitor C 4, C5 form dc bias circuit, and resistance R 25 is formed isolation circuit with capacitor C 6, and quartz crystal Y1, adjustable capacitor C 8 are formed filtering circuit with adjustable inductance L1.

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