CN209132203U - Concrete mix moisture percentage measuring device based on TDT with phase bit comparison - Google Patents
Concrete mix moisture percentage measuring device based on TDT with phase bit comparison Download PDFInfo
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- CN209132203U CN209132203U CN201821986260.0U CN201821986260U CN209132203U CN 209132203 U CN209132203 U CN 209132203U CN 201821986260 U CN201821986260 U CN 201821986260U CN 209132203 U CN209132203 U CN 209132203U
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Abstract
The concrete mix moisture percentage measuring device based on TDT with phase bit comparison that the utility model discloses a kind of.Obtain mix moisture percentage indirectly according to dielectric permittivity, the dielectric constant of medium obtains when being by measuring electromagnetic wave signal along the transmission line being placed in medium；When electromagnetic wave is transmitted along TDT probe, since the end of probe is not open circuit, the signal after electromagnetic wave one-way transmission need to be only detected, and there is no regulations for the detection for reflecting signal.Based on the principle, there can be transmission delay when transmitting in the medium due to electromagnetic wave, the method that the utility model uses phase bit comparison, pass through one Time delay measurement circuit of AD8302 integrated chip design, Time delay measurement circuit and sensor probe is integrated, analog quantity and digital quantity can be exported, measurement accuracy significantly improves, cost is far below the TDT sensor device of same type, has good application prospect.
Description
Technical field
The utility model belongs to circuit and technical field of information processing in electronic information, especially belongs to a kind of electromagnetic wave and is passing
Time-Domain Technique field is transmitted on defeated line, is related to a kind of concrete mix mixture moisture percentage essence based on TDT with phase bit comparison
True measuring device.
Background technique
Scholar Chernyak has been systematically carried out the research of the dielectric property of soil first, he " wet soil dielectric property is ground
Study carefully method " make soil physics scholar for the first time and has the cognition of globality to Dielectric Constant of NaCl Soil physical behavio(u)r.The dielectric property of soil
Theory can be applied in the measurement of concrete mix moisture percentage.It can be big by dielectric property method according to principle and realizing route
Generally be divided into following several types: Time Domain Reflectometry or transmission vector measurement principle, are handed over the reflective resolution of vectors measuring principle of frequency domain
Anti- measuring principle of fluid capacitance etc..
The principle of Time Domain Reflectometry (TDR) method is to measure time for propagating in the medium of electric wave or speed, is defined with this
Dielectric constant, to obtain medium moisture percentage indirectly.TDR method, which measures concrete mix moisture percentage, has very high accuracy,
But there is also some drawbacks and limitations when practical for TDR technical application: the working frequency of TDR is higher, usually require that 1GHz with
On, it is relatively difficult and hardware cost is increased that this will cause board design；If concrete mix neutral and alkali ion
Concentration is higher, and TDR signal will appear apparent relaxation phenomenon in transmission, to cause that clearly waveform cannot be obtained, even
Back wave cannot be obtained；If medium quality of organic matter score is higher, using need to be corrected again when TDR method dielectric constant with containing wet
Relationship between rate, thus to improve the accuracy of measurement.The above problem all hinders TDR technology and uses and promote.
The principle of frequency domain bounce technique is to generate an ideal test frequency using signal source, measures skill using vector voltage
Art obtains the apparent permittivity ε of mediumrReal and imaginary parts.It can be calculated by the imaginary part of medium apparent dielectric constant
Concrete mix moisture percentage can be calculated according to the real part of dielectric permittivity in the conductivity of medium out.Experiment
Show: the desired frequency range of frequency domain bounce technique work is 20~30MHz, belongs to low frequency, and the dielectric constant pair of mixture
Proportion component is very sensitive, this makes measurement error larger.
Exchange capacitive reactance measuring principle is when testing signal along the transmission line being embedded in concrete mix medium
Frequency, obtain its dielectric constant, and then obtain moisture percentage.This kind of sensor normally run wave frequency range be 20~
150MHz, fast response time, Yi Shixian are at low cost.Sensor based on exchange capacitive reactance measuring principle is disadvantageous in that work
Frequency it is relatively low, the performance of sensor is easy to be influenced by extraneous factor, such as temperature, the conductivity of medium.
The sensor to come into operation now is substantially difficult to keep balance between accuracy and design cost, therefore needs to seek
Look for a principle advanced, circuit is simple, and measurement accuracy is high, reproducible, cost adaptable to dry concrete mixture
The circuit design method of cheap sensor.
Summary of the invention
Deficiency discloses one kind based on time-domain transmission (Time Domain to the utility model according to prior art
Transmissometry, TDT) with the grinding coagulation soil mixture moisture percentage device for accurately measuring of phase bit comparison and its measurement side
Method.The utility model use one Time delay measurement circuit of AD8302 phase bit comparison integrated chip design, by Time delay measurement circuit with
Sensor probe is integrated, can export analog quantity and digital quantity, realizes accurate acquisition concrete mix moisture percentage.
The utility model is achieved through the following technical solutions:
Concrete mix moisture percentage measuring device based on TDT with phase bit comparison, including signal source, phase comparator and
The Time delay measurement circuit that sensor probe is constituted, it is characterised in that:
The signal source is high-frequency oscillating circuits, constitutes parallel LC resonance circuit using voltage controlled oscillation, for being entire system
System provides lasting two-way high-frequency signal；Signal source is connect with phase comparator and sensor probe respectively, by first via high frequency
Signal is sent to sensor probe and forms test signal, and the second road high-frequency signal is sent to phase comparator and forms reference signal；
The sensor probe uses U-shaped double guide rail measuring probes；Measuring probe is embedded in concrete mix admittedly, one end
Connecting signal source, output end are connect with phase comparator test side；
The phase comparator for realizing two paths of signals phase-detection.
The Time delay measurement circuit is converted into the phase difference between test signal and reference signal direct current associated therewith
Signal；It tests signal and reference signal is sine voltage signal, frequency is identical, and phase is different.
The U-shaped probe length L of U-shaped double guide rail measuring probes is 20cm, and the diameter r of probe conductor material is 2mm, double
The distance between conductor R is 10mm.
The high-frequency oscillating circuits use voltage controlled oscillation integrated chip MC1648 chip, 12 foot TANK and 10 foot Bias it
Between external parallel LC resonance circuit.
The phase comparator uses AD8302 phase-detection chip.
Utility model device application measurement method is as follows:
U-shaped double guide rail measuring probes are embedded in concrete mix admittedly；
Signal source generates the identical high-frequency signal of two-way amplitude and phase, and first via high-frequency signal is sent sensor and is visited
Capitiform is sent to phase comparator and forms reference signal at test signal, the second road high-frequency signal；First via high-frequency signal is through passing
Phase comparator test side is sent to after sensor probe；
Delay circuit is converted into the phase difference between test signal and reference signal direct current signal associated therewith；Test
Signal and reference signal are sine voltage signal, and frequency is identical, and phase is different；
Concrete mix moisture percentage is obtained according to test signal and the equal phase difference of reference signal.
The utility model obtains mix moisture percentage indirectly according to dielectric permittivity, and dielectric permittivity is to pass through survey
It is obtained when measuring electromagnetic wave signal along the transmission line being placed in medium.When electromagnetic wave is transmitted along TDT probe, due to visiting
The end of head is not open circuit, therefore need to only detect the signal after electromagnetic wave one-way transmission, and the detection for reflecting signal is simultaneously
It is not specified by.Based on the principle, there can be transmission delay when transmitting in the medium due to electromagnetic wave, the utility model uses phase
The method compared, by one Time delay measurement circuit of AD8302 integrated chip design, by Time delay measurement circuit and sensor probe
It is integrated, analog quantity and digital quantity can be exported, measurement accuracy significantly improves, and cost is far below the TDT sensor of same type
Equipment, the concrete mix moisture percentage that utility model device measurement obtains is accurate, and detection is easy to use, has and answers well
Use promotion prospect.
Detailed description of the invention
Fig. 1 is utility model device composed structure block diagram；
Fig. 2 is utility model device principle process block diagram；
Fig. 3 is the U-shaped double guide rail measuring probe schematic diagrames of utility model device；
Fig. 4 is utility model device signal source partial circuit diagram；
Fig. 5 is utility model device phase detection principle block diagram；
Fig. 6 is the ideal individual features curve of phase difference under utility model device AD8302 measurement pattern；
Fig. 7 is utility model device phase-comparison circuit figure.
Specific embodiment
The present invention will be further described With reference to embodiment, and specific embodiment is to the utility model
The further explanation of principle, does not limit the utility model in any way, and technology same or like with the utility model does not have
Range beyond the utility model protection.
In conjunction with attached drawing.
Concrete mix moisture percentage Fundamentals of Sensors block diagram is as shown in Fig. 2, electromagnetic wave signal is divided into two-way.Pass through all the way
Transmission line is directly sent to the end A of phase comparator, as stablizing electromagnetic wave phase bit comparison benchmark.Another way signal passes through sensor
The end B of input phase comparator after probe carries out phase bit comparison with the sine wave phase reference signal sent from the end A.Initial shape
State, that is, pop one's head in it is exposed in air when, two paths of signals pass through path be ideally seen as it is approximately equal, when probe is embedded to coagulation
When in native mixture, the road B electromagnetic wave signal has the delay of certain time, phase comparator output one when reaching phase comparator
A reaction B lags behind the phase angle α of the A namely time difference T of two-way electromagnetic wave signal transmission.
Sensor probe ring shaped conductor length L it is known that electromagnetic wave conductor one way travel time T can along concrete mix
It is obtained by phase comparator measurement, this can be calculated thus according to the expression formula of concrete mix apparent dielectric constant
When concrete mix in free water content.
One, the design method of U-shaped double guide rail measuring probes.
The pictorial diagram of TDT soil moisture sensor probe is as shown in Figure 3.U-shaped probe can be regarded as one section of transmission line,
What surrounding was filled is that dielectric constant is εrConcrete mix medium, equivalent-circuit model be parallel double conducting wire transmission line.
(1) probe is matched with coax impedance
In the design of sensor probe unit, the problem of being related to impedance matching.If the impedance of probe and coaxial cable is not
Matching, test signal can generate reflection in probe head end, this reflection signal for reflecting signal and probe end be same frequency and
Equidirectional propagation, it can not be separated using circulator.This not only influences to be transferred to the energy of the test signal on probe,
And the phase and amplitude of measured signal can be changed, cause the signal propagation time measured and attenuation all with actually have partially
Difference.
Only as load impedance ZLIt is necessarily equal to the characteristic impedance Z of the transmission line0When, incidence wave does not just reflect.Therefore,
The matched probe used has to pass through meticulous design to reduce signal as far as possible at probe port (i.e. from instrument internal
The coaxial cable of extraction and the junction of probe) reflection.Only as Γ=0, back wave is not just had.If load impedance ZL
Equal to the characteristic impedance Z of the transmission line0, then reflection coefficient Γ=0.Transmission line just reaches matched load in this way, at this time incidence wave
Do not reflect.
The probe of concrete mix moisture percentage used in the utility model belongs to parallel double conducting wire transmission line, connects with probe
Be coaxial transmission line, the characteristic impedance of transmission line is a real number value.
The characteristic impedance model of coaxial cable are as follows:
Wherein: R is coaxial cable outer conductor copper mesh internal diameter；R is coaxial cable core wire outer diameter；ε dielectric between conductor
Relative dielectric constant.
The characteristic impedance model of parallel double conducting wire are as follows:
It follows that only as the characteristic impedance Z of coaxial cableCWith the characteristic impedance Z of sensor probeSAs far as possible one
When cause, the reflection of electromagnetic wave signal can be avoided.
(2) geometric parameter of probe unit
By the characteristic impedance model of parallel double conducting wire it is found that the characteristic impedance of two-conductor line is and conducting wire surrounding medium and leads
Line center away from and diameter of wire it is related.And measuring medium be variation, therefore the characteristic impedance most of the time and transmission high frequency
Signal impedance mismatches.Here, R is set to 10mm by us, and r is set to 2mm.
According to Utopian sensor probe length, the different sensor probe of L is produced.Pass through the qualitatively side of test
Method, to determine the probe length of TDT soil moisture sensor.Method is as follows:
1. the signal output end of Network Analyzer is connect in one end of TDT probe, while it is 1 signal of the channel of oscillograph is defeated
Enter end and is connected in parallel on interface.The other end of TDT probe connects channel oscilloscope 2.
2. the output signal frequency of Network Analyzer is tuned into 100MHz, slowly TDT probe is protruded into bucket at this time,
Waveform variation is observed, and records phase difference.
3. changing probe length L, repeat the above steps.
It is recorded by observation experiment as a result, finding when probe length L is about 20cm, probe submerges the phase in water completely
Difference is about 180 degree.So we select this length as the probe length of TDT sensor.
(3) selection of probe unit
The utility model is as shown in Figure 3 in probe unit used.It is stainless steel material used in probe unit, probe length
Degree L is 20cm, and the diameter r of probe conductor material is 2mm；The distance between two-conductor R is 10mm.U-shaped probe is TDT sensor
The classical architecture of probe, it is ensured that signal can return to receiving end, thus greatly reduce the difficulty of signal transit time measurement,
But this sonde configuration sacrifices convenience when measurement, is inserted directly into concrete mix that destroy compact structure complete
Property, it cannot achieve and insert i.e. brake, long-term fixation measuring can only be carried out in preparatory Transducers Embedded in Concrete mixture.
Two, Special electric magnetic wave signal source design method
Electromagnetic wave signal source is high-frequency oscillating circuits composition, to generate stable frequency signal, is provided for whole system
Lasting signal.In order to make TDT concrete mix moisture percentage measuring system measurement accuracy with higher, therefore oscillator must
There must be enough frequency stabilities.The voltage controlled oscillation integrated chip that the utility model uses is MC1648 chip.In 12 feet
(TANK) the external parallel LC resonance circuit between 10 feet (Bias) constitutes the high-frequency oscillating circuits of low distortion, such as Fig. 4 institute
Show.When concrete mix moisture percentage to be measured changes, the frequency for the high frequency sinusoidal signal that the pin 3 of MC1648 exports
Also it will change.
MC1648 uses ECL technique, and maximum operating frequency can reach 225MHz, which utilizes the symmetry to pipe
Reduce the influence for taking leave harmonic wave, stability height, the agc circuit being internally integrated makes the amplitude flatness of oscillator output signal
Preferably.LI and C2 realizes the frequency starting of oscillation in the external parallel LC resonance circuit MC1648, plays vibration frequency and is set as 100MHZ.Inductance L1
It is formed by diameter 0.2mm enameled wire loop coiling, totally 8 circle, coil diameter 0.5cm.Wherein, C2 takes 25PF, C3 and C4 for decoupling
Capacitor filters out power supply noise；C1 is high-frequency filter capacitor, filters out high-frequency parasitic interference.
Three, the design of phase-comparison circuit
TDT sensor probe is " U-shaped ", so each setting one at the probe of electromagnetic radiation end and signal output end
A signal sampling point, sensor circuit measurement is one way transmission of the electromagnetic wave in insertion concrete mix on optical waveguide probe
Time.However, the key that this process is realized is the design of Time delay measurement circuit.
(1) phase detection principle
The key of delay circuit is phase-detection.Its function mainly will be between the test signal and reference signal of input
Phase difference be converted into associated direct current signal, to be calculated for microprocessor after being digitized with A/D converter
Test the time of propagation of the signal on probe.Here test signal and reference signal is the sine voltage signal of same frequency,
Their phase is different.
The functional block diagrams of the phase detectors that the utility model uses is as shown in figure 5, wherein symbolIndicate analogue multiplication
Device, output signal are the products of two input signals.
Assuming that input signal u1, u2 is respectively as follows:
In formula, ω is signal angular frequency；U1、U2WithIt is the amplitude and initial phase of two signals respectively.They
Product are as follows:
First item is DC component in above formula, and size is related with the amplitude of u1, u2 and phase difference；Section 2 is secondary humorous
Wave signal.DC voltage V1 can be obtained after being filtered using low-pass filter to the output of multiplier, i.e.,
It is also related with their amplitude although V1 here is related to the phase difference of two signals, when phase invariant and
When signal amplitude changes, V1 can also change, this just gives and directly obtains phase difference from V1Bring difficulty.In order to
Solve the problems, such as this, phase shifter, which can be used, by 90 ° of phase change of signal u1 becomes u '1It is sent into second together with u2 again afterwards
Multiplier obtains:
DC voltage V2 can be obtained after being filtered using low-pass filter to the output of second multiplier, it may be assumed that
Phase differenceCalculated result is between -180 °~+180 °, in number positive period for determining the phase difference, i.e.,
The phase difference of any range can be measured.
(2) AD8302 working method
The phase-detection chip that the utility model is selected is AD8302.The chip will be in measuring amplitude and the capability set of phase
In one piece of integrated circuit, simplify the design of originally sufficiently complex width phase detection system, and system performance is improved.
Amplitude and phase difference between AD8302 energy two signals of precise measurement is based primarily upon the log compression function of logafier, leads to
Cross two of the precision-matched amplitude and phase measurements realized with logarithm sword wave device fastly to two input channels, can measure simultaneously from
Gain (Amplitude Ratio) and phase difference in low frequency to 2.7GHz frequency between two input signals.
AD8302 phase difference detection chip can measure from low frequency to two input signals in 2.7GHz frequency range it simultaneously
Between Amplitude Ratio and phase difference.The ideal response characteristic curve of the phase difference of AD8302 in measurement mode is as shown in Figure 6.It can see
Out, which directly exports the analog quantity of 0~1.8V, and corresponding is the phase difference for inputting two paths of signals.AD8302 is being surveyed
With 180 ° of phase range when amount.The phase range is also possible to either 0 °~+180 ° (centered on 90 °)
0 °~-180 ° (centered on -90 °).By AD8302 phase difference resonse characteristic at 0 °~+180 ° and at 0 °~-180 °
Slope it is different it is found that can determine that the phase difference of two measured signals is positive or is negative.Logafier in AD8302
Compression function with logarithm, therefore amplitude and phase are namely based on the realization of this function, can be expressed from the next:
VOUT=VSLPlog(VIN/VZ)
Amplitude and phase-detection equation are as follows:
VMAG=VSLPlog(VINA/VINB)
VPHS=Vφ[φ(VINA)-φ(VINB)]
The wherein physical significance of parameters are as follows:
VSLP: slope；VINA: input voltage；VZ: intercept；VMAG: amplitude compares output valve；VPHS: phase bit comparison output valve；
Vφ: slope.
Delay circuit is that the phase-detection function based on AD8302 chip realizes that circuit connection is as shown in Figure 7.
Claims (5)
1. the concrete mix moisture percentage measuring device based on TDT with phase bit comparison, including signal source, phase comparator and biography
The Time delay measurement circuit that sensor probe is constituted, it is characterised in that:
The signal source is high-frequency oscillating circuits, parallel LC resonance circuit is constituted using voltage controlled oscillation, for mentioning for whole system
For lasting two-way high-frequency signal；Signal source is connect with phase comparator and sensor probe respectively, by first via high-frequency signal
It is sent to sensor probe and forms test signal, the second road high-frequency signal is sent to phase comparator and forms reference signal；
The sensor probe uses U-shaped double guide rail measuring probes；Measuring probe is embedded in concrete mix admittedly, one end connection
Signal source, output end are connect with phase comparator test side；
The phase comparator for realizing two paths of signals phase-detection.
2. the concrete mix moisture percentage measuring device according to claim 1 based on TDT with phase bit comparison, feature
Be: the phase difference between test signal and reference signal is converted into direct current associated therewith by the Time delay measurement circuit to be believed
Number；It tests signal and reference signal is sine voltage signal, frequency is identical, and phase is different.
3. the concrete mix moisture percentage measuring device according to claim 2 based on TDT with phase bit comparison, feature
Be: the U-shaped probe length L of U-shaped double guide rail measuring probes is 20cm, and the diameter r of probe conductor material is 2mm, double to lead
The distance between body R is 10mm.
4. the concrete mix moisture percentage measuring device according to claim 2 based on TDT with phase bit comparison, feature
Be: the high-frequency oscillating circuits uses voltage controlled oscillation integrated chip MC1648 chip, between 12 foot TANK and 10 foot Bias
External parallel LC resonance circuit.
5. the concrete mix moisture percentage measuring device according to claim 2 based on TDT with phase bit comparison, feature
Be: the phase comparator uses AD8302 phase-detection chip.
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| CN109342515A (en) * | 2018-11-29 | 2019-02-15 | 中国水利水电第七工程局有限公司 | Concrete mix moisture percentage measuring device and its measurement method based on TDT with phase bit comparison |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109342515A (en) * | 2018-11-29 | 2019-02-15 | 中国水利水电第七工程局有限公司 | Concrete mix moisture percentage measuring device and its measurement method based on TDT with phase bit comparison |
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