CN102914568B - Soil moisture sensor with replaceable probe and measuring method of soil moisture sensor - Google Patents

Abstract

The invention discloses a soil moisture sensor with a replaceable probe and a measuring method thereof. The sensor comprises a sensor probe, a sensor probe interface, a signal drive module, a high-frequency signal source, a matching impedance, a high-frequency detection module and a conditioning module, and the sensor probe Connected with the sensor probe interface, the high-frequency signal source, signal drive module, matching impedance and sensor probe interface form a detection loop. The voltage at both ends of the matching impedance is output to the conditioning module after high-frequency detection and differential processing, and the signal is output after conditioning. This method is based on the linear relationship between the output voltage of the sensor, soil moisture, and the root mean square of the solution dielectric constant established by the probe before replacement, and through the conditioning module, the output of the replaced probe in the same known solution It is equal to the output value of the probe before replacement, and the conditioned sensor can be directly used for detection. The invention has the advantages of simple structure, convenient operation, stability and reliability, and low power consumption.

Description

A soil moisture sensor with a replaceable probe and its measuring method

technical field

The invention relates to the field of farmland soil information collection, in particular to a soil moisture sensor with a replaceable probe and a measuring method thereof.

Background technique

Water in the soil is not only an important substance for crop growth, but also provides an important way for the exchange of various nutrients and energy between crops and soil. Therefore, it is of great significance to measure the moisture in the farmland. At present, there are many kinds of sensors for detecting moisture in farmland. Among them, a soil moisture sensor based on dielectric theory is more commonly used. This type of sensor usually uses Time Domain Reflectometry (TDR) and Frequency Domain (Frequency Domain, FD) These two technical means are realized. The TDR method is to measure the time required for the electromagnetic wave pulse to propagate along the transmission line of known length in the soil medium, and then estimate the mixed dielectric constant of the water-bearing soil to obtain the moisture content information. The FD method is to determine the soil moisture content by directly measuring the change of the impedance of the soil probe.

CN101216439 discloses a soil moisture measuring instrument and method based on the TDR method. The method measures the soil moisture content through the reflection time difference of the pulse signal at the beginning and end of the sensor probe. Each measurement of this type of sensor requires an ergodic process of various states, and the required time is usually several seconds or even more than 20 seconds, and the real-time performance is poor.

CN101281152 discloses a soil moisture sensor based on the FD method. The sensor sends out a 20KHz pulse square wave excitation signal through a soil probe and receives the peak signal of the charging voltage at both ends of the sensor to obtain soil moisture information. Due to the low frequency of the excitation signal, this method is greatly affected by the conductivity of the soil.

In the existing soil moisture sensors based on the FD method, the probes are fixed, that is, the length and diameter of the probes are installed in advance, and the measured soil moisture information is the average result of the area where the probes are located. In the research and application of crop water migration and moisture control with different root system lengths, the overall or local soil moisture information of the crop root system is usually required. Obviously, the existing devices and methods cannot fully meet the requirements.

Therefore, it is of great application value to study a sensor that can replace the sensor head according to the measurement needs.

Contents of the invention

The main purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and provide a soil moisture sensor with a replaceable probe. The sensor is based on the dielectric principle and improved on the basis of the traditional FD detection method. The length and diameter of the probe can be adjusted. It can be replaced according to the actual measurement needs. For example, the probe of the corresponding length can be selected according to the root system length of different crops, so that the soil moisture information in the root system can be measured, which has the advantage of accurate measurement. Another object of the present invention is to provide a measurement method based on the above-mentioned soil moisture sensor with a replaceable probe.

The purpose of the present invention is achieved through the following technical solutions: a soil moisture sensor with a replaceable probe, comprising a sensor housing, a sensor probe, an input-output interface placed inside the sensor housing, a sensor probe interface and a detection circuit, the detection circuit comprising Power supply module, signal drive module, high-frequency signal source, matching impedance, high-frequency detection module and conditioning module, in which the input and output interfaces are respectively connected to the power supply module and the conditioning module, and the external power supply is supplied to the power supply module through the input and output interfaces. The power supply module is Each module in the detection circuit provides working voltage; during measurement, the sensor probe pre-selected according to the measurement needs is connected to the sensor probe interface, and the high-frequency signal source, signal drive module, matching impedance and sensor probe interface are connected in sequence to form a detection circuit. The high-frequency detection module performs high-frequency detection and differential processing on the voltage at both ends of the matching impedance, and then outputs it to the conditioning module. After conditioning, the signal is output to an external processor through the input and output interfaces.

Preferably, the matching impedance is an inductive element.

Preferably, the sensor probe is composed of three stainless steel probes of the same specification, and the length of the probes is determined under the following constraints according to the measurement requirements:

$\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span>$

$\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; ;</span>$

Among them, when the sensor probe impedance meets the condition of formula (1), it is capacitive, and when it meets the condition of formula (2), it is inductive, L is the length of the probe, ε is the equivalent dielectric constant of the water-containing soil, and f is the excitation signal frequency , c is the propagation velocity of electromagnetic wave in vacuum. The constraints represented by formula (1) and formula (2) essentially restrict the range of use of the sensor, that is, the sensor is meaningful only when it meets condition 1 or condition 2, otherwise, the sensor may output wrong results , that is to say, for a sensor output result, the probe impedance can theoretically be capacitive reactance or inductive reactance.

Furthermore, the plurality of probes are arranged equidistantly, and in order to avoid contact between adjacent probes, the diameter of the probes should be smaller than the distance between the probes.

Preferably, the voltage range of the external power supply to the power module through the input and output interface is 4.2-16V DC. Using such a range value can adapt to the voltage output of power supplies with different specifications.

Further, the power module generates two kinds of operating voltages of ±V _d , wherein the operating voltage of the high-frequency detection module is -V _d ; the operating voltage of the conditioning module is ±V _d , and the high-frequency signal source and the signal driving module work The voltage is +V _d .

Furthermore, the operating voltage V _d generated by the power module in the sensor is ±4 volts direct current.

Preferably, the high-frequency signal source adopts a passive crystal oscillator with a frequency of 100 MHz to generate a sine wave high-frequency signal.

Furthermore, the sine wave high-frequency signal generated by the high-frequency signal source provides an excitation signal with a peak-to-peak value between 0.9-1.1V for the probe impedance through the signal driving module.

Preferably, the magnitudes of the matching impedance and the probe impedance are in the same or adjacent orders of magnitude.

Preferably, the conditioning module performs zero point adjustment and gain adjustment on the output voltage after the high-frequency detection module, and makes the sensor measurement results output in the form of voltage or current under different output signal loss requirements.

A measurement method based on the replaceable soil moisture sensor of the above-mentioned probe, specifically comprising the following steps:

(1) First determine the length and diameter of a set of probes under the following constraints, where L is the length of the probe, ε is the equivalent dielectric constant of the water-containing soil, f is the frequency of the excitation signal, and c is the electromagnetic wave in a vacuum The speed of propagation in

$\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

$\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; ;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Then install the probe on the sensor probe interface;

(2) Place the sensors in several soil samples with known moisture and several organic solutions with known dielectric constants, read the output results of the sensors, and establish the sensor output voltage V _out , soil moisture θ, and the dielectric constant of the organic solution respectively. root mean square electric constant The linear relationship between any two, namely:

V _out = f ₁ (θ) (3)

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

(3) Place the sensor in the actual soil to be tested, and obtain the soil moisture according to the formula (3) in step (2);

(4) When replacing the probe according to the measurement requirements, if the sensitivity of the selected probe is equal to the sensitivity of the probe used in step (1), then replace it directly for actual measurement, where the sensitivity K and the probe length L, diameter The relationship of d is as follows:

K=38+0.935L+6.08d; (6)

If not equal, go to step (5);

(5) After the probe is replaced, adjust the conditioning module in the sensor. The adjustment steps are: according to the output value of the probe in the known organic solution before the replacement in step (2), place the replaced probe here. Then adjust the conditioning module so that the output value is equal to the previous output value. After the adjustment is completed, it can be applied to the actual measurement.

Furthermore, in the step (5), when selecting a known organic solution for conditioning, the organic solution corresponding to the maximum dielectric constant is selected.

When the length of the sensor probe cannot meet the requirements of the soil depth, multiple sensors can be used for measurement at the same time. During the measurement process, in order to avoid the mutual influence between the electromagnetic fields of different sensors, the sensors should work in different periods.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The probe of the soil sensor in the present invention can be replaced, so that it can measure different crops and different soil layers without replacing the entire sensor. The structure is simple, the cost is low, and the use is convenient.

2. Compared with the soil moisture sensor with a fixed probe, the sensor of the present invention has obvious advantages in application. The sensor with a fixed probe measures the average soil moisture content within the probe length range in the soil. The sensor also measures the average moisture within the probe length range, but since this sensor can select sensors with different length probes to respond to soil moisture information in different depth ranges, especially when the probe length is as short as possible, it can be regarded as a Point-on-point measurements, so measurements are more accurate.

Description of drawings

Fig. 1 is the structural representation of device of the present invention;

Figure 2 is the relationship between the sensor output of d=3mm and L=40mm probes, soil moisture, and the root mean square of the dielectric constant of the organic solution;

Figure 3 is the output result of the d=3mm, L=40mm probe sensor in the organic solution;

Fig. 4 is the output result of probe sensor with d=3mm, L=150mm in organic solution.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example 1

As shown in Figure 1, a soil moisture sensor with a replaceable probe includes a sensor housing 1, a sensor probe 8, an input and output interface 2 placed inside the sensor housing 1, a sensor probe interface 7 and a detection circuit, and the detection circuit includes Power supply module 3, signal drive module 4, high-frequency signal source 5, matching impedance Zm6, high-frequency detection module 9 and conditioning module 10, wherein the input and output interfaces 2 are respectively connected to the power supply module 3 and conditioning module 10, and the external power supply is input and output through The interface 2 supplies power to the power supply module 3, and the power supply module 3 provides working voltage for each module in the detection circuit; during measurement, the sensor probe 8 pre-selected according to the measurement needs is connected to the sensor probe interface 7, and the high-frequency signal source 5, signal drive Module 4, matching impedance 6 and sensor probe interface 7 are connected in sequence to form a detection loop. High-frequency detection module 9 performs high-frequency detection and differential processing on the voltages ( _va , v _b ) at both ends of matching impedance 6 to obtain V _{o and} output it to Conditioning module 10, the signal is conditioned and output to an external processor through the input and output interface 2.

In this embodiment, the matching impedance 6 is an inductive element. The magnitudes of the matching impedance 6 and the probe impedance are in the same or adjacent orders of magnitude. The voltage V _in supplied by the external power supply to the power module 3 through the input and output interface 2 ranges from 4.2 to 16 volts direct current. The power supply module 3 _produces two kinds of operating voltages of ±V _d , wherein the operating voltage of the high-frequency detection module 9 is -V _d ; The operating voltage is +V _d . In this embodiment, V _d is ±4 volts direct current. The high-frequency signal source 5 uses a passive crystal oscillator with a frequency of 100 MHz to generate a sine wave high-frequency signal, and the sine wave high-frequency signal provides an excitation signal with a peak-to-peak value between 0.9-1.1V for the probe impedance through the signal driving module. The conditioning module 10 performs zero point adjustment and gain adjustment on the output voltage after the high frequency detection module 9, and makes the sensor measurement results output in the form of voltage V _out or current I _out under different output signal loss requirements.

The sensor probe 8 is composed of three stainless steel probes with the same specification, and the length of the probes is determined under the following constraints according to the measurement needs:

$\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span>$

$\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; ;</span>$

Among them, when the sensor probe impedance meets the condition of formula (1), it is capacitive, and when it meets the condition of formula (2), it is inductive, L is the length of the probe, ε is the equivalent dielectric constant of the water-containing soil, and f is the excitation signal frequency , c is the propagation velocity of electromagnetic wave in vacuum. The constraints represented by formula (1) and formula (2) essentially restrict the range of use of the sensor, that is, the sensor is meaningful only when it meets condition 1 or condition 2, otherwise, the sensor may output wrong results , that is to say, for a sensor output result, the probe impedance can theoretically be capacitive reactance or inductive reactance.

The plurality of probes are arranged equidistantly, and in order to avoid contact between adjacent probes, the diameter d of the probes should be smaller than the distance D between the probes.

A measurement method based on the replaceable soil moisture sensor of the above-mentioned probe, specifically comprising the following steps:

(1) First determine the length and diameter of a set of probes under the following constraints, where L is the length of the probe, ε is the equivalent dielectric constant of the water-containing soil, f is the frequency of the excitation signal, and c is the electromagnetic wave in a vacuum The speed of propagation in

$\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

$\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; ;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Then install the probe on the sensor probe interface.

(2) Place the sensors in several soil samples with known moisture and several organic solutions with known dielectric constants, read the output results of the sensors, and establish the sensor output voltage V _out , soil moisture θ, and the dielectric constant of the organic solution respectively. root mean square electric constant The linear relationship between any two, namely:

V _out = f ₁ (θ) (3)

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

As shown in Figure 2, it is the relationship diagram between d=3mm, L=40mm probe sensor output, soil moisture and organic solution dielectric constant root mean square.

Taking d=3mm, L=40mm probe as an example, the output results of the sensor in different organic solutions are shown in Figure 3. It can be seen that within the measurement range, V _d shows a downward trend, and V _o shows an upward trend, indicating that the probe impedance Z _l in this measurement range is capacitive, and the capacitance value changes from small to large.

The output results of sensors with d=3mm and L=150mm probes in different organic solutions are shown in Figure 4. It can be seen that within the measurement range, the value of V _b decreases first and then increases, contrary to V _b , the value of V _o increases first and then decreases, and the minimum value of V _b and the maximum value of V _o are both at 6 No. 1 sample (dielectric constant ε=25), indicating that Z _l changes capacitively before sample No. 6, and then inductively changes (theoretically, the Z _l impedance characteristic transition position should be the dielectric constant corresponding to the maximum value of V _o ) .

(3) Place the sensor in the actual soil to be tested, and obtain the soil moisture according to the formula (3) in step (2).

(4) When replacing the probe according to the measurement requirements, if the sensitivity of the selected probe is equal to the sensitivity of the probe used in step (1), then replace it directly for actual measurement, where the sensitivity K and the probe length L, diameter The relationship of d is as follows:

K=38+0.935L+6.08d; (6)

If not equal, go to step (5). For example, the probe with d=3mm, L=60mm has the same sensitivity as the probe with d=6mm, L=40.5mm, and it can be replaced directly in theory.

(5) After the probe is replaced, adjust the conditioning module in the sensor. The adjustment steps are: for the output value of the probe in the known organic solution before the replacement in step (2), select the organic solution corresponding to the maximum dielectric constant. solution, place the replaced probe in this known organic solution, and then adjust the conditioning module so that its output value is equal to the previous output value. After the adjustment is completed, it can be applied to the actual measurement.

Present embodiment is the research that carries out based on following subject:

Topic 1, Research on Paddy Field Soil Moisture Detection Method Based on Dielectric Theory, the fourth batch of special funding from China Postdoctoral Science Foundation, 201104361, 2010-2013.

Topic 2, Environmental Information Sensing Technology and Equipment of Agricultural Product Origin, National 863 Major Project, 2011AA100704, 2011-2013.

The above topics belong to the key technology research field of the perception layer in the agricultural Internet of Things, which has great practical application prospects and high scientific research value. In a large number of practical applications, the soil sensor described in this embodiment realizes that the probe can be replaced, so that it can measure different crops and different soil layers, the measurement is accurate, and it has the advantages of simple structure, low cost and convenient use.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (2)

1. A measuring method of a probe replaceable soil moisture sensor, is characterized in that, comprises the following steps: (1) First determine the length and diameter of a set of probes under the following constraints, where L is the length of the probe, ε is the equivalent dielectric constant of the water-containing soil, f is the frequency of the excitation signal, and c is the electromagnetic wave in a vacuum The speed of propagation in $\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ $\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; ;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ Then install the probe on the sensor probe interface; (2) Place the sensors in several soil samples with known moisture and several organic solutions with known dielectric constants, read the output results of the sensors, and establish the sensor output voltage V _out , soil moisture θ, and organic solution dielectric constant respectively. root mean square electric constant The linear relationship between any two, namely: V _out = f ₁ (θ) (3) ${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$ $\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$ (3) The sensor is placed in the actual soil to be measured, and the soil moisture is obtained according to the formula (3) in the step (2); (4) When replacing the probe according to the measurement requirements, if the sensitivity of the selected probe is equal to the sensitivity of the probe used in step (1), then directly replace it for actual measurement, where the sensitivity K and the probe length L, diameter The relationship of d is as follows: K＝38+0.935L+6.08d; (6) If not equal, then enter step (5); (5) After the probe is replaced, adjust the conditioning module in the sensor. The adjustment steps are: according to the output value of the probe in the known organic solution before the replacement in step (2), the replaced probe is also placed here. Then adjust the conditioning module so that the output value is equal to the previous output value. 2. the measuring method of the replaceable soil moisture sensor of probe according to claim 1, it is characterized in that, in described step (5), when selecting known organic solution to condition, when selecting dielectric constant maximum corresponding organic solutions.