CN102914568A - 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 of the soil moisture sensor. The moisture sensor comprises the sensor probe, a sensor probe connector, a signal driving module, a high-frequency signal source, a matching impedance, a high-frequency wave detection module and a conditioning module, wherein the sensor probe is connected with the sensor probe connector, the high-frequency signal source, the signal driving module, the matching impedance and the sensor probe connector form a detection loop, voltage at two ends of the matching impedance are output to the conditioning module after being subjected to high-frequency wave detection and difference, and signals are output after being conditioned. Output value of the new probe in the given solution is equal to the output value of the replaced probe by the conditioning module according to linear relations between every two of sensor output voltage, soil moisture, solution dielectric constant mean square root of the probe before replacement, and the sensor after being conditioned can be directly used for detecting. The soil moisture sensor with the replacement probe has the advantages of simple structure, convenience in operation, stability, reliability and low power consumption.

Description

The interchangeable soil moisture sensor of a kind of probe and measuring method thereof

Technical field

The present invention relates to the farm land soil information collecting field, particularly the interchangeable soil moisture sensor of a kind of probe and measuring method thereof.

Background technology

Water in the soil is not only the important substance of plant growth, and also various nutrition and the energy exchange for crop and soil provides the important channel.Therefore measure significant to the moisture in the farmland.The sensor that detects at present moisture in the farmland has a variety of, wherein commonly used have a kind of soil moisture sensor based on dielectric Theory, such sensor adopts time domain reflectometry (Time Domain Reflectometry usually, TDR) and frequency domain method (Frequency Domain, FD) these two kinds of technological means realize, the TDR method is to propagate required time by measuring electromagnetic impulse known length transmission line in the soil media, then estimates the mixing specific inductive capacity of watered ground and then obtains moisture information.The FD method is the variation by direct measurement soil probe impedance, thereby determines soil moisture content.

CN101216439 discloses a kind of soil moisture measurement unit based on the TDR method and method, and the method is poor in the reflection interval of sensor probe top and terminal by pulse signal, thereby measures soil moisture content.This class methods sensor is measured at every turn needs an ergodic process, and in the several seconds even more than 20 seconds, real-time is relatively poor usually for required time.

CN101281152 discloses a kind of soil moisture sensor based on the FD method, and this sensor sends 20KHz pulse square wave pumping signal by the soil probe and receives the peak signal of its two ends charging voltage, and then obtains soil moisture information.The method is subjected to that conductivity affects larger in the soil because exciting signal frequency is lower.

In existing soil moisture sensor based on the FD method, probe all is fixed, and namely length and the diameter of probe are mounted in advance, and measured soil moisture information is the average result in probe zone of living in.In the researchs such as the crop water migration of different root lengths, soil moisture content control are used, usually need the overall or local soil moisture information of crop root scope, obvious existing apparatus and method can not satisfy its requirement fully.

Therefore, research is a kind of can have great using value according to the sensor that the measurement needs are replaced sensor probe.

Summary of the invention

Fundamental purpose of the present invention is to overcome the shortcoming of prior art with not enough, provide a kind of probe interchangeable soil moisture sensor, this sensor is based on the dielectric principle, improve on traditional FD detection method basis, length and the diameter of probe can be replaced according to practical measurement requirement, for example can select according to the Different Crop root length probe of corresponding length, thereby can measure root system scope soil moisture information, have and measure accurately advantage.Another object of the present invention is to provide a kind of measuring method based on the interchangeable soil moisture sensor of above-mentioned probe.

Purpose of the present invention realizes by following technical scheme: the interchangeable soil moisture sensor of a kind of probe, comprise sensor outer housing, sensor probe, place the IO interface of sensor outer housing inside, sensor probe interface and testing circuit, described testing circuit comprises power module, the signal driver module, high-frequency signal source, matched impedance, high frequency detection module and conditioning module, wherein IO interface is connected with conditioning module with power module respectively, external power source is powered to power module by IO interface, and power module provides operating voltage for each module in the testing circuit; When measuring, be connected with the sensor probe interface according to measuring the previously selected sensor probe of needs, high-frequency signal source, signal driver module, matched impedance and sensor probe interface connect successively, form and detect the loop, high frequency detection module carries out outputing to conditioning module after high frequency detection and the difference processing to the voltage at matched impedance two ends, and signal outputs to ppu by IO interface after conditioning.

Preferably, described matched impedance is inductive element.

Preferably, described sensor probe is comprised of three identical stainless steel probes of specification, and the length of probe is determined under following constraint condition according to measuring needs:

$0<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\frac{\mathrm{\&pi;}}{2};$

$\frac{\mathrm{\&pi;}}{2}<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\mathrm{\&pi;};$

Wherein, be capacitive when formula (1) condition is satisfied in the sensor probe impedance, be perception when satisfying formula (2) condition, L is the length of probe, and ε is the effective dielectric constant of watered ground, and f is exciting signal frequency, and c is electromagnetic wave velocity of propagation in a vacuum.What formula (1), the represented constraint condition of formula (2) retrained in essence is the usable range of sensor, be sensor only satisfy condition 1 or use during condition 2 be only significant, otherwise, sensor may the output error result, that is to say, a sensor Output rusults, probe impedance can be capacitive reactance in theory, also can be induction reactance.

Further, described some probes equidistantly discharge, and contact for fear of adjacent probe, and described probe diameter is less than the spacing between the probe.

Preferably, described external power source is 4.2 ~ 16 volts of direct currents by the voltage range of IO interface supply power module.Adopt such value range, can adapt to the Voltage-output of different size power supply.

Further, described power module generation ± V _dTwo kinds of operating voltage, the operating voltage of its medium-high frequency detection module is-V _dThe operating voltage of conditioning module is ± V _d, the operating voltage of high-frequency signal source, signal driver module is+V _d

Further, the operating voltage V that power module produces in the described sensor _dBe ± 4 volts of direct currents.

Preferably, described high-frequency signal source proportion is the passive crystal oscillator of 100MHz and produces sinusoidal wave high-frequency signal.

Further, the sinusoidal wave high-frequency signal of high-frequency signal source generation provides the pumping signal of peak-to-peak value between 0.9-1.1V through the signal driver module for probe impedance.

Preferably, the amplitude of described matched impedance and probe impedance is in identical or consecutive number magnitude.

Preferably, adjust and gain is adjusted by zero point to carrying out through the output voltage after the high frequency detection module for described conditioning module, under different output signal losses requires, makes sensor measurement with voltage or current forms output.

A kind of measuring method based on the interchangeable soil moisture sensor of above-mentioned probe specifically may further comprise the steps:

(1) at first satisfying length and the diameter of determining one group of probe under the following constraint condition, wherein L is the length of probe, and ε is the effective dielectric constant of watered ground, and f is exciting signal frequency, and c is electromagnetic wave velocity of propagation in a vacuum;

$0<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\frac{\mathrm{\&pi;}}{2};---\left(1\right)$

$\frac{\mathrm{\&pi;}}{2}<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\mathrm{\&pi;};---\left(2\right)$

Then probe is installed in the sensor probe interface;

(2) sensor is placed respectively the known soil sample of several moisture and the known organic solution of several specific inductive capacity, the read sensor Output rusults is set up respectively sensor output voltage V _Out, soil moisture θ, organic solution specific inductive capacity root mean square

Linear relationship between any two, that is:

V _out=f ₁(θ) （3）

$V_{\mathrm{out}}=f_2\left(\sqrt{\mathrm{\&epsiv;}}\right)---\left(4\right)$

$\mathrm{\&theta;}=f_3\left(\sqrt{\mathrm{\&epsiv;}}\right)---\left(5\right);$

(3) sensor is positioned in the actual soil to be measured, namely obtains soil moisture according to the formula (3) in the step (2);

(4) when changing probe according to measurement demand, if the sensitivity of the probe that selected probe sensitivity and step (1) adopt equate, then directly change, for actual measurement, the relational expression of its medium sensitivity K and probe length L, diameter d is as follows:

K=38+0.935L+6.08d；（6）

If unequal, then enter step (5);

(5) after probe is replaced, the conditioning module in the sensor is regulated, the step of regulating is: according to replacing it the output valve of front probe in known organic solution in the step (2), probe after replacing also is placed in this known organic solution, then conditioning module is adjusted, its output valve is equated with before output valve.After finishing adjusting, namely can be applicable to actual measurement.

Further, in the described step (5), when selecting known organic solution to nurse one's health, corresponding organic solution when selecting specific inductive capacity maximum.

When sensor probe length can not satisfy the depth of soil requirement, can adopt simultaneously a plurality of sensors to measure, in the measuring process, for fear of influencing each other between the different sensors electromagnetic field, sensor should carry out work at times.

The present invention compared with prior art has following advantage and beneficial effect:

1, the probe of soil sensor can be replaced among the present invention, thereby can measure for Different Crop, different soil, need not to change whole sensor, and is simple in structure, with low cost, easy to use.

2, compare with the soil moisture sensor of static probe, sensor of the present invention has obvious advantage in application, the sensor measurement of static probe be the average soil water content in the probe length scope in the soil, although this patent sensor measurement also is the interior average moisture of probe length scope in itself, but because this sensor can select the sensor of different length probe with the soil moisture information of response different depth scope as required, especially, when probe length as far as possible in short-term, can be considered a measurement on the point, it is more accurate therefore to measure.

Description of drawings

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

Fig. 2 is the relation that adopts between d=3mm, the output of L=40mm probe sensor and soil moisture, the organic solution specific inductive capacity root mean square;

Fig. 3 adopts d=3mm, the Output rusults of L=40mm probe sensor in organic solution;

Fig. 4 is for adopting d=3mm, the Output rusults of L=150mm probe sensor in organic solution.

Embodiment

The present invention is described in further detail below in conjunction with embodiment and accompanying drawing, but embodiments of the present invention are not limited to this.

Embodiment 1

As shown in Figure 1, the interchangeable soil moisture sensor of a kind of probe, comprise sensor outer housing 1, sensor probe 8, place the IO interface 2 of sensor outer housing 1 inside, sensor probe interface 7 and testing circuit, described testing circuit comprises power module 3, signal driver module 4, high-frequency signal source 5, matched impedance Zm6, high frequency detection module 9 and conditioning module 10, wherein IO interface 2 is connected with conditioning module with power module 3 respectively and is connected, to power module 3, power module 3 provides operating voltage for each module in the testing circuit to external power source by IO interface 2 power supplies; When measuring, be connected with sensor probe interface 7 according to measuring the previously selected sensor probe 8 of needs, high-frequency signal source 5, signal driver module 4, matched impedance 6 and sensor probe interface 7 connect successively, form and detect loop, the voltage (v at 9 pairs of matched impedance 6 two ends of high frequency detection module _a, v _b) carry out obtaining V after high frequency detection and the difference processing _oOutput to conditioning module 10, signal outputs to ppu by IO interface 2 after conditioning.

In the present embodiment, described matched impedance 6 is inductive element.The amplitude of described matched impedance 6 and probe impedance is in identical or consecutive number magnitude.Described external power source is by the voltage V of IO interface 2 supply power modules 3 _InScope is 4.2 ~ 16 volts of direct currents.Described power module 3 generation ± V _dTwo kinds of operating voltage, the operating voltage of its medium-high frequency detection module 9 is-V _dThe operating voltage of conditioning module 10 is ± V _d, the operating voltage of high-frequency signal source 5, signal driver module 4 is+V _dV in the present embodiment _dBe ± 4 volts of direct currents.Described high-frequency signal source 5 proportions are the passive crystal oscillator of 100MHz and produce sinusoidal wave high-frequency signal, and sinusoidal wave high-frequency signal provides the pumping signal of peak-to-peak value between 0.9-1.1V through the signal driver module for probe impedance.Output voltage after 10 pairs of processes of described conditioning module high frequency detection module 9 carries out adjusting zero point and gaining and adjust, and under different output signal losses requires, makes sensor measurement with voltage V _OutOr current forms I _OutOutput.

Described sensor probe 8 is comprised of three identical stainless steel probes of specification, and the length of probe is determined under following constraint condition according to measuring needs:

$0<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\frac{\mathrm{\&pi;}}{2};$

$\frac{\mathrm{\&pi;}}{2}<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\mathrm{\&pi;};$

Wherein, be capacitive when formula (1) condition is satisfied in the sensor probe impedance, be perception when satisfying formula (2) condition, L is the length of probe, and ε is the effective dielectric constant of watered ground, and f is exciting signal frequency, and c is electromagnetic wave velocity of propagation in a vacuum.What formula (1), the represented constraint condition of formula (2) retrained in essence is the usable range of sensor, be sensor only satisfy condition 1 or use during condition 2 be only significant, otherwise, sensor may the output error result, that is to say, a sensor Output rusults, probe impedance can be capacitive reactance in theory, also can be induction reactance.

Described some probes equidistantly discharge, and contact for fear of adjacent probe, and described probe diameter d is less than the space D between the probe.

A kind of measuring method based on the interchangeable soil moisture sensor of above-mentioned probe specifically may further comprise the steps:

(1) at first satisfying length and the diameter of determining one group of probe under the following constraint condition, wherein L is the length of probe, and ε is the effective dielectric constant of watered ground, and f is exciting signal frequency, and c is electromagnetic wave velocity of propagation in a vacuum;

$0<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\frac{\mathrm{\&pi;}}{2};---\left(1\right)$

$\frac{\mathrm{\&pi;}}{2}<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\mathrm{\&pi;};---\left(2\right)$

Then probe is installed in the sensor probe interface.

(2) sensor is placed respectively the known soil sample of several moisture and the known organic solution of several specific inductive capacity, the read sensor Output rusults is set up respectively sensor output voltage V _Out, soil moisture θ, organic solution specific inductive capacity root mean square

Linear relationship between any two, that is:

V _out=f ₁(θ) （3）

$V_{\mathrm{out}}=f_2\left(\sqrt{\mathrm{\&epsiv;}}\right)---\left(4\right)$

$\mathrm{\&theta;}=f_3\left(\sqrt{\mathrm{\&epsiv;}}\right)---\left(5\right);$

As shown in Figure 2, be the graph of a relation between d=3mm, the output of L=40mm probe sensor and soil moisture, the organic solution specific inductive capacity root mean square.

Take d=3mm, L=40mm probe as example, the Output rusults of sensor in different organic solutions as shown in Figure 3.Can find out in measurement range V _dOn a declining curve, V _oIn rising trend, show at this measurement range probe impedance Z _lAll be capacitive, capacitance changes from small to big.

The Output rusults of sensor in different organic solutions of d=3mm, L=150mm probe as shown in Figure 4.Can find out in measurement range V _bValue reduces first rear increase, with V _bOn the contrary, V _oValue first increases and then decreases, and V _bMinimal value and V _oMaximum value all be in No. 6 samples (DIELECTRIC CONSTANT ε=25), show Z _lBefore No. 6 samples, be capacitive and change, be afterwards perception and change (Z in theory _lImpedance operator transition position should be V _oThe corresponding specific inductive capacity of maximal value).

(3) sensor is positioned in the actual soil to be measured, namely obtains soil moisture according to the formula (3) in the step (2).

(4) when changing probe according to measurement demand, if the sensitivity of the probe that selected probe sensitivity and step (1) adopt equate, then directly change, for actual measurement, the relational expression of its medium sensitivity K and probe length L, diameter d is as follows:

K=38+0.935L+6.08d；（6）

If unequal, then enter step (5).For example the probe of d=3mm, L=60mm has identical sensitivity with the probe of d=6mm, L=40.5mm, can directly replace use in theory.

(5) after probe is replaced, the conditioning module in the sensor is regulated, the step of regulating is: for replacing it the output valve of front probe in known organic solution in the step (2), corresponding organic solution when selecting the specific inductive capacity maximum, probe after replacing also is placed in this known organic solution, then conditioning module is adjusted, its output valve is equated with before output valve.After finishing adjusting, namely can be applicable to actual measurement.

The present embodiment is based on the research that following problem is carried out:

Problem 1, based on the paddy soil moisture detecting method research of dielectric Theory, the 4th batch of China's post-doctors science fund subsidized 201104361,2010-2013 especially.

Problem 2, agricultural product home environment information Perception technology and equipment, National 863 major project, 2011AA100704,2011-2013.

Above-mentioned problem all belongs to sensing layer gordian technique research field in the agriculture Internet of Things, has great actual application prospect and higher scientific research value.And the described soil sensor of the present embodiment has realized that probe is replaceable in a large amount of practical applications, thereby can measure for Different Crop, different soil, measures accurately, and has advantages of simple in structure, with low cost, easy to use.

Above-described embodiment is the better embodiment of the present invention; but embodiments of the present invention are not restricted to the described embodiments; other any do not deviate from change, the modification done under Spirit Essence of the present invention and the principle, substitutes, combination, simplify; all should be the substitute mode of equivalence, be included within protection scope of the present invention.

Claims (10)

1. One kind the probe interchangeable soil moisture sensor, it is characterized in that, comprise sensor outer housing, sensor probe, place IO interface, sensor probe interface and the testing circuit of sensor outer housing inside, described testing circuit comprises power module, signal driver module, high-frequency signal source, matched impedance, high frequency detection module and conditioning module, wherein IO interface is connected with conditioning module with power module respectively, external power source is powered to power module by IO interface, and power module provides operating voltage for each module in the testing circuit; When measuring, be connected with the sensor probe interface according to measuring the previously selected sensor probe of needs, high-frequency signal source, signal driver module, matched impedance and sensor probe interface connect successively, form and detect the loop, high frequency detection module carries out outputing to conditioning module after high frequency detection and the difference processing to the voltage at matched impedance two ends, and signal outputs to ppu by IO interface after conditioning.
2. 2. the interchangeable soil moisture sensor of probe according to claim 1 is characterized in that, described matched impedance is inductive element.
3. 3. the interchangeable soil moisture sensor of probe according to claim 1 is characterized in that, described sensor probe is comprised of three identical stainless steel probes of specification, and the length of probe is determined under following constraint condition according to measuring needs:

   $0<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{C}<\frac{\mathrm{\&pi;}}{2};$

   $\frac{\mathrm{\&pi;}}{2}<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\mathrm{\&pi;};$

   Wherein, L is the length of probe, and ε is the effective dielectric constant of watered ground, and f is exciting signal frequency, and c is electromagnetic wave velocity of propagation in a vacuum;

   Described probe diameter is less than the spacing between the probe.
4. 4. the interchangeable soil moisture sensor of probe according to claim 1 is characterized in that, described external power source is 4.2 ~ 16 volts of direct currents by the voltage range of IO interface supply power module.
5. 5. the interchangeable soil moisture sensor of probe according to claim 4 is characterized in that, described power module generation ± V _dTwo kinds of operating voltage, the operating voltage of its medium-high frequency detection module is-V _dThe operating voltage of conditioning module is ± V _d, the operating voltage of high-frequency signal source, signal driver module is+V _d
6. 6. the interchangeable soil moisture sensor of probe according to claim 5 is characterized in that, the operating voltage V that power module produces in the described sensor _dBe ± 4 volts of direct currents.
7. 7. the interchangeable soil moisture sensor of probe according to claim 1 is characterized in that, described high-frequency signal source proportion is the passive crystal oscillator of 100MHz and produces sinusoidal wave high-frequency signal;

   The amplitude of described matched impedance and probe impedance is in identical or consecutive number magnitude;

   Adjust and gain is adjusted by zero point to carrying out through the output voltage after the high frequency detection module for described conditioning module, under different output signal losses requires, makes sensor measurement with voltage or current forms output.
8. 8. the interchangeable soil moisture sensor of probe according to claim 7 is characterized in that, the sinusoidal wave high-frequency signal that high-frequency signal source produces provides the pumping signal of peak-to-peak value between 0.9-1.1V through the signal driver module for probe impedance.
9. 9. the measuring method based on the interchangeable soil moisture sensor of each described probe of claim 1-8 is characterized in that, may further comprise the steps:

   (1) at first satisfying length and the diameter of determining one group of probe under the following constraint condition, wherein L is the length of probe, and ε is the effective dielectric constant of watered ground, and f is exciting signal frequency, and c is electromagnetic wave velocity of propagation in a vacuum;

   $0<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{c}<\frac{\mathrm{\&pi;}}{2};---\left(1\right)$

   $\frac{\mathrm{\&pi;}}{2}<\frac{2\mathrm{\&pi;fL}\sqrt{\mathrm{\&epsiv;}}}{C}<\mathrm{\&pi;};---\left(2\right)$

   Then probe is installed in the sensor probe interface;

   (2) sensor is placed respectively the known soil sample of several moisture and the known organic solution of several specific inductive capacity, the read sensor Output rusults is set up respectively sensor output voltage V _Out, soil moisture θ, organic solution specific inductive capacity root mean square Linear relationship between any two, that is:

   V _out=f ₁(θ) （3）

   $V_{\mathrm{out}}=f_2\left(\sqrt{\mathrm{\&epsiv;}}\right)---\left(4\right)$

   $\mathrm{\&theta;}=f_3\left(\sqrt{\mathrm{\&epsiv;}}\right)---\left(5\right);$

   (3) sensor is positioned in the actual soil to be measured, namely obtains soil moisture according to the formula (3) in the step (2);

   (4) when changing probe according to measurement demand, if the sensitivity of the probe that selected probe sensitivity and step (1) adopt equate, then directly change, for actual measurement, the relational expression of its medium sensitivity K and probe length L, diameter d is as follows:

   K=38+0.935L+6.08d； （6）

   If unequal, then enter step (5);

   (5) after probe is replaced, the conditioning module in the sensor is regulated, the step of regulating is: according to replacing it the output valve of front probe in known organic solution in the step (2), probe after replacing also is placed in this known organic solution, then conditioning module is adjusted, its output valve is equated with before output valve.
10. 10. the measuring method of the interchangeable soil moisture sensor of probe according to claim 9 is characterized in that, in the described step (5), and when selecting known organic solution to nurse one's health, corresponding organic solution when selecting specific inductive capacity maximum.

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