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

CN101216439 discloses a kind of soil moisture measurement unit and method based on TDR 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 required time is conventionally in the several seconds even more than 20 seconds, and real-time is poor.

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

In the existing soil moisture sensor based on FD method, probe is all fixed, and length and the diameter of probe are mounted in advance, and measured soil moisture information is the average result in probe region of living in.In the research application such as the crop water migration to different root lengths, soil moisture content control, conventionally need crop root scope totally or local soil moisture information, obvious existing apparatus and method can not meet its requirement completely.

Therefore, study a kind of sensor that can need to replace sensor probe according to measurement and there is great using value.

Summary of the invention

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

Object 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, be placed in the IO interface of sensor outer housing inside, sensor probe interface and testing circuit, 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, power module provides operating voltage for each module in testing circuit, when measuring, according to measuring, need previously selected sensor probe to be connected with sensor probe interface, high-frequency signal source, signal driver module, matched impedance and sensor probe interface connect successively, form and detect loop, high frequency detection module carries out outputing to conditioning module after high frequency detection and 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 need to be determined according to measuring under following constraint condition:

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

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

Wherein, when sensor probe impedance meets formula (1) condition, be capacitive, while meeting formula (2) condition, be perception, the length that L is probe, the effective dielectric constant that ε is watered ground, f is exciting signal frequency, 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 output error result, that is to say, a sensor Output rusults, probe impedance can be capacitive reactance in theory, can be also induction reactance.

Further, described some probes equidistantly discharge, and for fear of adjacent probe, contact, and described probe diameter is less than the spacing between 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 _d; The 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 in described sensor, power module produces _dfor ± 4 volts of direct currents.

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

Further, 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 signal driver module for probe impedance.

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

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

A measuring method based on the interchangeable soil moisture sensor of above-mentioned probe, specifically comprises the following steps:

(1) first meeting length and the diameter of determining one group of probe under following constraint condition, the length that wherein L is probe, the effective dielectric constant that ε is watered ground, f is exciting signal frequency, 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 arranged on to sensor probe interface;

(2) sensor is placed in respectively to soil sample and the known organic solution of several specific inductive capacity that several moisture are known, read sensor Output rusults, sets 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 actual soil to be measured, according to the formula (3) in step (2), obtains soil moisture;

(4) when changing probe according to measurement demand, if the sensitivity of the probe that selected probe sensitivity adopts with step (1) equate, 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, enter step (5);

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

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

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

Compared with prior art, tool has the following advantages and beneficial effect in the present invention:

1, in the present invention, the probe of soil sensor can be replaced, thereby can measure for Different Crop, different soil, without changing whole sensor, 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 within the scope of probe length in soil, although this patent sensor measurement is also the average moisture within the scope of probe length 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 point, therefore it is more accurate to measure.

Accompanying drawing explanation

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

Fig. 2 is the relation adopting between d=3mm, the output of L=40mm probe sensor and soil moisture, 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

Below in conjunction with embodiment and accompanying drawing, the present invention is described in further detail, 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, be placed in 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 10 with power module 3 respectively, external power source is powered to power module 3 by IO interface 2, power module 3 provides operating voltage for each module in testing circuit, when measuring, according to measuring, need previously selected sensor probe 8 to be connected with sensor probe interface 7, 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 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 generations ± V _dtwo kinds of operating voltage, the operating voltage of its medium-high frequency detection module 9 is-V _d; The operating voltage of conditioning module 10 is ± V _d, the operating voltage of high-frequency signal source 5, signal driver module 4 is+V _d.V in the present embodiment _dfor ± 4 volts of direct currents.The passive crystal oscillator that described high-frequency signal source 5 proportions are 100MHz also produces 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 signal driver module for probe impedance.10 pairs of the described conditioning module output voltage after high frequency detection module 9 carries out adjustment at zero point and gain is adjusted, 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 need to be determined according to measuring under following constraint condition:

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

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

Wherein, when sensor probe impedance meets formula (1) condition, be capacitive, while meeting formula (2) condition, be perception, the length that L is probe, the effective dielectric constant that ε is watered ground, f is exciting signal frequency, 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 output error result, that is to say, a sensor Output rusults, probe impedance can be capacitive reactance in theory, can be also induction reactance.

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

A measuring method based on the interchangeable soil moisture sensor of above-mentioned probe, specifically comprises the following steps:

(1) first meeting length and the diameter of determining one group of probe under following constraint condition, the length that wherein L is probe, the effective dielectric constant that ε is watered ground, f is exciting signal frequency, 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 arranged on to sensor probe interface.

(2) sensor is placed in respectively to soil sample and the known organic solution of several specific inductive capacity that several moisture are known, read sensor Output rusults, sets 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, organic solution specific inductive capacity root mean square.

D=3mm, the L=40mm probe of take is example, and the Output rusults of sensor in different organic solution 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 the sensor of d=3mm, L=150mm probe in different organic solution as shown in Figure 4.Can find out in measurement range V _bvalue first reduces rear increase, with V _bon the contrary, V _ovalue first increases and then decreases, and V _bminimal value and V _omaximum value all 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 actual soil to be measured, according to the formula (3) in step (2), obtains soil moisture.

(4) when changing probe according to measurement demand, if the sensitivity of the probe that selected probe sensitivity adopts with step (1) equate, 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, 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 sensor is regulated, the step regulating is: for replacing it the output valve of front probe in known organic solution in step (2), corresponding organic solution while selecting specific inductive capacity maximum, probe after replacing is also placed in this known organic solution, then conditioning module is adjusted, its output valve is equated with output valve before.Complete after adjusting, can be applicable to actual measurement.

The present embodiment is the research of carrying out based on following problem:

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

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 agriculture Internet of Things, has great actual application prospect and higher scientific research value.And soil sensor described in the present embodiment is in a large amount of practical applications, realized probe replaceable, thereby can measure for Different Crop, different soil, measure accurately, and have advantages of simple in structure, with low cost, easy to use.

Above-described embodiment is preferably 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 principle, substitutes, combination, simplify; all should be equivalent substitute mode, within being included in protection scope of the present invention.

Claims (2)

1. a measuring method for the interchangeable soil moisture sensor of probe, is characterized in that, comprises the following steps:

(1) first meeting length and the diameter of determining one group of probe under following constraint condition, the length that wherein L is probe, the effective dielectric constant that ε is watered ground, f is exciting signal frequency, 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 arranged on to sensor probe interface;

(2) sensor is placed in respectively to soil sample and the known organic solution of several specific inductive capacity that several moisture are known, read sensor Output rusults, sets 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 actual soil to be measured, according to the formula (3) in step (2), obtains soil moisture;

(4) when changing probe according to measurement demand, if selected probe sensitivity equates with the sensitivity of the probe that step (1) adopts, 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, enter step (5);

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

2. the measuring method of the interchangeable soil moisture sensor of probe according to claim 1, is characterized in that, in described step (5), and when selecting known organic solution to nurse one's health, corresponding organic solution while selecting specific inductive capacity maximum.