CN201464410U - High-frequency capacitance type soil humidity sensor - Google Patents

Abstract

The utility model relates to a high-frequency capacitance type soil humidity sensor, comprising a power supply module, a high-frequency circuit, an amplifying circuit, a reforming frequency dividing circuit and a processor; the high-frequency circuit, the amplifying circuit, the reforming frequency dividing circuit and the processor are sequentially connected in series; the high-frequency circuit comprises a capacitance probe. The high-frequency capacitance type soil humidity sensor can realize real-time measurement of the soil humidity and has high resolution ratio, strong suitability, low cost and wide application range.

Description

The high-frequency capacitive soil humidity sensor

Technical field

The utility model relates to the soil moisture measurement technical field, is specially the high-frequency capacitive soil humidity sensor.

Background technology

Intelligent irrigation control system is realized monitoring and the control to soil moisture in agricultural production, the realization of this system needs a kind of device with high measurement accuracy, high stability and high reliability and the real-time measured soil humidity of energy.At present, the measuring method of soil moisture has: oven drying method, NEUTRON METHOD, electric-resistivity method, capacitance method, TDR (Time Domain Reflectometry) method and SWR (standing wave ratio) method etc.Oven drying method is more traditional method, though its measuring accuracy than higher, time measuring period is long, the incompatibility real-time is measured, and can't be used for real-time irrigation.NEUTRON METHOD is to utilize hydrogen atom that the absorption of the ray of neutron source emission is come moisture in the measured soil, and is real-time, but neutron ray can damage the environment and the mankind.Electric-resistivity method and capacitance method are to utilize the dielectric property of soil, the water cut of indirect measured soil, and measuring speed is fast, but its shortcoming is relatively poor to the adaptability of soil, in order to measure more accurate soil water content, need set up calibration curve for every kind of soil.TDR method measured soil moisture is quick, the precision height, but its prices are rather stiff, be unfavorable for promoting on a large scale.The scope that the SWR method is used now is more extensive, but its multiple-pin type structure is unfavorable for inserting soil, and is yielding, perishable, can bring error to measurement.

The utility model content

The purpose of this utility model is at deficiency of the prior art, and a kind of high-frequency capacitive soil humidity sensor of measured soil moisture in real time is provided.

The utility model is achieved through the following technical solutions:

A kind of high-frequency capacitive soil humidity sensor comprises power module, high-frequency circuit, amplifying circuit, plastic sub-frequency circuit and processor; High-frequency circuit, amplifying circuit, plastic sub-frequency circuit and processor are connected successively; High-frequency circuit comprises capacitance probe Cp.

Wherein, high-frequency circuit, amplifying circuit, plastic sub-frequency circuit, processor are connected with power module respectively.

High-frequency circuit can be the LC oscillatory circuit, and before capacitance probe Cp inserted the LC oscillatory circuit, the oscillation frequency of LC oscillatory circuit was 120MHz.After capacitance probe inserted the LC oscillatory circuit, the oscillation frequency of LC oscillatory circuit was 80MHz～120MHz.Capacitance probe Cp can for needle-like, tabular and cylindric in a kind of.

Power module can comprise the integrated chip LM317 and the integrated chip AS1117 of series connection.

The LC oscillatory circuit can comprise triode Q1, resistance R 1, resistance R 2, resistance R 3, resistance R 4, capacitor C 1, capacitor C 2, capacitor C 3, capacitor C 4, inductance L 1 and capacitance probe Cp.

Amplifying circuit can comprise the two-stage amplifying circuit, wherein first order amplifying circuit can comprise metal oxide semiconductor field effect tube Q2, resistance R 5, resistance R 6, resistance R 7, diode D1, diode D2 and capacitor C 6, second level amplifying circuit can comprise triode Q3, resistance R 8, resistance R 9, resistance R 10, resistance R 11, and capacitor C 7, capacitor C 8.

Plastic sub-frequency circuit can comprise integrated chip SN74AHCT14 and integrated chip SN74F161.Processor can be the C8051F930 single-chip microcomputer.

Technique scheme has following advantage:

1. the utility model adopts the high frequency capacitance measuring technique, by the measuring-signal frequency, has avoided distorted signals, has guaranteed the accuracy of measuring.

2. capacitance probe of the present utility model can enlarge its usable range for needle-like, tabular or cylindric.

3. the utility model adopts high-performance, high-precision singlechip technology, finishes the computing of frequency signal, has guaranteed moisture data computing and measuring accuracy.

Description of drawings

Fig. 1 is the system architecture synoptic diagram of the soil humidity sensor of the utility model embodiment;

Fig. 2 is the schematic diagram of medium-high frequency circuit embodiment illustrated in fig. 1;

Fig. 3 is the schematic diagram of middle amplifying circuit embodiment illustrated in fig. 1;

Fig. 4 is the schematic diagram of middle power module embodiment illustrated in fig. 1;

Fig. 5 is the schematic diagram of middle plastic sub-frequency circuit embodiment illustrated in fig. 1;

Fig. 6 is the schematic diagram of middle processor embodiment illustrated in fig. 1.

Embodiment

Below in conjunction with drawings and Examples, embodiment of the present utility model is described in further detail.Following examples are used to illustrate the utility model, but are not used for limiting protection domain of the present utility model.

According to the system architecture synoptic diagram of the high-frequency capacitive soil humidity sensor of the utility model embodiment as shown in Figure 1.This high-frequency capacitive soil humidity sensor comprises: power module 101, and the high-frequency circuit 102 that is connected with power module 101 respectively, amplifying circuit 103, plastic sub-frequency circuit 104 and processor 105; High-frequency circuit 102, amplifying circuit 103, plastic sub-frequency circuit 104 and processor 105 are connected successively.

Wherein, the circuit theory diagrams of high-frequency circuit 102 are the LC oscillatory circuit as shown in Figure 2, by the triode Q1 of 2N2222A model, resistance R 1, R2, R3 and R4, capacitor C 1, C2, C3, C4, inductance L 1 and capacitance probe Cp form, Cp is a capacitance probe, for example is needle-like.Resistance R 1, R2, R3 and R4 provide suitable quiescent point for the LC oscillatory circuit; Capacitor C 2 and C3 determine the positive feedback coefficient of LC oscillatory circuit, and the ratio range of positive feedback coefficient can be 1/2～1/8; C1 is a coupling capacitance; Inductance L 1 and capacitor C 4 guarantee that oscillation frequency is 120MHz before capacitance probe Cp inserts the LC oscillatory circuit.The frequency computation part formula of LC oscillatory circuit is as follows:

$f=\frac{1}{2\mathrm{\π}\sqrt{\mathrm{LC}}}---\left(1\right)$

Wherein, L=L1, when Cp did not have place in circuit, the electric capacity in the LC oscillatory circuit was

Because capacitor C 2 is far longer than the appearance value of capacitor C 4, capacitor C 3 is far longer than the appearance value of capacitor C 4, so capacitor C 2, C3 can ignore to the influence of oscillation frequency.After capacitance probe Cp inserted the LC oscillatory circuit, the electric capacity in the LC oscillatory circuit was C=C4+Cp, and by formula (1) as can be known, this moment, the oscillation frequency of LC oscillatory circuit reduced, and was 80MHz～120MHz.

Experiment shows that when oscillation frequency surpassed 30MHz, oscillation frequency mainly was subjected to the influence of soil water content, and be subjected to the influence of soil salt very little, when frequency surpassed 100MHz, soil moisture was subjected to the influence of soil type also smaller, so the oscillation frequency of this circuit design is 120MHz.What of soil moisture content can cause the variation of soil dielectric constant, and then influence the variation of capacitance probe Cp, and the variation of capacitor C p can cause the variation of oscillation frequency again.Therefore, can come the moisture of measured soil by the oscillation frequency of metering circuit.

The schematic diagram of amplifying circuit as shown in Figure 3, the two-stage amplifying circuit that comprises series connection, first order amplifying circuit comprises MOSFET (metal oxide semiconductor field effect tube) Q2 (its model for example is 2SK241), resistance R 5, R6, R7, diode D1, diode D2 and capacitor C 6.Resistance R 5, R6 and R7 provide quiescent point for amplifying circuit, and diode D1, D2 provide temperature compensation for amplifying circuit, and capacitor C 6 strobes.Second level amplifying circuit comprises triode Q3 (its model for example for 2SC2570), resistance R 8, R9, R10, R11, and capacitor C 7, C8.Resistance R 8, R9, R10, R11 make it be operated in linear amplification region for Q3 provides suitable quiescent point, and capacitor C 7, C8 play the stopping direct current effect.By the two-stage amplifying circuit, the high frequency small-signal is amplified, so that frequency signal is carried out shaping and frequency division at plastic sub-frequency circuit.

The schematic diagram of power module as shown in Figure 4, power module adopts integrated chip LM317 and AS1117 to form, its effect is to provide electric energy for whole sensor.

The schematic diagram of plastic sub-frequency circuit comprises high speed integrated chip SN74AHCT14 and SN74F161 as shown in Figure 5.Chip SN74AHCT14 is used for frequency signal is carried out shaping, and chip SN74F161 is used for frequency signal is carried out frequency division.

The schematic diagram of processor is the C8051F930 single-chip microcomputer as shown in Figure 6.Its effect is that the frequency signal behind the frequency division is gathered and handled, then output.

The annexation of system embodiment illustrated in fig. 1 for example is: extremely shown in Figure 6 as Fig. 2, integrated chip LM317 output+5V voltage in the power module, should+5V voltage is input to the input end of chip AS1117 by voltage stabilizing diode D6, and link to each other with SN74F161 Vcc pin separately with integrated chip SN74AHCT14 in the plastic sub-frequency circuit; Integrated chip AS1117 output+3.3V voltage in the power module, should+the 3.3V voltage pin links to each other with the VDD/DC+ pin of processor; Vcc pin in high-frequency circuit and the amplifying circuit can import+5V or+3.3V, if+5V then links to each other with the output pin of integrated chip LM317 in the power module, if+3.3V then links to each other with the output pin of integrated chip AS1117 in the power module.

Need to prove that the capacitance probe in the foregoing description also can adopt other shapes, for example tabular or cylindric.

The principle of work of present embodiment is: when capacitance probe inserts in the soil, soil serves as the dielectric between the two-plate of capacitance probe, the change of soil moisture can make the dielectric constant between the two-plate change, and then make the dielectric of capacitance probe change, and then the appearance value of capacitance probe is changed; And capacitance probe is as the part of high-frequency circuit, and the variation of capacitance probe appearance value can change the oscillation frequency of high-frequency circuit.High-frequency circuit sends to amplifying circuit with frequency signal and amplifies, carry out being converted to behind shaping and the frequency division frequency signal that can be gathered by processor through plastic sub-frequency circuit then, then, processor is handled output to frequency signal, has so just measured the content of soil moisture indirectly by the variation of survey frequency signal.

As can be seen from the above embodiments, embodiment of the present utility model is by adopting the high frequency capacitance measuring technique, by measuring the moisture that soil has been measured in variation that appearance value by capacitance probe changes caused oscillation frequency indirectly, and this sensor resolution height, adaptability is strong, cost is low, applied range.

The above only is a preferred implementation of the present utility model; should be understood that; for those skilled in the art; under the prerequisite that does not break away from the utility model know-why; can also make some improvement and modification, these improve and modification also should be considered as protection domain of the present utility model.

Claims (8)

1. a high-frequency capacitive soil humidity sensor is characterized in that, comprises power module, high-frequency circuit, amplifying circuit, plastic sub-frequency circuit and processor; Described high-frequency circuit, described amplifying circuit, described plastic sub-frequency circuit and described processor are connected successively; Described high-frequency circuit comprises capacitance probe.

2. high-frequency capacitive soil humidity sensor as claimed in claim 1 is characterized in that, described high-frequency circuit, described amplifying circuit, described plastic sub-frequency circuit, described processor are connected with power module respectively.

3. high-frequency capacitive soil humidity sensor as claimed in claim 1 is characterized in that, described high-frequency circuit is the LC oscillatory circuit, and before described capacitance probe inserted described LC oscillatory circuit, the oscillation frequency of described LC oscillatory circuit was 120MHz.

4. high-frequency capacitive soil humidity sensor as claimed in claim 3 is characterized in that, after described capacitance probe inserted described LC oscillatory circuit, the oscillation frequency of described LC oscillatory circuit was 80MHz～120MHz.

5. as each described high-frequency capacitive soil humidity sensor of claim 1 to 4, it is characterized in that, described capacitance probe be needle-like, tabular and cylindric in a kind of.

6. as each described high-frequency capacitive soil humidity sensor of claim 1 to 4, it is characterized in that described power module comprises integrated chip LM317 and integrated chip AS1117.

7. as claim 3 or 4 described high-frequency capacitive soil humidity sensors, it is characterized in that described LC oscillatory circuit comprises triode Q1, resistance R 1, resistance R 2, resistance R 3, resistance R 4, capacitor C 1, capacitor C 2, capacitor C 3, capacitor C 4, inductance L 1 and described capacitance probe.

8. as each described high-frequency capacitive soil humidity sensor of claim 1 to 4, it is characterized in that, described amplifying circuit comprises the two-stage amplifying circuit, wherein, first order amplifying circuit comprises metal oxide semiconductor field effect tube Q2, resistance R 5, resistance R 6, resistance R 7, diode D1, diode D2 and capacitor C 6, second level amplifying circuit comprises three utmost points

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