CN1504745A

CN1504745A - Capacitive pulse digital three-port soil humidity transducer not influenced by impurity

Info

Publication number: CN1504745A
Application number: CNA021537569A
Authority: CN
Inventors: 王桂芬
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-12-04
Filing date: 2002-12-04
Publication date: 2004-06-16

Abstract

A condenser type impulse digital three end type soil (or powder articles) moisture (water content) transducer not influenced by impurity, wherein a computer impulse digital technique is utilized to measure the moisture (water content) value in soil or powdered material, the conductive metallic ions and impurity in soil are seen as a fixed constant, so the sensor output value is only related to the moisture (water content) therein, its transducer is a three-end type. The transducer has simple structure with no need of computer interface, it possesses strong anti-interference capability which facilitates remote transmission.

Description

Be not subjected to the capacitive pulse digit trifocal soil humidity sensor of impurity effect

Technical field: the invention belongs in the electronic information technical field in order to the sensor class of Information Monitoring, it is the measuring sensor of a kind of soil (comprising flour) humidity (water cut), and soil humidity sensor has resistor-type, conductivity type, capacitor type etc.This sensor adopts capacitance probe, so belong to capacitive based.Transmitter in the sensor has analog electrical pressure type and pulse digit formula multiple, and the transmitter in this sensor belongs to the pulse digit formula.It can be made into the portable type handheld instrument, also can be made into the desk-top instrument that multimetering follows survey.

Background technology: the method for present soil humidity measuring has multiple, as negative pressure method, conductance method, electric-resistivity method, microwave method, three point measurement methods, local space psychrometric method etc.Their parts that all comes with some shortcomings, though as the negative pressure method can only be with range estimation resistance, electricity is led and the available electrical measurement of microwave method, they can not get rid of the interference effect that metallic ion rose in the soil.And the electrical quantity of these metallic ions and impurity is difficult to distinguish mutually with the variation of humidity.Therefore precision is not high; Three point measurement method calculation of complex, the local space rule is different and unstable being affected because of the saturation value of slaine in the soil, so it is different with the principle of measurement humidity in the air to measure humidity in soil, it must get rid of the influence of metal impurities in the soil (or powder), and capacity type soil humidity sensor designs for this reason.

Summary of the invention: task first of the present invention must be got rid of effects of Metallic Impurities in the soil; Second must simple to operate, with low cost, good stability.Strong antijamming capability is arranged and be convenient to performance such as long-distance transmissions, sell the weak point of soil humidity sensor to overcome existing market.In order to realize first task, the present invention adopts the sensitive element of capacitance type sensor probe as humidity in the soil (water cut).Because capacitor is made up of two metal sheets.Capacitor volume not only with the size and the distance dependent of two metal sheets, and relevant with the specific inductive capacity of contained material in the two metal sheets.In soil, generally contain slaine, organic impurities and moisture, under certain concrete environment, the specific inductive capacity of slaine and organic impurities is more changeless, and the specific inductive capacity of the humidity in the soil (moisture) is because of the different variations that do not stopping with wind speed of humidity in water injection rate and the extraneous weather, thereby influence the variation of capacitance, the so just variation that can find out humidity the soil (water cut) from the changes in capacitance value.Adopt the pulse digit generator as transmitter for the task of finishing second raising performance that reduces cost, make it directly to export numerical information, thereby can improve antijamming capability and be convenient to long-distance transmissions.Specific embodiments is described below:

The responsive part of the humidity (water cut) of condenser type pulse digit trifocal soil moisture (water cut) sensor is made up of two metallic conduction sheets, one end of two metal sheets is cemented by the insulating material that does not absorb water, add a macromolecular material garden tubular type sheath, making the distance between two is a steady state value, make it not be subjected to displacement and be out of shape, two metal sheets makes it to have good water isolating being coated with ceramic glaze and through high temperature sintering curing after cleaning.Two metal sheets is a rectangle, has arc obtuse angle, garden, sheet metal on-fixed end can insert soil down, and establishing the area that inserts the soil part is A, and the distance between two metal sheets is d, and this just constitutes a metal capacitor, and profile as shown in Figure 1.Its capacitance C can be represented by the formula:

C＝(∑o*∑x*A)/d (1)

∑ o represents the specific inductive capacity of capacitor in the air in the formula; ∑ x represents the specific inductive capacity of capacitor in the tested soil.Can be divided into the specific inductive capacity of general material and the specific inductive capacity of water cut (humidity) in ∑ x specific inductive capacity again, the former represents that with ∑ m the latter represents that with ∑ w (1) formula can be rewritten as so

C＝(∑o*∑m*∑w*A)/d (2)

In actual applications, in certain concrete environment, ∑ o, ∑ m in the formula,, A, d etc. are fixed values, its integrated value can be regarded a constant K o as

Make Ko=(∑ o* ∑ m*A)/d

So (2) formula can be rewritten as:

C＝Ko∑w (3)

Therefore can think that the variation of electric capacity can represent the variation of soil moisture (water cut), this capacitance be placed a resistance-capacitance oscillator loop, as shown in Figure 2.Its output frequency value f can be represented by the formula

f＝1/(K*R*C) (4)

K is a constant in the formula, and R is the resistance value of oscillation circuit, and C is the capacitance of capacitive humidity sensor.If get recurrence interval T that just can this oscillator reciprocal

T＝1/f

So T=K*R*C (5)

K, R are fixed value order: Kc=K*R

T=Kc*C (6) then

Therefore the output recurrence interval of available oscillator is represented humidity (water cut) value in the soil.With the transmitter that resistance-capacitance oscillator is formed, preceding usefulness two lines link with the capacitance sensing type probe, afterwards link with three lines and computing machine or instrument, and its block scheme as shown in Figure 3.

Consider the content of soil difference in all parts of the country, as the NORTHWEST CHINA area is loess zone, southern area is the laterite area, the Northeast is a blackland, the composition and the content of various places metallic ion have nothing in common with each other, thereby the specific inductive capacity difference of various places dry soil, so just be difficult to formulate the unified soil moisture standard in the whole nation, for a clear and definite and stable numerical value is arranged, specific inductive capacity with capacitor probe in the air when this sensor dispatches from the factory is an initial value, with dielectric constant values in 1% sodium chloride (NaCl) salt solution as two calibration points, being set in the air sensor output recurrence interval is 500us, (quite frequency values is 2000Hz) sensor output cycle in 1%NaCL solution is 1000us (quite frequency is 1000Hz).The user can choose local typical representational soil as sample when practical application.For example: select 1000 grams dry soil to be measured to remove that the hard thing of stone is broken to be placed in the container, this sensor insertion is recorded its output recurrence interval width, add 10 grams then respectively, 20 grams are until the water of saturation value, and measure separately recurrence interval, in order to reduce measuring error, can survey and get its mean value standby (if must get its inverse as display instrument) for several times with frequency meter.

Compared with prior art advantage that is had or good effect after this capacitive pulse digit trifocal soil moisture (water cut) sensor is made, are compared with traditional negative pressure method tensiometer with range estimation, and it is an electronic digital type; Compare with resistance-type, conductance type, all kinds of electronic type tensiometer of microwave method, it is not subjected to the interference of impurity such as metallic ion in the soil; Compare with the soil humidity sensor that the middle formation local space of placing into the soil is surveyed its rh value, it is not subjected to the different influence of slaine saturation value in the environment; Compare with the three point method tensiometer, it does not need complicated calculating, directly sense data.In general; This sensor also has more following unique advantages:

1), the major advantage of this sensor is to adopt the capacitive pick-up probe, can make a distinction the humidity in the soil (water cut) and slaine and other impurity, thereby have good humidity measurement precision.

2) sensor has only three extension lines, and is simple to operate, and digital direct-reading is also directly corresponding with tested humidity (water cut), as long as good the instruments and outfit of back, peasant masses and workman that general culture is lower also can manipulate.

3) this sensor is pulse digit output, in whole conversion process of energy, these links of amplification, shaping, V/I, I/V and analog to digital conversion without traditional analog voltage amount, it do not need any external device can with computing machine or the work of digital instrument direct interface, make information age automatic measuring and controlling and data storage become simple.It also has strong antijamming capability except that with low cost, and is convenient to long-distance transmissions.

4) probe of this sensor is made up of high-quality ceramic glaze sheet metal, has the anti-outlet capacity of good protection against the tide, thereby has good measuring accuracy and high stability.

5) this sensor make only indicate when dispatching from the factory in the air and 1% common salt salt solution in time (or frequency) of 2, dry soil during actual use the and the digital value in the saturation water choose representational soil by user oneself and water quality is determined, so just can avoid in all parts of the country, thereby usability is widely arranged because of the different errors of soil property with fork-like farm tool used in ancient China with water quality.

Brief Description Of Drawings

Fig. 1 is a capacitive soil moisture sensing probe profile synoptic diagram

(a) front elevation (b) side view

1: lead 2: sark 3: sheet metal

Fig. 2 is pulse digital signal generator circuit figure

1 operational amplifier, 3 soil capacitors

The output of 2 oscillation resistances, 4 transmitters

Fig. 3 is a trifocal soil humidity sensor wiring diagram

1: transmitter 2: the soil moisture sensing probe

3: power lead 4: signal output

5: ground wire

Implement mode of the present invention specific embodiments of the present invention and can divide two classes substantially, a class is portable, and capacitance probe and transmitter are connected, and transmitter is contained among the pipe of garden, and the garden pipe can be for the hand-held usefulness of operating personnel.Before each operation, remove stone and other hard things in the tested soil earlier, the rectangle condenser plate probe with sensor inserts in the soil (or dusty material) of certain depth again.This sensor also must be used with general digital frequency meter and time measuring instrument, so that can on-the-spot directly reading numerical values.Another kind of embodiment is that capacitive sensing probe and transmitter are separated, and the centre connects with two-wire.Sensing probe is embedded in the soil, and transmitter is placed on desktop or the shelf to connect with computing machine or desk-top instrument, to carry out the detection that follows back of multiple spot soil moisture.

Sensor has been applied in warmhouse booth, flower planting, water conservancy irrigation system and concrete and has stirred many occasions, receives very good effect.

Claims

1, a kind of soil humidity sensor is characterised in that it is a kind of capacitor type trifocal soil humidity sensor that is not subjected to the pulse digit output that impurity in the soil disturbs, and it has strong antijamming capability, be convenient to long-distance transmissions and be easy to and computer interface.This sensor comprises soil moisture (water cut) sensing probe and a digital transmitter, and both can fit together becomes the hand-held soil humidity sensor, also can both separately connect ingredient with the desk-top instrument that becomes multimetering with lead.

2, soil humidity sensor as claimed in claim 1, wherein used soil moisture sensing probe is characterised in that by the capacitor of being made up of two rectangle sheet metals as detection probe, the surface of two metal sheets scribbles the ceramic glaze film of one deck through high temperature sintering, and this film has and do not absorb water and nonconducting insulating property.Be separated with one section insulating material that does not absorb water between two metal sheets one end securely, so that the influence that the space length size between the two metal sheets is not changed by external force or environment temperature parameter, its thickness should be determined according to user's request.The sheet metal stiff end is added with the garden tubular overwrap that a usefulness macromolecular material is made outward, and the blended rubber stick is fixed, to guarantee capacitor two metal sheets and not deformation of distance thereof.The stiff end of the two metal sheets of capacitor has lead to draw to be connected with transmitter respectively.The other end mill of two metal sheets has the obtuse angle, to be convenient to insert soil.

3, soil humidity sensor as claimed in claim 1, wherein transmitter is characterised in that it is a pulse digit generator, detect the capacitance parameter ingredient of the capacitive character sensing probe of humidity as the pulse digit generator, so the output recurrence interval of transmitter (inverse of frequency) public tested humidity (water cut) is direct corresponding relation, that is to say that humidity is bigger in the soil, the cycle of output pulse is longer.Cycle as the output of sensor in dry air pulse is 500 μ s (quite repetition frequency 2000Hs), and the cycle of sensor output pulse is 1000 μ s (quite repetition frequency 1000Hs) in the salt 1% (NaCl) water.Sensor output do not need to take over again what device can with computing machine or frequency, time measuring instrument interface and cooperating.Transmitter has 5 extension lines, and wherein two link to each other with the soil moisture sensing probe, and three link to each other with main frame in addition: wherein one for power supply supply lines, one for ground wire, another root are output line, easy and simple to handle, so the title trifocal.