CN100392383C - Impedance type soil moisture sensor and making process thereof - Google Patents
Impedance type soil moisture sensor and making process thereof Download PDFInfo
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- CN100392383C CN100392383C CNB2005100413927A CN200510041392A CN100392383C CN 100392383 C CN100392383 C CN 100392383C CN B2005100413927 A CNB2005100413927 A CN B2005100413927A CN 200510041392 A CN200510041392 A CN 200510041392A CN 100392383 C CN100392383 C CN 100392383C
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Abstract
The present invention relates to an impedance type soil moisture sensor. Two electrodes are arranged in a resistance block. The impedance type soil moisture sensor is characterized in that the resistance block is composed of filling materials filled in a china clay head, wherein the filling materials are mixed according to the proportion of sandy loam and gesso from 3: 1.8 to 2.2, wherein the Sio 2 is the main part in the sandy loam, and artificial structure modifying agents are added. The present invention has the prioritization proposal that high polymer fixing agents are added to the filling materials, the china clay head is pasted with a PVC pipe, and a temperature sensor is arranged in the pipe to correct the conductance change caused by the temperature change. Polyacrylamide, the soil load of which is 0.1%, is used for the artificial structure modifying agents, and 1 gram per liter of polypropylene oxamide solution is used for high polymer used for fixing. The present invention also provides a making method of the new impedance type soil moisture sensor. The granule composition of the resistance block is changed by the present invention, and thereby, the resistance response curved line of the resistance block is changed at the time of different water suction force; the impedance type soil moisture sensor with wider moisture measuring range can be made.
Description
Technical field
The present invention relates to a kind of soil instrument, be specifically related to a kind of impedance type soil moisture sensor, and the manufacture craft of this impedance type soil moisture sensor.
Background technology
At present, farmland moisture condition observes and predicts the pressure resistance type soil moisture sensors that adopt in real time.It is on the basis of tensiometer, combines with the differential pressure type pressure transducer.This soil moisture sensor has higher mensuration precision and stability, is easy to demarcate, and price is medium.But in actual applications, have the following disadvantages: 1. its soil water suction measurement range is 0～85Kpa, instructs requirement though be fit to the irrigation of many crop high-yield cultivatings; But on arid area and drought-enduring plant, its dry end test specification is wide inadequately, and application is restricted.2. owing to need in sensor, add water, therefore, just be difficult to adopt for unattended survey station every certain hour.3. the face of land need be exposed in this sensor upper end, has increased trouble for management and protection.
Also having a kind of soil moisture sensor commonly used is to adopt the gypsum resistance bolck, and its traditional structure is: inside and outside two annulus of being made up of stainless steel cloth are respectively as two electrodes, and wrap up with gypsum and to make the plaster block moisture transducer.This soil moisture sensor, its relative merits are compared with the pressure resistance type soil moisture sensor, just in time are in complementary situation.The scope of this sensor test soil water suction is at 60～300Kpa.It can test relatively drier soil, and cost is lower, and convenient management is imbedded operations such as not needing to add later water in the soil.But can not accurately measure in 0～60Kpa soil water suction scope.Another problem is that the soil conductivity temperature influence is bigger.
The gypsum resistance bolck is little in the measured resistance value difference of 0～60Kpa water suction force scope, and the result is comparatively disorderly, has limited its application in farmland moisture condition observes and predicts.The reason that produces this phenomenon is a too homogeneous of used landplaster particle grade, and their grade concentrates on 30～150 microns, lacks each grade particles of＞150 microns and＜30 microns, almost do not have in the plaster block＞50 microns than coarse porosity.Because lack coarse porosity, the plaster block retentiveness is stronger, in the antecedent soil moisture process, to about the native water suction force 60Kpa, water cut does not almost have any variation in the gypsum resistance bolck from water saturation.That is to say that the water-filling situation has no change in the plaster block porous body.So that when measuring 0～60Kpa water suction force section, resistance value does not have marked change.If there is the macropore of some in the block, when water suction force increased, moisture was discharged from the macropore, and when electric current is flowed through these blocks, its tortuous degree will increase, and impedance increases.After suction reaches certain level (as behind＞the 60Kpa), block is just significantly discharged moisture, and its current impedance increases.Because the grade of gesso concentrates too much on silt-size, lack clay.Therefore, by the same token, when suction further increased, during as＞300Kpa, the relation curve slope was excessive between its resistance and suction, also influences widening of its dry end test specification.
Summary of the invention
The objective of the invention is to utilize suitable material and technology, the particle that changes resistance bolck is formed, and changes the electrical response curve of resistance bolck when different water suction force, so that produce novel impedance type soil moisture sensor hygrometric wider range, inexpensive.Simultaneously, the application also will provide the production method of this sensor.
The technical scheme of finishing the foregoing invention task is:
Impedance type soil moisture sensor, two electrodes place resistance bolck, it is characterized in that, and described resistance bolck is made of the inserts that is seated in the pot clay end, and the composition of this inserts is: to contain SiO
2Be that main sand loam mixes with 3: 1.8～2.2 ratio with gesso,, simultaneously, in this base-material, be added with artificial structure's modifying agent as base-material.
Above-described artificial structure's modifying agent can be selected from following high molecular polymer: the high molecular polymer of the soil particles of reuniting such as polyacrylamide (PAM), polyvinyl alcohol (PVA) or polyacrylonitrile.Wherein the polyvinyl alcohol (PVA) consumption is wanted big (account for dry ground and weigh 0.2%); And agglomeration can not last till that polyacrylonitrile (account for dry ground and weigh 0.15%) function was the same with PAM 3 years, but the monomer whose severe toxicity is noted gas defence when handling soil.Account for native 0.05～0.2% the polyacrylamide (PAM) that weighs so the application recommends to adopt, its optimal values is 0.1%.
Describedly " contain SiO
2Be main sand loam " composition be: sand grains: 90～91%, powder: 3～4%, clay: 6～7%.The application recommends following optimal proportion, sand grains: 90.07%, and powder: 3.22%, clay: 6.71%.
The specification of described pot clay end, can be with reference to following size: external diameter be 20mm, and long 70mm, internal diameter are 10mm.
Described " sand loam mixes with 3: 1.8～2.2 ratio with gesso ", the application recommends: sand loam mixes with the ratio that gesso adopted 3: 2.
The further improvement of such scheme can have following prioritization scheme:
1, for making sensor have certain intensity, be seated in the inserts in the pot clay end, also be added with fixing agent, described fixing agent is a high molecular polymer.
2, have pvc pipe in the pot clay end gluing, temperature sensor is installed in the pipe, in order to proofread and correct the variation of the electric conductivity value that causes because of temperature variation.
3, place two electrodes of resistance bolck to adopt two parallel stainless steel electrodes.
The high molecular polymer of described fixedly usefulness can adopt the high molecular polymer identical with artificial structure's modifying agent: high molecular polymers such as polyacrylamide (PAM), polyvinyl alcohol (PVA) or polyacrylonitrile, wherein, the polyacrylamide addition is 3～5 milliliters of the solution of concentration 0.9～1.1 grams per liter, the polyacrylonitrile addition is 3～5 milliliters of the solution of 1.4～1.6 grams per liters, and the polyvinyl alcohol (PVA) addition is 3～5 milliliters of the solution of 1.9～2.1 grams per liters.
The manufacture craft of impedance type soil moisture sensor of the present invention may further comprise the steps:
Sand loam is air-dry, and the levigate 1mm sieve of crossing mixes with 3: 2 weight ratio with gesso, constitutes the base-material of sensor inserts, and is standby;
Add in above-mentioned base-material with artificial structure's modifying agent aqueous solution, the ratio that base-material adds texture modifier is a per mille (potpourri: PAM=1000: 1).The amount that adds solution makes base-material be in the field capacity state.
Polyacrylamide is with after inserts fully mixes, air-dry, cross the 1mm sieve, constitute inserts (constitute of final resistance bolck);
Above-mentioned inserts is filled in the pot clay end, two parallel stainless steel electrodes are placed filler.
The top mouth of pot clay end is sealed with 704 silicon rubber and 1: 4 epoxy glue of epoxy resin, and go between at the electrode tip welding cable.
In prioritization scheme, also can increase respectively has following steps:
1, a segment length is glued on pot clay end for the 100mmPVC pipe, installation one precision is ± 0.3 ℃ a temperature sensor in pipe, in order to proofread and correct the variation of the electric conductivity value that causes because of temperature variation.
2, add packing material typing in the pot clay end for making, the malleable configuration state does not drip fixing agent to packing material, makes the structure of filling material further fixing.
Described fixing agent is a high molecular polymer: high molecular polymers such as polyacrylamide (PAM), polyvinyl alcohol (PVA) or polyacrylonitrile, wherein, the polyacrylamide addition is 3～5 milliliters of the solution of concentration 0.9～1.1 grams per liter, the polyacrylonitrile addition is 3～5 milliliters of the solution of 1.4～1.6 grams per liters, and the polyvinyl alcohol (PVA) addition is 3～5 milliliters of the solution of 1.9～2.1 grams per liters.The application recommends to adopt 4 milliliters of the polyacrylamide solutions of 1 grams per liter.
3, treat epoxy resin cure after, the sensor tentatively made immerses in the water, makes water saturation in the pot clay end, dries (or oven dry 24 hours in 80 ℃ of baking ovens, to dry).Aforesaid operations is three times repeatedly, finished product.
The performance of sensor
1. the test specification of sensor and precision:
After tested, the soil water suction test specification of novel impedance type soil moisture sensor obviously increases than former gypsum resistance bolck, reaches 5Kpa～10Mpa, and it measures precision is ± 3Kpa that it will be fit to all kinds of farmlands and crop is used.Fig. 2 is the calibration curve of two different impedance type soil moisture sensors, and as can be seen from Figure, soil water suction is in the scope of 5Kpa～10Mpa, and sensor resistance and soil water suction have good response relation, and the form of calibration curve is:
logR＝alogS+b
In the formula, R is for measuring the resistance value of gained; S is the soil water suction value; A, b are constant.
By demarcating 20 impedance type soil moisture sensors, the result shows: the R of all calibration curves
2All, can reach the demarcation necessary requirement greater than 0.98.
2. temperature is to the conductivity test correction for drift:
Because temperature directly influences the variation (output of sensor) of electric conductivity value, so, with a high-precision temperature sensor sensor output is proofreaied and correct.We have tested temperature sensor electrical have been led the influence of output, and draw calibration curve (Fig. 3), the R of this calibration curve
2=0.9953＞0.99, and the consistance of the temperature variant amplitude of each sensor is very good, by this calibration curve the electric conductivity value unification that the electric conductivity value conversion of sensor output becomes under 25 ℃ is compared, and demarcates.
Novel impedance type soil moisture sensor provided by the invention and manufacture craft thereof, the particle that has changed resistance bolck is formed, thereby changed the electrical response curve of resistance bolck when different water suction force, can produce novel impedance type soil moisture sensor hygrometric wider range, inexpensive.
Description of drawings
Fig. 1 is the impedance type soil moisture sensor synoptic diagram;
Fig. 2-1, Fig. 2-2 is the impedance type soil moisture sensor calibration curve;
Fig. 3 represents the relation of sensor output and temperature variation;
Fig. 4 is the result of sensor output repeatability.
Embodiment
Specifically, the composition of each several part and manufacture craft are as follows:
The material of sensor is formed:
Desirable resistance bolck should be a thickness distribution of pores porous body comparatively uniformly.Therefore, must select for use the material of the suitable collocation of thickness machinery particle to form resistance bolck.Through repetition test, we select a kind of SiO of containing for use
2Be main sand loam (sand grains: 90.07%, powder: 3.22%, clay: 6.71%) mix with 3: 2 ratio, make base-material making resistance bolck with this potpourri with gesso.Because the thickness many places of gesso are in the powder state, after sand loam mixed, its porous body of forming had hole composition uniformly.
For the further coarse porosity that increases＞300 microns, make resistance bolck when standing 5～10Kpa suction, have the responding ability of resistance change.We adopt the technology of adding artificial structure's modifying agent polyacrylamide (PAM) to make it reunionization, increase the ratio of coarse porosity.
Sensor production technology:
1., sand loam is air-dry, the levigate 1mm sieve of crossing is with the ratio mixing for standby use of gesso with 3: 2 (weight ratio).
2., with water: the ratio of polyacrylamide=100: 1, polymkeric substance is added in the hot distilled water, constantly heating, and agitated liquid is dissolved fully until polymkeric substance, cools off standby.
3., the ratio that soil of making and gesso potpourri add texture modifier is a per mille (potpourri: PAM=1000: 1).The solution amount that adds potpourri should make potpourri be in the field capacity state.Solution amount deficiency, texture modifier are difficult for giving full play to agglomeration; Excessive, puddling phenomenon easily takes place, be unfavorable for that also coarse porosity forms.Polyacrylamide is with after inserts fully mixes, air-dry, cross the 1mm sieve, obtain final resistance bolck constitute.
4., take by weighing 6.3 these potpourris of gram, divide 4 times and pack in the specific pot clay end with identical density, two parallel stainless steel electrodes are placed filler.(annotate: soil: gypsum is 3: 2 a potpourri, and physical strength is more much lower than pure gypsum.Potpourri behind the adding polymkeric substance can not pass through sinter molding.For making sensor have certain intensity, be 20mm with the potpourri external diameter of packing into, long 70mm, internal diameter are typing in the pot clay end of 10mm.)
5., add packing material typing in the pot clay end, malleable configuration state not drips the polyacrylamide solution of 10 grams per liters to packing material, makes the structure of filling material further fixing for making.
6., use the top mouth sealing of epoxy resin and silicon rubber epoxy glue (weight ratio 4: 1) with pot clay end.And go between at the electrode tip welding cable.
7., a segment length is glued on pot clay end for 100mmPVC pipe, a precision be installed be ± 0.3 ℃ temperature sensor in pipe, the variation of the electric conductivity value that causes because of temperature variation in order to correction.
8., treat epoxy resin cure after, the sensor tentatively made immerses in the water, makes water saturation in the pot clay end, dries (or oven dry 24 hours in 80 ℃ of baking ovens, to dry) again.Aforesaid operations is three times repeatedly, finished product.(see figure 1)
The performance of sensor
The test specification of sensor and precision:
After tested, the soil water suction test specification of novel impedance type soil moisture sensor obviously increases than former gypsum resistance bolck, reaches 5Kpa～10Mpa, and it measures precision is ± 3Kpa that it will be fit to all kinds of farmlands and crop is used.Fig. 2 is the calibration curve of two different impedance type soil moisture sensors, and as can be seen from Figure, soil water suction is in the scope of 5Kpa～10Mpa, and sensor resistance and soil water suction have good response relation, and the form of calibration curve is:
logR＝alogS+b
In the formula, R is for measuring the resistance value of gained; S is the soil water suction value; A, b are constant.
By demarcating 20 impedance type soil moisture sensors, the result shows: the R of all calibration curves
2All, can reach the demarcation necessary requirement greater than 0.98.
Temperature is to the conductivity test correction for drift:
Because temperature directly influences the variation (output of sensor) of electric conductivity value, so, with a high-precision temperature sensor sensor output is proofreaied and correct.We have tested temperature sensor electrical have been led the influence of output, and draw calibration curve (Fig. 3), the R of this calibration curve
2=0.9953＞0.99, and the consistance of the temperature variant amplitude of each sensor is very good, by this calibration curve the electric conductivity value unification that the electric conductivity value conversion of sensor output becomes under 25 ℃ is compared, and demarcates.
The temperature variant formula of sensor output conductance value is:
L
t＝(1+0.0245(T-25℃))L
25℃
In the formula, L
tThe electric conductivity value of soil moisture sensor output during for t ℃; L
25 ℃The electric conductivity value of soil moisture sensor output when being 25 ℃; T is the temperature of tested soil.
Among Fig. 3, L
t/ L
25 ℃Under same water regime, the soil conductivity value under t ℃ and the ratio of 25 ℃ of following soil conductivity values.
The sensor reappearance is measured:
Be the calibration curve reappearance problem that prevents to cause owing to the filler structural instability, we are by adding Polyacrylamide, and the method for carrying out repeatedly alternation of wetting and drying is stablized the structure of filler.Fig. 4 is the reperformance test of novel impedance type soil moisture sensor of our development.As seen from Figure 4, the result of twice repetition of sensor is gratifying.
Two, the application of sensor
1. the demarcation of sensor:
The demarcation of sensor can be carried out on the suction force plate instrument, records soil water suction--sensor electrical conductance relation curve.Also the soil moisture sensor of making can be imbedded in the tested original-state soil, and imbed mercury tensiometer and compare, carrying out by water saturation--the sensor water characteristic of dry run is demarcated, draw the response curve of the electric conductivity value (after the temperature correction) of soil water suction and soil moisture sensor output, i.e. calibration curve.Calibration curve is generally the log-linear relation of resistance and soil water suction, the coefficient R of demarcation
2＞0.98.In addition, can demarcate, record soil moisture content with gravimetric method--the conductivity relation curve.
2. sensor application
Calibrated sensor promptly can be applicable to the monitoring of soil moisture content.
1. before using, soil moisture sensor should soak more than 3 hours in water.
2. punch to predetermined depth with earth boring auger burying underground a little of choosing.At the bottom of the hole, pour about 5 milliliters of mud (sensor is contacted closely with soil) into, soil moisture sensor is inserted in the hole.Bar soil tamping on every side will be moulded.The flow of water probe depth of burying is with the distance calculation on pot clay end middle part to the face of land.
3. imbed tested soil after 12 hours, can carry out the sensor conductance measurement.Measure two interelectrode electric conductivity values with conductivity meter during mensuration, and according to measured temperature, be corrected to electric conductivity value under 25 ℃ with formula (1), and convert resistance value to, substitution calibration curve then can be obtained the soil water suction (or soil moisture content) of this moment.
The invention is not restricted to these disclosed embodiments, the present invention will cover the scope described in the patent claims, and the various distortion of claim scope and equivalence variation.
Claims (10)
1. impedance type soil moisture sensor, two electrodes place resistance bolck, it is characterized in that, and described resistance bolck is made of the inserts that is seated in the pot clay end, and the composition of this inserts is: to contain SiO
2Be that main sand loam mixes with 3: 1.8～2.2 ratio with gesso,, simultaneously, in this base-material, be added with artificial structure's modifying agent as base-material.
2. according to the described impedance type soil moisture sensor of claim 1, it is characterized in that, be seated in the inserts in the pot clay end that also be added with fixing agent, described fixing agent is a high molecular polymer.
3. according to claim 1 or 2 described impedance type soil moisture sensors, it is characterized in that, have pvc pipe, temperature sensor is installed in the pipe, in order to proofread and correct the variation of the electric conductivity value that causes because of temperature variation in the pot clay end gluing.
4. according to the described impedance type soil moisture sensor of claim 3, it is characterized in that,
Described artificial structure's modifying agent is selected from the high molecular polymer of the following soil particle of reuniting: polyacrylamide, polyvinyl alcohol (PVA) or polyacrylonitrile, and wherein the polyvinyl alcohol (PVA) consumption accounts for dry ground and weighs 0.2%; The polyacrylonitrile consumption accounts for dry ground and weighs 0.15%; It is heavy by 0.05～0.2% that the polyacrylamide consumption accounts for soil;
The high molecular polymer of the described soil particle of reuniting adopts the high molecular polymer identical with artificial structure's modifying agent: polyacrylamide, polyvinyl alcohol (PVA) or polyacrylonitrile, wherein, the polyacrylamide addition is 3～5 milliliters of the solution of concentration 0.9～1.1 grams per liter, the polyacrylonitrile addition is 3～5 milliliters of the solution of 1.4～1.6 grams per liters, and the polyvinyl alcohol (PVA) addition is 3～5 milliliters of the solution of 1.9～2.1 grams per liters;
Describedly " contain SiO
2Be main sand loam " composition be: sand grains: 90～91%, powder: 3～4%, clay: 6～7%.
5. according to the described impedance type soil moisture sensor of claim 4, it is characterized in that,
Contain SiO in the resistance bolck
2Be that master's the sand loam and the ratio of gesso adopted 3: 2;
Described artificial structure's modifying agent adopts soil to weigh 0.1% polyacrylamide;
The described high molecular polymer that can reunite soil particle adopts the polyacrylamide solution of 1 grams per liter;
Describedly " contain SiO
2Be main sand loam " composition be: sand grains: 90.07%, powder: 3.22%, clay: 6.71%;
The specification of described pot clay end: external diameter is 20mm, and long 70mm, internal diameter are 10mm.
6. according to claim 4 or 5 described impedance type soil moisture sensors, it is characterized in that, place two electrodes of resistance bolck to adopt two parallel stainless steel electrodes.
7. according to the manufacture craft of the described impedance type soil moisture sensor of claim 1, may further comprise the steps:
Sand loam is air-dry, and the levigate 1mm sieve of crossing mixes with 3: 2 weight ratio with gesso, constitutes the base-material of sensor inserts, and is standby;
Add artificial structure's modifying agent aqueous solution in above-mentioned base-material, the solution amount of its adding makes base-material be in the field capacity state;
Polyacrylamide is with after the base-material of inserts fully mixes, air-dry, cross the 1mm sieve, constitute inserts;
Above-mentioned inserts is filled in the pot clay end, two parallel stainless steel electrodes are placed filler;
The top mouth of pot clay end is sealed, and go between at the electrode tip welding cable.
8. according to the manufacture craft of the described impedance type soil moisture sensor of claim 7, it is characterized in that, also be provided with following steps: a segment length is glued on pot clay end for the 100mmPVC pipe, installation one precision is ± 0.3 ℃ a temperature sensor in pipe, in order to proofread and correct the variation of the electric conductivity value that causes because of temperature variation.
9. according to the manufacture craft of the described impedance type soil moisture sensor of claim 7, it is characterized in that, also be provided with following steps: drip fixing agent to packing material, make the structure of filling material further fixing,
Described fixing agent is a high molecular polymer: polyacrylamide, polyvinyl alcohol (PVA) or polyacrylonitrile, wherein, the polyacrylamide addition is 3～5 milliliters of the solution of concentration 0.9～1.1 grams per liter, the polyacrylonitrile addition is 3～5 milliliters of the solution of 1.4～1.6 grams per liters, and the polyvinyl alcohol (PVA) addition is 3～5 milliliters of the solution of 1.9～2.1 grams per liters.
10. according to the manufacture craft of claim 7 or 8 or 9 described impedance type soil moisture sensors, it is characterized in that, 4: 1 epoxy resin of weight ratio and silicon rubber epoxy glue are adopted in the sealing of potter's clay crown mouth, simultaneously, also be provided with following steps: after treating epoxy resin cure, the sensor of tentatively making immerses in the water, make water saturation in the pot clay end, dry, aforesaid operations is three times repeatedly again, finished product.
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| CN106841321A (en) * | 2017-02-15 | 2017-06-13 | 上海花小二科技有限公司 | The manufacture craft of resistor-type soil moisture sensor |
| CN107384422A (en) * | 2017-07-25 | 2017-11-24 | 安徽天知蓝农林科技有限公司 | A kind of fruit tree planting soil modifying agent |
| CN108802105A (en) * | 2018-03-08 | 2018-11-13 | 清华大学 | A kind of section type soil moisture content monitor being adapted to agricultural irrigation |
| WO2020077440A1 (en) * | 2018-10-19 | 2020-04-23 | Hortau Inc. | Porous medium parameter measurement device |
| CN110579512B (en) * | 2019-10-09 | 2024-02-20 | 清华大学 | Manufacturing and calibrating method of filter type soil moisture sensor |
| CN112042506A (en) * | 2020-05-27 | 2020-12-08 | 宁波大叶园林工业股份有限公司 | Soil humidity alarm with soil standard wetting box |
| CN114199955A (en) * | 2022-01-05 | 2022-03-18 | 南京审计大学 | Cylindrical honeycomb ceramic soft soil water content test probe device |
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| CN86202206U (en) * | 1986-04-19 | 1987-07-29 | 中国农业科学院农业气象研究室 | Resistance sensor for investigating moisture of soil |
| US5430384A (en) * | 1994-07-22 | 1995-07-04 | Onset Computer Corp. | Temperature compensated soil moisture sensor |
| JPH07244040A (en) * | 1994-03-07 | 1995-09-19 | Asia Kosoku Kk | Method and device for measuring soil moisture |
| CN2575668Y (en) * | 2002-11-01 | 2003-09-24 | 北京农业信息技术研究中心 | Multiside biological chip |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN86202206U (en) * | 1986-04-19 | 1987-07-29 | 中国农业科学院农业气象研究室 | Resistance sensor for investigating moisture of soil |
| JPH07244040A (en) * | 1994-03-07 | 1995-09-19 | Asia Kosoku Kk | Method and device for measuring soil moisture |
| US5430384A (en) * | 1994-07-22 | 1995-07-04 | Onset Computer Corp. | Temperature compensated soil moisture sensor |
| CN2575668Y (en) * | 2002-11-01 | 2003-09-24 | 北京农业信息技术研究中心 | Multiside biological chip |
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