Title of Invention

"CONTINUOS SOIL MOISTURE RECORIDER"

Abstract A continuous soil moisture recorder comprising an U-tube manometer (1) wherein a nichrome resistance wire (4) is placed inside one of the limb (2) and an insulated copper wire (9) is placed in the other limb (3) of the said manometer which is filled with mercury (6) to a desired height, the fist limb (2) is connected with a tensiometer by a flexible reinforced P.V.C. pipe (5),both the ends of the resistance wire are connected with insulated wires, said two insulated wires coming out of the manometer are connected to an amplifying circuit (8) for interfacing with the clock driven data logger.
Full Text This invention relates to a continuous soil moisture recorder .
There is major current concern in the effective conservation and protection of water, this interest is likely to increase with attention focused on the irrigated agriculture. Soil water monitoring is an important aspect in scheduling of irrigation and modelling studies deal with estimation of evapotranspirationt losses to ground water and soil moisture distribution from a point source/line source emission devices under varied soil conditions. It is desired to develop an instrument, which could monitor and record the temporal distribution of the soil moisture for above purposes.
The various methods of monitoring soil moistue monitoring are either very sophisticated using digital computers or are manual. Most common methods to monitor soil moisture are Gravimetric method. Times Domain Refleetrometry (T.D.R), Neutron probe, Resistance blocks and tensiometers. The Gravimetric method is manual. In manual operation it is very difficult to control irrigation at the pre-determined value of soil moisture tension. This results in either over or under irrigation, which adversely affects the crop yield. Time Domain Reflectrometry and Neutron probe give accurate- results but are very costly and require technical know-how for their operation, whereas resistance blocks give distorted readings in case the salt content of the soil or irrigation water. Making use of soil water suction, as the
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indicator for recording soil moisture is the most economic and reliable method. However, above devices not have continuous monitoring arrangement. Keeping this in view a continuous soil moisture recorder has been developed.
The object of the invention is that the instrument can operate up to a maximum soil moisture tension of 0.65 atmosphere.
Another object of the invention is that the circuit used in the instrument has provision to magnify/reduce least count and
To set any initial observation of soil moisture on chart of recorder an adjustment knob has been provided on the panel board of the instrument.
According to the present invention there is provided the continuous soil moisture recorder comprising an U-tube manometer wherein a no-chrome"1 resistance wire is placed inside one of the limb and an insulated copper wire is placed in the other limb of the said manometer which is filled with mercury to a desired height, the first limb is connected with a tensiometer by a flexible reinfoced P.V.C. pipe both the ends of the resistance wire are connected with insulated wires, said two insulated wires coming out of the manometer are connected to an amplifying circuit for interfacing with the clock driven data logger.
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The nature of the invention, its object and further advantages residing in the same will be apparent from the following description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawings.
Fig. 1 shows the details of modified manometer Fig. 2 shows the details of the sensor assembly Fig. 3 shows the calibration curve of continuous soil moisture recorder
Fig. 4 Instrument assembly showing the level of mercury for saturated soil and position of sensors.
The movement of mercury in the modified manometer tube caused by change in soil moisture tension, is recorded in terms of change in voltage across the resistance wire. The effective resistance of the selected resistance wire depends on the length of wire above mercury column, given by
R= 6xL/A (1)
R1 - Effective Resistance (ohms) 6 = Resistivity of wire (ohm-cm)
L - Length of resistance wire (cm)
2) A - Area of cross section of wire (cm
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In the above equation, the values of CT and A arc constant and the value of R changes as the L ( the total effective length of resistance wire) changes which in tun depends on the height of the mercury colunm. The voltage across wire can be explained as
Vout= RlVin/(Rl + M (2)
Resistance R,, has constant value and R. is the effective resistance offered by resistance wire. V is the input voltage across R. and £„ placed in series and V is the output voltage across R..
The output voltage V is then amplified by Op-Amp I.C. used in the developed circuit for interfacing with the data logger.
MATERIAL USED
Tensiometer, fiber reinforced polyvinyl chloride flexible tube, modified manometer, 70 cm long resistance wire of 24 ohm resistance, mercury, +12 volt DC power supply unit and clock driven analog type data logger ( 220 volt, 50Hz A.C, power supply) .
An I.C. chip, one transistor, five resistances, two potentiometers and two capacitors for fabricating electronic circuit.


FABRICATION
The mchrome resistance wire (A) is placed inside the one of the limb (2) of the U-tube manometer (1). This limb (2) of the manometer is connected with the tensiometer not shown by flexible reinforced P.V.C. pipe (5).Insulated copper wire (9) is placed in the other limb (3) of the U-tube manometer (1). Both the ends of resistance wire are connected with insulated wires. The mercury (6) is filled in the manometer (1) tube to a desired height. A hole (7) was pricked in the reinforced P.V.C. pipe (5) connected to the tensiometer to take out the insulated wire. All the connections were sealed with adhesive (Fig. 2). Two insulated wires coming out of the manometer are connected to the developed amplifying circuit (8) for interfacing with the clock driven data logger. The circuit has provision to start reading at any initial value of mercury column and also to vary the amplification factor for desired sensitivity.
CALIBRATION
Height of mercury column was varied by creating vacuum with the help of injection syringe. Resistance of wire, amplified voltage and reading on the data logger were noted for corresponding height of mercury column. The experiment was repeated thrice with a pair reading for the same position of mercury column i.e. one for rising of mercury column and another
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for falling of mercury column in the manometer. The calibration curve between height of mercury column and reading on the data logger are shown in the Fig. 3.
TESTING OF CONTINUOUS SOIL MOISTURE RECORDER
The testing of developed soil moisture recorder was done in the laboratory condition. A representative soil sample of the field was sieved and kept in a testing pot. The soil was fully saturated with water. The tensiometer was placed in saturated soil vertically at desired depth and connected to manometer using a reinforced transparent P.V.C. pipe. The soil was allowed to dry. Rise in mercuy level due to suction in the tensiometer with time was recorded by the recorder. The data logger recorded the observed changes in the soil moisture tension with time. The maximum soil moisture tension of 65 kPa could be observed through tensiometer. The soil was again moistened with the help of 2 liter per hour dripper. Drop in the mercury level of manometer due to decrease in the suction with time was also recorded with the help of soil moisture recorder. The instrument was tested for drying and wetting phase of soil several times and it is found working satisfactory. The developed instrument can be used successfully for continuous soil moisture recording up to 65 kPa.soil moisture tension.
The invention described hereinabove is in relation to non-limiting embodiments as defined by the accompanying claims.
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WE CLAIM:
1. A continuous.soil.moisture recorder with a U-tube
characterized in that,said manomecer compress

manometer (1) a nichrome. resistance wire (4) placed inside one of the limb (2) and an insulated copper wire (9) is placed in the other limb (3) of the said manometer which is filled with mercury (6) to a desired height, the first limb (2) is connected with a tensiometer by a flexible reinforced P.V.C. pipe (5), both the ends of the resistance wire are connected with insulated wires, said two insulated wires coming out of the manometer are connected to an amplifying circuit (8) for interfacing with the clock driven data logger.
2. A continuous soil moisture recorder as claimed in claim
1 wherein a hole has been provided in the reinforced PVC pipe
(5) connected to said tensiometer to take out the insulated
wire.
3. A continuous soil moisture recorder as claimed in claim
1 wherein the resistance wire-paced inside the manometer is
70 cm long of 24 ohms resistance.
4. A continuous soil moisture recorder as claimed in claim
1 wherein said clock driven analog type data logger operates
in 220V, SOHz AC, power supply.

5. A continuous soil moisture recorder as claimed in claim 1 wherein said modified manometer with 12V power supply and data logger is provided with an electronic circuit comprising an I.C. chip, one transistor , five resistors, two potentiometers and two capacitors.
A continuous soil moisture recorder comprising an U-tube manometer (1) wherein a nichrome resistance wire (4) is placed inside one of the limb (2) and an insulated copper wire (9) is placed in the other limb (3) of the said manometer which is filled with mercury (6) to a desired height, the fist limb (2) is connected with a tensiometer by a flexible reinforced P.V.C. pipe (5),both the ends of the resistance wire are connected with insulated wires, said two insulated wires coming out of the manometer are connected to an amplifying circuit (8) for interfacing with the clock driven data logger.



Documents:


Patent Number 201951
Indian Patent Application Number 07/CAL/1999
PG Journal Number 08/2007
Publication Date 23-Feb-2007
Grant Date 23-Feb-2007
Date of Filing 04-Jan-1999
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY
Applicant Address KHARAGPUR 721 302,
Inventors:
# Inventor's Name Inventor's Address
1 AJAY JOSHI DEPT. AGRIL & ENGG, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR 721 302,
2 K.N. TIWARI DEPT. AGRIL & ENGG, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR 721 302,
3 SWAPAN BANERJEE DEPARTMENT OF ELECTRICAL COMMUNICATION, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR 721 302,
PCT International Classification Number G 11B 3/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA