PROJECT TITLE

DEVLOPMENT OF LOW COST TIME DOMAIN REFLECTOMETER SYSTEM FOR SOIL MOISTURE

MEASUREMENT

Bhushan N. Patil (ME Final YEAR)

(DIGITAL ELECTRONICS)

PRESENTED BY:-

S.S.B.T’s COET, Bambhori, Jalgaon

GUIDED BY:-

Dr. P. H. Zope(ASSISTANT PROFESSOR)

(E & TC DEPARTMENT)

CONTENTS

Aim Objectives and Necessity System Concept Literature Survey System Design Calibration Results And Discussion System Measurement And Analysis Comparative Analysis Advantages, Limitations and Remedy Applications Conclusion References

AIM

Basic aim of this project is to develop an fully Integrated Electronic System, to provide

low cost, highly accurate solution for soil moisture measurement

Fig. TDR measurement system

OBJECTIVES AND NECESSITY

OBJECTIVES : To reduce the cost of the previously developed system To design universal system to measure soil moisture with high accuracy To provide most reliable and universal solution for soil moisture measurement To design a system which can work even at higher frequency (in MHz range)

NEED OF SOIL MOISTURE MEASUREMENT : In agriculture & Plant science field to determine best time to Sow & plow the

field. Various physical & chemical properties of soil changes with amount of moisture

present in soil. To measure changes in infiltration, irrigation. To study ground water recharge & Evapo-transpiration. It is also important in the fields like Hydrology, Forestry, Agrology. To study & determine the parameters like soil profile, surface tension related

with civil & soil engineering.

SYSTEM CONCEPT WHAT IS TIME DOMAIN REFLECTOMETER ?

TDR is a very much popular concept related to the measurement of the frequency dependent characteristics such as electric & dielectric properties of various materials & substances.

PRINCIPLE OF OPERATION :Based on the principle of measurement of propagation time required by

EM wave for transmission and reflect back.

Ka = (c/v)2 = [(c × t)/(2 × L)]2 …………………….(i)

Here, c is the velocity of electromagnetic waves in a vacuum and L is the length of the transmission line present in the soil (in m or ft).

Fig Working principle of TDR system Graph-Typical waveforms

Fig. a) Equivalent electrical circuit model for the laboratory setup presented

Fig. b) Equivalent electrical circuit model for an optimized TDR system, the generator output impedance matches the line

impedance

EQUIVALENT ELECTRICAL CIRCUIT MODEL:

Fig. Soil Sensor Used for Moisture Measurement

LITERATURE SURVEY

Technique Principle used and Methodology Photograph

1. Gravimetric

Method(GM)

Depends on the weight of original sample and oven dried sample.1. Take Weight of the original sample (Wt)2. Apply oven drying at 105oC for 24 Hr & weight (Ws).3.

2.Neutron

Moderation(NM)

Depends on the amount collision between fast neutrons and Hydrogen atoms present in moisture1. Insert probe into access tube installed in soil. 2. Linear calibration between the count rate of slowed

neutrons gives the reading of % moisture content.

3.TDR

Depends on the propagation time required by EM wave to transmit and reflect back from sensor transmission waveguide1. Insert probe into access tube & transmit EM wave. 2. The propagation time required for transmit & reflect

back gives the % moisture content depending on the dielectric constant

REVIEW OF DIFFERENT SOIL MOISTURE MEASUREMENT TECHNIQUES:

Technique Principle used and Methodology Photograph

4.FDR

It is a dielectric method obtaining moisture content by observing response at different frequencies1. Probe is introduced into soil 2. After applying electric field gives reading due to capacitance

effect

5.ADR

Depends on the change in amplitude of transmitted wave after reflecting from the section of different impedance depending on content of moisture1. EM wave is generated & transmitted using sensor2. Amplitude change gives the reading

6.PT

Based on the property of the travelling sinusoidal wave showing relative phase after travelling a fixed distance.1. EM is generated and transmitted 2. Phase difference at the start & end fives the reading

7.TDT

Similar to TDR measurement of the propagation time only change is that measured over known distance.1. Methodology is exactly similar to TDR system

8.Tensiometer

Depends on the suction produced by water into sealed tube coming into equilibrium with the soil solution through porous medium1. Tip of ceramic cup is placed into the soil 2. Water is drawn out side to form equilibrium a suction is

created inside tube3. Depending on the amount of suction produced moisture

content is indicated

Parameter GM NM TDR FDR ADR PT TDT Tensiometer

1) Requirement of Specific Calibration N N Y Y Y Y Y N

2) Affected by Soil Salinity & air gaps N Y N/Y Y Y Y Y N

3) Measurement at different depths Y Y N Y N N N N

4) Connection with Data Logger N N Y Y Y Y Y N

5) Time efficient N N Y Y Y Y Y N

6) Permanent Installation N Y Y Y Y Y Y N

7) Safety Y N Y Y Y Y Y Y

8) Automation N N Y Y Y Y Y N

COMPARISION OF DIFFERENT SOIL MOISTURE MEASUREMENT TECHNIQUES

NAME ADVANTAGES DISADVANTAGES

Campbell Scientific TDR

Integration in automated measurement system

Required additional ext. control setup

Lee et al Random equivalent sampling TDR Required two extremely stable oscillators

Xudong et al Developed TDR based cable fault diagnosis system

Expensive off the shelf laboratory equipment

Purisima et al Developed field programmable gate array based TDR system

Direct sampling scheme is limited

Negrea and Rangu

Small microcontroller-based sequential sampling with three programmable delay lines

Resolution is only 250 ps

Schimmer et al

Portable high-frequency TDR meter. Ability to be Used even at very high frequency components up to a few GHz

Very low overall recording time, limited temporal resolution, high power consumption, need for calibration, & sometimes, limited availability on the market

Sokoll and Schimmer

Replaced the programmable delay lines by two programmable but free-running oscillators. excellent performance and high accuracy

The system cannot easily be adapted for long transmission lines required in many geological and agricultural applications

REVIEW OF DIFFERENT TDR SYSTEM:

SYSTEM DESIGN

BASIC BLOCK DIAGRAM

Fig. Basic block diagram of Proposed System

Sr. No. COMPONENT FUNCTION COST

01 Microcontroller Board To implement Microcontroller and assembly 125

02 MICROCONTROLLER (AT89S52) CPU of system 90

03 MAX-232ECPE Serves as TTL Converter 25

04 RS 232 Cable Provide communication between controller and GSM module 45

05 Regulator IC-L7805CV Provide regulated 5V supply 25

06 Relay (VK8FF-S-DC5V-C) Provide switching between GSM and sensor 85

07 LCD (JHD162A16*2) Display VWC and propagation Time to travel EM wave 180

08 MICRO-CHIP (PIC16F1516-I/SO) Generate, transmit and receive reflected EM wave to and from transmission waveguide 2000

09 GSM (SIM-300 V702) Provide wireless communication 1600

10 Supply Unit To provide Power supply 80

11 Other Expenses 120

Total Project Cost 4375/-Rs

COMPONENTS REQUIRED AND FUNCTION

Table : List of Components required, functions provided and cost

Circuit Connections:

Component Pins ConnectionsLCD Display DB0-DB7 P2.0-P2.7 of Microcontroller

RS,R/W,E P1.0,P1.1,P1.2 of MicrocontrollerVss LED+ and GND pin of Soil Sensor

Vcc LED- and Supply pin of Soil Sensor

Relay N/C Tx/out Pin of Soil SensorN/O GSM module through MAX232 and P3.0Com Collector terminal of Relay Driver circuitry

Soil Sensor Supply Vcc pin of LCD Display

GND With Vss pin of the LCD Display

Tx/out N/C pin of RelayMicrocontroller Port 2 Data pins of LCD Display.

P1.0,P1.1,P1.2 Control pins of LCD Display.P0.0 Emitter terminal of Relay Driver circuitryP0.2 Base terminal of Relay Driver circuitry

P3.0 N/O pin of Relay, GSM module through MAX232

Driver Circuitry of Relay:

Driver Circuitry of Relay used

Photograph of the Relay Used

COMPLETE CIRCUIT DIAGRAM OF SYSTEM

Fig. Complete circuit diagram of the Developed System

PHOTOGRAPH

Fig. Photograph of the Developed System

CALIBRATION OF THE SYSTEM

Available methods for calibrating TDR instruments :

1. Using empirical function- This is the traditional method which relates dielectric

constant of soil and soil moisture content

2. Using Neutron probe – Much popular but require authentication and also it is risky

one.

3. Using dielectric mixing – Here relationship between modelled bulk dielectric

constant with the individual dielectric values of specific components of the soil

system like water, mineral grains, bound water and air.

4. Using bulk density values, volumetric water content and depth- Serious

limitation of this method that it is not practical for heterogeneous soil samples.

5. Using Gravimetric method - It is the most accurate and proven method for

calibrating moisture measuring instrument. So, this method is selected for TDR

calibration

CALIBRATION USING GRAVIMETRIC METHOD :

Requirements :• Oven with 1000-1050C temperature • A balance of precision of ±0.001 g.• Aluminium weigh tins • Tool to collect soil samplesProcedure :i. A weight of original soil sample is taken and noted as Wt .ii. Place the sample in the oven 1050C, and dry for 24 hours.iii. Weight of oven dried sample is taken and noted as Ws

iv. % Volumetric Water Content is calculated using following formula:

v. Measurement of original soil sample using TDR meter is taken in parallel so travelling TIME (Ts) and it’s proportional COUNT is noted.

vi. Now, % VWC by Gravimetric Method per TDR COUNT is determined as:

% VWC (yn) = 100 x

The soil moisture content may be expressed by Weight as the ratio of the mass of water present to the dry to the dry weight of the soil sample, or by volume as ratio of volume of water to the total volume of the soil sample.

vi. Same procedure is repeated for number of samples and then Average of all the % VWC per Count is taken. In this way TDR instrument is calibrated.

vii. % VWC by TDR now can be calculated simply as:

RESULTS AND DISCUSSION

Table indicates the results of soil moisture measurement by Gravimetric Method and TDR Method.

Percent moisture i.e. volumetric water content measurement by gravimetric method is calculated from oven drying technique by determining the weights of the original soil sample (Wt) and oven dried sample(Ws).

% VWC (yn) = 100 x Here: Wt = Weight of soil and water, Ws = Dry soil weight

Percent soil moisture measurement is done with the reference of Gravimetric method, as GM is used as calibration technique for TDR method. TDR indicates the propagation time (Ts) required by EM wave to transmit and reflect back through the soil sample and a count proportional this Time.

Percent per count is calculated as:

% VWC by TDR now can be calculated as:

Results for different soil samples:

Gravimetric Method TDR MethodSample Wt

(gm)Ws

(gm)% VWC

(yn)TIME

Ts

(ms)

COUNT % VWC Per

COUNT

Avg. % VWC Per

COUNT

% VWC(xn)

I.150 128.08 17.11 11.25 96 0.1782

0.178917.17

150 124.30 20.68 13.24 113 0.1830 20.21

150 116.77 28.46 19.69 168 0.1694 30.05

150 111 35.14 22.27 190 0.1849 33.99

II.150 125.66 19.37 18.05 154 0.1258

0.128819.84

150 123.95 21.02 18.75 160 0.1314 20.61

150 122.60 22.35 20.27 173 0.1292 22.28

III.150 127.66 17.50 12.42 106 0.1651

0.161817.15

150 116.67 28.51 20.74 177 0.1611 28.64

150 115.50 29.87 21.45 183 0.1632 29.61

150 111.34 34.72 25.78 220 0.1578 35.60

Table :Final results of Soil Moisture Measurement for Different Soil Sample

GRAPHICAL PRESENTATION OF MEASURED DATA

1 2 3 400.020.040.060.080.1

0.120.140.160.180.2

% VWC Per COUNT For Different Soil Samples

% V

WC

Per

COU

NT

12

34

050

100150200250

12.42 ms20.74 ms 21.45 ms 25.78 ms

106 177 183 220

17.15% 28.64% 29.61%35.60%

TIME, COUNT and % VWC for soil sample III

TIME COUNT % VVC

TDR

COU

NT

Graph : Plot of TIME, COUNT and % VWC for Soil Sample-III

Graph : Plot of Percent VWC by GM per TDR COUNT for Different Soil Samples

STATISTICAL ANALYSIS

Statistical analysis is much important in the study of any analytical instrument. Analysis of the

measurement results stated in the table done using the standard formulae used for statistical

analysis. All of these formulae are considered with the reference of book Electronic Instrumentation

and Measurement by H. S. Kalsi [18].

1) Percentage error: “It is the deviation of the true value (measured value) from the expected value”. It

is determined by

Here,

2) Relative accuracy is determined by: “It is the degree of exactness (closeness) of a measurement

compared to the expected (desired) value”. It is determined as:

Percent accuracy is determined by:

Sample (yn) (xn) e = yn - xn %E A % a

I.17.11 17.17 -0.06 -0.35 0.9965 99.65

20.68 20.21 0.47 2.27 0.9773 97.73

28.46 30.06 -1.6 -5.62 0.9438 94.38

35.14 33.99 1.15 3.27 0.9673 96.73

Average % E = 2.88 % Average % a = 97.12 %

II.19.37 19.84 -0.47 -2.43 0.9757 97.57

21.02 20.61 0.41 1.95 0.9805 98.05

22.35 22.28 0.07 0.31 0.9969 99.69

Average % E = 1.56 % Average % a = 98.44 %

III.17.50 17.15 0.35 2.00 0.9800 98

28.51 28.64 -0.13 -0.45 0.9955 99.55

29.87 29.61 0.28 0.93 0.9907 99.07

34.72 35.60 -0.88 -2.53 0.9747 97.47

Average % E = 1.48 % Average % a = 98.52 %

Table : Percent Error and Percent Accuracy of the system

3) Arithmetic mean:

Here, xn = Value of nth measurement

n = Total numbers of measurements

4) Precision (P) :

5) Deviation from mean (dn):

6) Average Deviation (Davg):

7) Standard Deviation (δ):

“It is the most probable value of a measured variable of the taken number of readings”.

“It is a quantitative or numerical indication of the closeness of measured value with which a repeated set of measurement of the same variable agree with the average set of measurements”. It is determined as:

“The departure of a given reading from the arithmetic mean of the group of readings“.

“It is an indication of the precision of the instrument used in measurement”.

Sample xnP Davg δ

I.

x1 = 0.1849

0.1789

0.9665 d1 = 0.0060

0.0051 0.0081x2 = 0.1830 0.9771 d2 = 0.0041

x3 = 0.1782 0.9961 d3 = -0.0007

x4 = 0.1694 0.9469 d4 = -0.0095

II.x1 = 0.1258

0.12880.9767 d1 = -0.0030

0.0020 0.0040x2 = 0.1314 0.9798 d2 = 0.0026

x3 = 0.1292 0.9969 d3 = 0.0004

III.

x1 = 0.1651

0.1622

0.9821 d1 = 0.0029

0.0020 0.0036x2 = 0.1611 0.9932 d2 = -0.0011

x3 = 0.1632 0.9938 d3 = 0.0010

x4 = 0.1592 0.9815 d4 = 0.0020

Table- Precision, Average Deviation and Standard Deviation of the system

Precision, Average Deviation and Standard Deviation of the system:

1 2 3 40.00%

20.00%

40.00%

60.00%

80.00%

100.00%

17.15% 28.64% 29.61% 35.60%

17.50%28.51% 29.87% 34.72%

98.00% 99.55% 99.07% 97.47%% VWC and % Accuracy (% a) for Soil Sample III

% VWC by TDR % VWC by GM % a

Graph : Plot of Percent VWC and % Accuracy for Soil Sample III

Graph- Plot of Avg. Deviation, Standard Deviation (δ) and Avg. % Error for different Soil Samples

GRAPHICAL PRESENTATION OF CALCULATED DATA

S-IS-II

S-III

00.0050.01

0.0150.02

0.0250.03

0.00510.002 0.002

0.00690000000000001

0.0028 0.0022

0.02880.0156 0.0148

Avg. Deviation, Standard Deviation and avg. Error

Davg δ Average (E)

Technique Operating Range(ft3 per ft3)

Accuracy(ft3 per ft3)

Measurement volume Cost

Neutron Moderation 0 to 0.6 ± 0.005 Sphere(radius 6-16

inches) $10,000-15,000

TDR 0.05 to saturation ± 0.01About 1.2 inches

radius around waveguide

$400-23,000

FDR 0 to saturation ± 0.01 Sphere(radius 1.6 inches)

$100-3,500

ADR 0 to saturation ± 0.01 to 0.05 Cylinder (radius 1.2 inches) $500-700

PT 0.05 to 0.5 ± 0.01 Cylinder $200-400

TDT 0 to 0.7 ± 0.05 Cylinder (radius 2 inches) $400-1,300

Tensiometer 0-0.80 bar ±0.01 bar Sphere (Greater than 4 inch radius) $75-250

COMPARISION WITH DIFFERENT SOIL MOISTURE MEASUREMENT TECHNIQUES :

COMPARATIVE ANALYSIS

ADVANTAGES, LIMITATIONS AND REMEDY ADVANTAGES : Low cost. Higher accuracy. Simple software and hardware design. Wireless transmission of the readings is possible. Fault detection and correction is easy as compared to existing system. No need of frequent maintenance, low maintenance cost. Easily expanded using multiplexing. Varity of sensor probes availability. Very less soil disturbance. Insensitive to normal salinity. LIMITATIONS :• Encounters problem at high salinity condition• Specific calibration required REMEDY :• Problem at high salinity condition can be easily solved using coated TDR probes with

Polyolefin coating.• Remedy to second limitation is to gather data base of large numbers of soil samples

APPLICATIONS APPLICATIONS :i. In agriculture and plant science field to determine best time to sow and plow the

field. ii. In the Drainage engineering to measure changes in infiltration and irrigation.iii. To study ground water recharge and Evapo-transpiration. iv. It is also important in the fields like Hydrology, Forestry and Agrology. v. In the study of various physical and chemical properties of soil which changes

with amount of moisture present in soil. vi. To study and determine the parameters like soil profile, surface tension related

with civil and soil engineering.vii. Automation of Irrigation and Mushroom cultivationviii. For solid waste management for decomposition of waste

CONCLUSIONCONCLUSION : We are succeeded to provide low cost solution for soil moisture measurement.

Ideal method for soil moisture measurement is yet to be perfected. A TDR instrument also has limitations like high cost, need of specific

calibration, inaccuracy at higher salinity conditions. This system design is a step towards the perfection of this technique as it removes the limitation of the high cost.

Need of the specific calibration can be minimize in the future by collecting large data base from large number of different soil samples.

Solution for the reduction of inaccuracy problems faced at higher salinity condition is also available; some of the researchers are trying to solve this problem with the use of polyolefin coated TDR probes.

FUTURE SCOPE : Increasing accuracy and system performance using different material for TDR

probe design. Use of polyolefin coated probes to reduce problem faced at higher salinity

conditions. Reducing need of specific calibration by collecting large amount of data base.

Fig. Coaxial Cable Construction [28](A) Insulating Jacket (B) Braided Shield Wire (C) Insulating Dielectric Material (D) Inner

Conducting Wire (Source: Belden Cable)

PUBLICATIONSPublications in International Journal:

1. Bhushan N. Patil, P. H. Zope & K. S. Patil, “A Review of Various Soil Moisture Measurement

Techniques”, Cyber Times International Journal of Technology & Management Vol. 7 Issue 2, April

2014 – September 2014. P.P. 247-254. Available at: http://journal.cybertimes.in/?q=Vol-7-Issue-2

2. Bhushan N. Patil, P. H. Zope & K. S. Patil, “Development of Low Cost TDR System for Soil

Moisture Measurement”, International Journal of Advanced Research in Education & Technology

Vol. 2 Issue 3, July to Sept, 2015.3. Bhushan N. Patil, “A Review of ECG Monitoring System Using Wavelet Transform”, International

Journal of Research in Advent Technology (IJRAT) Volume 2, Issue 4, 15 April 2014.

 

Publication in International Conference:

Bhushan N. Patil, P. H. Zope, K. S. Patil, “A Review of Various Soil Moisture Measurement

Techniques”, International Conference on Global Trends in Engineering, Technology and

Management, Jan 9th & 10th 2015.

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APPENDICES-I

Soil Moisture Measurement using Gypsum Block Technique at Irrigation & Drainage Engineering Department of College of Agricultural Engineering and Technology, Akola.

Fig- Soil Moisture Measurement using Gypsum Block Technique

Visit to College of Agricultural Engineering and Technology, Akola.