development of low cost tdr system for soil moisture measurement
TRANSCRIPT
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.