International Journal of Advanced Scientific and Technical Research
Available online on http://www.rspublication.com/ijst/index.html
Issue 6 volume 6, November-December 2016
ISSN 2249-9954
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New high accuracy inductive electronic pluviometer (IEP)
for simultaneous rainfall measurement
Zakaryae. EZZOUINE 1#1, Abdelrhani. NAKHELI 2#2
#1 Department of physics, Spectrometry Laboratory of Materials and Archaeomaterials
LASMAR, Faculty of Sciences, University Moulay Ismail , Meknes, Morocco.
#2 Department of Electrical Engineering, ESTM, University Moulay Ismail, Meknes,
Morocco.
E-mail: [email protected]
ABSTRACT
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Rainfall measurement system is a very important useful tool in agricultural and weather
forecasting system. This paper describes an improved Inductive Electronic Pluviometer (IEP)
which is based on measuring the magnetic fields between two coils. The instrument presented
in this article used to collect and measure precipitation (falling water), it enables also to
measure volume, velocity, flow rate and the intensity of precipitation accurately in real time.
The experimental data is recorded and analyzed by LabVIEW software. The acquisition
program saves the data reading and shows specific calculated for display. Laboratory
experiments using a nozzle type rainfall simulator have been conducted. A description of the
device and the results obtained are presented. The IEP system has been largely tested under
same natural rain conditions with a perfect resolution up to 1 µm and accuracy equal to ±1%
at 0.01 µm/min and ±2.5% at 0.04 µm/min with an error of not more than 5%. This device
can also be useful for rainfall prediction.
Key words: Electromagnetic, Inductive Electronic Pluviometer (IEP), measurement, rainfall
parameters, monitoring, LabVIEW software.
Corresponding Author: Dr. Zakaryae. EZZOUINE
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INTRODUCTION
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Rainfall measurements play a key role in many climatological, hydrological and Climate
Change and forecast the rainfall applications [1-3].
The efficiency of a Rainfall measurement system was mainly determined by two related
factors, which is the position of the Rainfall measurement sites and also reliable observer of
the system. In short, the system is completely un-automated and it is highly dependent to the
user constant involvement for accurate reading. As were suggested by Bleasdale [4].
The typically erratic development of Rainfall measurement system networks in the past
was very largely determined by two factors, namely the need to find conventionally
satisfactory Rainfall measurement sites, and the need to obtain the services of good observers.
Great positioning to place the Rainfall measurement system was very essential as it enables
more stable and accurate reading.
The necessity of the constant observation of a system is a limitation of the system itself.
Bleasdale emphasized that recording Rainfall measurement at present are not readily
available, and fully automated instrument that can function and to be left unattended for a
period of time without frequent servicing is needed. The research done by Bleasdale targeted
United Kingdom as the subject of the research primarily Britain and Wales [5].
Scientific studies regarding hydrological cycle uses precipitation (rainfall and snowfall)
measurement as a basic input for all practical practice. Disturbance of nature, high variability
in time and space, and also sensitivity to environmental conditions such as wind, precipitation
is extremely difficult to measure accurately [6-7].
In the literature, there is many version and design of Instruments and Observing Methods
used to measure rain fall [8-12], [3], [13-17]. The different in design and function is optional
but still the main purpose to build rain gauge is to measure the cumulative rain fall over
certain area in certain time. Currently graduated cylinders, weighing gauge, tipping bucket are
examples of more commonly used device for rain measurement system [7], [18-19]. A
standard rain gauge includes a funnel that flows water into graduated cylinder [20].
Measurement is taken as the cylinder enables reading of water collected. One of the
weaknesses of the system is that it can easily be overflow after some period. This overflow of
the gauge would be a serious obsolete in data measurement [20].
The construction of conventional rain gauge is simple and can be easily built. The reading
has to be taken regularly and the gauge is to be emptied frequently [21]. So this nonautomated system needs constant observation. Measurement of precipitate can be done by
measuring either height or volume of the precipitate [22].
The weighing-type recording gauge is a device to measure the quantity of chemicals
contained in the locations atmosphere [23]. This is extremely helpful for scientists studying
the effects of greenhouse gases released into the atmosphere and their effects on the levels of
the acid rain. The Optical Spectro Pluviometer designed to perform real-time measurements
of the drop size and the terminal drop velocity [24].
The application of coil sensor [25] as inductive electronic pluviometer is presented in this
article [26]. The figure 1 shows a simplified diagram of the IEP basic.
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Issue 6 volume 6, November-December 2016
ISSN 2249-9954
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Fig 1: Operating principle basic in the inductive sensor scheme
Its transfer function V = f (B) results from the fundamental Faraday’s law of induction [27-28]:
e  n.
d
dB
dH
 n. A.
   0 .n. A.
dt
dt
dt
(1)
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where Φ is the magnetic flux passing through a coil with an area A and a number of turns n.
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In this paper, an IEP sensing system is introduced, which can operate with a LabVIEW
program produced for rapid-response, and monitoring the rainfall parameters by detecting the
change in inter coil distance and transform it to a voltage from calibration curve of sensor.
This work can help the high school students to learn precipitation characteristics; also can
help them in understanding and predicting of the rainfall parameters by recording the
experimental data.
This article describes the setup and the results of the experiment, which includes the
calibration of the IEP and the measurement of the rainfall. Section1 describes the principle of
the IEP; the representation of the experimental set-up design is given in the Section 2, the
section 3 presents the results and discussions. Finally, we conclude the paper by presenting
the main achievements of our work.
DESCRIPTION OF THE INDUCTIVE SENSOR
The Inductive sensor is a precision instrument for accurately measuring displacement. The
simplified schematic diagram, presented in figure 2, shows the operational and measurement
principles of the Inductive transducer, that are based on the Ampere’s law rather than the
Faraday’s law between two flat coils, placed in parallel. One of the flat coils (Fixed Coil) is
fixed on an insulating horizontal support and the other flat coil (Moving Coil) are wound on
an insulating cylinder of 2 cm in diameter. The entire system formed (fixed flat coil, moving
flat coil and calibrated spring) is aligned on the same vertical axis.
The fixed coil is energized by an oscillator of Clapp, therefore, it is traversed by a
sinusoidal current which creates a sinusoidal magnetic induction variable along its axis. This
induction produces a variable flux Φ and a variable induced electromotive force on the
electrons of the other coil (moving coil).
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ISSN 2249-9954
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Fig 2: Design of the Inductive Sensor
EXPERIMENTAL SET-UP
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The voltage generated in the measuring coil is due to electromagnetic induction. Assume
that the measuring coil is small and that the magnetic field at a given instant of time is
approximately uniform over the area of the measuring coil. The output signal, V, of the
inductive sensor depends on the rate of change of flux density, dB/dt, therefore a small
difference in distance changes the gradient of magnetic field is detected by the sensor
element. In this way it is possible to measure relatively small magnetic field from a
micrometric change of the distance between two coils.
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The equipment depicted in figure 3 consists of a receptacle “Funnel” to collect
precipitation a tap for adjusting the rate of water outflow to ensure that the equipment was
able to deliver a steady water flow (hence a steady simulated rainfall rate) and a measuring
part to measure and record its amount. The measuring part consists of an inductive sensor
with a detection probe attached; its lower part is sunk into the storage tank “Cylinder of
transparent glass” for measuring the amount of water collected.
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Fig 3: Experimental setup system for rainfall measurement.1,Calibred
spring;2,hooks;3,measuring coil;4,recepting coil;5,detection probe;6,cylinder of transparent
glass;7,water;8,vinyl tube;9,float;10,funnel (rain receiver); 11, flow rate adjusting cock; 12,water
supply opening;13,water tank;14,DAQ device;15, Computer.
The above system were equipped with a separate experiment was conducted which
confirmed that the equipment was capable of delivering an increasing water flow up.
The experiment set-up includes also an electronic circuit for adapting the out signal of
sensor (see the next paragraph for more information). The software implemented on an
analog-digital acquisition card “NI USB 6281 DAQ” by National Instruments, combined with
a Personal Computer used to measure the out voltage of sensor on a virtual millimeter create
in LabVIEW Hardware, this program allows also the storage of the volume and velocity of
precipitation and the arrival time of each drop. These parameters are obtained in real time on a
basis of one minute.
Electronic circuit
The out signal of the Inductive displacement transducer can be adapted by an electronic
card which is presented in figure 4.
This signal should be amplified to increase the resolution and reduce noise. For the highest
possible accuracy, the signal should be amplified so that the maximum voltage range of the
conditioned signal equals the maximum input range of the analog-to-digital converter (ADC).
The electronic card includes an oscillator of Clapp generates the alternating current, and a
converter the measured signal into a calibrated DC output.
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ISSN 2249-9954
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Fig 4: Schematic representation electronic sensor card
The presence of the offset voltage and associated zero drift are a significant problem in the
correct design of such transducers. For this reason, an additional potentiometer is sometimes
used in the electronic card for offset correction and for adjusting of sensor sensitivity.
Ultimately the out signal to convert the output signal is converted to a digital form and then to
perform digital integration.
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Measuring principles
From the experimental presented in the previous Section, the water tank is like as a vessel
containing water equivalent to precipitation of 0.2 µm to 1 µm.
As shown in Figure 5, rainfall can be calculated by simply measuring height h of collected
water in a vessel of uniform cross section.
Fig 5: Obtaining height from volumetric formula
For device which measures the volume of precipitation  , the system usually uses
cylindrical container. By simple calculation, h can be obtained from said volume as written
below.
S   .r 2
(2)
   .r 2 .h
(3)
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where h is en mm
V is the volume in mm3,
r is the radius of funnel in mm.
The principle of rainfall intensity measurement in this Inductive Electronic Pluviometer is
based on measurement of the time interval  between successive drops. The mean rainfall
intensity R (mm/h) in the interval  (s) is:
R
3600h

(4)
where h is the rainfall depth (mm).
The velocity of precipitation was calculated in accordance with equation 5, using the
simulated rainfall rate r and the surface s:

sR
t
(5)
where  is in mm/sec, h is the surface in mm2, R rainfall rate in mm/s and t is the time.
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RESULTS AND DISCUSSION
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The voltage is that a flow out of the inductive sensor is recorded. Theoretically, the output
voltage is linearly proportional to the water level. The IEP have strongly suggested that
proportional relationship between water contain and output voltage can be highly beneficial as
it can be used by gauge telemetry system. It can measure rain accurately, and it is possible to
integrate this system with proper output display module. The amplitude of the signal variation
is proportional to the cross-section of the drop, which the difference of distance inter coil in
presence and absence of water is the main variables in this mechanism.
Calibration of the sensor element
In order to study the variability of the rainfall field at small scale, the sensing of the IEP
must be calibrated with a controlled mass and displacement.
The characteristic curve of the sensor, v=f(m), is obtained by hooking the masses of
precision ranging from 0g to 9mg by steps of 1mg (see fig.6), and by raising the
corresponding voltage.
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Fig 6: Calibration curve of the sensor m=f (V)
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We can use the characteristic of spring K to convert the applied mass into displacement for
determining the relationship between the displacement and the out signal of sensor, d=f (v) as
is shown in figure 7.
Fig 7: Calibration curve of the sensor d=f (V)
The effective distance inter coil d (µm) is computed from the current out voltage of sensor
by the following formula:
d  0.0061 V  5.67455
(6)
Software
A LabVIEW program running on the PC retrieves data from the sensor via the acquisition
card. Figure 8 shows the graphical user interface (GUI) on the PC monitor. When the liquid
level demonstration system is on, the real-time level data, rainfall flow rate, rainfall intensity,
velocity and supply voltage are displayed.
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ISSN 2249-9954
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Fig 8: System GUI shown on PC monitor.Weather Monitoring Software
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The LabVIEW program includes basic calibration and advanced calibration to achieve a
more accurate measurement. Basic calibration is used to determine the distance inter coil (the
displacement).The software of the monitoring system permits also to select the time of
acquisition. The detection probe must be submerged into water during the calibration and
measurement processes.
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Rainfall parameters measurement
The data obtained from the experimental setup system are given in the table below.
Table1. Tabulates the rainfall parameters measurement for the experimental setup system for
different time
Inter coil
Level
Time Voltage
distance
Displacement variation
Surface
Velocity
(min)
(mv)
(mm)
(mm)
(mm)
(µm^2)
(µ/s)
0
797.60
0.80919
---------------------------------------------2
797.70
0.80858
0.00061
0.000610 1.1304*E-10 1.0826*E-30
4
797.81
0.807909
0.000671
0.001281 1.1304*E-10 1.1367*E-30
6
797.92
0.807238
0.000671
0.001952 1.1304*E-10 1.1548*E-30
8
798.03
0.806567
0.000671
0.002623 1.1304*E-10 1.1638*E-30
10
798.14
0.805896
0.000671
0.003294 1.1304*E-10 1.1692*E-30
12
798.25
0.805225
0.000671
0.003965 1.1304*E-10 1.1728*E-30
14
798.35
0.804615
0.000610
0.004575 1.1304*E-10 1.1599*E-30
16
798.44
0.804066
0.000549
0.005124 1.1304*E-10 1.1367*E-30
18
798.53
0.803517
0.000549
0.005673 1.1304*E-10 1.1187*E-30
20
798.61
0.803029
0.000488
0.006161 1.1304*E-10 1.0934*E-30
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ISSN 2249-9954
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A record for a precipitation (The device provides an increased flow rate) by the system
during 20 min is shown in figure 9.
Fig 9: Precipitation intensity measurement versus time interval ∆t.
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In figure 9, it can be seen the rainfall intensity measured by our sensor every two minutes
over a period of twenty minutes.
From the experimental results presented in the Table 1, the volume  was calculated in
accordance with Equation (3), using the level variation measured by the sensor. The rainfall
flow rate that IEP sensor can accurately measure is µ/s of rain per second. Using the rainfall
rate R and the Volume  measured. The rainfall rate was then plotted against the Volume
 as shown in the figure 10.
Fig 10: The Flow rate of precipitation of the corresponding voltage of IEP
The precipitation parameters are approximately proportional to the out voltage of system
(see fig.11).
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Fig 11: The precipitation volume of the corresponding voltage of IEP
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Based on the results obtained and graph plotted, we can infer that there is a linear
relationship between the voltage of system and the volume of water collected.
Then the Volume of rainfall between two different times is measured.
  (1.45023  E 15 )V  797.6
(7)
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We can thus apply this relationship into the study of frequency of rain droplets with
rainfall quantity. When measuring near-instantaneous rainfall rates, the time interval over
which the recording is performed determines the accuracy of the result. For this experimental
setup, the volume of precipitation generally increases with the rainfall rate throughout the
calibration range from 5.7462  E-19 to 6.22505  E-19µm/s.
During the experimental measurement, it was observed that as the rainfall rate increased,
there was a tendency for the water to stay longer in the collecting funnel. It took time for the
water to drain away, and the situation worsened with higher rainfall rates as more water
accumulated. This resulted in the build-up of a larger static water pressure inside the funnel,
which favored the formation of larger water drops. This observation was consistent with the
general trend of precipitation volume increasing with the rainfall rate (figure 10).
CONCLUSION
In summary, a novel system was presented for the estimation of rainfall parameters based
on a stable inductive electronic pluviometer (IEP) with comprehensive data manipulation is
designed and developed. The out signal of the system processing has been performed by the
LabVIEW Hardware. The electronics and the conception of the sensor are not sophisticated
which makes the instrument easy to calibrate, reliable, movable and robust. Data is recorded
and analyzed before the output is displayed. The instrument measures parameters rainfalls
accurately, saves the data reading and shows specific calculated for display. This system was
conducted with the objective of studying the relationship between the voltage and the
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parameters of rainfall, so as to produce a device that is mobile, speed and able to reduce the
errors and inconvenience of existing conventional rain gauges at an affordable cost.
The present work provides a simple mechanical construction together with very
sophisticated firmware can guarantee perfect performance than ordinary self-recording
rainfall parameters.
The simplicity, low computational complexity, and the high detection rate make the
proposed IEP system attrac-tive for real time, prediction weather applications.
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