Agricultural
Communication
Biosci. Biotech. Res. Comm. 11(2): 246-250 (2018)
Design of a probe type
in situ
electronic grain moisture
measurement system
A.K. Rai, Bharati Dass and V.K. Tiwari
Jawaharlal Nehru Agricultural University, Jabalpur (M.P.) India-482004
ABSTRACT
With the increased mechanization of harvesting operation, crop is harvested at high moisture and cannot be stored
for longer period unless it is dried. Thus there is a need of equipment for determining moisture of grain. The same
equipment may be used for determining moisture at the time of harvest also. The importance of grain-moisture and
the use of electrical moisture meters for measurement are discussed brie y. References to earlier work with such
moisture meters are cited (Young 1983, Nelson 2000), and a brief description of variation of electrical or dielectric
properties with grain moisture are discussed. The information available in the literature on the dielectric proper-
ties of grain is reviewed from the viewpoint of its usefulness in grain-moisture measurement. Factors other than
moisture that in uence the dielectric properties of grain are elaborated. The authors have designed an in situ grain
moisture meter for major crops like wheat, paddy, soybean. Most of the moisture meters available are desk type and
are designed for in situ moisture measurement (Rai et al 2005). At present moisture meter and samplers are not inte-
grated. In this design sensor and grain sampler are integrated in one unit. It will be low cost, portable and easy to use.
KEY WORDS: MOISTURE CONTENT, CAPACITANCE, DIELECTRIC PROPERTIES, SENSOR, DESICCANT, DISTILLATION. GRAVIMETRIC, PROBE
246
ARTICLE INFORMATION:
*Corresponding Author: akrai_jnau@yahoo.co.in
Received 19
th
March, 2018
Accepted after revision 22
nd
June, 2018
BBRC Print ISSN: 0974-6455
Online ISSN: 2321-4007 CODEN: USA BBRCBA
Thomson Reuters ISI ESC / Clarivate Analytics USA and
Crossref Indexed Journal
NAAS Journal Score 2018: 4.31 SJIF 2017: 4.196
© A Society of Science and Nature Publication, Bhopal India
2018. All rights reserved.
Online Contents Available at: http//www.bbrc.in/
DOI: 10.21786/bbrc/11.1/8
INTRODUCTION
Moisture is an important criterion for pricing and pro-
curement (at minimum support price) of agriculture
produce. Farmers with high moisture produce is penal-
ized directly by a lower price for excess moisture and
farmer with low moisture produce is penalized indi-
rectly for supplying dry matter instead of water to the
purchases.
Inexpensive method with ease and suf cient accu-
racy for determining moisture content of grain is not
available for farmers. In most of the cases farmer relies
upon his experience to estimate the moisture content.
Farmers normally used observation by biting or feel-
A.K. Rai, Bharati Dass and V.K. Tiwari
ing. Regardless of the method used for determining
the moisture content, there are possibilities of error in
making the determination. The major problem is that of
securing a sample which is representative of the entire
lot of material. To reduce the possibilities of error sev-
eral samples should be obtained from different location
in the bin, container or bag. Usually a large sample is
obtained which is taken to the laboratory for determin-
ing the moisture content. Moisture content determina-
tion within one percent accuracy is suf cient to estab-
lish storage period for grains, as considerable money is
lost each year because of over drying (Rai et al 2005).
The authors have theoretically designed a hand held
grain moisture meter for exclusive use at farmers level,
Krishi Upaj Mandi, ware houses and Food Corporation of
India during procuring and storage. The aim is to develop
a device for measuring grain moisture, based on the prin-
ciple of capacitance measurement. At present moisture
meter and sampler are not integrated. It is proposed that a
digital hand held battery operated portable moisture meter
with integrated grain sampling unit and display unit will
be designed. This unit will be tested rigorously at mandi
with paddy, soybean and wheat at large scale. The sen-
sor would be of capacitance type either in the cylindrical
shape or miniature parallel plates to be integrated in the
sampling device. The principle of operation will be based
on dielectric method i.e. Capacitance (Dass et al 2010).
The sensor and measurement device will be internally
connected on a single module. Attempts will be made to
make the system compact and rigid.
Usually farmers bring their produce to Mandi for its
sell. The keeping quality of grain largely depends on the
moisture content. Therefore, moisture measurement at
Mandi will be helpful in nalizing drying process for
safe storage of food grains.
MOISTURE MEASUREMENT TECHNIQUES
Various grain moisture measurement techniques are
available i.e. direct as well as indirect methods. The
direct method includes oven method, drying with desic-
cant and distillation method (Rai et al 2005, Hall 1970,
Zeleny 1960). Direct methods involve either gravimet-
ric or volumetric procedures. Such methods are cum-
bersome and time consuming. Other methods such as
infrared and microwave (Nelson 2004) are very costly
and needs elaborate calibration from variety to variety.
It is thought to use capacitance (dielectric) measurement
method as it is easy, simple and low cost (Nelson 1987).
PROPOSED DEVICE
The proposed device will be fabricated along with capac-
itive probe type sensor. The device will be developed
consisting following components:
• The size and shape of grain sampler will be opti-
mized.
• The sampled grain will be directly taken into sen-
sor for better accuracy and instant measurement.
• A sampling probe for insertion into grain heaps/
bags will be developed and standardized.
• A LCD based digital display integrated with the sam-
pler and sensor for quick measurement of moisture.
• The Geometry of probe will be optimized / redesigned.
• The sample holder may be in the form of Auger
(parkhi). Various sizes of parkhi’s will be fabri-
cated and the capacitance response in the moisture
range 8-25% will be studied.
• Sizes, shape and capacity of sensor will be opti-
mized for best result in above range.
• If needed some modular arrangement will be made
to incorporate grain collector of miniature size to
increase the sample volume.
• The circuit will be designed using Op Amps, Analog
and Digital ICs having LCD Display (Theraja 1980).
• Additional feature of above system will be equipped
with graphical display system of the moisture indi-
cators.
• Initially the meter will be calibrated for wheat, paddy
and soybean crop. Thereafter, depending on the
requirement and accuracy obtained other commodi-
ties may be taken for calibration (Rai et al 2005).
OPERATING PRINCIPLE
A coaxial type sensor ( g. 1) will be developed using
dielectric properties of grain moisture.
Capacitance of Coaxial type sensor is given by
C = 2πH/{log(R-r)}
(where R and r is radius of outer and inner cylinder and
H = height of the cylinder)
= K
2
,
Where = dielectric constant, K
2
= constant for xed
geometry (R,r,H)
Different sizes of coaxial type sensor will be fab-
ricated for the purpose. Since a capacitor is physical
device, a change in its capacitance is due to dielectric
constant K
2
. The ratio of dielectric constants of water,
dry grain and air is 80:5:1 respectively (Nelson 1982,
Nelson 1991). Calibration curve will be obtained (Gough
1983). Various grain samples with different moisture
levels will be collected for each crop. Measurement will
be performed at length with different shape/size of sen-
sors and will be excited in the range of radio frequency
i.e. 1-50 MHz and frequency optimization will be carried
out. Signal Conditioning and ampli cation will be car-
ried out as per requirement. Initially it will be calibrated
for paddy, soybean and wheat. A conceptual sampling
probe is shown in g 2.
BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS DESIGN OF A PROBE TYPE
IN SITU
ELECTRONIC GRAIN MOISTURE MEASUREMENT SYSTEM 247
A.K. Rai, Bharati Dass and V.K. Tiwari
FIGURE 2. Parakhi (Grain sampling device)
FIGURE 1. Coaxial Type Sensor
FIGURE 3. Block diagram of the System
PROCESS SCENARIO
The circuitry will consist of RF Oscillator, Signal con-
ditioning circuit, Ampli cation and Display units etc
(Mathur 2002, Hall 1986, Gaonkar 1989). The process
diagram is shown in g 3 and excitation circuit in g 4
(Kant 2010).
MATERIALS AND METHODS
The following methodology is proposed:
• The present status of moisture measurement will
be visualized by visiting FCI, SWC, farmer’s eld,
Krishi Upaj Mandi etc.
248 DESIGN OF A PROBE TYPE
IN SITU
ELECTRONIC GRAIN MOISTURE MEASUREMENT SYSTEM BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS
A.K. Rai, Bharati Dass and V.K. Tiwari
• The standard procedure laid down by Association
of Analytical Chemist (AOAC) method will fol-
lowed during calibration and testing of unit at dif-
ferent moisture levels (8-25%).
• Once relationship of the sensor output and cor-
relation factor for other variable is established, the
design of the sensor in respect of size, shape etc
will be freeze.
• The design work of electronic circuit consisting of
oscillator, signal conditioning, A to D conversion
etc (Mottershead, 1985) will be taken into account.
• The integration of sensor and other measuring unit
will be done.
CALIBRATION AND TESTING OF THE DEVICE
The relationship between the electrical properties and
grain moisture content vary with grain type, variety,
temperature, packing density etc. For calibrating the
device, samples of known moisture content will be pre-
pared (Gough 1983).
• Long duration performance of the system will be
tried in Mandi / Warehouses.
• Moisture range will be 8-25% with accuracy of
+/-1 % and will be calibrated for Wheat, Paddy
and Soybean in the rst phase.
• Testing and eld trial will be conducted (Gough
1983).
RESULT AND DISCUSSION
This device will facilitate easy, simple and accurate
insitu measurement of grain moisture of different crop.
This will be useful for monitoring moisture migration of
grain stored at Food Corporation of India, central and
state warehouses, farmer’s eld, Krishi Upaj Mandi, etc.
Before harvest during each Rabi and Kharif crop
season, the Government of India announces the mini-
mum support prices (MSP), to facilitate procurement of
food grains. Government establish a large number of
purchase centres at various mandis and key points. For
paddy maximum limit of moisture content is noti ed as
17 percent on wet basis (GoI 2017).
For Wheat procurement more than 18,000 procure-
ment centers are operating in Rabi Market Season (RMS)
2018-19 & for Rice procurement more than 35,000 pro-
curement centres are operating in Kharif Market Season
(KMS) 2017-18.
Its utility will be extended to these centers for ensur-
ing procurement as per schedule of speci cation noti-
ed by Government of India (GoI 2017) i..e. .moisture
content 17 % (wet basis). Thus there is need and demand
of thousands of moisture meters to decide the condi-
tion of crop falling under uniform speci cation, to avoid
unnecessary rejection of lot due to over moisture.
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FIGURE 4. Bridge circuit for measurement of grain
BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS DESIGN OF A PROBE TYPE
IN SITU
ELECTRONIC GRAIN MOISTURE MEASUREMENT SYSTEM 249
A.K. Rai, Bharati Dass and V.K. Tiwari
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250 DESIGN OF A PROBE TYPE
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ELECTRONIC GRAIN MOISTURE MEASUREMENT SYSTEM BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS