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A LOW COST FIELD USABLE PORTABLE DIGITAL GRAIN MOISTURE METER WITH DIRECT DISPLAY...
#1

A LOW COST FIELD USABLE PORTABLE DIGITAL GRAIN MOISTURE
METER WITH DIRECT DISPLAY OF MOISTURE (%)

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ABSTRACT:-
Moisture content of grain is one of the important parameters always considered
when deciding the quality and price of grain, at the stage of harvesting, storage, processing and
marketing. Grain having excess moisture content, if stored for long duration, will spoil due to
insect/fungus infestation. Portable, field usable, and easy-to-use direct moisture (%) display Grain
Moisture Meter is a necessity for the benefit of farmers. The types of Grain Moisture Meters available
in the market are with look-up tables, which cause inconvenience when carrying out measurements.
We have developed a grain moisture meter, which due to its novel design, eliminates this problem
and gives moisture (%) directly on a LCD display. The novelty of this instrument is that it is
compact, easy-to-use, portable, and field usable. The moisture meter is based on the principle of
dielectric constant variations due to change in moisture. Changes of moisture content affect the
dielectric constant of the grain, which in turn makes variation in capacitance. The resultant
capacitance variation is converted to voltage variation and calibrated in terms of moisture
percentage. On the basis of rigorous experiments the meter has been calibrated for wheat, paddy,
soybean, sunflower & mustard. However, the user can calibrate the meter at his level for other
grains also. The developed instrument is working satisfactorily for all practical purposes in the
range of 5-25 % of grain moisture with an accuracy of 1% .
INTRODUCTION
The quality of grain is influenced by its moisture content.
Knowledge of the moisture content of food grains is
required for various reasons such as the need to know
the optimum stage of harvesting, whether the grains could
be stored for extended period of time, to decide the price
of grains, and for research and development (R & D)
purposes. Conventional methods of moisture
measurements in grains like oven-dry method, distillation
method, drying with desiccants etc., are time-consuming
laboratory methods. Fast as well as field usable portable
Grain Moisture Meter is a necessity to meet the
requirements of farmers, grain storage personnel, and
agricultural products marketing corporations. The paper
explains the design and development of a low cost
portable Digital Grain Moisture Meter.
The methods for determining moisture content of grains
can be divided into direct and indirect methods. Ovendry
method, distillation, drying with desiccants etc., are
direct methods, whereas those based on either electrical
resistance, dielectric (capacitance), chemical, hygrometry,
nuclear magnetic resonance or microwave spectroscopy
etc., are indirect methods.
Oven-dry method is a widely recognized method [1,2] for
determining moisture of grains. It is a basic method against
which other indirect method based moisture meters are
calibrated. Two general procedures are available in ovendry
method: (i) Grind the grain and dry it in the oven for 1
to 2 hours at 130 C or (ii) Place the whole grain in the
oven at a temperature of 100 C for 72 - 96 hours. After
heating the grains are transferred to a desiccator where
they are allowed to cool to room temperature. The loss in
AJST, Vol. 6, No. 1: June, 2005 98
A. K. RAI
weight is determined and the moisture content calculated
either by wet basis or dry basis.
In the distillation method [1,2] moisture is removed by
heating the grain in oil and the loss of weight of the sample
determined. In the case of desiccant drying [1,2], moisture
content of a product is determined by placing the sample
near an efficient drying agent like anhydrous sulphuric
acid in a closed container. The loss in weight is determined
and moisture (%) is calculated.
All the above-mentioned methods have the disadvantages
of being time-consuming laboratory methods, and chances
of errors occurring during measurements are more if the
measurements are not done carefully.
Indirect methods involve the measurement of certain
property of the material, which depends upon the moisture
content. Any one of the direct methods explained above
is used to calibrate the systems based on indirect methods.
Chemical method for moisture measurement normally adds
certain chemicals, which decompose or combine with water.
Calcium carbide method [3], calcium hydride method [1]
and Karl Fischer method [4] etc. are some of the chemical
methods. In hygrometry method [2] relative humidity of
the air in equilibrium with the material (grain) is used as a
measure of the moisture content.
Moisture measurement by nuclear magnetic resonance
(NMR) depends on the detection of the hydrogen nuclei
within the material. The magnetization in the sample is
converted to a voltage, which is proportional to the number
of hydrogen nuclei present in the sample. This method is
not specific for moisture itself but is specific for hydrogen
nuclei [11]. An advantage of this method is that it is rapid,
has high accuracy, and is a non-destructive measurement
technique. Its disadvantages are that the method senses
total hydrogen rather than water, and requires expensive
equipment.
Microwave spectroscopy [1] is yet another method in
which the attenuation of microwaves vary with moisture
content of grain, but the method is quit expensive. Another
indirect method is electrical resistance or conductivity
method [1,2] and the principle is based on the resistance
or conductivity of the material under test. That resistance
is influenced by many factors other than moisture content,
the error due to non-uniform distribution of moisture, and
physical contact with the material are major problems in
this method. Furthermore the method cannot give accurate
results [5] if moisture level is less than 7% or greater than
23%.
Another popular method of moisture measurement is the
capacitance (dielectric) method [1,2]. Instruments based
on this technique are subject to less error that arise from
non-uniform distribution of moisture and physical contact
with the material under test. This method permits moisture
measurement over a wider range than conductance
method, and properly calibrated capacitance type grain
moisture meters work satisfactorily within 1% accuracy,
which serves almost all practical purposes in agriculture.
The paper explains the development of grain moisture
meter based on the capacitance principle.
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