In industry, determining the moisture level in substances has variety of purposes.
In agriculture, moisture level in grain such as paddy, beans or corn is measured
to control the quality of products and facilitate in research and development.
Besides, agriculture researchers perform assessment of soil quality and organic
resource quality by monitoring the moisture level.
To measure the moisture content, the conductance of a substance must be determined.
The electrical conductivity or resistance type instruments measure the ability
of sample to conduct a current relative to its moisture content. In addition,
conductivity of the substrate increases as the moisture content increases. Based
on Ohm s Law V=IR, lower resistance gives higher voltage drop and thus
measures higher moisture level.
Some devices use sophisticated methods for instance infrared, radio frequency,
or microwave techniques to evaporate water from a sample. This latest technology
determined the high production cost of the detector.
Moisture content of agricultural products is one of the most important for
determining proper time for harvesting and the potential for safe storage.
The objective of this paper is to discuss the design of a device that can measure
moisture content in order to help farmers. This requires determining the percentage
of moisture in the paddy after drying process in order to prevent from too much
breakage during milling process. The device must be easy to use and cost effective.
For this study, factors that can affect the measurement such as sample temperature,
soil mineral and pH value are held constant. Some other factors such as distribution
of moisture in sample, size and density of sample are considered insignificant
to the measurement. The specific measurement range of the detector for this
research is from 20-25% of moisture content before drying and 14% moisture content
In line with the new emphasis to revitalize agriculture sector as the third
engine of growth, Malaysia government allocated a total of RM 11.4 billion in
the 9th Malaysia Plan (9 MP) to implement various agricultural programs and
projects. To develop and modernize the agriculture industry, the government
is focusing on automation, precision farming and implementing various mechanisms.
Rice production is one of the agriculture sectors in Malaysia that play an
important role. The country will be able to achieve self-sufficiency in rice
production provided farmers incorporate the latest farming technologies in paddy
cultivation as mentioned by Oryza (2004).
Also, researches have proved that moisture content in soil also affect the
agricultural process as water is essential in plant growth. Without water, normal
plant functions are disturbed, and the plant gradually wilts, stops growing
and dies. However, Scherer et al. (1996) mentioned
that excessive moisture may lead to destruction of the roots by root rot and
the yellowing of plant leaves.
According to Davis (1944), the optimum harvest moisture
content for the paddy of the Caloro variety was 20-24%. Pominski
et al. (1961), showed that the paddy moisture content had a significant
effect on milling yields of Bluebonner 50 long grain rice. They selected samples
with moisture content ranging from10-14% and concluded that for each 1% decrease
in moisture content, head yields and total yields increased 3 and 0.7% respectively.
As for rice breakage, samples with moisture content of 12-16%, Dilday
(1987) concluded that rice breakage decreased with increased paddy moisture
Afzalinia et al. (2004) found that the paddy
moisture content had a significant effect on rice breakage of the whitener and
the entire miliing system so that the rice breakage decreased with increased
paddy moisture content. As mentioned by Luh (1991), the
minimum total rice breakage occurred at the range of 12-14% moisture content;
therefore this range was optimum moisture content for the paddy and the milling
It was reported by Peuty et al. (1994) that
the paddy drying conditions affected the breakage of rice during the milling
process so that the rice breakage increased rapidly with decreasing moisture
content of the air used to dry the paddy.
MATERIALS AND METHODS
Interviews were done to gather information from the farmers and the MARDI (Malaysian
Agricultural Research and Development Institute) official. Then a survey was
done on the existing devices like moisture analyzer, sensor and software. The
detector circuit is designed and later proceeds with a laboratory experiment
to determine the relationship between voltage and moisture content. The experiment
was based on Gravimetric technique, i.e., removing water from sample to determine
moisture content. For the sample preparation, the procedures of the experiment
are as follow:
||Weigh sample and container in grams
The percentage of moisture content is calculated by equation:
||Wet weight sample in grams
||Dry weight sample in grams
The grain will lose weight due to loss of moisture. To determine the final
weight of grain, it will be:
For instance, to dry 500 grams of paddy harvested at 25%MC and dried down to
14%MC, this will result to:
The method used in determining the moisture content is using the principle
of electrical conductivity. By applying Ohm s Law, wet sample has higher
moisture content and has lower resistance than dry sample. The measured parameters
are the moisture content and voltage relationship.
Interview: According to the farmers that were interviewed, drying of
paddy takes 2-3 days while dryness determination is by using heels or biting
a kernel of paddy. Breakage of rice will occur if the moisture content in paddy
is too high during milling process.
From the MARDI officer, the moisture content of paddy before milling process
is said to be 13% in order to prevent from rice breakage. The price of the existing
devices in the market is very expensive.
The correct moisture content is needed to obtain high yields as it is essential
to mill paddy rice. Paddy is at its highest milling potential when its moisture
content is at 14%. The paddy will be affected whether the moisture content is
too high or too low (Table 1).
Delays in drying of wet paddy cause quality deterioration and discoloration
which will occur within 2-3 days after threshing. Paddy with high moisture content
(>20%MC) must be dried down to 18% which is known as skin dry then to 14%
to preserve milling, cooking smell and eating qualities. The key to post production
is correct timing of operations and grain moisture content.
Moisture detector for paddy: The detector is capable to measure the
moisture content of paddy. The main component used is LM3914, LED dot/bar display
|| Weights of paddy in the experiment
It is a monolithic integrated circuit that senses analog voltage and drives
10 LEDs, providing a linear analog display. It has an adjustable voltage reference
that is divided by series resistors and used as the reference voltages for 10
comparators that drive the LEDs, with their current determined by the load.
The outputs from LM 3914 are grouped together to become only 3 final outputs
which represent red, yellow and green LEDs. It is also acting as the voltmeter
with 10 equal steps and each LED indicated 125 mV across the sample. An 1.2
kΩ resistor is LED brightness controller.
The probes: A pair of probes is used as the sensing element to detect
the moisture content in the sample. This is a pair of steel nails with 7cm.
long and 4mm. in diameter and was chosen as it has good electric conductivity.
The probes are inserted into the substances to measure the electrical resistance/conductance
between them. The probes apply DC current to the sample that is between them
and the LM 3914 displays the resulting voltage. The function of the probes depends
on the nature properties of water. Water contains electrolytes, which are compounds
that ionize in water, and produce a solution that conducts electricity. Wet
sample has higher moisture content which has more ions and be able to conduct
electricity well. By applying Ohm s Law, it has lower resistance compared
to dry sample which has less ions and higher resistance.
Experimental results: Gravimetric measurement technique is used in the
experiment. This is removing of water from the sample. The percentage of moisture
content for dry, medium and wet sample has been set based on the results of
the experiment (Table 2).
The data in Table 3 indicates the initial weight and the
final weight of the paddy used in the experiment in accordance to the target
moisture content of 14, 18 and 20% which were classified as dry, medium wet
and wet sample, respectively.
Three trials had been completed through the experiment. The sample resistance
was calculated based on the circuit configuration. Ten LEDs were used and the
output of the circuits were grouped in order to have the final output of only
3 and these are as follows:
||From 1st -4th LEDs lighted-wet sample-Red on
||From 5th-8th LEDs lighted-medium wet sample-Yellow on
||From 9th-10th LEDs lighted-dry sample -Green on
The Theory of Conductivity was implemented to detect the wetness or dryness
of paddy in order to design a paddy moisture content detector. Gravimetric technique
was applied in the conduct of the experiment in order to calculate the percentage
of moisture content for calibration purposes.
The detector was able to measure the moisture content of paddy. It was shown
that the percentage of moisture content for the paddy was detected using LEDs,
red, yellow and green for wet, medium wet and dry samples respectively. In order
to enhance the accuracy of the detector, further laboratory testing must be
done and also, its usage could be extended to other agricultural products.