DMM B18 Manual
(English)
JULY 2022
Page
3
1.
INTRODUCTION
1.1
Principle:
DMM B18 digital moisture meter works on the radio-frequency (RF) dielectric method. This method
measures moisture content in sample by sensing the dielectric constant of the sample. The dielectric constant
is a measure of a material’s ability to store electrical charge when placed in an electric field. Because of its
molecular structure, water has a very high dielectric constant (approximately 80) compared to other grain
constituents (2 to 3). The RF dielectric method is influenced significantly by grain kernel structure and
composition, moisture distribution within kernels and grain temperature, necessitating individual calibration
equations for different grain types.
1.2
Calibration method:
DMM B18 digital moisture meter is calibrated using a standard process. This calibration process consists of
determining individual calibration equation by establishing a co-relation between the measured dielectric
constant of the sample and the standard reference method. The standard reference methods used are Oven
Drying Method and Toluene method (Dean-Stark) as applicable for the sample. The calibration equation
compensates the temperature variation of the sample too.
I.
The Oven Drying Method: References for the standard methods used:
ISO 712: 1998 : Cereal and cereal products :Determination of moisture content - Routine reference
method
IS 4333(part 2) : 2002 (Reaffirmed in 2012) : Method of analysis for food grains, Determination of
moisture content
Method
: The sample is ground after pre conditioning. It is dried in a preheated oven at a temperature
of 130
0
C+/- 3
0
C for 2-3 hrs till constant weight of the sample is achieved.
ISO 6540 : Maize-Determination of moisture content in milled grains and whole grains
Method
: The sample is ground after pre conditioning. It is dried in a preheated oven at a temperature
of 130
0
C+/- 3
0
C for 4 hrs till constant weight of the sample is achieved.
ISO 665: 2002 - Determination of moisture and volatile matter for oilseeds
IS 3579-1966 (Reaffirmed in 2000): Method of test for Oilseeds.
Method
: The sample is ground after pre conditioning. It is dried in a preheated oven at a temperature
of 103
0
C+/- 2
0
C for 6-7 hrs till constant weight of the sample is achieved.
II.
Distillation Method (The Dean and Stark) : References for the standard methods used:
ISO 939-2021: Spices and condiments- Determination of moisture content
Method
: A known weight of sample is placed in a flask with an organic solvent toluene which is
insoluble with water and has higher boiling point and less density than water. This flask is attached to
a condenser and the mixture is heated. The water in the sample evaporates and moves up into the
condenser where it is cooled and converted back into liquid water, which then trickles into the
graduated tube. When no more water is collected in the graduated tube (this process takes around 1
hr), distillation is stopped and the volume of water is read from the tube. This water is directly
proportional to the moisture content in the sample.
