2. What is Moisture ?
● Moisture is simply water diffused in a relatively small quantity.
● Nearly all materials contain at least a diminutive volume of moisture as a component of the
molecular makeup.
● Moisture is given in the mass of materials, however the relative percentage is dynamic and
therefore not constant.
3. What is the moisture content ?
Moisture content can be thought of as the amount of water in a material or substance.
Generally, H2O content is difficult to measure because of the complex intermolecular bonding
properties within the substance matrix.
4. How Does Moisture Impact Materials?
Excessive or deficient moisture content of a substance can adversely impact the physical properties of a material.
Weight, thermal expansion, amalgamation and electrical conductivity can be altered by even a minute presence of
moisture.
Understanding and maintaining the correct moisture content of a material is essential for manufacturing processors and
testing laboratories.
The identification and efficient operation of reliable moisture analysis equipment is an essential component of any
production or laboratory environment.
The thermogravimetric method is universally recognised as an efficient, reliable and cost-effective method for
determining moisture content, and can be utilised in virtually any such environment.
5. Types Of Moisture Measurement
Drying Method
The Karl Fischer method
The dielectric method
The infrared absorption method
Neutron analyzer
The crystal oscillation method
7. The Thermogravimetric Analysis Method
The principle of the thermogravimetric method of moisture content determination is defined as the weight loss of mass
that occurs as the material is heated. The sample weight is taken prior to heating and again after reaching a steady-state
mass subsequent to drying. Various thermogravimetric methods and technologies can be used for sample drying; for
example, the halogen technological thermo-radiation drying method is a universally applicable, highly efficient and
practical test procedure for in-process testing. The thermogravimetric drying process has many advantages, notably this
type of testing is simple and generally does not require high capital investment.
In combining state-of-the-art thermogravimetric drying and halogen heating with highly accurate weighing technology,
for example, the Ohaus MB45 moisture analyser delivers a fast, precise method of completing a wide variety of moisture
analysis procedures. The MB45 is suitable for sampling applications in the food processing, pharmaceutical and chemical
industries, providing loss on drying results for volatile content in powders, pastesand/or liquids.
8. The oven Drying Method
Oven drying methods for moisture determination are commonly used for commercial purposes. The
oven-drying methodology consists of heating by convection with forced or circulating hot air. The accuracy
and moisture range that oven-drying techniques offer is very similar to other thermogravimetric methods.
Primary disadvantages of using oven-drying methods include time and non-portability. For complete and
accurate results with oven drying moisture analysis techniques, the ramp up and soaking times are rather
long. This practice may hinder actual production value with lengthy material quality feedback for quick
decision making at the point of production.
Oven drying techniques are normally implemented away from the actual production area further adding
lag time and ambient changes to the test process. Most oven drying methods do not contain a precision
weighing balance-type instrument to measure and record mass changes. Mass determinations for before
and after measurement recording must be implemented manually by the technician, increasing the chance
for error. Most oven drying methods do not allow the continuous referencing, graphing and recording of
substance mass changes creating a void of data between the test start point and dry state status.
9. The Halogen Drying Method
Method-The technology of halogen drying is an excellent method for moisture content determination. Halogen
moisture analysis can be used for determining the moisture content of virtually any substance. The technology uses a
halogen radiator in conjunction with an integrated precision balance for detection, measurement and recording of
sample weight during H2O vaporisation from the test procedure.
Halogen drying is up to twice as fast as traditional infrared technology (drying time may vary depending on
substance type). Halogen radiators are more responsive in heating and cooling requirement cycles than infrared
heaters; the accelerated responsiveness saves actual test cycle time . Halogen operating advantages are more
efficient than other methods because of the technology of small intense heating elements used as the substrate for the
thermo radiator. The glass sheath design encases the inert halogen gas for quick heat conduction, full heating power
can be reached within seconds of the test start.
Halogen and infrared drying methods both operate with similar accuracy. Generally, if testing parameters of the
manufacturer are followed, accuracy levels of 0.1 per cent to 0.5 per cent can be attained. The moisture test range for
both methods ranges from 0.5 percent to 99 percent of the sample substance.
10. Karl Fischer Method of Moisture Detection
Karl Fischer Titration is a technique for the determination of moisture content. The technique was
developed by a chemist named Karl Fischer. It is based on a reagent which reacts with water and
converts the water into a non-conductive chemical. Karl Fisher provides for the specific detection of
water content in a product.There are two methods used to perform the Karl Fischer titration test.
(1) Volumetric Karl Fischer
(2) Coulometric Karl Fischer.
11. Coulometric Karl Fischer
In this approach, the reagent and solvent are combined in the titration cell. When a sample is
introduced into the titration cell and dissolved, reagent is released by the induction of an electrical
current. The amount of current required to convert the water is the determinant of the amount of
moisture. Coulometric Karl Fischer instrument is often referred to as a coulometer.
The advantage of Coulometric Karl Fischer method is the capability to accurately measure small
amounts of moisture. Sensitivity of these instruments is as low as 0.1 microgram (µg) of water. This
method is normally used for moisture content below 1% or for samples where the moisture is less
than 200 micrograms.
12. Volumetric Karl Fischer
With this method, the moisture determination is based on the amount, or volume, of reagent used to
convert the water. In the Volumetric Method, samples are dissolved in a solvent before the titration
begins. A reagent is added until the water is removed.
The volumetric method is ideal when working with samples containing higher levels of moisture
(generally over 1% or 2%) but also when samples may contain ketones and or aldehydes.
13. The Dielectric Method
The emergence of high value differentiated products demands even greater moisture measurement accuracy and
uniformity and presents new challenges.Moisture content is one of the most critical grain quality measurements
because of the dielectric economic significance of the fraction of the total product weight that is water and because
moisture content largely determines the rates at which the grain will degrade during handling and storage Because of
its significance moisture content is measured and used to compute the price virtually every time grain is sold.
The radio frequency dielectric method measure moisture content in grain by swensing the dielectric constant of grain
samples.The RF dielectric method presents an attractive model relatively simple calibration development,and
moderate manufacturing cost
14. RF Methods
This method relies on the relatively high dielectric of water relative to most solids.
Numerous techniques have been developed to determine dielectric, including radio frequency, microwave,
and time domain reflectometry. In order to measure the relative dielectric of a material it is necessary to
electrically couple the material to the sensing circuit. This may be done by placing the material between two
parallel electrodes, but this does not lend itself readily to online application. If the sensing circuit operates at
radio frequency, it is fairly simple to propagate RF energy through the material and thus couple to the product
without physical contact. Planar fringe field electrodes provide a single-sided measurement structure less
obstructive to the process.
The electrical analogy of a solid product is a capacitor in parallel with a leakage conductance. These
components are both influenced by moisture, but whereas dielectric is related in a very predictable manner,
the loss factor is not. The combined components represent a complex impedance which can be easily
measured, but which may be influenced by variables other than just moisture.
15. True dielectric moisture instruments are rare, since most of the low cost instruments make no
attempt to separate the dielectric and loss components. The lowest cost instruments make little or
no attempt to even measure the combined impedance with any long-term stability and
repeatability. The Sensortech Systems Dielectric Measurement Technique is refined to the extent
where the two components are completely isolated and can be measured independently. The
patented resonant frequency principle improves accuracy and repeatability.
● It is a penetrating measurement and can be measure non-homogeneous products.
● It has a large measurement area that provides a more representative, bulk average
moisture for the product.
● It is relatively inexpensive compared to other online techniques.
● It is very reliable and robust, with no moving parts to wear or break down.
● The various mechanical sensor designs suit a wide range of process conditions and can
be used in high temperature environments.
16. The IR technic
The near infrared reflectance, NIR or IR, technique is a widely used technology for online moisture testing. Its
popularity is due in large part to the ease with which it can be applied.
A light source (typically quartz halogen bulb) is collimated and filtered into specific wavelengths. The filters,
mounted in a rotating wheel, chop the light into a series of pulses of specific wavelength. The filtered beam is
directed onto the surface of the product to be measured. A portion of the light is reflected back to a detector
(usually lead sulfide). Specific wavelengths of light are absorbed by water. If the filters are chosen such that
one wavelength will be absorbed by water (sample beam) and one wavelength will be unaffected by water
(reference beam), then the amplitude ratio of the two reflected wavelengths will be proportionate to the amount
of water in the product. The ratio technique eliminates effects of product distance and source aging.
● Ease of application. Typically mounted 6 to 10 inches above product. Moderate product height
variations have little influence on measurement.
● Small spot measurement area in conjunction with scanning frame provides product profile.
● Specific wavelengths may be chosen to measure variables other than moisture.
17. Neutron Moisture meter
A Neutron moisture meter is a moisture meter utilizing neutron scattering. The meters are most
frequently used to measure the water content in soil or rock. The technique is non-destructive, and is
sensitive to moisture in the bulk of the target material, not just at the surface.
Water, due to its hydrogen content, is an effective neutron moderator, slowing high-energy neutrons.
With a source of high-energy neutrons and a detector sensitive to low-energy neutrons , the detection rate
will be governed by the water content of the soil between the source and the detector. The neutron source
typically contains a small amount of a radionuclide. Sources may emit neutrons during spontaneous
fission, as with californium alternatively, an alpha emitter may be mixed with a light element for a nuclear
reaction yielding excess neutrons, as with americium in a beryllium matrix.
