Principle of Loss-on-Drying Moisture Analyzers

Loss-on-drying, also called the heated weight-loss method, is a physical method for determining moisture: heating drives off and dries out the water in the material. The traditional and most common approach is the oven method — the sample is dried in an oven, weighed on an electronic balance before and after, and the moisture value calculated by hand. One sample takes 2–4 hours to test this way; for fast-paced manufacturers the oven method seriously drags down production efficiency and no longer meets their needs.

Halogen heating technology heats up 40% faster than the conventional infrared heating technology on the market

Against this backdrop, VicoMeter moisture analyzers use a highly efficient drying heater — a premium ring halogen lamp (far-infrared fast moisture analyzers use a far-infrared dark-field heater) — to heat samples in place of the traditional oven, heating quickly and evenly. The VicoMeter loss-on-drying fast moisture analyzer integrates and upgrades the oven-drying method, perfectly combining the heating, weighing, operation, and intelligent human-machine modules. The system stops intelligently based on the determination trend, analyzes the sample's moisture, and displays the result directly on screen — one-touch start delivers reliable results consistent with the oven method. A typical sample takes only minutes, far more efficient than the oven method, and these analyzers are widely favored and well reviewed by industrial users.

Principle and Development of Karl Fischer Moisture Analyzers

Proposed by Karl Fischer in 1935, this volumetric method is the most specific and accurate for water—now the standard method for many substances.

Its titration and coulometric forms suit many inorganic and organic compounds—the globally recognized classic for rapidly determining moisture in liquids, solids, and gases, widely used in petroleum, chemicals, power, pharmaceuticals, pesticides, and research.

Beyond a good instrument, check for interferences, size samples properly, and operate carefully. In 1935 Karl Fischer proposed the volumetric (visual) method of GB6283 for colorless liquids; the electrolytic method followed, and combining the coulometer with volumetric analysis produced the coulometric method of GB7600. Karl Fischer thus divides into volumetric and coulometric branches, both standard methods for calibrating other methods and instruments.

Moisture Reaction Principle

When iodine oxidizes sulfur dioxide, a certain amount of water participates in the reaction: I₂+SO₂+2H₂O=2HI+H₂SO₄ The reaction is reversible; an alkaline substance must be added, and the reagent must include methanol or another solvent with active OH groups so pyridine sulfuric anhydride converts into stable methyl sulfuric acid pyridinium hydrogen.

In KF coulometric titration, the required iodine is generated directly by electrolysis; water content is calculated from the charge-iodine relationship. When free iodine appears, the voltage across the Pt indicator electrodes drops sharply—marking the endpoint.

Electrolysis Reaction (Faraday's Law of Electrolysis)

During electrolysis, the electrode reactions are:

Anode: 2I--2e→I₂

 Cathode: I₂+2e→2I- ，2H++2e→H₂↑

From the above, 1 mol of iodine oxidizing 1 mol of sulfur dioxide requires 1 mol of water. Electrolyzing 1 mol of iodine requires 2×96493 C (Faraday constant 9.6493×10000 C/mol), consuming 18 g of water.

From Faraday's law of electrolysis, M×10-6/18=Q×10-3/2*9.6493, so M=Q/10.722

Where: W--moisture content (μg); Q--electrolysis charge (mC); 18--molecular weight of water.

Principle of Online Near-Infrared Moisture Analyzers

O-H bonds in water and C-H bonds in organics absorb NIR light at specific wavelengths; reflected energy is inversely proportional to absorbing molecules. The analyzer tracks NIR energy changes at a specific wavelength based on water's absorption.

Water molecules vibrate at specific energy bands—O-H bonds stretching, contracting, twisting. NIR bands are especially strong for water and easy to generate, filter, and detect; moisture-measuring wavelengths stay within 1-2.5 μm.

Absorption depends on water molecules encountered and absorption strength—proportional to moisture. As a reflectance method it is also affected by the material's reflectance and absorption; NIR measurement is non-destructive, non-contact, and real-time.

Working Principle of Online Near-Infrared Moisture Monitoring Systems

Multiple NIR beams focus onto the material surface; reflected beams are received by an advanced optical detection system with an embedded high-performance DSP chip for fast processing, storage, and display—outstanding accuracy and stability.

Many materials absorb infrared at specific wavelengths only; at least two are selected—a reference wavelength (not absorbed by material or water) and a measurement wavelength (absorbed by water only).

Precision filters on a rotating wheel pass reference and measurement pulses alternately onto the sample; the two timed pulses reflect to a detector as two signals. The reference shows expected reflection; the measurement is attenuated by water absorption. Combined into a ratio, differences from other moisture levels are proportional to moisture differences.

The signal strengths of the two channels combine into: R/M X M1/R1=ratio

Where: R--reference channel of the product beam

M--measurement channel of the product beam

M1--measurement channel of the compensation beam

R1--reference channel of the compensation beam

If drift occurs, M and M1 shift equally, canceling out in the ratio and preserving stability.

Principle of Online Microwave Moisture Analyzers

Microwave attenuation and phase shift depend on the medium's dielectric constant and loss tangent—far higher for polar water than ordinary media. Moisture is calculated from received attenuation and phase shift.

Because microwaves penetrate the process material completely, all physical moisture is measured—not only surface moisture but also internal moisture. This technology ensures very high measurement accuracy and precision, and the material's color and surface structure do not affect the results. It can be widely applied to coal, sinter (pellet) mixtures, iron ore, chemicals, bauxite, nickel ore, sugar, tobacco, bagasse, grain, silicon, wood, wool, papermaking, sand, polymers, cotton and other non-conductive materials.

A Detailed Look at Online Microwave Moisture Analyzers

The probe measures 150-200 mm deep, analyzing total (core and surface) moisture; deep penetration means surface dirt does not matter.

The variation of relative permittivity is the key principle; simply:

Water's εr≈80 versus ~1-10 for most materials (sand/gravel 3-4)—a large measurable difference.

Moisture is measured directly from this difference and output as a mass-percentage standard signal.

In other words: the more water a material contains, the closer its relative permittivity εr approaches 80.

Signals are obtained as material passes the sensor—even on fast lines; stationary bulk materials can also be measured.