Principles of 5 Common Moisture Measurement Instruments

Moisture measurement can be industrial production control analysis, or quality inspection of industrial and agricultural products; moisture can be measured from tons of product, or only a few microliters of test solution can be used in the laboratory for moisture analysis; it can be water content. A constant moisture analysis of several to several tens of percent, or a trace moisture analysis with a moisture content of only one millionth or less.

Water analysis methods can generally be divided into two major categories, namely physical analysis and chemical analysis. Classical moisture analysis methods have gradually been replaced by various moisture analysis methods. Currently, there are mainly five types of moisture analyzers currently on the market1. Karl Fischer moisture analyzer:

The Karl Fischer method, which is referred to as the Fischer method, is a volumetric separation method for measuring moisture content proposed by Karl Fischer in 1935. The Fischer method is the most specific and accurate method for determining water in various types of chemical methods. Although it is a classical method, it has been improved in recent years, improving accuracy and expanding the measurement range. It has been listed as a standard method for determination of moisture in many substances.

The Fischer-Tropsch method is an iodometric method. The basic principle is that when oxidizing sulfur dioxide with iodine, the need for quantitative water to participate in the reaction:

12 Ten S02 Ten 2H2O=2HI Ten H2SO4

The above reaction is reversible. In order to move the reaction in the positive direction and quantitatively, basic substances must be added. Experiments have shown that pyridine is the most suitable reagent, while pyridine also has the ability to combine with iodine and sulfur dioxide to reduce the vapor pressure of both. Therefore, the reagent must be added to methanol or another solvent containing a reactive OH group to convert the pyridine anhydride pyridine to a stable methyl bisulfate.

2. Infrared moisture meter:

Infrared heating mechanism: Absorption, reflection, and transmission occur when far-infrared radiation is radiated to an object. However, not all molecules can absorb far-infrared radiation, and only those polar molecules that show electricity can work. Water, organic substances, and high molecular substances have a strong ability to absorb far-infrared rays. When these substances absorb the far-infrared radiation energy and make its molecules, the frequency of natural vibrations and rotations of atoms coincide with the frequency of far-infrared radiation, molecules or atoms are likely to resonate or rotate, resulting in greatly increased movement and conversion into The heat energy raises the temperature inside, so that the substance is quickly softened or dried.

The general heating method is the use of heat conduction and convection, the need to spread through the media, slow speed, high energy consumption, and far-infrared heating is the use of heat radiation, without media transmission. At the same time, since the radiant energy is proportional to the fourth power of the heating element, it not only saves energy, but also has high speed and high efficiency. In addition, far-infrared rays have a certain penetrating power, because the heated and dried substance absorbs far-infrared radiation energy at a certain depth and at the same time, and generates a self-heating effect, so that the solvent or water molecules evaporate, and the heat is even, thereby avoiding Deformation and qualitative change due to different degree of thermal expansion, so that the appearance of the material, physical and mechanical properties, fastness and color, etc. remain intact.

Infrared moisture analyzers are mainly determined by infrared radiation heaters and electronic balances for their accuracy and stability.

(Infrared radiation heater: tungsten wire vacuum tube can radiate near-infrared rays, silicon carbide is a long-wavelength far-infrared radiation heater, quartz glass and ceramic infrared heaters can radiate mid-infrared rays)

Infrared Moisture Analyzer The "dry reduction method" of the well-known standard measurement method of the moisture measurement standard is very similar to an infrared moisture meter of heat drying and mass measurement. The "dry reduction method" of the accepted standard method is also called (105 °C for 5 hours), (135 °C for 3 hours), and the like, and the sample is dried in a dryer for a long time. To accurately determine the mass change before and after drying, the water content was calculated. For this reason, the measurement personnel need to be very proficient in equipment and technology. Since it takes a long time for the measurement, it is difficult to quickly measure a large number of samples. Therefore, for the measurement of a wide variety of samples with a high degree of accuracy, it is not necessary to do so except for an infrared moisture meter. Although there are some other electrical and optical measurement methods, they are all special instruments that limit the measurement object. In terms of versatility, they are far less than infrared moisture meters.

Scope of application: It can measure food-related articles such as cereals, starch, flour, dry noodles, brewed goods, seafood, processed fish products, processed meat products, seasoning, noodles, hearts, dairy products, dried foods, vegetable oils, and pharmaceuticals. , ore sand, coke, glass raw materials, cement, chemical fertilizers, paper, pulp, cotton, all kinds of fiber and other industrial products.

3. Dew point moisture meter:

The dew-point moisture analyzer is easy to operate, the instrument is not complicated, and the measured results are generally satisfactory. It is often used for the determination of trace moisture in permanent gas. However, this method interferes more. Some cold-changeable gases, especially at higher concentrations, interfere with condensation than water vapor.

4. Microwave moisture meter:

The microwave moisture analyzer uses a microwave field to dry the sample to accelerate the drying process. It has the characteristics of short measurement time, convenient operation, high accuracy and wide application range. It is suitable for grain, paper, wood, textile and chemical products, etc. The determination of moisture in powdered and viscous solid samples can also be applied to the determination of moisture in petroleum, kerosene and other liquid samples.

5. Coulomb moisture meter:

Coulomb moisture meters are often used to determine the moisture content of gases. This method is easy to operate, quick to respond, and especially suitable for the determination of trace moisture in gases. If you use ordinary chemical methods, it is very difficult. However, electrolytic methods are not suitable for the determination of alkaline substances or conjugated diolefins.