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Principles of 5 Common Moisture Measuring Instruments

Date:2020-08-04

Moisture Analyzer Manufacturer shares this article with you.

Halogen moisture analyzer

1. Karl Fischer Moisture Analyzer:

The Karl Fischer method is abbreviated as the Fischer method, which is a volumetric separation method for measuring moisture proposed by Karl Fischer in 1935. The Fisher method is the most specific and accurate method for water among all kinds of chemical methods for determining the moisture of a substance. Although it is a classic method, it has been improved in recent years to increase the accuracy and expand the measurement range. It has been listed as a standard method for the determination of moisture in many substances.

The Fischer method is an iodometric method, and its basic principle is that when iodine is used to oxidize sulfur dioxide, a certain amount of water is required to participate in the reaction:

I2 ten SO2 ten 2H2O=2HI ten H2SO4

The above reaction is reversible. In order to move the reaction in the positive direction and proceed quantitatively, an alkaline substance must be added. Experiments have proved that pyridine is the most suitable reagent, and pyridine can also combine with iodine and sulfur dioxide to reduce the vapor pressure of the two. Therefore, the reagent must be added to methanol or another solvent containing active OH groups to convert sulfuric anhydride pyridine into stable methyl hydrogensulfate pyridine.

2. Infrared moisture meter:

Infrared heating mechanism: When far infrared rays are radiated to an object, absorption, reflection and transmission can occur. However, not all molecules can absorb far-infrared rays, only those polar molecules that exhibit electricity can work. Water, organic substances and polymer substances have a strong ability to absorb far infrared rays. When these substances absorb the energy of far-infrared radiation and make the natural vibration and rotation frequency of molecules and atoms consistent with the frequency of far-infrared radiation, the resonance or rotation of molecules and atoms is extremely prone to occur, causing the movement to be greatly intensified and converted into The heat energy raises the temperature inside, so that the substance is quickly softened or dried.

The general heating method uses heat conduction and convection, which needs to be propagated through a medium, which is slow and consumes a lot of energy, while far-infrared heating uses heat radiation without medium propagation. At the same time, because the radiant energy is proportional to the fourth power of the temperature 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 penetration ability. Because the heated and dried material absorbs far-infrared radiation energy at a certain depth at the same time as the surface molecules, it produces self-heating effect, so that the solvent or water molecules evaporate and heat evenly, thus avoid The deformation and qualitative changes caused by different thermal expansion degrees keep the appearance, physical and mechanical properties, fastness and color of the material intact.

Moisture Analyzer

Moisture Analyzer

Infrared Moisture Analyzer is mainly determined by infrared radiant heater and electronic balance to determine its accuracy and stability.

Infrared radiation heater: Tungsten filament 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.

The infrared moisture meter is an infrared moisture meter that is very similar to the infrared moisture meter for heat drying and mass measurement, which is the "dry loss method" of the recognized standard measurement method for moisture measurement. The "dry loss method", which is a recognized standard measurement method, is also called (105°C 5 hours method), (135°C 3 hours method), etc. The sample is placed in a dryer and heated and dried for a long time. To accurately measure the mass change before and after drying, to calculate the moisture content. To this end, the measurement personnel are required to be very proficient in equipment and technology. Because the measurement takes a long time, it is difficult to quickly measure a large number of samples. Therefore, for high-accuracy measurement of a wide variety of samples, no other thoughts except infrared moisture meter. Although there are some other electrical and optical measurement methods, they are all dedicated instruments that limit the object of measurement. From the perspective of versatility, they are far inferior to infrared moisture meters.

Infrared radiation heater: Tungsten filament 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.

The infrared moisture meter is an infrared moisture meter that is very similar to the infrared moisture meter for heat drying and mass measurement, which is the "dry loss method" of the recognized standard measurement method for moisture measurement. The "dry loss method", which is a recognized standard measurement method, is also called (105°C 5 hours method), (135°C 3 hours method), etc. The sample is placed in a dryer and heated and dried for a long time. To accurately measure the mass change before and after drying, to calculate the moisture content. To this end, the measurement personnel are required to be very proficient in equipment and technology. Because the measurement takes a long time, it is difficult to quickly measure a large number of samples. Therefore, for high-accuracy measurement of a wide variety of samples, no other thoughts except infrared moisture meter. Although there are some other electrical and optical measurement methods, they are all dedicated instruments that limit the object of measurement. From the perspective of versatility, they are far inferior to infrared moisture meters.

Scope of application: It can measure grains, starch, flour, dried noodles, brewed products, seafood, processed fish products, processed edible meat products, spices, points, hearts, dairy products, dried foods, vegetable oils and other food-related items, medicines , Ore sand, coke, glass raw materials, cement, chemical fertilizers, paper, pulp, cotton, various 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 gases. However, this method has a lot of interference, and some easy-to-cold exchange gases will condense before water vapor and cause interference, especially when the concentration is high.

4. Microwave moisture meter:

The microwave moisture analyzer uses the microwave field to dry the sample and accelerates 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, textiles and chemical products. The determination of moisture in powdery and viscous solid samples can also be applied to the determination of moisture in petroleum, kerosene and other liquid samples.

5. Coulomb moisture meter:

Coulometric moisture analyzers are commonly used to determine the moisture in the gas. This method is simple to operate and quick to respond, and is especially suitable for the determination of trace moisture in gas. If it is determined by a general chemical method, it is very difficult. But the electrolysis method is not suitable for the determination of alkaline substances or conjugated diolefins.