Classification of Mainstream Moisture Meters and Characteristics of Each Moisture Meter

At present, the main products of the moisture analyzer industry are chemical moisture analyzer (Karl Fischer moisture analyzer) and physical moisture analyzer (infrared moisture analyzer). Karl Fischer moisture analyzer is divided into Karl Fischer volumetric method and Karl Fischer Coulomb method; infrared moisture analyzer is divided into infrared incandescent moisture analyzer and halogen ring moisture analyzer, which is the characteristics of each moisture analyzer:

A: Chemical Moisture Analyzer 1) Karl Fischer's Volumetric Method Moisture Measurement Principles The Karl Fischer volumetric method is based on electrochemical reactions when determining moisture content:

I2+2eó2I-

When both I2 and I- are present in the solution in the reaction cell, the reaction proceeds simultaneously at both the positive and negative ends of the electrode, ie, I2 is reduced at one electrode and I- is oxidized at the other electrode, thus at two There is current passing between the electrodes. If there is only I-in solution and no I2 is present at the same time, no current passes between the two electrodes.

The Karl Fischer reagent contains active ingredients such as pyridine and iodine, which are metered into the reaction cell and can react with the water in the test solution as follows:

H2O+SO2+I2+3C5H5N→2C5H5N•HI+C5H5N•SO3

C5H5N•SO3 CH3OH→C5H5N•HSO4CH3

C5H5N•HI→C5H5N•H I-

The reaction continues, continuously consuming water, generating I-, until the end of the reaction titration, water consumption is complete. At this time, there was a trace amount of Karl Fischer reagent that did not react, and I2 and I- were present at the same time. The solution between the two platinum electrodes started to conduct electricity, and the current reached the end point and the titration was stopped. The moisture content in the solution is thus calibrated by measuring the volume (capacity) of the spent Karl Fischer reagent.

(2) Measurement principle of the Karl Fischer coulometry (electricity method) The coulometric method is based on the fact that after dissolving a sample in an electrolyte solution containing a certain solvent of iodine, water consumes iodine, but the required iodine is no longer used. Calibrated iodine-containing reagents are used for titration. Instead, the iodide ions in the solution are oxidized to iodine by an electrolysis process:

2I ̄—2e─→I2

The iodine produced reacts with the water in the sample. The end point is indicated by a double platinum electrode. When the concentration of iodine in the electrolyte returned to its original concentration, the electrolysis was stopped. Then according to Faraday’s law of electrolysis:

CMi•t

m=---------×-----=---------

96500n10722

Calculate the moisture content of the sample to be tested.

B: Physical Moisture Analyzer [About Infrared Bulb], consisting of a fused quartz tube and a radiating element. Infrared light bulbs are focused heating for industrial heating or drying, such as glass products, metal parts, circuit board packaging, film, etc. , And other drying, drying, heating, quartz near-infrared, far infrared lamps using transparent or translucent quartz glass as the lamp shell can produce near-infrared radiation lines or far-infrared radiation lines, is a typical ancient heating method, we Ultraviolet lamps are also used to treat certain skin ailments or to get bronzed skin that can be obtained in sunlight when exposed indoors.

In addition, the main component of the physical moisture analyzer is the load cell. The term of the load cell is the heart of the moisture analyzer. The accuracy of the load cell is directly related to the stability and accuracy of the measurement of the moisture analyzer. [Strain Sensor] The strain sensor is based on the A sensor that measures the strain caused by force deformation of an object. The strain gauge is attached to the west and cantilever beam (elastic element). When the measured object moves, the measuring rod moves, and the tension spring extends, so that the cantilever beam is deformed, thereby causing the strain gauge resistance to change. This method can be used to measure force. Physical parameters such as displacement, pressure, acceleration, etc. Its characteristics: simple structure, low cost, light weight, but the accuracy is limited, can not do very high precision;

[Electromagnetic balance sensor] The working principle is to measure the mass of the measured object without measuring the weight of the weight. Instead, it uses the principle of electromagnetic force to balance the gravity of the measured object. The weighing pan is connected with the coil through the bracket connecting rod. In the weighing range, when the gravity of the measured weight acts on the coil through the connecting rod bracket, the direction is upward. At this moment, if there is a current through the magnetic field, the coil will generate an electromagnetic wave. Its characteristics are accurate weighing, reliable, stable performance, strong repeatability, fast and clear display, and an automatic detection system, a simple automatic calibration device, and overload protection.

The ring-shaped halogen lamp ensures that the sample is heated evenly and the operation is simple and accurate. The biggest difference between a halogen ring lamp and an infrared incandescent lamp is that the halogen lamp is filled with some halogen gas (usually iodine or bromine) in its glass case. Its advantages are clean, no accessories, easy installation, and controllable temperature. . The working principle is: When the filament heats up, the tungsten atom is evaporated and then moves toward the glass tube wall. When it approaches the glass tube wall, the tungsten vapor is cooled to about 800 DEG C. and combined with halogen atoms to form a tungsten halide (iodine Tungsten or tungsten bromide). The tungsten halide continues to move toward the center of the glass tube and returns to the oxidized filament. When it is hot, it will be re-decomposed into halogen vapor and tungsten. The tungsten is then deposited on the filament to make up for the evaporated part. Through this regeneration cycle, the useful life of the filament is not only greatly extended (almost 4 times that of the infrared incandescent lamp).