Test Method For Moisture Regain Of Cotton Fiber - Electric Detector Method

Abstract: in this paper, starting from the principle of electrical measuring device, the analysis is made. Regain Several main influencing factors of measurement are presented, and some suggestions to avoid these measurement errors are put forward.

Key words: moisture regain; electric detector method; influencing factors

The national standard "test method of raw cotton moisture regain" GB/T6102.2-2009 was formally implemented in September 1, 2009. The appendix of the standard appendix as the data appendix provides the testing instrument XJ130 for the moisture regain of cotton fibers. The instrument is a more intelligent test instrument for raw cotton moisture regain developed recently. Compared with the previous model Y412B, the instrument has been greatly changed. The main changes are as follows: the measuring voltage of the electric sensor is changed from (360+5) V to DC (90+1); the pressure range of the handle is changed from (735+49) N to (735+30) N; and the temperature and humidity probes are added. The measuring principles and factors affecting the measurement results are briefly analyzed as follows:

One measure principle

The method of electrical measurement is to measure the moisture regain of cotton by means of the relationship between the moisture regain and electrical conductivity of cotton. That is to say, the raw cotton is placed between the two plates of the electrical detector, and the moisture regain of the raw cotton is indirectly determined by the size of the raw cotton current under certain conditions such as the area of the two plate, fiber quality, voltage and pressure.

2 factors affecting test results

According to the measuring principle of the instrument, we can know that there are three main factors that affect the test results, namely, the pressure between two poles, the voltage of the plate, and the quality of the sample.

2.1 the effect of the pressure between the two plates on the test results.

The natural cotton fiber is bulky and the resistance becomes large and unstable. Therefore, a certain mechanical pressure must be applied to keep the tested cotton fiber at a certain density and conduct stability. Because the pressure between two plates determines the density of cotton fiber, if a certain amount of cotton fiber is small, the density will be large and the conductivity will be strong. Otherwise, the volume will be large, the density is small, and the conductivity will be weak. In addition, if the specimen between the plates is placed unevenly, the larger the load is, the better the conductive performance will be. Therefore, the moisture regain value should be greater than that of the uniform plate. During the usual inspection process, cotton samples should be placed evenly to ensure the consistency of the cotton samples between the plates.

2.2 voltage between plates

The voltage difference between the two plates is also different. The higher the voltage, the smaller the resistance of the tested sample. The new voltage is changed from original (360+5) V to DC (90+1). There are two main reasons for its analysis. First, although high voltage will measure a more stable current, it will cause safety hazards in the use process. Two, the voltage between the electrodes is very unstable, and there is a big error in the measurement, which can not reflect the reversion rate of the sample.

Two point three Sample quality

Test method: cotton fiber with different quality was tested in the same environment to observe the influence of the quality change on moisture regain. A total of 11 samples were taken from 40~60g with 2G as the unit of mass change. The test conditions were temperature 20 C and relative humidity 65.6%.

The test results are shown in Table 1.

It is not difficult to see through experiments that the moisture regain measured by 44~56g is more uniform. The reason for analysis is: the density of sample is too small and the pressure is definite, resulting in small current through the plate, and the increase of measurement error. But the specimen is too large. Because the space between the plates is relatively fixed and the pressure is relatively fixed, it is easy to cause unevenness of the sample density and affect the stability and accuracy of the test results. Therefore, in the testing process, the experiment is strictly in accordance with the standard (50 + 5) g to ensure the accuracy and reliability of the experimental data.

2.4 other influencing factors

In addition to the instrument itself and operational factors, the depth of sampling is also one of the important factors affecting its moisture regain. As the inner layer of the cotton bag is less volatile than the outer layer, the moisture regain of the deeper part is more stable according to the tests taken from different depths. This requires us to sample strictly at the cotton bales 10~15cm when sampling.

3 conclusion

Moisture regain is one of the important items of cotton inspection index. It relates to the real weight of cotton, which involves the vital interests of buyers and sellers, and has great influence on storage management and spinning process. Only by being familiar with the testing principle of moisture regain, mastering the testing methods and taking full account of the factors that affect the results, we can achieve a definite goal and accurately measure the true value in the testing process.