The Measuring Method And System For Determining Moisture Content Of Ultra-dry Powder Material

The study belongs to the research fields of micro-moisture, it is one part of research contents of technology innovation fund project of small and medium enterprises in China "Yunnan flower essential oil, pigment separation and purification technology integration" (08C26215302346). The moisture content of powder material is an important circle for the agency of production, processing and storing. By now the extensively used powder material moisture measurement methods in China basically are the microwave drying method and oven-drying method. But they have the disadvantages, such as long time consuming, too large, and the show of screen not intuitive and so on. In the abroad, the measuring instrument of powder material is not only too expensive, but also it is hard to maintenance, needing to protect nuclear radiation and it is not easy to promotion. Therefore, it is all-important for us to design a steady performance, higher adjustability, lower cost, more exact measurement and easy operating measurement system on moisture measurement of powder material.The objectives of this work are:(1) to research the measuring system for determining moisture content of ultra-dry powder material by capacitance humidity sensor and relative signal and data analysis; (2) to compare moisture content of ultra-dry powder material between humidity sensor and oven-drying.The methods of measurement moisture content of powder material were summarized in this paper at the present. After systematically comparing and analyzing the advantage & disadvantage of the ultra-dry powder materials moisture measurement apparatus in detail, the paper put forward a new testing system of ultra-dry powder material, the system made up by the core of lower sensor 12 bit DAQP-12 data acquisition card and HM1520LF humidity sensor. The system has the merit of speediness, higher presision, easy to carrying and lower cost. The interface PCMCIA of DAQP-12 data acquisition card transmitted the received datas to the computer computational analysis, which is especially propitious to test in the powder material moisture measurement system of field work. HM1520LF (range:0～20%, temperature scope:-40℃～60℃) is suitable to apply to the lower humidity measurement system, and adapt to the ultra-dry powder material (1%～8%) moisture measurement.In this paper, we had completed the selection and construction about the hardware modules of the sensor measurement system. It included HM1520LF lower humidity sensor module, data acquisition card DAQP-12module, human-computer interaction module and power source module and so on.The paper completes the modularization design of the software. The software system can be divided into the following module:The main system program, the conversion sub-program of volt and humidity, and the database configuration dialogue sub-program, which were written based on LabVIWE. The data processing program of excluding alternative singularity with first order defference method and median method and inertia filtering model were written based on Matlab7.0.The paper mades use of the moisture measurement system of ultra-dry powder materials based on virtual instrument mentioned system, and selected seven ultra-dry powder materials to be tested in the experiment respectively. The measured value for one specimen was a raw data sequence of 20～40 raw data sequence collected on single-point from each sample respectively. Then we averaged of the datas after the curve of the raw data sequence, after filtering using excluding alternative singular, was processed by inertia filtering model. Comparing and analyzing the relative error between measurement value and true value accordingly. The result shows that the maximal relative error of moisture content between humidity sensor method and oven-drying method is 2.21% and the average error is 0.79%, both less than 5% (confidence interval 95% for 5 samples). It is showed that the precision of measurement system is acceptable.Innovative points of this paper:it is the first time to study the moisture measurement method and system of ultra-dry powder; it integrated the virtual instrument technology and PCMCIA serial interface technology of DAQP-12 data acquisition card; the system can achieve two kinds of collection methods including timing acquisition and event-driven acquisition; implemented data management by PC and using Access application software to store data for data read and playbacked; adopting the modified first order difference method to replace and alternative the singular value, and acquire the new forecast, so the results can be further pre-oprimal.It is concluded that the humidity sensor may be a powerful tool for determining "the true moisture content" of ultra-dry powder material, as demonstrated for the seven selected powder. Furthermore, the data preprocessing and data secondary processing both play a certain positive role in making the amendments the result of moisture content of powder material, thus it further ensure the reliability and stability of measurement value.