Research On Soft Measurement Of Internal Temperature And Relative Humidity In Sealed Packages

The temperature and relative humidity inside sealed packages is important for the quality and safety of products sealed. If the internal situation of the sealed packages can be detected in time, and some steps can be made, then we can reduce the economical loss of the long time stored products. Therefore, to solve the detection of internal relative humidity and temperature inside sealed packages is imperative.The conventional measurement methods of humidity and temperature need to contact the air inside packages, which needs to put the sensors into the packages. The sealed packages do not contain a detect hole, so internal relative humidity and temperature cannot be detected without destroying the packages using the conventional method. Using the soft sensor technology, which is inferential estimation of the unmeasured variables from secondary variables that can be easily detected, can realize the measurement of the internal relative humidity and temperature.This thesis introduces the situation of temperature and relative humidity inside sealed packages and effects on the internal relative humidity and temperature. The temperature and relative humidity was analyzed using soft sensor technology. The mathematical model of relative humidity was established based on the moisture content inside packages, moisture permeation of packaging materials and moisture sorption of packaged products. This model indicates the relationship between the inside relative humidity and the temperature, relative humidity of the sealing up and storing environment. Simulation using MATLAB was also carried out. Simulation results indicate that the temperature and relative humidity of the sealing up environment determines the initial humidity value, the temperature change determines the direction of the humidity curve, and the difference of inside and outside relative humidity determines the slope of the humidity curve. As time goes by, the inside relative humidity asymptotically approaches the outside relative humidity.According to the modeling and the practical experimental condition, a short term experiment project using a regulable temperature and humidity box and a long term experiment project in the storehouse were designed. And the HT-1 temperature& humidity meter was designed. Then a two-month long experiment was carried out in the lab with a simplified metal box. Combining with modeling by mechanism and experience, the temperature and relative humidity models for a special package have been determined.The simulation results and experiment results show the practicability of using soft sensor technology to measure the internal temperature and relative humidity of sealed packages. And they also validate the internal temperature and relative humidity models. To guarantee the quality of products stored, the sealing up environment should have low temperature and humidity, and the packages should be sealed while the storing environment should maintain normal temperature and dryness.