Development Of A Portable Moisture Detector Of The Building Envelope Based On ARM7TDMI

Since the thermal insulation property of building envelope has intimate relations with its energy saving performance, it is essential to have field detection before delivery. The moisture content is an important parameter which has an influence on thermal performance. So it will provide important parameters for thermal insulation property of building envelope, by accurately measuring the moisture content distribution in depth direction of wall.In this paper, based on the properties of building envelope, we proposed a novel detecting scheme: using planar capacitive sensor as the humidity sensor to detect the moisture content, and make a thorough study on related fundamental theory as well as the influence factors of detecting the moisture content of building envelope.The capacitor, field intensity and the depth of penetration of the planar capacitor have been deduced by theoretical analysis and a simulation by Maxwell finite element software was made to lay a theoretical foundation for designing the humidity sensor. Moreover, combined with actual detection situation,cautions and influence factors are studied.Then a group of sensors which have different penetration depth and sensitivity are developed on the precondition that eliminate human influence.For the purpose of little capacitor,high precision,anti-interference ability,this paper designed a electric circuit for testing minimal capacitor.Afterwards, the feasibility of the humidity sensors are verified by lots of experiments. The chromatographic theory is used in the layered experiments. And by analyzing the results, the feasibility and deficiency of the scheme are discussed.Finally, in order to design a portable instrument, LPC2214 which belonged to the series of PHIPLIS's ARM7TDMI embedded chip was adopted as key controlled CPU, and the modules of most little system, conversion of A/D as well as communication agreement are completed. In addition,for the purpose of improving the mutual performance between human and machine, the LCD function was extended to the system. Besides, based on ADS1.2 software development tools, the application subprograms according to each function module have been complied and used to realization the data acquisition, procession and display. The system's function and performance have achieved the expected requirements.