Design Of Protable Detector For Formaldehyde On Site

Formaldehyde is the main indoor air pollutants, seriously affecting people's health. Currently the method of detection of formaldehyde have disadvantages as testing a long cycle, the operation is not convenient, equipment bulky and expensive and so on. Formaldehyde-site of the main detector electrochemical sensor detection principle, detection accuracy is not high, susceptible to environmental influences. The topic for the lack of conventional detection of formaldehyde and the current domestic market needs, design a high precision and low cost, to achieve on-site detection of formaldehyde analyzer.This study is the concentration of formaldehyde in indoor air testing of the various principles and methods of operation, site-specific detector features, select the phenol formaldehyde reagent spectrophotometric detection principle, based on the proposed light-emitting diodes with a fixed wavelength and the corresponding photo detector circuit replace the laboratory complex optical system design, the design module manipulation to constant gas sampling and analysis modules into one, to achieve on-site inspection.This paper is designed according to principles of formaldehyde detection detector system structure. Modular hardware design, the optical detection module, constant current gas sampling module, A/D converter module, interactive modules and MCU external circuit module, of which optical detection module and the constant gas sampling module is the key point. This paper introduces the basic principles and structure of photoelectric detection, compared to selected photoelectric detector and the integrated operational amplifier, research design applicable to the detection of formaldehyde photoelectric detector preamplifier circuit.According to the design of hardware and software modules the same sampling design, the main program and the interruption subprogram. Routines, including data collection and storage routines, constant gas sampling subroutine, human-computer interaction and data processing subroutine subprogram. Gas sampling subroutine in CC Fuzzy PID algorithm to control the vacuum pump to improve the accuracy of gas sampling.Upon completion of the instrument hardware and software design, based on this paper focuses on the formaldehyde content in correspondence with the photoelectric conversion data curve fitting method of least squares method and the interpolation algorithm and application characteristics of the structure. Formaldehyde content according to a linear relationship with absorbance was linear piecewise interpolation method, interpolation method for defects, to optimize its fuzzy math, that fuzzy interpolation method, while ensuring the accuracy of calibration points to reduce and simplify online calibration operation process.