| Safety incidents such as gas explosion and leakage of gas such as CO occur frequently under coal mine,and endanger people's lives and property.At present,detection instruments for flammable gas such as CO and CH4 are mostly developed by the infrared absorption spectroscopy technology,the core of the detection instruments are infrared light sources,infrared detectors and other semiconductor devices.The temperature is very important of infrared light source.The changes of temperature directly affect the accuracy of gas detection.Therefore,the development of high performance semiconductor device temperature control system is the key to the gas detection system.This paper designed a temperature control system for CO and CH4 gas detection using semiconductor laser and infrared LED semiconductor light emitting devices.It can be used for the temperature control not only of semiconductor light emitting devices with built-in thermoelectric cooler?TEC?,but also of those without thermoelectric cooler and thermistor over a wide variation range of ambient temperature.Firstly,this paper introduced the principle of infrared absorption spectroscopy technology and the derivation of the formula of Beer-lambert law detailedly.At the same time,described the principle of PID controller and its parameter setting method,and analyzed the reason of choosing the integral-limited digital PID algorithm.Secondly,a semiconductor device temperature control circuit for infrared gas detection was designed.Different driving modes of TEC were designed for semiconductor devices with or without TEC.The hardware part consisted of two parts.The first part realized the temperature control of the built-in TEC semiconductor device,and consisted of the main controller,the temperature acquisition circuit,and the TEC current control circuit.The second part realized the temperature control of semiconductor devices without TEC,which consisted of the auxiliary controller,temperature acquisition circuit,MOS switch circuit and four stage TEC.In addition,key circuit,serial port communication circuit and LCD circuit were designed to facilitate human-computer interaction.Thirdly,this paper introduced the software part of the system,mainly including:main program,A/D acquiring program,D/A outputting program,PWM waveform generation program,integral-limited PID control program,interrupt program and other programs,and designed the upper computer by LabVIEW.Finally,the experiments were carried out to verify the performance and reliability of the developed temperature control system.Using the developed temperature control system,the temperature control accuracy of a semiconductor laser with a built-in TEC is±0.01?,the response time is less than 1 s,and temperature stability reaches 0.0048?;The temperature control experimental results of a semiconductor source without TEC show that the temperature control accuracy are respectively±0.05?,±0.01?,±0.02?at an ambient temperature of-18?,room temperature and 40?.The output spectrum of a 1.563?m laser is measured continuously for 5hours by the developed temperature controller,which generates a stable peak wavelength.1.653?m laser is used to carry out methane gas detection experiments with the developed temperature control system and commercial temperature control system respectively.Compared with the commercial controller,the concentration fluctuation range of the temperature controller developed in this paper is smaller,and the lower limit of detection is obtained. |
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