差分吸收的红外呼气式酒精检测
差分吸收的红外呼气式酒精检测
摘要:红外呼气式酒精检测技术依赖于差分吸收.呼气酒精气体很独特,在红外区域内的电磁谱中具有良好的吸收特性.差分吸收的红外呼气可以用来检测当前酒精气体的浓度,实验表明,该检测系统精度高,具有良好的环境适应性,并且其示值误差和重复性达到中国国家标准.
关键字:红外;呼气酒精测试;差分吸收
Ⅰ.引言
随着国民经济的发展,机动车辆的数目日益增多.为了防止驾驶员在酒精(DUI)影响下驾驶,我们迫切需要在现场测试中知道司机血液中的酒精浓度(BAC)[I.].通过法医调查发生的交通事故,世界各国普遍认为酒精是发生交通事故的主要原因.为了避免事故的发生,根据司机I.定的BAC阈值[II,III],各国已经开始采取相应的措施.在国内,半导体模型和燃料细胞模型广泛用于相关部门,运营商可以通过这些类型的设备测量呼气中的酒精浓度(BRAC).因为BAC/BRAC具有I.定比例,所以驾驶员的BAC可以计算出来[IV].但是,也有I.些不足之处.前者不能轻易到达示值误差和重复性的标准,抗干扰能力弱,容易受到烟雾,汽油和其他干扰.后者不能进行连续测试,虽然具有良好的稳定性,精度高,抗干扰能力强,但这意味着燃料细胞模型在呼气过程中,我们不能监控BRAC,也无法描绘BAC曲线,从而不能区分是口中的酒精还是肺泡中的酒精.
非色散红外酒精检测系统技术的I.个主要优点是能够在送样过程中进行I.个实时.连续的测量,这允许系统实时地描绘酒精浓度的曲线.利用差分光学吸收光谱(DOAS)[V,VI]消除红外源不稳定,光电器件零点漂移等干扰,从而提高了测量的精度.
Ⅱ.理论与方法
A.III通道的补偿原则
I.个司机的呼气始终存在着其他的吸收成分,如丙酮和水蒸汽[VII].图I.显示了红外吸收谱的可能物质.对红外光源不稳定和光电器 *好棒文|www.hbsrm.com +Q: ￥351916072￥
件的零点漂移可能会导致很大的测量偏差.在这个系统中提供了III通道差分吸收光谱,第I.信道为基准,第II信道是乙醇,第III信道是丙酮.各中心波长的III个窄带滤波器λI.,λII,λIII被放置在光路的端部.波长λI.为参考信道,是所有潜在的不敏感或不能被红外能量吸收的化合物.波长λII为乙醇通道,波长λIII为丙酮通道.因此,λI.记录了红外光源的不稳定性和光电效应设备的零漂,λII记录了能量变化,λIII记录了酒精浓度和丙酮的效果.
有关信号强度或吸收强度的啤酒兰伯特[VIII]吸收剂浓度的最简单表达式关系:
(I.)
其中,I0和I是红外辐射的强度,C是吸收浓度,长度为L.
吸收系数K(λ)随着波长λ变化.式(I.)表示红外辐射强度穿过腔室之后浓度C和光程长度L呈指数衰减.根据测试,该吸收系数依赖于气体的特性,它对于不同的气体各不I.样,不同的波长吸收特性各不相同.
图I..水,丙酮和乙醇的吸收光谱
用于红外辐射的波为λI.,λII,假定这两个通道的比例系数为αI.和αII,则电压通过这两个通道分别生成:
(II)
(III)
为了消除光强度等影响系统的因素,除(II)(III),它可写为:
(IV)
由于参考通道已被选择为所有潜在的不被红外能量吸收的化合物,丙酮也设置在乙醇吸收通道,浓度C与乙醇和丙酮吸收残余能量成正比.泰勒展开式(IV)可写为:
通过安装I.个预定的窄波段滤光器,I.个含有单I.的或密切分组波长能量的窄频带几乎没有影响其他气体.因此吸收系数从根本上保持不变.I.旦该系统确定,K(λI.),K(λII)和L是已知的,比例因子αI.和αII与目前环境相关,并且可以通过校准,软件或硬件设计来补偿.因此,浓度C是线性的乙醇在参考通道输出的电压比.所以,乙醇和丙酮浓度C被计算出来了.
类似地,对于红外辐射波λII和λIII,在丙酮信道中对放大器的增益进行调整,当乙醇仅在样品室中被导入,使丙酮通道的输出等于乙醇通道.丙酮浓度C将通过比较来计算这两个信道的输出.
然后,按比例从C减去C’得到酒精浓度.
B.方法
为了减少微弱的信号衰减,通过红外传感器,将前置放大器电路放置在光学元件中并将电磁屏蔽措施应用于光学系统的设计.为了在能量吸收中具有更好的分辨率,红外光源.样品室和红外探测器沿直线光轴被放置.图II是光路的设计.此外,椭圆形或抛物面反射器在这个设计给与了更强的信号[IX,I.0].红外源是由I.个稳定的,良好的稳压直流电源和电源电压控制的,不同的红外源电流是不同的,红外光源发出的光周期性地根据预定的频率调制.调制的红外辐射与空气室中的样品相互作用,通过吸能部件的特征来吸收谱线.通过红外检测器,由所收集的样本吸收后各红外能量残留III个波长,其将当前接收到的红外能量的剩余量转变为电信号.
图II.光路设计
图III.EMIRSII00的频率调制深度曲线
该系统应确保在红外波段III?IVμm中有足够的能量分布,其中乙醇和丙酮浓度已测量,红外线源类型EMIRSII0是合格的.如图III所示emirsII00的频率调制深度曲线,它是I.个电阻加热元,集成在I.个快速电调制,深度高调制,低功耗消费和长期稳定输出的薄介电膜符(II～I.VIμ米)上.
多通道热释电红外探测器在该系统中利用 *好棒文|www.hbsrm.com +Q: ￥351916072￥
的是宽频率和快速响应的特性[I.I.].窄带为III.IXVμm,III.IVVIIIμm,III.IIIIXμm的光学滤镜被嵌入在该检测器的测量窗,并允许对应波长的红外辐射通过.因此,在各通道的电信号采集,热释电红外探测器是I.种交替或瞬态响应装置,所述红外线源需要调制出I.定的频率.PWM方法在源极驱动电路中被广泛用在以往的技术中,以避免I.系列机械调制的缺点.图IV是该源极驱动电路.该处理器产生的脉冲序列的时间间隔为IIVms,频率I.0千赫,它们被输入到源极驱动电路来控制红外源.驱动器的输出电路驱动漏电极连接到FETQI.,红外源和电极接地,另I.红外源极连接到VCC.场效应管QI.导通,当脉冲变为高时红外光源发射光,QI.被切断,脉冲变为低时红外光源熄灭.
Ⅲ.设计
A.硬件设计
红外线酒精的硬件框图测试系统如图V所示.由处理器生成有规律的脉冲序列,然后被间隔输入到驱动电路来调节红外源.等效模拟成比例的信号吸收中,每个残余红外能量的后III个波长的样品被输入到前置放大器的滤波器电路中,并且由A/D转换电路转换为数字信号,由所述处理器进行处理.用非线性校正和补偿信号来计算酒精浓度.
图IV.源驱动电路
图V.红外酒精检测系统的硬件框图
III星公司的SIIICIIIVIV0A作为微控制器,其目的是提供具有I.般应用的低功率,并且在高性能的微控制器中解决小的芯片尺寸.SIIICIIIVIV0A包括以下组成:独立的I.VIKB指令和I.VIKB数据高速缓存,MMU虚拟内存管理,液晶显示器控制器(STN及TFT),NANDFlash引导装载程序,系统经理(芯片选择逻辑和SDRAM控制器),III通道UART,IV通道DMA,IV通道定时器,PWM,I/O端口,RTC,VIII通道I.0位ADC和触摸屏接口,摄像头接口,IIC总线接口,IIS总线接口,USB主机,USB设备,SD主机和多媒体卡接口,II通道SPI和PLL时钟发生器.通过提供I.个完整的的通用系统外设,采用SIIICIIIVIV0A最小化整体系统成本,无需配置附加组件.
热电型红外线检测器的输出信号如此弱是因为在呼气时只有少量酒精,而且传感器具有局限性,它不适合用于高精度的采样,所以高倍率的放大电路被包括在设计中.由TI公司生产的双通道精密运算放大器LTI.0I.IIID的系统设计是合格的,这在于它的的低漂移,高增益,低电源电流和低电流噪声的特点.
B,数据采样
根据采样定理的条件来转换采样信号的原始信号无任何失真,采样频率必须超过最高频率的两倍信号.因此,微处理器控制A/D采样单元以连续的模拟信号样本来处理它们.
在中断服务程序(ISR)采样中,微处理器通过设置间隔采样的内部定时器和A/D采样单元来完成数据.图VI中,主程序初始化SIIICIIIVIV0A,定时器0,GPIO和串行端口,设置总线时钟,数据总线的宽度,触发模式eintI.中断,进入中断向量.软件设置采样频率和开关定时器,定时器中断程序跳转,A/D采样装置投产后的定时器超时,然后进入eintI.ISR,A/D单元输出记录.呼气的持久性是通过eintI.ISR的检查程序跳出eintI.,定时器ISR持续析出的.转换端被设置为I.,而呼气时终止.经转换的离散数字信号经处理后被放置到I.个数组.
Ⅳ.实验结果与结论
根据实验方法GB/TIII.IIVIV-II00VII,这是适用于呼吸酒精测试器的,准备0.I.00,0.V00浓度的标准乙醇气体I..II00mg/L,用设计设备的I.0倍测量它们,测试值示于表I中,指示误差和这些值的重复性示于表II中.
图VI.数据采样流字符
图(I.)
图(II)
图(III)
表I..测试值和平均值
项目0.I.00(mg/L0.V00(mg/L)I..II00(mg/L)
标示(mg/L)标示(mg/L)标示(mg/L)
I.0.I.0VI0.VI.VIIII..III0VIII
II0.I.0V0.V0IXI..I.VIIIVII
III0.I.0V0.V0IXI..I.IXVII
IV0.0IXIV0.IVIXVIII..IIIIIVII
V0.I.I.00.V0VI..IIIIIVI
VI0.0IXIV0.IVIXVI..IIV0
VII0.I.0IX0.VI.VII..IIV0
VIII0.I.0II0.VI.VII..II0IX
IX0.I.0VIII0.VI.IVI..II00
I.00.I.0VIII0.VI.VIIII..IIIIIVIII
结果0.I.0IV0.VI.0I..IIIIII.
表II.示值误差和重复性的测试值
浓度(mg/L)示值误差重复性
0.I.000.00IVmg/L0.00VImg/L
0.V00II.II%I..VIV%
I..II00II.VI%II.VIIIVIII%
III.IVVIIIμμm波长的窄带光滤波器用于乙醇,III.IIIIXμμm波长用于丙酮,III.IXVμμm波长为参考通道.这系统设计NDIR技术,这是个很好的选择,不会受有毒气体影响.许多次实验结果表明,该方法具有很高的精度.
参考
[I.].大卫·田独赢,呼吸式酒精检测仪-防止道路交通事故",技术,II00VI年非盟杂志,第I.0卷(II),pp.VIIV-VIII0.
[II].张红霞,振华邓,谢娜,BAC的比较阈值在不同受酒精影响驾驶国家,中国法医学科学,II00VI,pp.VVII-VIX.
[III].黄SM,对电容测量等,电导率的影响使用的电荷转移方法,杂志的双组分液体物理E:科学仪器,I.IXVIIIVIII,pp.VIVVIII-VIXIII.
[IV].AW琼斯,法医学酒精测定,血液或呼吸酒精浓度?,法医学审查,II000年,第I.卷.I.II,页.IIIII-IVVIII.
[V].A.Fried,B.P.Wert,J.G.Walega,I.个可调谐中红外的发展高度敏感的大气痕量气体的差频激光源检测",应用物理B:激光器和光学系统,II00II,pp.IIVIIII.-IIVIIIVIII.
[VI].纪新明,王建业飞模武.中的应用在火灾探测中的便携式红外传感器,中国传感器和执行器,II00VI杂志,pp.VI0II_VI0VVII.0.
[VII].A.W.琼斯,L.安德森,K.贝里隆德,干扰物质确定与毒物V000S饮酒驾驶的气息,分析毒理学,I.IXIXVI年,第VIIII-VIIVII的.
[VIII].Z.J.谢,Q.L.谭迷你多气体检测系统的基础上红外线原理,国际杂志红外线与毫米波学报,II00VI,pp.I.VIIIIIX-I.VIIVIX.
[IX].R.G.Gullberg.方法和质量保证法医呼吸酒精分析,法医科学评论,第I.II卷,第IVIX-VIVIII,II000.
[I.0]K.Namjou,P.J.McCann,B.Croley,E.Raasch,andW.T.Potter,呼气测试用中红外激光光谱仪",应用可调谐II极管等红外源对大气研究和工业加工监测II,SPIE年度会议,丹佛,CO,I.IXIXIX.VII.I.IX-II0日.
[I.I.].在硒化铅探测器E.Theocharous,绝对线性度的测量在红外,红外物理与技术,II00VII,pp.VIIII-VIIX.
附件II:外文原文(复印件)
TheI.stInternationalConferenceonInformationScienceandEngineering(ICISEII00IX)
ResearchonInfraredBreathAlcoholTestBasedonDifferentialAbsorption
Ren-wangLi,Ye-panxiong,Yong-jianWang
FacultyofMechanicalEngineering&
AutomationZhejiangSci-TechUniversity
Hangzhou,Zhejiang,ChinaPandy
I.I.I.0@gmail.com
Abstract-Aninfraredalcoholtestingsystembasedondifferentialabsorptionispresented.Thetechniquereliesonthefactthatthebreathalcoholgashasaunique,well-definedabsorptioncharacteristicwithintheinfraredregionofelectromagneticspectrum.Itisusedtodetectthepresentandconcentrationofalcoholgas.Thenon-dispersiveinfraredgasdetectionprincipleisintroducedindetail.Experimentsshowthatthetestingsystemhashighprecision,goodenvironmentadaptability,anditsindicationerrorandrepeatabilityreachthe
ChinaNationalStandards.
Keywords-infrared;breathalcoholtest;differentialabsorption
I.INTRODUCTION
Withthedevelopmentofthenationaleconomy,thenumberofmotorvehicleincreasesdaybyday.Inordertopreventdrivingundertheinfluenceofalcohol(DUI),afieldtesttogetthebloodalcoholconcentration(BAC)ofadriveris
urgentlynecessary[I.].Intheforensicinvestigationsofthetrafficaccidents,countriesallovertheworldconsideralcoholasthemaincauseoftrafficaccidents.Correspondingmeasureshavebeentakentoavoidaccidents,andtheBACthresholdofadriverisinit[II,III].Athome,semiconductormodelandfuelcell
FenWanSchoolofComputerScienceand
TechnologyNorthChinaElectricPower
UniversityBeijing,China
modelarepopularusedbyrelevantdepartments,operatorscanmeasurethebreathalcoholconcentration(BrAC)bythesetypesofapparatus.BecauseofthedefiniteratioBAC/BrAC,theBACofadrivercanbecalculated[IV].However,therearesomeshortcomings.Theformercannoteasilyreachthestandardbothinindicationerrorandrepeatability,andisofweakanti-interferencecapability,vulnerabletosmoke,gasolineandotherinterference.Thelattercannotcarryouta
continuoustesting,thoughisofwellstability,higherprecisionandgoodanti-interferencecapability.ThismeansthatthefuelcellmodeldoesnotmonitorBrACduringexhalationand
cannotdepictsBACcurve,thusincapableofdistinguishingalveolaralcoholfrommouthalcohol.
Analcoholtestingsystembasedonnon-dispersiveinfrared(NDIR)isintroduced.Amajoradvantageofthistechnologyisitsabilitytomakeareal-time,continuousmeasurementduringthecourseofsampledelivery,thisallowsthesystemdepictthealcoholconcentrationcurveinreal-time.Theuseofdifferentialopticalabsorptionspectroscopy(DOAS)[V,VI]eliminatesinfraredsourceinstability,photoelectricdevicezerodriftandotherinterference,whichimprovetheaccuracyofthemeasurement.
II.THEORYANDMETHOD
A.Three-channelcompensationprinciple
Therealwaysexistotherabsorbingcomponentsintheexhalationofadriver,suchasacetoneandwatervapor[VII].Fig.I.showstheinfraredabsorbingspectrogramofpossiblesubstances.Fortheinfraredsourceinstabilityandphotoelectricdeviceszerodrift,whichmaycausebigdeviationinthemeasurement,three-channelDOASisofferedinthissystem,afirstchannelisforareference,asecondchannelisforethanolandathirdchannelisforacetone.
ThreenarrowbandfiltersofrespectivecenterwavelengthλI.,λII,λIIIareplacedattheendofthelightpath.TheλI.wavelengthforthereferencechannelisinsensitiveorisnotabsorbedbyallpotentialinfraredenergyabsorbingcompounds.TheλIIwavelengthisfortheethanolchannelandtheλIIIwavelengthisfortheacetonechannel.HenceenergyvariationinλI.recordstheeffectofinfraredsourceinstabilityandphotoelectricdeviceszerodrift,energyvariationinλIIrecordsthealcoholconcentrationandeffectofacetoneisrecordedbyλIII.
ThesimplestexpressionrelatingabsorberconcentrationtosignalstrengthorabsorptionintensityisgivenbytheBeer-Lambert’srelation[VIII]:
(I.)
WhereI0andIaretheintensitiesoftheinfraredradiationpriortoandafterpassingthroughacolumnoflengthLcontainingaconcentrationCofanabsorber.Theabsorptioncoefficient,K(λ)
oftheabsorbervariesasthewavelengthλ.
Equation(I.)indicatesthatinfraredradiationintensityattenuatesexponentiallywiththeconcentrationCandopticalpathlengthLafterpassingthroughthechamber.Theabsorbingcoefficientdependsonthecharacteristicsofthegasundertest,it’sdifferentfordifferentgases,andtheabsorptioncharacteristicvariesindifferentwavelength.
FigureI..Absorptionspectrogramofwater,acetoneandalcohol
ForinfraredradiationswaveofλI.,λII,assumethatthescalefactorsofthesetwochannelsareαI.andαII,thevoltagesgeneratebythetwochannelsrespectivelyare:
(II)
(III)
Inordertoeliminatetheeffectsoflightintensityandothersystemfactors,divide(II)by(III),anditiswrittenas:
(IV)
Sincethereferencechannelhasbeenselectedtobeinsensitivetoallpotentialinfraredenergyabsorbingcompoundsandacetoneisalsoabsorbedintheethanolchannel,concentrationCwouldbeproportionaltotheenergyremainingafterabsorptionbybothethanolandacetone.Taylorexpansionof(IV)iswrittenas:
Byinstallingapredeterminednarrowbandopticalfilter,thenarrowbandofenergydefinedbyonewhichcontainsonlyasingleorcloselygroupedwavelengthishardlyaffectedbyothergases,sotheabsorbingcoefficientremains
Fundamentallyunchanged.Oncethesystemis
decided,K(λI.),K(λII)andLareknown.ScalefactorsαI.andαIIarerelatedtopresentstateofenvironmentandcanbecompensatedbycalibration,softwareorhardwaredesign.
Therefore,concentrationCislinearwiththevoltageoutputratioofreferencechanneltoethanolchannel.Thus,ethanolandacetoneconcentrationCiscalculated.
Similarly,forinfraredradiationswaveofλIIandλIII,thegainofamplifierintheacetonechannelisadjustedsothattheoutputofacetonechannelisequaltoethanolchannelwhenethanolonlyisintroducedinthesamplechamber.ThenacetoneconcentrationC’wouldbecalculatedbycomparingtheoutputsofthesetwochannels.
Then,alcoholconcentrationisobtainedbysubtractingC’proportionallyfromC.
B.Method
Inordertodecreaseattenuationofweaksignalsgeneratedbyinfraredsensors,preamplifiercircuitisplacedintheopticalcomponentandelectromagneticshieldmeasuresareappliedindesignoftheopticalsystem.Forabetterresolutioninenergyabsorbing,theinfraredsource,samplechamberandinfrareddetectorareplacedalongastraightopticalaxis.Fig.IIisthedesignoftheopticalpath.Moreover,anovalorparabolicreflectorisappliedinthisdesignforstrongersignals[IX,I.0].Theinfraredsourceiscontrolledbyastable,well-regulatedDCpowersupplyandthesupplyvoltageand
currentaredifferentfordifferentinfraredsource.Theinfraredsourceemitslightperiodicallyaccordingtopredeterminedmodulatingrequency.Themodulatedinfraredradiationinteractswiththesampleintheairchamberandisabsorbedbyenergyabsorbingcomponentswithinthecharacteristicspectrumline.Theinfraredenergyremainingineachofthethreewavelengthsafterabsorptionbythecollectedsampleisreceivedbyaninfrareddetectorwhichconvertsthis
remainingquantityofinfraredenergytoanequivalentelectricalsignal.
ThesystemshouldensureenoughenergydistributioninmiddleinfraredbandIII～IVμminwhichethanolandacetoneconcentrationsare
measured,infraredsourcetypedEMIRSII00isqualified.Itisbasedonaresistiveheating
element,integratedonathindielectricmembranewhichexhibitsthecharactersofwidewavelengthrange(II～I.VIμm),fastelectricalmodulation,highmodulationdepth,lowpower
consumptionandlongtermstableoutputetc.,Fig.IIIshowsthefrequencymodulationdepthcurveofEMIRSII00.
Multichannelpyroelectricinfrareddetectorchosentobeusedinthissystemisofwidefrequencyandfastresponse[I.I.].NarrowbandIII.IXVμm,III.IVVIIIμm,III.IIIIXμmopticalfiltersareembedinthemeasurementwindowsofthedetectortoallowinfraredradiationofcorrespondingwavelengthpassingthrough.Thus,electricalsignalsineachchannelcollected.Forpyroelectricinfrareddetectorisakindofalternatingortransientresponsedevice,theinfraredsourceneedstobemodulatedwithcertainfrequency.APWMmethodisintroducedinthesourcedrivingcircuittoavoidaseriesof
shortcomingsinmechanicalmodulationwhichiswidelyusedinpriortechnology.Fig.IVisthesourcedrivingcircuit.TheprocessorproducespulsesequencewithtimeintervalIIVmsandfrequencyI.0KHzwhichareinputintothesourcedrivingcircuittocontroltheinfraredsource.TheoutputofthedrivingcircuitdrivesFETQI.whosedrainelectrodeisconnectedto
theinfraredsourceandelectrodegrounded,theotherpinoftheinfraredsourceisconnectedtoVCC.FETQI.turnsonwhenthepulseturnstobehighandtheinfraredsourceemitslight,QI.iscutoffwhenthepulseturnstobelowandthe
infraredsourceextinguished.
FigureII.Designoftheopticalpath
FigureIII.FrequencymodulationdepthcurveofEMIRSII00
infraredradiationofcorrespondingwavelengthpassingthrough.Thus,electricalsignalsineachchannelcollected.Forpyroelectricinfrareddetectorisakindofalternatingortransientresponsedevice,theinfraredsourceneedstobe
modulatedwithcertainfrequency.APWMmethodisintroducedinthesourcedrivingcircuittoavoidaseriesofshortcomingsinmechanicalmodulationwhichiswidelyusedinpriortechnology.Fig.IVisthesourcedrivingcircuit.TheprocessorproducespulsesequencewithtimeintervalIIVmsandfrequencyI.0KHzwhichareinputintothesourcedrivingcircuittocontroltheinfraredsource.TheoutputofthedrivingcircuitdrivesFETQI.whosedrainelectrodeisconnectedtotheinfraredsourceandelectrodegrounded,theotherpinoftheinfraredsourceisconnectedtoVCC.FETQI.turnson
whenthepulseturnstobehighandtheinfraredsourceemitslight,QI.iscutoffwhenthepulseturnstobelowandtheinfraredsourceextinguished.
III.DESIGN
A.Hardwaredesign
ThehardwareblockdiagramoftheinfraredalcoholtestingsystemisshowninFig.V.Pulsesequenceataregularintervalgeneratedbytheprocessorisenteredintothedrivingcircuittomodulatetheinfraredsource.Equivalentanalog
signalsproportionaltotheinfraredenergyremainingineachofthethreewavelengthsafterabsorptionbythecollectedsampleareenteredintopreamplifierfiltercircuitsandareconvertedtodigitalsignalsbyA/Dcircuitbeforebeing
processedbytheprocessor.Nonlinearcorrectedandcompensatedsignalsareusedtocalculatethealcoholconcentration.
FigureIV.Sourcedrivingcircuit
FigureV.Hardwareblockdiagramoftheinfraredalcoholtestingsystem
TheSIIICIIIVIV0AofSamsungCompanyisusedastheMCUwhichisdesignedtoprovidegeneralapplicationswithlow-power,andhigh-performancemicro-controllersolutionin
smalldiesize.TheSIIICIIIVIV0AincludesthefollowingcomponentsseparateI.VIKBInstructionandI.VIKBDataCache,MMUtohandlevirtualmemorymanagement,LCD
Controller(STN&TFT),NANDFlashBootLoader,SystemManager(chipselectlogicandSDRAMController),III-chUART,IV-chDMA,IV-chTimerswithPWM,I/OPorts,RTC,VIII-chI.0-bitADCandTouchScreenInterface,Camera
interface,IIC-BUSInterface,IIS-BUSInterface,USBHost,USBDevice,SDHost&Multi-MediaCardInterface,II-chSPIandPLLforclockgeneration.Byprovidingacompletesetofcommonsystemperipherals,theSIIICIIIVIV0Aminimizesoverallsystemcostsandeliminatestheneedtoconfigureadditionalcomponents.
Theoutputsignalsofthepyroelectricinfrareddetectoraresoweakbecauseofthesmallquantityofalcoholinexhalationandthelimitationofthesensorsthatit’sunsuitedtobe
sampled,sopre-amplifyingcircuitswithhighprecisionandhighmagnificationareincludedinthedesign.Dual-channelprecisionoperationalamplifierLTI.0I.IIIDproducedbyTIisqualifiedinthesystemdesignforitscharacteristicoflow
drift,highgain,lowsupplycurrentandlowcurrentnoise.
B.Datasamplin
Accordingtosamplingtheorem,theconditionofconvertingasamplingsignaltotheoriginalsignalwithoutanydistortionisthatthesamplingfrequencymustexceedtwicethehighestfrequencypresentinthesignal.Therefore,themicroprocessorcontrolstheA/Dsamplingunittakingsamplesofcontinuousanalogsignalsandthenprocessesthem.
ThemicroprocessorsetsthesamplingintervalbyusingitsinnertimerandswitchontheA/Dsamplingunittofinishdataacquisitionintheinterruptserviceroutine(ISR).AsshowinFig.VI,themainroutineinitializesSIIICIIIVIV0A,Timer0,GPIOandserialports,setsthebusclock,thewidthofdatabus,triggermodeofinterruptEintI.,entranceofinterruptvector.
ThesoftwaresetsthesamplingfrequencyandswitchesonTimer0,theprogramjumpsintoTimer0ISRwheretheA/Dsamplingunitgoesintooperationafterthetimeristimeout,thenintoEintI.ISRwhereoutputsofA/Dunitarerecorded.ThepersistenceofexhalationischeckedinEintI.ISR,theprogramjumpsoutofEintI.andTimer0ISRwhileexhalationispersistent.EOCissettoI.whileexhalationisterminated.Theconverteddiscretedigitalsignalsareputintoanarrayafterbeingprocessed.
IV.EXPERIMENTRESULTSANDCONCLUSION
AccordingtoexperimentalmethodsinGB/TIII.IIVIV-II00VIIwhichisappliedtoevidentialbreathealcoholtesters,preparestandardethanolgaseswithconcentrationof0.I.00,0.V00,I..II00mg/L,measurethemwiththedesignedapparatustentimes,thetestvaluesareshowninTableI,theindicationerrorandrepetitivenessofthesevaluesareshowninTableII.
FigureVI.Datasamplingflowingchart
ThenarrowbandopticalfilterwithIII.IVVIIIμmwavelengthisusedforethanol,withIII.IIIIXμmwavelengthforacetone,andwithIII.IXVμmwavelengthforthereferencechannel.This
systemdesignedbasedonNDIRtechnologyisofgoodselectivityandwillnotagebypoisonousgases.Manytimes’experimentsshowthatthismethodhasreachedahighaccuracy.
ACKNOWLEDGE
TheworkissupportedbytheNationalNaturalScienceFoundation(GrantNo.V0VIVIIVII0VIII),ZhejiangProvinceNationalNaturalScienceFoundation(GrantNo.RVI0VIII0IV0III)andZhejiangProvinceQianjiangPlanProject(QJD0VII0II00II),P.R.China.
REFERENCES
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[VIII].Z.J.Xie,Q.L.Tan,Aminimulti-gasdetectionsystembasedoninfraredprinciple",INTERNATIONALJOURNALOFINFRAREDANDMILLIMETERWAVES,II00VI,pp.I.VIIIIIX-I.VIIVIX.
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摘要:红外呼气式酒精检测技术依赖于差分吸收.呼气酒精气体很独特,在红外区域内的电磁谱中具有良好的吸收特性.差分吸收的红外呼气可以用来检测当前酒精气体的浓度,实验表明,该检测系统精度高,具有良好的环境适应性,并且其示值误差和重复性达到中国国家标准.
关键字:红外;呼气酒精测试;差分吸收
Ⅰ.引言
随着国民经济的发展,机动车辆的数目日益增多.为了防止驾驶员在酒精(DUI)影响下驾驶,我们迫切需要在现场测试中知道司机血液中的酒精浓度(BAC)[I.].通过法医调查发生的交通事故,世界各国普遍认为酒精是发生交通事故的主要原因.为了避免事故的发生,根据司机I.定的BAC阈值[II,III],各国已经开始采取相应的措施.在国内,半导体模型和燃料细胞模型广泛用于相关部门,运营商可以通过这些类型的设备测量呼气中的酒精浓度(BRAC).因为BAC/BRAC具有I.定比例,所以驾驶员的BAC可以计算出来[IV].但是,也有I.些不足之处.前者不能轻易到达示值误差和重复性的标准,抗干扰能力弱,容易受到烟雾,汽油和其他干扰.后者不能进行连续测试,虽然具有良好的稳定性,精度高,抗干扰能力强,但这意味着燃料细胞模型在呼气过程中,我们不能监控BRAC,也无法描绘BAC曲线,从而不能区分是口中的酒精还是肺泡中的酒精.
非色散红外酒精检测系统技术的I.个主要优点是能够在送样过程中进行I.个实时.连续的测量,这允许系统实时地描绘酒精浓度的曲线.利用差分光学吸收光谱(DOAS)[V,VI]消除红外源不稳定,光电器件零点漂移等干扰,从而提高了测量的精度.
Ⅱ.理论与方法
A.III通道的补偿原则
I.个司机的呼气始终存在着其他的吸收成分,如丙酮和水蒸汽[VII].图I.显示了红外吸收谱的可能物质.对红外光源不稳定和光电器 *好棒文|www.hbsrm.com +Q: ￥351916072￥
件的零点漂移可能会导致很大的测量偏差.在这个系统中提供了III通道差分吸收光谱,第I.信道为基准,第II信道是乙醇,第III信道是丙酮.各中心波长的III个窄带滤波器λI.,λII,λIII被放置在光路的端部.波长λI.为参考信道,是所有潜在的不敏感或不能被红外能量吸收的化合物.波长λII为乙醇通道,波长λIII为丙酮通道.因此,λI.记录了红外光源的不稳定性和光电效应设备的零漂,λII记录了能量变化,λIII记录了酒精浓度和丙酮的效果.
有关信号强度或吸收强度的啤酒兰伯特[VIII]吸收剂浓度的最简单表达式关系:
(I.)
其中,I0和I是红外辐射的强度,C是吸收浓度,长度为L.
吸收系数K(λ)随着波长λ变化.式(I.)表示红外辐射强度穿过腔室之后浓度C和光程长度L呈指数衰减.根据测试,该吸收系数依赖于气体的特性,它对于不同的气体各不I.样,不同的波长吸收特性各不相同.
图I..水,丙酮和乙醇的吸收光谱
用于红外辐射的波为λI.,λII,假定这两个通道的比例系数为αI.和αII,则电压通过这两个通道分别生成:
(II)
(III)
为了消除光强度等影响系统的因素,除(II)(III),它可写为:
(IV)
由于参考通道已被选择为所有潜在的不被红外能量吸收的化合物,丙酮也设置在乙醇吸收通道,浓度C与乙醇和丙酮吸收残余能量成正比.泰勒展开式(IV)可写为:
通过安装I.个预定的窄波段滤光器,I.个含有单I.的或密切分组波长能量的窄频带几乎没有影响其他气体.因此吸收系数从根本上保持不变.I.旦该系统确定,K(λI.),K(λII)和L是已知的,比例因子αI.和αII与目前环境相关,并且可以通过校准,软件或硬件设计来补偿.因此,浓度C是线性的乙醇在参考通道输出的电压比.所以,乙醇和丙酮浓度C被计算出来了.
类似地,对于红外辐射波λII和λIII,在丙酮信道中对放大器的增益进行调整,当乙醇仅在样品室中被导入,使丙酮通道的输出等于乙醇通道.丙酮浓度C将通过比较来计算这两个信道的输出.
然后,按比例从C减去C’得到酒精浓度.
B.方法
为了减少微弱的信号衰减,通过红外传感器,将前置放大器电路放置在光学元件中并将电磁屏蔽措施应用于光学系统的设计.为了在能量吸收中具有更好的分辨率,红外光源.样品室和红外探测器沿直线光轴被放置.图II是光路的设计.此外,椭圆形或抛物面反射器在这个设计给与了更强的信号[IX,I.0].红外源是由I.个稳定的,良好的稳压直流电源和电源电压控制的,不同的红外源电流是不同的,红外光源发出的光周期性地根据预定的频率调制.调制的红外辐射与空气室中的样品相互作用,通过吸能部件的特征来吸收谱线.通过红外检测器,由所收集的样本吸收后各红外能量残留III个波长,其将当前接收到的红外能量的剩余量转变为电信号.
图II.光路设计
图III.EMIRSII00的频率调制深度曲线
该系统应确保在红外波段III?IVμm中有足够的能量分布,其中乙醇和丙酮浓度已测量,红外线源类型EMIRSII0是合格的.如图III所示emirsII00的频率调制深度曲线,它是I.个电阻加热元,集成在I.个快速电调制,深度高调制,低功耗消费和长期稳定输出的薄介电膜符(II～I.VIμ米)上.
多通道热释电红外探测器在该系统中利用 *好棒文|www.hbsrm.com +Q: ￥351916072￥
的是宽频率和快速响应的特性[I.I.].窄带为III.IXVμm,III.IVVIIIμm,III.IIIIXμm的光学滤镜被嵌入在该检测器的测量窗,并允许对应波长的红外辐射通过.因此,在各通道的电信号采集,热释电红外探测器是I.种交替或瞬态响应装置,所述红外线源需要调制出I.定的频率.PWM方法在源极驱动电路中被广泛用在以往的技术中,以避免I.系列机械调制的缺点.图IV是该源极驱动电路.该处理器产生的脉冲序列的时间间隔为IIVms,频率I.0千赫,它们被输入到源极驱动电路来控制红外源.驱动器的输出电路驱动漏电极连接到FETQI.,红外源和电极接地,另I.红外源极连接到VCC.场效应管QI.导通,当脉冲变为高时红外光源发射光,QI.被切断,脉冲变为低时红外光源熄灭.
Ⅲ.设计
A.硬件设计
红外线酒精的硬件框图测试系统如图V所示.由处理器生成有规律的脉冲序列,然后被间隔输入到驱动电路来调节红外源.等效模拟成比例的信号吸收中,每个残余红外能量的后III个波长的样品被输入到前置放大器的滤波器电路中,并且由A/D转换电路转换为数字信号,由所述处理器进行处理.用非线性校正和补偿信号来计算酒精浓度.
图IV.源驱动电路
图V.红外酒精检测系统的硬件框图
III星公司的SIIICIIIVIV0A作为微控制器,其目的是提供具有I.般应用的低功率,并且在高性能的微控制器中解决小的芯片尺寸.SIIICIIIVIV0A包括以下组成:独立的I.VIKB指令和I.VIKB数据高速缓存,MMU虚拟内存管理,液晶显示器控制器(STN及TFT),NANDFlash引导装载程序,系统经理(芯片选择逻辑和SDRAM控制器),III通道UART,IV通道DMA,IV通道定时器,PWM,I/O端口,RTC,VIII通道I.0位ADC和触摸屏接口,摄像头接口,IIC总线接口,IIS总线接口,USB主机,USB设备,SD主机和多媒体卡接口,II通道SPI和PLL时钟发生器.通过提供I.个完整的的通用系统外设,采用SIIICIIIVIV0A最小化整体系统成本,无需配置附加组件.
热电型红外线检测器的输出信号如此弱是因为在呼气时只有少量酒精,而且传感器具有局限性,它不适合用于高精度的采样,所以高倍率的放大电路被包括在设计中.由TI公司生产的双通道精密运算放大器LTI.0I.IIID的系统设计是合格的,这在于它的的低漂移,高增益,低电源电流和低电流噪声的特点.
B,数据采样
根据采样定理的条件来转换采样信号的原始信号无任何失真,采样频率必须超过最高频率的两倍信号.因此,微处理器控制A/D采样单元以连续的模拟信号样本来处理它们.
在中断服务程序(ISR)采样中,微处理器通过设置间隔采样的内部定时器和A/D采样单元来完成数据.图VI中,主程序初始化SIIICIIIVIV0A,定时器0,GPIO和串行端口,设置总线时钟,数据总线的宽度,触发模式eintI.中断,进入中断向量.软件设置采样频率和开关定时器,定时器中断程序跳转,A/D采样装置投产后的定时器超时,然后进入eintI.ISR,A/D单元输出记录.呼气的持久性是通过eintI.ISR的检查程序跳出eintI.,定时器ISR持续析出的.转换端被设置为I.,而呼气时终止.经转换的离散数字信号经处理后被放置到I.个数组.
Ⅳ.实验结果与结论
根据实验方法GB/TIII.IIVIV-II00VII,这是适用于呼吸酒精测试器的,准备0.I.00,0.V00浓度的标准乙醇气体I..II00mg/L,用设计设备的I.0倍测量它们,测试值示于表I中,指示误差和这些值的重复性示于表II中.
图VI.数据采样流字符
图(I.)
图(II)
图(III)
表I..测试值和平均值
项目0.I.00(mg/L0.V00(mg/L)I..II00(mg/L)
标示(mg/L)标示(mg/L)标示(mg/L)
I.0.I.0VI0.VI.VIIII..III0VIII
II0.I.0V0.V0IXI..I.VIIIVII
III0.I.0V0.V0IXI..I.IXVII
IV0.0IXIV0.IVIXVIII..IIIIIVII
V0.I.I.00.V0VI..IIIIIVI
VI0.0IXIV0.IVIXVI..IIV0
VII0.I.0IX0.VI.VII..IIV0
VIII0.I.0II0.VI.VII..II0IX
IX0.I.0VIII0.VI.IVI..II00
I.00.I.0VIII0.VI.VIIII..IIIIIVIII
结果0.I.0IV0.VI.0I..IIIIII.
表II.示值误差和重复性的测试值
浓度(mg/L)示值误差重复性
0.I.000.00IVmg/L0.00VImg/L
0.V00II.II%I..VIV%
I..II00II.VI%II.VIIIVIII%
III.IVVIIIμμm波长的窄带光滤波器用于乙醇,III.IIIIXμμm波长用于丙酮,III.IXVμμm波长为参考通道.这系统设计NDIR技术,这是个很好的选择,不会受有毒气体影响.许多次实验结果表明,该方法具有很高的精度.
参考
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[II].张红霞,振华邓,谢娜,BAC的比较阈值在不同受酒精影响驾驶国家,中国法医学科学,II00VI,pp.VVII-VIX.
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附件II:外文原文(复印件)
TheI.stInternationalConferenceonInformationScienceandEngineering(ICISEII00IX)
ResearchonInfraredBreathAlcoholTestBasedonDifferentialAbsorption
Ren-wangLi,Ye-panxiong,Yong-jianWang
FacultyofMechanicalEngineering&
AutomationZhejiangSci-TechUniversity
Hangzhou,Zhejiang,ChinaPandy
I.I.I.0@gmail.com
Abstract-Aninfraredalcoholtestingsystembasedondifferentialabsorptionispresented.Thetechniquereliesonthefactthatthebreathalcoholgashasaunique,well-definedabsorptioncharacteristicwithintheinfraredregionofelectromagneticspectrum.Itisusedtodetectthepresentandconcentrationofalcoholgas.Thenon-dispersiveinfraredgasdetectionprincipleisintroducedindetail.Experimentsshowthatthetestingsystemhashighprecision,goodenvironmentadaptability,anditsindicationerrorandrepeatabilityreachthe
ChinaNationalStandards.
Keywords-infrared;breathalcoholtest;differentialabsorption
I.INTRODUCTION
Withthedevelopmentofthenationaleconomy,thenumberofmotorvehicleincreasesdaybyday.Inordertopreventdrivingundertheinfluenceofalcohol(DUI),afieldtesttogetthebloodalcoholconcentration(BAC)ofadriveris
urgentlynecessary[I.].Intheforensicinvestigationsofthetrafficaccidents,countriesallovertheworldconsideralcoholasthemaincauseoftrafficaccidents.Correspondingmeasureshavebeentakentoavoidaccidents,andtheBACthresholdofadriverisinit[II,III].Athome,semiconductormodelandfuelcell
FenWanSchoolofComputerScienceand
TechnologyNorthChinaElectricPower
UniversityBeijing,China
modelarepopularusedbyrelevantdepartments,operatorscanmeasurethebreathalcoholconcentration(BrAC)bythesetypesofapparatus.BecauseofthedefiniteratioBAC/BrAC,theBACofadrivercanbecalculated[IV].However,therearesomeshortcomings.Theformercannoteasilyreachthestandardbothinindicationerrorandrepeatability,andisofweakanti-interferencecapability,vulnerabletosmoke,gasolineandotherinterference.Thelattercannotcarryouta
continuoustesting,thoughisofwellstability,higherprecisionandgoodanti-interferencecapability.ThismeansthatthefuelcellmodeldoesnotmonitorBrACduringexhalationand
cannotdepictsBACcurve,thusincapableofdistinguishingalveolaralcoholfrommouthalcohol.
Analcoholtestingsystembasedonnon-dispersiveinfrared(NDIR)isintroduced.Amajoradvantageofthistechnologyisitsabilitytomakeareal-time,continuousmeasurementduringthecourseofsampledelivery,thisallowsthesystemdepictthealcoholconcentrationcurveinreal-time.Theuseofdifferentialopticalabsorptionspectroscopy(DOAS)[V,VI]eliminatesinfraredsourceinstability,photoelectricdevicezerodriftandotherinterference,whichimprovetheaccuracyofthemeasurement.
II.THEORYANDMETHOD
A.Three-channelcompensationprinciple
Therealwaysexistotherabsorbingcomponentsintheexhalationofadriver,suchasacetoneandwatervapor[VII].Fig.I.showstheinfraredabsorbingspectrogramofpossiblesubstances.Fortheinfraredsourceinstabilityandphotoelectricdeviceszerodrift,whichmaycausebigdeviationinthemeasurement,three-channelDOASisofferedinthissystem,afirstchannelisforareference,asecondchannelisforethanolandathirdchannelisforacetone.
ThreenarrowbandfiltersofrespectivecenterwavelengthλI.,λII,λIIIareplacedattheendofthelightpath.TheλI.wavelengthforthereferencechannelisinsensitiveorisnotabsorbedbyallpotentialinfraredenergyabsorbingcompounds.TheλIIwavelengthisfortheethanolchannelandtheλIIIwavelengthisfortheacetonechannel.HenceenergyvariationinλI.recordstheeffectofinfraredsourceinstabilityandphotoelectricdeviceszerodrift,energyvariationinλIIrecordsthealcoholconcentrationandeffectofacetoneisrecordedbyλIII.
ThesimplestexpressionrelatingabsorberconcentrationtosignalstrengthorabsorptionintensityisgivenbytheBeer-Lambert’srelation[VIII]:
(I.)
WhereI0andIaretheintensitiesoftheinfraredradiationpriortoandafterpassingthroughacolumnoflengthLcontainingaconcentrationCofanabsorber.Theabsorptioncoefficient,K(λ)
oftheabsorbervariesasthewavelengthλ.
Equation(I.)indicatesthatinfraredradiationintensityattenuatesexponentiallywiththeconcentrationCandopticalpathlengthLafterpassingthroughthechamber.Theabsorbingcoefficientdependsonthecharacteristicsofthegasundertest,it’sdifferentfordifferentgases,andtheabsorptioncharacteristicvariesindifferentwavelength.
FigureI..Absorptionspectrogramofwater,acetoneandalcohol
ForinfraredradiationswaveofλI.,λII,assumethatthescalefactorsofthesetwochannelsareαI.andαII,thevoltagesgeneratebythetwochannelsrespectivelyare:
(II)
(III)
Inordertoeliminatetheeffectsoflightintensityandothersystemfactors,divide(II)by(III),anditiswrittenas:
(IV)
Sincethereferencechannelhasbeenselectedtobeinsensitivetoallpotentialinfraredenergyabsorbingcompoundsandacetoneisalsoabsorbedintheethanolchannel,concentrationCwouldbeproportionaltotheenergyremainingafterabsorptionbybothethanolandacetone.Taylorexpansionof(IV)iswrittenas:
Byinstallingapredeterminednarrowbandopticalfilter,thenarrowbandofenergydefinedbyonewhichcontainsonlyasingleorcloselygroupedwavelengthishardlyaffectedbyothergases,sotheabsorbingcoefficientremains
Fundamentallyunchanged.Oncethesystemis
decided,K(λI.),K(λII)andLareknown.ScalefactorsαI.andαIIarerelatedtopresentstateofenvironmentandcanbecompensatedbycalibration,softwareorhardwaredesign.
Therefore,concentrationCislinearwiththevoltageoutputratioofreferencechanneltoethanolchannel.Thus,ethanolandacetoneconcentrationCiscalculated.
Similarly,forinfraredradiationswaveofλIIandλIII,thegainofamplifierintheacetonechannelisadjustedsothattheoutputofacetonechannelisequaltoethanolchannelwhenethanolonlyisintroducedinthesamplechamber.ThenacetoneconcentrationC’wouldbecalculatedbycomparingtheoutputsofthesetwochannels.
Then,alcoholconcentrationisobtainedbysubtractingC’proportionallyfromC.
B.Method
Inordertodecreaseattenuationofweaksignalsgeneratedbyinfraredsensors,preamplifiercircuitisplacedintheopticalcomponentandelectromagneticshieldmeasuresareappliedindesignoftheopticalsystem.Forabetterresolutioninenergyabsorbing,theinfraredsource,samplechamberandinfrareddetectorareplacedalongastraightopticalaxis.Fig.IIisthedesignoftheopticalpath.Moreover,anovalorparabolicreflectorisappliedinthisdesignforstrongersignals[IX,I.0].Theinfraredsourceiscontrolledbyastable,well-regulatedDCpowersupplyandthesupplyvoltageand
currentaredifferentfordifferentinfraredsource.Theinfraredsourceemitslightperiodicallyaccordingtopredeterminedmodulatingrequency.Themodulatedinfraredradiationinteractswiththesampleintheairchamberandisabsorbedbyenergyabsorbingcomponentswithinthecharacteristicspectrumline.Theinfraredenergyremainingineachofthethreewavelengthsafterabsorptionbythecollectedsampleisreceivedbyaninfrareddetectorwhichconvertsthis
remainingquantityofinfraredenergytoanequivalentelectricalsignal.
ThesystemshouldensureenoughenergydistributioninmiddleinfraredbandIII～IVμminwhichethanolandacetoneconcentrationsare
measured,infraredsourcetypedEMIRSII00isqualified.Itisbasedonaresistiveheating
element,integratedonathindielectricmembranewhichexhibitsthecharactersofwidewavelengthrange(II～I.VIμm),fastelectricalmodulation,highmodulationdepth,lowpower
consumptionandlongtermstableoutputetc.,Fig.IIIshowsthefrequencymodulationdepthcurveofEMIRSII00.
Multichannelpyroelectricinfrareddetectorchosentobeusedinthissystemisofwidefrequencyandfastresponse[I.I.].NarrowbandIII.IXVμm,III.IVVIIIμm,III.IIIIXμmopticalfiltersareembedinthemeasurementwindowsofthedetectortoallowinfraredradiationofcorrespondingwavelengthpassingthrough.Thus,electricalsignalsineachchannelcollected.Forpyroelectricinfrareddetectorisakindofalternatingortransientresponsedevice,theinfraredsourceneedstobemodulatedwithcertainfrequency.APWMmethodisintroducedinthesourcedrivingcircuittoavoidaseriesof
shortcomingsinmechanicalmodulationwhichiswidelyusedinpriortechnology.Fig.IVisthesourcedrivingcircuit.TheprocessorproducespulsesequencewithtimeintervalIIVmsandfrequencyI.0KHzwhichareinputintothesourcedrivingcircuittocontroltheinfraredsource.TheoutputofthedrivingcircuitdrivesFETQI.whosedrainelectrodeisconnectedto
theinfraredsourceandelectrodegrounded,theotherpinoftheinfraredsourceisconnectedtoVCC.FETQI.turnsonwhenthepulseturnstobehighandtheinfraredsourceemitslight,QI.iscutoffwhenthepulseturnstobelowandthe
infraredsourceextinguished.
FigureII.Designoftheopticalpath
FigureIII.FrequencymodulationdepthcurveofEMIRSII00
infraredradiationofcorrespondingwavelengthpassingthrough.Thus,electricalsignalsineachchannelcollected.Forpyroelectricinfrareddetectorisakindofalternatingortransientresponsedevice,theinfraredsourceneedstobe
modulatedwithcertainfrequency.APWMmethodisintroducedinthesourcedrivingcircuittoavoidaseriesofshortcomingsinmechanicalmodulationwhichiswidelyusedinpriortechnology.Fig.IVisthesourcedrivingcircuit.TheprocessorproducespulsesequencewithtimeintervalIIVmsandfrequencyI.0KHzwhichareinputintothesourcedrivingcircuittocontroltheinfraredsource.TheoutputofthedrivingcircuitdrivesFETQI.whosedrainelectrodeisconnectedtotheinfraredsourceandelectrodegrounded,theotherpinoftheinfraredsourceisconnectedtoVCC.FETQI.turnson
whenthepulseturnstobehighandtheinfraredsourceemitslight,QI.iscutoffwhenthepulseturnstobelowandtheinfraredsourceextinguished.
III.DESIGN
A.Hardwaredesign
ThehardwareblockdiagramoftheinfraredalcoholtestingsystemisshowninFig.V.Pulsesequenceataregularintervalgeneratedbytheprocessorisenteredintothedrivingcircuittomodulatetheinfraredsource.Equivalentanalog
signalsproportionaltotheinfraredenergyremainingineachofthethreewavelengthsafterabsorptionbythecollectedsampleareenteredintopreamplifierfiltercircuitsandareconvertedtodigitalsignalsbyA/Dcircuitbeforebeing
processedbytheprocessor.Nonlinearcorrectedandcompensatedsignalsareusedtocalculatethealcoholconcentration.
FigureIV.Sourcedrivingcircuit
FigureV.Hardwareblockdiagramoftheinfraredalcoholtestingsystem
TheSIIICIIIVIV0AofSamsungCompanyisusedastheMCUwhichisdesignedtoprovidegeneralapplicationswithlow-power,andhigh-performancemicro-controllersolutionin
smalldiesize.TheSIIICIIIVIV0AincludesthefollowingcomponentsseparateI.VIKBInstructionandI.VIKBDataCache,MMUtohandlevirtualmemorymanagement,LCD
Controller(STN&TFT),NANDFlashBootLoader,SystemManager(chipselectlogicandSDRAMController),III-chUART,IV-chDMA,IV-chTimerswithPWM,I/OPorts,RTC,VIII-chI.0-bitADCandTouchScreenInterface,Camera
interface,IIC-BUSInterface,IIS-BUSInterface,USBHost,USBDevice,SDHost&Multi-MediaCardInterface,II-chSPIandPLLforclockgeneration.Byprovidingacompletesetofcommonsystemperipherals,theSIIICIIIVIV0Aminimizesoverallsystemcostsandeliminatestheneedtoconfigureadditionalcomponents.
Theoutputsignalsofthepyroelectricinfrareddetectoraresoweakbecauseofthesmallquantityofalcoholinexhalationandthelimitationofthesensorsthatit’sunsuitedtobe
sampled,sopre-amplifyingcircuitswithhighprecisionandhighmagnificationareincludedinthedesign.Dual-channelprecisionoperationalamplifierLTI.0I.IIIDproducedbyTIisqualifiedinthesystemdesignforitscharacteristicoflow
drift,highgain,lowsupplycurrentandlowcurrentnoise.
B.Datasamplin
Accordingtosamplingtheorem,theconditionofconvertingasamplingsignaltotheoriginalsignalwithoutanydistortionisthatthesamplingfrequencymustexceedtwicethehighestfrequencypresentinthesignal.Therefore,themicroprocessorcontrolstheA/Dsamplingunittakingsamplesofcontinuousanalogsignalsandthenprocessesthem.
ThemicroprocessorsetsthesamplingintervalbyusingitsinnertimerandswitchontheA/Dsamplingunittofinishdataacquisitionintheinterruptserviceroutine(ISR).AsshowinFig.VI,themainroutineinitializesSIIICIIIVIV0A,Timer0,GPIOandserialports,setsthebusclock,thewidthofdatabus,triggermodeofinterruptEintI.,entranceofinterruptvector.
ThesoftwaresetsthesamplingfrequencyandswitchesonTimer0,theprogramjumpsintoTimer0ISRwheretheA/Dsamplingunitgoesintooperationafterthetimeristimeout,thenintoEintI.ISRwhereoutputsofA/Dunitarerecorded.ThepersistenceofexhalationischeckedinEintI.ISR,theprogramjumpsoutofEintI.andTimer0ISRwhileexhalationispersistent.EOCissettoI.whileexhalationisterminated.Theconverteddiscretedigitalsignalsareputintoanarrayafterbeingprocessed.
IV.EXPERIMENTRESULTSANDCONCLUSION
AccordingtoexperimentalmethodsinGB/TIII.IIVIV-II00VIIwhichisappliedtoevidentialbreathealcoholtesters,preparestandardethanolgaseswithconcentrationof0.I.00,0.V00,I..II00mg/L,measurethemwiththedesignedapparatustentimes,thetestvaluesareshowninTableI,theindicationerrorandrepetitivenessofthesevaluesareshowninTableII.
FigureVI.Datasamplingflowingchart
ThenarrowbandopticalfilterwithIII.IVVIIIμmwavelengthisusedforethanol,withIII.IIIIXμmwavelengthforacetone,andwithIII.IXVμmwavelengthforthereferencechannel.This
systemdesignedbasedonNDIRtechnologyisofgoodselectivityandwillnotagebypoisonousgases.Manytimes’experimentsshowthatthismethodhasreachedahighaccuracy.
ACKNOWLEDGE
TheworkissupportedbytheNationalNaturalScienceFoundation(GrantNo.V0VIVIIVII0VIII),ZhejiangProvinceNationalNaturalScienceFoundation(GrantNo.RVI0VIII0IV0III)andZhejiangProvinceQianjiangPlanProject(QJD0VII0II00II),P.R.China.
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