模电设计 温度计英文.docx

模电设计 温度计英文.docx

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模电设计温度计英文

TemperatureMeasurement,Amplification,DisplayandAlarmSystem

LiLanxin

21120821

1.Tasksandrequirements

Roomtemperatureismeasuredbytheplatinumthermistor,andthealarmsoundswhenthetemperatureishigherthanthereferencevoltage.

1.Themeasurementregionis0℃～100℃,theoutputvoltageis0～1V,themeasurementerroracceptableisin±1℃.

2.DisplaythetemperaturewiththedigitalvoltmeterwhichisDoubleintegraltype.

3.Thecircuitdetectstheovertemperatureupperorlowerthanthenormalregion0℃～100℃,andproducesalarmvoice,theerrorshouldbeintheregionof±1℃.

4.Thealarmshouldbedisplayedbyboththelightandthevoice.

2. Designprinciple

Thecircuitusedtoplatinumthermalresistance,throughtheplatinumresistanceheatatdifferenttemperaturedifferentofthisprinciple,thetemperaturesignalcanbeconvertedtovoltagesignal,throughtothevoltageofseriesofprocessing,willeventuallyvoltagevariationthroughdigitaltubedisplayofdigital,soastorealizethemeasurementofthetemperature.Onthebasisofthebasicfunctions,whichcanrealizethefunctionofthealarmsound,etc.Isduetothedigitaldisplayfunctionofdigitalsignalscanberealized,andthecollectionoftemperatureisananalog,somustconductaADconversion.Thisdesigncanbedividedintofourmodules.

Designprincipleexpressedbyblockdiagramisasfollows:

3.Moduledesignandanalysis

（1）Temperature---voltageconversionunit

Thismoduleistorealizetheplatinumthermalresistancetemperatureintoavoltagesignal,andthevoltagesignalthroughtheop-ampoutput.

Temperatureisabasicphysicalquantities,alltheprocessofnatureiscloselyrelatedwithtemperature.Thetemperaturesensoristheearliestdevelopment,themostwidelyusedtypeofsensor.Temperaturesensorhasfourmaintypes:

thermocouple,thermalresistance,resistancetemperaturedetector（RTD）andtheICtemperaturesensor.ICtemperaturesensorandincludestwotypes,thatis,analogoutputanddigitaloutput.Platinumthermalresistanceisoneofthemostcommonlyusedinthermalresistancesensors. 

Wechosetheplatinumthermalresistanceasthemaindesigndirection.Platinumthermalresistanceofoneohmresistancearethecharacteristicsofeachchange,thetemperatureisabout2.5℃,specificmathematicalformulais:

－200℃

Rt100=100×[1+A×t+B×t×t+C×t×t×t×（t-100）]

（1）

0℃<=t<=850℃，Rt100=100×（1+A×t+B×t×t）

（2）

So,A＝3.90802×10－3；

B＝5.80×10－7；

C＝4.2735×10－12。

Platinumthermalresistancemeasurementrange:

200℃~+800℃,Pt100andvibrationresistance,goodstability,highaccuracy,highpressureresistance,etc.Chooseplatinumthermalresistancecompositeourexperimentrequirements,andcompositeourpracticalability.Platinumthermalresistanceisthekeytotheexperiment,itdirectlyaffectstheanalogtodigitalconversion.Becauseeverychange1ohmplatinumthermalresistance,intheory,isequivalenttoachangeinthetemperatureof2.5℃,soyoucanmakeat0℃withreferencetotheplatinumresistanceofthermalresistanceandotherplatinumthermalresistancetemperatureresistanceasavariable'svalue,thedifferencebetweenavariable'svalueandreferencevaluemultipliedby2.5isthetemperatureofthetime.

Ifexpressedinformulais:

T=[R（t）-R0]×A（3）

Type,Tsaidrelativeto0℃temperature;R（t）saidinthecurrenttemperatureplatinumthermalresistanceoftheactualvalue;R0saidat0℃platinumthermalresistanceoftheresistance;Aconstant2.5℃.Withthisformulacanclearlyknowhowtoconvertbetweenthetemperatureandtheresistance,whichimplementstheT~Rdirectconversion.Sothecoreofourworkishowtolinearchangesreflectchangesofvoltagelinearresistance.

Scheme1:

thebridgecombinedwithdifferentialamplifiercircuit

Settheinputvoltageof2.5V,becauseistheplatinumresistancethermistor,throughitscurrentcannottoobig,orbecauseoftoomuchelectricityheatingwillinfluencetheaccuracyofthemeasuringtemperature.Wearegoingtotentimestheinputvoltagenarrow,soitmeetstherequirements.Thenafterthefirstop-ampcircuitoutputvoltageiszero

U=（Rp/1100-1/11）*Ui

Inordertomaketheoutputvoltageisjustrightfortemperature10times,afterthefirstshipmentweputvoltageexpand11times,whenafterthesecondoperationalamplifieroutputvoltage

Uo=（Rp/100-1）*Ui

Suchtheoreticalcalculationoftheplatinicresistancevalueper1ohmoutputvoltagechanges25mv.Butthatisjustthetheoreticalcalculation,becauseinpractice,wefoundthateachresistanceisnotasaccurateaswethought,therearesomewireresistancewillalsohavesomeerror,weputtheRor1000ohmresistorsettosliderheostat,around1000ohms,toreducetheerror.

Solution2:

directlyUSESwheatstonebridgetodotemperature-voltageconversion

（2）Theanalog-to-digitalconversionunit

ThispartchoosesA/Dconversionchip,aslongasthefunctionofeachpinclearanalysiscandirectlyconvertanalogtodigitalquantity,A/DconversionchipchooseMC14433.MC14433convertstheinputanalogoutputBCDcodefromQ1toQ4.MultichannelgatingsignalmodulationDS1~DS4consistsofmulti-channelswitchoutput,ateachendoftheA/Dconversioncycle,outputAsignalEOCfirst,againordinaloutputDS1,DS2,DS3,DS4,DS1...

DS1~DS4sequencediagramisasfollows:

DS1

DS2

DS3

DS4

Becauseoftheclockcycleisverysmall,soinaccordingtothehumaneyecan'tidentifythisorder.ThisunitweadoptwidelyusedmatureA/Dconversioncircuitisasfollows:

（3）Decoding,driveanddisplaycircuit

Fromadccircuitoutput,accordingtodigitalquantitycannotbedirectlyusedforneedafterdecodinganddrivetothemoduleonthedigitaltubedisplaytheA/DconverterofQ1toQ3outputdatathroughMC14511chipdatalatches,decoding,anddrivetheLEDdigitaltube,toinputdatastrobe,digitaltubetodisplaythedatayouneed.LEDdigitaltube,achoiceisdonebyMC1413chip,thechipismainlytogettheoutput,inputleveltochooseatotalofYinLEDdigitaltubecanrealizethefunctionofthepart.

AboutMC14433:

MC14433ismonolithicthreeandAhalfA/Dconverter,whichintegratesthedoubleintegralA/DconverterallCMOSanalogcircuitsanddigitalcircuits.MC14433haslessexternalcomponents,highinputimpedance,widerangeofsupplyvoltage,lowpowerconsumption,highprecision,andhaszeroself-adjustmentandautomaticpolartransformationfunction,aslongasAsmallamountoftheexternalresistancecapacitycanconstituteAcompletepieceofA/Dconverter.Itsmainfeaturesareasfollows:

Accuracy:

+/-0.05%

Analoginputvoltagerange:

1.999Vand199.9mVtwogears

Conversionrate:

2to25/s

Inputimpedance:

greaterthan1000mΩ

Powersupplyvoltage:

+/-4.8V-V+8

Powerconsumption:

8mw（+5vpowersupplyvoltage,thetypicalvalues）

MC14433'smainpurposeisdigitalvoltmeter,digitalthermometerandotherkindsofdigitalinstrumentandcomputerdataacquisitionsystemofA/Dconversioninterface.AdoptsbitBCDoutputdynamicscanningmethod,namely,thousands,hundreds,10andbitsBCDtime-sharinginQ0,Q3outputinturn,atthesametimeintheDS1-outputDS4synchronouswordgate,veryconvenienttorealizethedynamicdisplayoftheLED.

（4）Alarmsystem

Thebasicprincipleisasfollows:

Uhtolimitalarmvoltage,Ulforthelowerlimitalarmvoltage.

WhentheUi>Uh,theoutputoftheop-ampA1Uo1=+Uom,theoutputoftheop-ampA2Uo2=-Uom,conductionD1,D2cut-off,voltageregulatortubeDzworkinvoltagestate,outputUo=+Uz.

WhenUl

WhentheUi

SowhentheUibeyondtheupperandlowerlimit,Uo=+Uz,weusedthelightemittingdiodeandabuzzer,atthistimetoreporttoalarmsystem.

Censoredbyswitchcontrol.

Thisunitweusewindowcomparator,circuitisasfollows:

4.Componentlist

Temperaturedisplay,soundandlightalarmandmutecircuitcomponentlist

Type

Nameoftype

Parameter

Number

Resistance

10

2

100

14

500

1

1K

10

10K

4

20K

2

4.7K

2

470K

2

Resistancebox

1

resistance

10K

2

Capacity

nonpolarity

0.1u

4

0.05u

1

heteropolarity

250u

1

Diode

2

Luminousdiode

red

1

green

1

Stabilivolt

5V

1

Audion

NPN

2

Integratedamplifier

OP07

2

LM119

1

LM386

1

Integratedchip

MC1403

1

MC14433

1

MC1413

1

CC4511

1

FourdigitLEDnixietube

1

Loudsapaker

1

Switch

2