模电设计 温度计英文Word格式文档下载.docx

模电设计 温度计英文Word格式文档下载.docx

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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℃<

t<

0℃，

Rt100=100×

[1+A×

t+B×

t×

t+C×

（t-100）]

（1）

0℃<

=t<

=850℃，Rt100=100×

（1+A×

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<

Ui<

Uh,theoutputoftheop-ampA1Uo1=-Uom,theoutputoftheop-ampA2Uo2=-Uom,D1deadline,asD2,outputUo=0.

WhentheUi<

Ul,theoutputoftheop-ampA1Uo1=-Uom,theoutputoftheop-ampA2Uo2=+Uom,D2conduction,D1cut-off,voltageregulatortubeDzworkinvoltagestate,outputUo=+Uz.

SowhentheUibeyondtheupperandlowerlimit,Uo=+Uz,weusedthelightemittingdiodeandabuzzer,atthistimetoreporttoalarmsystem.

Censoredbyswitchcontrol.

Thisunitweusewindowcomparator,circuitisasfollows:

4.Componentlist

Temperaturedisplay,soundandlightalarmandmutecircuitcomponentlist

Type

Nameoftype

Parameter

Number

Resistance

10

2

100

14

500

1

1K

10K

4

20K

4.7K

470K

Resistancebox

resistance

Capacity

nonpolarity

0.1u

0.05u

heteropolarity

250u

Diode

Luminousdiode

red

green

Stabilivolt

5V

Audion

NPN

Integratedamplifier

OP07

LM119

LM386

Integratedchip

MC1403

MC14433

MC1413

CC4511

FourdigitLEDnixietube

Loudsapaker

Switch