Qhov no yog thawj tsab xov xwm nyob rau hauv ib tug thib ob series. Kab lus no yuav xub tham txog keeb kwm thiab tsim cov nyom ntawmThermistor raws li qhov kub thiab txiasKev ntsuas ntsuas, nrog rau lawv qhov kev sib piv nrog cov ntsuas kub tsis kam (RTD) ntsuas qhov ntsuas kub. Nws tseem yuav piav qhia txog kev xaiv ntawm thermistor, kev teeb tsa kev lag luam tawm, thiab qhov tseem ceeb ntawm sigma-delta analog-to-digital converters (ADCs) hauv thaj chaw thov no. Tshooj thib ob yuav piav qhia yuav ua li cas txhawm rau txhim kho thiab ntsuas qhov kawg thermistor-based ntsuas system.
Raws li tau piav nyob rau hauv tsab xov xwm dhau los, Optimizing RTD Temperature Sensor Systems, RTD yog ib qho resistor uas nws kuj txawv nrog kub. Thermistor ua haujlwm zoo ib yam li RTDs. Tsis zoo li RTDs, uas tsuas yog muaj qhov ntsuas kub zoo, lub thermistor tuaj yeem muaj qhov zoo lossis qhov kub tsis zoo. Tsis zoo kub coefficient (NTC) thermistor txo lawv qhov tsis kam raws li qhov kub thiab txias nce, thaum zoo kub coefficient (PTC) thermistors ua rau lawv tsis kam thaum kub nce. Ntawm daim duab. 1 qhia cov lus teb cov yam ntxwv ntawm NTC thiab PTC thermistor thiab muab piv rau RTD nkhaus.
Nyob rau hauv cov nqe lus ntawm qhov kub thiab txias, RTD nkhaus yog ze li ntawm linear, thiab lub sensor npog ntau qhov kub thiab txias ntau dua li cov thermistor (feem ntau -200 ° C txog + 850 ° C) vim qhov tsis-linear (exponential) ntawm tus thermistor. RTDs feem ntau yog muab rau hauv cov qauv kev paub zoo, thaum thermistor nkhaus sib txawv los ntawm cov chaw tsim khoom. Peb yuav tham txog qhov no kom ntxaws hauv tshooj lus qhia kev xaiv thermistor ntawm kab lus no.
Thermistor yog tsim los ntawm cov ntaub ntawv sib xyaw, feem ntau yog ceramics, polymers, lossis semiconductors (feem ntau yog hlau oxides) thiab cov hlau ntshiab (platinum, nickel, lossis tooj liab). Thermistors tuaj yeem kuaj xyuas qhov kub thiab txias hloov sai dua li RTDs, muab cov lus qhia sai dua. Yog li ntawd, cov thermistors feem ntau yog siv los ntawm cov sensors hauv cov ntawv thov uas xav tau tus nqi qis, me me, cov lus teb sai dua, muaj kev nkag siab zoo dua, thiab qhov ntsuas kub tsawg, xws li kev tswj hluav taws xob, kev tswj xyuas hauv tsev thiab lub tsev, cov chaw soj nstuam, lossis kev sib txuas txias rau cov thermocouples hauv kev lag luam. los yog cov ntawv thov kev lag luam. lub hom phiaj. Daim ntawv thov.
Feem ntau, NTC thermistor yog siv rau qhov ntsuas kub kom raug, tsis yog PTC thermistors. Qee cov PTC thermistors muaj uas tuaj yeem siv rau hauv kev tiv thaiv overcurrent circuits lossis ua fuses resettable rau daim ntawv thov kev nyab xeeb. Kev tiv thaiv-kub nkhaus ntawm PTC thermistor qhia txog thaj tsam NTC me me ua ntej mus txog qhov hloov pauv (lossis Curie point), saum toj no uas qhov kev tawm tsam tau nce siab los ntawm ntau qhov kev txiav txim siab ntawm qhov ntau ntawm ntau degrees Celsius. Nyob rau hauv cov xwm txheej overcurrent, PTC thermistor yuav ua kom muaj zog ntawm tus kheej cua sov thaum hloov qhov kub thiab txias, thiab nws qhov kev tiv thaiv yuav nce siab, uas yuav txo cov tswv yim tam sim no rau lub cev, yog li tiv thaiv kev puas tsuaj. Qhov hloov pauv ntawm PTC thermistor feem ntau yog nruab nrab ntawm 60 ° C thiab 120 ° C thiab tsis haum rau kev tswj qhov ntsuas kub hauv ntau hom kev siv. Kab lus no tsom mus rau NTC thermistors, uas feem ntau tuaj yeem ntsuas lossis saib xyuas qhov kub ntawm -80 ° C txog + 150 ° C. NTC thermistors muaj qhov ntsuas tsis kam ntawm ob peb ohms mus rau 10 MΩ ntawm 25 ° C. Raws li qhia hauv daim duab. 1, qhov kev hloov pauv ntawm kev tiv thaiv ib degree Celsius rau cov thermistor yog ntau tshaj li qhov ntsuas kub tsis kam. Piv nrog rau cov thermistor, lub thermistor lub siab rhiab heev thiab tus nqi siab ua rau nws yooj yim rau nws cov khoom siv hluav taws xob, vim tias cov thermistor tsis tas yuav muaj kev teeb tsa tshwj xeeb, xws li 3-xaim lossis 4-xaim, kom them nyiaj rau cov hmoov txhuas. Tus thermistor tsim siv tsuas yog ib qho yooj yim 2-xaim teeb tsa.
High-precision thermistor-raws li ntsuas kub yuav tsum tau ua cov teeb liab ua tiav, kev hloov pauv analog-rau-digital, linearization, thiab them nyiaj, raws li qhia hauv daim duab. 2.
Txawm hais tias lub teeb liab sawb yuav zoo li yooj yim, muaj ntau qhov nyuaj uas cuam tshuam qhov loj, nqi, thiab kev ua haujlwm ntawm tag nrho cov motherboard. ADI's precision ADC portfolio suav nrog ntau qhov kev daws teeb meem, xws li AD7124-4 / AD7124-8, uas muab ntau qhov zoo rau kev tsim qauv thermal vim tias feem ntau ntawm lub tsev thaiv kev xav tau rau daim ntawv thov yog built-in. Txawm li cas los xij, muaj ntau yam kev sib tw hauv kev tsim thiab ua kom zoo dua cov thermistor-raws li ntsuas kub ntsuas kev daws teeb meem.
Kab lus no tham txog txhua yam ntawm cov teeb meem no thiab muab cov lus pom zoo rau kev daws teeb meem thiab ua kom yooj yim rau kev tsim cov txheej txheem rau cov tshuab no.
Muaj ntau ntau yamNTC Thermistorsntawm kev ua lag luam niaj hnub no, yog li xaiv tus thermistor txoj cai rau koj daim ntawv thov tuaj yeem ua haujlwm txaus ntshai. Nco ntsoov tias cov thermistors tau teev los ntawm lawv tus nqi nominal, uas yog lawv cov nominal tsis kam ntawm 25 ° C. Yog li ntawd, 10 kΩ thermistor muaj qhov nominal tsis kam ntawm 10 kΩ ntawm 25 ° C. Thermistors muaj nominal los yog yooj yim kuj qhov tseem ceeb xws li los ntawm ob peb ohms mus rau 10 MΩ. Thermistors uas tsis tshua muaj kev ntsuas (nominal kuj ntawm 10 kΩ lossis tsawg dua) feem ntau txhawb qis qis qis, xws li -50 ° C txog +70 ° C. Thermistors nrog cov kev ntsuas siab dua tuaj yeem tiv taus qhov kub txog li 300 ° C.
Cov khoom siv thermistor yog ua los ntawm cov hlau oxide. Thermistors muaj nyob rau hauv pob, radial thiab SMD duab. Thermistor hlaws yog epoxy coated los yog iav encapsulated rau kev tiv thaiv ntxiv. Epoxy coated pob thermistors, radial thiab nto thermistor yog tsim rau kub txog li 150 ° C. Cov iav hlaws thermistor yog tsim rau ntsuas qhov kub thiab txias. Txhua hom txheej / ntim kuj tiv thaiv corrosion. Qee cov thermistor kuj tseem yuav muaj vaj tse ntxiv rau kev tiv thaiv ntxiv hauv qhov chaw hnyav. Bead thermistors muaj lub sijhawm teb sai dua li radial / SMD thermistors. Txawm li cas los xij, lawv tsis zoo li ruaj. Yog li ntawd, hom thermistor siv nyob ntawm qhov kawg daim ntawv thov thiab ib puag ncig uas lub thermistor nyob. Lub sij hawm ntev stability ntawm lub thermistor nyob ntawm nws cov khoom, ntim, thiab tsim. Piv txwv li, epoxy-coated NTC thermistor tuaj yeem hloov 0.2 ° C hauv ib xyoos, thaum lub tshuab thermistor kaw tsuas yog hloov 0.02 ° C hauv ib xyoos.
Thermistor tuaj nyob rau hauv qhov sib txawv. Tus qauv thermistors feem ntau muaj qhov tseeb ntawm 0.5 ° C txog 1.5 ° C. Lub thermistor kuj ntsuas thiab beta tus nqi (qhov piv ntawm 25 ° C rau 50 ° C / 85 ° C) muaj qhov kam rau ua. Nco ntsoov tias tus nqi beta ntawm lub thermistor txawv ntawm cov chaw tsim khoom. Piv txwv li, 10 kΩ NTC thermistor los ntawm cov tuam txhab sib txawv yuav muaj qhov sib txawv beta. Rau cov tshuab muaj tseeb dua, thermistors xws li Omega ™ 44xxx series tuaj yeem siv. Lawv muaj qhov tseeb ntawm 0.1 ° C lossis 0.2 ° C tshaj qhov kub ntawm 0 ° C txog 70 ° C. Yog li ntawd, qhov ntau ntawm qhov kub thiab txias uas tuaj yeem ntsuas tau thiab qhov tseeb uas yuav tsum tau muaj tshaj qhov ntsuas kub no txiav txim siab seb cov thermistor puas haum rau daim ntawv thov no. Thov nco ntsoov tias qhov siab dua qhov tseeb ntawm Omega 44xxx series, tus nqi siab dua.
Txhawm rau hloov tsis kam mus rau degrees Celsius, tus nqi beta feem ntau yog siv. Tus nqi beta yog txiav txim siab los ntawm kev paub txog ob lub ntsiab lus kub thiab qhov sib raug zoo ntawm txhua qhov ntsuas kub.
RT1 = Kub tiv taus 1 RT2 = Kub ua haujlwm 2 T1 = Kub 1 (K) T2 = Kub 2 (K)
Tus neeg siv siv tus nqi beta ze tshaj plaws rau qhov ntsuas kub uas siv hauv qhov project. Cov ntaub ntawv thermistor feem ntau teev cov nqi beta nrog rau qhov ua siab ntev ntawm 25 ° C thiab kam rau siab rau tus nqi beta.
Ntau dua precision thermistors thiab siab precision txiav kev daws teeb meem xws li Omega 44xxx series siv Steinhart-Hart sib npaug los hloov tsis kam mus rau degrees Celsius. Qhov sib npaug 2 yuav tsum muaj peb qhov A, B, thiab C, rov muab los ntawm cov chaw tsim khoom sensor. Vim tias qhov sib npaug sib npaug yog tsim los siv peb lub ntsiab lus kub, qhov sib npaug ua rau txo qhov kev ua yuam kev los ntawm linearization (feem ntau yog 0.02 ° C).
A, B thiab C yog qhov tsis tu ncua los ntawm peb qhov ntsuas kub. R = thermistor tsis kam hauv ohms T = kub hauv K degrees
Ntawm daim duab. 3 qhia tau hais tias tam sim no excitation ntawm lub sensor. Tsav tam sim no yog siv rau lub thermistor thiab tib lub sijhawm tam sim no yog siv rau qhov ntsuas qhov tseeb; ib tug precision resistor yog siv raws li ib tug siv rau kev ntsuas. Tus nqi ntawm qhov siv resistor yuav tsum ntau dua los yog sib npaug rau qhov siab tshaj plaws ntawm cov thermistor tsis kam (nyob ntawm qhov ntsuas kub qis tshaj hauv qhov system).
Thaum xaiv qhov excitation tam sim no, qhov siab tshaj plaws ntawm cov thermistor yuav tsum rov muab coj los rau hauv tus account. Qhov no ua kom ntseeg tau tias qhov hluav taws xob thoob plaws lub sensor thiab cov khoom siv hluav taws xob yog ib txwm nyob rau theem uas tau txais los ntawm cov khoom siv hluav taws xob. Qhov chaw tam sim no yuav tsum muaj qee qhov chaw headroom lossis tso zis sib piv. Yog tias lub thermistor muaj qhov ua haujlwm siab ntawm qhov ntsuas qhov ntsuas qis tshaj plaws, qhov no yuav ua rau lub zog tsav tam sim no tsawg heev. Yog li ntawd, qhov voltage generated hla lub thermistor ntawm qhov kub thiab txias yog me me. Programmable nce qib tuaj yeem siv los ua kom zoo dua qhov ntsuas ntawm cov cim qis qis no. Txawm li cas los xij, qhov nce yuav tsum tau programmed dynamically vim hais tias lub teeb liab theem ntawm lub thermistor txawv heev nrog kub.
Lwm qhov kev xaiv yog los teeb tsa qhov nce tab sis siv lub zog tsav tam sim no. Yog li ntawd, raws li lub teeb liab theem ntawm lub thermistor hloov, tus nqi tam sim no tus nqi hloov dynamically thiaj li hais tias qhov voltage tsim nyob rau hauv lub thermistor nyob rau hauv lub teev input ntau yam ntawm cov khoom siv hluav taws xob. Tus neeg siv yuav tsum xyuas kom meej tias qhov hluav taws xob tsim tawm thoob plaws qhov kev siv resistor kuj yog nyob rau theem uas tau txais los ntawm cov khoom siv hluav taws xob. Ob qho kev xaiv yuav tsum muaj kev tswj hwm qib siab, kev saib xyuas tas li ntawm qhov hluav taws xob hla lub thermistor kom cov khoom siv hluav taws xob tuaj yeem ntsuas lub teeb liab. Puas muaj kev xaiv yooj yim dua? Xav txog voltage excitation.
Thaum DC voltage siv rau lub thermistor, tam sim no los ntawm lub thermistor cia li ntsuas raws li lub thermistor tsis kam hloov. Tam sim no, siv lub ntsuas ntsuas ntsuas qhov ntsuas qhov ntsuas tsis yog siv cov ntsuas ntsuas, nws lub hom phiaj yog xam cov tam sim no ntws los ntawm lub thermistor, yog li tso cai rau ntsuas ntsuas ntsuas ntsuas. Txij li thaum tsav hluav taws xob kuj tseem siv los ua ADC siv lub teeb liab, tsis tas yuav tsum muaj theem nce. Lub processor tsis muaj lub luag haujlwm ntawm kev saib xyuas lub thermistor voltage, txiav txim siab seb lub teeb liab yuav ntsuas tau los ntawm cov khoom siv hluav taws xob, thiab xam seb qhov twg tsav nce / tam sim no tus nqi yuav tsum tau kho. Qhov no yog txoj kev siv hauv kab lus no.
Yog tias lub thermistor muaj qhov ntsuas me me thiab qhov ua haujlwm tsis kam, qhov hluav taws xob lossis qhov kev tawm dag zog tam sim no tuaj yeem siv. Hauv qhov no, tus tsav tam sim no thiab nce tuaj yeem kho tau. Yog li, lub Circuit Court yuav ua tau raws li qhia nyob rau hauv daim duab 3. Txoj kev no yog yooj yim nyob rau hauv uas nws muaj peev xwm tswj tau qhov tam sim no los ntawm lub sensor thiab cov ntaub ntawv resistor, uas yog ib qho tseem ceeb nyob rau hauv tsis tshua muaj zog daim ntaub ntawv. Tsis tas li ntawd, nws tus kheej cua sov ntawm lub thermistor yog qhov tsawg.
Voltage excitation kuj tseem siv tau rau cov thermistor nrog cov kev ntsuas qis. Txawm li cas los xij, tus neeg siv yuav tsum nco ntsoov xyuas kom meej tias tam sim no los ntawm lub sensor tsis siab dhau rau lub sensor lossis daim ntawv thov.
Voltage excitation ua kom yooj yim rau kev siv thaum siv lub thermistor nrog qhov ntsuas qhov ntsuas loj thiab qhov kub ntau. Loj nominal kuj muab ib qho kev lees paub ntawm cov ntsuas tam sim no. Txawm li cas los xij, cov neeg tsim qauv yuav tsum xyuas kom meej tias qhov tam sim no nyob rau ntawm qhov kev lees paub ntawm tag nrho cov kev ntsuas kub uas txhawb nqa los ntawm daim ntawv thov.
Sigma-Delta ADCs muaj ntau qhov zoo thaum tsim lub thermistor ntsuas qhov system. Ua ntej, vim hais tias lub sigma-delta ADC resamples cov analog tawm tswv yim, kev lim tawm sab nraud yog khaws cia rau qhov tsawg kawg nkaus thiab tsuas yog qhov yuav tsum tau ua yog RC lim yooj yim. Lawv muab kev yooj yim hauv cov lim hom thiab tso zis baud tus nqi. Built-in digital filtering tuaj yeem siv los txwv kev cuam tshuam hauv cov khoom siv hluav taws xob. 24-ntsis li xws li AD7124-4 / AD7124-8 muaj tag nrho cov kev daws teeb meem txog 21.7 khoom, yog li lawv muab kev daws teeb meem siab.
Kev siv cov sigma-delta ADC ua kom yooj yim rau cov thermistor tsim thaum txo cov kev qhia tshwj xeeb, cov nqi siv hluav taws xob, chaw ua haujlwm, thiab lub sijhawm ua lag luam.
Kab lus no siv AD7124-4/AD7124-8 raws li ADC vim tias lawv tsis muaj suab nrov, tsis tshua muaj tam sim no, precision ADCs nrog built-in PGA, built-in reference, analog input, thiab siv tsis.
Txawm hais tias koj tab tom siv tsav tam sim no lossis tsav voltage, qhov ratiometric configuration yog pom zoo nyob rau hauv uas cov ntaub ntawv voltage thiab sensor voltage los ntawm tib qhov chaw tsav. Qhov no txhais tau hais tias txhua qhov kev hloov pauv ntawm qhov excitation yuav tsis cuam tshuam qhov tseeb ntawm qhov ntsuas.
Ntawm daim duab. 5 qhia cov tsav tam sim no rau lub thermistor thiab precision resistor RREF, qhov hluav taws xob tsim thoob plaws RREF yog qhov siv hluav taws xob rau kev ntsuas lub thermistor.
Lub teb tam sim no tsis tas yuav tsum yog qhov tseeb thiab yuav tsis ruaj khov vim tias muaj kev ua yuam kev hauv thaj chaw tam sim no yuav raug tshem tawm hauv qhov teeb tsa no. Feem ntau, tam sim no excitation yog nyiam dua voltage excitation vim superior rhiab heev tswj thiab zoo suab nrov tiv thaiv thaum lub sensor nyob rau hauv tej thaj chaw deb qhov chaw. Hom kev tsis ncaj ncees no feem ntau yog siv rau RTDs lossis cov thermistor nrog cov nqi qis. Txawm li cas los xij, rau lub thermistor nrog tus nqi siab dua thiab muaj kev nkag siab ntau dua, lub teeb liab theem tsim los ntawm txhua qhov kub hloov pauv yuav loj dua, yog li siv qhov hluav taws xob excitation. Piv txwv li, 10 kΩ thermistor muaj qhov tsis kam ntawm 10 kΩ ntawm 25 ° C. Ntawm -50 ° C, qhov tsis kam ntawm NTC thermistor yog 441.117 kΩ. Qhov tsawg kawg nkaus tsav tam sim no ntawm 50 µA muab los ntawm AD7124-4 / AD7124-8 generates 441.117 kΩ × 50 µA = 22 V, uas yog siab dhau thiab sab nraum qhov kev khiav hauj lwm ntau ntawm ADCs uas muaj nyob rau hauv daim ntawv thov no. Thermistors kuj feem ntau txuas nrog lossis nyob ze ntawm cov khoom siv hluav taws xob, yog li kev tiv thaiv kev tsav tsheb tsis tas yuav tsum muaj.
Ntxiv ib qho kev nkag siab resistor nyob rau hauv series raws li ib tug voltage divider Circuit Court yuav txwv qhov tam sim no los ntawm lub thermistor rau nws yam tsawg kawg nkaus kuj nqi. Nyob rau hauv no configuration, tus nqi ntawm qhov kev nkag siab resistor RSENSE yuav tsum sib npaug zos rau tus nqi ntawm lub thermistor tsis kam ntawm ib tug reference kub ntawm 25 ° C, thiaj li hais tias cov zis voltage yuav sib npaug zos rau lub midpoint ntawm lub reference voltage ntawm nws nominal kub. 25 ° CC Ib yam li ntawd, yog siv 10 kΩ thermistor nrog kev ua haujlwm ntawm 10 kΩ ntawm 25 ° C, RSENSE yuav tsum yog 10 kΩ. Raws li qhov kub hloov pauv, qhov tsis kam ntawm NTC thermistor kuj hloov, thiab qhov sib piv ntawm cov tsav hluav taws xob hla lub thermistor kuj hloov, uas ua rau cov zis hluav taws xob yog proportional rau qhov tsis kam ntawm NTC thermistor.
Yog tias qhov kev siv hluav taws xob xaiv tau siv los ua lub zog thermistor thiab / lossis RSENSE phim ADC siv hluav taws xob siv rau kev ntsuas, lub kaw lus tau teeb tsa rau qhov ntsuas ntsuas ntsuas (Daim duab 7) kom txhua qhov kev cuam tshuam txog qhov yuam kev voltage yuav raug tshem tawm.
Nco ntsoov tias txawm tias qhov kev nkag siab resistor (voltage driven) los yog tus siv resistor (tam sim no tau tsav) yuav tsum muaj qhov pib ua siab ntev thiab qis qis, vim tias ob qho tib si kuj tuaj yeem cuam tshuam qhov tseeb ntawm tag nrho cov kab ke.
Thaum siv ntau lub thermistor, ib qho kev tawm dag zog tuaj yeem siv tau. Txawm li cas los xij, txhua tus thermistor yuav tsum muaj nws tus kheej precision siab resistor, raws li qhia hauv daim duab. 8. Lwm qhov kev xaiv yog siv ib qho kev sib txuas sab nraud lossis qhov hloov pauv qis hauv lub xeev, uas tso cai rau sib koom ib qho kev txiav txim siab zoo resistor. Nrog rau qhov kev teeb tsa no, txhua tus thermistor xav tau qee lub sijhawm daws teeb meem thaum ntsuas.
Hauv cov ntsiab lus, thaum tsim lub thermistor-raws li ntsuas qhov ntsuas kub, muaj ntau cov lus nug los xav txog: kev xaiv sensor, sensor wiring, tivthaiv xaiv kev lag luam tawm, ADC configuration, thiab yuav ua li cas cov kev sib txawv no cuam tshuam rau tag nrho qhov tseeb ntawm lub system. Cov kab lus txuas ntxiv hauv cov kab no piav qhia yuav ua li cas txhawm rau txhim kho koj lub system tsim thiab tag nrho cov peev txheej yuam kev kom ua tiav koj lub hom phiaj kev ua haujlwm.
Post lub sij hawm: Sep-30-2022