Lesi isihloko sokuqala ochungechungeni olunezingxenye ezimbili.Lesi sihloko sizoxoxa kuqala ngomlando kanye nezinselelo zokuklama zeizinga lokushisa elisekelwe ku-thermistoramasistimu okulinganisa, kanye nokuqhathanisa kwawo ne-resistance thermometer (RTD) izinhlelo zokulinganisa izinga lokushisa.Izophinde ichaze ukukhethwa kwe-thermistor, ukucushwa kokuhwebelana, nokubaluleka kweziguquli ze-sigma-delta analog-to-digital (ADCs) kule ndawo yohlelo lokusebenza.I-athikili yesibili izocacisa ukuthi ungalungiselela kanjani futhi uhlole isistimu yokugcina esekelwe ku-thermistor.
Njengoba kuchazwe ochungechungeni lwe-athikili edlule, I-Optimizing RTD Temperature Sensor Systems, i-RTD iyisivikeli esi ukumelana kwaso kuyahlukahluka nezinga lokushisa.Ama-thermistors asebenza ngokufanayo nama-RTD.Ngokungafani nama-RTD, ane-coefficient yokushisa ephozithivu kuphela, i-thermistor ingaba ne-coefficient yokushisa ephozithivu noma engalungile.Izifudumezi ze-thermist ezinegative (NTC) zinciphisa ukumelana kwazo njengoba izinga lokushisa likhuphuka, kuyilapho ama-thermistors e-positive coefficient (PTC) akhulisa ukumelana kwawo njengoba izinga lokushisa likhuphuka.Emkhiwaneni.1 ikhombisa izici zokuphendula ze-NTC ne-PTC thermistors ezijwayelekile futhi iziqhathanise namajika e-RTD.
Ngokwezinga lokushisa, ijika le-RTD licishe lilingane, futhi inzwa ihlanganisa izinga lokushisa elibanzi kakhulu kunama-thermistors (ngokuvamile -200 ° C kuya ku-+850 ° C) ngenxa yemvelo engaqondile (exponential) ye-thermistor.Ama-RTD ngokuvamile ahlinzekwa ngamajika ajwayelekile ajwayelekile, kuyilapho amajika e-thermistor ehluka ngomkhiqizi.Sizoxoxa ngalokhu ngokuningiliziwe esigabeni somhlahlandlela wokukhetha i-thermistor yalesi sihloko.
Ama-thermistors enziwe ngezinto eziyinhlanganisela, ngokuvamile i-ceramics, ama-polymers, noma ama-semiconductors (imvamisa ama-oxide ensimbi) nezinsimbi ezihlanzekile (i-platinum, nickel, noma ithusi).Ama-thermistors angakwazi ukubona ukushintsha kwezinga lokushisa ngokushesha kunama-RTD, anikeze impendulo esheshayo.Ngakho-ke, ama-thermistors ngokuvamile asetshenziswa izinzwa ezinhlelweni ezidinga izindleko eziphansi, usayizi omncane, impendulo esheshayo, ukuzwela okuphezulu, kanye nebanga lokushisa elilinganiselwe, njengokulawula ugesi, ukulawulwa kwendlu nesakhiwo, amalabhorethri esayensi, noma isinxephezelo sendawo ebandayo yama-thermocouples kwezohwebo. noma izicelo zezimboni.izinjongo.Izinhlelo zokusebenza.
Ezimweni eziningi, ama-thermistors e-NTC asetshenziselwa ukulinganisa izinga lokushisa okunembile, hhayi ama-thermistors e-PTC.Amanye ama-thermistor e-PTC ayatholakala angasetshenziswa kumasekhethi okuvikela okudlulele noma njengamafuse asethwa kabusha ezinhlelo zokuphepha.Ijika lokumelana nezinga lokushisa le-thermistor ye-PTC libonisa isifunda esincane kakhulu se-NTC ngaphambi kokufinyelela endaweni yokushintsha (noma iphoyinti le-Curie), ngaphezu kwalokho ukumelana kuphakama ngokucijile ngama-oda amaningana obukhulu ebangeni lama-degree Celsius amaningana.Ngaphansi kwezimo ze-overcurrent, i-thermistor ye-PTC izokhiqiza ukuzifudumeza okuqinile lapho izinga lokushisa lokushintsha lidlula, futhi ukumelana kwayo kuzokhuphuka kakhulu, okuzonciphisa okwamanje okokufaka ohlelweni, ngaleyo ndlela kuvimbele umonakalo.Indawo yokushintsha yama-thermistors e-PTC ngokuvamile iphakathi kuka-60°C no-120°C futhi ayifaneleki ukulawula ukukalwa kwezinga lokushisa kuhlelo olubanzi lwezinhlelo zokusebenza.Lesi sihloko sigxile kuma-thermistors e-NTC, ngokuvamile angakala noma aqaphe amazinga okushisa ukusuka ku- -80°C kuya ku-+150°C.Ama-thermistors e-NTC anezilinganiso zokumelana ezisuka kuma-ohm ambalwa kuye ku-10 MΩ ku-25°C.Njengoba kuboniswe emkhiwaneni.1, uguquko lokumelana ngedigri Celsius yama-thermistors lugqama kakhulu kunamathemometha okumelana.Uma kuqhathaniswa nama-thermistor, ukuzwela okuphezulu kwe-thermistor kanye nenani eliphezulu lokumelana kwenza kube lula ukujikeleza kwayo okokufaka, njengoba ama-thermistors awadingi noma yikuphi ukucushwa kwezintambo okukhethekile, njenge-3-wire noma 4-wire, ukunxephezela ukumelana nomthofu.Idizayini ye-thermistor isebenzisa kuphela ukucushwa okulula kwe-2-wire.
Ukulinganisa izinga lokushisa okusekelwe ku-thermistor okunembe kakhulu kudinga ukucutshungulwa kwesignali okunembile, ukuguqulwa kwe-analog-to-digital, umugqa, kanye nesinxephezelo, njengoba kuboniswe ku-fig.2.
Nakuba uchungechunge lwesignali lungabonakala lulula, kunezinto ezimbalwa eziyinkimbinkimbi ezithinta usayizi, izindleko, nokusebenza kwebhodi lomama lonke.Iphothifoliyo ye-ADI enembayo ye-ADC ihlanganisa izixazululo ezimbalwa ezihlanganisiwe, njenge-AD7124-4/AD7124-8, ehlinzeka ngenani lezinzuzo zomklamo wesistimu eshisayo njengoba iningi lamabhulokhi wokwakha adingekayo wohlelo lokusebenza akhelwe ngaphakathi.Kodwa-ke, kunezinselelo ezahlukahlukene ekuklameni nasekulungiseleleni izixazululo zokulinganisa izinga lokushisa ezisekelwe ku-thermistor.
Lesi sihloko sidingida ngayinye yalezi zinkinga futhi inikeza izincomo zokuzixazulula kanye nokwenza lula inqubo yokuklama yalezi zinhlelo.
Kunezinhlobonhlobo eziningiAma-thermistors e-NTCemakethe namuhla, ngakho ukukhetha i-thermistor efanele yohlelo lwakho lokusebenza kungaba umsebenzi onzima.Qaphela ukuthi ama-thermistors afakwe kuhlu ngevelu yawo yokulinganisa, okuwukumelana kwawo okuzisholo kokuthi 25°C.Ngakho-ke, i-thermistor engu-10 kΩ inokumelana okujwayelekile okungu-10 kΩ ku-25°C.Ama-thermistors anenani eliyisisekelo noma eliyisisekelo lokumelana ukusuka kuma-ohm ambalwa kuye ku-10 MΩ.Ama-thermistors anezilinganiso eziphansi zokumelana (ukumelana okulinganiselwe okungu-10 kΩ noma ngaphansi) ngokuvamile asekela amazinga okushisa aphansi, afana -50°C kuya ku-+70°C.Ama-thermitors anezilinganiso eziphakeme zokumelana akwazi ukumelana nezinga lokushisa elifinyelela ku-300°C.
I-elementi ye-thermistor yenziwe nge-metal oxide.Ama-thermistors atholakala ngebhola, i-radial kanye ne-SMD shapes.Ubuhlalu be-Thermistor buyi-epoxy coated noma ingilazi ehlanganiswe ukuze kuvikeleke okwengeziwe.Ama-thermistors ebhola ahlanganiswe nge-epoxy, ama-radial kanye nama-surface thermistors afanele izinga lokushisa elifinyelela ku-150°C.Ama-thermistors obuhlalu bengilazi afanele ukukala amazinga okushisa aphezulu.Zonke izinhlobo zokumboza/zokupakisha nazo zivikela ekugqwaleni.Amanye ama-thermistors azoba nezindlu ezengeziwe zokuvikela okungeziwe ezindaweni ezinokhahlo.Izifudumezi zobuhlalu zinesikhathi sokuphendula esisheshayo kune-radial/SMD thermistors.Nokho, azihlali isikhathi eside.Ngakho-ke, uhlobo lwe-thermistor olusetshenzisiwe luncike ekusetshenzisweni kokuphela kanye nemvelo lapho i-thermistor ikhona.Ukuzinza kwesikhathi eside kwe-thermistor kuncike ezintweni zayo, ukupakishwa, kanye nomklamo.Isibonelo, i-epoxy-coated NTC thermistor ingashintsha u-0.2°C ngonyaka, kuyilapho i-thermistor evaliwe ishintsha kuphela u-0.02°C ngonyaka.
Ama-thermitors afika ngokunemba okuhlukile.Izifudumezi ezijwayelekile ngokuvamile zinokunemba okungu-0.5°C kuya ku-1.5°C.Isilinganiso sokumelana ne-thermistor kanye nevelu ye-beta (isilinganiso esingu-25°C kuya ku-50°C/85°C) sinokubekezelela.Qaphela ukuthi inani le-beta le-thermistor liyahlukahluka ngomkhiqizi.Isibonelo, ama-thermistors angu-10 kΩ NTC avela kubakhiqizi abahlukene bazoba namanani ahlukene e-beta.Ukuze uthole amasistimu anembe kakhudlwana, ama-thermistors afana nochungechunge lwe-Omega™ 44xxx angasetshenziswa.Zinokunemba okungu-0.1°C noma u-0.2°C ngaphezu kwezinga lokushisa lika-0°C kuya ku-70°C.Ngakho-ke, ububanzi bamazinga okushisa angakwazi ukukalwa kanye nokunemba okudingekayo kulolo banga lokushisa inquma ukuthi izifudumezi zilufanele yini lolu hlelo lokusebenza.Sicela uqaphele ukuthi ukuphakama kokunemba kochungechunge lwe-Omega 44xxx, izindleko ziphezulu.
Ukuguqula ukumelana kube amadigri Celsius, inani le-beta livame ukusetshenziswa.Inani le-beta linqunywa ngokwazi amaphuzu amabili okushisa kanye nokumelana okuhambisanayo endaweni ngayinye yezinga lokushisa.
RT1 = Ukumelana nezinga lokushisa 1 RT2 = Ukumelana nezinga lokushisa 2 T1 = Izinga lokushisa 1 (K) T2 = Izinga lokushisa 2 (K)
Umsebenzisi usebenzisa inani le-beta eliseduze nebanga lokushisa elisetshenziswe kuphrojekthi.Iningi lemininingwane yedatha ye-thermistor yenza uhlu lwenani le-beta kanye nokubekezelela ukumelana no-25°C kanye nokubekezelela ivelu ye-beta.
Ama-thermistors anembe kakhulu nezisombululo zokunqanyulwa okunembayo okuphezulu njengochungechunge lwe-Omega 44xxx zisebenzisa i-equation ye-Steinhart-Hart ukuguqula ukumelana kube ngamadigri Celsius.I-equation 2 idinga ama-constants amathathu A, B, no-C, aphinde anikezwe umkhiqizi wezinzwa.Ngenxa yokuthi ama-coefficients equation akhiqizwa kusetshenziswa amaphuzu amathathu okushisa, isibalo esiwumphumela sinciphisa iphutha elethulwa umugqa (ngokuvamile u-0.02 °C).
U-A, B no-C yizinto ezingaguquki ezisuselwe emazingeni amathathu okushisa.R = ukumelana ne-thermistor ku-ohms T = izinga lokushisa ngamadigri angu-K
Emkhiwaneni.3 ikhombisa isasasa lamanje lenzwa.Idrayivu yamanje isetshenziswa ku-thermistor futhi okwamanje okufanayo kusetshenziswe ku-resistor enembile;i-resistor enembile isetshenziswa njengereferensi yokulinganisa.Inani lereferensi yokumelana kufanele libe likhulu noma lilingane nenani eliphakeme kakhulu lokumelana ne-thermistor (kuya ngezinga lokushisa eliphansi elikalwa ohlelweni).
Lapho ukhetha i-excitation current, ukumelana okuphezulu kwe-thermistor kumele kuphinde kucatshangelwe.Lokhu kuqinisekisa ukuthi i-voltage kuyo yonke inzwa kanye nokumelana nesithenjwa kuhlala kusezingeni elamukelekayo kuma-electronics.Umthombo wamanje wenkambu udinga i-headroom noma ukufanisa okukhiphayo.Uma i-thermistor inokumelana okuphezulu ekushiseni okuphansi okulinganisekayo, lokhu kuzoholela ekushayeleni kwamanje okuphansi kakhulu.Ngakho-ke, i-voltage ekhiqizwa kuyo yonke i-thermistor ekushiseni okuphezulu incane.Izigaba zokuzuza ezihlelekayo zingasetshenziswa ukuthuthukisa ukukalwa kwalezi zimpawu ezisezingeni eliphansi.Kodwa-ke, inzuzo kufanele ihlelwe ngokuguquguqukayo ngoba ileveli yesiginali evela ku-thermistor iyahluka kakhulu ngezinga lokushisa.
Enye inketho ukusetha inzuzo kodwa usebenzise i-dynamic drive yamanje.Ngakho-ke, njengoba ileveli yesignali evela ku-thermistor ishintsha, inani lamanje ledrayivu lishintsha ngokushintshashintshayo ukuze i-voltage ethuthukiswe kuyo yonke i-thermistor ibe ngaphakathi kwebanga lokokufaka elishiwo ledivayisi ye-elekthronikhi.Umsebenzisi kufanele aqinisekise ukuthi i-voltage ethuthukiswe kuyo yonke i-reference resistor iphinde ibe sezingeni elamukelekayo kuma-electronics.Zombili izinketho zidinga izinga eliphezulu lokulawula, ukuqapha okuqhubekayo kwe-voltage kuyo yonke i-thermistor ukuze i-electronics ikwazi ukukala isignali.Ingabe ikhona inketho elula?Cabangela i-voltage excitation.
Uma i-DC voltage isetshenziswa ku-thermistor, i-current ngokusebenzisa i-thermistor iyazikala ngokuzenzakalelayo njengoba ukumelana ne-thermistor kushintsha.Manje, kusetshenziswa i-resistor yokulinganisa ukunemba esikhundleni sereferensi resistor, injongo yaso iwukubala okwamanje egeleza ku-thermistor, ngaleyo ndlela kuvunyelwe ukumelana ne-thermistor ukuthi kubalwe.Njengoba i-voltage yokushayela iphinda isetshenziswe njengesignali yereferensi ye-ADC, asikho isigaba sokuzuza esidingekayo.Iphrosesa ayinawo umsebenzi wokuqapha i-voltage ye-thermistor, inquma ukuthi izinga lesiginali lingalinganiswa ngezinto zikagesi, futhi ibale ukuthi iyiphi inzuzo yedrayivu/inani lamanje elidinga ukulungiswa.Lena indlela esetshenziswe kulesi sihloko.
Uma i-thermistor inesilinganiso esincane sokumelana nebanga lokumelana, i-voltage noma i-excitation yamanje ingasetshenziswa.Kulokhu, idrayivu yamanje kanye nenzuzo ingalungiswa.Ngakho, isifunda sizoba njengoba kuboniswe ku-Figure 3. Le ndlela ilula ngoba kungenzeka ukulawula okwamanje ngokusebenzisa inzwa kanye ne-reference resistor, okubalulekile ekusetshenzisweni kwamandla aphansi.Ngaphezu kwalokho, ukuzifudumeza kwe-thermistor kuyancishiswa.
I-voltage excitation ingasetshenziselwa ama-thermistors anezilinganiso eziphansi zokumelana.Kodwa-ke, umsebenzisi kufanele aqinisekise njalo ukuthi okwamanje ngenzwa akuphakeme kakhulu kwinzwa noma uhlelo lokusebenza.
I-voltage excitation yenza kube lula ukusetshenziswa uma usebenzisa i-thermistor enesilinganiso esikhulu sokumelana nebanga lokushisa elibanzi.Ukumelana okukhudlwana okulinganiselwe kunikeza izinga elamukelekayo lamanje elilinganiselwe.Nokho, abaklami kudingeka baqinisekise ukuthi okwamanje kusezingeni elamukelekayo kulo lonke uhla lwezinga lokushisa elisekelwa uhlelo lokusebenza.
Ama-Sigma-Delta ADC anikeza izinzuzo ezimbalwa lapho uklama isistimu yokulinganisa i-thermistor.Okokuqala, ngenxa yokuthi i-sigma-delta ADC yenza isampula kabusha okokufaka kwe-analog, ukuhlunga kwangaphandle kugcinwa kuncane futhi okuwukuphela kwemfuneko isihlungi esilula se-RC.Banikeza ukuguquguquka kohlobo lokuhlunga kanye nezinga lokuphuma kwe-baud.Ukuhlunga kwedijithali okwakhelwe ngaphakathi kungasetshenziswa ukucindezela noma yikuphi ukuphazamiseka kumadivayisi axhaswe ngamapayipi amakhulu.Amadivayisi angama-24-bit afana ne-AD7124-4/AD7124-8 anokulungiswa okugcwele okungafika kumabhithi angama-21.7, ngakho ahlinzeka ngokulungiswa okuphezulu.
Ukusetshenziswa kwe-sigma-delta ADC kwenza idizayini ye-thermistor ibe lula ngenkathi kunciphisa ukucaciswa, izindleko zesistimu, indawo yebhodi, nesikhathi sokumaketha.
Lesi sihloko sisebenzisa i-AD7124-4/AD7124-8 njenge-ADC ngoba inomsindo ophansi, yamanje ephansi, ama-ADC anembayo ane-PGA eyakhelwe ngaphakathi, ireferensi eyakhelwe ngaphakathi, okokufaka kwe-analog, kanye ne-reference buffer.
Kungakhathaliseki ukuthi usebenzisa idrayivu yamanje noma i-voltage yedrayivu, ukucushwa kwe-ratiometric kuyanconywa lapho i-voltage eyireferensi kanye ne-sensor voltage kuvela kumthombo ofanayo wedrayivu.Lokhu kusho ukuthi noma yiluphi ushintsho emthonjeni wokuvusa angeke luthinte ukunemba kwesilinganiso.
Emkhiwaneni.5 ikhombisa idrayivu eqhubekayo ye-thermistor kanye ne-precision resistor RREF, i-voltage ethuthukiswe kuyo yonke i-RREF i-voltage eyireferensi yokulinganisa i-thermistor.
Inkundla yamanje ayidingi ukuthi inembe futhi ingase ingazinzi kangako njengoba noma imaphi amaphutha kumkhakha wamanje azosuswa kulokhu kulungiselelwa.Ngokuvamile, ukuvuswa kwamanje kukhethwa ngaphezu kokuvuswa kwamandla kagesi ngenxa yokulawula ukuzwela okuphakeme kanye nokuvikeleka komsindo okungcono uma inzwa itholakala ezindaweni ezikude.Lolu hlobo lwendlela yokuchema ngokuvamile lusetshenziselwa ama-RTD noma ama-thermistors anamanani aphansi okumelana.Kodwa-ke, ku-thermistor enenani eliphakeme lokumelana nokuzwela okuphezulu, izinga lesignali elikhiqizwa ukuguquka kwezinga lokushisa ngalinye lizoba likhulu, ngakho-ke kusetshenziswa i-voltage excitation.Isibonelo, i-thermistor engu-10 kΩ inokumelana no-10 kΩ ku-25°C.Ku-50°C, ukumelana kwe-NTC thermistor kungu-441.117 kΩ.Ubuncane bedrayivu bamanje obungu-50 µA obuhlinzekwa yi-AD7124-4/AD7124-8 bukhiqiza u-441.117 kΩ × 50 µA = 22 V, ephakeme kakhulu futhi engaphandle kwebanga lokusebenza lama-ADC amaningi atholakalayo asetshenziswa kule ndawo yohlelo lokusebenza.Ama-thermistors nawo avame ukuxhunywa noma abekwe eduze kwe-electronics, ngakho-ke ukungavikeleki ukushayela okwamanje akudingeki.
Ukwengeza i-resistor nomuzwa ochungechungeni njengesekethe yesihlukanisi se-voltage kuzokhawulela i-current nge-thermistor kunani layo elincane lokumelana.Kulokhu kumisa, inani le-resistor RSENSE kufanele lilingane nenani lokumelana ne-thermistor ezingeni lokushisa eliyinkomba elingu-25°C, ukuze i-voltage ephumayo ilingane nendawo emaphakathi ye-voltage yereferensi ekushiseni kwayo okujwayelekile 25°CC Ngokufanayo, uma i-thermistor engu-10 kΩ ekwazi ukumelana no-10 kΩ ku-25°C isetshenziswa, i-RSENSE kufanele ibe ngu-10 kΩ.Njengoba izinga lokushisa lishintsha, ukumelana kwe-thermistor ye-NTC nakho kuyashintsha, futhi isilinganiso se-voltage yedrayivu ku-thermistor nayo iyashintsha, okuholela ekutheni i-voltage ephumayo ilingane nokumelana kwe-NTC thermistor.
Uma ireferensi kagesi ekhethiwe esetshenziselwa ukunika amandla i-thermistor kanye/noma i-RSENSE ifana ne-voltage eyireferensi ye-ADC esetshenziselwa ukulinganisa, isistimu isethelwe esilinganisweni se-ratiometric (Umfanekiso 7) ukuze noma imuphi umthombo we-voltage wephutha elihlobene nesasasa uchemile ukuze ususwe.
Qaphela ukuthi i-resistor yenzwa (eqhutshwa i-voltage) noma i-reference resistor (eqhutshwa manje) kufanele ibe nokubekezelela okuphansi kokuqala kanye nokukhukhuleka okuphansi, njengoba kokubili okuguquguqukayo kungathinta ukunemba kwayo yonke isistimu.
Uma usebenzisa ama-thermistors amaningi, i-voltage eyodwa yokuvuselela ingasetshenziswa.Kodwa-ke, i-thermistor ngayinye kufanele ibe ne-resistar yayo enembayo, njengoba kuboniswe kumfanekiso.8. Enye inketho ukusebenzisa i-multiplexer yangaphandle noma iswishi emelana kancane kusimo, okuvumela ukwabelana ngesivikeli somqondo esisodwa sokunemba.Ngalokhu kumisa, i-thermistor ngayinye idinga isikhathi sokumisa lapho ikalwa.
Kafushane, lapho uklama isistimu yokulinganisa izinga lokushisa esekelwe ku-thermistor, kunemibuzo eminingi okufanele icatshangelwe: ukukhethwa kwezinzwa, izintambo zenzwa, ukuhweba okukhethiwe kwengxenye, ukulungiswa kwe-ADC, nokuthi lezi ziguquko ezihlukahlukene zikuthinta kanjani ukunemba okuphelele kwesistimu.I-athikili elandelayo kulolu chungechunge ichaza indlela yokuthuthukisa ukwakheka kwesistimu yakho kanye nesabelomali sephutha lesistimu iyonke ukuze ufeze ukusebenza kwakho okuhlosiwe.
Isikhathi sokuthumela: Sep-30-2022