Wannan shine labarin farko a cikin silsilar kashi biyu.Wannan labarin zai fara tattauna tarihi da ƙalubalen ƙira nazafin jiki na tushen thermistorTsarin aunawa, da kuma kwatanta su da tsarin ma'aunin zafin jiki na juriya (RTD).Hakanan zai bayyana zaɓin thermistor, daidaitawar ciniki-offs, da mahimmancin sigma-delta analog-to-digital converters (ADCs) a cikin wannan yanki na aikace-aikacen.Labari na biyu zai yi daki-daki yadda ake ingantawa da kimanta tsarin ma'aunin tushen thermistor na ƙarshe.
Kamar yadda aka bayyana a cikin jerin labarin da ya gabata, Inganta Tsarin Sensor na RTD Temperature Sensor, RTD resistor ne wanda juriyarsa ya bambanta da zafin jiki.Thermistors suna aiki daidai da RTDs.Ba kamar RTDs ba, waɗanda ke da madaidaicin madaidaicin zafin jiki kawai, thermistor na iya samun madaidaicin ƙimar zafin jiki mai kyau ko mara kyau.Masu amfani da zafin jiki mara kyau (NTC) suna rage juriya yayin da zafin jiki ya tashi, yayin da ma'aunin zafin jiki mai kyau (PTC) yana haɓaka juriya yayin da zafin jiki ya tashi.A kan fig.1 yana nuna halayen amsawa na al'ada na NTC da PTC thermistors kuma yana kwatanta su zuwa masu lanƙwasa na RTD.
Dangane da kewayon zafin jiki, lanƙwan RTD ya kusan kusan layi ɗaya, kuma firikwensin yana rufe kewayon zafin jiki mai faɗi fiye da thermistor (yawanci -200 ° C zuwa + 850 ° C) saboda yanayin yanayin thermistor wanda ba na layi ba (fasalin).Yawancin lokaci ana ba da RTDs a cikin sanannun madaidaitan lanƙwasa, yayin da masu lanƙwasa thermistor suka bambanta ta masana'anta.Za mu tattauna wannan dalla-dalla a cikin sashin jagorar zaɓi na thermistor na wannan labarin.
Ana yin thermistors daga kayan haɗin gwiwa, yawanci yumbu, polymers, ko semiconductors (yawanci ƙarfe oxides) da ƙarfe mai tsabta (platinum, nickel, ko jan ƙarfe).Thermistors na iya gano canjin zafin jiki da sauri fiye da RTDs, suna ba da amsa da sauri.Saboda haka, na'urori masu auna firikwensin suna amfani da thermistors a aikace-aikace waɗanda ke buƙatar ƙarancin farashi, ƙarami, amsa mai sauri, mafi girman hankali, da iyakataccen kewayon zafin jiki, kamar sarrafa kayan lantarki, sarrafa gida da gini, dakunan gwaje-gwaje na kimiyya, ko ramuwar haɗin sanyi don ma'aunin zafi da sanyio a cikin kasuwanci. ko aikace-aikacen masana'antu.dalilai.Aikace-aikace.
A mafi yawan lokuta, ana amfani da thermistors NTC don ingantacciyar ma'aunin zafin jiki, ba masu zafin jiki na PTC ba.Wasu na'urori masu zafi na PTC suna samuwa waɗanda za a iya amfani da su a cikin da'irar kariya ta wuce gona da iri ko azaman fis ɗin sake saitawa don aikace-aikacen aminci.Matsakaicin juriya-zazzabi na PTC thermistor yana nuna ƙaramin yanki na NTC kafin ya isa wurin sauyawa (ko Curie point), wanda ke sama da juriya yana tashi da ƙarfi ta umarni da yawa na girma a cikin kewayon digiri Celsius da yawa.A karkashin yanayin da ya wuce kima, PTC thermistor zai haifar da zafi mai karfi lokacin da zafin jiki ya wuce, kuma juriya zai tashi sosai, wanda zai rage yawan shigar da tsarin, ta haka zai hana lalacewa.Wurin sauyawa na thermistors PTC yawanci tsakanin 60 ° C da 120 ° C kuma bai dace da sarrafa ma'aunin zafin jiki a cikin aikace-aikace da yawa ba.Wannan labarin yana mai da hankali kan masu amfani da thermistors na NTC, wanda yawanci zai iya aunawa ko saka idanu yanayin zafi daga -80°C zuwa +150°C.NTC thermistors suna da ƙimar juriya daga ƴan ohms zuwa 10 MΩ a 25°C.Kamar yadda aka nuna a cikin fig.1, canjin juriya a kowane digiri Celsius na thermistors ya fi bayyana fiye da na ma'aunin zafi da sanyio.Idan aka kwatanta da thermistors, babban zafin na'urar thermistor da ƙimar juriya mai girma yana sauƙaƙa da hanyoyin shigar da shi, tunda masu amfani da wutar lantarki ba sa buƙatar wani saitin wayoyi na musamman, kamar 3-waya ko 4-waya, don rama juriyar gubar.Zane na thermistor yana amfani da saitin waya 2 mai sauƙi kawai.
Babban ma'aunin zafin jiki na tushen thermistor yana buƙatar daidaitaccen sarrafa sigina, jujjuyawar analog-zuwa-dijital, layin layi, da diyya, kamar yadda aka nuna a fig.2.
Kodayake sarkar siginar na iya zama mai sauƙi, akwai rikitattun abubuwa da yawa waɗanda ke shafar girma, farashi, da aikin gabaɗayan uwayen uwa.Madaidaicin fayil ɗin ADI na ADC ya haɗa da hanyoyin haɗin kai da yawa, irin su AD7124-4/AD7124-8, waɗanda ke ba da fa'idodi da yawa don ƙirar tsarin thermal kamar yadda yawancin tubalan ginin da ake buƙata don aikace-aikacen an gina su.Koyaya, akwai ƙalubale daban-daban a cikin ƙira da haɓaka hanyoyin ma'aunin zafin jiki na tushen thermistor.
Wannan labarin ya tattauna kowane ɗayan waɗannan batutuwa kuma yana ba da shawarwari don warware su da kuma ƙara sauƙaƙe tsarin ƙira don irin waɗannan tsarin.
Akwai iri-iri iri-iriNTC thermistorsa kasuwa a yau, don haka zabar madaidaicin thermistor don aikace-aikacenku na iya zama ɗawainiya mai ban tsoro.Lura cewa ana lissafin thermistors ta ƙimar ƙimar su, wanda shine juriya na ƙima a 25°C.Saboda haka, 10 kΩ thermistor yana da juriya mara kyau na 10 kΩ a 25 ° C.Thermistors suna da ƙima na ƙima ko ƙimar juriya na asali daga ƴan ohms zuwa 10 MΩ.Thermistors tare da ƙananan ƙimar juriya (juriya na ƙima na 10 kΩ ko ƙasa da haka) yawanci suna tallafawa ƙananan kewayon zafin jiki, kamar -50°C zuwa +70°C.Thermistors tare da mafi girman juriya ratings iya jure yanayin zafi har zuwa 300 ° C.
An yi sinadarin thermistor ne da karfe oxide.Ana samun masu zafi a cikin ƙwallon ƙwallon ƙafa, radial da sifofin SMD.Thermistor beads an shafe epoxy ko gilashin lullube don ƙarin kariya.Epoxy rufaffiyar ball thermistors, radial da surface thermistors sun dace da yanayin zafi har zuwa 150°C.Gilashin bead thermistors sun dace don auna yanayin zafi.Duk nau'ikan sutura/marufi kuma suna kare kariya daga lalata.Wasu masu zafin jiki kuma za su sami ƙarin matsuguni don ƙarin kariya a cikin yanayi mara kyau.Bead thermistors suna da saurin amsawa fiye da radial/SMD thermistors.Duk da haka, ba su da dorewa.Sabili da haka, nau'in thermistor da aka yi amfani da shi ya dogara ne akan aikace-aikacen ƙarshe da kuma yanayin da thermistor yake.Tsawon dogon lokaci na thermistor ya dogara da kayan sa, marufi, da ƙira.Misali, thermistor NTC mai rufin epoxy na iya canza 0.2°C a kowace shekara, yayin da rufaffiyar thermistor kawai ke canza 0.02°C a shekara.
Thermistors sun zo cikin daidaito daban-daban.Madaidaitan thermistors yawanci suna da daidaiton 0.5°C zuwa 1.5°C.Ƙimar juriya na thermistor da ƙimar beta (rabin 25°C zuwa 50°C/85°C) suna da haƙuri.Lura cewa ƙimar beta na thermistor ya bambanta ta masana'anta.Misali, 10 kΩ NTC thermistors daga masana'antun daban-daban zasu sami ƙimar beta daban-daban.Don ƙarin ingantattun tsarin, ana iya amfani da thermistors kamar jerin Omega™ 44xxx.Suna da daidaito na 0.1°C ko 0.2°C akan kewayon zafin jiki na 0°C zuwa 70°C.Saboda haka, kewayon yanayin zafi da za'a iya aunawa da daidaiton da ake buƙata akan wannan kewayon zafin jiki yana ƙayyade ko thermistors sun dace da wannan aikace-aikacen.Lura cewa mafi girman daidaiton jerin Omega 44xxx, mafi girman farashi.
Don sauya juriya zuwa digiri Celsius, ana yawan amfani da ƙimar beta.Ana ƙayyade ƙimar beta ta hanyar sanin ma'aunin zafin jiki guda biyu da madaidaicin juriya a kowane wurin zafin jiki.
RT1 = Juriya na zafi 1 RT2 = Juriya na zafi 2 T1 = Zazzabi 1 (K) T2 = Zazzabi 2 (K)
Mai amfani yana amfani da ƙimar beta mafi kusa da kewayon zazzabi da aka yi amfani da shi a cikin aikin.Yawancin takaddun bayanan thermistor suna lissafin ƙimar beta tare da juriya a 25°C da juriya don ƙimar beta.
Madaidaicin madaidaicin thermistors da ingantattun hanyoyin ƙarewa kamar su jerin Omega 44xxx suna amfani da ma'aunin Steinhart-Hart don canza juriya zuwa digiri Celsius.Matsakaicin 2 yana buƙatar madaidaitan A, B, da C guda uku, wanda masana'antun firikwensin suka sake bayarwa.Saboda ana samar da ma'auni ta hanyar amfani da maki zafin jiki guda uku, sakamakon sakamakon yana rage girman kuskuren da aka gabatar ta hanyar layi (yawanci 0.02 ° C).
A, B da C sune madaidaitan da aka samo daga madaidaitan yanayin zafi guda uku.R = juriya na thermistor a ohms T = zazzabi a digiri K
A kan fig.3 yana nuna tashin hankali na yanzu na firikwensin.Ana amfani da Drive current akan thermistor kuma ana amfani da wannan halin yanzu akan madaidaicin resistor;Ana amfani da madaidaicin resistor azaman ma'auni don aunawa.Dole ne ƙimar maƙasudin ƙira ya zama mafi girma ko daidai da ƙimar mafi girman juriya na thermistor (dangane da mafi ƙarancin zafin jiki da aka auna a cikin tsarin).
Lokacin zabar halin yanzu tashin hankali, matsakaicin juriya na thermistor dole ne a sake la'akari da shi.Wannan yana tabbatar da cewa ƙarfin lantarki a fadin firikwensin da kuma resistor na tunani koyaushe yana kan matakin da na'urar lantarki ke karɓa.Madogaran filin na yanzu yana buƙatar wasu madaidaicin ɗaki ko fitarwa.Idan thermistor yana da babban juriya a mafi ƙanƙanta zafin jiki, wannan zai haifar da ƙarancin tuƙi.Saboda haka, ƙarfin lantarki da aka samar a fadin thermistor a babban zafin jiki yana da ƙananan.Za a iya amfani da matakan riba mai tsari don inganta ma'aunin waɗannan ƙananan sigina.Koyaya, dole ne a tsara ribar da ƙarfi saboda matakin sigina daga thermistor ya bambanta sosai da zafin jiki.
Wani zaɓi shine saita riba amma amfani da ƙarfin halin yanzu.Saboda haka, yayin da matakin sigina daga thermistor ke canzawa, ƙimar motsi na yanzu yana canzawa da ƙarfi ta yadda ƙarfin wutar lantarki da aka haɓaka a kan thermistor yana cikin kewayon shigar da na'urar lantarki.Dole ne mai amfani ya tabbatar da cewa ƙarfin wutar lantarki da aka haɓaka a kan abin da ake magana da shi shima yana kan matakin karɓuwa ga na'urorin lantarki.Duk zaɓuɓɓukan biyu suna buƙatar babban matakin sarrafawa, saka idanu akai-akai na ƙarfin lantarki a cikin thermistor domin na'urorin lantarki su iya auna siginar.Akwai zaɓi mai sauƙi?Yi la'akari da tashin hankali irin ƙarfin lantarki.
Lokacin da aka yi amfani da wutar lantarki na DC akan thermistor, na yanzu ta hanyar thermistor yana yin awo ta atomatik yayin da juriyar thermistor ke canzawa.Yanzu, ta yin amfani da ma'aunin ma'aunin ma'auni maimakon na'ura mai mahimmanci, manufarsa ita ce ƙididdige abubuwan da ke gudana ta cikin thermistor, don haka ba da damar ƙididdige juriya na thermistor.Tunda kuma ana amfani da wutar lantarki azaman siginar tunani na ADC, ba a buƙatar matakin riba.Processor ba shi da aikin sa ido kan wutar lantarki ta thermistor, tantance ko matakin siginar za a iya auna shi ta hanyar lantarki, da ƙididdige abin da riba / ƙimar halin yanzu ke buƙatar daidaitawa.Wannan ita ce hanyar da aka yi amfani da ita a cikin wannan labarin.
Idan thermistor yana da ƙaramin juriya da kewayon juriya, ana iya amfani da ƙarfin lantarki ko tashin hankali na yanzu.A wannan yanayin, ana iya gyara halin yanzu da riba.Don haka, kewayawa za ta kasance kamar yadda aka nuna a cikin Hoto na 3. Wannan hanya ta dace a cikin cewa yana yiwuwa a sarrafa halin yanzu ta hanyar firikwensin da kuma resistor, wanda ke da mahimmanci a cikin ƙananan aikace-aikacen wuta.Bugu da ƙari, an rage yawan zafin jiki na thermistor.
Hakanan za'a iya amfani da tashin hankali na wutar lantarki don thermistors tare da ƙananan ƙimar juriya.Koyaya, dole ne mai amfani koyaushe ya tabbatar da cewa na yanzu ta hanyar firikwensin bai yi girma da firikwensin ko aikace-aikacen ba.
Ƙarfin wutar lantarki yana sauƙaƙa aiwatarwa lokacin amfani da thermistor tare da babban ƙimar juriya da kewayon zafin jiki mai faɗi.Babban juriya na ƙididdigewa yana ba da ingantaccen matakin ƙididdiga na halin yanzu.Duk da haka, masu zanen kaya suna buƙatar tabbatar da cewa halin yanzu yana kan matakin da aka yarda da shi akan duk yanayin zafin jiki wanda aikace-aikacen ke tallafawa.
Sigma-Delta ADCs suna ba da fa'idodi da yawa yayin zayyana tsarin ma'aunin thermistor.Na farko, saboda sigma-delta ADC yana sake yin samfurin shigarwar analog, ana kiyaye tacewa ta waje zuwa ƙarami kuma kawai abin da ake buƙata shine matattar RC mai sauƙi.Suna ba da sassauci a nau'in tacewa da fitarwar baud.Za a iya amfani da ginanniyar tacewa na dijital don murkushe duk wani tsangwama a cikin na'urori masu ƙarfin lantarki.Na'urorin 24-bit irin su AD7124-4/AD7124-8 suna da cikakken ƙuduri har zuwa 21.7 bits, don haka suna samar da babban ƙuduri.
Amfani da sigma-delta ADC yana sauƙaƙa ƙirar thermistor sosai yayin da rage ƙayyadaddun bayanai, farashin tsarin, sararin allo, da lokacin kasuwa.
Wannan labarin yana amfani da AD7124-4/AD7124-8 a matsayin ADC saboda ƙananan amo, ƙananan halin yanzu, daidaitattun ADCs tare da ginanniyar PGA, ginanniyar tunani, shigarwar analog, da buffer tunani.
Ko da ko kana amfani da drive halin yanzu ko drive ƙarfin lantarki, a ratiometric sanyi ana shawarar a cikin abin da tunani irin ƙarfin lantarki da firikwensin ƙarfin zo daga wannan drive tushen.Wannan yana nufin cewa duk wani canji a cikin tushen tashin hankali ba zai shafi daidaiton ma'aunin ba.
A kan fig.5 yana nuna madaidaicin motsi na yanzu don thermistor da daidaitaccen resistor RREF, ƙarfin lantarki da aka haɓaka akan RREF shine ma'aunin wutar lantarki don auna thermistor.
Yanayin halin yanzu baya buƙatar zama daidai kuma yana iya zama ƙasa da kwanciyar hankali saboda duk wani kurakurai a cikin filin na yanzu za a kawar da su a cikin wannan tsarin.Gabaɗaya, an fi son tashin hankali na yanzu fiye da tashin wutar lantarki saboda mafi girman kulawar ji da kuma mafi kyawun rigakafin amo lokacin da firikwensin yana cikin wurare masu nisa.Irin wannan hanyar son zuciya galibi ana amfani da ita don RTDs ko thermistors tare da ƙananan ƙimar juriya.Koyaya, don thermistor tare da ƙimar juriya mafi girma da haɓaka mafi girma, matakin siginar da kowane canjin zafin jiki zai haifar zai zama mafi girma, don haka ana amfani da kuzarin ƙarfin lantarki.Misali, thermistor 10 kΩ yana da juriya na 10 kΩ a 25°C.A -50 ° C, juriya na thermistor NTC shine 441.117 kΩ.Matsakaicin abin tuƙi na 50 µA wanda AD7124-4/AD7124-8 ke bayarwa yana haifar da 441.117 kΩ × 50 µA = 22 V, wanda ya yi tsayi da yawa kuma a waje da kewayon aiki na mafi yawan samuwa ADCs da ake amfani da su a wannan yankin aikace-aikacen.Hakanan ana haɗa ma'aunin zafi da sanyio ko suna kusa da na'urorin lantarki, don haka ba a buƙatar rigakafi don tuƙi na yanzu.
Ƙara ma'ana a cikin jeri azaman mai rarraba wutar lantarki zai iyakance halin yanzu ta hanyar thermistor zuwa mafi ƙarancin juriya.A cikin wannan saitin, ƙimar ma'aunin ma'ana RSENSE dole ne ya zama daidai da ƙimar juriya na thermistor a ma'aunin zafin jiki na 25 ° C, don haka ƙarfin fitarwa zai zama daidai da matsakaicin matsakaicin ƙarfin wutar lantarki a ƙimar ƙimar sa. 25°CC Hakazalika, idan ana amfani da thermistor 10 kΩ tare da juriya na 10 kΩ a 25°C, RSENSE yakamata ya zama 10 kΩ.Yayin da yanayin zafi ya canza, juriya na thermistor na NTC shima yana canzawa, kuma rabon wutar lantarki a cikin thermistor shima yana canzawa, wanda ya haifar da ƙarfin fitarwa ya yi daidai da juriya na thermistor na NTC.
Idan zaɓaɓɓen bayanin irin ƙarfin lantarki da aka yi amfani da shi don ƙarfafa thermistor da/ko RSENSE ya dace da ƙarfin nunin ADC da aka yi amfani da shi don aunawa, an saita tsarin zuwa ma'aunin ma'auni (Hoto 7) ta yadda duk wani tushen wutar lantarki mai alaƙa da tashin hankali zai kasance mai son cirewa.
Lura cewa ko dai ma'ana resistor (voltage driven) ko kuma resistor (wanda ke gudana a halin yanzu) yakamata ya sami ƙarancin juriya na farko da ƙananan drift, saboda duka masu canji na iya shafar daidaiton tsarin gaba ɗaya.
Lokacin amfani da thermistors da yawa, ana iya amfani da ƙarfin motsa jiki ɗaya.Duk da haka, kowane thermistor dole ne ya sami nasa madaidaicin abin da ya dace, kamar yadda aka nuna a fig.8. Wani zaɓi shine a yi amfani da na'urar multixer na waje ko ƙananan juriya a cikin jihar da ke kunne, wanda ke ba da damar raba daidaitaccen ma'ana.Tare da wannan saitin, kowane thermistor yana buƙatar wasu lokacin daidaitawa lokacin da aka auna.
A taƙaice, lokacin zayyana tsarin ma'aunin zafin jiki na tushen thermistor, akwai tambayoyi da yawa da za a yi la'akari da su: zaɓin firikwensin, firikwensin firikwensin, cinikin zaɓin zaɓi, daidaitawar ADC, da kuma yadda waɗannan sauye-sauye daban-daban ke shafar daidaiton tsarin gaba ɗaya.Labari na gaba a cikin wannan jeri yana bayanin yadda ake haɓaka ƙirar tsarin ku da kasafin kuɗin kuskuren tsarin gabaɗaya don cimma aikin da kuke niyya.
Lokacin aikawa: Satumba-30-2022