Iyi ndi nkhani yoyamba m'nkhani ziwiri.Nkhaniyi iyamba kukambirana za mbiri ndi zovuta zamapangidwe akutentha kochokera ku thermistormachitidwe oyezera, komanso kuyerekezera kwawo ndi machitidwe oyezera kutentha kwa resistance thermometer (RTD).Ifotokozanso za kusankha kwa thermistor, kusinthana kwa kasinthidwe, komanso kufunikira kwa sigma-delta analog-to-digital converters (ADCs) m'derali.Nkhani yachiwiri ifotokoza mwatsatanetsatane momwe mungakwaniritsire ndikuwunika kayezedwe komaliza kotengera thermistor.
Monga tafotokozera m'nkhani yapitayi, Kukonzekera kwa RTD Temperature Sensor Systems, RTD ndi chotsutsa chomwe kukana kwake kumasiyana ndi kutentha.Ma thermitors amagwira ntchito mofanana ndi RTDs.Mosiyana ndi ma RTD, omwe ali ndi coefficient yabwino ya kutentha, thermistor ikhoza kukhala ndi kutentha kwabwino kapena koyipa.Negative temperature coefficient (NTC) thermitors amachepetsa kukana kwawo pamene kutentha kumakwera, pamene ma thermitors abwino (PTC) amawonjezera kukana kwawo kutentha kumakwera.Pa mkuyu.1 ikuwonetsa momwe amayankhira a NTC ndi PTC thermistors ndikufanizira ndi ma curve a RTD.
Pankhani ya kutentha kwamtundu, RTD curve ili pafupi ndi mzere, ndipo sensa imaphimba kutentha kwakukulu kwambiri kusiyana ndi thermistors (nthawi zambiri -200 ° C mpaka + 850 ° C) chifukwa cha chikhalidwe chopanda mzere (exponential) cha thermistor.Ma RTD nthawi zambiri amaperekedwa mumayendedwe odziwika bwino, pomwe ma curve a thermistor amasiyana ndi wopanga.Tidzakambirana izi mwatsatanetsatane mu gawo lotsogolera kusankha thermistor m'nkhaniyi.
Ma thermitors amapangidwa kuchokera ku zinthu zophatikizika, nthawi zambiri za ceramic, ma polima, kapena semiconductors (nthawi zambiri ma oxide achitsulo) ndi zitsulo zoyera (platinamu, faifi tambala, kapena mkuwa).Ma thermitors amatha kuzindikira kusintha kwa kutentha mwachangu kuposa ma RTDs, kupereka mayankho mwachangu.Chifukwa chake, ma thermistors amagwiritsidwa ntchito kwambiri ndi masensa pamapulogalamu omwe amafunikira mtengo wotsika, kukula kochepa, kuyankha mwachangu, kukhudzika kwakukulu, komanso kutentha pang'ono, monga kuwongolera zamagetsi, kuwongolera nyumba ndi nyumba, ma laboratories asayansi, kapena kubweza kozizira kwa ma thermocouples pazamalonda. kapena ntchito zamakampani.zolinga.Mapulogalamu.
Nthawi zambiri, ma thermistors a NTC amagwiritsidwa ntchito poyeza kutentha, osati PTC thermistors.Ma thermitors ena a PTC alipo omwe angagwiritsidwe ntchito m'mabwalo otetezedwa opitilira muyeso kapena ngati ma fuse osinthika kuti agwiritse ntchito chitetezo.Kukaniza-kutentha pamapindikira a PTC thermistor limasonyeza dera laling'ono kwambiri NTC isanafike lophimba mfundo (kapena Curie mfundo), pamwamba pa kukana limatuluka kwambiri ndi malamulo angapo kukula mu osiyanasiyana madigiri angapo Celsius.Pazifukwa zowonjezereka, PTC thermistor idzapanga kudziwotcha kwamphamvu pamene kutentha kwasintha kumadutsa, ndipo kukana kwake kudzakwera kwambiri, zomwe zidzachepetse zomwe zikuchitika panopa ku dongosolo, potero kupewa kuwonongeka.Malo osinthira a PTC thermistors nthawi zambiri amakhala pakati pa 60 ° C ndi 120 ° C ndipo siwoyenera kuwongolera miyeso ya kutentha m'mapulogalamu osiyanasiyana.Nkhaniyi ikunena za ma thermistors a NTC, omwe amatha kuyeza kapena kuyang'anira kutentha kuyambira -80°C mpaka +150°C.Ma thermistors a NTC ali ndi mavoti okana kuyambira ma ohm angapo mpaka 10 MΩ pa 25°C.Monga momwe tawonetsera mkuyu.1, kusintha kwa kukana pa digiri Celsius kwa ma thermistors kumamveka bwino kuposa kukana ma thermometers.Poyerekeza ndi ma thermistor, kukhudzika kwakukulu kwa ma thermistor ndi kukana kwakukulu kumapangitsa kuti mawotchi ake aziyenda mosavuta, chifukwa ma thermistors safuna mawilo apadera, monga waya 3 kapena 4-waya, kuti alipire kukana kutsogolera.Mapangidwe a thermistor amagwiritsa ntchito mawonekedwe osavuta a 2-waya.
Kuyeza kutentha kwapamwamba kwambiri kwa thermistor kumafuna kusinthika kwachindunji, kutembenuka kwa analogi-to-digital, linearization, ndi malipiro, monga momwe tawonetsera mkuyu.2.
Ngakhale unyolo wamawu ungawoneke ngati wosavuta, pali zovuta zingapo zomwe zimakhudza kukula, mtengo, ndi magwiridwe antchito a bolodi lonselo.Zolemba zolondola za ADI za ADC zikuphatikiza mayankho angapo ophatikizika, monga AD7124-4/AD7124-8, omwe amapereka maubwino angapo pamapangidwe amagetsi otenthetsera chifukwa midadada yomangira yofunikira pakufunsira imamangidwa.Komabe, pali zovuta zosiyanasiyana pakupanga ndi kukonza njira zoyezera kutentha kwa thermistor.
Nkhaniyi ikufotokoza chilichonse mwa nkhanizi ndikupereka malingaliro othetsera komanso kufewetsa kamangidwe ka machitidwe otere.
Pali zosiyanasiyanaMa thermitors a NTCpamsika lero, kotero kusankha thermistor yoyenera pa ntchito yanu kungakhale ntchito yovuta.Dziwani kuti ma thermitors amalembedwa ndi mtengo wawo wadzina, womwe ndi kukana kwawo mwadzina pa 25 ° C.Chifukwa chake, chotenthetsera cha 10 kΩ chimakhala ndi kukana mwadzina kwa 10 kΩ pa 25°C.Ma thermistors ali ndi zodziwikiratu kapena zoyambira kukana kuyambira ma ohm ochepa mpaka 10 MΩ.Ma thermitors okhala ndi miyeso yotsika yokana (kukana mwadzina kwa 10 kΩ kapena kuchepera) nthawi zambiri amathandizira kutsika kwa kutentha, monga -50°C mpaka +70°C.Ma thermitors omwe ali ndi mphamvu zolimbikira amatha kupirira kutentha mpaka 300 ° C.
Thermistor element imapangidwa ndi metal oxide.Ma Thermistors amapezeka mu mpira, ma radial ndi mawonekedwe a SMD.Mikanda ya Thermistor imakutidwa ndi epoxy kapena magalasi otsekedwa kuti atetezedwe.Ma thermistors a mpira okhala ndi epoxy, ma radial ndi pamwamba ndi oyenera kutentha mpaka 150 ° C.Magalasi otenthetsera mikanda ndi oyenera kuyeza kutentha kwambiri.Mitundu yonse ya zokutira/zopaka imatetezanso ku dzimbiri.Ma thermitors ena adzakhalanso ndi nyumba zina zowonjezera chitetezo m'malo ovuta.Ma thermistors a mikanda amakhala ndi nthawi yoyankha mwachangu kuposa ma radiation / SMD thermistors.Komabe, sizikhala zolimba.Choncho, mtundu wa thermistor wogwiritsidwa ntchito umadalira mapeto a ntchito ndi malo omwe thermistor ili.Kukhazikika kwa nthawi yayitali kwa thermistor kumadalira zinthu zake, kuyika kwake, komanso kapangidwe kake.Mwachitsanzo, chotenthetsera cha NTC chokhala ndi epoxy chingasinthe 0.2 ° C pachaka, pomwe chotenthetsera chosindikizidwa chimangosintha 0.02 ° C pachaka.
Ma thermitors amabwera molondola mosiyanasiyana.Ma thermitors okhazikika amakhala ndi kulondola kwa 0.5°C mpaka 1.5°C.Mlingo wa kukana kwa thermistor ndi mtengo wa beta (chiyerekezo cha 25°C mpaka 50°C/85°C) chimakhala chololera.Dziwani kuti mtengo wa beta wa chotenthetsera umasiyana ndi wopanga.Mwachitsanzo, zotenthetsera 10 kΩ NTC zochokera kwa opanga osiyanasiyana zidzakhala ndi ma beta osiyanasiyana.Pamakina olondola kwambiri, ma thermistors monga Omega™ 44xxx angagwiritsidwe ntchito.Ali ndi kulondola kwa 0.1 ° C kapena 0.2 ° C pa kutentha kwa 0 ° C mpaka 70 ° C.Choncho, kusiyanasiyana kwa kutentha komwe kungayesedwe ndi kulondola kofunikira pa kutentha kumeneku kumatsimikizira ngati ma thermitors ali oyenera kugwiritsa ntchito pulogalamuyi.Chonde dziwani kuti kulondola kwa mndandanda wa Omega 44xxx kumapangitsa kuti mtengo wake ukhale wokwera.
Kutembenuza kukana kukhala madigiri Celsius, mtengo wa beta umagwiritsidwa ntchito nthawi zambiri.Mtengo wa beta umatsimikiziridwa podziwa magawo awiri a kutentha ndi kukana kofananira pa kutentha kulikonse.
RT1 = Kutentha kwa kutentha 1 RT2 = Kutentha kwa kutentha 2 T1 = Kutentha 1 (K) T2 = Kutentha 2 (K)
Wogwiritsa amagwiritsa ntchito mtengo wa beta womwe uli pafupi kwambiri ndi kutentha komwe kumagwiritsidwa ntchito pulojekitiyi.Zosungira zambiri za thermistor zimalemba mtengo wa beta limodzi ndi kukana pa 25°C ndi kulolerana kwa mtengo wa beta.
Ma thermistor olondola kwambiri komanso mayankho olondola kwambiri monga Omega 44xxx amagwiritsira ntchito equation ya Steinhart-Hart kutembenuza kukana kukhala madigiri Celsius.Equation 2 imafuna zokhazikika zitatu A, B, ndi C, zoperekedwanso ndi wopanga sensa.Chifukwa ma equation coefficients amapangidwa pogwiritsa ntchito mfundo zitatu za kutentha, zotsatira zake zimachepetsa cholakwika chomwe chimayambitsidwa ndi mzere (nthawi zambiri 0.02 °C).
A, B ndi C ndi zokhazikika zomwe zimachokera ku magawo atatu a kutentha.R = kukana kwa thermistor mu ohms T = kutentha mu K madigiri
Pa mkuyu.3 ikuwonetsa chisangalalo chamakono cha sensa.Kuthamanga kwamakono kumagwiritsidwa ntchito pa thermistor ndipo zamakono zomwezo zimagwiritsidwa ntchito pazitsulo zolondola;chotsutsa cholondola chimagwiritsidwa ntchito ngati chisonyezero cha kuyeza.Mtengo wotsutsa wotsutsa uyenera kukhala waukulu kuposa kapena wofanana ndi mtengo wapamwamba kwambiri wa kukana kwa thermistor (malingana ndi kutentha kochepa kwambiri komwe kumayesedwa mu dongosolo).
Posankha mphamvu yosangalatsa, kukana kwakukulu kwa thermistor kuyenera kuganiziridwanso.Izi zimatsimikizira kuti voteji kudutsa sensa ndi zotsutsa zolembera nthawi zonse zimakhala pamlingo wovomerezeka kumagetsi.Gawo lomwe lilipo pano limafunikira mutu wamutu kapena zofananira.Ngati thermistor ili ndi kukana kwakukulu pa kutentha kochepa kwambiri, izi zidzapangitsa kuti galimoto ikhale yotsika kwambiri.Choncho, magetsi opangidwa kudutsa thermistor pa kutentha kwakukulu ndi kochepa.Magawo opindula otheka angagwiritsidwe ntchito kukulitsa kuyeza kwa ma siginecha otsika awa.Komabe, phindu liyenera kukonzedwa mwamphamvu chifukwa mulingo wazizindikiro kuchokera ku thermistor umasiyana kwambiri ndi kutentha.
Njira ina ndikukhazikitsa phindu koma gwiritsani ntchito dynamic drive current.Chifukwa chake, pamene mulingo wa siginecha kuchokera ku thermistor ukusintha, mtengo wapano pagalimoto umasintha kwambiri kotero kuti voteji yomwe imapangidwa kudutsa thermistor ili mkati mwazolowera zomwe zafotokozedwa pazida zamagetsi.Wogwiritsa ntchitoyo awonetsetse kuti voteji yomwe idapangidwa podutsa chotsutsa ilinso pamlingo wovomerezeka kumagetsi.Zosankha zonsezi zimafuna kulamulira kwakukulu, kuyang'anitsitsa nthawi zonse mphamvu yamagetsi kudutsa thermistor kuti magetsi athe kuyeza chizindikiro.Kodi pali njira yosavuta?Ganizirani za mphamvu yamagetsi.
Mphamvu ya DC ikagwiritsidwa ntchito pa chotenthetsera, mphamvu yapano kudzera mu chotenthetsera imangodziwikiratu ngati kukana kwa thermistor kumasintha.Tsopano, pogwiritsa ntchito chopimitsira choyezera cholondola m'malo mwa chotsutsa chofotokozera, cholinga chake ndikuwerengera zomwe zikuyenda kudzera mu thermistor, motero kulola kukana kwa thermistor kuwerengedwa.Popeza magetsi oyendetsa galimoto amagwiritsidwanso ntchito ngati chizindikiro cha ADC, palibe gawo lopindula lomwe likufunika.Purosesa ilibe ntchito yoyang'anira magetsi a thermistor, kudziwa ngati mlingo wa chizindikiro ukhoza kuyesedwa ndi zamagetsi, ndikuwerengera zomwe zimayendetsa galimoto / mtengo wamakono uyenera kusinthidwa.Iyi ndi njira yomwe yagwiritsidwa ntchito m'nkhaniyi.
Ngati chotenthetsera chili ndi kagawo kakang'ono kokana ndi kukana, mphamvu yamagetsi kapena kusangalatsa kwapano kungagwiritsidwe ntchito.Pankhaniyi, kuyendetsa panopa ndi phindu likhoza kukhazikitsidwa.Choncho, dera lidzakhala monga momwe tawonetsera pa Chithunzi 3. Njirayi ndi yabwino chifukwa ndizotheka kulamulira panopa kupyolera mu sensa ndi zotsutsa zotsutsa, zomwe zimakhala zofunikira pakugwiritsa ntchito mphamvu zochepa.Kuonjezera apo, kudziwotcha kwa thermistor kumachepetsedwa.
Mphamvu yamagetsi imatha kugwiritsidwanso ntchito kwa ma thermistors omwe ali ndi mphamvu zochepa zokana.Komabe, wogwiritsa ntchito nthawi zonse ayenera kuwonetsetsa kuti zomwe zilipo kudzera pa sensayo sizikwera kwambiri pa sensa kapena kugwiritsa ntchito.
Kukoka kwa magetsi kumathandizira kukhazikitsa mukamagwiritsa ntchito chotenthetsera chokhala ndi mphamvu yayikulu yokana komanso kutentha kosiyanasiyana.Kukana kwakukulu mwadzina kumapereka mlingo wovomerezeka wamakono oveteredwa.Komabe, okonza amafunika kuonetsetsa kuti zamakono zili pamlingo wovomerezeka pamtundu wonse wa kutentha wothandizidwa ndi ntchitoyo.
Sigma-Delta ADCs imapereka maubwino angapo popanga makina oyezera kutentha.Choyamba, chifukwa sigma-delta ADC imayesanso kulowetsa kwa analogi, kusefa kwakunja kumachepetsedwa ndipo chofunikira chokha ndi fyuluta ya RC yosavuta.Amapereka kusinthasintha kwamtundu wa fyuluta ndi kuchuluka kwa baud.Zosefera za digito zomangidwira zitha kugwiritsidwa ntchito kupondereza kusokoneza kulikonse pazida zoyendetsedwa ndi mains.Zipangizo za 24-bit monga AD7124-4/AD7124-8 zili ndi malingaliro athunthu mpaka 21.7 bits, kotero zimapereka kusamvana kwakukulu.
Kugwiritsa ntchito sigma-delta ADC kumathandizira kwambiri mapangidwe a thermistor pomwe amachepetsa tsatanetsatane, mtengo wamakina, malo a board, komanso nthawi yogulitsa.
Nkhaniyi imagwiritsa ntchito AD7124-4/AD7124-8 monga ADC chifukwa ndi phokoso lochepa, laling'ono lamakono, ma ADC olondola omwe ali ndi PGA yomangidwa, zolemba zomangidwa, zolowetsa analogi, ndi buffer.
Mosasamala kanthu kuti mukugwiritsa ntchito magetsi oyendetsa galimoto kapena magetsi oyendetsa galimoto, makonzedwe a ratiometric akulimbikitsidwa momwe voteji yowonetsera ndi sensa yamagetsi imachokera ku gwero lomwelo.Izi zikutanthauza kuti kusintha kulikonse kwa gwero lachisangalalo sikudzakhudza kulondola kwa muyeso.
Pa mkuyu.5 ikuwonetsa kuyendetsa kwanthawi zonse kwa thermistor ndi precision resistor RREF, voliyumu yomwe idapangidwa kudutsa RREF ndiye voteji yoyezera chotenthetsera.
Zomwe zili m'munda siziyenera kukhala zolondola ndipo zikhoza kukhala zosakhazikika monga zolakwika zilizonse zomwe zili m'munda panopa zidzathetsedwa pakukonzekera uku.Nthawi zambiri, chisangalalo chapano chimakondedwa kuposa kusangalatsa kwamagetsi chifukwa cha kuwongolera kwamphamvu kwambiri komanso chitetezo chokwanira cha phokoso pamene sensa ili kumadera akutali.Njira iyi ya kukondera nthawi zambiri imagwiritsidwa ntchito pa ma RTD kapena ma thermistors okhala ndi zinthu zochepa zokana.Komabe, kwa thermistor yokhala ndi mtengo wokana kwambiri komanso kukhudzika kwakukulu, mulingo wa siginecha wopangidwa ndi kusintha kulikonse kwa kutentha udzakhala wokulirapo, kotero kukweza kwamagetsi kumagwiritsidwa ntchito.Mwachitsanzo, chotenthetsera cha 10 kΩ chimakhala ndi kukana kwa 10 kΩ pa 25°C.Pa -50 ° C, kukana kwa thermistor ya NTC ndi 441.117 kΩ.Kuyendetsa pang'ono kwa 50 µA komwe kumaperekedwa ndi AD7124-4/AD7124-8 kumapanga 441.117 kΩ × 50 µA = 22 V, yomwe ili yokwera kwambiri komanso kunja kwa ma ADC ambiri omwe amapezeka m'derali.Ma thermistors nthawi zambiri amalumikizidwa kapena amakhala pafupi ndi zamagetsi, kotero chitetezo choyendetsa pakali pano sichofunika.
Kuwonjezera chopinga champhamvu pamndandanda ngati gawo logawa ma voltage kumachepetsa zomwe zikuchitika kudzera pa thermistor mpaka pamtengo wake wokana.Mu kasinthidwe awa, mtengo wa sensor resistor RSENSE uyenera kukhala wofanana ndi mtengo wa kukana kwa thermistor pa kutentha kwa 25 ° C, kuti voteji yotulutsa ikhale yofanana ndi midpoint ya voteji pakutentha kwake mwadzina. 25°CC Momwemonso, ngati chotenthetsera cha 10 kΩ chokhala ndi kukana kwa 10 kΩ pa 25°C chikugwiritsidwa ntchito, RSENSE iyenera kukhala 10 kΩ.Pamene kutentha kumasintha, kukana kwa thermistor ya NTC kumasinthanso, ndipo chiŵerengero cha magetsi oyendetsa galimoto kudutsa thermistor amasinthanso, zomwe zimapangitsa kuti magetsi atuluke azikhala ofanana ndi kukana kwa NTC thermistor.
Ngati voteji yosankhidwa yomwe imagwiritsidwa ntchito popatsa mphamvu chotenthetsera ndi/kapena RSENSE ikugwirizana ndi voteji ya ADC yomwe imagwiritsidwa ntchito poyezera, makinawo amayikidwa muyeso wa ratiometric (Chithunzi 7) kotero kuti gwero lililonse lolakwika lokhudzana ndi chisangalalo likhale losakondera kuti lichotse.
Zindikirani kuti sensor resistor (voltage driven) kapena reference resistor (yoyendetsedwa pano) iyenera kukhala ndi kulolerana kocheperako komanso kutsika pang'ono, chifukwa mitundu yonse iwiri imatha kukhudza kulondola kwadongosolo lonse.
Mukamagwiritsa ntchito ma thermitors angapo, voteji imodzi yosangalatsa ingagwiritsidwe ntchito.Komabe, thermistor iliyonse iyenera kukhala ndi chopinga chake cholondola, monga momwe tawonetsera mkuyu.8. Njira ina ndikugwiritsa ntchito chosinthira chowonjezera chakunja kapena chowongolera chotsika paboma, chomwe chimalola kugawana chopinga chimodzi cholondola.Ndi kasinthidwe uku, thermistor iliyonse imafunikira nthawi yokhazikika ikayesedwa.
Mwachidule, popanga dongosolo la kuyeza kutentha kwa thermistor, pali mafunso ambiri oti muganizirepo: kusankha kwa sensa, wiring sensor, kugulitsa chigawo chosankha, kusintha kwa ADC, ndi momwe mitundu yosiyanasiyanayi imakhudzira kulondola kwadongosolo lonse.Nkhani yotsatira pamndandandawu ikufotokoza momwe mungakwaniritsire kapangidwe kanu kadongosolo komanso bajeti yonse yolakwika kuti mukwaniritse zomwe mukufuna.
Nthawi yotumiza: Sep-30-2022