Riba:
- Ikon kafa daidaitattun sigogin sarrafa sigina kamar mitar samfur, nau'in tacewa da taga tare da AI
- Ikon samar da lambar Python don FFT, tace ƙira da nazarin amo da duba Nyquist da aliasing
- Ikon tabbatar da fassarar bakan da aka samar da AI ta hanyar kwatanta shi da aunawa da tsammanin jiki
Raw bayanai daga firikwensin, makirufo, ko layin wutar lantarki kadai sau da yawa ba shi da ma'ana; Wajibi ne don aiwatarwa da fassara shi akan ma'aunin mitar, amplitude da lokaci. Cire bakan tare da FFT, tace amo, gane alamar girgizawa ... Waɗannan duk sarrafa sigina ne kuma AI yana haifar da lambar Python mai sauri a cikin wannan yanki, ya bayyana ra'ayoyi, ƙididdige ƙimar tacewa. Amma ƙaramin kuskuren siginar sigina (kuskuren mitar samfur, taga kuskure, tsallake ikon Nyquist) shiru yana lalata duk binciken; Lambar ba ta ba da kurakurai ba, tana ba da sakamako mara kyau. A cikin wannan rukunin, za mu rufe saita madaidaitan sigogi tare da AI, bincika lambar da aka samar dangane da Nyquist da aliasing, da kuma tabbatar da fassarar bakan tare da gaskiyar zahiri.
Ma'auni na asali: Samfura, Nyquist, Aliasing
Ka'idar farko ta sarrafa siginar dijital ita ce ka'idar Nyquist-Shannon: don wakiltar sigina daidai, mitar samfurin dole ne ta kasance aƙalla sau biyu mafi girman abin da ke cikin siginar. In ba haka ba, ƙananan mitoci za su bayyana azaman ƙananan mitoci (aliasing) kuma wannan ba za a iya juyawa ba.
Mitar mafi girma a cikin sigina: f_max = 2 kHzMahimmancin mitar samfur: f_s ≥ 2 · f_max = 4 kHzDon barin gefe a aikace: f_s ≈ 5 · f_max = 10 kHz an zaɓi Hakanan, analogin anti-aliasing filter dole ne KAFIN samfur.
Tsanaki: Lokacin da AI ke ba da shawarar mitar samfur, tabbatar da bincika idan yana samar da Nyquist bisa mafi girman ɓangaren siginar ku. Lambar tana gudana ba tare da kurakurai ba ko da a ƙananan mitar samfur; amma sakamakon ba daidai ba ne saboda aliasing. Bugu da ƙari, babu wata software da za ta iya gyara wannan kuskure ba tare da tacewa ba a cikin hardware.
Ƙaddamarwa da Taga don FFT
Matsakaicin mita na FFT ya dogara da mitar samfur da adadin samfurori: Δf = f_s / N. Don ƙuduri mafi kyau ko dai tattara ƙarin samfurori ko zaɓi ƙananan f_s (ba tare da karya Nyquist ba). Bugu da ƙari, katsewar da ke tsakanin farkon da ƙarshen siginar yana haifar da "leakayen leka"; Don rage wannan, ana amfani da ayyukan taga kamar Hann da Hamming.
f_s = 10 kHz, N = 1024 samfurori Ƙirar mitar: Δf = 10000 / 1024 ≈ 9.77 HzTotal lokacin rikodi: T = N / f_s = 1024 / 10000 ≈ 102.4 ms
Ƙirƙira da Duba FFT da Lambar Tace
Ƙayyade mitar samfur, nau'in taga, da sikelin axis a sarari lokacin neman lambar FFT daga AI. Lambar mai zuwa tana fitar da sigina mai girma mai gefe ɗaya:
shigo da numpy kamar npfs = 10000 # mitar samfur (Hz) - tabbatar da Nyquist!N = 1024t = np.arange(N) / fs# siginar samfurin: 500 Hz + 1500 Hzx = np.sin(2*np.pi*500*t) + 0.5*np np.hanning(N) # windowing: yana rage yawan ruwan lefi wanda aka daidaita ta hanyar samun# duba mafi girman mitoci = f[np.argsort(mag)[-2:]]buga("Mafi yawan mitoci (Hz):",np.sort(kololuwa)))
Lokacin duba wannan lambar za a tambaye ku: Shin axis mitar da gaske Hz ne ko kuma ana amfani da fihirisar samfurin (rfftfreq)? An daidaita girman girman tagar? Shin kololuwar 500 da 1500 Hz da ake tsammanin suna faruwa da gaske a waɗannan wuraren? Idan ka tabbatar da lambar tare da sanannen siginar gwaji (mitar mitar sine), za ka tabbatar da ƙarfin gwiwa da axis da daidaitawa.
Rauni Mai Sauƙi / Ƙarfi Mai ƙarfi
RAUNI: "Aiwatar da FFT zuwa wannan bayanan." na dijital.- Alama iyakar Nyquist (5 kHz) akan jadawali Lura cewa axis zai canza idan mitar samfurin ba daidai ba ce."
Tace Zane da Nazarin Surutu
AI na iya haifar da ƙananan / high/bandpass tace coefficients (FIR/IIR). Amma dole ne a duba mitar yankewa, tsari da kwanciyar hankali na tacewa. Yana iya haifar da rashin zaman lafiya mai girma da ɓata lokaci, musamman a cikin matatun IIR. Bayan zayyana matatar, zayyana amsawar mitar (Bode-like) don ganin cewa yanke yana a daidai wurin da ba a so a cikin mashigin wucewa.
Aiki na yau da kullun a cikin binciken amo shine raba siginar gaske daga amo. Anan, kimanta kofa da aka ba da shawarar AI ko tace a kan bandwidth na zahiri na siginar: idan ainihin siginar ku yana a 0-500 Hz, wani sashi a 2 kHz yana iya yiwuwa amo ko tsangwama. AI yana ba da ƙididdiga; Kuna yin fassarar zahiri.
Tabbatar da Fassarar Spectrum tare da Gaskiyar Jiki
Lokacin fassara bakan, AI yana yin ma'ana amma ba koyaushe cikakkun bayanai ba kamar "Akwai kololuwa a 50 Hz, wannan tsangwama ce ta grid." Kwatanta waɗannan maganganun tare da tsammanin jiki: Shin da gaske tsarin yana da haɗin haɗin kai na 50 Hz? Shin mitar jujjuyawa da ake tsammanin ana tsammanin suna kusa a cikin bakan jijjiga na mota? Idan zai yiwu, maimaita auna tare da hanya ta biyu (mabambanta firikwensin, software daban-daban) kuma duba kololuwa iri ɗaya.
Alamomi: Ga kowane fassarar bakan, "wane abu na zahiri wannan kololuwar yayi dace da?" Yi tambaya. 50/100/150 Hz cibiyar sadarwa da masu jituwa, mitar jujjuyawar da yawa a cikin na'urori masu jujjuya, da sauyawar mita a cikin sauya kayan wuta sune sanannun sa hannu. Kololuwar da ba a sani ba ko dai wani lamari ne na gaske ko kuskuren aunawa/sarrafawa; Bincike duka biyun.
Mini Case
Injiniyan R&D yana auna girgizar fan kuma yana da AI ta fassara bakan. "Akwai babban kololuwa a 1200 Hz, wannan na iya haifar da gazawa," in ji AI. Injiniyan yana sarrafa saurin fan: 1800 rpm = 30 Hz. Ana sa ran mitoci masu ɗaukar nauyi da ruwan wukake za su kasance a wasu dabi'u masu dacewa da wannan zagayowar; 1200Hz bai dace da kowane ɗayan waɗannan ba. Yana sarrafa mitar samfur: siginar tana ɗaukar abun ciki har zuwa 2 kHz, amma 2 kHz kawai aka ƙirƙira, don haka cin zarafin Nyquist. Kololuwa a 1200 Hz mitar fatalwa ce ta haifar da aliasing. Lokacin da na ƙara mitar samfur zuwa 8 kHz, ƙimar ƙarya ta ɓace. Darasi: Koyaushe gwada fassarar bakan tare da sake zagayowar jiki/tsawon mitoci da ingantaccen samfuri.
Kuskuren gama gari
- Zaɓin mitar samfur ba tare da duba ma'aunin Nyquist ba; Kallon aliasing.
- Barin mitar FFT a ma'aunin samfurin maimakon Hz.
- Kuskure zubewar kallo azaman sigina ba tare da taga ba.
- Ba daidaita girman ta yawan windows/samfurori ba.
- Ba duba IIR tace kwanciyar hankali da murdiya lokaci.
- Fassarar bakan kololuwa ba tare da gwada su ba cikin tsammanin saurin juzu'i/mita na zahiri.
A takaice
- Mitar samfurin dole ne ya zama aƙalla sau biyu mafi girman ɓangaren siginar; In ba haka ba, aliasing zai rushe dukan bincike.
- Ƙaddamarwar FFT Δf = f_s/N; Zaɓi N da f_s gwargwadon buƙatarku.
- Windowing yana rage zub da jini; normalize da amplitude bisa ga taga riba.
- Tabbatar da lambar AI tare da sanannun siginar gwaji don tabbatar da axis da daidaitawa.
- Duba daidaiton tacewa da amsa mitar ta hanyar tsara shi.
- Koyaushe gwada fassarar bakan tare da tsammanin mitar jiki.
Aikin aikace-aikace
Ƙirƙirar siginar gwaji na mitar sananne (misali 500 Hz + 1500 Hz sine). Nemi FFT da lambar tacewa daga AI. Sa'an nan: (1) tabbatar da cewa an cika ma'aunin Nyquist, (2) duba cewa kololuwar FFT a zahiri suna bayyana a 500 da 1500 Hz, (3) da gangan rage mitar samfurin ƙasa da Nyquist kuma lura da yadda aliasing ke haifar da kololuwa. Kula da abubuwan lura da sigar da kuka gyara.