Moving-average-accelerometer

Moving-average-accelerometer

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Im dalam proses pembuatan quadcopter. Pada titik ini saya mengalami masalah dengan perhitungan sudut MPU-6050. Ketika quadcopter stasioner dengan motor di negara bagian dan Im memiringkannya, pembacaan sudut di semua 3 sumbu itu bagus, tapi ketika motor berada dalam keadaan aktif, pembacaan mulai melonjak ke mana-mana dan bahkan bisa berbeda dari nilai sebenarnya sebesar 20 derajat. Saya menganggap efek ini disebabkan getaran mekanis yang disebabkan oleh motor. Saya menyertakan gambar papan MPU-6050 dan grafik pembacaan sudut MPU-6050 pada sumbu X menggunakan filter Kalman, filter pelengkap dan MPU-6050 DMP (Kalman dan implementasi filter komplementer serta kode pemrosesan untuk grafik berasal dari Kristian Lauszus GitHub, DMP digunakan dengan perpustakaan Jeff Rowberg I2Cdev). Saya menghubungkan kedua MPU ke mikrokontroler yang berbeda, sehingga tidak akan terhubung secara elektrik dengan quadcopter dan mount MPU on board dengan dua spong dari kedua sisi MPU. Hasilnya hampir sama. Jadi sekarang saya benar-benar tahu bahwa kebisingan (setidaknya sebagian besar kebisingan) tidak berhubungan dengan noise pengalihan listrik dari motor. Getaran adalah alasan mengapa saya melepaskan proyek quadcopter saya sekitar setahun yang lalu. Tapi, masalahnya bisa dipecahkan, sangat menyebalkan untuk mengerjakannya. Saya kira Anda menggabungkan data accelerometer dan gyro (filter Kalman dan Comp. Adalah algoritma fusi sensor). Bisakah Anda mencoba menyesuaikan nilainya sehingga gyro memiliki kuotasi yang jauh lebih tinggi dari hasil dan akselerometer hanya mengoreksi gyro drift. Anda juga bisa mencoba low pass filter (dalam perangkat lunak) sudut. Dan, solusi mekanis (nilon spacer, frame lebih bagus, dll) juga membantu. Ndash Mishony 17 Mei 16 di 13:12 Dalam kasus pemrograman DMP MPU saya menggunakan sketsa contoh Arduino Jeff, saya baru saja mengubah tingkat FIFO dari 100 Hz menjadi 25 Hz karena FIFO meluap banyak, Jika implementasi filter Kristian: tingkat sampel adalah 1 KHz FSYNC dinonaktifkan dan mengatur penyetelan 260 Hz Acc, penyaringan 256 Hz Gyro, gyro sampling 8 KHz Rentang Skala Penuh adalah 1.77250degs accelerometer Rentang Skala Penuh adalah 1772g PLL yang disetel dengan mode giroskop referensi sumbu X yang dinonaktifkan. Garis lurus hitam mewakili 0 derajat. Garis filter Kalman juga berwarna hitam, sulit dilihat karena nilai Kalman mendekati filter pelengkap. Ndash Martynas Janknas 17 Mei 16 at 17:07 Pastikan rangkaian daya tinggi yang menggerakkan saham ESC Anda memiliki kesamaan dengan rangkaian sinyal daya rendah dari mikrokontroler. Saya menemukan ini sangat penting saat membangun quad saya, karena juga menyebabkan beberapa kesalahan pada sistem lain seperti RxTx. Menjawab 24 Mei 16 jam 15:34 saya telah berhasil mengembangkan pengendali terbang tricopter, saya juga mengalami masalah dengan getaran sehingga satu-satunya cara untuk menghilangkannya adalah dengan memulai dari motor awal dan keseimbangan, baling-baling, dll, hanya dengan itu Anda harus menjadi Baik untuk pergi.Jika Anda membeli pengontrol penerbangan Anda akan melihat bahwa itu tidak akan bekerja dengan benar dengan perangkat keras Anda kecuali Anda menyeimbangkan semuanya. Anda juga harus memfilter hasil dari pembacaan dari giroskop. Saya telah menggunakan filter rata-rata bergerak dengan hasil yang baik. Di sini Anda bisa melihat beberapa pengujian dan mesin terbang. Semoga berhasil dengan proyek Anda. Pengukuran vibrasi Getaran dapat dianggap sebagai gerakan osilasi atau berulang dari suatu benda di sekitar posisi ekuilibrium. Posisi ekuilibrium adalah posisi yang akan dicapai objek ketika gaya yang bekerja di atasnya adalah nol. Getaran biasanya terjadi karena efek dinamis dari toleransi manufaktur, kelonggaran, penggulungan dan kontak gosok antara bagian-bagian mesin dan kekuatan yang tidak seimbang pada anggota yang berputar dan timbal balik. Seringkali, getaran kecil yang tidak signifikan dapat merangsang frekuensi resonansi beberapa komponen struktural lainnya dan diperkuat menjadi sumber getaran dan kebisingan utama. Terkadang getaran mekanis sangat dibutuhkan. Misalnya, kita menghasilkan getaran dengan sengaja di pengumpan komponen, pemadat beton, pemandian pembersih ultrasonik, latihan batuan dan driver tumpukan. Mesin uji getar digunakan secara luas untuk memberikan tingkat energi getaran yang terkontrol ke produk dan sub-rakitan di mana diperlukan untuk memeriksa respons fisik atau fungsional dan memastikan resistibilitasnya terhadap lingkungan getaran. Apa getaran Getaran tubuh menggambarkan gerakan berosilasi tentang posisi referensi. Frekuensi siklus gerak yang lengkap terjadi selama periode satu detik disebut frekuensi dan diukur dalam hertz (Hz). Gerak dapat terdiri dari komponen tunggal yang terjadi pada frekuensi tunggal, seperti pada garpu tala, atau beberapa komponen yang terjadi pada frekuensi yang berbeda secara bersamaan, seperti gerakan piston pada mesin pembakaran dalam. Pada gambar di bawah ini kita bisa melihat gerak garpu tala. Garpu tuning adalah resonator akustik dalam bentuk garpu dua cabang. Ini bergema pada nada konstan tertentu saat diatur bergetar dengan memukulnya ke permukaan atau dengan benda dan memancarkan nada musik murni. Sinyal dari menyetel garpu di DEWESoft recorder. Pada gambar di bawah ini kita bisa melihat gerak gerak piston, yang bisa ditemukan di mesin pembakaran dalam. Sinyal dari gerakan piston di DEWESoft recorder. Sinyal getaran dalam praktik biasanya terdiri dari banyak frekuensi yang terjadi secara bersamaan sehingga kita tidak bisa langsung melihat hanya dengan melihat pola amplitudo-waktu, berapa komponennya, dan frekuensi berapa yang terjadi. Komponen ini bisa diungkap dengan memplotkan amplitudo getaran terhadap frekuensi. Terobosan sinyal getaran menjadi komponen frekuensi individual disebut analisis frekuensi, sebuah teknik yang dapat dianggap sebagai landasan pengukuran diagnostik getaran. Grafik yang menunjukkan tingkat getaran sebagai fungsi frekuensi disebut spectrogram frekuensi. Ketika frekuensi menganalisis getaran mesin biasanya kita temukan sejumlah komponen frekuensi periodik terkemuka yang berhubungan langsung dengan pergerakan fundamental berbagai bagian mesin. Dengan analisis frekuensi, kita, oleh karena itu, dapat melacak sumber getaran yang tidak diinginkan. Komponen tunggal dan beberapa Getaran mesin Sebagian besar dari kita terbiasa dengan getaran yang bergerak bergetar - berosilasi. Ada berbagai cara untuk mengatakan bahwa ada sesuatu yang bergetar. Kita bisa menyentuh benda bergetar dan merasakan getarannya. Kita juga bisa melihat pergerakan benda bergetar. Terkadang getaran menciptakan suara yang bisa kita dengar atau panas yang bisa kita indra. Getaran mesin hanyalah gerakan maju mundur mesin atau komponen mesin. Setiap komponen, yang bergerak maju mundur atau berosilasi, bergetar. Getaran mesin bisa mengambil berbagai bentuk. Komponen mesin mungkin bergetar pada jarak besar atau kecil, cepat atau lambat, dan dengan atau tanpa suara atau panas yang jelas. Getaran mesin seringkali sengaja dirancang dan memiliki tujuan fungsional. Di lain waktu, getaran mesin bisa tidak disengaja dan menyebabkan kerusakan mesin. Berikut adalah beberapa contoh getaran mesin yang tidak diinginkan. Apa yang menyebabkan getaran mesin Hampir semua getaran mesin disebabkan oleh satu atau beberapa sebab: kekuatan berulang - Sebagian besar getaran mesin disebabkan oleh gaya pengulangan yang serupa dengan yang menyebabkan kapal naik ke batu. Mengulang kekuatan seperti tindakan ini pada komponen mesin dan menyebabkan mesin bergetar. Kelonggaran - Kelonggaran bagian-bagian mesin menyebabkan mesin bergetar. Jika bagian menjadi longgar, getaran, yang biasanya dapat ditolerir, bisa menjadi tidak terkendali dan berlebihan. Resonansi - Mesin memiliki tingkat osilasi alami. Getaran menyebabkan Tingkat Getaran Amplitudo getaran adalah karakteristik yang menggambarkan tingkat keparahan getaran dan dapat dihitung dalam beberapa cara. Pada diagram, hubungan antara tingkat puncak ke puncak, tingkat puncak, tingkat rata-rata dan tingkat RMS gelombang sinus ditunjukkan. Nilai peak-to-peak menunjukkan ekskursi maksimum gelombang, kuantitas yang berguna dimana, misalnya, perpindahan getaran bagian mesin sangat penting untuk tekanan maksimum atau pertimbangan clearance mekanis. Nilai puncak sangat berharga untuk menunjukkan tingkat guncangan durasi pendek dan lain-lain. Namun, seperti dapat dilihat dari gambar, nilai puncak hanya menunjukkan tingkat maksimum yang telah terjadi dan riwayat waktu gelombang tidak diperhitungkan. Nilai rata-rata yang diperbaiki, di sisi lain, memang mempertimbangkan sejarah waktu gelombang namun dianggap sebagai kepentingan praktis terbatas karena tidak memiliki hubungan langsung dengan kuantitas fisik yang berguna. Nilai RMS adalah ukuran amplitudo yang paling relevan karena dibutuhkan keduanya, sejarah waktu gelombang diperhitungkan dan memberi nilai amplitudo yang berhubungan langsung dengan kandungan energi, dan oleh karena itu kemampuan destruktif dari getaran. Parameter Parameter getaran Ketika kita melihat garpu tala bergetar, kita mempertimbangkan amplitudo gelombang saat perpindahan fisik garpu berakhir ke kedua sisi posisi diam. Selain perpindahan, kita juga bisa menggambarkan pergerakan kaki garpu dalam hal kecepatan dan percepatannya. Bentuk dan periode getaran tetap sama apakah itu perpindahan, kecepatan atau percepatan yang sedang dipertimbangkan. Perbedaan utama adalah bahwa ada perbedaan fasa antara kurva waktu amplitudo dari tiga parameter seperti yang ditunjukkan pada gambar. Kecepatan dalam 90 fasa dengan perpindahan, dan akselerasi dalam 180 fasa dengan perpindahan. Untuk sinyal sinusoidal, perpindahan, amplitudo kecepatan dan percepatan dihubungkan secara matematis dengan fungsi frekuensi dan waktu, hal ini ditunjukkan secara grafis pada diagram. Jika fase terbengkalai, seperti yang selalu terjadi saat membuat pengukuran rata-rata waktu, maka tingkat kecepatan dapat diperoleh dengan membagi sinyal percepatan dengan faktor yang sebanding dengan frekuensi, dan perpindahannya dapat diperoleh dengan membagi sinyal percepatan dengan faktor Sebanding dengan kuadrat frekuensi. Dengan mendeteksi percepatan getaran, kita tidak terikat pada satu parameter saja. Dengan integrator elektronik, kita bisa mengubah sinyal akselerasi menjadi kecepatan dan perpindahan. Parameter getaran hampir secara universal diukur dalam satuan metrik sesuai dengan persyaratan ISO. Konstanta gravitasi g masih banyak digunakan untuk tingkat akselerasi meski berada di luar sistem ISO unit koheren. Bila pengukuran vibrasi pita frekuensi tunggal yang lebar dibuat, pilihan parameter penting jika sinyal memiliki komponen pada banyak frekuensi. Pengukuran perpindahan akan memberi komponen frekuensi rendah yang paling berat dan pengukuran akselerasi yang berbeda akan menurunkan tingkat terhadap komponen frekuensi tinggi. Pengalaman menunjukkan bahwa nilai RMS keseluruhan kecepatan getaran yang diukur pada kisaran 10 sampai 1000 Hz memberikan indikasi terbaik tentang tingkat keparahan getaran. Penjelasan yang mungkin adalah bahwa tingkat kecepatan yang diberikan sesuai dengan tingkat energi tertentu sehingga getaran pada frekuensi rendah dan tinggi sama-sama tertimbang dari sudut pandang energi getaran. Dalam prakteknya, banyak mesin memiliki spektrum kecepatan yang cukup datar. Hal ini membawa kita pada pertimbangan praktis yang dapat mempengaruhi pilihan parameter. Hal ini menguntungkan untuk memilih parameter yang memberi spektrum frekuensi rata-rata untuk memanfaatkan keseluruhan rentang dinamis (perbedaan antara nilai terkecil dan terbesar yang dapat diukur) dari instrumentasi. Untuk alasan ini, parameter kecepatan atau percepatan biasanya dipilih untuk tujuan analisis frekuensi. Karena pengukuran akselerasi tertimbang terhadap komponen getaran frekuensi tinggi, parameter ini cenderung digunakan di mana rentang frekuensi yang diminati mencakup frekuensi tinggi. Sifat sistem mekanis sedemikian rupa sehingga perpindahan yang cukup besar hanya terjadi pada frekuensi rendah, oleh karena itu, pengukuran perpindahan memiliki nilai terbatas dalam studi umum getaran mekanis. Bila jarak antara unsur-unsur mesin kecil dipertimbangkan, perpindahan getaran tentu saja merupakan pertimbangan penting. Pemindahan sering digunakan sebagai indikator ketidakseimbangan pada bagian mesin yang berputar karena perpindahan yang relatif besar biasanya terjadi pada frekuensi rotasi poros, yang juga merupakan frekuensi minat terbesar untuk tujuan penyeimbangan. Apa itu akselerasi dan apa itu accelerometer Akselerasi adalah laju di mana kecepatan suatu benda berubah relatif terhadap waktu (ini merupakan turunan dari vektor kecepatan sebagai fungsi waktu sebuah dvdt). Ini adalah hasil bersih dari setiap dan semua kekuatan yang bekerja pada suatu objek. Secara umum kita memiliki dua tugas pengukuran dasar untuk akselerasi: percepatan akibat getaran benda uji akselerasi akibat perubahan kecepatan benda, seperti kendaraan (mobil, pesawat terbang). Ada perbedaan besar pada Melakukan dua tugas pengukuran ini. Informasi yang paling penting, saat mengukur akselerasi getaran, adalah bagian dinamis dari sinyal (objek tidak bergerak). Saat mengukur menikung atau mempercepat pembuatan kendaraan, hasil yang paling penting adalah bagian statis dari sinyal yang menghasilkan perubahan kecepatan. Oleh karena itu sensor untuk mengukur perubahan pergerakan kendaraan harus memiliki kemungkinan untuk mengukur akselerasi statis (seperti gravitasi) sedangkan sensor untuk mengukur getaran biasanya memiliki bagian statis yang terlepas dari hasil yang sudah ada pada desain sensor. Hal ini juga penting untuk diketahui karena kecepatannya adalah derivasi perpindahan (v dsdt), kita juga dapat mengukur percepatan dengan mengukur kecepatan dan menurunkan sinyal atau dengan mengukur perpindahan dan derivasi ganda. Ini adalah kasus praktis saat mengukur perpindahan permukaan dengan menggunakan probe laser atau eddy current. Hal ini juga sangat umum untuk juga menggunakan pengukuran percepatan untuk mengukur kecepatan dan perpindahan. Prinsip integrasi berbeda. Saat mengintegrasikan pergerakan kendaraan, akselerasi statis akan menghasilkan perubahan kecepatan (dan perpindahan). Kita perlu tahu bahwa karena pengukuran akselerasi memiliki kesalahan, hasilnya akan melayang dalam kecepatan dan jarak. Drift ini ditentukan oleh kualitas sensor akselerasi. Dengan sensor yang sangat bagus, kapal selam bisa, misalnya, berlari selama berminggu-minggu dan masih menghitung lokasi mereka yang sebenarnya, namun di dunia normal kita tidak seberuntung itu karena bagian dinamis dari sinyal jauh lebih tinggi dan tingkat perubahannya juga lebih tinggi. Biasanya, kita menggunakan sensor yang berbeda untuk mengkompensasi kesalahan. Salah satu kombinasi sensor yang digunakan sangat sering adalah accelerometersrate sensor turnGPS. Saat mengukur getaran, bagian statis tidak penting dan karena itu harus dilepas saat diintegrasikan oleh filter frekuensi tinggi. Jenis pengukuran Pengukuran percepatan dibagi ke dalam kategori berikut: Getaran - objek dikatakan bergetar saat ia melakukan gerakan osilasi mengenai posisi ekuilibrium. Getaran ditemukan di lingkungan transportasi dan dirgantara atau seperti yang disimulasikan oleh sistem shaker. Shock - eksitasi transien mendadak dari struktur yang umumnya menggairahkan struktur resonansi. Gerak - gerakan adalah kegiatan yang bergerak lambat seperti gerakan lengan robot atau pengukuran suspensi otomotif. Seismik - Ini lebih merupakan gerakan atau getaran berfrekuensi rendah. Pengukuran ini biasanya membutuhkan accelerometer resolusi tinggi dengan noise rendah. Accelerometer Accelerometer adalah perangkat yang menghasilkan sinyal listrik (voltase, charge.) Sebanding dengan percepatan yang dialami. Ada beberapa teknik untuk mengubah percepatan menjadi sinyal listrik. Kami akan memberikan gambaran umum sebagian besar saat itu dan kemudian melihat secara singkat beberapa orang lainnya. Prinsip dasar accelerometer Sebagian besar akselerometer didasarkan pada Hookes dan Newtons hukum pertama dan kedua. Hukum Hookes menyatakan bahwa gaya F yang dibutuhkan untuk memperpanjang atau memampatkan pegas sebanding dengan perubahan jarak x dengan faktor k (karakteristik faktor konstan musim semi). Persamaannya adalah F k x. Newtons hukum pertama menyatakan bahwa suatu benda tetap berada pada posisi diam atau terus menerus untuk bergerak dengan kecepatan konstan, kecuali jika ditindaklanjuti oleh kekuatan lain. Hukum keduanya menyatakan bahwa gaya F yang dibuat oleh benda bergerak sama dengan massanya m kali percepatan a, memberikan persamaan F ma. Cara yang paling umum, untuk memanfaatkan undang-undang ini, adalah menunda massa pada mata air dari bingkai yang mengelilingi massa (seperti pada gambar di bawah). Saat bingkai diguncang, ia mulai bergerak, menarik massa bersamaan dengan itu. Jika massa mengalami percepatan yang sama dengan frame, perlu ada kekuatan yang diberikan pada massa, yang akan menyebabkan perpanjangan mata air. Kita dapat menggunakan sejumlah transduser perpindahan (seperti transduser kapasitif) untuk mengukur defleksi ini. Accelerometer umum terdiri dari massa, pegas atau sistem yang serupa, dan transduser perpindahan: Dua konfigurasi accelerometer piezoelektrik umum digunakan: Tipe kompresi dimana massa menggunakan gaya tekan pada elemen piezoelektrik Tipe geser di mana massa Menggunakan gaya geser pada elemen piezoelektrik. Hukum fisika Jenis akselerometer Accelerometer dirancang dengan menggunakan berbagai prinsip penginderaan. Berikut adalah ikhtisar dan ringkasan singkat untuk memberi Anda pemahaman yang lebih baik tentang mereka: Piezoelectric - Bekerja berdasarkan kemampuan bahan piezoelektrik untuk mengubah potensi listriknya saat berada dalam tekanan. Mereka menawarkan keunggulan unik, dibandingkan dengan accelerometers lainnya. Mereka memiliki rentang dinamis yang lebar. Linearitas yang sangat baik, rentang frekuensi yang lebar (dari beberapa Hz sampai 30 kHz), adalah satu-satunya alat ukur yang mampu mengukur percepatan akselerasi, namun tidak mampu mengukur respons DC. Karena mereka tidak memiliki daya tahan bagian yang bergerak meningkat. Dan tidak seperti sensor lain mereka tidak memerlukan sumber daya eksternal. Piezoresistive - Bekerja sama dengan bahan piezoelektrik, dengan perbedaannya adalah, hal itu mengubah hambatan listrik material, dan bukan potensi listriknya. Sensor ini mampu melakukan pengukuran hingga 1000 G, memiliki respons DC yang benar dan biasanya digunakan pada struktur mesin mikro. Capacitive - Berkas logam atau beberapa fitur mesin mikro lainnya menghasilkan kapasitansi, yang diubah saat sensor dipercepat. Mereka paling sering digunakan dalam accelerometers MEMS (Micro-Electro-Mechanical System) dan memiliki karakteristik yang sama seperti potensiometer dalam hal frekuensi, dynamic range, dan respon DC. Potensiometrik - Lengan penghapus potensiometer dilekatkan pada massa pegas, yang menghasilkan perubahan atau hambatan saat pegas bergerak. Frekuensi alami perangkat ini umumnya kurang dari 30 Hz, sehingga membatasi pengukuran frekuensi rendah. Mereka juga memiliki rentang dinamik yang terbatas, namun dapat mengukur ke 0 Hz (respon DC) Efek hall - Sebuah magnet menempel pada pegas, dan ketika gaya diterapkan, ia akan bergerak menyebabkan perubahan pada medan listrik aula. elemen. Magnetoresistif - Bekerja sama seperti sensor efek aula, dengan perbedaannya adalah bahwa elemen resistansi magnet digunakan sebagai pengganti elemen hall. Fiber Bragg kisi - Setiap perubahan pada pitch kisi dari serat optik menghasilkan perubahan panjang gelombang Bragg, dari mana kita dapat menghitung percepatan. Perpindahan panas - Sumber panas tunggal dipusatkan pada substrat. Thermoresistor sama-sama ditempatkan terpisah pada keempat sisi sumber panas. Bila sensor dipercepat maka gradien panas akan asimetris karena perpindahan panas konveksi. Sebagian besar produsen memiliki berbagai macam accelerometers dan pada pandangan pertama, ini mungkin pilihan yang luar biasa. Sekelompok kecil tipe tujuan umum akan memenuhi sebagian besar kebutuhan. Ini tersedia dengan konektor top atau side mounted dan memiliki sensitivitas pada kisaran 1 sampai 10 mV atau pC per ms2. Akselerometer DEWESoft Akselerometer yang tersisa dibuat untuk aplikasi tertentu. Misalnya, accelerometers ukuran kecil yang ditujukan untuk pengukuran tingkat tinggi atau frekuensi tinggi dan untuk penggunaan pada struktur, panel, dll yang halus dan beratnya hanya 0,5 sampai 2 gram. Jenis tujuan khusus lainnya dioptimalkan untuk: pengukuran simultan di tiga bidang yang saling tegak lurus suhu tinggi tingkat getaran yang sangat rendah tingkat guncangan tingkat tinggi kalibrasi accelerometers lainnya dengan perbandingan dan untuk pemantauan permanen mesin industri. Sensor akselerator piezoelektrik Kapasitif Piezoelektrik adalah kemampuan beberapa bahan (terutama kristal dan keramik tertentu - bahan piezoelektrik yang dikenal adalah kuarsa, turmalin, keramik (PTZ), GAPO4.) Untuk menghasilkan potensial listrik sebagai respons terhadap tekanan mekanis yang diterapkan. Ini bisa berupa pemisahan muatan listrik melintasi kisi kristal. Jika bahannya tidak hubung singkat, muatan yang diberikan menyebabkan tegangan melintasi material. Bahan yang menghasilkan muatan listrik saat gaya diterapkan pada mereka menunjukkan apa yang dikenal sebagai efek piezoelektrik. Sensor percepatan piezoelektrik bekerja berdasarkan prinsip bahwa bahan piezoelektrik (biasanya keramik feroelektrik buatan polarisasi) dibangun di antara bagian bawah rumahan sensor dan massa seismik. Saat sensor digerakkan, massa ini memampatkan bahan piezoelektrik yang menghasilkan keluaran voltase sangat kecil. Dikumpulkan pada elektroda, sinyal muatan listrik impedansi tinggi dapat dikondisikan oleh elektronik internal atau eksternal untuk tujuan pengukuran. Accelerometer yang mengandung elektronika internal diklasifikasikan sebagai Integrated Electronic Piezoelectric (IEPE), namun sering disebut oleh pengguna sebagai accelerometer voltase tegangan. Akselerometer piezoelektrik memerlukan amplifier muatan eksternal untuk pengkondisian sinyal yang disebut accelerometers mode charge. Modus voltometer piezoelektrik voltase menggabungkan built-in, sinyal mikro-elektronik. IEPE telah diadopsi sebagai standar oleh industri sensor, analisa, dan akuisisi data produsen. Sensor piezoelektrik umumnya digunakan dalam analisis modal, skrining tekanan lingkungan, peristiwa piroteknik, uji getaran pesawat terbang, uji terbang pesawat terbang dan perawatan prediktif dan preventif. Modus kecepatan voltase - IEPE Semua voltase mode voltase ini didukung oleh tegangan DC yang diatur dan 2 sampai 20 mA eksitasi sensor arus konstan pada dua skema kawat sederhana. Elektronik built-in mengubah sinyal muatan impedansi tinggi yang dihasilkan oleh bahan piezoelektrik menjadi sinyal tegangan impedansi rendah yang dapat digunakan tepat di dalam transduser. Karena outputnya adalah impedansi rendah, sinyal dapat ditransmisikan melalui jarak kabel yang panjang dan digunakan di lapangan kotor atau lingkungan pabrik yang bising dengan sedikit degradasi. Sensor IEPE membutuhkan catu daya 4 mA atau 8 mA dan mereka biasanya memberikan sinyal 5 volt, sehingga lebih mudah untuk mentransfer sinyal ini melalui kabel yang lebih lama. Selain itu, amplifier untuk sensor ini jauh lebih mudah dibangun, dan karenanya lebih murah daripada sensor piezoelektrik biasa. Rentang pengukuran amplitudonya cukup terbatas. Kita hampir tidak bisa menemukan sensor yang berukuran lebih dari 100g. Ada sumbu tunggal sekaligus sensor triaksial. Akhir-akhir ini, ukuran yang sangat bagus telah tersedia - seseorang dapat menemukan sensor triaksial seperti sebuah kubus berukuran sesedikit 10 mm, dan dengan berat ringan 5 gram. Kita bisa menggunakan DEWESoft Sirius atau DEWE-43 untuk mengukur dengan sensor ini. Sirius ACC dapat langsung menghubungkan sensor IEPE sementara STG, STG-M atau DEWE-43 membutuhkan adaptor MSI-BR-ACC untuk mengukur dengan sensor ini. Charge mode accelerometers Mengisi mode accelerometers piezoelektrik mengeluarkan sinyal muatan listrik impedansi tinggi yang dihasilkan langsung dari elemen penginderaan piezoelektrik. Transduser ini memerlukan penguat muatan eksternal (pilihan yang lebih baik) atau konverter muatan dalam untuk mengubah sinyal muatan impedansi tinggi ke rendah. Sinyal voltase impedansi cocok untuk keperluan pengukuran. Karena output adalah impedansi tinggi, sinyal muatan sangat sensitif terhadap kebisingan dari lingkungan sekitar dan beberapa tindakan pencegahan penting harus dilakukan untuk pengukuran yang tepat. Kabel koaksial low noise khusus harus digunakan antara transduser dan penguat muatan eksternal. Kabel ini diperlakukan secara khusus (misalnya dilumasi dengan grafit) untuk mengurangi efek suara triboelectric, atau motion-induced, noise. Selain itu, penting untuk mempertahankan resistansi insulasi tinggi dari transduser, kabel, dan konektor dengan membuatnya tetap kering dan sangat bersih. Dengan tindakan pencegahan ini dibandingkan dengan pengoperasian sederhana accelerometer voltase, accelerometers mode charge umumnya hanya digunakan pada suhu tinggi, aplikasi akselerasi tinggi atau jika pelanggan memiliki ratusan stok pada stok sensor IEPE belum tersedia. Selain itu, accelerometer piezoelektrik adalah self-generating sehingga tidak memerlukan catu daya. Tidak ada bagian yang bergerak yang aus, dan akhirnya, akselerasi keluaran proporsionalnya bisa diintegrasikan untuk memberi kecepatan dan perpindahan sinyal proporsional. Kita bisa menggunakan Sirius CHG secara langsung karena mendukung input charge dan MULTI, STG atau DEWE-43 dengan MSI-BR-CH, tapi pastikan rentang dinamisnya cukup untuk aplikasi Anda. Karakteristik penting terakhir dari semua transduser piezoelektrik (mode voltase dan mode charge sama) adalah perilaku AC mereka. Bahan piezoelektrik tidak dapat menahan muatannya karena input statis. Dengan kata lain, hanya merasakan kejadian dinamis dan karenanya tidak bisa digunakan untuk mengukur akselerasi DC. Desain elektronik penguat muatan (baik terintegrasi internal maupun eksternal) menentukan pasangan AC frekuensi rendah dari sinyal pengukuran. Khas frekuensi rendah kinerja accelerometers piezoelektrik berkisar dari beberapa Hz. Perbandingan antara sensor mode IEPE dan Charge: Sensor akselerasi statis - Sensor MEMS Baik, sensor muatan dan tipe sensor IEPE memiliki keterbatasan umum: keduanya tidak dapat mengukur akselerasi statis. Mereka biasanya mulai mengukur dari 0,3 Hz sampai 10 Hz, tergantung sensornya. Untuk pengukuran frekuensi statis atau sangat rendah, pengguna perlu menggunakan jenis sensor yang berbeda. Tipe yang sangat populer adalah sensor Sistem Elektro-Elektro (atau MEMS). Ini sebenarnya microchip yang memiliki struktur mekanis (balok kantilever atau seismik) yang mengubah sifat listriknya (biasanya kapasitansi) yang berkaitan dengan akselerasi. Antarmuka kapasitif memiliki beberapa fitur menarik. Dalam kebanyakan teknologi mikromachining, dibutuhkan sedikit atau minimal pengolahan. Kapasitor dapat beroperasi baik sebagai sensor dan aktuator. Mereka memiliki sensitivitas yang sangat baik dan mekanisme transduksi tidak sensitif terhadap suhu. Penginderaan kapasitif tidak tergantung pada bahan dasarnya dan bergantung pada variasi kapasitansi saat geometri kapasitor berubah. Accelerometer MEMS yang khas terdiri dari massa bukti bergerak dengan pelat yang dilekatkan pada sistem suspensi mekanis ke kerangka acuan, seperti yang ditunjukkan pada gambar di bawah ini: Sensor MEMS sangat istimewa, karena digunakan untuk mengukur gempa bumi atau gerakan lambat lainnya. Namun dengan berkembangnya teknologi airbag, ada kebutuhan besar untuk membuat sensor berbiaya rendah yang mengukur akselerasi statis. Oleh karena itu, solusi chip tunggal muncul untuk tujuan ini. Akhir-akhir ini sensor ini digunakan juga pada sistem gyro berbiaya rendah dan kita dapat menemukan sensor yang juga memiliki bandwidth yang cukup baik hingga beberapa kHz dan tingkat kebisingan yang cukup rendah (meski masih lebih besar dari sensor IEPE dengan rentang pengukuran yang sama). Mereka menjadi sangat diperlukan. Di industri otomotif, teknologi komputer dan audio-video. Memilih sensor yang tepat Saat memilih jenis sensor, penting untuk menjawab pertanyaan berikut: Apa yang kita ukur dan dalam kondisi mana Apa faktor yang relevan mengenai pengukuran kita Apa yang ingin kita dapatkan dari pengukuran kita dalam hal kualitas, Kuantitas, dan harga Berikut adalah ringkasan singkat dari karakteristiknya. Isolasi tanah Accelerometer dengan isolasi tanah biasanya memiliki dasar pemasangan yang terisolasi dan sekrup pemasangan yang terisolasi, atau dalam beberapa kasus, seluruh kasus percepatan adalah tanah yang diisolasi. Isolasi tanah menjadi penting saat permukaan artikel uji bersifat konduktif dan potensial tanah. Perbedaan tingkat tegangan dasar antara instrumentasi elektronik dan accelerometer dapat menyebabkan loop tanah menghasilkan data yang keliru. Sensitivitas Sensitivitas adalah karakteristik pertama yang biasanya dipertimbangkan. Idealnya kita menginginkan tingkat output yang tinggi, tapi di sini kita harus berkompromi karena sensitivitas tinggi biasanya memerlukan perakitan piezoelektrik yang relatif besar dan akibatnya unit yang cukup besar dan berat. Dalam keadaan normal, sensitivitas bukanlah masalah penting karena preamplifier modern dirancang untuk menerima sinyal tingkat rendah ini. Rentang frekuensi rendah Persyaratan untuk pengukuran getaran biasanya sensor memiliki cutoff high pass yang lebih rendah daripada frekuensi yang diminati perangkat yang saat ini sedang diuji. Pada mesin berputar yang biasanya berjalan dengan 50 Hz, kita bisa memilih sensor dengan cut off 5 Hz. Saat mengukur getaran bangunan atau kapal, tingkat ini harus sangat rendah. Hal lain yang penting, untuk dipertimbangkan, adalah bandwidth sejak semakin rendah, semakin lama waktu pemulihan dari guncangan atau kelebihan beban. Selain itu, amplifier harus mengikuti bandwidth sensor. It's nice jika penguat memiliki setidaknya dua rentang agar lebih fleksibel dalam pengukuran. Aplikasi khas untuk pengukuran frekuensi rendah adalah gulungan gilingan kertas. Mereka memiliki frekuensi 15 Hz, dimana pengguna membutuhkan sensor dengan bandwidth 0,3 Hz atau kurang. Untuk aplikasi tersebut, charge atau IEPE paling sesuai. Jika kita perlu mengukur akselerasi statis maka teknologi sensor yang berbeda, seperti sensor MEMS, sangat dibutuhkan. Rentang frekuensi rendah, di mana accelerometer memberikan keluaran yang sebenarnya, terbatas pada frekuensi rendah di akhir praktik, oleh dua faktor. Yang pertama adalah cut-off frekuensi rendah penguat yang mengikutinya. Hal ini biasanya tidak menjadi masalah karena batas biasanya di bawah satu Hz. Yang kedua adalah efek dari fluktuasi suhu sekitar, dimana akselerometer sensitif. Dengan accelerometers tipe geser modern, efek ini minimal, memungkinkan pengukuran di bawah 1 Hz untuk lingkungan normal. Bandwidth (frequency range) Mechanical systems tend to have much of their vibration energy contained in the relatively narrow frequency range between 10 Hz to 1000 Hz but measurements are often made up to say 10 kHz because interesting vibration components are often present at these higher frequencies. Therefore, we must ensure, when selecting an accelerometer, that the frequency range covers the range of interest. The upper limit is determined by the resonant frequency of the mass-spring system of the accelerometer itself. As a rule of thumb, if we set the upper-frequency limit to one-third of the accelerometers resonance frequency, we know that vibration components measured at the upper-frequency limit will be in error by no more than 12. With small accelerometers where the mass is small, the resonant frequency can be as high as 180kHz, but for the somewhat larger, higher output, general purpose accelerometers, resonant frequencies of 20 to 30kHz are typical. We need to be careful about the increased sensitivity at sensor high-frequency end due to its resonance. Reading in this area will be too high but can be removed in the frequency domain if sensor transfer characteristics is known (by using transfer curves in DEWESoft). Amplitude range Charge sensors have the biggest amplitude ranges (special designed shock sensors can have more than 100 000 g amplitude range), but IEPE are also fairly high (up to 1000 g). MEMS sensors usually have very limited range (up to few hundred g). For general purposes, it is best to use IEPE, whereas for high levels piezoelectric sensors are better. Sometimes (for example for seismic applications) an accelerometer with high sensitivity is required (2 g or lower range). Maximum shock level The charge sensors are the least sensitive to shock. They can sustain up to 100 000 g of shock while IEPE can usually take not more than 5 000 to 10 000 g. MEMS sensors are even more sensitive to shock. Noise level The residual noise level defines the lowest amplitude level of what the sensor will measure. This is also the reason why we should take a sensor with the optimum measurement range because sensors with a higher range will also have a higher noise level. IEPE sensors have very high dynamic range (we can see signals better than 160 dB below the maximum range). Charge sensors are similar, but we need to consider that the noise can be easily generated in the cable. MEMS sensor is much worse in dynamic range limited by internal electronics. Temperature range All the sensors, that include electronics, have a limited high-temperature range, up to 130 deg C. The temperature range of charge sensors is much higher - even up to 500 deg C. Please note however that this also requires a high-temperature cable. All piezoelectric materials are temperature dependent so that any change in the ambient temperature will result in a change in the sensitivity of the accelerometer. Piezoelectric accelerometers also exhibit a varying output when subjected to small temperature fluctuations, called temperature transients, in the measuring environment. This is normally only a problem when very low level or low-frequency vibrations are being measured. Modern shear type accelerometers have a very low sensitivity to temperature transients. When accelerometers are to be fixed to surfaces at higher temperatures than 250C, a heat sink and mica washer can be inserted between the base and the measuring surface. With surface temperatures of 350 to 400C, the accelerometer base can be held below 250C by this method. A stream of cooling the air can provide additional assistance. MEMS sensor temperature range is limited by internal electronics (from -40C to 125C). In some applications, like modal testing, weight can be a big factor due to the mass loading effect. The added mass to the structure changes the dynamic behavior, so ideally a sensor should have no mass at all. That is the kind of hard to achieve by normal design, but we can use laser contactless sensors in such cases. As a general rule, the accelerometer mass should be no more than one tenth of the dynamic mass of the vibrating part onto which it is mounted. Ground loops The ground loop currents can flow in the shield of accelerometer cables because the accelerometer and measuring equipment are earthed separately. The ground loop is broken by using an isolated sensor, an isolated amplifier or electrically isolating the accelerometer base from the mounting surface by means of an isolating stud. Cable noise Cable noise is mainly the issue of piezoelectric accelerometers having a high output impedance. These disturbances can result from triboelectric noise or electromagnetic noise. Triboelectric noise is often induced into the accelerometer cable by mechanical motion of the cable itself. It originates from local capacity and charge changes due to dynamic bending, compression and tension of the layers making up the cable. This problem is avoided by using a proper graphitized accelerometer cable and taping or gluing it down as close to the accelerometer as possible. Electromagnetic noise is often induced in the accelerometer cable when it is placed in the vicinity of running machinery. Transverse vibrations Piezoelectric accelerometers are sensitive to vibrations acting in directions other than coinciding with their main axis. In the transverse plane, perpendicular to the main axis, the sensitivity is less than 3 to 4 of the main axis sensitivity (typically lt 1). As the transverse resonant frequency normally lies at about 13 of the main axis resonant frequency this should be considered where high levels of transverse vibration are present. Accelerometer mass Choosing the mounting position for the accelerometer The sensors can be mounted in different ways. The bandwidth of the sensor is especially sensitive to the way it is mounted. The method of mounting the accelerometer to the measuring point is one of the most critical factors in obtaining accurate results from practical vibration measurements. Sloppy mounting results in a reduction in the mounted resonant frequency, which can severely limit the useful frequency range of the accelerometer. Stud - it is best to drill a hole in the test specimen and fix the sensor to the surface with a screw. This should not affect any sensor property. Obviously, in some cases a customer might not be particularly thrilled to do this, for example, to his brand new prototype of an airplane wing. Adhesive - another type of mounting, which doesnt affect the bandwidth that much is a thin double sided adhesive tape or bees wax (this is limited in its temperature range). Magnet - a very widely used mounting technique for machine diagnostics is to mount the sensor on a magnet. This will still produce a good bandwidth, but of course, the surface must be ferromagnetic (not aluminum or plastic). On sensors where we can use the mounting clip, we can glue the mounting clip up front and then just attach the sensor itself. A quick and dirty solution is also to hold down the sensor with the a hand on a rod. This is useful for some places which are hard to reach, but the bandwidth will be cut to 12 kHz. The accelerometer should be mounted so that the desired measuring direction coincides with its main sensitivity axis. Accelerometers are also slightly sensitive to vibrations in the transverse direction, but this can normally be ignored as the transverse sensitivity is typically less than 1 of the main axis sensitivity. A graph below is showing the bandwidth reduction from different mounting methods: Mounting option Eddy-current sensor Eddy-current sensors are noncontact devices capable of high-resolution measurement of the position andor change of position of any conductive target. Eddy-current sensors are also called inductive sensors, but generally eddy current refers to precision displacement instruments and inductive refers to inexpensive proximity switches. High resolution and tolerance of dirty environments make eddy-current sensors indispensable in todays modern industrial operations. Eddy-current sensors operate with magnetic fields. The driver creates an alternating current in the sensing coil at the end of the probe. This creates an alternating magnetic field with induces small currents in the target material - these currents are called eddy currents. The eddy currents create an opposing magnetic field which resists the field being generated by the probe coil. The interaction of the magnetic fields is dependent on the distance between the probe and the target. As the distance changes, the electronics sense the change in the field interaction and produce a voltage output which is proportional to the change in distance between the probe and target. The target surface must be at least three times larger than the probe diameter for normal, calibrated operation. Eddy-current sensors are used to detect surface and near-surface flaws in conductive materials, such as metals. Eddy current inspection is also used to sort materials based on electrical conductivity and magnetic permeability, and measures the thickness of thin sheets of metal and nonconductive coatings such as paint. Detects surface and near surface defects. Only conductive materials can be inspected. Test probe does not need to contact the part Ferromagnetic materials require special treatment to address magnetic permeability. Method can be used for more than flaw detection. Depth of penetration is limited. Minimum part preparation is required Flaws, that lie parallel to the inspection probe coil winding direction, can go undetected Tolerance of dirty environments Skill and training required is more extensive than other techniques. Not sensitive to material in the gap between the probe and target Surface finish and roughness may interfere. Less expensive and much smaller than laser interferometers Reference standards are needed for setup Position measurement Eddy-Current sensors are basically position measuring devices. Their outputs always indicate the size of the gap between the sensors probe and the target. When the probe is stationary, any changes in the output are directly interpreted as changes in position of the target. This is useful in: automation requiring precise location machine tool monitoring final assembly of precision equipment such as disk drives precision stage positioning Vibration measurement Measuring the dynamics of a continuously moving target, such as a vibrating element, requires some form of noncontact measurement. Eddy-Current sensors are useful whether the environment is clean or dirty and the motions are relatively small. Eddy-current sensors also have high-frequency response (up to 80 kHz) to accommodate high-speed motion. They can be used for: drive shaft monitoring vibration measurements Eddy-current sensor Lets do some vibration measurements in DEWESoft. Since the vibration is difficult to visualize and since there were lots of questions about the difference between acceleration, vibration velocity, and displacement, it is helpful to actually show the vibration. This example has a shaker with an attached light plastic structure that has a low natural frequency. At the same time, a video of the movement of this beam was taken with a high-speed camera. This helps to really see the vibrations as they were measured with the accelerometer. It is always advisable to use a measurement device with anti aliasing filter. Otherwise, we can never be sure that the measurement is correct. Quite often acceleration in a high-frequency range (around 20 kHz) is very high. If a device without anti aliasing filters is used, and samples with lower sampler rates are taken, those high frequencies will be mirrored in the lower range. Especially for the measurements like modal analysis this is the most important criteria. Below is the analog channel setup. There are two ACC modules we will use for the measurement of vibrations. Lets look how to scale the measurements. Sensor setup There are three ways to perform the setup of the sensor: user can enter it from the calibration sheet, user can calibrate it with the calibrator, user can use TEDS technology to read out calibration values. Entering the setup from the calibration sheet. It is helpful to take a look at the sensor calibration sheet. There is the sensitivity of the sensor, expressed either in mV(ms2) or mVg (or both) for IEPE sensors and in pCg for piezoelectric (charge) sensors. The picture below shows the calibration data sheet for a triaxial sensor. The Reference sensitivity is the key value to be entered in the DEWESoft setup. First, as usual, we should enter the Units of measurement. In this case, we use ms2. Then it is the best to go to the Scaling by function section. We check the Sensitivity box and enter 9.863 mV(ms2) in the sensitivity field. Also do not forget to set IEPE measurement. The second way is to do the calibration. We can use a standard old accelerometer calibrator which outputs 10 ms2 peak level acceleration (7,07 ms2 RMS). The sensor is attached to the calibrator, and the acceleration level is adjusted to the sensor mass. Then we enter in Scaling by two points the acceleration level of 7,07 ms2 and click calibrate from RMS. The current measured voltage level in mV is written to the second point scaling. There we can already see if the calibration was successful or not. In the data preview, we can see that the peak level is approximately 10 ms2 and the RMS is around 7,07. We can also select the Scaling by function and compare measured sensitivity to the calibration data sheet. The third, quite a new way of sensor setup, is the use of an electronic calibration sheet - TEDS. With a TEDS sensor, it is quite easy to select settings. Plug in the sensors in Sirius ACC, run DEWESoft and the sensors should be recognized immediately. TEDS works only if the amplifier is in IEPE mode (it doesnt work in the voltage mode). If this is set up later (after the first scan) or if we plug in the sensor when DEWESoft is already running on the setup screen, the TEDS sensors need to be rescanned. This can be done by clicking on the AMPLIFIER column caption on the basic setup screen and selecting the Rescan modules option. TEDS will also work with MSI-BR-ACC. When a sensor is correctly recognized, scaling factors, sensor serial number, and Recalibration date will be read from the sensor. In the setup screen, the user doesnt we have to enter the sensitivity since it is already filled in from the sensor. This principle is easy and straightforward, and it prevents user errors. Math setup - velocity and displacement The second step is to calculate the vibration velocity and the displacement. This can be achieved in the math section with the filter, since the integrator is actually nothing more than a filter. We enter integration and double integration in the setup - first will be the integrator (for calculation of vibration velocity) and the second one will be the double integrator (for measurement of the displacement). Lets go to the channel setup of the first math formula. First, we need to choose the input channels. We must select Acceleration. It is quite a common error to forget to choose the correct input channel, so it is advisable to do this step first. Then we should choose the Integration as math operation. Since the DC offset is merely an error in measurement and calculation, we need to set up the high pass filter (in Flow field) to cut off the DC offset. For single integration, the Order of the filter needs to be at least two(if filter order is one, there will be static offset left in the result, if there is no filter, it will drift away). Next, we enter the units. If the integration is from acceleration to velocity and the acceleration unit is ms2, the output unit is normally ms. If the scale is 1, the units are in ms. If we choose the scaling factor 1000, we will have units in mms. It is also interesting to know the vibration displacement. For this, we should setup another channel by again selecting Acceleration and selecting double integration. Since the double integrator is in fact a second order filter, we need to set the high pass filter to the Order at least three or higher. Usually the displacement caused by the vibration is not visible by the eye, and is measured in micrometers, but since this measurement has quite high values, the output unit was set to be in mm. The scaling factor is therefore again 1000. We can already see in the preview that the peak-peak movement is around 15 mm and since this is a value which can be confirmed with the eye, we can be sure that the scaling factors and the settings are correct. Channel setup - velocity and displacement Displacement and vibration velocity can also be calculated from the acceleration in DEWESoft much easier. Just go to the setup of the acceleration channel from which you want to get displacement or velocity. Displacement To get displacement check the checkbox at Displacement. When the displacement checkbox is checked the following setup will appear. The input signal is signal from accelerometer and displacement is second integration of acceleration. To get vibration velocity check the checkbox at Velocity. When the velocity checkbox is checked the following setup will appear. The input signal is signal from accelerometer and velocity is integration of acceleration. Vibration analysis - acceleration, velocity and displacement In the analysis mode, we can look through the data. Here, one picture is put on top of another to see the movement of the accelerometer. The first picture below is the upper point of displacement. On the scope of the right, we can see nicely that the acceleration, displacement, and velocity are phases shifted. On the recorder graph below, we can analyze the acceleration, velocity, and displacement. The displacement (blue curve) is in the upper position. The velocity (red curve) is zero - this is also clear because the upper point is a turnaround and before reaching this point on the top, the velocity is decreased and at the top point, the velocity is zero. The acceleration (green curve) at the top is at maximum in the negative direction. Acceleration is the rate of change of the velocity. We can see from the velocity curve that the rate of change is at a maximum at the top therefore the acceleration is at its maximum at the top dead point Now lets go to the next significant point of the movement - the center point. We can see that it is the center point because the displacement is in the middle. The velocity of the center is at a maximum in the negative direction. The beam is reaching the middle point with the maximum velocity, and it will slowly start to decelerate. Acceleration at that point is zero - when a body is standing still or moves with constant velocity, its acceleration is zero. This can be confirmed by observing the blue acceleration curve. The third significant point is the bottom point. Here, a top point is shown in the background for reference. Displacement is at the lowest point, velocity is zero and will continue to increase, the acceleration is at a maximum in the positive direction - the speed is changing at a maximum rate at this point. We conducted a simple experiment to get a better feeling about the vibration measurement. In practice, the vibration measurement would surely look different, but we would use the same basic principles as shown in this example. Vibration measurement - example Lets do some vibration measurements in DEWESoft. Since vibration is difficult to visualize and since there were lots of questions about the difference between acceleration, vibration velocity and displacement, it is helpful to actually show the vibration. Measurement was made with our new shaker. We tested our new product KRYPTON. Vibration durability test Video shows the vibration durability test of our latest product - KRYPTON. On the picture below we can see the screenshot from a software that runs the shaker. We set the frequency sweep from 10 Hz to 250 Hz, and the maximum acceleration was up to 33 g. On the shaker near KRYPTON, the DEWESoft accelerometer was fixed with a glue. Lets see the signal from the accelerometer. Lets take a look at the maximum acceleration detected by DEWESoft accelerometer. As it is seen in the picture, maximum was at 325.9 ms2, which is 33 g. We have also made a formula for vibration velocity and displacement like it was described on previous pages. The result is already known. Shock test Next test was shock test. Product is exposed to multiple shocks that reach 50 ms2 in our case, but can go up to 100 ms2. Next measurement was made with drop test. As you can see in the video below the product is lifted up, and then falls down, because of gravity. When the aluminium plate hits the ground, the object under test can be hit with 900 g. In our case, KRYPTON was hit with 957.5 ms2 which is equivalent to almost 100 g. Envelope detection Envelope detection is a procedure for early detecting of faults on ball bearings. To add a new envelope detection math module go to a math section and select Envelope detection under Add math section. Envelope detector has several stages and for each stage the parameters must be set: Calculation type defines the principle of calculation: Filtering - uses filter procedure for envelope calculation. Filtering is a standard procedure for calculating envelope used also in other implementations. Peak detection - uses the procedure of detecting peak values in the signal. Peak detection is a procedure which calculates amplitudes more exact than filtering. Use Bandpass checkbox enables or disables the first stage of calculation - band pass filtering. Acceleration sensor measures entire frequency range and acquires unbalance, misalignment and other faults on the machine. Ball bearing errors have very low energy and, therefore, is a small contribution to entire frequency spectrum. Signal band At signal band setup, we have to define lower and upper frequency limit Envelope band At envelope band setup, we have to define lower and upper frequency limit Bearing database In bearing database, we select the type of the machinery. If it is not listed you can add your own in XML database file. The frequency of interest is automatically calculated based on a geometry. When an error of the ball bearing occurs, it will produce ringing with a frequency which corresponds to its natural frequency. This ringing will repeat each time when a damaged part of the ball hits the ring or vice versa. We have to know also that inner ring, outer ring, cage and balls have different typical repeating frequency depending on the geometry of the bearing and the rotational frequency. To only focus on these high frequencies of the ringing, we have to look at the original frequency spectrum. We have generated a sine wave which have a small 10 kHz rings on top. In the frequency domain, we dont see at all the frequency that the ringing repeats, but only a major sine wave (could come from unbalance) and very high frequency coming from the bearing. Bandpass filtering in the envelope detector must be set to remove all components except ringing of the ball bearing. This can be usually found around 10 kHz. In our example, I have set lower frequency limit to 6 kHz and upper limit to 12 kHz to get all the energy. Signal after filtering would look like this: Only high frequency remains, but we still dont see the main low frequency with which the rings are repeating.Therefore, we have to apply an envelope to the signal. Envelope will draw a curve around the peaks of the signal, producing only positive part of the data. To do correct amplitude, we have to choose the Envelope band frequency. Bearings usually have typical frequencies up to 500 Hz and we also might want to Remove DC component in order to see nice frequency spectrum without large DC value coming from DC offset. After this filter, the signal looks like in the picture below and frequency spectrum of the envelope signal reveals the frequency of hits. This was simulated case to see the math procedure behind calculation. In reality, the signal will look like this. Not much to see from the time signal, but with calculation of typical frequencies we can see that the outer ring frequency is clearly shown in the FFT of the envelope signal. Following picture shows the typical damage of the outer ring of the large bearing (courtesy of Kalmer d.o.o. Trbovlje).Evil Mad Scientist Laboratories Using an ADXL330 accelerometer with an AVR microcontroller The last decade has seen more than an order of magnitude drop in the price of accelerometers. devices capable of measuring physical acceleration (often in more than one direction). History suggests that whenever a useful technology makes a precipitous drop in price, unexpected applications follow, and that8217s exactly what has happened in this case. Starting from zero and summing up acceleration, you can use an accelerometer to find velocity, and from that derive relative position information. By measuring the acceleration due to gravity, one can also determine orientation (technically, inclination)8211 you can tell which way it8217s pointing. Those are pretty useful skills for a chip And so as bulk prices for tiny chip-scale three-axis accelerometers have begun to approach 5, they have started to appear in all kinds of mass-market applications that you might not have predicted: laptop computers (for hard drive protection), smart phones and cameras (for orientation8211 e.g. portrait vs. landscape on the iPhone), cameras for image stabilization, and quite visibly in the controllers for Nintendo8217s Wii system. With all that promise, you might think that an accelerometer is a difficult beast to harness. That turns out not to be the case. In this little project we demystify the mighty accelerometer and show you how to get started playing with one. In the spirit of hobbyist electronics we do this the easy way8211 without designing a PCB or even soldering any surface-mount components. Note: An updated version of this article is now available here . Our project consists of two main elements: the accelerometer chip and a microcontroller that will read out the data and display it. Let8217s first focus on the accelerometer. We8217ll be using the ADXL330, which is a very popular little XYZ accelerometer made by Analog Devices. It8217s actually the same chip that you would find as the accelerometer inside the Nintendo Wiimote controller. Purchased one at a time, on its own, this chip costs about 11.50 from Digi-Key. and the price goes down to about 7.25 in large quantity. (If you are Nintendo, the price is even lower.) One of the downsides to new and fancy devices like these is that they tend to come in unfriendly packages. The ADXL330 is only available in a 16-pin LFCSP that8217s a plastic package 4 mm X 4 mm, with pins that can be seen through a good magnifying glass. While it8217s hard to work with on it8217s own, there actually is a good solution for playing with this: get a breakout board. This breakout board from SparkFun comes complete with a ADXL330 accelerometer soldered in place. The relevant connections to the chip are broken out into a row of 0.18243 spaced holes (which I have filled in with a six-pin header) and the three sensitivity axes of the chip are clearly labeled with bright markings on the silkscreen layer8211 a nice touch. The board is Sparkfun SKU: SEN-00692. 35. Yes, it costs a fair bit more than the bare chip itself, but the price is fair and the convenience factor can8217t be beat. (If cost really is an issue, one potential option is to actually use Nintendo8217s buying power to your benefit: disassemble a wii nunchuk controller (20) to get at the similar accelerometer that lives in it. You could even take apart the Wiimote itself, if you can get a good price on the unit. In any case, getting at the connections to the chip will be much more difficult than just buying a decent breakout board.) The accelerometer actually has a very simple analog interface. We only really need to connect to five pins on it. First, it wants power. It needs 1.8-3.6 V (and ground), and just to keep our discussion simple, let8217s plan on using 3V for everything8211 either use a single lithium coin cell two alkaline AA cells in series. The chip also has three analog outputs8211 one for each direction. On these outputs, 1.5 V (really, halfway between the power and ground rails) represents zero acceleration, and deviations from that, either higher or lower, represent higher or lower accelerations. The chip is sensitive to accelerations of - 3 g in each direction. (There is a sixth pin on the breakout board, which is for a self-test feature on the ADXL330 that we will not be using.) Next, we need a simple microcontroller to read out the analog outputs and process them. We8217re using the Atmel ATmega48, a member of the ATmega4888168 series of AVR microcontrollers. If you8217re new to programming AVR microcontrollers, you have an extra step and some reading to do here. (And, as it turns out, this actually is an excellent example of a 8220first8221 microcontroller project for anyone.) To get up to speed, please read LadyAda8217s tutorial. As is explained in the tutorial, you will need an AVR programmer (e.g. USBtinyISP. 22) and a working installation of the (free) AVR software toolchain. Now we come to actually building up the hardware. The first step is to build a simple target board for the ATmega48 a board on which the chip can be programmed. As explained in that article, we need a socket for the AVR (28-pin 0.38243 DIP), a 6-pin DIL header, a battery holder (in this case lithium coin cell or 2 X AA), and a piece of prototyping perfboard to build it all on. Besides those, we also have the accelerometer breakout board, of course. From the battery (left side) we hook the postive end to the indicated pins (Vcc, V) of the microcontroller (3 places), the ISP header, and the ADXL330 breakout board. The negative side of the battery is our effective ground, and get wired up to the ground pins of the microcontroller (2 places), the ISP header, and the ADXL330 breakout board. The four remaining pins on the ISP connector (the 2 x 3 header) also need to be wired up to the matching pins on the microcontroller: MOSI, MISO, SCK and RESET. We have skipped drawing the wires here to keep the diagram from looking like this. Hopefully, you learned connect-the-dots long before soldering. P Next, wire up the outputs of the ADXL330 board to the ADC inputs of the microcontroller as shown. X output to pin 28, Y to pin 27, Z to pin 26. Finally, we add some indicators: two LEDs (one red, one blue) for each of the three axes. The big idea is that when there is no acceleration in (say) the X axis direction, both LEDs are off. When it detects acceleration one way, the red LED lights up (and lights up more, the harder the acceleration is) and it lights up blue for acceleration in the opposite direction. (Naturally, the other two axes work the same way.) To do this, we8217re using the pulse width modulation outputs from the three timers (timer 0, timer 1, and timer 2) on the microcontroller. Each timer has two outputs, called 8220output compare8221 pins A and B, which go to the two LEDs. The six outputs are called OC0A, OC0B, OC1A, OC1B, OC2A, and OC2B, and are hooked up to the LEDs as indicated in the diagram. The AVR can directly drive LEDs of either color, without a series resistor, when powered by a lithium coin cell. However, it turns out that the AVR cannot be programmed in the circuit if the red LEDs are hooked up as shown but without the series resistors. (That8217s because of the difference in LED forward voltage for the two colors.) If you use an alkaline battery to run this circuit, you may wish to put a small resistor ( 30 ohms) in series with the blue LEDs as well. Two minor details, not shown in the diagrams. First, the ADXL330 breakout board is socketed8211 I cut apart a dip chip socket to make a holder for the breakout board 6-pin header so that it doesn8217t have to be permanently soldered to this setup. Secondly, I added a small power switch by the battery holder that lets you switch the circuit on or off easily. You can download the firmware program (C code) for the AVR here (11 kB .ZIP file). It8217s a very simple AVR-GCC program, licensed under the GPL. It reads in three analog inputs sequentially, and lights up the six display LEDs depending on the values that it reads. Once you8217ve gotten the AVR programmed, it should be ready to go and show you outputs that depend on the acceleration. As you swing it around, even fast, you can see the LEDs responding to motion in the different directions. If you aren8217t wildly swinging the board around, what you8217ll see is just the steady-state gravitational acceleration displayed. You might call it a precision tilt sensor, and it can tell you which way is up. If we tilt our board left or right, such that the X-axis is now pointing slightly up or down (slightly with or slightly against gravity) you can see the X-axis LED pair, which is the on the left, switch from red to blue: If instead we tilt the board forward and back, such that the Y axis is along or against gravity, you see the same thing for the middle pair of LEDs: Finally, the Z indicator pair, on the right, is blue until you turn the board upside down8211 or shake it up and down. So that8217s it: a working 8220Hello world8221 for an accelerometer, all the way up to blinking LEDs. Our C code is intentionally simple, and ready to mod. What can you do with it Soon, your little homebrew robot8211 or maybe gigantic evil death machine8211 will be able to tell how far it8217s been, which way it8217s facing, and which way is up. We think that this a useful building block, and we8217ll be interested to see what other new things people build with it. Note: An updated version of this article is now available here . Post navigation Good job, there are not too many accelerometer interface articles out there. I have a question, is this accelerometer able to be used for vibrational measurements You say quotAs you swing it around, even fast, you can see the LEDs responding to motion in the different directions.quot I am currently designing a system that records wheel flats on railway wagons, and was wondering if such a system would pick up such a vibrational anomaly Can you describe the amount of movement required to change the LEDs A video of you shaking your system around (slow, easy 8211 fast, hard) would be awesome You certainly could use the accelerometer for vibrational measurements. The particular response of the LEDs is really easy to change and if you wanted to, you could make the display much more sensitive than I have here. Excellent, thats great. This could help me in my endless quest for stabilized video from a bicycle mount. Is there any way to take the - 3V and drive a 6-12V linear actuator with fast smooth motion If so then I could get rid of all my aluminum arms bearings, springs, Too cool. Thanks That certainly could be done. The chip output is 0-3 V, by the way (or - 1.5 V from 1.5 V), not - 3 V. What kind of a drive depends on what type of actuator you8217re using, but it doesn8217t sound like a big challenge to do what ever kind of level translation and high-current buffering you might need. Great work first all. By the I8217m working on my final year project making use of DsPIC P30F6014A to read in analogue outputs of the adxl330 x,y,z pins. I got few questions though 1) what is the best reference voltage that can be chosen for DsPic P30F6014A when interfacing adxl330 to get better results 2) The out impedance of adxl330 is 32k,PIC amp Atmel processors require 10k or less. How did you go about this Some suggesting using OPAM non-inverting. Your help is very much appreciate. Email me at keleisteinyahoo.co.uk 1) Use a voltage reference chip. TI makes a number of good ones, for example. 2) The Atmel chips do not quotrequire 10k or less,quot they just recommend it for fastest response, and in this context 32 k is not far from 10 k in any case. for your case you seem to have used 3volts for your reference voltage. Did you connect your vref- to the ground How about deriving 3volts using voltage divider, are there any complications Excellent stuff Keep it up Hi, Thanks for this excellent tutorial. It8217s my first try on an AVR and I managed to get it working (amazing), but can8217t figure one thing out The led8217s dont show any difference between soft shaking and hard shaking. Ive previously made a setup with an Arduino and Nunchuck (which is eventually the same hardware as this tutorial, if I understand well) and that gives a very nice difference between soft and hard shaking. Should this setup do that as well, or would it be able to I have no experience in C so have a hard time trying to understand and reconfigure the script, so any clues to where to look and how to amend which part of the code would be much appreciated. Also another question, would it be a problem to run this on 4.5V or more I8217d like to get more light out of it. Many thanks When built correctly, this project should give smoothly changing LED output8211 able to detect and display small angles. Hi, Thanks for your reply. I didn8217t mean the transition is not smooth 8211 the brightness changes very smoothly when tilting the device, which strength I was also able to amend in the code with the (originally) 2 multiplier. What I meant though is acceleration, instead of tilt. If I suddenly move the device straight up, it does give a quick flicker, which is always the same, where as in the Arduino setup the sudden move up is noted much more detailed, and there is a difference in brightness levels with upward moves of different intensity. I hope I8217m being clear Sounds like a software difference. This program gives real-time output, with no averaging or smoothing. Look at the algorithm used in the other one, if you want to replicate that behavior. quotArduinoquot is not really different from quotAVRquot 8212 the same code will run on this processor whether you give it a new brand name or not. hello im working with ADXL 330 TO MONITOR THE HUMAN ACTIVITY. PLEASE HELP BY GIVING IDEA ABOUT HARD WARE DETAILS peterece1987yahoo hello friends i have question, can i measure distance of one point to end point by ADXL330 if your answer yes. how can i do i integrate twice from accelaration please help me8230 i would this module in submarine to measure distance8230 I8217m looking into intigrating the adxl330 chip into my L3 university project. What I need to know is can the chip sense when it is being twistedspun around Ie, it is flat on a surface and twistedturned as if there was a pivot in the middle of the chip. I hope this explanation makes sense :) No. What you8217re looking for is called a quotrate gyroquot chip. part of my project involved using the accelerometer to connect to the PIC16f877 so that we can read the acceleratio for 3-axis (X,Y,and Z) from the PIC16f877 to pc. if You have the code to reading of the data I would be very happy if will be able to send me the code And also if you have the circuit of the connection pic to adxl330. This is most interesting. Do you know the resolution values for the various acc chips available. If one were to use 1 vs 10 vs 50 chips in an array, could you increase the resolution (accuracy) of the readings. I am interested in measuring gravity to a high degree, perhaps 10-8 of 1G, typical for gravity meters. The iPhone uses an ST LIS331DL chip: -2g but if I read the specs right, it only has 8 bits so that8217s 128 parts per 1g, not a great resolution. If I read that as bad, then it might take a truck load to get down to what I8217m looking for. Is there anything more accurate gtDo you know the resolution values for the various acc chips available. The sensors are analog. The bit resolutions that we discuss are internal to the microcontroller and are unrelated to the sensor outputs. Hii Thanks for a great articles on accelerometers for beginners. Well there is a problem that i want to discuss. Is it possible to note the reading of a point for instance (x6, y5 and z2) through an accelerometer. Actually i am working on a project in which a robot can note the reading of a point and save it in the micro-controller and then it can visit the point again when commanded. Any guidance regarding this will really help me. Thanks Unless you had some very strong gravity-generating material at the origin of this plot, this particular chip wouldn8217t be able to tell you where a point in space iswas. It can tell you which way in all three dimensions the chip is tilting, but it can8217t give you relative distances from an origin. Well, okay, I take that back. In the very first part of the article, it discusses that you can calculate velocity and then distance based on acceleration, but I wouldn8217t exactly call it quoteasyquot to do in a small robot, IMHO. So is there any way that we can get the coordinates of a point in space Although the space will be limited like (-10 to 0 to 10). Or is there any other sensor or perhaps some logic of the algorithm that can be programmed into the controller. Secondly i cant figure out the above C program for the AVR controller. I think i m a bit weak in C controller programming. so can you please just share us the step by step logic that8217s being used in the program, so that i can program it for PIC or 8051 in assembly. amp Thanks for your help quotSo is there any way that we can get the coordinates of a point in spacequot The short answer (again): No. quotAlthough the space will be limited like (-10 to 0 to 10). Or is there any other sensor or perhaps some logic of the algorithm that can be programmed into the controller.quot If you have a robot that is programmed to move to a specific place, and then move to another point based simply on coordinates, all you need to do is keep track of the coordinates of where you start, and then move to where you want to go. If you8217re at 0,0, and want to move to 2,0, you program the bot to move to 2,0, and then it stores the fact that it8217s at 2,0. To move to -5, -8, the bot would need to move -7 units X and -8 units Y. Repeat ad infinitum. You can8217t use an accelerometer to figure out where you are on that grid. You just keep track of it as you go along (at a basic level) Thanks for ur reply. i got it this time, Can you please simplify the above program made in C. I mean please just tell us the logic behind this program. Well i think is that the accelerometer gives a pulse every time its tilted in any direction. So the controller is programmed so that when ever the accelerometer readings go high they send a pulse to the led8217s. Am i right and how do u program it for the strong led blinking, so that when the accelerometer is tilted powerfully the led8217s too light-up strongly. I8217m not sure how to answer this. You say, quotIs it possible to note the reading of a point for instance (x6, y5 and z2) through an accelerometer.quot The accelerometer reads acceleration 8212 not quotpointsquot whatever those are. If you mean, quotcan an accelerometer measure where in space it isquot The answer is simply quotno.quot I was curious about this as well, as I am constructing a similar project. I see that you had labeled the microprocessor with three input pins and three output pins, to represent the X, Y, and Z planes of the one accelerometer. But I also saw unlabeled pins. Are there more input pins and output pins that can handle more accelerometer chips If not, is there another microprocessor that could Any advice you could give on this would be greatly appreciated. gt8230you had labeled the microprocessor with three input pins and three output pins, gtto represent the X, Y, and Z planes of the one accelerometer. The X, Y, and Z labels are only on the accelerometer outputs, not on the microcontroller inputs. gtBut I also saw unlabeled pins. Are there more input pins and output pins that can gthandle more accelerometer chips If not, is there another microprocessor that could I8217m not sure why you8217d want output pins for this. There are six analog inputs on this particular AVR, so you can read out the complete output of two accelerometers. Other AVRs, and other microcontroller types as well, sometimes have more or fewer analog inputs. Would you happen to know of a particular model that has 15 (or more) inputs 8211 to handle 5 accelerometers Thanks again for your input. This has helped tremendously. You might look at the xmega chips some of them have up to 16 accelerometers. We recently wrote about them here.
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