{"id":2138,"date":"2023-04-07T21:01:25","date_gmt":"2023-04-07T21:01:25","guid":{"rendered":"https:\/\/vibromera.eu\/?p=2138"},"modified":"2026-05-24T01:07:27","modified_gmt":"2026-05-24T01:07:27","slug":"anvendelse-av-fouriertransformasjon-til-analyse-av-vibrasjonssignaler","status":"publish","type":"post","link":"https:\/\/vibromera.eu\/nb\/example\/application-of-the-fourier-transform-to-the-analysis-of-vibration-signals\/","title":{"rendered":"Anvendelse av Fouriertransformasjon til analyse av vibrasjonssignaler."},"content":{"rendered":"<h1>Anvendelse av Fourier-transformasjonen i analysen av vibrasjonssignaler<\/h1>\n<p style=\"text-align: right\">Andrei Shelkovenko. En av utviklerne og grunnleggeren av Vibromera.<br \/>\nOversettelsen av artikkelen kan inneholde un\u00f8yaktigheter.<\/p>\n<h2>Fouriertransformasjon og signalspektrum<\/h2>\n<p>I mange tilfeller best\u00e5r oppgaven i \u00e5 finne (beregne) <a href=\"https:\/\/vibromera.eu\/nb\/glossary\/spectrum\/\">spektrum<\/a> av et signal er som f\u00f8lger. Det finnes en ADC, som ved hjelp av samplingen <a href=\"https:\/\/vibromera.eu\/nb\/glossary\/frequency\/\">hyppighet<\/a> Fd omformer det kontinuerlige signalet, som kommer inn p\u00e5 inngangen i l\u00f8pet av tiden T, til digitale m\u00e5leverdier \u2013 N stykker. Deretter sendes denne rekken av m\u00e5leverdier til et program (for eksempel <span><a href=\"http:\/\/www.siarion.net\/rus\/free\/fourierscope\" target=\"_blank\" rel=\"noopener\">FourierScope<\/a><\/span>) som gir N\/2 noen numeriske verdier.<\/p>\n<p>For \u00e5 sjekke om programmet fungerer som det skal, lager vi en matrise av pr\u00f8ver som en sum av to sin(10*2*pi*x)+0,5*sin(5*2*pi*x) og mater den inn i programmet. Programmet tegnet f\u00f8lgende:<br \/>\n<div id=\"attachment_2139\" style=\"width: 650px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2139\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US725.webp\" alt=\"Fouriertransformasjon og signalspektrum\" width=\"640\" height=\"299\" class=\"size-full wp-image-2139\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US725.webp 640w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US725-600x280.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US725-300x140.webp 300w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><p id=\"caption-attachment-2139\" class=\"wp-caption-text\"><em><i><span>Fig.1 Grafen over tidsfunksjonen til signalet<\/span><\/i><\/em><\/p><\/div><\/p>\n<p>&nbsp;<\/p>\n<div id=\"attachment_2140\" style=\"width: 650px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2140\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US779.webp\" alt=\"Fig.2 Graf over signalspekteret\" width=\"640\" height=\"353\" class=\"size-full wp-image-2140\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US779.webp 640w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US779-600x331.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US779-300x165.webp 300w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><p id=\"caption-attachment-2140\" class=\"wp-caption-text\">Fig.2 Graf over signalspekteret<\/p><\/div>\n<p>&nbsp;<\/p>\n<p>There are two <a href=\"https:\/\/vibromera.eu\/nb\/glossary\/harmonics\/\">harmoniske<\/a> p\u00e5 spektrumgrafen \u2013 5 Hz med en amplitude p\u00e5 0,5 V og 10 Hz med en amplitude p\u00e5 1 V; alt stemmer med formelen for det opprinnelige signalet. Alt er i orden, programmet fungerer som det skal.<\/p>\n<p>Det betyr at hvis vi mater et reelt signal fra en blanding av to sinusoider til ADC-inngangen, vil vi f\u00e5 et lignende spektrum best\u00e5ende av to overtoner.<\/p>\n<p>S\u00e5 v\u00e5r <strong><b><span>ekte <\/span><\/b><\/strong>m\u00e5lt signal <strong><b><span>av 5 sekunders varighet<\/span><\/b><\/strong>, digitalisert av ADC, dvs. representert ved <strong><b><span>av diskret <\/span><\/b><\/strong>pr\u00f8ver, har en <strong><b><span>diskret ikke-periodisk <\/span><\/b><\/strong>spektrum.<br \/>\n<em><i><span>Fra et matematisk synspunkt - hvor mange feil i denne setningen? <\/span><\/i><\/em><\/p>\n<p>La oss n\u00e5 pr\u00f8ve \u00e5 m\u00e5le det samme signalet i 0,5 sekunder.<\/p>\n<div id=\"attachment_2141\" style=\"width: 615px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2141\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1459.png\" alt=\"Fig.3 Grafen for funksjonen sin(10*2*pi*x)+0,5*sin(5*2*pi*x) for en m\u00e5leperiode p\u00e5 0,5 sek.\" width=\"605\" height=\"317\" class=\"size-full wp-image-2141\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1459.png 605w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1459-600x314.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1459-300x157.webp 300w\" sizes=\"auto, (max-width: 605px) 100vw, 605px\" \/><p id=\"caption-attachment-2141\" class=\"wp-caption-text\">Fig.3 Grafen for funksjonen sin(10*2*pi*x)+0,5*sin(5*2*pi*x) for en m\u00e5leperiode p\u00e5 0,5 sek.<\/p><\/div>\n<p>&nbsp;<\/p>\n<div id=\"attachment_2142\" style=\"width: 650px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2142\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1564.webp\" alt=\"Fig.4 Spektrum av funksjonen\" width=\"640\" height=\"351\" class=\"size-full wp-image-2142\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1564.webp 640w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1564-600x329.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1564-300x165.webp 300w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><p id=\"caption-attachment-2142\" class=\"wp-caption-text\">Fig.4 Spektrum av funksjonen<\/p><\/div>\n<p>&nbsp;<\/p>\n<p>Det er noe som ikke stemmer her! Overtonen ved 10 Hz tegnes normalt, og i stedet for overtonen ved 5 Hz er det noen uklare overtoner.<\/p>\n<p>P\u00e5 Internett sier de at det er n\u00f8dvendig \u00e5 legge til nuller p\u00e5 slutten av pr\u00f8ven, og spekteret vil bli tegnet normalt.<\/p>\n<div id=\"attachment_2143\" style=\"width: 650px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2143\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1861.png\" alt=\"Fig.5 Vi har lagt til nuller i pr\u00f8ven opp til 5 sek.\" width=\"640\" height=\"334\" class=\"size-full wp-image-2143\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1861.png 640w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1861-600x313.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1861-300x157.webp 300w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><p id=\"caption-attachment-2143\" class=\"wp-caption-text\">Fig.5 Vi har lagt til nuller i pr\u00f8ven opp til 5 sek.<\/p><\/div>\n<p>&nbsp;<\/p>\n<div id=\"attachment_2144\" style=\"width: 650px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2144\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1916.webp\" alt=\"Fig. 6. Oppn\u00e5dd spektrum.\" width=\"640\" height=\"352\" class=\"size-full wp-image-2144\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1916.webp 640w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1916-600x330.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US1916-300x165.webp 300w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><p id=\"caption-attachment-2144\" class=\"wp-caption-text\">Fig. 6. Oppn\u00e5dd spektrum.<\/p><\/div>\n<p>&nbsp;<\/p>\n<p>Det er ikke det i det hele tatt. Jeg m\u00e5 forholde meg til teorien. La oss g\u00e5 til <span><a href=\"https:\/\/ru.wikipedia.org\/wiki\/\u0420\u044f\u0434_\u0424\u0443\u0440\u044c\u0435\" target=\"_blank\" rel=\"noopener\"><strong><b>Wikipedia<\/b><\/strong><\/a><\/span>\u00a0- kilden til kunnskap.<\/p>\n<h2>Kontinuerlig funksjon og dens Fourier-representasjon<\/h2>\n<p>Matematisk sett er signalet v\u00e5rt med en varighet p\u00e5 T sekunder en funksjon f(x) gitt p\u00e5 intervallet {0, T} (X er i dette tilfellet tid). En slik funksjon kan alltid representeres som en sum av harmoniske funksjoner (sinus eller cosinus) p\u00e5 formen:<\/p>\n<div id=\"attachment_2145\" style=\"width: 368px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2145\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US2409.png\" alt=\"Kontinuerlig funksjon og dens Fourier-representasjon\" width=\"358\" height=\"62\" class=\"size-full wp-image-2145\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US2409.png 358w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US2409-300x52.webp 300w\" sizes=\"auto, (max-width: 358px) 100vw, 358px\" \/><p id=\"caption-attachment-2145\" class=\"wp-caption-text\">\u00a0(1), der:<\/p>\n<p><\/p><\/div>\n<p>k er tallet p\u00e5 den trigonometriske funksjonen (tallet p\u00e5 den harmoniske komponenten, tallet p\u00e5 den harmoniske).<br \/>\nT - segment der funksjonen er definert (varigheten av signalet)<br \/>\nAk- amplituden til den k-te harmoniske komponenten,<br \/>\n\u03b8k- den opprinnelige fasen til den k. harmoniske komponenten<br \/>\nHva betyr det \u00e5 \"representere funksjonen som summen av seriene\"? Det betyr at ved \u00e5 legge sammen verdiene av de harmoniske komponentene i Fourier-serien i hvert punkt, f\u00e5r vi verdien av funksjonen i dette punktet.<br \/>\n(Mer presist vil middelkvadratavviket til serien fra funksjonen f(x) g\u00e5 mot null, men til tross for middelkvadratkonvergensen trenger ikke Fourier-serien til en funksjon \u00e5 konvergere mot denne punkt for punkt. )<br \/>\nDenne serien kan ogs\u00e5 skrives p\u00e5 formen:<\/p>\n<div id=\"attachment_2146\" style=\"width: 229px\" class=\"wp-caption alignleft\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2146\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US3314.png\" alt=\"(2),\" width=\"219\" height=\"62\" class=\"size-full wp-image-2146\" \/><p id=\"caption-attachment-2146\" class=\"wp-caption-text\">(2),<\/p><\/div>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>hvor <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US3326.webp\" alt=\"Fourier transform equation (2) for vibration signal analysis\" width=\"29\" height=\"33\" class=\"wp-image-2147 size-full alignnone\" \/> den k-te komplekse amplituden.<\/p>\n<p>&nbsp;<\/p>\n<p>eller<\/p>\n<div id=\"attachment_2148\" style=\"width: 481px\" class=\"wp-caption alignleft\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2148\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US3362.png\" alt=\" (3)\" width=\"471\" height=\"62\" class=\"size-full wp-image-2148\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US3362.png 471w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US3362-300x39.webp 300w\" sizes=\"auto, (max-width: 471px) 100vw, 471px\" \/><p id=\"caption-attachment-2148\" class=\"wp-caption-text\">(3)<\/p><\/div>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>Forholdet mellom koeffisientene (1) og (3) uttrykkes ved f\u00f8lgende formler:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US3464.png\" alt=\"Formula relating the Fourier series coefficients\" width=\"156\" height=\"46\" class=\"size-full wp-image-2149 alignleft\" \/><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US3470.png\" alt=\"Fourier series coefficient formula\" width=\"148\" height=\"58\" class=\"size-full wp-image-2150 alignleft\" \/><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: left\">Merk at alle disse tre representasjonene av Fourier-serier er helt ekvivalente. Noen ganger n\u00e5r man arbeider med Fourier-serier, er det mer praktisk \u00e5 bruke eksponenter med imagin\u00e6rt argument i stedet for sinus og cosinus, dvs. \u00e5 bruke Fouriertransformasjon p\u00e5 kompleks form. Men det er praktisk for oss \u00e5 bruke formel (1), der Fourier-serien er representert som en sum av cosinus med tilsvarende amplituder og faser. Uansett er det feil \u00e5 si at resultatet av Fouriertransformasjonen av det reelle signalet vil v\u00e6re komplekse harmoniske amplituder. Som Wiki korrekt sier: \"Fouriertransformasjonen (\u2131) er en operasjon som avbilder en funksjon av en reell variabel til en annen funksjon ogs\u00e5 av en reell variabel.\"<\/p>\n<p>&nbsp;<\/p>\n<p><strong><u><b><span>Poenget:<\/span><\/b><\/u><\/strong><strong><b><span><br \/>\n<\/span><\/b><\/strong><strong><b><span>Det matematiske grunnlaget for spektralanalyse av signaler er Fouriertransformasjonen.<\/span><\/b><\/strong><strong><b><span><br \/>\n<\/span><\/b><\/strong><strong><b><span><br \/>\n<\/span><\/b><\/strong><strong><b><span>Fouriertransformasjonen gj\u00f8r det mulig \u00e5 representere en kontinuerlig funksjon f(x) (signal) definert i intervallet {0, T} som en sum av et uendelig antall (uendelig serie) trigonometriske funksjoner (sinus og\/eller cosinus) med bestemte amplituder og faser, ogs\u00e5 i intervallet {0, T}. En slik serie kalles en Fourier-serie.<\/span><\/b><\/strong><\/p>\n<p>Legg merke til noen flere punkter som det er n\u00f8dvendig \u00e5 forst\u00e5 for \u00e5 kunne anvende Fouriertransformasjonen korrekt i signalanalyse. Hvis vi betrakter Fourier-serien (summen av sinuskurver) p\u00e5 hele X-aksen, vil vi se at utenfor intervallet {0, T} vil Fourier-seriefunksjonen periodisk gjenta v\u00e5r funksjon.<\/p>\n<p>I grafen i figur 7 er for eksempel den opprinnelige funksjonen definert p\u00e5 intervallet {-T\\2, +T\\2}, og Fourier-serien representerer en periodisk funksjon definert p\u00e5 hele x-aksen.<\/p>\n<p>Dette skyldes at sinusoidene i seg selv er periodiske funksjoner, slik at summen av dem ogs\u00e5 vil v\u00e6re en periodisk funksjon.<\/p>\n<div id=\"attachment_2151\" style=\"width: 674px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2151\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US5209.png\" alt=\"Figur 7 Representasjon av en ikke-periodisk kildefunksjon ved hjelp av en Fourier-serie\" width=\"664\" height=\"250\" class=\"size-full wp-image-2151\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US5209.png 664w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US5209-600x226.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US5209-300x113.webp 300w\" sizes=\"auto, (max-width: 664px) 100vw, 664px\" \/><p id=\"caption-attachment-2151\" class=\"wp-caption-text\">Figur 7 Representasjon av en ikke-periodisk kildefunksjon ved hjelp av en Fourier-serie<\/p><\/div>\n<p>Derfor:<\/p>\n<p>V\u00e5r opprinnelige funksjon er en kontinuerlig, ikke-periodisk funksjon definert p\u00e5 et segment med lengden T.<br \/>\nSpektret til denne funksjonen er diskret, det vil si at det er representert som en uendelig serie av harmoniske komponenter - en Fourier-serie.<br \/>\nFaktisk definerer Fourier-serien en periodisk funksjon som sammenfaller med v\u00e5r funksjon p\u00e5 intervallet {0, T}, men denne periodisiteten er ikke avgj\u00f8rende for oss.<\/p>\n<p>Neste.<\/p>\n<p>Periodene til de harmoniske komponentene er multipler av intervallet {0, T}, der den opprinnelige funksjonen f(x) er definert. Med andre ord er periodene til de harmoniske komponentene multipler av varigheten til signalm\u00e5lingen. For eksempel er perioden til den f\u00f8rste overtonen i en Fourier-serie lik intervallet T der funksjonen f(x) er definert. Perioden til den andre harmoniske i en Fourier-serie er lik intervallet T\/2. Og s\u00e5 videre (se figur 8).<\/p>\n<div id=\"attachment_2152\" style=\"width: 687px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2152\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US6155.png\" alt=\"Fig. 8 Perioder (frekvenser) for de harmoniske komponentene i Fourier-serien (her er T=2\u03c0).\" width=\"677\" height=\"362\" class=\"size-full wp-image-2152\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US6155.png 677w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US6155-600x321.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US6155-300x160.webp 300w\" sizes=\"auto, (max-width: 677px) 100vw, 677px\" \/><p id=\"caption-attachment-2152\" class=\"wp-caption-text\">Fig. 8 Perioder (frekvenser) for de harmoniske komponentene i Fourier-serien (her er T=2\u03c0).<\/p><\/div>\n<p>F\u00f8lgelig er frekvensene til de harmoniske komponentene multipler av 1\/T. Det vil si at frekvensene til de harmoniske komponentene Fk er Fk= k\\T, der k har verdier fra 0 til \u221e, for eksempel k=0 F0=0; k=1 F1=1\\T; k=2 F2=2\\T;k=3 F3=3\\T;.... Fk= k\\T (ved null frekvens, en konstant komponent).<\/p>\n<p>La v\u00e5r utgangsfunksjon v\u00e6re et signal som er registrert i l\u00f8pet av T=1 sek. Da vil perioden til den f\u00f8rste overtonen v\u00e6re lik signalets varighet T1=T=1 sek. og frekvensen til overtonen er lik 1 Hz. Perioden for den andre overtonen vil v\u00e6re lik varigheten av signalet v\u00e5rt delt p\u00e5 2 (T2=T\/2=0,5 sek.) og frekvensen er lik 2 Hz. For den tredje harmoniske er T3=T\/3 sek. og frekvensen er 3 Hz. Og s\u00e5 videre.<\/p>\n<p>Steget mellom overtonene er i dette tilfellet 1 Hz.<\/p>\n<p>Dermed kan et signal med en varighet p\u00e5 1 sekund dekomponeres i harmoniske komponenter (for \u00e5 f\u00e5 et spektrum) med en frekvensoppl\u00f8sning p\u00e5 1 Hz.<br \/>\nFor \u00e5 \u00f8ke oppl\u00f8sningen med en faktor 2 til 0,5 Hz, m\u00e5 m\u00e5letiden \u00f8kes med en faktor 2 til 2 sekunder. Et 10 sekunders signal kan dekomponeres i harmoniske komponenter (spektrum) med en frekvensoppl\u00f8sning p\u00e5 0,1 Hz. Det finnes ingen andre m\u00e5ter \u00e5 \u00f8ke frekvensoppl\u00f8sningen p\u00e5. Du kan utforske dette forholdet med v\u00e5r <a href=\"https:\/\/vibromera.eu\/nb\/calculators\/fft-resolution-calculator\/\">FFT-oppl\u00f8sningskalkulator<\/a>.<\/p>\n<p>Det er mulig \u00e5 \u00f8ke signalets varighet p\u00e5 en kunstig m\u00e5te ved \u00e5 legge til nuller i utvalget av pr\u00f8ver. Men det \u00f8ker ikke den reelle frekvensoppl\u00f8sningen.<\/p>\n<h2>Diskrete signaler og diskret Fourier-transformasjon<\/h2>\n<p>Med utviklingen av digital teknologi har m\u00e5tene \u00e5 lagre m\u00e5ledata (signaler) p\u00e5 endret seg. Mens man tidligere kunne ta opp et signal p\u00e5 en b\u00e5ndopptaker og lagre det analogt p\u00e5 et b\u00e5nd, blir signalene n\u00e5 digitalisert og lagret i filer i datamaskinens minne som et sett med tall (tellinger).<\/p>\n<p>Det vanlige opplegget for signalm\u00e5ling og digitalisering ser ut som f\u00f8lger.<\/p>\n<p>M\u00e5leomformer -- Signal normaliserer -- ADC -- Datamaskin<br \/>\n(<em><i><span>Fig.9 Skjematisk oversikt over m\u00e5lekanalen)<\/p>\n<p><\/span><\/i><\/em><\/p>\n<p>Signalet fra m\u00e5leomformeren g\u00e5r til ADC-en i en tidsperiode T. Signalavlesningene (sampling) som mottas i l\u00f8pet av tiden T, overf\u00f8res til datamaskinen og lagres i minnet.<\/p>\n<div id=\"attachment_2154\" style=\"width: 650px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2154\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US8285.webp\" alt=\"Fig.10 Digitalisert signal - N pr\u00f8ver mottatt for tiden T\" width=\"640\" height=\"327\" class=\"size-full wp-image-2154\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US8285.webp 640w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US8285-600x307.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US8285-300x153.webp 300w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><p id=\"caption-attachment-2154\" class=\"wp-caption-text\">Fig.10 Digitalisert signal - N pr\u00f8ver mottatt for tiden T<\/p><\/div>\n<p>Hvilke krav stilles til parametrene for signaldigitalisering? En enhet som konverterer det analoge inngangssignalet til en diskret kode (digitalt signal) kalles en analog-til-digital-omformer (ADC) (\u00a9 Wiki).<\/p>\n<p>En av de grunnleggende parametrene for ADC er den maksimale samplingsfrekvensen - frekvensen for sampling av et signal som er kontinuerlig i tid. Samplingsfrekvensen m\u00e5les i hertz. ((\u00a9 Wiki))<\/p>\n<p>If\u00f8lge Kotelnikovs teorem kan et kontinuerlig signal som har et spektrum begrenset av frekvensen Fmax, rekonstrueres fullstendig og entydig fra sine diskrete samplinger tatt med tidsintervaller T = 1\/2*Fmax, dvs. med en frekvens Fd \u2265 2*Fmax, der Fd er samplingsfrekvensen og Fmax er den maksimale frekvensen i signalspekteret. Med andre ord m\u00e5 frekvensen for signaldigitalisering (samplingsfrekvensen til ADC) v\u00e6re minst 2 ganger h\u00f8yere enn den maksimale frekvensen til signalet vi \u00f8nsker \u00e5 m\u00e5le.<\/p>\n<p>Og hva skjer hvis vi tar pr\u00f8ver med lavere frekvens enn Kotelnikovs teorem krever?<\/p>\n<p>I dette tilfellet er det en \u00ab<a href=\"https:\/\/vibromera.eu\/nb\/glossary\/aliasing\/\">aliasering<\/a>I dette tilfellet oppst\u00e5r det en \"aliasing\"-effekt (ogs\u00e5 kjent som stroboskopisk effekt, moir\u00e9-effekt), der et h\u00f8yfrekvent signal etter digitalisering blir til et lavfrekvent signal som faktisk ikke eksisterer. I fig. 11 er den r\u00f8de sinuskurven med h\u00f8y frekvens det virkelige signalet. Den bl\u00e5 sinuskurven med lavere frekvens er et fiktivt signal som oppst\u00e5r fordi det i l\u00f8pet av samplingstiden har g\u00e5tt mer enn en halv periode av det h\u00f8yfrekvente signalet.<\/p>\n<div id=\"attachment_2156\" style=\"width: 730px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2156\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US9777.webp\" alt=\"Fig. 11. Opptreden av et lavfrekvent spuri\u00f8st signal ved for lav samplingsfrekvens\" width=\"720\" height=\"255\" class=\"size-full wp-image-2156\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US9777.webp 720w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US9777-600x213.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US9777-300x106.webp 300w\" sizes=\"auto, (max-width: 720px) 100vw, 720px\" \/><p id=\"caption-attachment-2156\" class=\"wp-caption-text\">Fig. 11. Opptreden av et lavfrekvent spuri\u00f8st signal ved for lav samplingsfrekvens<\/p><\/div>\n<p>&nbsp;<\/p>\n<p>For \u00e5 unng\u00e5 aliasing-effekten, brukes et spesielt anti-aliasing-filter (<a href=\"https:\/\/vibromera.eu\/nb\/glossary\/low-pass-filter\/\">lavpassfilter<\/a>) er plassert foran ADC-en. Den slipper gjennom frekvenser som er lavere enn halvparten av ADC-ens samplingsfrekvens og demper h\u00f8yere frekvenser.<\/p>\n<p>For \u00e5 beregne signalspektrumet ut fra dets diskrete pr\u00f8ver, m\u00e5 de diskrete <a href=\"https:\/\/vibromera.eu\/nb\/glossary\/fft\/\">Fourier-transformasjon (DFT)<\/a> brukes. Merk igjen at spektrumet til et diskret signal \u00abper definisjon\u00bb er begrenset til en frekvens Fmax som er mindre enn halvparten av samplingsfrekvensen Fd. Derfor kan spektrumet til et diskret signal representeres ved summen av <u>en endelig <\/u>antall overtoner, i motsetning til den uendelige summen for Fourier-serien til et kontinuerlig signal, hvis spektrum kan v\u00e6re ubegrenset. If\u00f8lge Kotelnikovs teorem m\u00e5 den maksimale frekvensen til en overton v\u00e6re slik at den utgj\u00f8r minst to samplinger, slik at antall overtoner er lik halvparten av antall samplinger i et diskret signal. Det vil si at hvis det er N pr\u00f8ver i pr\u00f8ven, vil antall overtoner i spekteret v\u00e6re N\/2.<\/p>\n<p>Betrakt n\u00e5 den diskrete Fouriertransformasjonen (DFT).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US10917.png\" alt=\"Discrete Fourier transform (DFT) equation\" width=\"502\" height=\"190\" class=\"aligncenter size-full wp-image-2157\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US10917.png 502w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US10917-300x114.webp 300w\" sizes=\"auto, (max-width: 502px) 100vw, 502px\" \/><\/p>\n<p>Sammenligning med Fourier-serien<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US10958.png\" alt=\"Discrete Fourier transform spectrum formula compared with the Fourier series\" width=\"440\" height=\"98\" class=\"aligncenter size-full wp-image-2158\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US10958.png 440w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US10958-300x67.webp 300w\" sizes=\"auto, (max-width: 440px) 100vw, 440px\" \/><\/p>\n<p>Som vi ser, er de sammenfallende, bortsett fra at tiden i FFT er diskret og antall overtoner er begrenset til N\/2, som er halvparten av antall samples.<\/p>\n<p>DFT-formler skrives i dimensjonsl\u00f8se heltallsvariabler k, s, der k er antall signalpr\u00f8ver og s er antall spektralkomponenter.<br \/>\nVerdien s viser antall fullharmoniske svingninger per periode T (varigheten av signalm\u00e5lingen). Diskret Fourier-transformasjon brukes til \u00e5 finne amplituder og faser for de harmoniske svingningene numerisk, dvs. \"p\u00e5 datamaskinen\".<\/p>\n<p>Som allerede nevnt ovenfor, n\u00e5r vi dekomponerer en ikke-periodisk funksjon (signalet v\u00e5rt) i Fourier-serier, tilsvarer den resulterende Fourier-serien faktisk en periodisk funksjon med periode T (fig. 12).<\/p>\n<p>&nbsp;<\/p>\n<div id=\"attachment_2159\" style=\"width: 597px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2159\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US11706.png\" alt=\"Fig. 12. Periodisk funksjon f(x) med periode T0, med periode T&gt;T0\" width=\"587\" height=\"235\" class=\"size-full wp-image-2159\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US11706.png 587w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US11706-300x120.webp 300w\" sizes=\"auto, (max-width: 587px) 100vw, 587px\" \/><p id=\"caption-attachment-2159\" class=\"wp-caption-text\">Fig. 12. Periodisk funksjon f(x) med periode T0, med periode T&gt;T0<\/p><\/div>\n<p>&nbsp;<\/p>\n<p>Som det fremg\u00e5r av figur 12, er funksjonen f(x) periodisk med perioden T\u2080. Men siden m\u00e5lepr\u00f8velengden T ikke er lik funksjonens periode T\u2080, har funksjonen som fremkommer som en Fourier-rekke et bruddpunkt ved punktet T. F\u00f8lgelig vil spektrumet til denne funksjonen inneholde et stort antall h\u00f8yfrekvente harmoniske. Dette fenomenet kalles <a href=\"https:\/\/vibromera.eu\/nb\/glossary\/spectral-leakage\/\">spektral lekkasje<\/a>, og i praksis reduseres den med <a href=\"https:\/\/vibromera.eu\/nb\/glossary\/windowing\/\">vindusbygging<\/a> signalet f\u00f8r transformasjonen. Hvis varigheten av m\u00e5lepr\u00f8ven T falt sammen med perioden til funksjonen T\u2080, ville spektrumet man fikk etter Fourier-transformasjonen bare inneholde den f\u00f8rste harmoniske (en sinuskurve med en periode som tilsvarer pr\u00f8vens varighet), fordi funksjonen f(x) er en sinuskurve.<\/p>\n<p>DFT-programmet \"vet\" med andre ord ikke at signalet v\u00e5rt er en \"del av en sinuskurve\", men pr\u00f8ver \u00e5 representere en periodisk funksjon som har en diskontinuitet p\u00e5 grunn av diskontinuiteten i de enkelte delene av sinuskurven.<\/p>\n<p>Resultatet er at det oppst\u00e5r overtoner i spekteret, som totalt sett skal representere formen p\u00e5 funksjonen, inkludert denne diskontinuiteten.<\/p>\n<p>For \u00e5 f\u00e5 et \"korrekt\" spektrum av et signal som er en sum av flere sinuskurver med forskjellige perioder, er det derfor n\u00f8dvendig at en <u>helt antall perioder med <\/u>hver sinuskurve skal v\u00e6re til stede i l\u00f8pet av signalets m\u00e5leperiode. I praksis kan denne betingelsen oppfylles med en tilstrekkelig lang varighet p\u00e5 signalm\u00e5lingen.<\/p>\n<p>&nbsp;<\/p>\n<div id=\"attachment_2160\" style=\"width: 808px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2160\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US13102.png\" alt=\"Fig.13 Eksempel p\u00e5 kinematisk feilsignalfunksjon og spektrum for en girkasse\" width=\"798\" height=\"426\" class=\"size-full wp-image-2160\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US13102.png 798w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US13102-600x320.webp 600w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US13102-300x160.webp 300w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US13102-768x410.png 768w\" sizes=\"auto, (max-width: 798px) 100vw, 798px\" \/><p id=\"caption-attachment-2160\" class=\"wp-caption-text\">Fig.13 Eksempel p\u00e5 kinematisk feilsignalfunksjon og spektrum for en girkasse<\/p><\/div>\n<p>&nbsp;<\/p>\n<p>Ved kortere varighet vil bildet se \"d\u00e5rligere\" ut:<\/p>\n<p>&nbsp;<\/p>\n<div id=\"attachment_2161\" style=\"width: 583px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2161\" src=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US13237.png\" alt=\"Fig.14 Eksempel p\u00e5 rotorsvibrasjonsfunksjon og -spektrum\" width=\"573\" height=\"420\" class=\"size-full wp-image-2161\" srcset=\"https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US13237.png 573w, https:\/\/vibromera.eu\/wp-content\/uploads\/2023\/04\/\u041f\u0440\u0438\u043c\u0435\u043d\u0435\u043d\u0438\u0435-\u043f\u0440\u0435\u043e\u0431\u0440\u0430\u0437\u043e\u0432\u0430\u043d\u0438\u044f-\u0424\u0443\u0440\u044c\u0435-\u0434\u043b\u044f-\u0430\u043d\u0430\u043b\u0438\u0437\u0430-\u0432\u0438\u0431\u0440\u043e\u0441\u0438\u0433\u043d\u0430\u043b\u043e\u0432-en-US13237-300x220.webp 300w\" sizes=\"auto, (max-width: 573px) 100vw, 573px\" \/><p id=\"caption-attachment-2161\" class=\"wp-caption-text\">Fig.14 Eksempel p\u00e5 rotorsvibrasjonsfunksjon og -spektrum<\/p><\/div>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>I praksis kan det v\u00e6re vanskelig \u00e5 forst\u00e5 hva som er \"ekte komponenter\" og hva som er \"artefakter\" for\u00e5rsaket av uoverensstemmelse mellom komponentperioder og signalets samplingsvarighet eller \"hopp og brudd\" i b\u00f8lgeformen. Det er selvsagt en grunn til at ordene \"reelle komponenter\" og \"artefakter\" st\u00e5r i anf\u00f8rselstegn. Tilstedev\u00e6relsen av mange overtoner p\u00e5 spektrumgrafen betyr ikke at signalet v\u00e5rt faktisk best\u00e5r av dem. Det er som \u00e5 tro at tallet 7 \"best\u00e5r\" av tallene 3 og 4. Tallet 7 kan betraktes som summen av 3 og 4 - det er riktig.<\/p>\n<p>S\u00e5 signalet v\u00e5rt ... eller rettere sagt ikke engang \"signalet v\u00e5rt\", men en periodisk funksjon som er sammensatt ved \u00e5 gjenta signalet v\u00e5rt (sample), kan ogs\u00e5 representeres som en sum av overtoner (sinusb\u00f8lger) med bestemte amplituder og faser. Men i mange tilfeller som er viktige i praksis (se figurene ovenfor), er det faktisk mulig \u00e5 relatere overtonene i spekteret ogs\u00e5 til reelle prosesser som har syklisk karakter og bidrar vesentlig til signalets form.<\/p>\n<h2>Noen resultater<\/h2>\n<p>1. Et reelt m\u00e5lesignal med T sekunders varighet digitalisert av ADC, dvs. representert ved et sett med diskrete samplinger (N deler), har et diskret ikke-periodisk spektrum representert ved et sett med overtoner (N\/2 deler).<\/p>\n<p>2. Signalet representeres av et sett med gyldige verdier, og dets spektrum representeres av et sett med gyldige verdier. Frekvensene til de harmoniske er positive. Bare fordi det er matematisk mer praktisk \u00e5 representere spekteret i kompleks form ved hjelp av negative frekvenser, betyr ikke det at \"dette er riktig\" og \"det er slik du alltid b\u00f8r gj\u00f8re det\".<\/p>\n<p>3. Signalet som m\u00e5les p\u00e5 tidspunkt T, bestemmes bare p\u00e5 tidspunkt T. Hva som skjedde f\u00f8r vi begynte \u00e5 m\u00e5le signalet, og hva som vil skje etter det, er ukjent for vitenskapen. Og i v\u00e5rt tilfelle er det ikke interessant. FFT av det tidsbegrensede signalet gir dets \"virkelige\" spektrum, i den forstand at det under visse betingelser gj\u00f8r det mulig \u00e5 beregne amplitude og frekvens for komponentene.<\/p>\n<p>&nbsp;<\/p>","protected":false},"excerpt":{"rendered":"<p>Application of the Fourier Transform to the Analysis of Vibration Signals Andrei Shelkovenko. One of the developers and founder of Vibromera. The translation of the article may contain inaccuracies. Fourier transform and signal spectrum In many cases the task of obtaining (calculating) the spectrum of a signal is as follows. [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":2161,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ai_generated_summary":"","footnotes":""},"categories":[4],"tags":[],"class_list":["post-2138","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-example"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/posts\/2138","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/comments?post=2138"}],"version-history":[{"count":1,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/posts\/2138\/revisions"}],"predecessor-version":[{"id":101508,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/posts\/2138\/revisions\/101508"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/media\/2161"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/media?parent=2138"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/categories?post=2138"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/nb\/wp-json\/wp\/v2\/tags?post=2138"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}