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A notch filter — also called a band-stop filter, band-reject filter, or frequency trap — is a frequency-selective signal-processing element that strongly attenuates vibrasiya components inside a narrow frequency band while letting everything outside that band pass essentially unchanged. It is the exact opposite of a bant keçirici filtr: rather than passing one band and blocking the rest, it blocks one band and passes the rest. Within the toolkit of siqnal filtrləmə, the notch is the surgical instrument.

In Vibrasiya Analizi, notch filters remove dominant interference such as 50/60 Hz electrical noise, suppress an overwhelming vibration component (a very large 1× balanssızlıq that masks everything else), or knock down a resonance that obscures diagnostic detail. In effect they let the analyst “see around” a dominant frequency to reveal weaker but diagnostically important components hiding beneath it in the spektr.

1. Filter Characteristics

Mərkəzi (Notch) Tezliyi

• The frequency of maximum attenuation — the one being “notched out”.
• Xüsusi müdaxiləyə və ya arzuolunmaz tezlikə köklənmişdir
• Attenuation is typically 40–60 dB at the center.

Çentik bant genişliyi

• Narrow notch: rejects a very selective frequency range (high Q).
• Wide notch: rejects a broader frequency band (low Q).
• Q factor: center frequency divided by bandwidth.
• Tipik: Q = 10–50 for vibration applications.

Zəifləmə dərinliyi

• How far the notch frequency is reduced.
• Typically 40–60 dB, equivalent to a 100–1000× reduction.
• Higher-order filters provide deeper notches.
• Adjacent frequencies are minimally affected when the design is good.

2. Common Applications

Electrical Interference Removal

Eliminating power-line noise is the classic use:

• 60 Hz notch: removes 60 Hz electrical pickup in North America.
• 50 Hz notch: removes 50 Hz interference in Europe and Asia.
• Harmoniklər: 120/180/240 Hz və ya 100/150/200 Hz-də əlavə çentiklər
• Fayda: a cleaner spectrum that reveals the underlying mechanical vibration.
• Diqqət: do not use it if 2× line frequency (120 or 100 Hz) carries diagnostic value — that band is a key indicator of Elektrik nasazlıqları mühərriklərdə.

Dominant Component Suppression

• Severe unbalance: notch out an overwhelming 1× to expose other components.
• High gear mesh: remove a dominant dişli şəbəkə tezliyi to reveal bearing frequencies.
• Strong resonance: suppress a structural rezonans to see the excitation behind it.
• Məqsəd: reveal masked diagnostic information.

Sensor Resonance Elimination

• Remove artifacts from sensor mounting resonance.
• Place the notch at the mounting-resonance frequency, which varies with the mounting method.
• Ensures the measurement represents the machine, not the sensor.

Avoiding Aliasing Artifacts

• Notch out a specific high frequency before downsampling.
• Prevents ləqəb of a known strong component.
• Complements the anti-aliasing aşağı ötürmə filtr rather than replacing it.

3. Design Considerations

Dar Çentik (Yüksək Q)

• Üstünlük: surgical removal of a single frequency with minimal effect on neighbours.
• Dezavantaj: the target frequency must be precisely known and stable.
• Misal: a 60.0 Hz ± 0.5 Hz notch for electrical interference.

Geniş Çentik (Aşağı Q)

• Üstünlük: captures frequency variations, so the tuning is less critical.
• Dezavantaj: may affect frequencies you wanted to keep.
• Misal: a 1× ± 5 Hz notch to remove unbalance that drifts with qaçış sürəti fluctuations.

Dərinlik və Genişlik Mübadiləsi

• Deeper notches (greater than 60 dB) often require a wider bandwidth.
• Çox dar çentiklər dərin zəifləməyə nail ola bilməz
• Optimise the balance to suit the application.

4. Advantages and Limitations

Üstünlüklər

• Removes dominant interfering frequencies.
• Reveals masked diagnostic components.
• Improves use of the available Dinamik diapazon.
• Lets the analyst focus on weaker but important signals.

Məhdudiyyətlər və Xəbərdarlıqlar

• Removes information: the notched-out content is lost permanently from the filtered record.
• Can hide problems: if the notched frequency had diagnostic value, the fault is missed.
• Phase distortion: notch filters significantly affect faza near the notch frequency.
• Zəng: sharp notches can create time-domain artifacts in the zaman dalğa forması.
• Use cautiously: a notch should complement, never replace, unfiltered analysis.

5. Ən yaxşı təcrübələr

When to Use a Notch Filter

• Known interference such as electrical noise is obscuring the measurement.
• A dominant component (severe unbalance) is preventing full use of dynamic range.
• Unfiltered analysis has already confirmed the notched frequency is not diagnostic.
• You want to reveal a weak signal for detailed examination.

When Not to Use One

• Routine screening measurements — use unfiltered data for general diaqnoz.
• When the notched frequency has diagnostic value.
• Before you understand the full unfiltered spectrum.
• As a substitute for fixing the actual interference source.

Sənədlər

• Always document when a notch filter was used.
• Record the notch frequency and bandwidth.
• Keep the unfiltered data for reference.
• Note the reason for notch filtering in the diaqnostik hesabat.

6. Implementation

Avadanlıq Notch Filtrləri

• Fixed frequency, typically 50 or 60 Hz.
• Switched in and out as needed.
• An analog circuit inside the instrument.
• Operates in real time.

Proqram Notch Filtrləri

• Applied to digitised data after acquisition.
• Adjustable center frequency and bandwidth.
• Different notch parameters can be tried and compared.
• Non-destructive — the original data is preserved.

7. The Notch Filter in Field Practice

In day-to-day field work the notch filter earns its keep when a single frequency drowns out everything you need to see. A common case is a rotor with a large unbalance: a portable analyser such as the Balanset-1A 1×-i ölçür amplituda və faza directly for balanslaşdırma, and once that dominant 1× component has been corrected, the spectrum opens up so the smaller bearing and gear signatures become readable without any notch at all. That illustrates the golden rule — wherever possible, cure the source rather than mask the symptom. The notch remains the right tool when the offending frequency is genuinely external, such as 50/60 Hz pickup on the cabling, and is confirmed to carry no mechanical meaning.

Notch filters are specialised signal-processing tools that selectively remove narrow frequency bands from a vibration signal. They are powerful for eliminating interference and revealing masked components, but they must be used judiciously and with full awareness of what is being discarded — always confirming that the notched frequencies hold no important diagnostic content.

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