Seismik Datchikni Tushunish
A seismik datchik — seismik sensor yoki inersial datchik deb ham ataladi — bu vibration sensor that uses an internal seismic mass (a “proof mass”) suspended on springs or compliant flexures as an inertial reference, allowing it to measure the absolute motion of the sensor base. When the housing vibrates, the relative motion between the suspended mass and the housing is converted into an electrical signal that represents the vibration. Depending on where the measurement frequency lies relative to the mass-spring system’s tabiiy chastotasi, the sensor works in one of two regimes: above resonance the mass tends to stay still in space and the relative motion follows the housing displacement (the classic seismometer and velocity-pickup regime), while below resonance the small residual deflection of the mass is proportional to the housing acceleration (the accelerometer regime). The defining feature is that the reference is carried inside sensor ichida joylashgan, shuning uchun tashqi qo'zg'almas mos yozuv nuqtasi talab qilinmaydi.
“Seismik” nomi zilzila o'lchash asboblaridan kelib chiqqan: seysmometrdagi osilgan massa yer silkinayotganda nisbatan harakatsiz qoladi. Mashina monitoringida ham tezlik datchiklari and akselerometrlar bu ma'noda seismik datchiklar hisoblanadi, garchi atama ko'pincha klassik tezlik sensori bilan bog'liq bo'lsa ham.
1. Ishlash Printsipi
Massa-Prujina-Amortizator Tizimi
Har qanday seismik datchik, mohiyatan, to'rtta funksional qismdan iborat kichik mexanik tebranuvchidan iborat:
- Seismic mass: sensor korpusi ichida osib qo'yilgan kalibrlangan etalon massa.
- Spring: massani tayyorlovchi mexanik prujinalar yoki ingichka egiluvchan elementlar.
- Damping: rezonansni bartaraf etuvchi havo, magnit (vixr tok) yoki suyuqlik so'ndirishi.
- Transduction: massa bilan korpus o'rtasidagi nisbiy harakatni kuchlanishga aylantiradigan element.
Chastota javob mintaqalari
How the sensor behaves depends entirely on where the excitation frequency falls relative to its own natural frequency — and the two main sensor families deliberately work on opposite sides of the resonance:
- Below natural frequency (accelerometer regime): mass and housing move essentially together, and the small residual deflection of the mass is proportional to the housing acceleration. Piezoelectric and MEMS accelerometers work here, below their high mounted resonance.
- Tabiiy chastotada: the system resonates — output is amplified but distorted and unreliable, so measurement near resonance is avoided.
- Above natural frequency (seismometer regime): the mass effectively stays put while the housing vibrates around it, and the relative motion follows the housing displacement (or velocity). Displacement seismometers and moving-coil velocity pickups work here, above their low natural frequency.
- Usable ranges: a velocity pickup is conventionally used above roughly 2× its natural frequency, where its response has settled and is flat; an accelerometer is used well below its mounted resonance — typically up to about one-third of it for good accuracy.
2. Seismik datchiklar turlari
Tezlik datchiklari (harakatlanuvchi o'ram)
- Magnit qo'zg'almas o'ram ichida prujinalar yordamida to'xtatilgan (yoki aksincha).
- Magnit va o'ram o'rtasidagi nisbiy tezlik elektromagnit induksiya orqali kuchlanish hosil qiladi.
- Tabiiy chastota odatda 8–15 Hz.
- Taxminan 16–30 Hz dan yuqorida ishlatish mumkin.
- Signal integratsiyasiga ehtiyoj sezmasdan tezlikni to'g'ridan-to'g'ri o'lchaydi.
Accelerometers
- Piezoelectric turlari massaning inersiya kuchini his qilish uchun piezoelektrik kristaldan foydalanadi.
- MEMS turlari mikro-ishlov berilgan elementda sig'im yoki piezoresistiv sezgichdan foydalanadi.
- Much higher (mounted) natural frequency, typically 10–30 kHz.
- Unlike velocity pickups, used below resonance: usable from about 1 Hz up to roughly one-third of the mounted resonance frequency.
- Tezlanishni o'lchaydi, uni tezlikka yoki siljishga integrallash mumkin.
3. Seismik va Seismik Bo'lmagan Sensorlar
Seismik sensorlar guruhini tashqi tayanch nuqtasiga tayanadigan sensorlar bilan taqqoslash orqali yaxshiroq tushunish mumkin.
Seismik Sensorlar (Inersial Tayanch)
- Akselerometrlar va tezlik o'lchagichlari.
- Inersial fazodagi mutlaq harakatni o'lchaydi.
- To'g'ridan-to'g'ri tebranuvchi konstruksiyaga o'rnatiladi.
- Tayanch sifatida o'z ichki massasiga ega.
- Mashinalar monitoringida eng keng tarqalgan tanlov.
Seismik Bo'lmagan Sensorlar (Tashqi Tayanch)
- Proksimlik zondlari (vixrtoklarli sensorlar).
- Ikki yuzaning nisbiy harakatini o'lchaydi.
- O'lchash uchun statsionar montaj nuqtasiga muhtoj.
- Odatda val harakatini podshipnikka nisbatan o'lchaydi.
- Quyidagi turdagi mashinalarda val tebranishini o'lchash standarti sirt podshipniklari.
4. Seismik Dizaynning Afzalliklari
O'z-O'ziga To'liq Tayanch
- Tashqi tayanch tizimiga ehtiyoj yo'q.
- Sensor tebranuvchi konstruksiyaning deyarli istalgan joyiga o'rnatilishi mumkin.
- U inersial fazoda haqiqiy mutlaq harakatni o'lchaydi.
Versatility
- Bir turdagi sensor juda ko'p ilovalar uchun mos keladi.
- Ham vaqtinchalik o'lchovlar, ham doimiy o'rnatmalar uchun yaroqli.
- Mashinadan mashinaga osongina ko'chirish mumkin.
Ushbu ko'p qirralilik tufayli ko'chma asboblar ularga tayanadi. Ikki kanalli Balanset-1A, masalan, o'lchov ma'lumotlarini podshipnik korpuslariga mahkamlangan akselerometrlardan oladi — bu o'z-o'ziga moslashuvchi seysmosensoerlar bo'lib, ular uchun qattiq mos nuqta talab etilmaydi; shuning uchun muhandis ob'ektda balanslashtirish jarayonida o'lchov nuqtalari va mashinalar o'rtasida tezda harakat qila oladi.
5. Limitations
Chastota javob chegaralari
- Velocity pickups cannot measure reliably below roughly 2× their natural frequency; moving-coil types in particular respond poorly below 15–20 Hz. There is an inherent trade-off: a lower natural frequency gives better low-frequency reach but demands a larger, heavier sensor.
- Accelerometers lose accuracy as the measurement frequency approaches their mounted resonance; the practical upper limit (typically about one-third of the mounted resonance) depends strongly on the mounting method (see ISO 5348).
- At the very low end, accelerometer response is limited by the sensing element and amplifier electronics rather than the seismic suspension — typically down to about 0.5–1 Hz for standard industrial units.
Korpus harakatini o'lchash
- Sensor to'g'ridan-to'g'ri valning emas, balki podshipnik korpusining harakatini ko'rsatadi.
- Korpus vibratsiyasi val vibratsiyasi bilan bir xil emas — u podshipnik qattiqlik ko'rsatkichi va atrofdagi konstruksiya orqali filtrlanadi.
- Valning haqiqiy orbita traektoriyasi muhim bo'lgan hollarda esa yaqinlik zondlaridan foydalanish zarur.
6. Qo'llanilishi
Mexanizmlar texnik holatini monitoring qilish
- Podshipnik korpusi vibratsiyasini o'lchash.
- Umumiy vibratsiya darajasini kuzatib borish.
- Bearing-defect detection.
- Aylanuvchi mexanizmlarning umumiy diagnostikasi.
Konstruktiv vibratsiya
- Binolar va poydevorlarning tebranishini o'lchash.
- Zilzilalarni seismik monitoring qilish.
- Mexanizmlardan tarqaladigan tuproq orqali o'tadigan tebranish.
Modal Analysis
- Tuzilmaning kalibrlangan zarba ta'siriga javobini o'lchash.
- Determining tabiiy chastotalar and mode shapes.
- Building the chastotali javob funktsiyalari used in modal analysis.
Seismic transducers, using an internal suspended mass as an inertial reference, form the foundation of vibration measurement on rotating machinery. Grasping the seismic principle — how a suspended mass enables absolute-motion measurement, and why velocity pickups work above their natural frequency while accelerometers work below their mounted resonance — explains both the strengths and the limits of these twin workhorses of every industrial vibration-analysis programme.
