What Are Car Alarm Sensors and How Do They Work?

Pressure Sensors

Another way to detect breaking glass, as well as somebody opening the door, is to measure the air pressure in the car. Even if there is no pressure differential between the inside and outside, the act of opening a door or forcing in a window pushes or pulls on the air in the car, creating a brief change in pressure.
You can detect fluctuations in air pressure with an ordinary loudspeaker driver. A loudspeaker has two major parts:

• 
  A wide, movable cone
  
• 
  An electromagnet, surrounded by a natural magnet, attached to the cone
  

When you play music, an electric current flows back and forth through the electromagnet, which causes it to move in and out. This pushes and pulls the attached cone, forming air-pressure fluctuations in the surrounding air. We hear these fluctuations as sound.
This same system can work in reverse, which is what happens in a basic pressure detector. Pressure fluctuations move the cone back and forth, which pushes and pulls the attached electromagnet. If you've read How Electromagnets Work, you know that moving an electromagnet in a surrounding natural magnetic field generates an electrical current. When the brain registers a significant current flowing from this device, it knows that something has caused a rapid pressure increase inside the car. This suggests that somebody has opened a door or window, or made a very loud noise.
Some alarm-system designs utilize the car's built-in stereo speakers as pressure sensors, but others have separate devices that are specifically designed for detection.
Pressure sensors, glass-breakage sensors and door sensors all do a pretty good job of detecting someone breaking into a car, but some thieves and vandals can do a lot of damage without ever making it inside. In the next section, we'll look at some security systems that keep tabs on what's going on outside your car.
Ko'pincha shoshayotgan avtomobil o'g'rilari mashinaga kirish uchun qulflarni o'chirib qo'yish bilan aralashmaydilar: ular shunchaki derazani sindirishadi. To'liq jihozlangan avtomobil signalizatsiya tizimi ushbu bosqinni sezadigan qurilmaga ega.

Eng keng tarqalgan shisha sindirish detektori miyaga ulangan oddiy mikrofondir. Mikrofonlar havo bosimi o'zgarishidagi o'zgarishlarni o'lchaydi va bu naqshni o'zgaruvchan elektr tokiga aylantiradi. Shishani sindirish o'ziga xos ovoz chastotasiga ega (havo bosimining o'zgarishi namunasi). Mikrofon buni miyaga yuboradigan ma'lum chastotadagi elektr tokiga aylantiradi.

Miyaga boradigan yo'lda, oqim [url='8895:8'] krossoverdan o'tadi, bu elektr moslamasi faqat

ma'lum bir chastota diapazonidagi elektr energiyasi. Krossover shunday tuzilganki, u faqat oynani sindirish chastotasiga ega bo'lgan oqimni o'tkazadi. Shu tarzda, faqat ma'lum bir tovush signalni ishga tushiradi va boshqa barcha tovushlar e'tiborga olinmaydi.

Bosim datchiklari
Shisha singanligini, shuningdek kimdir eshikni ochayotganini aniqlashning yana bir usuli - bu avtomobildagi havo bosimini o'lchashdir. Ichkarida va tashqarisida bosim farqi bo'lmasa ham, eshikni ochish yoki derazani majburlash harakati avtomobildagi havoni itarib yoki tortib, bosimning qisqa o'zgarishini keltirib chiqaradi.

Oddiy karnay drayveri yordamida havo bosimining o'zgarishini aniqlashingiz mumkin. Karnay ikkita asosiy qismdan iborat:

Keng, harakatlanuvchi konus
Konusga biriktirilgan tabiiy magnit bilan o'ralgan elektromagnit
Musiqa chalayotganingizda, elektr toki elektromagnit orqali oldinga va orqaga oqadi, bu uning ichkariga va tashqariga harakatlanishiga olib keladi. Bu biriktirilgan konusni itaradi va tortadi, bu atrofdagi havoda havo bosimining tebranishlarini hosil qiladi. Biz bu tebranishlarni tovush sifatida eshitamiz.

Xuddi shu tizim teskari tartibda ishlashi mumkin, bu asosiy bosim detektorida sodir bo'ladi. Bosim tebranishlari konusni oldinga va orqaga siljitadi, bu esa biriktirilgan elektromagnitni itaradi va tortadi. Agar siz “Elektromagnitlar qanday ishlaydi” kitobini o‘qigan bo‘lsangiz, bilasizki, elektromagnitni atrofdagi tabiiy magnit maydonda harakatlantirish elektr tokini hosil qiladi. Miya ushbu qurilmadan oqayotgan sezilarli oqimni qayd etganda, u nimadir mashina ichidagi bosimning tez oshishiga sabab bo'lganini biladi. Bu kimdir eshik yoki derazani ochganini yoki juda baland ovozda ovoz chiqarganini ko'rsatadi.

Ba'zi signal tizimlari dizaynlari avtomobilning o'rnatilgan stereo karnaylaridan bosim sensori sifatida foydalanadi, ammo boshqalarda aniqlash uchun maxsus mo'ljallangan alohida qurilmalar mavjud.

Bosim datchiklari, shisha sindirish datchiklari va eshik datchiklari kimningdir mashinaga bostirib kirayotganini aniqlashda juda yaxshi ish qiladi, biroq ba'zi o'g'rilar va buzg'unchilar uni hech qachon ichkariga kiritmasdan ko'p zarar etkazishi mumkin. Keyingi bo'limda biz avtomobilingiz tashqarisida sodir bo'layotgan voqealarni kuzatib boradigan ba'zi xavfsizlik tizimlarini ko'rib chiqamiz.