In the last section, we looked at door sensors, one of the most basic car alarm systems. These days, only the cheapest car alarm packages rely on door sensors alone. Advanced alarm systems mostly depend on shock sensors to deter thieves and vandals.
The idea of a shock sensor is fairly simple: If somebody hits, jostles or otherwise moves your car, the sensor sends a signal to the brain indicating the intensity of the motion. Depending on the severity of the shock, the brain signals a warning horn beep or sounds the full-scale alarm.
There are many different ways to construct a shock sensor. One simple sensor is a long, flexible metal contact positioned just above another metal contact. You can easily configure these contacts as a simple switch: When you touch them together, current flows between them. A substantial jolt will cause the flexible contact to sway so that it touches the contact below, completing the circuit briefly.
The problem with this design is that all shocks or vibrations close the circuit in the same way. The brain has no way of measuring the intensity of the jolt, which results in a lot of false alarms. More-advanced sensors send different information depending on how severe the shock is.
The sensor has only three major elements:
A central electrical contact in a cylinder housing
Several smaller electrical contacts at the bottom of the housing
A metal ball that can move freely in the housing
In any possible resting position, the metal ball is touching both the central electrical contact and one of the smaller electrical contacts. This completes a circuit, sending an electrical current to the brain. Each of the small contacts is connected to the brain this way, via separate circuits.
When you move the sensor, by hitting it or shaking it, the ball rolls around in the housing. As it rolls off of one of the smaller electrical contacts, it breaks the connection between that particular contact and the central contact. This opens the switch, telling the brain that the ball has moved. As it rolls on, it passes over the other contacts, closing each circuit and opening it back up, until it finally comes to a stop.
If the sensor experiences a more severe shock, the ball rolls a greater distance, passing over more of the smaller electrical contacts before it comes to a stop. When this happens, the brain receives short bursts of current from all of the individual circuits. Based on how many bursts it receives and how long they last, the brain can determine the severity of the shock. For very small shifts, where the ball only rolls from one contact to the next one, the brain might not trigger the alarm at all. For slightly larger shifts -- from somebody bumping into the car, for example -- it may give a warning sign: a tap of the horn and a flash of the headlights. When the ball rolls a good distance, the brain turns on the siren full blast.
In many modern alarm systems, shock sensors are the primary theft detectors, but they are usually coupled with other devices. In the next few sections, we'll look at some other types of sensors that tell the brain when something is wrong.
Avtomobil signallari zarba datchiklari
Oxirgi bo'limda biz eng asosiy avtomobil signalizatsiya tizimlaridan biri bo'lgan eshik sensorlarini ko'rib chiqdik. Hozirgi kunda faqat eng arzon avtomobil signalizatsiya paketlari faqat eshik sensorlariga tayanadi. Murakkab signalizatsiya tizimlari asosan o'g'rilar va vandallarning oldini olish uchun zarba sensorlariga bog'liq.
Shok sensori g'oyasi juda oddiy: agar kimdir sizning mashinangizni ursa, silkitsa yoki boshqa yo'l bilan harakatlantirsa, sensor miyaga harakatning intensivligini ko'rsatadigan signal yuboradi. Shokning og'irligiga qarab, miya ogohlantiruvchi shox signalini beradi yoki to'liq miqyosli signalni eshitadi.
Shok sensorini qurishning turli usullari mavjud. Bitta oddiy sensor bu boshqa metall kontaktning tepasida joylashgan uzun, moslashuvchan metall kontaktdir. Siz ushbu kontaktlarni oddiy kalit sifatida osongina sozlashingiz mumkin: ularni bir-biriga tegizsangiz, ular orasida oqim oqadi. Jiddiy silkinish egiluvchan kontaktni tebranishiga olib keladi, shunda u pastdagi kontaktga tegib, kontaktlarning zanglashiga olib keladi.
Ushbu dizayndagi muammo shundaki, barcha zarbalar yoki tebranishlar sxemani xuddi shunday yopadi. Miya tebranishning intensivligini o'lchash imkoniyatiga ega emas, bu esa ko'plab noto'g'ri signallarga olib keladi. Murakkab sensorlar zarba qanchalik kuchli ekanligiga qarab turli xil ma'lumotlarni yuboradi.
Sensor faqat uchta asosiy elementga ega:
Silindr korpusidagi markaziy elektr kontakti
Korpusning pastki qismida bir nechta kichikroq elektr kontaktlari
Korpusda erkin harakatlana oladigan metall to'p
Har qanday mumkin bo'lgan dam olish holatida metall to'p ham markaziy elektr kontaktiga, ham kichikroq elektr kontaktlaridan biriga tegadi. Bu miyaga elektr tokini yuborib, kontaktlarning zanglashiga olib keladi. Kichik kontaktlarning har biri miyaga shu tarzda, alohida zanjirlar orqali ulanadi.
Sensorni harakatga keltirganingizda, uni urish yoki silkitish orqali to'p korpus ichida aylanadi. U kichikroq elektr kontaktlaridan biridan aylanib chiqqach, ushbu kontakt va markaziy kontakt o'rtasidagi aloqani buzadi. Bu kalitni ochadi va miyaga to'p harakat qilganini aytadi. U aylanayotganda, u boshqa kontaktlardan o'tib, har bir zanjirni yopadi va oxiri to'xtaguncha uni qayta ochadi
. If the sensor experiences a more severe shock, the ball rolls a greater distance, passing over more of the smaller electrical contacts before it comes to a stop. When this happens, the brain receives short bursts of current from all of the individual circuits. Based on how many bursts it receives and how long they last, the brain can determine the severity of the shock. For very small shifts, where the ball only rolls from one contact to the next one, the brain might not trigger the alarm at all. For slightly larger shifts -- from somebody bumping into the car, for example -- it may give a warning sign: a tap of the horn and a flash of the headlights. When the ball rolls a good distance, the brain turns on the siren full blast.
In many modern alarm systems, shock sensors are the primary theft detectors, but they are usually coupled with other devices. In the next few sections, we'll look at some other types of sensors that tell the brain when something is wrong.
. Agar datchik kuchliroq zarbaga duchor bo'lsa, to'p to'xtab qolmasdan oldin kichikroq elektr kontaktlaridan o'tib, ko'proq masofani aylantiradi. Bu sodir bo'lganda, miya barcha alohida kontaktlarning zanglashiga olib keladigan qisqa oqimlarini oladi. Qancha portlashlar qabul qilishiga va ular qancha davom etishiga qarab, miya zarba zo'ravonligini aniqlay oladi. To'p faqat bitta kontaktdan ikkinchisiga o'tadigan juda kichik siljishlar uchun miya signalni umuman ishga tushirmasligi mumkin. Biroz kattaroq siljishlar uchun, masalan, kimdir mashinaga urilganda, bu ogohlantirish belgisini berishi mumkin: shoxning bosilishi va faralarning miltillashi. To'p yaxshi masofaga aylanganda, miya sirena to'liq portlashni yoqadi.
Ko'pgina zamonaviy signalizatsiya tizimlarida zarba sensorlari asosiy o'g'irlik detektorlari hisoblanadi, lekin ular odatda boshqa qurilmalar bilan birlashtiriladi. Keyingi bir necha bo'limlarda biz biror narsa noto'g'ri bo'lganida miyaga xabar beradigan boshqa turdagi sensorlarni ko'rib chiqamiz.
A lot of the time, car thieves who are in a hurry don't mess around with disabling locks to get into a car: They just bust a window. A fully equipped car alarm system has a device that senses this intrusion.
The most common glass-breakage detector is a simple microphone connected to the brain. Microphones measure variations in air-pressure fluctuation and convert this pattern into a fluctuating electrical current. Breaking glass has its own distinctive sound frequency (pattern of air-pressure fluctuations). The microphone converts this to an electrical current of that particular frequency, which it sends to the brain.
On its way to the brain, the current passes through a [url='8895:8']crossover, an electrical device that only conducts
electricity of a certain frequency range. The crossover is configured so that it will only conduct current that has the frequency of breaking glass. In this way, only this specific sound will trigger the alarm, and all other sounds are ignored.
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