NHÓM – LỚP Đ8-ĐTVT MEMBER: - Phạm Văn Thành Phạm Thị Bích Lụa Vũ Thị Ngát Nguyễn Thị Minh Thu Dương Thị Hồng Hoàng Thị Hường Lesson 5: Alarm Systems Task 1: Tuning- in Task 2: This diagram show a circuit of alarm systems There are seven: Bell, door switch, window fail, passive infra-red detector, pressure mat, sense circuit and key-operated switch control box The warning device is the bell Because, it protects the alarm system If the door is opened, the window is broken, when someone step on the pressure mat or when someone moves on motion sensors range, the bell will ring When a burglar disconnects the supply, this system won’t work Task 3: Door switch: magnetic switches Window foil: break detectors Pressure mat: pressure mats Passive infra-red detector: motion sensors Task 4: How could the system shown in Task be improved? Note your ideas Now read this text to check which of your ideas are described We can make the simple alarm circuit more effective by including some of these features Entry and exit delays! These mean you won’t set off the alarm when leaving or returning to the house On the better systems, the delays are adjustable An audible warning during the delay period is a useful reminder Automatic cut-off! This will stop the alarm after it has sounded for a set time, so that the noise doesn’t go on for hours if you’re not there to reset the system In better systems, the alarm automatically resets at the end of the alarm time Tamper protection The control panel incorporates sensors which will trigger the alarm if a burglar tries to force the box open Battery backup! This means the alarm will continue to work in a power cut, or if an intruder disconnects the mains supply Task 5: 2-e Action A burglar disconnects the supply The glass is broken Consequence The alarm continues to operate on batteries The foil breaks too 3-f A door is opened 4-a A window is opened 5-g You’re not there to reset the system A burglar tries to force the alarm open Someone steps on them A magnet on the door trips a switch on the frame A magnet on the moving part trips a switch The alarm stops after a set time Tamper sensors trigger the alarm Two thin metal plates come in contact 1-c 6-b 7-d Device Battery backup Break detectors Magnetic switches Magnet switches Automatic cutoff Tamper protection Motion sensors Task 6: If pressure mats are constantly walked on, two thin metal plates will come in contact If you fit an exit delay, you won’t set off the alarm when leaving the house If your system doesn’t have an automatic cut-off, the noise will go on for hours If a burglar walks in front of a motion sensor, the alarm will turn on Vibration sensors will respond if the window foil is broken Tamper sensors will trigger the alarm if a burglar tries to force the box open A magnet on the moving part trips a switch if the door is opened The alarm stops after a set time if it has an automatic cut-off devise Task 8: - Integrated circuit (1f) Circuit supply (2d) Alternating bias (3h) Primary cell (4b) Zener diode (5e) Remote control (6i) Reed switch (7c) Surface wave (8k) Vibration sensor (9a) Reverse current (10g) Main diagram (11j) Task 9: Sensing device LDR Thermistor Microphone Used to detect Light Heat Sound When light falls on the LDR, its resistance decreases Using RV1 to adjust the sensitivity of the input Term Cut- off Fixed resistor increases energize Slow To cause Forward bias Opposite saturation Variable resistor decreases De-energize rapid To prevent Alternating bias The transistor in Fig protected from a large back EMF by a diode which is connected in reverse bias across the relay Task 10: The diagram shows a reed switch The reeds sealed in a glass envelope to protect them Because it helps to prevent corrosion of the contacts When a magnet is brought close to the reeds, they are magnetized, attract each other, and close When the magnet is removed, the reed open Task 11: The components are: switch, alarm bell or buzzer, battery, reed switch A 9V battery is connected to a set alarm switch and a set alarm switch is connected to an alarm bell An alarm bell is linked to a reed switch The circuit is open and nothing happens The alarm will ring Because when the magnetic insert in frame is brought close to the reed through open, the reeds create a closed circuit and operate the circuit