Sirens An alarm means an instrument that issues an alarm signal. Used to signal the issuance of forecasts, alarms and de-alerting. Air defense warning refers to the alarm system set up during the war to prevent enemy air strikes. Is an important part of the city air defense project, is in the city by the air raid threatened to remind people to defend the air defense
According to the different principles of voice are:
1, electric alarm: the electrical energy into mechanical energy, and then converted into acoustic energy by the mechanical energy.
2, electro-acoustic alarm: the audio small signal amplified by low-frequency power into sound energy. That is, electrons can be converted into acoustic energy.
3, pneumatic alarm: the electrical energy into mechanical energy, and then converted into mechanical energy by the mechanical energy. From gas to energy.
According to the different conditions set:
1, fixed alarm: installed in a fixed location to use the alarm.
2, mobile alarm; installed in motor vehicles or take other forms of use in the movement of the alarm.
Sirens The infrared transmitter drives the infrared light emitting diode to emit a noisy modulated infrared beam. At a distance from the infrared transmitter, place an infrared receiver with the alignment. It receives the infrared radiation energy found by the transmitter through the phototransistor and converts it into an electrical signal via photoelectric turn abstraction. This electrical signal is sent to the alarm controller circuit via appropriate processing.
The optical system, which is placed at the beginning and the end, is generally used as an optical lens, which serves to focus the infrared beam into a finer parallel beam so that the energy of the infrared light can be centrally transmitted. Infrared light in the human eye can not see the spectral range, some people through this invisible blockade line, must all or part of the block infrared light beam. The intensity of the electrical signal output at the receiving end will be changed so that the alarm controller initiates the alarm signal. Infrared radio alarm is characterized by high reliability detection
Widely used in the perimeter prevention, urban security, villa walls, community perimeter, factory warehouses, companies, schools, families, warehouses, resources, oil and other fields.
The transmitter and the receiver are located in different positions divided into the opposite type of installation and reflective installation, reflective installation of the receiver is not directly receive the infrared light emitted by the transmitter, but received by the mirror or the appropriate reflection Objects (such as lime wall, door surface smooth paint layer) reflected back to the infrared beam. The alarm signal is issued when the position and direction of the reflecting surface are changed or one of the infrared emitting beam and the reflected light beam is blocked so that the receiver can not receive the infrared reflected light beam.
Sirens Forbidden City on the inside and outside the stone steps on the railings, if you carefully observe the top of the column will have a spherical carving, all were flower-shaped, and near the door outside a few at the top of all have pierced holes, This kind of thing is called "stone do not pull", also known as "stone sea Xiao", is the ancient alarm for the alarm device. Whenever the invasion of foreign enemies, war alarm or fire, the cavalry will use the mouth blowing stone ball hole, stone ball will be issued "woo, woo" similar to the sound of the sound of snails, that vigorous and clear voice will spread throughout the Forbidden City The When this alarm is created, how to blow the law, know very few people, only the flag was the pro-army or guardians, as well as the inner court guards eunuchs.