Easy self-learning video surveillance system and weak basic knowledge

The monitoring system believes that most of the power personnel are familiar. The monitoring system is widely used in factories, shopping malls, office buildings, and homes. What are the components of the monitoring system? What is the role in the monitoring system?

Monitoring systems can generally be divided into analog monitoring systems and digital monitoring systems. Previously, they were basically analog monitoring systems. Nowadays, digital monitoring systems are basically popularized. Below we take the analog monitoring system as an example.

The full analog video surveillance system is mainly composed of a camera, a video matrix, a monitor, an analog video recorder, etc., and the devices are connected by a cable such as a video cable or a control cable. Since the system is transmitted in pure analog mode, the transmission distance of the video cable (a few fiber optics) can not be too far, so the system is mainly used for monitoring in a small range, such as building monitoring, etc., the monitoring image can only be viewed in the control center.

A complete video surveillance system can be divided into front-end, back-end and transmission.

First, the monitoring system front end

1. Classification and application of surveillance cameras.

(1): Ordinary gun machine.

This type of camera is the most common surveillance camera, which means that it is made in accordance with the basic structure of the surveillance camera. What is emphasized here is the difference between the lenses. Normal, long-distance and wide-angle lenses can be mounted on the gun. According to the standard of the lens, the 6.0mm lens is used as the dividing line. Generally, it is a wide-angle lens, and the angle is generally greater than 30 degrees. Larger than the larger ones, the distance is generally greater than 30 meters.

(2): Hemispherical camera.

This type of camera is similar to other standards except that the casing is different from the ordinary gun.

(3): Infrared camera.

This kind of camera is a camera that enhances the night vision effect by using an infrared light on the basis of an ordinary camera. Some ordinary camera CCDs have an infrared function. For this type of camera, it is sufficient to directly install an infrared lamp. Some cameras do not have the infrared function, which requires the lens. It must be an infrared lens plus an infrared lamp to meet the requirements.

(4): Integrated camera.

This type of camera is also very frequently used. It is a special type of surveillance camera that integrates the zoom lens (divided into manual and automatic) with the basic components of the camera.

It generally has two purposes: one is to use with the spherical head, also known as the "calibre" in the ball machine; the second is to make a large shell in the infrared light, known as infrared integration Camera.

2. Control the cloud platform.

(1) Yuntai.

The gimbal is a device that carries the camera to rotate in both horizontal and vertical directions. It has two AC motors built in, which are responsible for horizontal and vertical movement; the angle of horizontal rotation is generally 350 degrees, the angle of vertical rotation is generally 75 degrees, and horizontal The angle of vertical rotation can be adjusted by adjusting the limit switch.

(2) PTZ decoder.

The PTZ decoder is a front-end device that provides driving power for controllable devices such as pan/tilt and zoom lenses and communicates with control devices such as a matrix. Usually, the decoder can control the pan, tilt, focus, aperture, and control of the wiper wiper, camera power, lighting, etc., and also provide several auxiliary function switches. To meet the actual needs of different users.

3. Video server.

The video server is mainly responsible for monitoring the data information management and network client authorization of the network. The video server consists of one or more analog video inputs, an image digital processor, a compression chip, and a video digital processor with network connectivity. The video server digitizes the input analog video signal and transmits it to the network in a digital signal mode, thereby realizing remote real-time monitoring.

Second, the monitoring system backend

1. DVR.

DVR (Digital VideoRecorder, DVR) It is a computer system for image storage processing. It has long-term recording, recording, remote monitoring and control of images/voices. DVRs combine video recorders, picture splitters, and pan/tilt lenses. Five functions, such as control, alarm control, and network transmission, can replace the functions of a large number of devices in the analog monitoring system with one device, and gradually gain an advantage in price. DVR uses digital recording technology, which is far superior to analog monitoring equipment in image processing, image storage, retrieval, backup, network transmission, remote control, etc. DVR represents the development direction of TV monitoring system, which is currently on the market. TV monitoring system shou selected products.

2. Video matrix.

Switch video images from any of the input channels to any of the output channels. Generally speaking, an M×N matrix means that it can support both M-channel image input and N-way image output. What needs to be emphasized here is that you must do anything, that is, an arbitrary input and an arbitrary output.

3. Display device.

The display of the video capture card is on the computer monitor. The DVR has two interfaces, which can be connected to the TV and LCD. Splicing screen, monitor, monitor, etc.

4. Control equipment.

The control device is used to control the camera, multi-screen switching, recording, photographing, and the like. All controllable cameras can be controlled by pressing the right mouse button on the open window screen, or by selecting the button on the right. Specifically, there are light switch, lens zooming far, zooming near focus, wiper switch, turning on/off two-way voice intercom, direction control, etc.

Third, the transmission end

1, optical fiber video cable.

(1) Multimode fiber.

Multi Mode Fiber: The center glass core is thicker (50 or 62.5 μm) and can transmit multiple modes of light. However, the dispersion between the modes is large, which limits the frequency at which digital signals are transmitted, and is more severe as the distance increases. Therefore, the distance traveled by multimode fiber is relatively close, usually only a few kilometers.

(2) Single mode fiber.

Single Mode Fiber: The center glass core is very thin (the core diameter is generally 9 or 10 μm) and can only transmit one mode of light. Therefore, the dispersion between the modes is small, suitable for remote communication, and the stability is good. The transmission distance of single-mode optical cable is longer, the theoretical can reach 120 kilometers (mainly looking at equipment, most of the current photoelectric conversion equipment is only 120 kilometers or less), and the transmission distance of multi-mode optical cable is only 2 kilometers.

2, optical transceiver.

(1) Working principle of optical transceiver

The optical transceiver is a device for converting optical signals and electrical signals to each other, and does not perform any compression on the transmitted signals. Its main function is to realize electro-optical and optical-electrical conversion.

(2) The typical physical interface of the optical transceiver is as follows:

BNC interface: BNC interface refers to coaxial cable interface, BNC interface is used for 75 ohm coaxial cable connection, providing two channels of receiving (RX) and transmitting (TX), which is used for connection of unbalanced signals. Fiber interface

Fiber Interface: A physical interface used to connect fiber cables. There are usually several types such as SC, ST, and FC.

RS-485 communication interface: RS-485 adopts balanced transmission and differential reception to realize communication: the transmitting end converts the TTL level signal of the serial port into differential signal A, B two-way output, which will be transmitted at the receiving end after cable transmission. The differential signal is restored to a TTL level signal. Since the transmission line usually uses twisted pair and differential transmission, it is extremely resistant to common mode interference. The bus transceiver has high sensitivity and can detect voltages as low as 200mV. Therefore, the transmission signal can be recovered beyond the kilometer. The maximum communication distance of RS-485 is about 1219M, and the maximum transmission rate is 10Mb/S. The transmission rate is inversely proportional to the transmission distance. At the transmission rate of 100Kb/S, the maximum communication distance can be achieved.

3. Optical cable terminal box.

The optical cable terminal box is mainly used for fixing the optical cable terminal, welding the optical cable and the pigtail, and accommodating and protecting the residual fiber. The terminal box is the place where the end of the optical cable is connected, and then accesses the optical switch through the optical jumper. Therefore, the terminal box is usually mounted on a rack and can accommodate a large number of fiber optic cable ends.