बिदेसमा काम गर्ने नेपाली चेलीको रुममा थाहै नदिई मालिकले राख्यो सिसि क्यामरा…चेतनाको लागि सक्दो सेयर गर्नुहोला
CCTV (Closed Circuit TV) uses one or more video cameras to transmit video and sometimes audio images to a monitor, set of monitors, or video recorder. The difference between CCTV and standard TV is that standard TV openly broadcasts signals to the public. CCTV is not openly transmitted to the public. CCTV uses either wireless or wired transmission to send the broadcast from the video cameras to the monitor(s) or recording device. Most CCTV systems are used for surveillance, which can include security monitoring, spying, or safety monitoring.
CCTV systems have become extremely popular over the last few decades as the technology has improved and become more affordable. The majority of CCTV cameras in use today are usually for surveillance and security purposes. CCTV systems can be found in almost every bank, casino, mall, and large department store. In fact, CCTV systems have become so affordable, most smaller mom and pop stores also have CCTV systems in them for security purposes.
Types of CCTV Cameras
There are many types of CCTV cameras. They can be categorized by the types of images they are able to capture, the amount of frames they can take per minute, the type of connection to the monitor or video recording device, whether they are able to move position, and special functions they can provide.
Types of Images: CCTV cameras generally take both black and white or color video images. In addition, many CCTV cameras even have night vision capabilities that allow a CCTV camera to view and record low light images using special technology.
Frames per Second: Frames per second is the amount of full frames that a video camera captures and sends to a recording device or monitor per second. While most CCTV camera systems easily capture 30 or more frames per second (30 fps is considered real time), the amount of video tape or digital storage would be enormous to record every moment of everyday. For most stores, speeds of 1 to 6 frames per second are more than enough to catch and record a perpetrator committing a crime.
Pan Tilt Zoom (PTZ) Cameras: These types of CCTV cameras allow a person controlling the surveillance of an area to move the camera remotely, usually with an RF or wired controller. Most movable cameras allow the person monitoring it to move the camera from right to left (pan), up and down (tilt), and from a tight angle to a wide angle (close up zoom).
Cameras with Special Accessories: Certain CCTV cameras have special functions that are made for specialty uses. For instance, there are extremely small surveillance cameras that are used for spying (Nanny Cams), night viewing, are vandal resistant, and that are specifically made for indoor or outdoor uses.
Wired Vs. Wireless Connection
There are two main types of connections for CCTV cameras: a fixed cable or a wireless connection.
Fixed Cable Connection
Fixed cable connection means that the camera is physically connected to the monitor or recording device via a cable. Coaxial cables that are similar to normal home TV cables are usually used. Lengths come in 25, 35, 50, 100, or 500 feet. As the distance increases, signal quality decreases. For distances longer than 100 or 200 feet, purchase higher quality coaxial cables such as RG59 coaxial cable for distances up to 600 feet and for distances more than 600 feet, but less than 2,000 feet, purchase CAT5 cable.
Most wireless CCTV cameras use the 2.4 Gigahertz frequencies to transmit their video images to a monitor or DVR (digital video recorder). Usually, frequencies can be slightly changed to have more than one group of cameras in a specific space. Wireless CCTV cameras that use this frequency can easily transmit through most walls and obstacles. However, each individual location will have its own operating limits. Expect most wireless CCTV cameras to send data to a range of about 200 feet. However, many will more likely work well when transmitting less than 150 feet. A clear line of sight transmission will always work best.
Obviously a wireless connection allows greater freedom to place CCTV cameras almost anywhere. While wireless CCTV cameras transmit their video images to a digital video recorder or monitor, many of these types of cameras must be plugged into an electrical outlet. There are, however, some CCTV cameras that are battery operated.
Tape vs. Digital Video Recorders
There are two main ways to record video images that CCTV cameras capture. They are analog tape and digital video recorders. Most analog video recorders use VCR tapes or standard VCRs to record the images or special security time-lapse VCRs to record images for a longer period of time.
VCR Tape Recorder
A tape recorder such as a security-time lapse VCR can record CCTV camera images in either black and white or color for 2,4, 6, 8, all the way up to 960 hours, which is 40 complete days. The determining factor is how many frames per second users intend to record and how many cameras are hooked up to the VCR for recording. For instance, if a user records 30 frames per second (real time video), he/she will only be able to get a few hours of video captured on the recorder. If users record one frame per second or less, they can record for dozens of hours before the video tape is full. VCRs are very practical, very reliable, and extremely affordable. Expect to pay only a few hundred dollars for a security VCR.
Digital Video Recorders
There are two types of DVRs (Digital Video Recorders). They are either stand alone devices or hard drives that are connected to a computer system. DVRs work similar to VCRs, but the images they capture from the CCTV camera is digital. The amount of digital images captured on a DVR is determined by a few factors including the frames per second recorded, the amount of cameras hooked up to the DVR device, the resolution that the DVR saves the images at, and the video compression used (e.g. MPEG4). For a common set up, where 4 cameras are shooting at 30 fps and an image resolution of 320 X 240 is being used, each camera only records when motion is on, and MPEG4 compression is used, users should be able fill up a 20 to 25 GB hard drive in about 80 hours.