1 Camera selection <br> <br> camera is the core equipment of TV monitoring system, according to user requirements, a reasonable choice is very important. The security monitoring TV monitoring system generally adopts a CCD camera, because it has a smaller size and lighter weight than the vacuum tube camera; the inertia is small; the sensitivity is high; the image uniformity is good; the impact resistance is good; and the service life is long. In actual projects, if the monitoring target illumination is not high and the user has high requirements for the monitoring image clarity, a black and white CCD camera should be selected; if the user requires color monitoring, the auxiliary lighting device should be considered, or the color black and white automatic conversion should be selected. The CCD camera, which automatically switches to black-and-white photography when the monitoring target illuminance does not meet the color camera requirements.
After determining whether to use a black-and-white camera or a color camera, the issue to be considered is the technical specifications of the camera. The main considerations are as follows.
1.1 resolution (clarity)
The ability to indicate the details of the camera's resolution of the image, usually represented by a television line (TVL). It depends on the number of pixels in the CCD chip, the resolution of the lens, and the bandwidth of the camera system.
The horizontal resolution of black-and-white camera is generally about 450 TVL. Considering construction and other factors, the final resolution of the system can meet the 380TVL specified in China's industry standard GB/T16676-1996.
Color camera horizontal resolution generally choose to be greater than 350TVL, because the human eye is difficult to distinguish finer colors, so that the choice can also meet the color monitoring system 270TVL requirements in GB/T16676-1996.
1.2 Sensitivity Under the condition that the lens aperture size is fixed, the minimum target surface illumination required to obtain the specified signal level is obtained. For example: When using the F1.2 lens, when the surface brightness of the subject is 0.04Lx, the amplitude of the camera output signal is 350mV, which is 50% of the maximum amplitude, then the sensitivity of this camera is said to be 0.04Lx/F1.2. . If the illuminance of the subject is low, the monitor screen will be a gray image that is difficult to distinguish. According to experience, the sensitivity of the selected camera is usually 1/10 of the illuminance of the subject's surface.
1.3 SNR is the ratio of signal voltage to noise voltage. The SNR of the CCD camera is typically between 45 and 55 dB. About 50dB is selected in the general TV monitoring system. This not only meets the requirements of the industry standard that the signal-to-noise ratio of the system is not less than 38dB, but more importantly, when the ambient illumination is insufficient, the higher the signal to noise ratio is, the more the camera image becomes. Clear.
1.4 Operating temperature -10 ~ +50 °C is the temperature index of most camera manufacturers. Depending on the area of ​​use temperature changes plus protection or special protection.
1.5 Power supply voltage Foreign camera AC voltage adaption range is generally 198 ~ 264V Anti-power supply voltage change ability is strong; domestic camera AC voltage adaptation range is generally 200 ~ 240V, anti-power supply voltage change ability is weak, generally used in the system to be stable Press the power supply.
2 shot selection <br> <br> lens variety, there are several classifications, we only talk about how to choose the camera lens from the control.
2.1 Manual Aperture Focus Lens This type of lens is used to monitor a fixed target and has a small change in illuminance. This lens is cheaper. The required focal length can be estimated by the following formula.
f=A·L/H
In the formula: f - lens focal length A - camera imaging surface height L - the subject to the lens distance H - the higher the subject focal length, the smaller the angle of view, the narrower the monitoring range; the smaller the focal length, the more the angle of view Large; the wider the monitoring range.
2.2 Automatic Aperture Prefocus Lens When the light flux entering the lens changes, the charge generated on the camera CCD imaging surface changes accordingly, causing the video signal level to change, producing a control signal that drives the micro motor in the lens forward or reverse Turn to adjust the aperture size. Select this lens when the illuminance of the field of view changes by more than 100 times. However, it should be noted that if the illuminance of the field of vision is not uniform, especially when the contrast between the monitoring target and the background light is large, the effect of using such a lens is not satisfactory.
2.3 Automatic Aperture Power Zoom Lens This lens has two micro motors compared to the auto iris fixed prime lens. One of the motors meshes with the zoom ring of the lens. When controlled rotation, the focal length of the lens can be changed; the other motor and the lens The focus ring engages and the lens finishes focusing when controlled. Due to the addition of two miniature motors, this lens is more expensive.
2.4 Electric three-variable lens Compared with the auto-iris zoom lens, only the adjustment of the aperture is changed from the automatic control mode to the remote control. It also contains three miniature motors connected to the controller via a set of 6-wire control wires. At present, this type of lens is used more often.
When selecting the lens, in addition to the lens that selects different control modes according to different occasions and different requirements, consider the following issues.
(1) The lens size must be the same as the camera imaging plane size. For example: 1/3" camera to choose 1/3" lens. When it is difficult to agree, a large-sized lens can be used with a small-size camera; otherwise, it cannot.
(2) The lens interface and the camera interface must be the same. If not, add a connection ring. For example, when a C-type lens is mounted on a CS-type camera, a connection ring must be added to the C-type lens. If the connection ring is not added, the protection glass of the CCD image plane may be damaged, causing damage to the CCD camera.
3 PTZ, protective cover, bracket, control decoder selection 3.1 PTZ PTZ can be simply understood as the base of the installed camera, but this base can be full (horizontal and vertical directions) or (horizontal) rotation. Therefore, the use of the head to expand the vision of the camera. In the television monitoring system, the pan-tilt is required for places that need to be monitored (such as a lobby). When choosing a PTZ, please note the following points.
(1) The load capacity of the selected PTZ is greater than 1.2 times the actual load. That is to say, the sum of the weights of all the devices on the platform is less than the load capacity of the platform. If the pan/tilt is fully loaded or overloaded, it can work without strong work, but the inertia at startup is large, especially when vertical rotation is more difficult. Greatly affected the effect of the tour.
(2) When the pan/tilt rotation stops, it should have better self-locking performance, and the return angle during braking should be less than 1.
(3) When the indoor pan/tilt is at the maximum load, the noise should be less than 50dB.
3.2 Protective cover The device used to protect the camera is called a protective cover. There are indoor and outdoor points, the main role of indoor protective cover is dust; and outdoor protective cover in addition to dust, the more important role is to protect the camera in a more hostile natural environment (such as rain, snow, low temperature, high temperature, etc.) jobs. This requires not only a strict sealing structure but also a wiper, shower device, etc., as well as a function of heating and cooling. This determined that the price of the outdoor protective cover is much higher than the indoor protective cover. When selecting the protective cover, it should also be noted that the nominal size of the protective cover is the same as the nominal size of the camera, that is, 1/3′′ camera uses 1/3′′ protective cover. If it is difficult to be consistent, a large size protective cover can be used with a small size camera;
3.3 Brackets Used to secure the components of the camera, wall mounted, hoisting and other types. The selection of the bracket is relatively simple, as long as its load capacity is greater than the total weight of the equipment installed on it, otherwise it is easy to cause the bracket to be deformed, and the pan-tilt rotates to generate jitter, which affects the quality of the monitoring image.
3.4 Control Decoders In TV surveillance systems with pan/tilt heads, motorized lenses, and outdoor housings, control decoders must be provided. In this way, controlling the corresponding keys of the keyboard in the control room can complete the control of the front-end equipment's various actions and functions. The control decoder must be of the same brand as the system host. This is because the communication protocols and encoding methods of the control decoders produced by different manufacturers and the system host are generally not the same unless a control decoder specifies the device and a brand in the specification. The host is compatible, otherwise it must not be used.
4 spotlights choice <br> <br> the vast majority of television cameras monitoring systems are equipped with rotating spotlights to assist in lighting, its biggest advantage is flexible, convenient, and inexpensive. Black-and-white television monitoring systems should be equipped with high-pressure mercury lamps; color television monitoring systems should be equipped with iodine-tungsten lamps. Infrared spotlights are used when surveillance at night is required. One type of infrared spotlight is to add a filter in front of an ordinary light, and the other is to consist of an array of infrared light emitting diodes. The former consumes a lot of energy, and often produces a "red storm" (due to the filter is not clean, a small amount of red light is seen by the human eye); the latter rarely produces a "red storm", but the irradiation distance is closer. In addition, it should be reminded that infrared spotlights do not work for color television monitoring systems because infrared light is filtered out by color filters in color cameras.
After determining whether to use a black-and-white camera or a color camera, the issue to be considered is the technical specifications of the camera. The main considerations are as follows.
1.1 resolution (clarity)
The ability to indicate the details of the camera's resolution of the image, usually represented by a television line (TVL). It depends on the number of pixels in the CCD chip, the resolution of the lens, and the bandwidth of the camera system.
The horizontal resolution of black-and-white camera is generally about 450 TVL. Considering construction and other factors, the final resolution of the system can meet the 380TVL specified in China's industry standard GB/T16676-1996.
Color camera horizontal resolution generally choose to be greater than 350TVL, because the human eye is difficult to distinguish finer colors, so that the choice can also meet the color monitoring system 270TVL requirements in GB/T16676-1996.
1.2 Sensitivity Under the condition that the lens aperture size is fixed, the minimum target surface illumination required to obtain the specified signal level is obtained. For example: When using the F1.2 lens, when the surface brightness of the subject is 0.04Lx, the amplitude of the camera output signal is 350mV, which is 50% of the maximum amplitude, then the sensitivity of this camera is said to be 0.04Lx/F1.2. . If the illuminance of the subject is low, the monitor screen will be a gray image that is difficult to distinguish. According to experience, the sensitivity of the selected camera is usually 1/10 of the illuminance of the subject's surface.
1.3 SNR is the ratio of signal voltage to noise voltage. The SNR of the CCD camera is typically between 45 and 55 dB. About 50dB is selected in the general TV monitoring system. This not only meets the requirements of the industry standard that the signal-to-noise ratio of the system is not less than 38dB, but more importantly, when the ambient illumination is insufficient, the higher the signal to noise ratio is, the more the camera image becomes. Clear.
1.4 Operating temperature -10 ~ +50 °C is the temperature index of most camera manufacturers. Depending on the area of ​​use temperature changes plus protection or special protection.
1.5 Power supply voltage Foreign camera AC voltage adaption range is generally 198 ~ 264V Anti-power supply voltage change ability is strong; domestic camera AC voltage adaptation range is generally 200 ~ 240V, anti-power supply voltage change ability is weak, generally used in the system to be stable Press the power supply.
2 shot selection <br> <br> lens variety, there are several classifications, we only talk about how to choose the camera lens from the control.
2.1 Manual Aperture Focus Lens This type of lens is used to monitor a fixed target and has a small change in illuminance. This lens is cheaper. The required focal length can be estimated by the following formula.
f=A·L/H
In the formula: f - lens focal length A - camera imaging surface height L - the subject to the lens distance H - the higher the subject focal length, the smaller the angle of view, the narrower the monitoring range; the smaller the focal length, the more the angle of view Large; the wider the monitoring range.
2.2 Automatic Aperture Prefocus Lens When the light flux entering the lens changes, the charge generated on the camera CCD imaging surface changes accordingly, causing the video signal level to change, producing a control signal that drives the micro motor in the lens forward or reverse Turn to adjust the aperture size. Select this lens when the illuminance of the field of view changes by more than 100 times. However, it should be noted that if the illuminance of the field of vision is not uniform, especially when the contrast between the monitoring target and the background light is large, the effect of using such a lens is not satisfactory.
2.3 Automatic Aperture Power Zoom Lens This lens has two micro motors compared to the auto iris fixed prime lens. One of the motors meshes with the zoom ring of the lens. When controlled rotation, the focal length of the lens can be changed; the other motor and the lens The focus ring engages and the lens finishes focusing when controlled. Due to the addition of two miniature motors, this lens is more expensive.
2.4 Electric three-variable lens Compared with the auto-iris zoom lens, only the adjustment of the aperture is changed from the automatic control mode to the remote control. It also contains three miniature motors connected to the controller via a set of 6-wire control wires. At present, this type of lens is used more often.
When selecting the lens, in addition to the lens that selects different control modes according to different occasions and different requirements, consider the following issues.
(1) The lens size must be the same as the camera imaging plane size. For example: 1/3" camera to choose 1/3" lens. When it is difficult to agree, a large-sized lens can be used with a small-size camera; otherwise, it cannot.
(2) The lens interface and the camera interface must be the same. If not, add a connection ring. For example, when a C-type lens is mounted on a CS-type camera, a connection ring must be added to the C-type lens. If the connection ring is not added, the protection glass of the CCD image plane may be damaged, causing damage to the CCD camera.
3 PTZ, protective cover, bracket, control decoder selection 3.1 PTZ PTZ can be simply understood as the base of the installed camera, but this base can be full (horizontal and vertical directions) or (horizontal) rotation. Therefore, the use of the head to expand the vision of the camera. In the television monitoring system, the pan-tilt is required for places that need to be monitored (such as a lobby). When choosing a PTZ, please note the following points.
(1) The load capacity of the selected PTZ is greater than 1.2 times the actual load. That is to say, the sum of the weights of all the devices on the platform is less than the load capacity of the platform. If the pan/tilt is fully loaded or overloaded, it can work without strong work, but the inertia at startup is large, especially when vertical rotation is more difficult. Greatly affected the effect of the tour.
(2) When the pan/tilt rotation stops, it should have better self-locking performance, and the return angle during braking should be less than 1.
(3) When the indoor pan/tilt is at the maximum load, the noise should be less than 50dB.
3.2 Protective cover The device used to protect the camera is called a protective cover. There are indoor and outdoor points, the main role of indoor protective cover is dust; and outdoor protective cover in addition to dust, the more important role is to protect the camera in a more hostile natural environment (such as rain, snow, low temperature, high temperature, etc.) jobs. This requires not only a strict sealing structure but also a wiper, shower device, etc., as well as a function of heating and cooling. This determined that the price of the outdoor protective cover is much higher than the indoor protective cover. When selecting the protective cover, it should also be noted that the nominal size of the protective cover is the same as the nominal size of the camera, that is, 1/3′′ camera uses 1/3′′ protective cover. If it is difficult to be consistent, a large size protective cover can be used with a small size camera;
3.3 Brackets Used to secure the components of the camera, wall mounted, hoisting and other types. The selection of the bracket is relatively simple, as long as its load capacity is greater than the total weight of the equipment installed on it, otherwise it is easy to cause the bracket to be deformed, and the pan-tilt rotates to generate jitter, which affects the quality of the monitoring image.
3.4 Control Decoders In TV surveillance systems with pan/tilt heads, motorized lenses, and outdoor housings, control decoders must be provided. In this way, controlling the corresponding keys of the keyboard in the control room can complete the control of the front-end equipment's various actions and functions. The control decoder must be of the same brand as the system host. This is because the communication protocols and encoding methods of the control decoders produced by different manufacturers and the system host are generally not the same unless a control decoder specifies the device and a brand in the specification. The host is compatible, otherwise it must not be used.
4 spotlights choice <br> <br> the vast majority of television cameras monitoring systems are equipped with rotating spotlights to assist in lighting, its biggest advantage is flexible, convenient, and inexpensive. Black-and-white television monitoring systems should be equipped with high-pressure mercury lamps; color television monitoring systems should be equipped with iodine-tungsten lamps. Infrared spotlights are used when surveillance at night is required. One type of infrared spotlight is to add a filter in front of an ordinary light, and the other is to consist of an array of infrared light emitting diodes. The former consumes a lot of energy, and often produces a "red storm" (due to the filter is not clean, a small amount of red light is seen by the human eye); the latter rarely produces a "red storm", but the irradiation distance is closer. In addition, it should be reminded that infrared spotlights do not work for color television monitoring systems because infrared light is filtered out by color filters in color cameras.
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