**1. Camera Selection**
A camera is the core component of a TV monitoring system, and choosing the right one is crucial based on user requirements. In security monitoring systems, CCD cameras are typically used because they are smaller, lighter, have lower inertia, higher sensitivity, better image uniformity, greater impact resistance, and longer service life compared to vacuum tube cameras.
In practical projects, if the illumination of the monitored area is low and high image clarity is required, a black-and-white CCD camera should be selected. If color monitoring is needed, auxiliary lighting or a camera that automatically switches between color and black-and-white modes should be considered. These cameras switch to black-and-white when the illumination is insufficient for color capture.
After deciding whether to use a black-and-white or color camera, the next step is to consider the technical specifications. Key factors include:
**1.1 Resolution (Clarity)**
Resolution refers to the ability of the camera to capture fine details, measured in television lines (TVL). It depends on the number of pixels in the CCD chip, lens quality, and the camera’s bandwidth. Black-and-white cameras usually offer around 450 TVL, while color cameras generally provide more than 350 TVL. For color systems, a minimum of 270 TVL is acceptable according to GB/T16676-1996.
**1.2 Sensitivity**
Sensitivity is the minimum illumination required to produce a specified signal level. For example, a camera with a sensitivity of 0.04Lx/F1.2 means it can operate under very low light conditions. If the scene is too dark, the image may appear gray and unclear. To ensure good visibility, the camera's sensitivity should be about 1/10th of the target's surface illumination.
**1.3 Signal-to-Noise Ratio (SNR)**
SNR measures the ratio of the signal to noise. CCD cameras typically have an SNR between 45–55 dB, with 50 dB being common. This not only meets industry standards but also ensures clearer images in low-light conditions.
**1.4 Operating Temperature**
Most cameras operate within -10°C to +50°C. Special protection may be needed in extreme environments.
**1.5 Power Supply Voltage**
Foreign cameras usually support a wide voltage range (198–264V), while domestic models typically require 200–240V. Stable power supply is recommended for domestic systems.
**2. Lens Selection**
There are several types of lenses, and here we focus on how to choose them based on control needs.
**2.1 Manual Aperture Focus Lens**
Used for fixed targets with stable illumination. Cheaper and suitable for static scenes. Focal length can be calculated using the formula: f = A × L / H.
**2.2 Auto-Iris Prefocus Lens**
Adjusts aperture automatically based on light changes. Ideal for areas with large variations in illumination. However, it may not perform well in high contrast or uneven lighting.
**2.3 Auto-Iris Zoom Lens**
Includes two motors for zoom and focus adjustments. More expensive but offers greater flexibility.
**2.4 Electric Three-Way Lens**
Similar to auto-iris zoom lenses, but the aperture adjustment is remote-controlled. Commonly used today.
When selecting a lens, ensure the size matches the camera’s imaging plane and the interface is compatible. Using a larger lens with a smaller camera is possible, but the opposite may damage the CCD.
**3. PTZ, Housing, Bracket, and Decoder Selection**
**3.1 PTZ (Pan-Tilt-Zoom)**
PTZ allows the camera to move horizontally and vertically, expanding its field of view. When selecting a PTZ, ensure its load capacity is at least 1.2 times the actual weight. It should also have good self-locking performance and minimal noise during operation.
**3.2 Protective Cover**
Protective covers shield the camera from dust, rain, and temperature extremes. Outdoor covers are more complex, often including heating, cooling, and wipers. They must match the camera’s size.
**3.3 Bracket**
Brackets secure the camera. Choose one with sufficient load capacity to prevent deformation or instability.
**3.4 Control Decoder**
Control decoders allow remote control of PTZ and motorized lenses. They must be compatible with the system host to ensure proper communication.
**4. Spotlight Selection**
Most systems use spotlights for additional lighting. Black-and-white systems use high-pressure mercury lamps, while color systems use iodine-tungsten lamps. Infrared spotlights are ideal for night vision. Some use filters, while others use infrared LEDs. The latter is less likely to cause a "red storm" but has a shorter range. Note that infrared lights do not work with color cameras due to color filters.
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