How to Select a Video Optical Terminal
To determine whether the performance and specifications of a [video optical terminal](
1 Technical Specification Considerations
Multi-channel digital video optical terminals can offer multiple functions, each with corresponding technical specification requirements, such as video specifications, audio specifications, asynchronous data specifications, and Ethernet specifications. For specific technical specifications, manufacturers should be required to provide third-party test certifications. Qualified contractors should, before selecting equipment, conduct re-testing based on the specifications provided by the manufacturer to verify the actual technical performance of the equipment and the credibility of the manufacturer. Here, two video specifications are briefly explained from an engineering perspective.
1.1 Sufficient 3dB Video Bandwidth
Video bandwidth is a frequently discussed topic. Insufficient video bandwidth results in unclear details in the surveillance image, lower horizontal resolution, and in severe cases, color distortion or loss. Due to the importance of video bandwidth to image quality, some unscrupulous manufacturers deliberately exaggerate the video bandwidth of their products to deceive customers. A manufacturer's multi-channel digital video optical terminal claims a video bandwidth of 8M, yet its publicly announced video sampling frequency is 12.5M. According to the Nyquist sampling theorem, to faithfully reproduce a signal, the sampling frequency must be at least twice the signal frequency. By this calculation, the theoretical video bandwidth of this manufacturer's optical terminal cannot possibly exceed 6.25M. Clearly, this is an exaggerated claim intended to deceive customers, and manufacturers lacking such business integrity should not be considered for selection. However, not all customers can accurately identify a manufacturer's deception. For general contractors and users, observing image details can provide a rough assessment of the device's video bandwidth.
1.2 Sufficiently Wide APL Range
APL, or Average Picture Level, is a method of measuring the average video luminance level and expressing it as a percentage of the maximum white level. When APL is low, the image is dark; when APL is high, the image is bright. Many contractors pay little attention to or are unfamiliar with this specification. However, if we mention a common issue encountered in some projects—where after video signals are transmitted through an optical terminal, when a large area of white appears in the picture (e.g., when a camera is exposed to strong light), the image on the monitor shakes horizontally—engineering personnel will certainly recognize this. This occurs because the APL range of video optical terminals produced by some manufacturers is too narrow. When a large area of white appears in the image signal, the DC component in each line of the image signal increases, causing the APL to rise, which in turn reduces or loses the amplitude of the horizontal sync signal, preventing the monitor from detecting horizontal sync and resulting in image shaking.
2 Reliability Considerations
As a security surveillance project, equipment reliability should be the primary consideration. Equipment reliability must be considered by the manufacturer during product design. However, some manufacturers may be unwilling or lack the knowledge to address this. Here, the following issues are briefly discussed from an engineering perspective.
2.1 Convenient Power Supply with Wide Input Voltage Range
Power supply is the fundamental guarantee for the normal operation of digital [video optical terminals](
2.2 Strong Temperature and Humidity Adaptability
In some security surveillance projects, optical terminals operate under harsh conditions, with wide temperature variations, high air humidity, and occasional power outages at some outdoor monitoring points. These conditions require multi-channel digital video optical terminals to have greater consideration for temperature range and allowable humidity to ensure stable operation in harsh environments and meet the needs of security surveillance.
In summary, users can evaluate equipment based on its technical specifications, reliability, and practicality when making a selection. By making more comparisons using the methods described above and developing a solution based on the actual project conditions, users will ultimately find the right multi-channel video optical terminal.