PTZ dome cameras: selection criteria.
When organizing a video surveillance system, many are faced with the problem of limitations in the possibility of installing cameras. In such cases, the choice is made in favor of PTZ dome cameras, the modern configuration of which appeared relatively recently, only in the mid-90s of the 20th century. It was then that it was possible to produce an acceptable camera rotation speed at that time.
Every year, PTZ dome cameras are improved and acquire new functions for more advanced video surveillance systems and for newly emerging tasks. When choosing such equipment, like any other, you need to be guided by a number of criteria.
First of all, you need to pay attention to compatibility with the equipment included in the project or already available. This means that the control protocol must match in the connecting devices. When designing a new system, it is recommended to choose equipment that uses widely used protocols, for example, from the Pelco family (Pelco P, Pelco D). This will help to avoid problems in case of expansion of the video surveillance system or replacement of equipment.
Depending on where the equipment will be installed, you need to choose an external (for the street) or internal (for the premises) dome camera. Outdoor cameras have a housing with heating that protects against external influences. You can also choose a vandal-proof camera if necessary.
Robotic cameras are available in two types: with medium-speed (9 to 36 g/s) and high-speed (120 to 400 g/s) pan/tilt devices. If your project involves using a large number of camera presets and includes pan/tilt on alarm, we recommend the high-speed type.
When choosing a PTZ dome camera, pay attention to the horizontal resolution, which determines the quality of shooting, which is expressed in TV lines (TVL). On average, a video camera provides a resolution of 380-570 TVL. Also, a determining factor in the quality of shooting is the aperture ratio of the camera lens. The smaller it is, the higher the image quality and, accordingly, the higher the value in TVL.
The video surveillance market is widely represented by dome cameras with a varifocal lens, thanks to which you can examine the required object by zooming in or out. The zoom factor of a video camera lens consists of optical and digital zoom, the value of which is specified by the manufacturer in the technical description. Digital zoom obtained by electronic processing degrades the image quality, so this parameter is of lesser importance from a practical point of view. Thus, a significant parameter of the lens is the optical zoom factor, which is usually from x10 to x36.
High-speed robotic cameras rotate quite quickly, up to 400 gr./s. When the rotary device stops or starts abruptly, the inertia of the movement causes the camera to shake, and the image on the monitor becomes blurry. To prevent this, high-quality equipment is equipped with a special mechanism for smooth but fast acceleration and braking. In some cases, the determining factor when choosing a camera may be the minimum rotation speed. At maximum magnification, the rotation speed is multiplied by the magnification, and video surveillance of a remote object becomes almost impossible.
The auto-flip function is convenient for manual control from the remote control, as it allows you to rotate the camera vertically by 180 degrees. When the rotation angle reaches 90 degrees (the camera looks down), the video module automatically flips 180 degrees so that the image on the screen does not flip.
Not all PTZ dome cameras can rotate in a 360 degree range. Some models have a rotation angle limitation, usually within 5–30 degrees, i.e. the camera has a dead zone.
Modern manufacturers offer robotic cameras with 64, 128, and 256 presets. This number usually exceeds real needs. The accuracy of camera positioning in the preset position is more important. High-quality cameras are positioned with an error of no more than 0.1 degrees from the specified preset.
Modern robotic cameras also have scanning functions; they have a menu displayed on the screen.
The most advanced robotic cameras additionally have:
alarm inputs for positioning based on alarm signals;
tours;
group tours;
target tracking (auto-tracking);
masking of surveillance zones (also depends on the model of the video module used).
All these features expand the freedom of using cameras to solve various problems.