Telemetry systems
Telemetry is the remote control of various devices.
With regard to video surveillance systems, this primarily means the ability to control various rotary devices.
In general, telemetry devices allow remote control of many devices that are part of security systems.
As for video surveillance, the need for remote control arose almost immediately after rotary cameras appeared.
Initially, the control of PTZ cameras looked like this: a regular motor in a special casing or in a standard case with a special platform on which the TV camera was installed. The motor turned the camera both horizontally and vertically.
Control was via wires, and a separate pair of control cables was used for each command.
Additional cables were also required to control the operation of the lens so that the focal length could be changed remotely, and the necessary focus and sharpness adjustments could be made.
The next stage was the use of the technology of “mixing” some control commands into the video signal received from the camera.
The receiving device received video signals from the camera, and control commands came from it «on the contrary».
These control signals for the telemetry device must be filtered out, because they are essentially interference for video signals. This is a fairly complex and expensive algorithm to implement.
In addition, there are strict restrictions on the transmission range of control signals, directly related to the transmission range of the video signal.
This method is now used extremely rarely.
The development of technology and engineering has made it possible to switch to the widely used interface line control using various standard protocols.
Telemetry signals are transmitted via a separate line.
The distance is limited only by the communication protocol used. If, for example, it is RS-485, then at a distance of up to 1500 meters, it is possible to ensure stable communication with the telemetry receiver. And the video signal can be transmitted via a twisted pair.
In systems built on the basis of using fiber-optic communication lines, interface communication lines are not needed.
Both telemetry commands and the video signal are transmitted via fiber-optic lines, and the range of signal transmission is practically unlimited.
In order to transmit these signals, special devices for converting the control signal from the remote control are needed.
As a rule, the design of the remote control itself already includes the ability to connect a communication line, interface or fiber-optic. And for reception, there are two options.
A stationary pan/tilt device with a corresponding telemetry command receiver, which is installed separately from the camera, can be used.
The second option is to use the widely used high-speed dome cameras, which have a built-in interface for receiving control signals, i.e., they contain a camera with a lens and a pan/tilt device in a single housing, as well as a control command receiver.
Each option has its pros and cons.
Rotary devices, especially in outdoor design, are rather bulky structures made in accordance with the conditions of outdoor use: sealing, built-in heaters, appropriate mechanisms that operate reliably at low temperatures.
Devices used for indoor installation are more compact, but still had to be installed separately from the camera with a motor, which was not always convenient for installers and users.
High-speed dome cameras have replaced stationary PTZ devices. These cameras are usually made in the form of a cylinder.
Inside there are motors, a frameless camera with a powerful lens. These devices have virtually no restrictions on indoor installation, the installer can always find an installation option that matches the design of the room.
One of the disadvantages of stationary PTZ devices is that they operate at a constant speed.
Moreover, this speed is not high.
High-speed dome cameras do not have this disadvantage. Moreover, new algorithms for generating control signals have appeared.
Remotes with joysticks have appeared, which significantly increased the convenience of control.
The joystick gives an alternating signal, the camera decoder receives it and activates the actuator of the PTZ mechanism.
Depending on the angle of the joystick, a command for the corresponding speed of camera movement is instantly generated.
This algorithm is called proportional control.
Dome cameras also have an internal logic device that, depending on the selected viewing angle of the object being observed, automatically regulates the speed of camera rotation.
If the viewing angle is narrow and the camera captures a distant object, its movement speed is limited. And, conversely, with a wide viewing angle, the camera movement speed increases. There is some proportionality here too.
High-speed dome cameras have proven their advantages and have been appreciated by installers and consumers.
Demand creates supply, and developers responded to market expectations quite quickly. High-speed dome cameras in outdoor design appeared. True, not immediately.
At first, outdoor housings in the form of spheres or hemispheres were used. Inside the housings, in addition to the camera, fans and heaters were installed, and sealing was ensured.
The next, completely natural stage was the appearance of outdoor high-speed dome cameras. These were already finished devices, in a sealed design, with all the necessary built-in equipment to ensure operation in any climatic conditions.
The functionality of high-speed dome cameras is very wide.
For example, you can program all the points that the camera needs to «look at» from the remote control. There can be many such preset points.
Manufacturers of some products claim the ability to have tens or even hundreds of preset points programmed in advance. This is an attractive feature for customers, but, to be honest, in my experience I have never encountered facilities that require more than 30-40 preset points to ensure security.
High-speed dome cameras have high speed of operation according to presets. In patrol mode, the camera can make a full turn in literally a second.
The camera can receive signals from security or fire alarms included in the security system. Moreover, both directly and through control and monitoring devices. That is, the security alarm is triggered, and the camera immediately directs its lens to this point.
This is very convenient, for example, when organizing perimeter security. High-speed dome cameras have quickly taken their niche in the security market.
Moreover, their expansion continues. Almost every year, leading manufacturers offer new models.
Nevertheless, stationary outdoor rotary devices have generally retained their positions.
Especially when equipping facilities that require video surveillance equipment with certain degrees of protection, for example, explosion-proof or fire-proof.
At such facilities, dome cameras have to be placed in special casings, and any additional casing is a loss. Losses in sensitivity, in the quality of the resulting image.
The use of stationary rotary devices is also preferable at sites where it is not possible to provide normal illumination and, therefore, IR illumination is required to obtain a normal image.
You can place a regular monochrome camera with a powerful lens and an IR illuminator on the platform to ensure that the image is captured at the desired point and that IR illumination is provided at that point. After all, it is not always possible to illuminate the entire area, but the need to monitor the situation nevertheless arises.
Cameras with fixed pan/tilt devices can be easily combined in one system with dome cameras.
A few words about remote controls.
There are simple remote controls without proportional control. They are used when cameras operate only in automatic mode at pre-programmed points.
Remote controls are also divided by the number of cameras they control. There are remote controls that can control only one camera, they are connected to it directly. Multifunctional remote controls are built on the principle of controlling some central device.
Through this device, the remote control can control all cameras included in the system. With the help of such remote controls, you can easily organize additional workstations for managing the system. Remote controls can communicate with each other using the same interface with which they are connected to the cameras.
In conclusion, I would like to note that improving equipment and expanding its functionality is a process that is almost constant.
For example, until recently each manufacturer had its own exchange protocol, but now almost everyone produces cameras and remote controls with a universal protocol.
That is, you can select the exchange protocol you need using software.
This has significantly simplified the creation of universal video surveillance systems using devices and devices from different manufacturers, which allows you to solve any of the most complex problems.