Recommendations for installing video surveillance systems.
Recommendations for installing video surveillance systems
Let's start with the camera's video source!
Its output stage is designed to work with a cable with a wave resistance of 75 Ohm, and has a signal amplitude of 1V. This rule applies to both mini cameras and large PTZ cameras with a controlled interface. That is, you need to clearly understand that the signal level and its noise immunity do not depend on the size and specifics of the camera.
A common mistake of designers: — I'll buy an all-weather PTZ camera with 1.5 km control, run all the wires, and get a perfect picture at the other end!
NO! He won't get anything except a blown output stage of the camera! Because at such distances there is practically nothing left from the video signal. Moreover, such a potential or interference can accumulate on the RK-75 that no grounding or protection will save either the camera or the recording device.
There are, of course, arm-thick feeders made of pure copper coated with silver. If you lay them in a shielded sleeve at a depth of half a meter, you may get a good image. But these are extreme and very expensive ways of building a system.
So let's get back to reality. As you've already guessed, and many have understood from their own experience, the length of the signal line is on average 100 m. In a good noise-resistant environment and using a good cable, you can build a 200 m line without consequences. But further increase threatens trouble one way or another. We pulled at 300 m, as honored installers who have been working in this field for many days will say, and everything works. But it's worth connecting an oscilloscope to the BNC connector and seeing what's happening with the signal shape (and in difficult atmospheric conditions, with the interference level), then everything immediately falls into place. In such bad projects, the survivability reserve of the camera output stage, as well as the absence of any atmospheric cataclysms near the object, help out.
Power lines, which are present in the neighborhood one way or another, create a big problem for receiving a high-quality signal. On the street, this is lighting, power lines, etc., indoors, mainly power plant equipment, fluorescent lamps, office equipment. Failure to comply with safety requirements and the absence of technically correct solutions are common. Therefore, it is not surprising that the same camera fails on Mondays at 8 am. The culprit may be a powerful compressor, the three-phase power supply of which runs close to your RK. And with low pressure in the air conditioning system, especially on Monday, when everyone comes to their stuffy offices, the starting current of tens of amperes along the three-phase line induces a destructive impulse for low-current circuits. There are a great many such mysterious examples, and it can be quite difficult to understand the reasons.
Considering the above, we can conclude: signal lines should use the highest quality cable with minimal copper resistance, a good screen, and a design that eliminates the accumulation or penetration of static charges and external interference. It is advisable to use copper conductors of the central core and braid. The dielectric material should be selected depending on the operating conditions, since cases when the line works perfectly indoors and does not work at all outdoors are quite common. The longer the line and the more intense the electromagnetic environment, the more consciously you need to approach the selection of signal lines.
The second very important nuance is the power supply of the video surveillance system. Here, perhaps, the greatest number of mistakes are made.
The first thing I would like to highlight from the general sheaf of problems:
GENTLEMEN, stop using adapters and similar power supplies! It is clear that when looking at the estimate for a video surveillance system, the cost of these adapters promotes the release of endorphins, but the results of this saving can be the most dismal! The practice of repairing and testing equipment, as well as working with clients (from designers to installers), say one thing — about 70% of equipment failures are the fault of power supplies!
Let's dwell on this issue from a technical point of view. There are 2 main types of power supplies: linear and pulse. In our case, any of them should provide the voltage and current consumption we need. It would seem, what else do we need? Current with a reserve, voltage is normal, protection in the form of a fuse is there. But no one ever asks a question about the ability of the internal units of the power supply to work on a large capacitive, inductive and reactive load! If you disassemble any power supply and look at the circuitry, it turns out that this technical solution of the stabilizer, for example, on the KREN12, is not intended to work with lines longer than 1 meter. Otherwise, this very KREN … is not responsible for its work. Moreover, such power supplies are linear, and work on the principle of limiting the input voltage to the level we need at the output. That is, at the input of this very KREN there is about 20 V, and at the output we get 12 V. In any emergency situation, we can get these same 20v consequences at the exit, I suppose, everyone knows.
A good option for use in a video surveillance system are specialized pulse power supplies. They are less sensitive to all the accompanying long routes, interference and resonance phenomena. The operating principle of pulse power supplies completely eliminates the excess of the output voltage above the specified one. Overload capacity and self-healing mode are normal parameters for them. Operation in a large range of line voltage and 100% current protection makes such power supplies an integral part of a professional video surveillance system.
Well, in conclusion of the article, we will talk about the most insidious enemy — interference and potential difference.
When designing a video surveillance system, many negative factors can be foreseen or avoided in one way or another. But it is almost impossible to prevent the occurrence of interference or unwanted potential difference between equipment in the system. Engineers who have experience in developing and installing a video surveillance system in a difficult environment with interference understand how much work and experience it takes to debug a ready-made system. Sometimes there are unpleasant cases that can be corrected only by tightening the signal and power lines in other ways. The culprit is interference or potential difference. Both the first and second troubles are very difficult to eliminate and at great expense. Therefore, when developing a system, it is imperative to have a grounding project for the facility and a high-current line diagram from the customer. And then, starting from this, wisely build your project. Otherwise, we will get what was written above. The potential difference will be equalized by a recorder or a capture card, which will inevitably eventually put them out of order, and the interference will spoil the image. Image interference and equipment failure threaten the customer's refusal of the camera at all with the argument that the «Chinese» camera for $30 shows better than this one for $2000.
Therefore, the main factors for installing video surveillance systems are as follows:
1) It is imperative to take into account and use grounding and neutral circuits.
2) It is necessary to take into account high-current and reactive loads near video surveillance lines.
3) Do not skimp on soldering, high-quality connectors and other connecting points. 4) It is important to check the potential difference in all circuits when connecting to high-current (power) and signal circuits. Sometimes the voltage in the circuit reaches 150 V and the current in such a circuit can disable the protection of recording devices or output stages of cameras. 5) Do not lay signal lines parallel to power lines. In some cases, the route of your lines coincides with high-voltage power lines, and it happens that installers pull power from the RK in one bundle. 6) It is necessary to provide general protection for the registration room, using proven stabilizers and suppressors of line voltage interference. 7) And the last, most important factor is that the video surveillance system must be designed correctly, using all available data about the object. By adhering to these rules, you can get guaranteed high-quality video. Good luck!
Technical Department Specialist Acumen Int. Corp.
Ivan Podgorny