|
We all know that video cameras are for indoor conditions and outdoor ones. In fact, these options, although they include 99.99% of video cameras sold, cover only a small fraction of the variety of conditions in which video surveillance systems can operate.
Firstly, even the so-called outdoor conditions can be different. In Moscow, it can really be from -20 to +30 degrees. But in Chukotka, no one is surprised by -60. Can outdoor cameras for Moscow really work on the street in Magadan? Of course not. However, there are also «Magadan» video cameras and they are produced almost in series. More precisely, there are casings that can ensure the operation of video cameras in such conditions. Please note that among imported products, the most cold-resistant heavy serial casings are usually specified for -46 degrees (this is -50 Fahrenheit). For domestic casings, -50 is sometimes specified, which is typical for military standards. However, the casing itself could work at lower temperatures. The temperature at which the casing provides acceptable conditions for specific video cameras for which the casing is intended is specified — usually for cameras with a minimum operating temperature of -10° Celsius. That is, the casing is capable of providing a temperature difference of 35-40 degrees. But there are serial video cameras and, most importantly, lenses for them, capable of operating at -20° and even at -30° Celsius. If you use them, such an assembly will be able to work at -55° or even -70°. In addition, special «cold» kits are produced for some casings: additional insulation, additional heater — they also allow you to lower the operating temperature by 10-15 degrees. Just do not forget that the total power of all heaters can reach 100-150 W. At worst, you can even additionally wrap the casing with a layer of thermal insulation yourself. In this case, the front window will be the thinnest place. Not only can it freeze and fog up if the casing heater is inconveniently located, but also huge temperature differences on the glass in many types of casings lead to the glass peeling off or cracking due to temperature deformations of the case. So it is possible to use the casing outside its standard temperature range, but at the user's own risk, and it would be better to first find a heat and cold chamber and run a specific type of casing at a temperature with some reserve.
It's worse if you want a PTZ camera. Theoretically, there are PTZ devices for low temperatures, but they are not mass-produced. For example, I know of only one such type, manufactured in the USA and has a supply voltage of 110 vac. You can try to insulate one of the mass-produced ones yourself by pasting it with heat insulator, but it is very likely that the most sensitive places, such as the gearbox, will be the coldest. Hardening grease will stop the PTZ device in the cold. Perhaps cheap devices with plastic non-lubricated gears will work better.
There is another proven method — to place a small high-speed dome camera inside a relatively large (10-20 inches) spherical housing — it will add 20 degrees to its temperature range. However, such spherical housings are made of acrylic, and it does not tolerate low temperatures well, gradually cracks, especially under high wind loads, so be prepared to change the transparent dome every spring. From experience, I can say that such a dome will survive one winter at the pole of cold, although it will noticeably become cloudy and covered with cracks. And when using housings outside their design temperature range, it is necessary to pay special attention to the cable entries. Rubber seals can behave poorly in the cold, and the insulation of the cables themselves cracks — it is better to additionally seal the cable entry points with an appropriate sealant.However, in our country we have a more or less clear idea of how to protect ourselves from low temperatures, especially those who live in such temperatures. The basic principle is simple — do not skimp on power and heat up as much as possible. And there is no one to protect yourself from at -60 on the street — at such a temperature, even criminals usually do not show their noses outside. But high temperatures are often a more serious problem (as well as high illumination). In Tashkent, it can be +50, and if the camera is in the sun, then instead of a standard visor, you often have to make additional hoods (protective visors) that protect the casing itself from direct sunlight from several sides. By the way, it was not for nothing that I mentioned high illumination: as a rule, standard lenses cannot cope with the dynamic range from the southern night to the southern day. And even if they formally cope, they degrade their parameters so much that in broad daylight the picture on the screen becomes worse than at night. At important sites in the southern republics, additional backup cameras with dark filters installed on the lenses are sometimes used to ensure good visibility in very bright sunlight.
We have considered how to expand the range of conditions for using video cameras by 10-20 degrees up and down. But temperature is not the only parameter of external conditions. And the capabilities of modern video cameras are not limited to this. There are (and are quite widespread) special video cameras for monitoring the process in smelting furnaces or in the furnace of a boiler house (power plant). In industrial conditions, such visual monitoring allows saving huge amounts of money (it is enough to save half a percent of fuel oil from two hundred tanks that come to the state district power plant daily). How are such video cameras arranged? Two main points: firstly, the casing of the camera itself is cooled (sometimes by a local refrigerator, including the throttle effect of a cylinder with compressed gas, but more often — with a connection to an industrial water supply). By the way, such cooled casings are sometimes used outside furnaces at metallurgical plants. Secondly, for peeping into the oven, a special lens is made, very long — half a meter or more (with an intermediate focus inside a long tube) and with a very small entrance pupil. Of course, the first lens in such a lens heats up to unimaginable temperatures (it can even be made of amorphous sapphire or another material), but the video camera itself is already outside the thick wall of the oven and is well insulated from the inevitably hot first lens of the objective.
There is another case — deep-sea video cameras. Of course, I do not mean those used to survey the bottom of the Mariana Trench, no, we are talking about cameras that are submerged several meters or tens of meters, both security (for underwater surveillance) and technological. The so-called hermetic housings are in fact far from hermetic. The best of them are usually marked IP65, i.e. protected from water jets from any direction, but if you try to dive, water will get inside and onto delicate electronics in a few minutes. Of course, if the housing has IP68, then it should theoretically ensure operation in a submerged state. However, very shallowly (if the manufacturer honestly indicates IP68, then it should also indicate the permissible depth). The most common cable entry seals will withstand external pressure at a depth of 1 m at best. However, it is also not difficult to ensure operation at greater depths; such video cameras are mass-produced; you just need to be careful when choosing and specify the permissible immersion depth.
An easier option for difficult conditions is the sea coast. Video cameras are not in the water, but the ingress of tiny drops of salt water, which is present in large quantities in the surf zone, can quickly disable the electronics. Therefore, completely sealed cameras are also needed, capable of withstanding changes in atmospheric pressure up to half an atmosphere (there is almost constant pressure inside the camera, but the external pressure depends on the weather). To ensure that an aggressive corrosive environment does not get inside, and to control the tightness, they are sometimes pre-inflated with dry nitrogen and with a built-in pressure sensor. While the pressure inside is higher than the external one, nothing will get inside. As soon as the pressure inside drops, it is necessary to repair the casing. True, in recent years, as video cameras become cheaper, they increasingly do without such a pressurization — yes, if the tightness is broken, the camera will soon fail — so what, it is cheaper to replace it than to carefully protect it from the external environment.
Another almost hermetic option is explosion-proof cameras. In fact, they may not be hermetic at all, it is enough for the cracks in the casing to be thin and long (according to formulas and standards). Then, even if an explosive mixture gets inside the casing and explodes there from heating or a random spark, the blast wave will not be able to spread outside the casing and will not cause a fire in the entire chemical plant. Such casings or ready-made video cameras are produced by many manufacturers both in our country and abroad, although in fact explosion-proof products are very rarely required. After all, only the premises and the immediate vicinity (several meters) around the buildings are dangerous. And security video cameras are usually installed outside the premises, and it is not at all difficult to install them outside the zone of possible explosive concentration.
Finally, I would like to remind you about such a threatening factor of the external environment as vandals. This danger is not at all rare. For example, one Western company advertised the heaviest, thickest cast housings for cameras with centimeter-thick glass as intended «for prisons and schools».
All such housings (or assembled cameras) are necessarily closed — spherical or multifaceted, with a device for adjusting the direction of the camera inside the housing: after all, to disable the camera, it is not necessary to break it — it is enough to turn it towards the wall.
There are different types of casings according to the level of protection, starting from plastic ones, designed to protect «from honest people» — these are installed in low corridors in places with a large flow of people, for example, in airports. Why in narrow passages? It's just that in large rooms it is enough to install a regular camera at a height of 4-5 m, and no vandals will be afraid of it. But in low corridors the camera is accessible to «jokers» passing by, so it has to be protected.
More protected casings are made of thick sheet metal and have strong glass that is difficult to break. The most protected casings can withstand even a pistol shot. All of these are strong enough to be unbreakable by hand, casings necessarily have secret screws that cannot be unscrewed by improvised means, or even cylinder locks. Often, casings are designed to be installed in the corner of two walls and a ceiling, from where they are especially difficult to pick out even for a persistent vandal.
In addition to armored cameras, I will mention such a category of vandal-proof video cameras as hidden cameras. Indeed, if a vandal does not see the camera, he will not be able to harm it. In addition, cameras with a micro lens, especially with a lens with a remote pupil, walled into the wall are easier to protect: you only need to protect a small hole in the lens with durable glass. The disadvantage of hidden cameras is the complexity of installation. Even the smallest camera is quite difficult to mount in a reinforced concrete wall and at the same time correctly adjust its angle of view. In addition, you can't go against physics, a good lens is necessarily a large lens. A small lens always gives a far from ideal image. However, as already mentioned, protection from vandals is relevant only in tight spaces, for which depth of field and the ability to work in a wide range of illumination are not so important.
Finally, I will list a number of special video cameras designed for special conditions. In particular, megapixel progressive scan cameras have long been used in computer vision systems, and now in many computerized security systems.
Ultra-high-speed video cameras, with frame rates reaching tens of thousands of frames per second, are used for technological monitoring of fast-moving objects, also, as a rule, with computer image processing — after all, a person is not able to distinguish 50 frames per second from 50,000 frames per second by eye.
Video cameras with an extended spectral range. The most well-known thermal imagers are those sensitive to radiation in the range of 3–10 microns, where the maximum radiation of objects (or rather, subjects) falls at a temperature of 36 degrees. Until recently, such cameras were necessarily strongly cooled themselves, but in recent years new sensors have been developed that can operate at room temperature.
There are also video cameras with sensitivity extended into the ultraviolet region. They are used with UV illumination for technological control of the purity of materials and surface purity – dust and organic dirt often glow in the UV range with appropriate illumination.
Ultra-high-sensitivity video cameras. Those that are not in advertising claims, but in reality are able to see individual photons. These cameras have a built-in electro-optical amplifier (usually based on microchannel plates), like in night vision devices.
EXHC (Videotec)
Explosion-proof Videotec EXHC housing, made of durable anti-corrosion aluminum alloy with a wall thickness of 10 mm, painted using powder coating. Explosion protection: EEx d IIC T6 (EXHC000) and EEx d IIB + H2 T6 (EXHD001). The housing is equipped with a heater and a sun shield. Standard equipment includes a heater, and can be additionally equipped with a sun visor.
|
