Security systems for facilities with severe operating conditions.
Sooner or later, any designer or installer has to face the task of equipping a facility with a security system where the operating conditions differ from the usual ones. And, accordingly, the usual set of equipment and solutions is not always suitable. Of course, you can somehow adapt the usual «office hardware», but here no one will give a guarantee that all this will work normally after the ceremonial handover of the facility. In this article, I would like to briefly consider what conditions are considered difficult and what can be recommended in this case when choosing equipment.
Let's list them in order:
climatic conditions,
dust,
electromagnetic radiation,
aggressive environments,
vibration,
explosion hazard.
Climatic conditions
Low or high operating temperatures, high atmospheric humidity are the most frequent companions of operating equipment outdoors. Although this may also apply to unheated premises, some types of industrial production, and all kinds of vehicles. Usually, for average Russian conditions, this range is from -40 ° C to +50 ° C. For northern regions or Siberia, this may be from -50 ° C to +50 ° C. If the technical characteristics of the equipment do not correspond to the specified range, and there is nothing better or there is, but it is very expensive, you will have to provide heating or cooling. Here, you need to pay attention to the increase in energy consumption of the entire system to ensure the desired microclimate, which as a result, at some stage of operation, may exceed the costs of equipment with an extended operating temperature range. In addition, you need to consider possible problems when turning off climate control systems, for example, when switching to backup power.High humidity or direct water ingress can also create many problems. The main methods of combating these factors are the use of sealed cases, coating printed circuit boards with electronic components with protective varnish, and using special adsorbents, such as silica gel. The latter is characterized by its huge surface area (up to 800 m2/g) and actively absorbs moisture.
As for the tightness of the housings, I think it is worth recalling and providing extremely useful information about the international classification of degrees of protection of the electrical equipment casing against the ingress of solid objects and water in accordance with the international standard IEC 60529. The marking of the degree of protection is carried out using the international protection sign (IP — IngressProtection) and two digits, the first of which means protection against the ingress of solid objects, the second — against the ingress of water. The code is IPXX, where in the X positions there are numbers or the symbol X, if the degree is not defined. The numbers may be followed by one or two letters providing additional information. For example, a household electrical outlet may have a protection degree of IP22 — it is protected from finger penetration and cannot be damaged by vertically or almost vertically dripping water. The maximum protection according to this classification is IP68: a dust-proof device that can withstand prolonged immersion in water.
Often, protection against liquid ingress automatically provides protection against penetration. For example, a device with liquid protection level 4 (direct splash) will automatically have protection against foreign objects at level 5.
Dust
The presence of a high concentration of dust in the air is often due to the specifics of the facility, for example, the production of cement, plasterboard, etc. Obviously, in such cases it is necessary to use products in housings that have an appropriate degree of protection against the penetration of foreign objects (IP classification — see above). However, sometimes for normal operation of the equipment an influx of this same dusty air is needed, for example, for cooling. Then you should take care of a reliable filtration system, as well as timely replacement of filter elements during operation. The same applies to smoke fire alarms, for the operation of which, as you know, air must enter the smoke chamber of the alarm. Products with built-in filters and forced air circulation through the smoke chamber are suitable here.
Electromagnetic radiation
A high level of external electromagnetic radiation (EMR) can negatively affect the performance of any electronic device. Interference can be of both natural (thunderstorm) and artificial origin (from operating electrical equipment or accumulated static electricity). Here, when choosing equipment, first of all, it is necessary to compare the possible level of EMR at the facility and the degree of protection of the device. Any equipment for security systems must undergo electromagnetic compatibility tests. GOST R 50009-2000 defines 4 degrees of severity of such tests. For use under normal conditions, it is sufficient to maintain the operability of the equipment with severity level 2. In conditions of a high level of EMR, for example, at electrical substations, industrial enterprises with powerful electrical equipment, it is necessary to choose products that can withstand severity level 3 or 4. In addition, it is imperative to meet all requirements for proper grounding of equipment and communication lines. Correctly select the type of signal and power cables and determine the locations of their installation so as to exclude the possibility of electromagnetic interference in them. To protect against lightning strikes, it is necessary to use special lightning protection hardware, which is installed in the gap of all cables leading to the street. And the cables themselves should be laid underground or in metal pipes. It is better to avoid «air», i.e. open cable laying. Only if all these requirements are met can the operability of the equipment be somehow guaranteed.
Corrosive and aggressive environments
The presence of high concentrations of water, salt vapor, mold, fungi and other nasty things in the air can quickly cause any equipment to fail. It's one thing when you are mentally prepared for this and provide for the necessary protective measures in advance, for example, on sea vessels. Often, designers or installers may not even guess what conditions the equipment may end up in. The experience of installing security systems in Moscow pedestrian crossings has shown that, at first glance, the operating conditions in a place that seems harmless are actually simply hellish. In winter, as you know, roads are actively doused with anti-icing reagents, and every year they become, in my opinion, more and more toxic. As a result, this chemistry on pedestrians' shoes is carried into the pedestrian crossing, toxic fumes instantly penetrate into the places where the equipment is installed, all this settles on the housings and cables and is capable of eating or covering everything that is possible with a noble green patina in a matter of weeks. In such cases, you need to be extremely careful when choosing technical solutions and try to protect devices, sensors, video cameras, cables, etc. as much as possible.
Vibration
Vibration is mainly encountered on moving objects. Sometimes manufacturers have special versions of standard products for use in transport in their product line, sometimes original products are developed. In any case, the design of the product body must ensure reliable fastening of the equipment. All cable connections must be protected from vibrations, otherwise the cable will simply fall out of the terminal block. The cables themselves must be secured along the entire length of the laying without sagging, friction with other objects must be excluded. The element base of the devices is also often specially selected for such use. For electronic components, there is a special Automotive version with an operating temperature range from -40 ° C to +125 ° C. For additional fixation of components, all printed circuit boards must be covered with protective varnish. To reduce possible consequences, various types of vibration dampers on elastic or spring elements are sometimes used. In general, the task of vibration protection mainly falls on the shoulders of the manufacturer, and the designer just needs to make the right choice of equipment.
Explosive
There are a number of facilities where there is a real risk of explosion due to the presence of certain chemical substances in the air in explosive concentrations. There are two categories of explosive premises. Category A — when the premises contain flammable gases, flammable liquids with a flash point of no more than 28 °C in such quantities that they can form explosive vapor-gas-air mixtures. Or there are substances and materials that can explode and burn when interacting with water, atmospheric oxygen or with each other. Category B — when the premises contain flammable dusts or fibers, flammable liquids with a flash point of more than 28 °C. Such conditions can be found in coal mines, chemical plants, and also in industries with high dust content. This is probably the most difficult and responsible case for a specialist making decisions on the selection of equipment or a technical solution, since the lives of many people may depend on the correctness of the choice. There are two groups of explosion protection of electrical equipment: I — mine electrical equipment; II – electrical equipment for indoor and outdoor installation (except for mine equipment). Each of these groups provides for several types of explosion protection. For safety systems, the two most relevant types are: explosion-proof enclosure and intrinsically safe electric circuit. In the first case, the equipment is placed in a durable enclosure that can withstand an internal explosion without detonating the surrounding explosive environment. In the second case, the occurrence of sparks in electrical circuits and conductors of the equipment is excluded. All equipment specially designed and certified for operation in explosive zones has a special marking, which begins with the Ex symbols and contains all the necessary information on the categories of premises and explosion protection groups. I think that no one doubts the need for a thorough approach to the selection of equipment and technical solutions for equipping such facilities.
In conclusion, I would like to note that, despite the complexity of designing and equipping facilities with severe operating conditions, a professional approach to the matter allows you to get highly effective security systems that work in any conditions. And what is important, for all categories of objects described in the article, there are solutions based on equipment from Russian manufacturers.