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Technológia optických vlákien v CCTV systémoch - praktické otázky
The main problem faced by the installer implementing video monitoring system is the choice of the appropriate type of fiber optic cable and wiring topology for the particular installation. Because the most common questions relate to installations where cameras are deployed on poles or lampposts, all the examples refer to this type of implementations, however the information is relevant to other types of installations, as well.
Optical fibers in CCTV - multimode or single-mode?
Generally, when selecting the equipment and cables, both the elements have to be compatible. If the connections between cameras and the switch are greater than 2 km, it is necessary to apply single-mode cables. Similarly to situations where one cable should transmit signals from dozens or hundreds of IP cameras. With such a wide band, the use of single-mode fibers should be a more preferred solution. The range of single-mode cables is broader, allowing for the selection of optimum cable, and the transmission line can be extended in the future beyond 2 km, if necessary.
The difference in the price of multimode and single-mode devices, often served as an argument for the option of applying the former, nowadays is negligible, at least in the case of transmission equipment for LAN and CCTV systems. And the cost of multimode cables is even higher, due to a more complicated production process. So, all the arguments are for single-mode solutions (greater distance, higher throughput, lower price).
The only argument for the choice of multimode fiber is the common opinion that this type of fibers can be spliced more easily. However, in the case of video monitoring systems the links are usually comparatively short and the optical power budgets are high, so the precision and attenuation of the splices are not so critical. Hence, a very popular option is the application of mechanical splices, with real attenuation up to 1 dB. Of course, regardless of the chosen solution, the installer should care for the greatest possible precision and quality of the splices, but in practice the choice of the type of fiber is not important in this regard.
Advantages of choosing cables with single-mode fibers:
- easier choice due to a broader range of the cables on the market
- ability to transmit signals at distances of tens of kilometers using typical equipment
- lower prices compared to multimode fibers due to lower production costs
- higher throughput capacity
- availability of cables with small bending radius, from 7.5 mm
Drawbacks of choosing cables with single-mode fibers:
- different versions of fibers may cause problems with splicing, it is recommended to unify the cables in the system
- in exceptional cases and depending on the equipment it may be necessary to use fiber optic attenuators for short distances - the information should be found in the data sheet of transmitters and receivers, especially on the transmitter output power and the receiver sensitivity
Topologies of fiber optic cabling in CCTV systems
Optical CCTV system with radial topology
A separate cable provided to each camera placed on a pole is the most versatile and the least labor-intensive solution, taking into account the splicing and protecting of optical fibers. However, it involves more effort when laying cables, as the overall length of the cable routes is greater.
In this topology, the structure of the cable is not a significant factor, as there are no branches along the paths. Of course, the cable must meet all the requirements necessary for the proper operation in the environmental conditions. An important parameter is the tensile strength, sufficient for operations connected with pulling in the cable to cable ducts. The most popular types of cables used in installations of this type include:
Regardless of the number of cameras on a pole, the transmission is performed only via two optical fibers. However, we recommend at least the minimum redundancy level - the application of optical fibers with 4 fibers.
The choice of radial topology radial also saves the space on the pole - the fiber optic cable can directly enter the installation box with the equipment: media converter, video converter, power supply, etc. Optical fibers from the cable have to be terminated with pigtails. The splices should be protected on a dedicated splice tray or in a suitable cassette. The pigtails should then be plugged into adapters. It would be extremely inadvisable to connect the pigtails directly into optical devices! The connections should be made with patch cords joining the opposite parts of the adapters with the inputs of the devices responsible for the conversion between optical and electrical signals. In the future, doing any servicing or maintenance, the installer will only risk a damage to the patch cord and not to the cable (which would cause the necessity of re-splicing).
Components of the implementation of a junction point in weatherproof box installed on a pole, which can provide a ready-made solution for many applications:
- R90603 - Waterproof Installation Box (250/310/145 mm, IP55)
- R90610D - Pole Mount (2 brackets)
- N29973 - Industrial PoE Switch ULTIPOWER 124P-4POE-20
- N93326 - Industrial Power Supply Mean Well MDR-60-48
- L5402 - Distribution/Termination Box ULTIMODE TB-02B (IP65)
- L3555 - Single-mode Pigtail ULTIMODE PG-55S (1xLC, 9/125) - 2 pcs.
- L4355 - Single-mode Adapter ULTIMODE A-555D (2xLC to 2xLC)
- L3215 - Single-mode Patch Cord ULTIMODE PC-515S (1xSC-1xLC, 9/125) - 2 pcs.
- E1412_1 - Cat 5e UTP Cable NETSET U/UTP PE (outdoor)
- L76004 - Universal Cable: ULTIMODE UNI-4SM-A (4xG.652.D)
IP cameras located on a pole can be connected to industrial switch via outdoor twisted-pair cable NETSET E1412. The Ultipower 124P N29973 switch also acts as an Ethernet to fiber media converter and PoE power supply for the cameras. In turn, the switch is powered by the Industrial Power Supply N93326 connected to AC power network (100-240 VAC). The switch is connected with the fiber optic system via two SC-LC L3215 patch cords.
The L76004 optical cable with four fibers enters the R90603 box and the L5402 distribution/termination box. The fibers are laid in several loops for the formation of a cable reserve, in case one needs to take the L5402 box outside. Two of them are spliced with L3555 pigtails (LC) with the use of the L5810 fusion splicer and L5554 heat-shrinkable protective tubes. Their LC connectors are plugged into the 2xLC to 2xLC L4355 single-mode adapter.
Line topology with cut points
Optical CCTV system with line topology
The question of the possibility to connect several camera points (poles) using one fiber optic cable is one of the most frequently asked by installers. There is such a possibility, but this option should be chosen by more experienced installers equipped with the right tools.
The cable that is run through the points must have an adequate number of fibers - at least 2 fibers for each point. For example, 5 poles will need at least 10 fibers, so the application of a 12J cable (with12 fibers), or, for redundancy, a 16J or 24J cable. However, an excessive redundancy will be the reason of unnecessary effort, so it is better not to exaggerate.
One of the options to run a multi-fiber cable through the camera point is to cut it on the pole, separate two fibers for connecting the local transmission device and splice the rest of the fibers led to the next pole. This leads to the following conclusions:
- the higher number of redundant fibers, the greater extra work is needed, because the installer should splice all the fibers,
- on the first pole the installer has to splice all fibers,
- on the last pole the installer has to splice only the fibers connecting the point.
The approach requiring cutting and splicing all the fibers may seem illogical, but many installers using professional and quick welding machines opt for such a solution, because it can be applied to any type of the cable (as opposed to the options described below), without paying attention to its structure, such as strengthening elements, central tube (if exists), its diameter etc. In addition, this approach allows the use of most of the commercially available joint/cable boxes.
Welding scheme for 12J cable and five CCTV poles - total of 38 splices
However, the installer of the system shown in the example above (5 poles, 12J cable) should realize that the total number of the necessary splices is 38, of which only 10 are the splices connecting fiber pigtails for the purpose of data transmission. The rest, i.e. 28 splices are only intermediate connections. So, this topology practically eliminates the application of mechanical splices due to high cost and risk of excessive attenuation of the longest paths (in the case of the last pole the transmission line includes 6 splices and the output power of an optical transmitter might be insufficient).
The pigtails are plugged into L4211 adapters. At the opposite side one can connect a duplex patch cord or optical cable terminated with two pigtails. Any installation on a pole has to be adequately protected pipes, also in the case of the patch cord between the box and installation box with active devices.
Thanks to three holes, the L5412 box is ideal for "pass through" applications,
with the opening for an additional patch cord in the middle part.
with the opening for an additional patch cord in the middle part.
Line topology without cut points
Due to the large amount of work needed in the implementation of installations with splicing of intermediate connections, installers often ask about the possibility of separating and cutting only two fibers that are necessary for connecting the devices on a pole, and remaining the rest of the fibers without cutting. Then it is necessary to splice only two fibers transmitting the data from the pole.
This method has both its supporters and critics. No need to cut and splice all the fibers is definitely a big plus, but on the other hand it can be very difficult job for the installer to safely take fibers out of the cable or cable tube without breaking some of them - which would result in the need for additional splices, as well.
The example below presents the application of the L56020 fiber-optic joint box for this type of installation. The first stage consisted in laying the L76012 fiber optic cable so that to leave a surplus length of the cable located by the box (no matter on which side). The length should be sufficient for pulling out the fibers intended for splicing. Generally, the methods of extracting the fibers depend on the structure of the cable, including the choice of the necessary tool(s) needed for safe opening of the jacket/tube and pulling out the fibers.
The 12 single-mode fibers of the L76012 universal fiber optic cable are contained in central gel-filled tube of 3 mm diameter. The tube is made of plastic, but is flexible enough for placing the cable in the L56020 joint box. The outer jacket can be stripped by L5922 stripper that can also be used for cutting and breaking the tube.
In order take out fibers located inside the tube, the installer should use the L5925 mid span access tool. The tool allows easy access to optical fibers in a loose buffer tube by precise shaving of its side. Such a window should always be shaved on straight fragment of the tube. This usually means the need for drawing out a longer portion of the cable, which should then be retracted.
There are two methods of taking out the fibers. In the first one, the installer operates on a short portion of the tube, around half a meter. After cutting out two ca. 5 cm windows on both ends of the portion with the use of the MSAT 5 L5925 tool, the installer should find and cut the required two fibers in one window and take them out through the second. Each of the two fibers has the length of about half a meter. With this method it is not possible to pull out longer portions of the fibers because of friction caused by the gel in the tube. In the case where one needs longer fiber segments for convenient splicing, it is possible to cut out additional windows in order to gradually pull fibers through the tube over the short distances between the windows.
View of the fiber optic cable tube with window made using the MSAT L5925 tool
The second method consists in removing the tube over the whole length needed for convenient operation, cutting the two fibers and protecting the rest of them. To get rid of the tube, it is necessary to cut window along the whole length and then cut off the remaining part. This way, the access to the fibers can be ensured over distances of many meters, but it is not recommended to exceed the length of 2 meters - the longer the intended window, the higher risk of damaging the cable (fibers) during the operation.
The fibers unused on the pole should be rolled into coil(s) and properly secured. Two selected fibers are cut and enter the splice cassette, where they are spliced with pigtails.
The pigtails are then connected via adapter(s) and patch cord to a media converter located in another weatherproof box. The patch cord (not shown in the pictures) should be inserted into the joint box trough the third opening (in the middle). If the patch cord is not intended for outdoor use, it must be protected by a pipe between the joint box and the installation box with the media converter.
The L56020 fiber-optic joint box is a universal installation box that can be used in CCTV systems independently from the installation method, both in the case of cutting all the fibers and cutting out windows for using only selected fibers. The main advantages of the box include compact size, means for good and safe organization of fibers inside it, and 3 points of entry.
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