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Which factors will affect the choice of equipment cables?
For laying cables for low voltage engineering projects, it is needed to choose wires according to the parameters from the front-end and back-end control equipments. In general, it should be considered factors such as allowed range of voltage loss, frequency specification, mechanism strength, laying environment and so on. Often the constructors of light current systems ignore the line voltage fluctuation problem. Especially when coming to calculating the system capacity and the line current-carrying capacity, the impact of equipment dynamical factors are often neglected, which affects the liability for the equipment. Using a 12V camera as an example, the current consumption for a colour camera is 350mA, and for a black and white camera, it is 150mA. If using 12V DC as power supply and several cameras are connected into a line, the image quality will be decreasing more and more at the end of line. This is because the chosen cable area is too small resulting in a high mains fluctuation. Another example is USA Dixin Community Main-Bus alarm system. It is required to add dozens or up to hundreds of family control terminals in the main line. If not fully considering the reactive mains fluctuation, the superimposed mains fluctuation will be very high at the end of the system, which will make the system unable to work properly. In normal situation, the longer the cable is, the higher the distributed resistance, the capacitance and the inductance are. These will superimpose a lot of interference, which causes the bad and unstable system performance.
To prevent mains fluctuation on the cable, some project constructors would adopt 220v alternating current supply. In order to save cost, they would put the high voltage cables and low voltage cables in the same cable channel. In this way it can decrease the mains fluctuation, but according to the standard, with the different voltage level, different equipment cables should be laid into different channels. It means the system cost would be increased. It is a whole system design issue to meet both the system technical requirement and the industrial standard. Moreover, except considering the attenuation by the length of cable and the numbers of the load, the system requirement for the frequency bandwidth, how the system is connected to the ground and the construction method would also be taken into consideration when designing communication link and control circuit, because all these will affect the usage of the system. If they are not handled properly, they will cause the mains fluctuation, coupling interference, waveform distortion and zigzag reflections to affect the system. Meanwhile, during construction and implementation, it is good to think about the related branch regulation, usual practice, the anti-interference performance of equipments, stability and application environment such specific factors.. |
