】 【Weak current college building intercom gate of Thunder and cautions.

<br> Spring and summer of severe convective weather, storm, Thunder weather occur from time to time, and the lightning caused casualties and property damage are shocking. Lightning is a convective cloud and between air and ground between discharge phenomena, instantaneous discharge voltage up .to millions of volts and surge current up to tens of thousands or even hundreds of thousands of amps, lightning seriously jeopardize the safety of life and property. In particular, building intercom door in outdoor, struck by lightning more likely, 2008 Lin'an city .has more than 100 building intercom door was lightning striking, there have been building intercom door repeatedly been lightning striking, give users a great use of inconvenience it has caused a large economic losses. These lightning incidents investigation and analysis, destroyed the main part is a .power supply unit, the Board, on speech machine, the main way of lightning attacks are: <br> (1) lightning. Lightning is a direct blow to the objects of lightning, near the ground thundercloud in projection from a specific charge on the .induction, when thundercloud with surface bumps between electric field strength to achieve air breakdown strength, breakdown discharge occurs, the thundercloud on surface projection from direct breakdown discharge as lightning. High buildings and its side vulnerable to lightning, building side of lightning can be called a .cut at Lei. <br> (2) lightning. By lightning facilities next to the metal conductors such as induction, indirectly against the object. Lightning induction is divided into two static induction and induction. Static induction is close to the ground because of a .thundercloud, on the top surface bumps out of a large number of specific charge of induction. When thundercloud and other thundercloud or other object after discharging, projection from the top of the accumulated charge immediately lose the shackles, showing a high voltage, lightning fast dissemination .of the form. Electromagnetic induction is due to direct lightning current in the surrounding space have rapidly changing magnetic field, near metal previous induction high voltage. No lightning lightning so violent, but it happens more than lightning probability is much higher. Because lightning occurs only .in thundercloud on Lightning will cause disaster on the ground, and lightning regardless of thundercloud on stroke, or thundercloud on thundercloud between stroke may occur and cause disaster. A lightning stroke can be larger and smaller local voltage induction leiguo occur at the same time, and .such induction high voltage, can signal cables, power line, telephone line and other metal wire transmission to long distances, the lightning extension. The main methods of lightning attacks should take the following measures to protect against: <br> I. building intercom door .products should have the lightning protection system. <br> People's Republic of China public security industry standard GA/T72-2005 the civilian buildings Talkback intercom system and electric control door General technical conditions "5.6 security requirements in the regulations: 5.6.1 dielectric strength .-system power supply Plug and power supply into the port with a bare metal parts of the shell should be capable of withstanding GB16769-1997 the security alarm equipment safety requirements and test methods "in table 2 of 45Hz ~ 65Hz AC voltage resistance strength test, .1 min should no breakdown and arcing phenomenon. <br> Current market most building intercom door power supply rated voltage 220V AC peak or synthetic 190 ~ 250V voltage, resistance strength test voltage should be 1.5kV. Meet this requirement, the only circuit at the .request of the sudden change in the system, but can't resist lightning-voltage, large current attacks. The current market the majority of residential building intercom doors are no lightning protection measures. Therefore, building intercom door due to lightning protection and grounding device .. <br> Building intercom door with power supply and signal circuit, two mine-protector should include lightning protection and lightning protection second signal. Lightning protectors of the main technical parameter should be the following: (1) nominal voltage Un. This value should .be a protected building intercom door of rated voltage, usually marked as 230V/50Hz. (2) rated voltage Uc (maximum continuous operating voltage). This value indicates that a lightning protector of the maximum continuous operating voltage. That is, to put in .long lightning protection for a specified client, and not caused by lightning protector properties and activate protection components of maximum voltage RMS. If 385VAC. (3) In nominal discharge current. It refers to the imposition of lightning protector 8 / 20 μ s standard lightning .bump a set amount, lightning protectors can withstand the maximum impulse current peak, maximum discharge current Imax. (4) it refers to the lightning protector imposed above 8 / 20 μ s pulse width of standard lightning impulse 1, lightning protectors for the tolerance of .maximum impulse current peak. When In = 20kA, Imax = 40kA. (5) voltage protection level Up. Lightning protector at both ends of the maximum value of voltage, two indicators: ① rated discharge current of residual voltage values, should exert 1.6kV .; ② <1 k V / μ s shock shock lightning protector when both ends of the voltage value, <260V. (6) response time tA. This value is reflected in the lightning protection for special elements of action sensitivity and breakdown times ., at one time changes depending on d μ / dt or the slope of the di / dt, lightning protectors of response time within 10 ~ 100ns. (7) data transfer rate Vs. Indicates how much a seconds transmission bit (bps), is .the signal data transfer system lightning protector correct selection of the reference value. Generally 500kbps ~ 100Mbps. (8) insertion loss AE. It mainly refers to the signal line protector, its meaning is at a given frequency of lightning protector insert before and after inserting .the ratio of voltage. Generic insertion loss AE <0.5dB. (9) the return loss AR. Refers to the transmission signal edge wave in protection devices (reflex point) is the ratio of reflected back, is a direct measure of protection devices .of the same system impedance matching performance. General return loss should be ≥ 20dB. <br> Lightning protector because the signal is in-line installation to the signal line, the choice of protection against lightning lightning protection to ensure that when protector can play a .protective effect, taking lightning protectors and signal line matching problems, so it should be the main considerations of choosing: ① voltage level selection.Signal cable lightning protectors of the maximum working voltage of choice, is the basis of the signal cable for data transmission voltage .to determine. It is a choice of signal lighting protector is an important parameter, lightning protectors of the maximum operating voltage must be greater than the signal line voltage of 1.2 times. ② rate matching option. Different signal system of transmission data rate, signal cable .lightning protection is installed in the signal line, the support of transfer rate should be not less than signal transmission rate of the system itself, otherwise it will cause the signal interruption or error rate increases, the impact of signal system to work properly. ③ selection .of interface type. Lightning protectors signal lines are installed in-line approach, in order to match the way online impedance and a minimum of contact resistance, and signal lines on the same type of interface, RJ, SD type interface to note the line to .meet, for coaxial connectors should pay attention to sex. <br> II. building intercom door installation should note the following: <br> 1, power box installation location should be the right choice. (1) avoid installation in houses around the side .wall, especially out of the side wall of the housing should not be installed to prevent lightning strikes. (2) avoid installed in a metal tube, pipe, pipe on the side of the wall, in particular distance metal water pipes, pipe is less .than 5 m with side walls of more can not be installed. <br> 2, power supply unit, the Board shall adopt the measures should be grounded to Earth, solid and reliable, grounding resistance than 0 should be ≤ Ω. <br> .3, wiring should be correct and reasonable. Power cable, signal cable should be in the room, try to avoid outdoor wiring, avoid and metal pipes, pipe, pipe with and cross-wiring, could not avoid and metal pipes, pipe, pipe .with the wiring, the distance between them should be ≥ 5 m. Wiring should be line wiring to minimize bending wiring. <br> 4. power supply box access power mode should be used in wiring socket mode, when the weather prevented or weather likely .to occur when the lightning, facilitate the timely cut off power supply to prevent the occurrence of lightning strikes. <br> <br> <br>.