Lightning protection measures and controllers for access control systems

2015-01-06 00:00

Today, with the rapid development of digital technology and network technology, access control technology has developed rapidly. The access control system has long gone beyond simple doorway and key management, and it has gradually developed into a complete access management system. It plays a huge role in administrative management work such as working environment safety, personnel attendance management, etc. Let's take a look at the access control system lightning protection and controller purchase problems!


Access control lightning protection means pay attention to the problem

At present, the rated voltage of most building intercom door power supplies on the market is 220V, the AC peak or synthetic voltage is 190~250V, and the test voltage of electrical strength should be 1.5kV. To meet this requirement, it can only meet the requirements of sudden changes in the circuit system, but it cannot resist the attack of lightning overvoltage and ultra-large current. At present, most residential buildings on the market do not have any lightning protection measures. Therefore, the building intercom door should have lightning protection and grounding device.


In the past, the walkie-talkie doors of some buildings were repeatedly damaged by lightning, which caused great inconvenience to users and caused greater economic losses. Through the investigation and cause analysis of these lightning incidents, the main components destroyed are the power box, circuit board, walkie-talkie, and the main ways of lightning attacks are:


(1) Direct lightning. Direct lightning is a direct strike on the object of lightning, close to the ground thundercloud on the protrusion induction of the opposite charge, when the electric field strength between the thundercloud and the ground protrusion reaches the air breakdown strength, breakdown discharge will occur, this thundercloud to the ground protrusion direct breakdown discharge is called direct lightning. Tall buildings and their sides are vulnerable to direct lightning, and direct lightning on the side of the building can be called side lightning.


(2) Induction thunder. It is indirectly hit by conductor sensing such as metal objects next to lightning strike facilities. Lightning inductance is divided into two types: electrostatic induction and electromagnetic induction. Electrostatic induction is formed due to the induction of a large number of anisotropic charges on top of the ground protrusions as thunderclouds approach the ground. When the thundercloud discharges with other thunderclouds or other objects, the charge accumulated at the top of the protrusion suddenly loses its restraint, showing a high voltage, and propagating at high speed in the form of lightning waves. Electromagnetic induction is formed due to the rapid change of strong magnetic field in the surrounding space by direct lightning current, inducing high voltages on nearby metals. Induction lightning is not as violent as direct lightning, but it has a much higher chance of happening than direct lightning. Because direct lightning only occurs when a thundercloud strikes the ground, it will cause disaster to the ground, while induction lightning can occur and cause disasters regardless of whether the thundercloud lightning strikes the ground or the lightning between thunderclouds and thunderclouds. A lightning strike can induce lightning overvoltage phenomenon in a relatively large range and multiple small parts at the same time, and this induced high voltage can be transmitted far away through metal wires such as signal lines, power lines, and telephone lines, resulting in an expanded range of lightning damage. The following measures should be taken to prevent the main ways of lightning strikes mentioned above:


1. The installation location of the power box should be selected correctly. (1) Avoid installing on the side walls around the house, especially on the side walls of the protruding house, to prevent direct lightning strikes. (2) Avoid installing on the wall on the side of the pipeline such as metal water pipe and gas pipe, especially the same side wall less than 5 meters away from the metal water pipe and gas pipe.


2. The power box and circuit board should take grounding measures, the grounding wire should be firm and reliable, and the grounding resistance should be ≤ 0.1Ω.


3. The wiring should be correct and reasonable. Power lines and signal lines should be distributed indoors, try to avoid outdoor wiring, avoid co-direction and cross-wiring with metal water pipes, gas pipes and other pipelines, and cannot avoid wiring in the same direction with metal water pipes, gas pipes and other pipelines, the distance between the two should be ≥ 5 meters. The wiring should be straight to minimize bending the wiring.


4. The access mode of the power box should adopt the wiring socket method, when weather prevention or weather changes may occur lightning, it is convenient to cut off the power supply in time to prevent lightning strikes.


High-quality access controller options

The access controller is the hub of the access control system, just like the engine in a car. The performance of the access controller directly affects the stability of the access control system, and the stability of the system directly affects the safety of the customer's life and property.


1. Anti-crash design

An access controller crash is like a car engine stalling. No matter how powerful the controller design is, if

There is a crash, the controller does not work, and any function cannot be reflected. If there is a crash in the application, it means that the area controlled by the controller cannot be accessed normally, and may even cause serious safety hazards and immeasurable losses.


Second, the capacity of the relay

The output of the door controller is controlled by a relay. When the controller is working, the relay should be opened and closed frequently, and every

There is an instantaneous current passing through the opening and closing. If the relay capacity is too small, the instantaneous current may exceed the capacity of the relay, which will soon damage the relay. In general, the relay capacity should be more than 3 times greater than the peak current of the electric lock.


Third, the protection of the controller

The working voltage of the components of the access controller is generally 5 volts, if the voltage exceeds 5 volts, the components will be damaged.

and makes the controller not work. This requires that all inputs and outputs of the controller have dynamic voltage protection to avoid it

A large external voltage may be applied to the controller and damage the components.


Fourth, the adaptive function of the front-end input device

Because different users and different applications have different requirements for the input device of the access control system. This requires access control

The device is compatible with a variety of front-end input devices (such as: support Wiegand26Bit, Wiegand32Bit, Wiegand27Bit, ABA (second track), object recognition technology, fingerprint recognition technology, inductive IC card, PIN keyboard, watermark magnetic card, etc.). And the input front end can be automatically detected.


5. Reliability of management software

A high-quality access control system requires not only a high-quality controller, but also highly reliable and fault-tolerant management software support.


6. After-sales service should include two aspects:

First, a complete technical support system, including the ability to provide localized pre-sales support and after-sales technical support; The second is strong follow-up research and development capabilities to ensure that products are continuous and advanced.


7. Quality certification

The sales of access controllers and system products in China must pass the "type inspection" (not commissioned inspection) of the Security and Police Electronic Products Testing Center of the Ministry of Public Security of China, and the software should pass the testing of the China Software Evaluation Center. Production should be produced by professional electronic manufacturers with ISO9000 certification, especially military enterprises.


VIII. Price

The experience of the IT industry tells us a truth: a powerful enterprise must have the ability to provide the society with high-quality and price-competitive products to meet the needs of customers, and at the same time ensure that engineers can get reasonable profit margins.