Network access control integrated wiring and access control security factor analysis

Engineering principles and transmission lines

The access control system is a subsystem of the entry and exit management system. Usually, it uses card swipe, password or human biometrics and other technologies. Under the control of the management software, it manages the entry and exit of personnel or vehicles, allowing people and vehicles that have obtained authorization to enter and exit to pass freely And those who should not go in are banned. Therefore, the access control system has become an indispensable configuration item in many places that need to verify the identity of people and vehicles. This issue will discuss the technology of access control network communication application.

Engineering principles and transmission lines

Engineering principles

The engineering principle of the access control system is basically similar to that of other automatic control systems or intelligent building systems. Its operation can be divided into three links: sensing, management and execution, but it is relatively compact and relatively simple.

Sensing: Card readers, password keyboards, various biometrics, exit buttons, and lock status sensors are all sensors. Their task is to accept commands, upload signals or upload them after verification (biometrics).

Management: The controller and management software are responsible for the management function of the access control system. After receiving the information from the sensor, they determine whether to open the door according to the time, card number and other information. ; When the lock status information is received, the timer will start, and the alarm will be given when it times out.

Execution: When the electric lock receives the command to open or close the door (power supply or power off), it "executes" the command to adjust the working state to be consistent with the command. The lock status sensor in the electric lock plays a role of feedback and supervision.

Some controllers can use relays to output control signals to control linked cameras and lights.

Transmission line

According to the working principle, there are the following transmission lines in the access control system:

power cable

Most of the power supply of the access control system comes from the UPS in the computer room, so as to avoid misoperation when the power is cut off. The power cord is usually in the way of 220V AC transmission, the purpose is to reduce the voltage drop of the power line. Next to the controller, it is equipped with a regulated power supply, which converts the AC 220V power supply into a DC 12V power supply, which is supplied to the controller and the electric lock respectively. The vast majority of electric locks used in access control systems belong to the 12V DC power supply mode. At the moment when the electric lock is broken, due to the effect of the electric lock neutral wire package (electromagnet coil), a strong current will be generated in the power line, it is easy to cause power supply fluctuations, and this power supply fluctuation is extremely detrimental to the stable operation of the controller Therefore, in the access control system with high reliability requirements, the controller and the electric lock use different power modules, that is, when 220V AC power is supplied to the controller, two 12V DC power modules are used for rectification / regulation, and then supplied separately. Electric lock and controller. The selection of various power cords is basically based on the electrician's manual, using standard power cords.

Controller signal cable

There are three groups of signal lines in the controller, which are connected to the card reader, the lock status sensor in the electric lock and the exit button. These three signal lines can be replaced with twisted pairs in integrated wiring. In order to avoid electromagnetic interference in the space, the signal line of the card reader should be shielded, and the other two signal lines can be shielded or unshielded.

Remote network signal line

The transmission from the controller to the management computer is mostly RS485. RS232 is available when the distance is short, and TCP / IP is used when the transmission rate is required to be fast. In order to avoid electromagnetic interference, this signal line should use shielded twisted pair. When the controller needs to use the output hard contacts to directly control the hard disk recorder (synchronized recording when the card is opened), this control line (2-core) should be shielded to avoid electromagnetic interference when the input signal amplitude of the hard disk recorder is small Cause a false trigger. However, if the power supply of the lighting lamp is directly transmitted by a hard contact, a power cord should be used.

According to the above analysis, when the transmission power supply is for electric locks, controllers and lighting lamps, the power cord should be used. Its cross-sectional area can be calculated based on the voltage drop and heat generated by the current, or it can be obtained from the electrician's manual. When transmitting sensor signals and control signals, shielded or unshielded wires should be selected according to the installation manuals of the card reader and controller. As the number of doors controlled by the access control system locks increases, the requirements for the transmission speed and wiring safety of the system network are becoming higher and higher, and the construction of the access control system must also carry out the construction of the integrated wiring system, so the network is used As a transmission line of the access control system, twisted pair has become the main choice of cable for the access control system. According to the analysis of various access control cables, the signal lines and control lines between the card reader, the controller, and the management computer can all use network twisted pairs.

In the case of simultaneous access control system and integrated wiring, for the remote network signal line using TCP / IP protocol, it is necessary to use twisted pair transmission. It can completely use the standard star structure of the integrated wiring system to achieve remote signal transmission. RS485 line and RS232 line can also use network twisted pair. According to the installation principle of access control controller, these devices should use shielded twisted pair to avoid misoperation caused by electromagnetic interference.

Precautions for comprehensive wiring of network applications

When using the integrated wiring system as the transmission line of the access control, the following factors should be noted: the wiring method should be in full accordance with the wiring rules on various access control equipment, and the detailed wiring diagram should be retained to avoid the pain of judging the line during maintenance. The shielding layer of the shielded twisted pair should be grounded according to the installation manual of the card reader and controller.

If the network shielded twisted pair is used to transmit TCP / IP, the shielding terminal wiring rules of the shielded integrated wiring system can be completely adopted. When using the TCP / IP protocol, it is best not to share the network switch with other intelligent systems (including office automation systems and other software systems) to avoid accidents in transmission due to protocol conflicts. When using the network TCP / IP protocol, the management computer of the access control system can be regarded as a server in the access control network, and it is connected to the distribution frame using twisted pair or optical cable. The integrated wiring system can be used in the access control system. This has been confirmed by the access control system suppliers and installers, but the cost, construction and performance should be comprehensively evaluated in the project to achieve the best results.

Security factors for access control

The above are on the analysis of the access control system. We need to pay attention to and pay attention to the part of the test in this issue. In addition, we have to analyze what influencing factors may exist in the security of the access control system. several aspects:

The distribution of the control unit The control unit must be placed in a special weak current room or equipment room for centralized management. The control unit and the card reader have the capability of long-distance signal transmission, but Wiegand (Wiegand), which can only transmit a few meters )protocol;

The power supply of the access controller must be equipped with a UPS system. When the external power supply cannot be provided, the access controller can continue to work for at least a few hours to prevent someone from cutting off the power and causing the access control to fail;

Power supply is very important in access control. It is a necessary premise to provide stable and clean working voltage for components, and it has good filtering and voltage stabilizing capabilities. In addition, it must have a strong anti-interference ability, including high-frequency induction signals, lightning strikes, etc .;

The access controller chassis must have certain anti-smashing, anti-prying, explosion-proof, fire-proof, and anti-corrosion capabilities to prevent various damages;

The access control unit must have various real-time alarm capabilities, such as power failure, UPS and other equipment fault prompts, warning messages that the chassis is opened, and alarm notification capabilities such as communication or line failure

The access control unit cannot directly use the switch value signal. Many signals of the access control system will only be output in the ON / OFF mode of the switch, such as the door magnetic signal and the exit button signal. Security

The overall architecture design of the access control unit is very important. A well-designed access control system should avoid the use of slot-type expansion boards as far as possible to prevent poor contact caused by oxidation due to long-term use;

The program design of the access control unit cannot be completely dependent on the computer and software. The computer is very unstable, so all logical judgments and the application of various advanced functions in a well-designed access control system must rely on the hardware system of the access control unit To be done;

The output of the access control unit is controlled by the relay. The relay works frequently. If the current capacity is too small, the relay will be damaged quickly. It is usually a large current inductance plus a resistor or reverse diode to protect the control unit;

The electric lock and execution unit includes various electronic locks, three-roller turns, car stoppers and other control equipment. These devices have different safety, convenience and reliability, and it is necessary to select the appropriate electronic lock according to the specific actual situation;

Sensors and alarm units should have certain anti-vandalism measures. A well-designed access control system can encrypt or convert the reed alarm signal and the exit button signal, such as TTL level signal or digital signal. At the same time, the access control system can also monitor the status of alarm, short circuit, safety, open circuit, request exit, noise, interference, shielding, equipment disconnection, anti-disassembly, etc., which can prevent the artificial shielding and destruction of the switch alarm signal and improve the security of the access control system .

The access control unit should be able to support multiple online communication modes, such as RS232, RS485, or TCP / IP, etc., and use the appropriate online mode under different circumstances to achieve system connection nationwide or even worldwide.