July 09, 2023

Classification and presentation of computer room low-current shielding functions

The basic principle of shielded computer room is based on design of Faraday cage. If not shielded, our electronic equipment will be exposed to strong sources of electromagnetic interference, such as direct or indirect lightning, resulting in equipment failure or malfunction. In worst case, it will be damaged. a relatively common manifestation of electromagnetic interference. Another phenomenon is that when we listen to radio, watch TV, or use a computer during a thunderstorm, there will be “squeaky” noises on radio, and image shake on TV and computer, etc. All of them caused by lightning interference, electromagnetic interference. Specific measures: use shielding products and ground them securely to block external electromagnetic interference and block electromagnetic waves generated by internal equipment, thus forming an equipotential body that can effectively shield electromagnetic interference.

Classification and presentation of computer room low-current shielding functions

1. Screening efficiency classification

Depending on effectiveness of shielding, it can be divided into following three types of shielding:

1: Electrostatic shielding

Electrostatic shielding to prevent electrostatic interference refers to electrostatic shielding, that is, container is made of a conductive material with low resistivity to limit power line inside container, and can also prevent external power. lines from entrance to inside of container. In electrostatic shielding, shield conductor must be grounded, and shield body and ground wire are metal materials with good electrical conductivity.

2: Electromagnetic shielding

Electromagnetic shielding prevents high-level electromagnetic interference and is used to suppress electromagnetic interference when noise source and sensitive equipment are far away. Electromagnetic shielding must shield both electrical and magnetic fields, usually using low resistivity conductor materials. Cosmic electromagnetic waves will cause reflection loss and absorption loss when they fall on surface of a metal body, so that electromagnetic energy is greatly attenuated to achieve purpose of shielding. In electromagnetic shielding, shield itself may not be grounded, but to avoid electrostatic coupling, electromagnetic shielding conductor is usually also grounded.

3: Magnetic shielding

Magnetic shielding is to prevent induction of low-frequency magnetic field, and shielding is difficult. Generally, metal materials with high magnetic permeability and low resistivity are used to form a shell of a certain thickness to limit magnetic field lines. inside low resistance shield. Magnetic field dissipation is basic principle of magnetic shielding. Similar to electromagnetic shielding, in magnetic shielding, whether shield housing is grounded or not does not affect shielding effectiveness. In order to prevent electrostatic induction in actual design, shield housing is usually connected to chassis (protective earth).

Second, some common components of a shielded computer room

1: protective shell

The containment contents mainly include hexagonal shielding materials, material-to-material connections, and support keels. Insulation treatment between six-panel hull, main keel, skin and ground. Among them, top and wall plates are made of 2.0mm thick cold rolled steel sheets, bottom plate is made of 3.0mm cold rolled steel sheets, and bearing keel is made offrom a steel profile. .

Process features:

A. All modules of device are bent and shaped in such a way as to provide greatest possible control of welding deformation on welded edge;

B. The herringbone lap joint technology is adopted, and welding process uses CO2 shielding gas welding to ensure that weld and body are slightly deformed, and to ensure that surface of steel plate is flat indoors.

C. The door frame is welded from various steels and steel keels, forming a self-supporting structure;

D. It is necessary to carry out strict anti-corrosion treatment inside and outside protective shell, and long-term use will ensure no rust;

E. The protective shell and frame are stable and reliable, long-term use guarantees performance, and overall mechanical performance meets following requirements: steel sheet unevenness ≤ 4mm/2m2, steel sheet verticality ≤ 10mm, body seismic index ≥ 8;

2: Screen door

(1) Manual mesh door

Structural features:

a. The lock is a two-point locking structure equipped with hinged pages and handles to realize rotational movement of door.

b.Using single-pole plug-in electromagnetic seal technology, composite knife edge, knife edge is made of high quality cold-rolled steel plate with good magnetic conductivity. After copper plating, it has good electrical conductivity and magnetic conductivity at same time, ensuring that screen door has excellent magnetic and electric field shielding properties.

c. Both knife edge and tongue contact part are made of same material, potential difference is similar, and there will be no electrical corrosion on contact surface, which can provide protection for a long time and improve reliability.

d.The reed is a detachable beryllium bronze tongue with a three-row structure. After vacuum heat treatment, it has good elasticity and wear resistance. It can effectively form an electromagnetic seal cavity, and electromagnetic seal is reliable. knife blade and cane After 30,000 connect and disconnect tests, it can still meet requirements of use. It is easy to replace after aging or damage, and length of each section is 180mm.

e. This screen door shape is a typical structural shape, and design process is relatively mature.

Classification and presentation of computer room low-current shielding functions

Shield Effectiveness:

Magnetic field: 14kHz≥70dB/150kHz≥100dB

Electric field: 200 kHz-50 MHz≥110 dB

Plane Wave: 50MHz-1GHz≥100dB

Microwave: 1 GHz - 10 GHz ≥100 dB - 10 - 18 GHz ≥ 90 dB

(2) Fully automatic mesh door

Structural features:

Automatic double track design, DC stepping motor, door leaf moves horizontally and vertically when door starts to open and close. The whole process is controlled by Mitsubishi PLC and touch screen, with simple operation, multi-point encoder and emergency stop device, multiple protections, accurate and stable operation, safety and reliability, and size can be customized according to user requirements. .

Classification and presentation of computer room low-current shielding functions

Shield Effectiveness:

Magnetic field: 14kHz≥75dB/150kHz≥100dB

Electric field: 200 kHz-50 MHz≥110 dB

Plane Wave: 50MHz-1GHz≥110dB

Microwave: 1 GHz-10 GHz≥100 dB

3: Ventilated Waveguide Window

Ventilation panels with honeycomb cut-off waveguide are mainly used in ventilation openings of electromagnetic protection facilities. They perform dual function of good shielding and ventilation. Different materials, coatings and shapes can be selected according to different occasions and conditions.

4: Network filter

Performance indicators

The biggest difference between coated safety glass and wire mesh safety glass is difference in light transmittance and shielding index. The biggest advantage of coated safety glass is that light transmittance is over 90% and shielding efficiency is up to about 30db, wire mesh safety glass The advantages of shielding efficiency are above 50db, but current maximum light transmittance is about 80%. The light transmission efficiency of screen glass with a screen effect of more than 70 dB is only about 40%. Users usually select window varieties according to specific design specifications. Used to stabilize output voltage of power supply, it can be basically understood as AC blocking and DC conducting. In case of an AC source, bandwidth is a single frequency.

5: Signal Filter

Main function:

The main function of signal line filter is to solve problem of cosmic electromagnetic interference, for example, when equipment emits strong electromagnetic interference into space or equipment is sensitive to cosmic electromagnetic interference. The connection between signal line cable and power line cable shown above causes conducted radiation to exceed standard at high frequencies, which is caused by high frequency interference on signal line connected to power line in space.


The signal filter is used to filter useful signal from input signal in order to filter out useless signal and noise interference. The principle is to use frequency response of loop, set range of its bandwidth to range of useful signals, and filter out other spectral components.

Classification and presentation of computer room low-current shielding functions

6: Shielded cabinet

Classification and presentation of computer room low-current shielding functions

(1), it can effectively suppress electromagnetic radiation leakage of information processing equipment such as computers, servers, switches, routers, etc., protect information security, and has strong electromagnetic interference protection and protects operators from electromagnetic radiation. damage;

(2) The product integrates technologies such as shielding, isolation, filtering, wave absorption and grounding, which can effectively suppress leakage of electromagnetic signals from network equipment and ensure security of confidential information;

(3), its electromagnetic shielding performance reaches level B in military standard GJB5792-2006 "Classification and measurement method of electromagnetic shielding body for military secret information system";

(4), beautiful appearance, convenient operation and high cost. Regardless of scale and complexity, it provides users with a more perfect, convenient and secure environment;

(5), main structural elements: a. Protective shell: fully sealed box, welded from cold-rolled steel sheets, undergone anti-corrosion treatment such as zinc plating and spraying; b. Security door: The material is carefully processed and door screen is made up of machined shielding tabs and door panels welded with cold rolled steel plates, C. Filter: The power supply filter has a wide rejection bandwidth and high insertion loss, d. Ventilation Waveguide Window: Honeycomb Ventilation Waveguide The window, top and bottom are equipped with 4 miniature axial exhaust fans to provide powerful exhaust;

Classification and presentation of computer room low-current shielding functions

7: Waveguide

For integrated wiring system, optical cable enters shielded computer room. The optical cable enters shielded computer room through waveguide, and waveguide length L is greater than 6d. Through optical transceiver in shielded computer room, electrical signal is converted into an optical signal, and then optical fiber passes through cut-off waveguide, and optical signal is converted into an electrical signal outside shielded computer room.

Third, shielded computer room construction standards

1: Extended

The focus of company's excellent design force, fully certified project, carefully designed, carefully selected, carefully built to ensure that each project in project is current first-class, moderately advanced, and computer room system can last a long time work efficiently.

2: Reliability

The use of high-quality materials, superior performance equipment and standardized construction technology, especially taking full advantage of computer room system engineering anti-interference protection and quick addition in case of accidents, to ensure that all connections are safe and reliable

3: Standard

Designed in strict accordance with relevant national standard "Computing Station Site Specification", drawing files are standardized and safe, and symbols and signs common to national standard are used to achieve universality, adjustability. , and convenient maintenance, and have detailed documentation.

4: Practicality

After implementation, division of computer room is reasonable, and technological process is as simple as possible, system wiring is thoughtful, comprehensive, convenient and flexible, and materials of different grades are selected according to requirements of each function Based on a complete consideration of ideal functioning of computer room system, its cost-effectiveness is optimal .

5: Scalability

This system can not only support existing system, but also have enough room for expansion in terms of spatial layout, network bandwidth, ports, etc., to facilitate further development of system and adapt it to future system. updates.

Fourth Screened Computer Room Acceptance Criteria

1: Classification criteria

a: When divided by function, room with an electromagnetic shield can be divided into two types: stationary and mobile.

b: Depending on engineering design of protective housing, electromagnetic shielding rooms can be divided into prefabricated, welded, direct-attached, etc.

2: Composition of standards to be achieved

CAir conditioning system: The air conditioning system can be installed separately or can be entered directly through waveguide window. However, power supply line of air conditioning unit, signal control line of indoor and outdoor installation, and air and water pipes must be shielded.

Fire alarm system: its alarm and associated control signal must be filtered.

Ground system: Single point grounding is required, and grounding resistance generally cannot exceed 1 ohm.

Power supply system: There must be a power supply system and an auxiliary power supply, and power supply cannot pass through leakage protection device.

3. The standard that parameters must conform to

Frequency range: 14 kHz, shielding efficiency: ≥70 dB.

Frequency range: 200 kHz, shielding efficiency: ≥100 dB.

Frequency range: 450KHz-50MHz, shielding efficiency: ≥100dB.

Frequency range: 50-100MHz, shielding efficiency: ≥100dB.

4: Reference standard

"Specification and Test Methods for Electromagnetically Shielded Rooms for Processing of Confidential Information" BMB3-1999

"General technical requirements and methods for testing rooms for electromagnetic shielding for military purposes" GJBz20219-94

"Electromagnetic Impulse Protection Design Rules" GJB3928-2000

"Measurement Method for Shielding Effectiveness of High-Performance Shielded Room" GB12190-90

5. Maintenance Method

1. The power supply of filter does not need to be connected to a leakage protection device, but it can be connected to a load breaker; if filter fails, power must be disconnected and then discharged before maintenance or replacement.

2. After product has been put into operation, it is strictly forbidden to subject it to strong impacts or make holes in shield.

3. It is strictly forbidden to penetrate opening of shielded waveguide with metal cables or pipes.

4. Keep edge of knife and notch on mesh door clean to ensure good mesh room performance.

5. Maintenance and cleaning method: wrap tongue part with a sheet of moisture-proof material, wrap it with degreasing gauze, moisten it with absolute alcohol, insert into groove and pull back and forth to wipe.

6. In order to ensure flexibility of opening and closing external transmission parts of mesh door, it should be lubricated irregularly.

7. If a tongue is found, loosen screws of tongue rod in time, remove damaged tongue and replace it with a new one.