Influence of electromagnetic interference on structured cabling systems

Today, companies are highly dependent on computer networks. In fact, they can hardly run effectively without high-tech electronic devices. Once purchased, the reliable operation of these electronic devices becomes crucial. System faults will not only lead to loss of business opportunities or reduction of production efficiency, but also cause a rapid decline in user confidence in the system. As a result, the user either tries to avoid the network and thus cannot gain all commercial advantages, or replaces the system with a more reliable product, resulting in additional costs.

The focus on electromagnetic compatibility (EMC) and the power to develop standards stems from the rapid growth of electronic devices, such as personal computers and local networks, from the increasing data rates of these devices. More importantly, the use of portable electronic devices has also experienced explosive growth, bringing unpredictable risks to the communication environment.

Modern electronic systems are mostly based on computers or microprocessors, which usually have harmful effects on high-frequency signals in the system. These effects come from the electromagnetic induction caused by the conducting current or electromagnetic field in the interface cable of another system. In addition, the system using digital electronic devices contains current and voltage High-Speed Switching circuits, which may lead to high-frequency electromagnetic radiation.

The topic of this article is electromagnetic compatibility EMC. It aims to enhance the understanding of electromagnetic compatibility EMC and related standards, and to discuss the impact of electromagnetic compatibility EMC on the wiring system.

Electromagnetic Effect

Electromagnetic effects can be divided into two categories. Category 1 refers to the ability of an electronic device to be faulty or damaged due to electromagnetic induction voltage and current, or to be immune to such faults or impacts. The second category is related to unnecessary electromagnetic noise emissions.

Today, the application of electronic devices has reached an unprecedented level. The reliability and fault resistance of the system may significantly affect the security, production efficiency, and reliability.

Apart from the electromagnetic radiation sensitivity of equipment or systems, the other important point is that electromagnetic radiation that significantly exceeds the normal signal level shall not be produced, either conducting or radiating. At present, many countries control it through strict legal means

What is electromagnetic interference?

Electromagnetic interference (EMI) has a wide range of meanings. It is the cause of the temporary or permanent failure of the electronic system. Its root cause may be the natural or man-made electromagnetic environment of the relevant system, it may also be the accidental induction of current and voltage from other devices through the interface cable.

High-frequency currents flowing through electronic and electrical systems may also cause electromagnetic interference. If the system is designed to withstand electromagnetic threats in the operating environment and does not emit electromagnetic radiation that exceeds the specified level, the system design complies with the electromagnetic compatibility standards.

To protect each device from any electromagnetic interference, the cost will be very high. This is the first step in the design to determine the level of protection required and evaluate the electromagnetic environment of the equipment.

Radiation

The time-varying Charge Distribution and current will generate electromagnetic waves. All electrical and electronic devices and systems contain wires that support time-varying currents and voltages. Therefore, more or less electromagnetic radiation is produced, depending on the following factors:

◆ Variable voltage and current size

◆ Wire length

◆ Voltage and current variation rate

◆ Ry layout between wires in the system and their relative grounding datum points.

It should be noted that, due to the rapid changes in current and voltage during the switching operation, even the DC (DC) system and the very low frequency system may produce significant electromagnetic radiation. This may cause a transient interference source.

Sensitivity

In order to find out the reasons for increasing sensitivity of modern electronic devices, we must first consider the huge progress made by miniaturization technology. Thanks to this progress, the power required to execute the same complex task is reduced, which means that the voltage and current used to transmit signals between the device and the device are also greatly reduced. Unfortunately, the results increase the significance of the interference signal. In addition to reducing the power level, miniaturization also shortens the distance between different regions of the equipment, thus increasing the interference probability.

Another factor that increases system sensitivity is the increase in circuit bandwidth, which is the result of faster processing. As mentioned above, this will not only generate useless electromagnetic (EM) radiation, but also make the system useless to respond to a wider frequency.

When the magnetic element in the electromagnetic field is combined with the loop in the electronic system, the induction voltage is generated. In addition, the normal wire that is aligned with the electric field element or the normal wire in the electric field element, such as reaching a certain length, this will generate an induction current. For systems with operating signal levels of several volts and/or operating current of several microamps, It is very vulnerable to electromagnetic interference if preventive measures are not taken. Many measures used to avoid sensitivity problems can also reduce electromagnetic radiation.

Electromagnetic interference Solution

As mentioned above, the comprehensive solution to the electromagnetic interference problem depends on the nature of the equipment and the disturbance resistance specifications to be followed.

All aspects of the design must be taken into account, from circuit boards to connectors, from cabinets to power supplies and interface cables.

The following are all design factors that help enhance the overall performance of the system, as are the active electronic devices and wiring systems:

◆ Printed Circuit Board Design

◆ Cabinet Design

◆ Connector Technology

◆ Power supply and interface cable

This article discusses the design of the interface cable.

Electromagnetic compatibility standards

The following are four categories of electromagnetic compatibility standards:

◆ Basic Standards

◆ General standards

◆ Product series standards

◆ Product Standards

General Standards, product series standards and product standards should refer to basic standards in terms of testing methods. The following are the standards related to lan and related equipment testing and compliance:

Radiology standards

◆ Iec cispr 22 or EN 55022-limitations and measurement methods on RF interference characteristics of information technology equipment

◆ IEC/EN 61000-6-3-General radiation Standard Part 1: residential, commercial and light industrial environments

◆ IEC/EN 61000-6-4-General radiation standards Part 2: Industrial Environment

Anti-disturbance Standard

◆ Iec cispr 24 or EN 55024-product standard: anti-disturbance degree of information technology equipment

◆ IEC/EN 61000-6-1-General anti-disturbance Standard Part 1: residential, commercial and light industrial environments

◆ IEC/EN 61000-6-2-General anti-disturbance Standard Part 2: Industrial Environment

◆ IEC 61000-4-basic electromagnetic compatibility Standard Series

Part 2: electrostatic discharge (ESD) Immunity Test

Part 3: test the immunity of the radiation field

Part 4: electrical fast transient pulse group (EFT)/burst immunity test

Part 5: Electrical disturbance resistance test

Part 6: conductive field immunity test

Part 8: electrical frequency magnetic field immunity test

The most common LAN hardware and structured cabling radiation and disturbance resistance standards are EN 55022 (iec cispr 22) and EN 55024 (iec cispr 24 ). EN 55022 specifies the requirements for radiation and conducting radiation in A and B environments. "Class A" corresponds to the commercial environment, and "Class B" refers to the residential environment.

Electromagnetic Compatibility and customer building Wiring

Most cable installers install passive systems such as cables, connectors, distribution frames, and sockets. Therefore, there are some problems in testing the electromagnetic compatibility of installed cabling networks. Computers and communication devices are usually connected to the installed cabling system by the network owner, rather than directly controlled by the wiring installer. Electromagnetic compatibility is the responsibility of manufacturers of networked computers and communication devices. Network cabling has clearly defined regulations such as 5e and cat6 cables. Therefore, the connection environment for computer equipment manufacturers to process is also very clear.

The electromagnetic compatibility of the cabling system can be considered as follows:Bytes

The manufacturer of electronic devices/systems considers the wiring specifications related to electromagnetic compatibility certification. Then, determine the product description for connecting different types of cables, such as 5e or 6 UTP.

The cabling system supplier is responsible for providing "System Integration" services and ensuring the overall system performance.

The Committee on all Cabling Standards will continue to investigate the electromagnetic performance of cabling systems. New and future versions of the current standard will include performance requirements and parameters to achieve outstanding electromagnetic performance.

Four Potential fields are:Bytes

The purpose is to control the differential-to-common-mode conversion limit of RF emissions. The opposite is anti-disturbance control)

Shielding system shielding effect cables plus connectors plus coupling attenuation and/or transmission impedance produced by connecting hardware)

Shielding System Integrity

Grounding specification for shielded cabling

In addition to such standards, the user shall also ensure that:

Electromagnetic compatibility between active and passive Products

Compatibility between cables, connectors, and connected hardware

Cabling must comply with relevant design and installation standards

Methods To overcome Electromagnetic Compatibility

A special problem with Lan is the interconnection with multiple cabling systems. As far as electromagnetic signals are concerned, cables are just an antenna that can effectively transmit common-mode signals. Therefore, the main purpose of LAN design must be to effectively limit such signals.

There are two common ways to ensure electromagnetic compatibility for communication links that do not include coaxial cables and optical cables-shielded twisted pair wires (FTP/STP) and unshielded twisted pair wires (UTP ).

In principle, the shielding system stores the entire link in a metal shielding body, and thus seems to be able to provide optimal electromagnetic compatibility control. In this solution, the external noise causes the current to flow in the shield body, and the result is an equivalent current with opposite polarity in the signal wire. This current flows through the impedance of the wire and shield body, generating noise voltage. When the whole loop includes the Grounding Connection of the shielding body) is collected, the noise voltage on the wire will offset the voltage on the shielding body. Unfortunately, to ensure the effectiveness of the shielded cabling system, the shielding body must be properly grounded at each end, which generally violates safety or other requirements. In addition, for complex installation systems, it is difficult to ensure that the shielding integrity remains unchanged. The shielding method adopts the "faradatag" Mode: place a conductive shielding body around the wire and all related interfaces. However, this mode depends largely on the integrity of the conductive shielding body and the grounding mode and location of the shielding body. It should be noted that the shielding body is also a conductor. If it fails to be properly processed as a shielding body, it will also transmit signals, transmit or accept noise like any other conductor. The following conditions must be met when you consider shielding the building cabling system:

◆ Proper cable Shielding Design

◆ Correct connector design

◆ The cables at the connector are correctly prefixed.

◆ Detailed installation procedures

◆ Clean power supply available

◆ Good grounding system available

◆ Good grounding Program

◆ Keep the Grounding Impedance low

The effectiveness of the UTP cable depends on the balance of the cable itself, and more importantly, the balance of the interface circuit. The differential signal is placed on a pair of cables at the transmitter end, and the two cables in the line pair are twisted to maintain high matching throughout the link. When this technology is used, any external noise will have the same impact on the two cables in the line. This is called common mode noise ). At the receiver end, the differential signal in the line pair is interpreted as data, while most common mode noise can be offset, or filtered out and ignored. This factor is taken into consideration in the design of the interface circuit, because it is a place where differential data signals are used to convert to useless common mode signals.

The purpose of balanced transmission is to ensure that an equivalent signal of the opposite polarity is generated on the twisted pair wire. These signals generate an Equivalent Electromagnetic Field with opposite polarity, and these magnetic fields offset each other, resulting in Zero radiation on the twisted pair. In addition, balanced transmission makes the noise effects on the two wires equal. As a result, the net noise signal is not transmitted to the receiver interface. Generally, the better the system balance, the less radiation the system has, and the stronger the anti-noise capability. As a cost-effective method to improve electromagnetic compatibility, the balance method is often ignored. For unused cable pairs at the interface, the common mode connection technology is usually used in electronic devices. The purpose is to provide a proper common-mode Grounding Impedance for the line pair to reduce the loop antenna of the common-mode signal and maintain balance for the unused line pair. Facts show that this method can greatly improve the electromagnetic compatibility of the system. It is also the method recommended by the LAN Standards Committee for all high-speed applications.

In fact, it is impossible to make the system in a perfectly shielded or perfectly balanced state. As with most technical questions, there is also an engineering compromise that requires careful assessment to find the best answer to a series of established conditions. The balanced UTP system is designed to achieve the highest possible anti-disturbance performance on the Interface electronic components and wiring components, cables, connectors and interconnected hardware, the practice of electronic designers to ensure the optimal electromagnetic compatibility of devices has become a standard practice. Thanks to this popular design model, UTP system installation and maintenance are more convenient and cost-effective. On the other hand, the FTP/STP system depends on the signal channel itself at the endpoint. From the transmitter to the receiver, including the terminal electronic components), the shielding performance of the link must be maintained; otherwise, the shielding effect will be greatly reduced. The installer must evaluate the system defects of each link. During installation, it is extremely difficult to verify the integrity of the shielding, so it is difficult to detect or correct defects. In addition, the design and structure of the shielding body also determine the performance and cost of wiring components and installation.

Electromagnetic compatibility and the US Solutions

When used in conjunction with the U. S. wiring system, well-designed, well-manufactured, installed IT equipment will meet the electromagnetic compatibility requirements. Although radiation tests in controlled laboratory environments may not take into account all the variables encountered on site, the cabling systems of the company have been successfully installed in many of the worst commercial and industrial environments, demonstrate good external noise immunity and no interference problems.

S. Government has conducted a comprehensive independent test of its cabling system. Both cables and connectors are verified independently and comply with the current international Cabling Standards. Although most electromagnetic compatibility standards do not apply directly to cabling systems, extensive tests conducted by the company provide a benchmark that allows manufacturers of active electronic components to focus on the compliance conditions of their devices.

To solve the electromagnetic compatibility problem and to ensure that the U. S. SYSTIMAX wiring system meets the current and subsequent electromagnetic compatibility requirements, we launched a u. S. SYSTIMAX electromagnetic compatibility test plan in 1990. Since then, we have made changes to ISO 8802-3 10BASE-T, 100BASE-T, 1000BASE-T, ISO 8802-5 16 Mb/s ring, ISO 9314 (ANSI X3.263) 100 Mb/s TP-PMD LAN and 155 Mb/s LAN compatible with ATM Forum were tested. Tests show that the customer of SYSTIMAX can eliminate any worries because their cabling systems comply with all standards.

The United States of America has released the channel performance guarantee, design and installation documentation and on-site test guide documentation, providing a strong backing for its solutions. These documents are essential, especially if the fixed device needs to comply with the EU's current electromagnetic compatibility Directive (2004/108/EC. In addition, has included electromagnetic compatibility compliance requirements in its SYSTIMAX application guarantee plan.

All in all, we provide the following suggestions for users who want to ensure that their networks meet the electromagnetic compatibility requirements. The main cause of radiation is the device connected to the LAN cabling system, such as the transceiver, hub, and PC. These devices must be tested and comply with the appropriate electromagnetic compatibility standards and have CE marks, an EU compliance label), installed correctly and used for intended purposes. The source system must comply with electromagnetic compatibility specifications, regardless of the type of UTP, FTP, or STP cable), as long as the device connected to the cabling system is designed to connect such cables and are certified. Installation of relevant cabling systems shall be based on the manufacturer's guide and/or recommendations for international, U.S. and EU Cabling Standards. It should be noted that the electromagnetic compatibility of the cabling system can be affected by the system installation method, especially for the FTP/STP cabling system. Although each user has different requirements, it is very important to choose a vendor system that can provide end-to-end performance guarantee. Such guarantees should also include detailed design, installation, testing and product documentation support.

1. Structured Cabling System and Its Application
2. Understanding structured cabling