15-06-2012, 12:08 PM
EMBEDDED SYSTEMS
Embedded systems .docx (Size: 60.44 KB / Downloads: 38)
Abstract:
Embedded systems can exist in environments that are very harsh and noisy, which can lead to potential problems with electromagnetic interference (EMI). EMI consists of any unwanted, spurious, conducted, or radiated signals of electrical origin that can cause degradation in equipment performance. Because of these problems, all components must comply with specifications to ensure electromagnetic compatibility (EMC), and there are numerous design methods that can be used to prevent EMI. During the development life cycle of an embedded system, the product must be designed to comply with EMC standards, and the product must also be tested for EMC. In addition, other forms of environmental reliability testing must also be performed to ensure dependable system performance in its natural environment. Currently, there is still work to be done to harmonize various EMC standards to reduce trade barriers between countries and different use sectors, like Defense and Civilian. Therefore, care must be taken in developing embedded systems for compliance with the appropriate standards.
Introduction
Embedded systems exist in a wide variety of environments. Because of this, special care must be taken in developing embedded systems that they can operate functionally in their intended environment. Many embedded systems exist in very harsh and noisy environments, which can lead to potential problems with electromagnetic interference (EMI). EMI consists of any unwanted, spurious, conducted, or radiated signals of electrical origin that can cause unacceptable degradation in system or equipment performance. Electromagnetic compatibility (EMC) is the ability of systems to function as designed, without malfunction or unacceptable degradation of performance due to EMI withing their operational environment. Any electrical, electromechanical, or electronic equipment must not adversely affect the performance of any other equipment or system as a result of EMI and vice versa. Examples of EMC problems include a computer interfering with FM radio reception, an operating vacuum cleaner causing "snow" on TV, a car radio buzzing when you drive under a power line, an airport radar interfering with laptop computer display, and a telephone being damaged by lightning-induced surges on phone line. [emclab99] While the effects of EMI are sometimes minor, like momentary interference on television, other times the effect may be more catastrophic. For example, a serious consequence can occur if a signal interferes with the operation of a medical equipment that was being used to monitor a patient in intensive care.
The origins of EMI are electrical, with the unwanted emissions being either conducted (voltages or currents) or radiated (electric or magnetic fields). For EMI to occur, 3 essential elements must exist: an electrical noise (EMI) source, a coupling path, and a victim receptor. The coupling path from a source to a receptor can be in 1 of 4 categories: conducted (electric current), inductively coupled (magnetic field), capacitively coupled (electric field), and radiated (electromagnetic field). [emclab99] More details will be given below about the sources and receptors. EMI can occur in 2 different situations: intersystem EMI and intrasystem EMI. Intersystem EMI occurs between 2 or more discrete systems while intrasystem EMI occurs between elements in the same system. [Violette87]
Key Concepts
Sources of EMI
An EMI source can be any device that transmits, distributes, processes, or utilizes any form of electrical energy where some aspect of its operation generates conducted or radiated signals that can cause equipment performance degradation. Figure 1 shows a taxonomy of the different sources of electromagnetic interference. A brief description of each category will be given below. [Violette87]
Receptors of EMI
Any EMI situation requires not only an emission source but also a receptor. A receptor is also called a "victim" source because it consists of any device, when exposed to conducted or radiated electromagnetic energy from emitting sources, will degrade or malfunction in performance. Many devices can be emission sources and receptors simultaneously. For example, most communication electronic systems can be emission and receptor sources because they contain transmitters and receivers. Figure 2 shows a taxonomy of different receptors that are susceptible to EMI. Similar to the emission source taxonomy, receptors can be divided into natural and man-made receptors. A brief description of each category will be given below. [Violette87]
EMC Design Considerations
During the design process, engineers must be certain that the system is designed to comply to EMC standards. There are many design considerations that need to be taken into account. While it is not the point of this paper to give detail explanations about EMC design techniques, brief descriptions will be given simply for an overview. Engineers needing more technical details can refer to any EMC handbook.
Cable wiring and harnessing is a significant EMI concern. Cables are required to distribute electrical power and transmit electrical signals for the operation of various systems. Since cables are usually routed to accomodate its function, it is often difficult to quantify its environment and it usually varies over both frequency and electric and magnetic field amplitudes. Cables can be EMI radiating sources if they act as radiating antennas, or be susceptible to EMI if they are receiving antennas. Cables can also be coupling paths. In addition, cables are sometimes harnessed together, so interference can also be between two cables that are close in proximity. Therefore, their performance is very difficult to predict. Many specifications classify wiring or cable types into four to six categories but these classifications are generally qualitative in nature. More quantitative classifications should look at levels of power transmitted, or susceptibility of termination. [Violette87]
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Embedded systems .docx (Size: 60.44 KB / Downloads: 38)
Abstract:
Embedded systems can exist in environments that are very harsh and noisy, which can lead to potential problems with electromagnetic interference (EMI). EMI consists of any unwanted, spurious, conducted, or radiated signals of electrical origin that can cause degradation in equipment performance. Because of these problems, all components must comply with specifications to ensure electromagnetic compatibility (EMC), and there are numerous design methods that can be used to prevent EMI. During the development life cycle of an embedded system, the product must be designed to comply with EMC standards, and the product must also be tested for EMC. In addition, other forms of environmental reliability testing must also be performed to ensure dependable system performance in its natural environment. Currently, there is still work to be done to harmonize various EMC standards to reduce trade barriers between countries and different use sectors, like Defense and Civilian. Therefore, care must be taken in developing embedded systems for compliance with the appropriate standards.
Introduction
Embedded systems exist in a wide variety of environments. Because of this, special care must be taken in developing embedded systems that they can operate functionally in their intended environment. Many embedded systems exist in very harsh and noisy environments, which can lead to potential problems with electromagnetic interference (EMI). EMI consists of any unwanted, spurious, conducted, or radiated signals of electrical origin that can cause unacceptable degradation in system or equipment performance. Electromagnetic compatibility (EMC) is the ability of systems to function as designed, without malfunction or unacceptable degradation of performance due to EMI withing their operational environment. Any electrical, electromechanical, or electronic equipment must not adversely affect the performance of any other equipment or system as a result of EMI and vice versa. Examples of EMC problems include a computer interfering with FM radio reception, an operating vacuum cleaner causing "snow" on TV, a car radio buzzing when you drive under a power line, an airport radar interfering with laptop computer display, and a telephone being damaged by lightning-induced surges on phone line. [emclab99] While the effects of EMI are sometimes minor, like momentary interference on television, other times the effect may be more catastrophic. For example, a serious consequence can occur if a signal interferes with the operation of a medical equipment that was being used to monitor a patient in intensive care.
The origins of EMI are electrical, with the unwanted emissions being either conducted (voltages or currents) or radiated (electric or magnetic fields). For EMI to occur, 3 essential elements must exist: an electrical noise (EMI) source, a coupling path, and a victim receptor. The coupling path from a source to a receptor can be in 1 of 4 categories: conducted (electric current), inductively coupled (magnetic field), capacitively coupled (electric field), and radiated (electromagnetic field). [emclab99] More details will be given below about the sources and receptors. EMI can occur in 2 different situations: intersystem EMI and intrasystem EMI. Intersystem EMI occurs between 2 or more discrete systems while intrasystem EMI occurs between elements in the same system. [Violette87]
Key Concepts
Sources of EMI
An EMI source can be any device that transmits, distributes, processes, or utilizes any form of electrical energy where some aspect of its operation generates conducted or radiated signals that can cause equipment performance degradation. Figure 1 shows a taxonomy of the different sources of electromagnetic interference. A brief description of each category will be given below. [Violette87]
Receptors of EMI
Any EMI situation requires not only an emission source but also a receptor. A receptor is also called a "victim" source because it consists of any device, when exposed to conducted or radiated electromagnetic energy from emitting sources, will degrade or malfunction in performance. Many devices can be emission sources and receptors simultaneously. For example, most communication electronic systems can be emission and receptor sources because they contain transmitters and receivers. Figure 2 shows a taxonomy of different receptors that are susceptible to EMI. Similar to the emission source taxonomy, receptors can be divided into natural and man-made receptors. A brief description of each category will be given below. [Violette87]
EMC Design Considerations
During the design process, engineers must be certain that the system is designed to comply to EMC standards. There are many design considerations that need to be taken into account. While it is not the point of this paper to give detail explanations about EMC design techniques, brief descriptions will be given simply for an overview. Engineers needing more technical details can refer to any EMC handbook.
Cable wiring and harnessing is a significant EMI concern. Cables are required to distribute electrical power and transmit electrical signals for the operation of various systems. Since cables are usually routed to accomodate its function, it is often difficult to quantify its environment and it usually varies over both frequency and electric and magnetic field amplitudes. Cables can be EMI radiating sources if they act as radiating antennas, or be susceptible to EMI if they are receiving antennas. Cables can also be coupling paths. In addition, cables are sometimes harnessed together, so interference can also be between two cables that are close in proximity. Therefore, their performance is very difficult to predict. Many specifications classify wiring or cable types into four to six categories but these classifications are generally qualitative in nature. More quantitative classifications should look at levels of power transmitted, or susceptibility of termination. [Violette87]
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