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EMC means "an electronic or electrical product shall work as intended in its environment. The electronic or electrical product shall not generate electromagnetic disturbances (interference), which may influence other products". In other words, EMC deals with problems of noise emission as well as noise immunity of electronic and electrical products and systems. Electromagnetic disturbances occur as conducted interference as well as radiated emissions and immunity problems.

The term conducted emissions refers to the mechanism that enables electromagnetic energy to be created in an electronic device and coupled to its AC power cord. Similarly to radiated emissions, the allowable conducted emissions from electronic devices are controlled by regulatory agencies. If a product passes all radiated emissions regulations but fails a conducted emissions test, the product cannot be legally sold.

The term radiated emissions refers to the unintentional release of electromagnetic energy from an electronic device. The electronic device generates the electromagnetic fields that unintentionally propagate away from the device’s structure. In general, radiated emissions are usually associated with non-intentional radiators, but intentional radiators can also have unwanted emissions at frequencies outside their intended transmission frequency band.

Conducted Immunity (also called Susceptibility) is a measure of the ability of electronic products to tolerate the influence of conducted electrical energy from other electronic products and electromagnetic phenomena.

Radiated Immunity (also called Susceptibility) is a measure of the ability of electronic products to tolerate the influence of radiated electrical energy from other electronic products and electromagnetic phenomena.

Simulates disturbances created by radio transmitters operating below 80 MHz (such as AM broadcast transmitters) that would typically be coupled onto a products interface cables.


Test Method

The test signal, amplitude modulated by a 1 kHz sine wave, is injected onto the AC or DC wires via a Coupling, Decoupling Network (CDN) while the frequency is varied. Unshielded cables can be tested using either a CDN, coupling clamp or current injection probe. Shielded cables are tested using direct injection, the signal is coupled through a 100-Ohm resistor onto the shield of the cable under test. The injection level is pre-calibrated using the appropriate calibration jig and is equivalent to the open circuit voltage at the output from the amplifier for an unmodulated signal.


The test level for the residential, commercial and light industrial generic standard is 3 Volts; for heavy industrial equipment the test level is 10 Volts.

Simulates disturbances created by radio transmitters such as cellular telephones, walkie-talkies, HAM radios, etc.


Test Method

The product is placed in a nominal test field. The field is swept across the frequency range, defined in the product or generic standard and is amplitude modulated by a 1 kHz sine wave (unless the product/generic standard specifies otherwise). The test field is pre-calibrated without a product in the test chamber. The test field must meet +6dB uniformity. The test levels are 3V/m and 10V/m.


The EUT is positioned so that the side under test is in the plane of the calibrated field. The test is repeated on each side of the EUT.

Electrostatic discharge (ESD) is the sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown. A buildup of static electricity can be caused by turbocharging or by electrostatic induction.

Simulates electrostatic discharge events directly to the product, or to a nearby conductive surface.


Test Method

The ESD test requires that discharges be made to all exposed surfaces of the EUT, including connector back shells. Contact discharge is to the conducting surfaces of the product and air gap discharges are to non-conducting surfaces. The test also requires that contact discharges be made to a horizontal reference plane and vertical reference plane at locations 10cm from the front, rear and sides of the EUT. The ESD Simulators/Generators/Guns can be used for ESD Testing.


Typical rise time of the ESD pulse waveform is approximately 0.7 - 1nS with a hold time of 30 - 60 nS. (See image)

 


The test simulates ESD events that occur when the user touches the equipment under test or nearby metallic objects (e.g. filing cabinets). The test levels for both the heavy industrial and light industrial/commercial/residential standards are ±2kV and ±4kV for the contact discharge method and ±2kV, ±4kV, and ±8kV for the air gap discharge method.

A transient event is a short-lived burst of energy in a system caused by a sudden change of state. The source of the transient energy may be an internal event or a nearby event. The energy then couples to other parts of the system, typically appearing as a short burst of oscillation.


In electrical and electronic engineering such electromagnetic pulses (EMP) occur internally as the result of the operation of switching devices. Engineers use voltage regulators and surge protectors to prevent transients in electricity from affecting delicate equipment. External sources include lightning (LEMP), electrostatic discharge (ESD) and nuclear EMP (NEMP).


Within Electromagnetic compatibility testing, transients are deliberately administered to electronic equipment for testing their performance and resilience to transient interference. Many such tests administer the induced fast transient oscillation directly, in the form of a damped sine wave, rather than attempt to reproduce the original source. International standards define the magnitude and methods used to apply them.

Simulates high frequency electrical disturbance on power and signal lines due to the switching of inductive loads on the AC line.


Test Method

The test waveform consists of a 15ms burst of pulses at 300ms intervals. The pulses have a rise time of 5ns and a dwell time of 50ns, with a repetition rate of 5 kHz.


For heavy industrial equipment the test levels are:

  • AC lines; ±2kV
  • DC lines;
  • ±2kV Signal lines on cables that could be longer than 3m; ±1kV
  • Process control lines and measurement lines; ±2kV

Noise is directly injected onto power lines through a capacitor and capacitive coupled onto I/O lines using a coupling trench. DC power ports connected to an AC-DC power adapter are not tested.

Surges, or transients, are brief overvoltage spikes or disturbances on a power waveform that can damage, degrade, or destroy electronic equipment within any home, commercial building, industrial, or manufacturing facility. Transients can reach amplitudes of tens of thousands of volts.

Simulates low frequency, high-energy electrical transients on power lines and long distance I/O lines (such as telephone lines) coupled from nearby lightning strikes.


Test Method

Test is applied to AC and DC power ports. The open circuit signal wave-shape has as 1.2µs rise time and 50µs hold time. Surges are applied in common mode (line-to-ground) and in differential mode (line-to-line). All surges are synchronized to the 0°, 90°, 180° and 270° phase angles of the AC voltage. DC power ports are not tested if they are connected to an AC-DC power adapter, in which case the AC-DC adapter should be submitted for testing.


Test levels for the residential, commercial and light industrial generic standard are 2kV common mode and 1kV differential mode on AC power lines. For DC power lines, the test levels are 0.5kV for both differential and common mode. Although the test is not currently required for the heavy industrial generic standard, it suggests test levels of 4kV common mode and 2kV differential mode.

Simulates brown outs and blackouts on AC power lines.


Test Method

This test is applied to AC power ports rated at less than 16 amps per phase. All voltage shifts are synchronized to the zero crossing of the AC voltage.


Typical test levels for the generic light industrial standard involve a 30 percent dip in the line voltage for 10ms, 60 percent dip for 100ms and dropout for 5000ms. There are currently no requirements for Heavy Industrial equipment.

All linear amplifier systems, when given a sufficiently strong input signal, will reach a point where the system departs from a linear relationship between input and output. At this point the system is said to be going into compression or beginning to saturate. Beyond this point, the linear relationship between input and output is no longer valid and the amplifier is no longer considered to be linear. An internationally recognised figure of merit, used for defining the extent of linearity of an amplifier, is the 1dB compression point. This is the point of –1dB departure from linearity. The output power of an amplifier cannot increase indefinitely and when an increase in input power generates no discernible increase in output power, the amplifier is said to be saturated, and by definition the output is not proportional to the input signal. This point is often referred to as Psat on a datasheet or sometimes P3dB. Generally, saturated power is of importance when considering the pulsed power requirements in something like automotive testing while linear power is of importance when considering the AM (amplitude modulation) waveform used in commercial EMC testing.

Spurious signal products are those introduced by the amplifier but which are non-signal related i.e. they are neither harmonics nor IM products. They may be caused by a low level instability in the amplifier (evidence of poor design) or they may be introduced into the amplifier from external sources e.g via the power supply, radiated interference or even local lighting. Spurious signal power is usually defined at a level relative to the fundamental signal and levels of minus 70dBc are typical for a good amplifier design. The most likely source of spurious in a well-designed amplifier will be the switching power supply, generating spurs at it’s operating frequency – which is usually 100’s of kHz. The area between the maximum spurious power level and P1dB, is the usable range over which the test engineer can be confident that the device under test is subjected only to an amplified reproduction of the input signal i.e. that it is not being modulated by the presence of spurs or high harmonic levels.

Having ascertained the definition of power, in terms of Psat and P1dB, and determined the potential usability of the product (with respect to harmonic distortion), the next area requiring attention are the parameter qualifiers attached to the data entries on the amplifier data sheet. There are several qualifiers of particular interest that are in general usuage. These are rated, typical and guaranteed minimum the qualifier “rated” is essentially meaningless from a user perspective – it is the descriptor that the manufacturer has assisgned to a product and it comes with no guarantees of performance. It is a term that is best ignored when making a purchasing decision.


The descriptor “typical” (or “nominal”) has widespread usuage.  In general terms it describes the most likely occuring value within a process which outputs a product of naturally occuring variances.  The output variation of such a process can be described in terms of a distribution around a mean (or typical) value.

An anechoic chamber is a room designed to completely absorb reflections of electromagnetic waves used for various EMC Testing. They are also insulated from exterior sources of noise. The combination of both aspects means they simulate a quiet open-space of infinite dimension, which is useful when exterior influences would otherwise give false results. The RF anechoic chamber is typically used to house the equipment for performing measurements of antenna radiation patterns, electromagnetic compatibility (EMC) and radar cross section measurements. EMC chambers allow for the performance of fast and efficient EMC radiated tests at a convenient location, without interference from the ambient electromagnetic environment.

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