CHOOSING
THE
CORRECT STANDARD
EMC standards are internationally harmonised however the extent of
adoption of EMC standards into the domestic regulations may vary
significantly between countries. In some cases, retesting will be necessary to
overcome national variations to the standards. This can be avoided by a well
planned EMC test and compliance program that also encompasses the national
variations of the target markets.
The ACA requires compliance with emission standards, no immunity requirements
are mandatory in Australia except for some medical devices.
*ACA/CISPR Standards
AS3548/CISPR 22/EN55022 :Information Technology Equipment. (ITE)
AS2064/CISPR 11/EN55011:Industrial Scientific and Medical (ISM) Equipment
AS/NZS 2557/CISPR 12 :Spark Ignition
AS/NZS 1053/CISPR 13/EN55013:TV, Radio Receivers
AS/NZS 1044/CISPR 14/EN55014:Domestic and Household Appliances.
AS/NZS 4051/CISPR 15/EN55015:Luminaires.
AS/NZS 1052/CISPR 16/EN55016:CISPR Measurement Methods and Apparatus.
AS/NZS 4251.1/EN50081-1:Generic Emission Standard.
AS/NZS 4052/CISPR 19:Microwave Ovens
*Non-ACA/CISPR Standards
AS/NZS4448/CISPR25: Vehicle Electronics, Protection of On-board Radio.
AS/NZS 4053/CISPR 20/EN55020:Immunity of TV
Contents
Compliance with immunity standards is mandatory for products to be sold
in any country of the European Union (EU). There is a very high cost in the
test facilities and the infrastructure required to adequately equip and
maintain an EMC test house with the capability to test to these standards. The
new IEC 1000-4 series of immunity standards has overcome the
deficiencies of the older IEC 801 series of standards however the cost
of establishment of the necessary test facilities is much greater. As the
new standards are published and as existing ones continually evolve, large
investment in capital equipment is required to upgrade existing facilities.
*Generic Immunity Standards
Published in Australia as
AS/NZS4053(EN55020) Immunity of TV, Radio and Audio Equipment
AS/NZS4252.1(EN50082-1) Generic Immunity Standard, Residential,Commercial, Light Industry.
AS/NZSxxx.2/(*EN50082-2) Generic Immunity Standard, Heavy Industry.
*Calls up basic EMC standards including the following:
ENV 50140 RF Radiated Immunity
ENV 50141 RF Conducted Disturbances
ENV 50204 Immunity to GSM/Pulsed RF
*Basic EMC Standards
IEC 61000-4-2 Part 2: Electrostatic Discharge Requirements
IEC 61000-4-3 Part 3: Radiated Electromagnetic Field Requirements
IEC 61000-4-4 Part 4: Electrical Fast Transient/Burst Requirements
IEC 61000-4-5 Part 5: Surge Immunity Requirements
IEC 61000-4-6 Part 6: Immunity to Conduct Disturbances Induced by RF Fields
IEC 61000-4-11 Part 11: Immunity to Supply Dips and Power Supply Variations.
Contents
Standards are updated continuously as their scope is increased and test
methods improved. Emission standards are derived from CISPR/IEC standards and
with few exceptions, they are adopted without change in Australia. (and most
other countries) Some minor national variations exist so it is recommended
that the status of the national standards with respect to the CISPR standards
be checked. This is particularly important when considering European (EN) or
Australian standards as there may be a lag of between 6 months to 2 years in their adoption as AS/NZS standards.
Contents
EMC test requirements for Australia are listed in the para 2.1 above and
they are met by application of the appropriate CISPR emission standard. The
purpose of emission testing is to verify that the product's spurious and
unintended emissions do not exceed a level that will interfere with the
operation of other electronic/electrical devices. In general, equipment is
classified as Class A (commercial/industrial) or Class B (Residential). The
Class A limits are relaxed by approximately 10 dB above the Class B limits.
* Conducted EMI Measurements
Conducted EMI is usually measured in the shielded enclosure with the device
configured such that all cables and peripherals are connected in a manner
consistent with normal operation. Conducted EMI is measured as the RF noise
voltage injected back into the mains supply by the device. Measurements are
made on both the active and neutral line in turn, over the frequency range 150
kHz to 30 MHz. The lower frequency extends to 9 kHz for some devices such as
lighting. The noise voltage must be below the limit set by the standard.
* Radiated EMI measurements
Radiated EMI must be measured at an open area test site (OATS) as defined in
CISPR 16/AS1052 or ANSI C63.4. This involves configuring the Equipment Under
Test (EUT) for normal operation, complete with all loads and peripherals. All
operating modes must be investigated and the worst case emissions from the
device must be measured. The measurements are usually performed with a
calibrated electric field strength measurement antenna at a distance of 10
metres from the EUT. The EUT is continually cycled through normal operations
while the Interference field strength emanating from it, is measured over the
range 30 MHz to 1000 MHz. The EUT is rotated about the azimuth so that the
direction of worst case radiation is captured. The emissions are further
maximised by adjusting the antenna height between 1 to 4 metres to detect the
maximum radiated interference field strength.
Ambient signals at the open area test site may mask the EUT emissions resulting
in inconclusive or flawed results. Preliminary or prescan measurements are
performed in the shielded enclosure, at known ambient frequencies to check for
the presence of emissions that may be masked by ambients at the OATS. EMC
Technologies Sydney (Colo) OATS has ambients well below the limit and this
allows rapid and accurate measurements.
It is not possible to perform a compliance test for radiated field strength in
a conventional shielded enclosure due to the gross measurement errors caused
chamber resonances and by reflections from the walls. A semi-anechoic
chamber, lined with RF absorber overcomes these problems however they cost
over $1 million so an OATS is much more economical. (and more accurate)
Contents
The proliferation of electronically controlled equipment in the
residential environments have forced governments to mandate standards to
maintain the quality and efficiency of the AC Power distribution systems. Mains
Harmonic emissions and the voltage flicker/fluctuations standards are mandated
by European EMC Directive 89/336/EEC for CE Marking purposes. In mid
1998, the scope of the EMC Directive is being extended to mandate compliance
with these standards for products intended for use in the commercial and light
industry environments. The EMC Framework Generic Emission standard
AS/NZS4251.1 (EN50081-1) calls up these standards however they
are currently excluded from the scope of the Australian regulations.
Harmonic emission and voltage fluctuation requirements apply to most products
used in a domestic residential environment including domestic appliances such
as refrigerators and washing machines, electric tools and other motor driven
devices. It also includes ITE, TV, Radio Receivers, Audio Amplifiers, devices
incorporating rectifiers, switching regulators, lighting equipment and
thyristor controlled devices.
Many designers currently lack knowledge on the performance of products against
these standards. Compliance can be difficult for some products particularly
switching regulator and thyristor controlled devices. Designers should
establish baseline levels and allow sufficient time for the development of
appropriate engineering solutions.
IEC 555-2/EN60555-2/AS/NZS2279-2: Harmonics, being replaced with-
IEC 1000-3-2:1994/EN61000-3-2 Harmonic Emissions
IEC555-3/EN60555-3/AS/NZS2279-3 Voltage fluctuations being replaced with-
IEC 1000-3-3:1994 Voltage Flicker and Fluctuations
Contents
Compliance with the EMC Directive requires that the device has an
adequate level of immunity to electromagnetic disturbances. This is best
achieved by testing to the appropriate immunity standards published in the
European Journal. (The European emission requirements are virtually identical
to the Australian EMC Framework so only the immunity tests need to be performed
once compliance with the Australian Framework has been established.)
Contents
The purpose of this test is to verify the product's immunity against
Electrostatic Discharge (ESD) generated by objects or persons coming into
contact with, or in the vicinity of the device. Persons or objects can
accumulate electrostatic charges which can reach to voltages above 15 kV.
Experience has shown that many unexplained malfunctions and damages are likely
to have been caused by ESD.
The EUT is subjected to ESD events by applying the discharge from the ESD
simulator to the surfaces of the EUT and in proximity to the EUT. The severity
level of the discharges is specified in the product standard and the EMC test
plan prepared by the manufacturer. The EUT is investigated for malfunction or
disturbance to all its operating modes. The pass/fail criteria must be defined
in the EMC test plan and are determined by the manufacturer of the product.
Contents
* Purpose of radiated Immunity Test
The purpose of this test is to verify the immunity of the product against
electromagnetic fields generated by radio transmitters, transceivers, mobile
GSM/AMPS cellular phones, and various industrial electromagnetic sources.
Radiated electromagnetic fields can be coupled into the interface cables which
provide a conductive path into the circuitry or they may be directly coupled
onto the printed circuit wiring when the assembly is not shielded. When the
amplitude of the RF field is sufficient, induced voltages and demodulated
carriers can disrupt the operation of a device.
* Performing the Radiated Immunity Test
This test is usually the longest and most difficult to perform, requiring very
expensive capital equipment and considerable expertise. As with other immunity
testing, pass/fail criteria must be defined by the manufacturer and a written
test plan submitted to the test house. The EUT must be arranged for normal
operation and in the most sensitive mode, while subjecting it to radiated
fields. Normal operation must be established within the test chamber while
exposing it to the leveled disturbance field as the frequency is swept over the
required frequency range of 80 MHz to 1000 MHz. Some radiated immunity
standards commence at a frequency of 27 MHz.
* Severity Levels
This standard normally requires immunity levels of 1 V/m, 3 V/m or 10 V/m
however equipment specifications may have there own requirements at particular
problem (interference) frequencies. It is in the manufactures interest for the
product to have an adequate level of immunity to radiated fields.
* Uniform Field Requirements
The new generic immunity standard EN50082-1:1997 calls up IEC/EN61000-4-3
which requires the establishment of a uniform test field over the area occupied
by the test sample. This is performed in an anechoic chamber lined with
ferrite absorber tiles, which serve to dampen reflections and resonances so
that a uniform test field can be established within the chamber. This
overcomes the deficiencies of conventional unlined chambers where reflections
and field gradients can cause sudden and often unrepeatable test failures. (The
semi-anechoic chambers are also ideal for accurate in-door precompliance
"no ambient" radiated emission measurements.)
* Semi-Anechoic Chamber Construction
The semi-anechoic chambers must accommodate the RF absorber on its walls and
ceiling. The mechanical and RF design specifications must accommodate the
very heavy ferrite tiles lining the chamber surfaces. The ferrite tiles are
mounted on a dielectric material and affixed to the chamber surfaces. In
unlined chambers, reflections from the metallic surfaces cause resonances and
standing waves which can produce peaks and troughs in the intensity of the test
field. Field gradients of up to 20 to 40 dB are common in unlined chambers and
this can induce sudden failure modes for what may appear to be a very low field
at the test sample. Chamber resonance results in poor test repeatability and a
high probability of "over testing". (This may result in the over design of the
product) These serious deficiencies are eliminated by the field homogeneity
requirements of the new immunity standard IEC61000-4-3.
* Hardware and Software Requirements for Field generation
High power broadband RF amplifiers are used over the frequency range of 26 MHz
to 2000 MHz to drive broadband transmitting antennas at a distance of 3 metres
from the device under test. Fully automated tests and calibrations are best
performed under software control to allow greater flexibility in the testing
and full control of all key parameters such as sweep rate, frequency dwell
time, modulation and field intensity. Software hooks allow synchronised
monitoring and stimulus of the EUT functionality. Interactive functions are
desirable so that real time changes in both the EMC test software and the EUT
parameters can be performed during the actual test. This user access feature
allows rapid logging of all test data for efficient evaluation and analysis
of the EUT EMC performance.
* Pyramidal Absorbers
The traditional pyramidal (cones) absorbers are effective however the large
pyramid dimensions leave an unacceptably small useable space within the
chamber. The length of the pyramidal absorber should be in the order of 100
cm for a lower frequency of 80 MHz, while lengths of over 2 metres are
required for operation at the lower frequency of 26 MHz. Clearly, the useable
space inside the chamber is severely reduced. The pyramidal absorbers also
have the disadvantage that they are fragile, easily damaged by bumping and also
highly flammable. The use of these absorbers on the floor of the chamber is
also impractical. Field strengths of over 200 V/m sustained for extended
periods of time result in a high risk of fire due to the heating of the
pyramidal absorber.
* Ferrite Tile Absorber
Ferrite tiles are space efficient however they add a considerable weight to
the chamber roof, walls and doors and consequently, the mechanical structure of
the chamber becomes significant. They operate effectively at low frequencies
however they become relatively in-effective at frequencies above 1000 MHz.
Ferrite tiles are very compact (100 mm by 100 mm by 6 mm thick) and withstand
field strengths of over 1000 V/m without the risk of fire hazards.
* Difficulties in Radiated Immunity Testing
There are inherent difficulties in performing radiated susceptibility
tests since the support equipment used to operate the EUT, provide stimulus
signals and to monitor its performance must itself be immune to the
susceptibility fields. This can often present difficulties, particularly when
the support equipment is complex and requires many cables and interfaces that
must connect to the EUT via penetrations through the shielded test chamber.
All cables penetrating the test chamber must be shielded and/or filtered in
order for them to be immune to the radiated test fields and to prevent the
degradation of the shielding performance of the test chamber. Compromising the
shielding performance of the test chamber will result in the unintended
radiation of the test fields into the environment and this may cause
interference problems to spectrum users. RF filtering of data or signal lines
is not always possible if there are high numbers involved or when high speed
data links are used. RF shielding of the test equipment and interface cables
can be difficult to achieve, even when using shielded interface cables since
the EUT configuration does not always lend itself to the maintenance of an effective RF shield.
* Personnel Safety Concerns - Non- Ionising Radiation
Electromagnetic fields within the test chamber may exceed the recommended
safety limits for exposure of personnel so an operator cannot be in the test
chamber to monitor the status or performance of the EUT. One solution is to
use a remotely controlled EMI hardened closed circuit TV system.
Contents
This purpose of this test is to verify the EUT immunity to bursts of short
duration fast rise time transients that may be generated by the switching of
inductive loads or contactors. The fast rise times and repetitive nature of
these test pulses results in the easy penetration of these spikes into the EUT
circuitry and this may disturb the EUT operation. The transients are applied
directly to the power mains and capacitively to signal lines. As with other
immunity tests, the test plan should require the EUT to be monitored for
pass/fail criteria while configured for normal operation.
Contents
The purpose of this test is to verify the EUT immunity to high energy surges
caused by overvoltage from switching, lightning and other similar transients.
Many equipment specifications, in particular ITE equipment, already require
compliance with this standard. This test can cause damage to the equipment
under test so it is best not to perform it unless the EUT has effective
transient suppression in-built.
Contents
\The purpose of this standard is to verify the EUT immunity against
conducted RF disturbances in the frequency range 9 kHz to 230 MHz. The EUT is
functioned and monitored in accordance with the prepared test plan while the RF
is injected onto the leads. All cables of the EUT can act as receptors of
radiated RF energy which can then appear on the cables as voltages up to 10
Vrms. This test can be difficult to perform as there are a multitude of
different networks and coupling units required.
Contents
The purpose of this standard is to verify that appliances and similar
devices have an adequate level of immunity to electromagnetic disturbances.
This is a product family standard for immunity. ESD, EFT, Radiated Immunity,
Conducted RF, Surges, Voltage Dips and Variations are covered.
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