RF Emission Testing
RF Emission Test
The radiated RF measurement according to CISPR 22 and CISPR 11 is usually
performed on an open area test site (OATS). An OATS setup is shown in
figure below.
Introduction to RF Emission:
Radio frequency emissions
tests are one of the basic requirements forelectromagnetic compatibility
compliance of most electronic and electricalproducts. Everything from
phones, serviceequipment and modern technological products go through
this process. Thepurpose of these tests is to ensure that other users
are protected from theemissions generated when the product is used in
their neighbourhood. Allcommercial products will be tested against the
standards which are mostly basedon CISPR tests.
IEC CISPR
publication 16-1: October 1999, “Specification for radio disturbanceand
immunity measuring apparatus and methods”, specifies the
characteristicsand performance of equipment for measuring
electromagnetic immunity in the frequency range of 9kHzto 18GHz. It
includes specifications for
a) The quasi-peak, peak, average and rms measuring receivers
b) Artificial mains networks
c) Current and voltage probes
d) Absorbing clamps
e) Antennas and test sites
There are basically 2 tests for RF Emissions. They are conducted and radiated emission tests.
Conducted RF Emission Test :
Conducted emissions tests use
an artificial mains network which is also knownas a Line Impedance
Stabilising Network(LISN) as a transducer between themains port of the
Equipment Under Test and the measuring receiver. It has 3 functionsas
described below.
a) Provides a stable, defined RF impedance
equivalent to 50 Ohm in parallelwith 50µH (or 50 Ohm/5µH for
high-current units) between the point ofmeasurement and the ground
reference plane.
b) Couples the RF interference from each of the supply phase lines to thereceiver, while blocking the LF mains voltage.
c) Attenuates external interference already present on the incoming mainssupply.
The internal circuit of the standard 50 Ohm/50µH LISN is shown below.
Introduction of RF Emission Test :
The radiated RF measurement according to CISPR 22 and CISPR 11 is usually
performed on an open area test site (OATS). An OATS setup is shown in
figure below.
Radio
frequency emissions tests are one of the basic requirements
forelectromagnetic compatibility compliance of most electronic and
electricalproducts. Everything from phones, serviceequipment and modern
technological products go through this process. Thepurpose of these
tests is to ensure that other users are protected from theemissions
generated when the product is used in their neighbourhood. Allcommercial
products will be tested against the standards which are mostly basedon
CISPR tests.
IEC CISPR publication 16-1: October 1999,
“Specification for radio disturbanceand immunity measuring apparatus and
methods”, specifies the characteristicsand performance of equipment for
measuring electromagnetic immunity in the frequency range of 9kHzto
18GHz. It includes specifications for
a) The quasi-peak, peak, average and rms measuring receivers
b) Artificial mains networks
c) Current and voltage probes
d) Absorbing clamps
e) Antennas and test sites
There are basically 2 tests for RF Emissions. They are conducted and radiated emission tests.
Conducted RF Emission Test
Conducted
emissions tests use an artificial mains network which is also knownas a
Line Impedance Stabilising Network(LISN) as a transducer between
themains port of the Equipment Under Test and the measuring receiver. It
has 3 functionsas described below.
a) Provides a stable, defined
RF impedance equivalent to 50 Ohm in parallelwith 50µH (or 50 Ohm/5µH
for high-current units) between the point ofmeasurement and the ground
reference plane.
b) Couples the RF interference from each of the supply phase lines to thereceiver, while blocking the LF mains voltage.
c) Attenuates external interference already present on the incoming mainssupply.
The internal circuit of the standard 50 Ohm/50µH LISN is shown below.
Although the LISN will reduce both the noise on
the mains supply and variations in the supply impedance, it does not do this
perfectly and a permanently installed RF filter at the mains supply to the test
environment is advisable. Ambient radiated signals should also be attenuated
and it is usual to perform the measurements inside a screened room, with the
walls and floor of the room forming the ground reference plane.
A typical setup for conducted emission is shown in the figure below.
Radiated RF Emission Test :
The radiated RF measurement according to CISPR 22 and CISPR 11 is usually
performed on an open area test site (OATS). An OATS setup is shown in
figure below.
Any open area test site is likely to suffer from ambient
signalswhich are generated in the neighbourhood and received on the
site, but notemitted from the EUT. These signals can easily exceed both
the EUT'semissions and the limit values at many frequencies. An
emissions plot whichcontains ambients is hard to interpret and, more
importantly, ambients whichmask EUT emissions make it impossible to
measure the EUT at thesefrequencies.
Ambient signals can be
classified into continuous narrowband, transient narrowband, continuous
broadband and transient broadband.
Continuous narrowband signals such as broadcast transmissions can betabulated for a given site and their frequencies avoided.
A
transient narrowband ambient allows a measurement to be made but the
testengineer needs to know when the ambient signal is present. The same
is truewith a transient broadband signal.
Continuous broadband
interference such as pulsed noise from, say, an arcwelder is more
difficult to deal with but a narrowband EUT emission can beextracted by
using the average detector with a narrow measuring bandwidth.
One way to avoid ambients altogether is to use a screened room for theradiated measurements.
The types of antennas used for the measurement and their frequencies is as below.
The above tests are typically conducted by test labs
which have the facilities to conduct the conducted and radiated
emissions. These tests are usually costly to setupand the choice of
whether to invest in these facilities will depend on the need and
frequency of testing the products. Usually they are used for research
and development purposes.
enjoy my blog
post by Pratik Gohel...:))
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