User manual

6
Subject to change without notice
Commonly asked questions
about pre-compliance
emissions testing
The EMC Directive has prompted a large selection
in the choice of EMC test instruments. In parti-
cular, a new class of low-cost pre-compliance
instruments has opened an debate on the merits
of this new class of instruments compared with
established high-cost EMC compliance test
equipment. In this situation it’s not surprising that
a high degree of confusion prevails. In order to
get a clear view of the situation, the rst step is to
dene compliance and pre-compliance EMC test
equipment and then establish how they differ.
HAMEG Instruments has considerable experience
with both types of equipment. We use high-cost
equipment for compliance testing and also specify
and design low-cost pre-compliance equipment.
As a result, we are well positioned to express a
balanced view in this debate.
The following questionnaire is a summary of com-
monly asked questions concerning the practical
use of HAMEG measuring equipment for EMC
pre-compliance testing and how useful EMC pre-
compliance instruments are in general.
How can pre-compliance instruments
be dened?
EMC standards for both radiated and conducted
emissions require that compliance measuring
equipment conforms to CISPR 16-1. This require-
ment implies that for full compliance tests you
need expensive, high-quality receivers. On the
other hand, you can use pre-compliance equip-
ment as tools to build EMC conformance into your
products during design and development. Often
the debate over compliance or pre-compliance
instruments reduces to a choice between a test
receiver or a spectrum analyzer. However, these
denitions and choices are not the whole story
because the way you make EMC measurements
can have more inuence on the validity of a test
than the type of equipment you use.
Why is there such a cost difference between
compliance and pre-compliance test instru-
ments?
Instruments for making compliance measure-
ments must conform to CISPR 16. This standard
details stringent requirements, and some are
costly to implement. Pre-compliance instruments
provide valuable measurements and possess
some of the features of compliance equipment.
Generally, though, precompliance instruments do
not need to conform fully to CISPR 16 and therefore
can cost less.
Compliance equipment is your rst choice if mo-
ney is no object. In reality, often you cannot justify
the cost of such equipment and need a more eco-
nomical approach. Pre-compliance instruments
cost less and can provide useful measurements,
but you must be aware of the difference between
the two types of equipment and what you get as a
measurement result. It is entirely possible to make
meaningless measurements with a US$50,000
CISPR-compliant receiver. Equally, you can make
valuable measurements with a US$5,000 pre-
compliance set-up.
How important is EMC training?
EMC training is vital irrespective of whether you
make compliance or pre-compliance measure-
ments. Much of the current debate regarding the
two types of instruments is rooted in misconcep-
tions that arise because of lack of knowledge and
training. Without proper training you can make
meaningless measurements irrespective of the
type of equipment you use.
How important is an instrument’s
amplitude accuracy?
An instrument’s amplitude accuracy is important,
but uncertainty for the whole measurement is of
equal importance. If total measurement uncer-
tainty is ±6dB, the additional uncertainty between
a ±0.5dB receiver accuracy and a ±dB spectrum
analyzer accuracy is small.
Should pre-compliance instruments
contain “CISPR bandwidths”?
The signicance of CISPR bandwidths depends if
your objective is full compliance or pre-compliance
testing. Not all pre-compliance equipment neces-
sarily contains CISPR-compliant bandwidths.
Co m m o nly a s ked Q u est i o n s