CISPR 22:2008/ISH2:2010
(Main)Interpretation Sheet 2 - Information technology equipment - Radio disturbance characteristics - Limits and methods of measurement
Interpretation Sheet 2 - Information technology equipment - Radio disturbance characteristics - Limits and methods of measurement
Feuille d'interprétation 2 - Appareils de traitement de l'information - Caractéristiques des perturbations radioélectriques - Limites et méthodes de mesure
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Standards Content (Sample)
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SC CIS I/Publication CISPR 22:2008, Sixth edition/I-SH 02
INFORMATION TECHNOLOGY EQUIPMENT –
RADIO DISTURBANCE CHARACTERISTICS –
LIMITS AND METHODS OF MEASUREMENT
INTERPRETATION SHEET 2
This interpretation sheet has been prepared by CISPR subcommittee I: Electromagnetic
compatibility of information technology equipment, multimedia equipment and receivers, of
IEC technical committee CISPR: International special committee on radio interference.
The text of this interpretation sheet is based on the following documents:
ISH Report on voting
CISPR/I//323/ISH CISPR/I/326/RVD
Full information on the voting for the approval of this interpretation sheet can be found in the
report on voting indicated in the above table.
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Introduction
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At the CISPR SC I plenary, held on the 27 October 2007, a decision was taken to set the
maintenance date for CISPR 22, Edition 6 to 2012. As a result the work identified within
CISPR/I/279/MCR will not be started for the time being. At the subsequent meeting of CISPR
SC I WG3 it was decided that 3 items within the MCR would benefit now from further
clarification and an interpretation sheet would be helpful to users of the standard, with the
intent of including this information in a future amendment to the standard.
The first draft of an interpretation sheet CISPR/I/290/DC addressed the 3 items, however it
was clear from the comments received (CISPR/I/293A/INF) that further work was required on
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the 3 item related to ISN selection, and it was decided that this would be the subject of a
separate document.
This information does not change the standard; it serves only to clarify the points noted.
CISPR SC I WG3 hopes that these clarifications will be of use to users and especially
laboratories testing to CISPR 22:2008 (Edition 6.0).
Selection of ISN for unscreened balanced multi-pair cables
Subclause 9.6.3.1 of CISPR 22 states that:
“When disturbance voltage measurements are performed on a single unscreened
balanced pair, an adequate ISN for two wires shall be used; when performed on
unscreened cables containing two balanced pairs, an adequate ISN for four wires shall
be used; when performed on unscreened cables containing four balanced pairs, an
adequate ISN for eight wires shall be used (see Annex D)”
Therefore the selection of ISN is based on the number of pairs physically in the cable, not the
number of pairs actually used by the interface in question.
April 2010 ICS 33.100.10 French text overleaf
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However, selection of a suitable ISN design from the examples given in Annex D requires
further consideration. The ISN designs given in Figures D.4 to D.7 are only appropriate for
use where all of the balanced pairs in the cable are ‘active’ and hence their use requires a
more detailed knowledge of the EUT port being tested. The ISN designs given in Figures D.1
to D.3 have no such limitation and are better suited to applications where the actual use of
the pairs is unknown.
The ISN designs given in Figures D.2 and D.3 are also suitable for measurements on
unscreened cables containing fewer balanced pairs than the maximum number of pairs the
ISN is designed for (see example 2).
The following definitions have been developed to help in determining what should be
considered an ‘active’ pair of conductors:
An active pair is a pair of conductors that completes an active digital, analogue,
or power circuit, or is terminated in a defined impedance, or is connected to earth or the
equipment frame/chassis.
NOTE These circuits include such applications as "Power over Ethernet".
A circuit is an active circuit when it is in a state that is performing its intended function,
which may include communications, voltage/current sensing, impedance matching or
power supply.
NOTE A conductor with no intended function is not part of an active circuit.
A measurement using an ISN described in Figures D.4 to D.7, when not all of the pairs are
‘active’, may result in a significant error in the measured emissions. It is therefore important
that test laboratories determine on which of the designs given in the annexes their particular
ISNs are based. From this they can then determine if they need to establish the number of
‘active’ pairs within the cable or not and then whether their ISNs are suitable for the port
being measured or whether an alternative measurement technique needs to be used.
This is applicable when measuring in accordance with 9.6.3.1 or 9.6.3.2.
It is recommended that test reports should make reference to:
• the ISN category used;
• the Annex D figure corresponding to their particular ISN design;
• the total number of pairs in the cable and number of these that where active.
Example 1:
The EUT has an Ethernet port to which either a CAT 5 or 6 cable is connected. Typically
these cables have four pairs requiring use of a four pair ISN. Transmission using 1000Base-T
Ethernet protocol uses all four pairs of a typical cable. Transmission using 10Base-T and 100
Base-T Ethernet protocol uses only two of the four pairs for communication. One of the
following ISNs could therefore be used:
1) ISN as shown in Figure D.3, or
2) ISN as shown in Figures D.6 or D.7 if it is known that all the pairs within the cable are
‘active’. This would be the case if a 1000BaseT Ethernet protocol were being used.
These ISNs would also be suitable for 10BaseT or 100BaseT protocol if the unused
pairs have controlled terminations in the EUT port by design, making all pairs ‘active’
from an EMC perspective.
Should an EUT with an Ethernet port be provided with a cable that contains only 2 pairs within
it, then any of the following types of ISN could be used: D2, D3, D4 or D5.
April 2010 ICS 33.100.10 French text overleaf
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Example 2:
The EUT has a single ADSL port and is provided with a cable containing 2 pairs. ADSL is a
single pair system so only 1 pair is active. The following ISNs could be used:
1) ISN as shown in Figure D.2 or D.3.
Cable length between ISN and EUT when measuring telecommunication ports
Subclause 9.5.1 of CISPR 22 requires that the distance between the ISN and the EUT be
nominally 0.8m and also clause 9.5.2 states that:
“Signal cables shall be positioned for their entire lengths, as far as possible, at a
nominal distance of 0,4 m from the ground reference plane (using a non-conductive
fixture, if necessary).”
No other requirement is given on the actual length of the cable to be used.
Measurements have shown that non-inductive bundling of any excess cable can result in
slightly higher emission levels measured at the ISN.
It is therefore recommended that the cable between the telecommunication port and the ISN
should be kept as short as possible, in order to avoid the need to bundle any excess, while
maintaining the requirements given in 9.5.1 and 9.5.2.
April 2010 ICS 33.100.10 French text overleaf
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SC CIS/I/Publication CISPR 22:2008, Sixième édition/I-SH 02
APPAREILS DE TRAITEMENT DE L'INFORMATION –
CARACTÉRISTIQUES DES PERTURBATIONS RADIOÉLECTRIQUES –
LIMITES ET MÉTHODES DE MESURE
FEUILLE D'INTERPRÉTATION 2
Cette feuille d’interprétation a été établie par le sous-comité I du CISPR: Compatibilité
électromagnétique des matériels de traitement de l'information, multimédia et récepteurs, du
comité d'études CISPR de la CEI: Comité international spécial des perturbations
radioélectrique
...
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