XT2640 Operating Manual
13 July 2016
Page 89 of 187
18.1.3
REPEATABILITY
REQUIREMENTS
Both EN61000‐3‐2 and ‐12 require that an assessment meet a repeatability requirement. For EN61000‐3‐2 this is contained in
clause 6.2.3.1 and in EN61000‐3‐12 it is contained in clause 4.2.3. In both cases it is required that better than 5% of the limit is
achieved in the repeatability of measurement of average individual harmonic currents, but it is stated in the standards that this is not
a requirement for assessment, but is a requirement for the selection of the assessment time.
The repeatability of the XT2640 itself is far beyond these requirements in general so is not a determining factor; the primary
determining factors being the repeatability of the supply source, the repeatability of the EUT harmonics themselves, and the test
time used for assessment.
Recommendation:
You must configure a test time suitable for the EUT which allows you to achieve this level of repeatability. See table 1 of
EN61000‐3‐12 and table 4 of EN61000‐3‐2 for some guidance regarding this.
The XT2640 enforces no minimum assessment time other than 1 second. For a stable EUT and a stable supply source the
standards provide no minimum assessment time as long as it is “
of
sufficient
duration
to
meet
the
requirements
for
repeatability
”. If the EUT and supply source can meet this requirement with a 1 second assessment time, then such a time
may be used, however you must ensure that the 1.5 second filtering required by the standards has fully settled prior to
starting an assessment so the EUT must have been powered and stable for at least 10 seconds prior to starting the
assessment, the XT2640 does not enforce this.
As stated in note 3 of figures A.1 and A.2 of EN61000‐3‐2 you may need to use a supply source which significantly exceeds
their stated requirements in order to meet the repeatability requirement with some EUTs. Although these notes suggest an
increased requirement for supply voltage stability, experience has shown that this also extends to waveform shape
repeatability.
With some EUTs you may need to decide whether the repeatability requirement is applicable to some or perhaps to all
harmonics. There are primarily two situations where this may be appropriate‐
Some EN61000‐3‐2 class C devices with low power levels are unlikely to enable you to meet this requirement for any
reasonable assessment time, primarily because there is no minimum current level stated for the repeatability
requirement as it is presently worded in EN61000‐3‐2.
If reporting an assessment of a EUT which is failing the assessment then some harmonics measured may be very
significantly higher than the limit, resulting in an unnecessarily small percentage of the measurement as the
repeatability requirement as it is presently worded in EN61000‐3‐2 (also in EN61000‐3‐12 but in practice this situation
is far less likely for that standard).
18.1.4
EUT
CLASSIFICATIONS
AND
LIMITS
SELECTION
For both EN61000‐3‐2 and ‐12 the XT2640 does not decide which classification a EUT falls into and which limits table to apply. It is
your responsibility to select the correct classification and/or limits table to apply when assessing a EUT following the guidelines of
each standard and taking into account the features of the specific EUT.
When an assessment is made the XT2640 takes and records internally all measurements required, and all supply voltage and
measurement testing is performed, in order to make an assessment result available for any classification in EN61000‐3‐2 or for any
limits table within EN61000‐3‐12. This means that you can freely make an assessment, and then check the results of that assessment
afterwards to any of the classifications (but not changing between standards). This also extends to the entry of reference levels for
current, watts, and PF which may be required for some classifications, and the nominal Unom and Fnom entries, and the Rsce entry;
all of these may be changed freely after an assessment without requiring that a new assessment be performed. This process is called
“reassess” in the XT2640; basically it is reassessment of measurement results already obtained from a prior assessment.
Recommendation:
When there is doubt regarding which classification or limits table to use it is recommended that an assessment be
performed to the desired standard, initially to any classification, and that you subsequently generate separate reports for
each possible classification which you decide upon. With the XT2640 there is no need to repeat the entire assessment
process to accommodate this.
You might consider making it your general practice to generate a final assessment report which contains the assessment of
the EUT to all classifications (or just to those which the EUT passes). This gives the benefit of removing any doubt
regarding whether the correct classification was chosen for a EUT and may help should later versions of EN61000‐3‐2
result in a change of classification of the EUT (as stated in clause 5 of EN61000‐3‐2 this may occur in the future). By pre‐
assessing a EUT against each classification you are already prepared for such future changes.
18.1.4.1
EN61000
‐
3
‐
2
CLASSIFICATIONS
AND
LIMITS
TABLE
SELECTION
The XT2640 performs assessments denoted using the same classifications of EUT for classes A, B and D as defined within EN61000‐
3‐2. However EN61000‐3‐2 sub‐classifies EUTs within its’ Class C classification into four sub‐classes, within the XT2640 these are
denoted as follows–
Class
C(tbl2)
: the sub‐class defined by the first paragraph of clause 7.3a) of this standard.
Class
C(tbl1)
: the sub‐class defined by the second paragraph of clause 7.3a) of this standard.
Class
C(tbl3)
: the sub‐class defined by the first set of requirements in clause 7.3b) of this standard.
Class
C(spcl)
: the sub‐class defined by the second set of requirements in clause 7.3b) of this standard.
By accommodating this expanded definition of Class C along with classes A, B and D, the table within EN61000‐3‐2 defining the limits
to be used for a EUT is thus explicitly defined and selected by the XT2640.
Recommendation:
