XT2640 Operating Manual
13 July 2016
Page 92 of 187
Phase shift and frequency response. If the device has a poor phase shift specification at 50/60Hz then it usually has a poor
frequency response at 2kHz. The difference between the input:output ratio at 2kHz to that at 50/60Hz should be <1%.
18.1.6
COMPLIANCE
TESTS
PERFORMED
BY
THE
XT2640
DURING
ASSESSMENT
The following tests are performed by the XT2640 to ensure that EUT assessment is performed in a manner compliant with the
standards.
18.1.6.1
TESTING
THE
SUPPLY
VOLTAGE
FOR
COMPLIANCE
With the XT2640, you may use any voltage source having suitable power sourcing capabilities. However it should be noted that the
local mains supply is often not suitable, particularly for EN61000‐3‐2 assessments.
In accordance with the requirements of EN61000‐3‐2 and ‐12 the supply voltage is continuously checked by the XT2640 throughout
the assessment of the EUT as follows. Note that although some tests are not required for some EUT classifications, the XT2640
always performs all of the tests, the EUT classification only affects whether the results of these tests are visible to you.
Voltage
: Each voltage is checked that it remains continuously within a ±2% range of the user specified nominal voltage
(Unom) as specified by EN61000‐3‐2 clause A.2a and ‐12 clause 7.2b.
Frequency
: The supply frequency is checked that it remains continuously within a ±0.5% range of the user specified
nominal frequency (Fnom) as specified by EN61000‐3‐2 clause A.2a and ‐12 clause 7.2b.
Frequency
Lock
: Short‐term variations in the supply frequency are continuously checked that they remain within the
±0.03% limit within every 200ms measurement period as specified by EN61000‐4‐7 clause 4.4.1 so is applicable to both
EN61000‐3‐2 and ‐12 assessments.
In most countries the local mains supply does not meet this requirement. In addition some AC sources may have
cycle‐to‐cycle jitter in excess of this requirement.
Voltage
Harmonics
: Each voltage is checked that it remains continuously within the specifications of EN61000‐3‐2 clause
A.2c. For EN61000‐3‐12 it is your responsibility to check the voltage harmonics of each supply phase voltage when the
supply is unloaded per clause 7.2d.
For EN61000‐3‐12 this can be performed using the XT2640 HARMONICS screen but it is not part of the
assessment process.
Voltage
Crest
Factor
: Each voltage is checked that its crest factor remains continuously within a modification of the range
specified by EN61000‐3‐2 clause A.2d, see below for a description of the modification to EN61000‐3‐2 requirements used
by the XT2640 in this regard. EN61000‐3‐12 contains no such requirement and crest factor is not checked when assessing
a EUT to that standard.
The crest factor of a pure, noiseless, sinewave is 1.414214 (= √2 to 7 significant figures) and if the EN61000‐3‐2
stated allowable range of 1.40 to 1.42 is taken strictly (assuming that all unstated digits are zeroes) then this
stated range only allows 0.4% for the total noise (always increases CF) + amplitude modulation (always increases
CF) + any distortion content which results in an increase in the crest factor, this may be overly restrictive in
practice. In the XT2640 it is assumed that the intention of the standard is to define a ±0.01 range centered on the
nominal value for a pure sinewave (instead of the 1.41 value as stated) so the actual allowed range for supply
voltage crest factor as checked by the XT2640 is from 1.404214 to 1.424214 (to 7 significant figures). It should be
noted that EN61000‐4‐7 clause 5.4.2.2d, although overridden in this regard by EN61000‐3‐2, states a required
range of 1.404 to 1.424.
There is no definition of any bandwidth required for this measurement in either of these standards, for example a
100GHz measurement bandwidth would certainly not result in a suitable application of this limit. So it is
assumed that a “reasonable” limit should be used and the XT2640 uses a 20kHz bandwidth limit for this
measurement.
Phase
of
Voltage
Peaks
: Each voltage is continuously checked that the phase position of both positive and negative peaks
are ±90°±3° as specified by EN61000‐3‐2 clause A.2d. EN61000‐3‐12 contains no similar requirement and the peak phase
position is not checked when assessing a EUT to that standard.
There is no definition of any bandwidth required for this measurement, for example a 100GHz measurement
bandwidth which could detect a noise pulse as short as 5ns would certainly not result in a suitable application of
this limit as the 3° range only allows for a small amount of voltage noise, particularly since every supply cycle
within the assessment period must meet this limit so even a very low probability noise event will cause a failure
of this requirement. So it is assumed that a “reasonable” bandwidth limit should be used and the XT2640 uses a
5kHz bandwidth limit for this measurement, but it should be noted that almost any such bandwidth restriction
results in a delay which varies with the frequency content and exact shape of the noise pulse, as is the case for the
XT2640, and this delay may result in the 3° range requirement having limited meaning in practice.
Inter
‐
phase
Voltage
Phasing
: The phase difference between every phase pair of a multi‐phase supply is required to be
within ±1.5° of 120° throughout the assessment period according to the requirements of both EN61000‐3‐2 clause A.2b
and ‐12 clause 7.2c. The XT2640 continuously checks this throughout the assessment if WIRING is configured for
3ø3w(3ch) or 3ø4w.
Recommendations:
The XT2640 neither stops the assessment, nor prevents an overall assessment pass/fail result of the EUT harmonics
emissions if any of these supply voltage tests fail. A separate indication is used denoting which (if any) of these tests fail.
Should any of these failures be detected (particularly Voltage Crest Factor and Phase of Voltage Peaks) then you are
recommended to reach a decision whether to‐
a)
Ignore the failure. This is a possibility if the EUT results indicate that it meets the harmonics requirements with a
high margin, particularly since in practice the presence of such supply failures would normally result in higher
