XT2640 Operating Manual
13 July 2016
Page 91 of 187
W channel type: 75‐600Vrms.
Voltage
Crest
Factor
: Solely limited by a maximum peak voltage of 1750Vpk.
Current
and
Current
Crest
Factor
: Any current in the following range for each current option (the channel type does not
affect the ranges allowed)‐
H current option: 3mA‐30Arms. Crest factor limited to the lower of 100 or a maximum peak current of 200Apk.
D current option (HI range selection): 2.5mA‐20Arms. Crest factor limited to the lower of 100 or a maximum peak current
of 150Apk.
D current option (AUTO range selection): 0.7mA‐20Arms. Crest factor limited to the lower of 100 or a maximum peak
current of 150Apk.
D current option (LO range selection): 0.7mA‐0.265Arms. Crest factor limited to the lower of 100 or a maximum peak
current of 1Apk.
Note that EN61000‐3‐2 disregards all harmonics <5mArms in applying assessment limits (see clause 6.2.3.4), so in practice
it is reasonable to assume that there is no requirement to assess EUTs with an RMS load current <5mA as in that case all
the harmonic assessment results would be disregarded.
Total
Power
Factor:
Any total power factor in the range 0.0001‐1.0.
Fundamental
Power
Factor
: Any fundamental power factor in the range 0.01‐1.0 (for EN61000‐3‐2 classes C(tbl3) and D
only, there is no fundamental power factor range limitation for the other classes or for EN61000‐3‐12).
Power
: Only limited by the voltage, current and power factor limitations stated above.
18.1.5.1
EXTERNAL
CURRENT
MEASUREMENTS
The use of external current devices with a XT2640 for any EN61000‐3‐2 compliance testing is not needed and should not be used
(unless the current option in the XT2640 is X).
18.1.5.1.1
Using
External
Current
Shunts
If necessary for EN61000‐3‐2, and as is often needed for EN61000‐3‐12 to accommodate its current requirements, the use of
external shunts in combination with the X current option in the XT2640 is recommended.
The requirements for external shunts, when needed for compliance with EN61000‐3‐2, ‐12 and EN61000‐4‐7 standards, are as
follows–
The resistance of the shunt must be such that the RMS voltage across the shunt is <0.15Vrms at the maximum expected
current draw of the EUT. This is a requirement of EN61000‐4‐7 clause 5.1, however that requirement may be considered
to be overridden by both EN61000‐3‐2 and ‐12 as discussed in section 18.1.1.
The power handling capability of the shunt and its ability to dissipate heat in your use of it must be such that there is less
than 1% difference between its value at low currents and that at the maximum expected EUT current.
The inductance of the shunt must be <10nH per mΩ resistance of the shunt. Note that resistors which are claimed to be
“non‐inductive” always have some inductance so you should consult the shunt resistor data sheet for a maximum
inductance value; if none is available then the shunt should not be used for this purpose. “Classical” DC shunts generally do
not meet this requirement, the use of “folded” or coaxial shunts is recommended. You should also consider that since shunt
inductance will always increase the measurement results for high order harmonics, so if the EUT is passing the
requirements with the shunt being used then it would also pass (possibly with a wider margin) with a “perfect” shunt.
The routing of the voltage sense wiring from the shunt to the XT2640 should be such that it alters the apparent impedance
of the shunt at 2kHz by less than 1%. This generally means that the voltage sense wiring must be a closely twisted pair
(not a coaxial cable) of thin gage wires (26awg or thinner is recommended) and that it is routed at right‐angles to the
current wiring for a distance of at least 1 foot from the shunt and its current carrying wiring. The routing of the wiring is
very dependent on many factors, some experimentation should be expected. Generally you can detect if the wiring is a
problem by simply changing it and noting any changes to the very high order harmonics measurements, but this assumes
that the load has sufficient such harmonic content and that it is not also affected by the changes to the wiring routing. You
should note that this effect can either raise or lower high order harmonic measurements, so can cause false passing or
failing indications on a EUT.
You should consider the operating environment of the shunt. Low resistance shunts typically have a high temperature
coefficient of resistance which will limit their ability to be used with accuracy in a poorly controlled environment.
The shunt must be mounted and protected such as too maintain a safe environment. The shunt is operating at an unsafe
voltage so you must ensure that there is sufficient mechanical shielding to ensure that objects such as defined by EN61010‐
1 cannot touch any live voltage part of the shunt.
18.1.5.1.2
Using
External
Inductive
Type
Current
Transducers
External inductive type current transducers such as coil or hall‐effect types are generally not recommended as few meet the
requirements. There are a few such devices which do meet the requirements however, so may be carefully considered. The
important features of such a device are‐
Accuracy. An overall accuracy of 1% (after calibration of the input:output ratio) is required. You should also consider the
reliance of the device on the position of the current carrying wire within its aperture; often this is a substantial effect at
these accuracy levels.
Distortion. This is often the dominant factor in deciding on a device. EN61000‐4‐7 requires that harmonics measurements
be made to within 0.15% of the fundamental at each harmonic up to the 40
th
, so it is recommended that the device have at
least twice this level of performance as typically there are other effects which are not apparent when initially choosing such
a device. Note, however, that the limits allowed for harmonics in EN61000‐3‐12 are much larger than this and so you
should also consider whether using lower performance transducers than this might be applicable.
