Datasheet

Test equipment and measurement of efficiency and light load performance AN4164
34/38 Doc ID 023660 Rev 1
In the case of high UUT input current (i.e. for measurements in heavy-load conditions), the
voltage drop can be relevant compared to the UUT real input voltage. If this is the case, the
switch in
Figure 52
can be changed to position 2 (see simplified scheme of
Figure 54
) where
the UUT input voltage is measured directly at the UUT input terminal and the input current
does not affect the measured input voltage.
On the other hand, the position of
Figure 54
may introduce a relevant error during light load
measurements, when the UUT input current is low and the leakage current inside the
voltmeter itself (which is not an ideal instrument and doesn't have infinite input resistance) is
not negligible. This is the reason why it is recommended to use the setting of
Figure 53
for
light load measurements and
Figure 54
for heavy load measurements.
If it is not clear which measurement scheme has the lesser effect on the result, try with both
and register the lower input power value.
As noted in IEC 62301, instantaneous measurements are appropriate when power readings
are stable. The UUT is operated at 100% of nameplate output current for at least 30 minutes
(warm-up period) immediately prior to conducting efficiency measurements. After this warm-
up period, the AC input power is monitored for a period of 5 minutes to assess the stability of
the UUT. If the power level does not drift by more than 5% from the maximum value
Figure 53. Switch in position 1 - setting for standby measurements
Figure 54. Switch in position 2 - setting for efficiency measurements
AM13106v1
V
+
-
A
~
AC
SOURCE
UUT
U.U.T.
AC
INPUT
Voltmeter
Ammeter
Wattmeter
AM13107v1
V
+
-
~
AC
SOURCE
UUT
U.U.T.
AC
INPUT
Voltmeter
Ammeter
A
Wattmeter