000-3-3 (IEC 61000-3-3). The
measurement of harmonic currents may be carried out without
using an additional external AC voltage source, provided that the
inherent low-voltage mains fulfills the requirements defined in the
Standard. Whether this is the case or not, can be determined in
a simple and precise manner by means of the function mains
analysis which can be recalled in the software.
As regards the measurement of voltage fluctuations and flicker
conforming to standards, an external zero-sequence field impe-
dance AC voltage source is imperative since measuring faults
may result from measurements on the mains supply system. To be
still able to perform reliable pre-compliance testing without AC
voltage source, the FHT-25 is equipped with a 16A flicker impe-
dance (approx.0.4 ) which can be connected, and by which any
measuring faults can be largely avoided. For tests which are in
absolute conformity with the standards, we offer a broad variety
of adequate AC voltage sources.
Construction:
The FHT-25 is a PC-aided testing equipment which can be ope-
rated with every commercial IBM compatible PC using the opera-
ting system Windows 95/98/NT. For the linkage between test
equipment and PC a data logging card (ISA-DAQ Card or PCI-
DAQ Card) is included in the delivery, which establishes the
connection between analog and digital world. Beside the basic
functions of harmonics and flicker testing, there exists a variety of
further applications, e.g. mains or performance analysis. The
waveform generator, which is integrated in the equipment, gene-
rates in its standard version a clean 50Hz sine wave for driving
a power amplifier (AC voltage source). By means of further,
optional software modules, the analysis and generation of wan-
ted and unwanted low-frequency signals up to 2.5kHz or
12.5kHz, are possible, depending on the capacity of the DAQ
Card. The equipment may thus be easily completed to be suitable
for performing further EMC tests. Some of these are, for example:
Functioning:
Immediately after installation of the DAQ Card as well as of the
control software, the equipment is ready for operation. The
connection of the EUT is realized via an earthed socket (Schu-
ko) integrated in the front panel of the equipment, or via labo-
ratory sockets. Feeding of the mains voltage to the EUT is reali-
zed via separate laboratory sockets at the rear side of the equip-
ment. The supply can be made optionally via the inherent low-
voltage mains or via the external AC voltage source.
After starting the software, a selection menu is offered with the
following functions: <Constant Harmonics> <Fluctua-
ting Harmonics> <Current Class D?> <Flicker>
<Mains Analysis>
.
<Current Class D?> :
The limit values for admissible harmonic currents are classified
according to the equipment classes A, B, C, and D. The classifi-
cation is as follows:
A:
Symmetric three-phase appliances and all other appli-
ances, except those mentioned in one of the following
classes.
B:
Portable electric tools
C:
Lighting equipment including dimming regulators
D:
Appliances which under given test conditions have
an input current of a special curve shape, and an
input power of P 600W.
With the menu item <Current Class D?> it is possible to verify
automatically if the EUT fulfills the criteria of a Class D equip-
ment. The respective display on the screen can be seen in
Picture 1.
<Constant Harmonics>
This menu option permits the measurement of even and uneven
harmonics up to the 40th order, conforming to standards. Befo-
re starting the measurement, the class (A,B,C or D), in which the
EUT is to be classified, has to be entered. By selecting the class,
the limit values admissible for the respective class are automati-
cally loaded so that it appears at once whether the EUT fulfills
the requirements defined by the Standard. The respective scre-
en display can be seen in Picture 2.
<Fluctuating Harmonics>
This menu option allows the measurement and analysis of fluc-
tuating harmonic currents resulting from variations of load of the
EUT. In this case an upper deviation by up to 1.5 as against the
limit values for harmonic currents of the orders 2 to 10 and 3 to
19 is admissible, if its duration is not exceeding 10% during an
observation period of 2.5 minutes. Harmonic currents which
continue, at the most, 10 seconds after switching On or Off
of the EUT, may be neglected when evaluating the EUT.
After starting the measurement, the apparent output and the
actual output of the EUT are first of all measured during the
observation period of 2.5 minutes, and their time domain is
IEC 61000-3-9
Emission of intermediate harmonics
IEC 61000-3-10 Emissions in the frequency range 2kHz to 9kHz
IEC 61000-4-13 Immunity to harmonics and
intermediate harmonics
IEC 61000-4-14 Immunity to voltage fluctuations
Picture1 shown on the screen. After expiration of the measuring period
all harmonics of the complete measuring duration are calcula-
ted, and their variation (selectable per ordinal) is represented
graphically on the upper half of the screen. In addition, the res-
pective admissible limit value as well as the limit value for the
admissible upper deviation by 1.5 are presented. To avoid
having to examine each individual harmonic (2nd to 40th
order), intermittent digits in the upper line of the window will
indicate for which harmonics the limit value was exceeded. The
presentation on the screen can be seen from Picture 3.
<Flicker>:
When starting the flicker measurement, a selection can be made
first of all between the measurement via integrated flicker impe-
dance or the measurement at the EUT connection. If pre-com-
pliance tests without external AC voltage source are reali-
zed, it is always recommended to measure via the integrated
flicker impedance. The control software now offers the possibili-
ty of measuring either short-time flicker (Pst) with a measuring
period of 10 minutes, or long-time flicker (Plt) with a measuring
period of up to 2 hours. For quick synoptic measurements, it is
also possible to select measuring periods of 1 or 5 minute(s).
After starting the measurement, the actual measuring values of
a measuring period of 1 minute (optionally flicker or voltage
fluctuations) are shown in the lower part of the screen. At the
end of the first minute the scaling changes, depending on the
measuring period; the previous measuring values, however, are
stored for a measuring period of 10 minutes and may be
viewed by shifting the scroll bar. Besides, at the end of the first
minute, the cumulative frequency function is presented in the
right upper half of the screen. This figure represents simplified
the percentage of the flicker values measured. Besides, the
actual supply voltage, the short-time flicker value determined
(Pst), the max. voltage fluctuation (dmax) in percent, as well as
the max. measured flicker value (Pmax) are shown on the scre-
en (see Picture 4).
Depending on the measuring period selected, between 1 to 12
short-time flicker values are determined which, together with the
maximum values, are transferred into the table as shown in Pic-
ture 5, after conclusion of the measurement. The calculation of
the long-time flicker value is made on the basis of the short-time
flicker values previously determined.
In the FHT-25, the complicated calculation methods for voltage
fluctuations and flicker, and thus the evaluation of the EUT with
respect to its compliance with the limit values prescribed by the
Standard, have been transferred completely to the software/PC
and are accomplished fully automatically. They are set forth in
the corresponding Standards (IEC 61000-3-3 / EN 60868).
<Mains Analysis>.
This additional function allows, in a simple way, to obtain a pre-
cise information on the quality of the inherent low voltage
mains. Thus it can be verified quickly, for instance, whether the
inherent mains fufills the quality requirements regarding measu-
rements of harmonic currents. Via a selectable measuring peri-
od, the mains voltage as well as the k-factor are shown numeri-
cally and graphically as minimum, maximum and average
values.
Storage and Printing of Measuring Results:
Each menu option offers the possibility of storing the measuring
data, recalling data already stored and/or printing measuring
records. Besides it is possible to export the measuring data to
other programs for further processing.
Picture 2
Picture 3
Picture 4
Picture 5 Technical Data:
Connecting possibilities:
Monitor outputs (BNC):
EUT voltage (Up/100)
EUT current (I/10)
Voltage via flicker impedance (U
F
/5)
Generator output (BNC):
0 to 10 V AC, 10 to 2.5kHz (FHT-25)
0 to 10 V AC, 10 to 12.5kHz (FHT-125)
0 to 10 V DC
D/A converter output
1 piece
Digital trigger input (TTL)
1 piece
Digital input/output
4 pieces
Input for external current clamp
1 piece
Max. measuring faults:
EUT current / voltage
< 0.1% (25�C)
< 0.2% (0�C - 40�C)
Nominal supply voltage (recovery time

= 27 s)
< 0.5 %
for flicker measurement
Voltage fluctuations
< 5%
Flicker impedance
Max. peak voltage
500 V
Max. peak current
68 A
(with internal current transformer)
Attenuation:
Antialiasing filter
> 70dB
Harmonics filter
f (-3dB) = 3Hz
fn + 15Hz, fn 15Hz>40dB
f(n-1), f(n+1)> 57dB
mains frequency > 68dB
General Data:
Temperature range:
0� to 40�C
Air humidity, max.
< 90%
Housing:
19 3HU
Weight:
10 kg
Volume of delivery:
FHT-25