8th Brazilian Congress on Metrology, Bento Gonçalves/RS, 2015
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Trilateral South American project: a reference system for measuring
electric power up to 100 kHz – progress report
Gregory A. Kyriazis 1, Lucas Di Lillo 2, Daniel Slomovitz 3, Ricardo Iuzzolino 2,
Eliana Yasuda 2, Leonardo Trigo 3, Héctor Laiz 2, Rosane Debatin 1, Ana Maria
R. Franco 1, Edson Afonso 1
1
Instituto Nacional de Metrologia, Qualidade e Tecnologia (Inmetro);
2
Instituto Nacional de Tecnología Industrial (INTI);
3
Administración Nacional de Usinas e Transmisiones Eléctricas (UTE)
E-mail: gakyriazis@inmetro.gov.br
Abstract: Three countries in South America are jointly developing a reference system
for measuring electric power up to 100 kHz. The objective is the construction of three
similar measuring systems, one for each institute. The measuring system is described
and its design requirements are presented. This project will contribute to provide
calibration services in measuring ranges still not covered by the three institutes.
Keywords: power, electric power, wideband wattmeter, sampling methods, regional
project.
1. INTRODUCTION
In the last decades, the increased use of nonlinear
loads in power distribution networks has caused a
significant increase in the waveform harmonics
degrading the quality of the power delivered to
the customer. The reliable measurement of
waveform harmonics requires refined techniques.
The nonlinear loads include the new
technologies of compact lighting and the use of
switching converters. The latter are used both in
transmission and distribution networks in power
electronics applications. Such loads also include
switched-mode power supplies (SMPS) used in
computers. SMPS switch voltages (in the order of
400 V) in frequencies in the range of kilohertz
producing harmonics beyond 1 MHz.
Comparisons on harmonic power are being
planned at the level of the Consultative
Committee on Electricity and Magnetism (CCEM)
and of the Inter-American System of Metrology
(SIM).
To address this concern, the Instituto Nacional
de Metrologia, Qualidade e Tecnologia (Inmetro),
in Brazil, the Instituto Nacional de Tecnología
Industrial (INTI), in Argentina, and the
Administración Nacional de Usinas e
Transmisiones Eléctricas (UTE), in Uruguay, are
jointly developing a reference system for
measuring electric power up to 100 kHz. The
objective is the construction of three similar
measuring systems, one for each institute. The
project is supported in part by the Conselho
Nacional de Desenvolvimento Científico e
Tecnológico (CNPq), in Brazil.

8th Brazilian Congress on Metrology, Bento Gonçalves/RS, 2015
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This project will contribute to provide
calibration services in measuring ranges still not
covered by the three institutes. The project will
also contribute to improve the traceability not
only of electric power but also of related
quantities like ac-dc transfer, voltage ratio, phase
angle, ac voltage and ac current.
2. MEASURING SYSTEM
Calibration systems for harmonic power
analyzers and power quality measuring
instruments generally consist of a digital
generator with two independent channels (one for
voltage and one for current). Arbitrary voltage
and current waveforms are programmed and
applied to the instrument under calibration. The
amplitude ratio and phase displacement of the
two signals can be adjusted by changing the
generator settings. Voltage dividers and current
shunts with flat responses in all the frequency
range of interest are used to convert with high
accuracy the high voltages and currents to the
relatively low voltages required by the digitizer
inputs. The harmonic parameters of such
waveforms and the electric power are estimated
from the digitized data and the resulting estimates
are compared with the readings of the device
under calibration.
The reference measuring system comprises
(see figure 1): an arbitrary waveform function
generator with two synchronized channels, a
power amplifier, a transconductance amplifier, a
resistive voltage divider, a current shunt and a
digitizer with two synchronized channels.
2.1. Arbitrary waveform function generator
Arbitrary waveform function generators based on
direct digital synthesis (DDS) present many
advantages in comparison with other techniques.
The DDS technique consists in the digital
processing to generate signals at different
frequencies and phases selectable by software
from a reference clock. It shows a higher
frequency resolution and a lower harmonic
distortion than those obtained through other
techniques (for instance, phase-locked loop). The
frequency stability in the DDS technique depends
only on the external reference oscillator
employed, thus allowing multiple devices to be
synchronized.

Figure 1. Simplified block diagram of the
reference measuring system. (GER1 – channel 1
of the arbitrary waveform function generator,
GER2 – channel 2 of the arbitrary waveform
function generator, A1 – power amplifier, A2 –
transconductance amplifier, D – resistive voltage
divider, S – current shunt, BUF – buffer, TC –
thermal converter, DIGITIZER – two-channel
digitizer, CLK – clock, and DUT – device under
calibration).
The design requirements are [1, 2, 3]: (a) two
synchronized channels; (b) low total harmonic
distortion: −80.37 dBc (@ 0.23 V, 1 kHz); (c)
frequency resolution: 1.41 nHz; (d) frequency
stability: 3.9 µHz (@ 0.23 V, 62.5 Hz, single-
tone signal); (e) frequency stability: 25 µHz (@
0.23 V, 1 kHz); (f) amplitude stability: 2.0 µV
(@ 0.227902 V, 62.5 Hz, single-tone signal); (g)

8th Brazilian Congress on Metrology, Bento Gonçalves/RS, 2015
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amplitude stability: 13 µV/V (@ 0.23 V, 1 kHz);
(h) frequency range: DC to 150 kHz (with a
slight increase in distortion); (i) internal reference
clock: 400 kHz +/− 20 Hz; (j) output amplitude:
1 V, 2 V, 5 V and 10 V peak-to-peak; (k) output
signal waveforms: single-tone sinusoidal, two-
tone sinusoidal, distorted sinusoidal, squarewave,
triangular and saw-tooth.
2.2. Power amplifier
The power amplifier is used to boost the output
of a channel of the dual-channel generator to a
nominal of 120 V RMS or 240 V RMS. In
addition, the amplifier is designed to supply up to
100-mA RMS to accommodate the burden
requirements without causing any significant
error. A prime goal is to maintain the excellent
short-term amplitude and phase stability inherent
in the digital generator. In addition, there is a
general need for a precision power amplifier that
will provide an output swing of several hundred
volts at moderate power levels while maintaining
good dc characteristics, stable gain, and wide
bandwidth.
The design requirements are [4]: (a) voltage
gain: 40 (nominal); (b) maximum output swing:
+/− 485 V, (340 V RMS); (c) maximum output
current: +/− 145 mA, (100 mA RMS); (d)
frequency response: DC to 150 kHz, 3 dB (240 V
RMS, 100 mA RMS); (e) load regulation:
20 ppm change (null load to full load @ 120 V
RMS, 1 kHz); (f) output noise: less than 50 mV
RMS (500 kHz bandwidth); (g) input impedance:
10 kΩ; (h) maximum slew rate: 400 V/µs.
2.3. Transconductance amplifier
A transconductance amplifier ideally produces a
current in a load proportional to an input voltage
and maintains that current independent of the
load terminal voltage. A total of 5 (five)
transconductance amplifiers are being designed
each covering the following ranges (full scale):
50 mA, 500 mA, 5 A, 20 A and 100 A.
The design requirements are [5, 6, 7]: (a)
transconductance stability (10 min): +/− (0.005%
reading + 0.005% range) @ 10 Hz to 10 kHz and
+/− (0.010% reading + 0.010% range) @ 10 kHz
to 100 kHz; (b) input voltage range (full scale):
5 V; (c) frequency range: 10 Hz to 100 kHz; (d)
compliance voltage: 7 V RMS; (e) total harmonic
distortion: −60 dB @ 10 Hz to 10 kHz, −50 dB
@ 10 kHz to 40 kHz, −40 dB @ 10 kHz to
100 kHz; (f) input impedance (differential input):
500 kΩ from each input terminal to chassis
ground; (g) output impedance: 50 mA –
10 kΩ // 1.4 nF, 500 mA – 10 kΩ // 1.4 nF, 5 A –
10 kΩ // 30 nF, 20 A – 2.5 kΩ // 120 nF, 100 A –
500 Ω // 600 nF.
2.4. Resistive voltage divider
There are 9 (nine) resistive voltage dividers to be
used one at a time whose (binary) nominal value
(from 4 V to 1024 V) depends on the test voltage
selected [8]. An additional 1024-V divider is
being also designed with different power
consumption for evaluation purposes. The
(binary) input resistances range from 1 kΩ @ 4 V
to 256 kΩ @ 1024 V. Their input capacitance is
always 33 pF. Thus the power amplifier output
current is always 0.004 A. The divider output
resistance is always 200 ohms. Thus the nominal
output voltage of the dividers is always 0.8 V.
The rated voltages were selected with binary
ratios to ease the step-up calibration of the
amplitude and phase errors with the dual-channel
digitizer. The nominal ranges of the dividers are
obtained from the voltage ratios 5, 10, 20, 40, 80,
160, 320, 640, and 1280, and the 0.8-V output
voltage.
The voltage dividers employ Vishay Z-Foil
audio resistors (VAR) with low dissipation factor
whose dissipated power in each resistor does not
exceed 100 mW. The main problem in the design
of voltage dividers is the undesired electric field

8th Brazilian Congress on Metrology, Bento Gonçalves/RS, 2015
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coupling. A guarding circuit needs to be designed
to reduce the influence of such electric fields.
2.5. Current shunt
There are 12 current shunts to be used one at a
time whose nominal value (20 mA, 50 mA,
100 mA, 200 mA, 0.5 A, 1 A, 2 A, 5 A, 10 A,
20 A, 50 A and 100 A) depends on the test
current selected [9, 10]. Their input resistances
range from 40 Ω @ 20 mA to 0.008 ohm @
100 A. Thus the nominal output voltage of the
shunts is always 0.8 V.
The current shunts employ Vishay Z-Foil
resistors (Z201) whose dissipated power in each
resistor does not exceed 0.33 W.
2.6. Dual-channel digitizer
A high-resolution, digital sampling system based
on a Sigma-Delta analog-to-digital converter
(Σ−∆ ADC) has been developed and
characterized [11]. The system has been modified
to accommodate two synchronized channels.
The “equivalent sampling rate (ESR)" is the
frequency with which the samples are outputted.
As the Σ−∆ ADC works through oversampling,
ESR = fs/OSR, where fs is the clock frequency
and OSR is the oversampling ratio. The ADC
allows a maximum clock frequency of 20 MHz
and an OSR between 32 and 256, that is,
20 MHz / 32 = 625 kHz is the maximum ESR.
The design requirements are [11]: (a) two
synchronized channels; (b) dynamic regime -
total harmonic distortion (THD): < −80 dBc (@
−51 dBFS (4.382 mV), 1 kHz); signal-to-noise
ratio (SNR): > 55 dBc (@ −51 dBFS (4.382 mV),
1 kHz); signal-to-noise-plus-distortion ratio
(SINAD): > 55 dBc; effective number of bits
(ENOB): 16 bits; intermodulation distortion
(IMD): < −75 dBc (@ −57 dBFS (2.180 mV), f1
= 1 kHz and f2 = 1.25 kHz); settling time: 24
samples or 375 µs (@ OSR = 256, ESR =
64 kHz); (c) stationary regime – noise referred to
input (RMS): < 10.25 LSB or 1.2 µV (@ ESR =
64 kHz); noise-free code resolution: 18 bits; (d)
overall bandwidth of the digital sampling system
(ADC + digital filters): 250 kHz; (e) input
impedance: 10 MΩ // 60 pF; (f) other important
characteristics: flat frequency response, high
linearity, minimum temperature dependence,
minimum dc offset, and auto-calibration.
3. PROJECT MANAGEMENT
The project is coordinated by Inmetro, who is
responsible for the purchase and transportation of
the components and parts needed to the
construction of the modules, and for the
transportation of the modules needed to the
assembly of the measuring systems, in each
partner country.
Inmetro is also responsible for the
development of the wideband power and
transconductance amplifiers and of new digital
sampling algorithms. INTI is responsible for the
development of the arbitrary waveform function
generator, the dual-channel digitizer and the
current shunts (and their calibration). UTE is
responsible for the development of the resistive
voltage dividers (and their calibration).
The project activities include the design,
layout and documentation of the printed circuit
boards of the modules, the design and
documentation of the electronic packaging of the
modules, the calibration of resistive voltage
dividers and current shunts, the design and
documentation of the software and firmware, and
the measuring system integration, testing and
documentation.
4. REFERENCES
[1] W. Adad, Investigación sobre la generación
de señales arbitrarias por el método de síntesis
digital directa para su aplicación a la metrología
eléctrica, Tese de Ingeniería, Facultad de

8th Brazilian Congress on Metrology, Bento Gonçalves/RS, 2015
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Ingeniería, Universidad de Buenos Aires, May
2010.
[2] W. Adad and R. Iuzzolino, “Arbitrary
function generator using direct digital synthesis”,
CPEM Digest, 1-6 July 2012, pp. 622-623.
[3] W. Adad and R. Iuzzolino, “Low distortion
signal generator based on direct digital synthesis
for ADC characterization”, ACTA IMEKO, Vol.
1, no. 1, pp. 59-64, July 2012.
[4] O. B. Laug, “A precision power amplifier for
power/energy applications”, IEEE Trans. Instrum.
Meas., Vol. 36, pp. 994-1000, Dec. 1987.
[5] O. B. Laug, “A wide-band transconductance
amplifier for current calibrations”, IEEE Trans.
Instrum. Meas., Vol.34, pp. 639-643, Dec. 1985.
[6] O. B. Laug, “A 100 A, 100 kHz
transconductance amplier”, IEEE Trans. Instrum.
Meas., Vol. 45, pp. 440-444, Jun. 1996.
[7] D. T. Hess and K. K. Clarke, “Evaluation of
100 Ampere, 100 kHz”, transconductance
amplifiers, CPEM Digest, 6-10 July 1998, pp.
611-612.
[8] D. Slomovitz, L. Trigo, G. Aristoy, M. Brehm
and G. A. Kyriazis, “Wideband resistive voltage
divider for a standard wattmeter”, XI SEMETRO,
Nov 30 - Dec 02, 2015, Bento Gonçalves, Brasil.
[9] E. Yasuda, L. Di Lillo and G. A. Kyriazis,
“Design and construction of new shunts for a
wideband sampling wattmeter”, XI SEMETRO,
Nov 30 - Dec 02, 2015, Bento Gonçalves, Brasil.
[10] K. -E. Rydler and V. Tarasso, “Extending
ac-dc current transfer measurement to 100 A, 100
kHz”, CPEM Digest, 8-13 June 2008, pp. 28-29.
[11] R. Iuzzolino, Josephson waveforms
characterization of a Sigma-Delta Analog-to-
digital converter for data acquisition in
metrology, Dr.-Ing. Dissertation, Technische
Universität Braunschweig, Aug. 2011, TU-BS
Diss. 2011, ISBN 978-3-86387-095-9.
ACKNOWLEDGMENTS
This work is supported in part by the Conselho
Nacional de Desenvolvimento Científico e
Tecnológico (CNPq), of the Ministry of Science,
Technology and Innovation of Brazil, under
Grant CNPq/Prosul Processo Nº 490271/2011-1.