Test Interfaces for the Alpha­A
Modular Measurement System
Concepts
FeaturesPrinciples of Operation
Application Examples
Introduction
When Novocontrol introduced theAlpha analyzer, it was soon accepted
as the most accurate and versatile
analysis tool for dielectric, conductiv­
ity, and impedance spectroscopy. The
Alpha analyzer combines a series of
exceptional features like ultra­wide im­pedance range, frequency range andhigh accuracy in a fully automated,easy to use instrument [1].
These properties represented a newlevel of performance, in particular for
dielectric spectroscopy with its ex­
traordinary requirements, e.g., an im­pedance range up to 100 TΩ and loss
factor accuracy down to 3·10­5. Over abroad frequency and temperature
range, the Alpha enables, e.g., thecomplete characterisation of low­loss
dielectrics and samples with thermally

activated isolator―conductor trans­
ition, a difficult if not impossible task
before the Alpha analyzer came to themarket. The device not only excels in
its core area of dielectric spectrocopy
but also acts as a standard imped­
ance analyzer in the low impedance
range. Due to its exceptional overall
performance, the Alpha analyzer is not
only the optimal tool for dielectric
spectroscopy but an improved analys­
is tool for all kinds of electric charac­
terisations, like, e.g.,● sensor characterizations (high preci­sion measurements of small capacit­ies)● analysis of semiconductors● electronic components● bio materials, proteins, organic tis­sues
● cellulose and papers● conductive polymers and organics● ion conductors, fuel cells● power lines, transformer oils
● self restoring fuses.

Alpha­A: highest overall per­formance for both general
purpose and special applica­tions
Nevertheless, customers frequently
demanded to combine the Alpha ana­lyzer's exceptional overall perform­
ance with additional special
functionality like, e.g., extended
voltage and current ranges, non­linear
analysis, high impedance three­ andfour­electrode measurements, higher
data acquisition rates and dc meas­
urement options, including potentio­
static and galvanostatic control
functions. For both technical and eco­Fig.1. Alpha­A modular series with mainframe and available test interfaces optimized for special applications.
1Test Interfaces for the Alpha­A Analyzer

nomical reasons, however, it is difficult
to implement all these particular op­
tions in one single instrument.
The Alpha­A series not only im­
proves the performance of the earlier
introduced Alpha analyzer, but also
gives access to all the special applica­
tions mentioned above. The newseries is realized as a modular meas­
urement system based on an Alpha­A
analyzer mainframe unit, connected toa series of test interfaces (one at atime) which are optimized for special
functions. In contrast to many othersolutions, the test interfaces are notlimited to a particular functionality but
offer highest accuracy, wide imped­
ance and frequency range, too. As aconsequence, all test interfaces arewell suited for a wide range of material
measurements from conductors toisolators.
This article provides an overview of
the new features of the Alpha­A
series, focussing on the test interfaces
and some basic applications. A sum­
mary, including main functions andkey specifications can be found in Tab.
1 at the end of this article. The basic
concepts, features and principles ofoperation of the Alpha­A series andthe economical Alpha and Beta series
can be found in the Novocontrol tech­nical brochure Alpha­A, Alpha andBeta High Performance Dielectric,
Conductivity and Electrochemical Im­
pedance Analyzers.

Extended voltage and cur­rent ranges
The high voltage interfaces
HVB 300, HVB 1000, and HVB 4000
produce output voltages up to±150 VP, ±500 Vp, and ±2000 Vp, re­spectively. For high current applica­
tions, the two POT/GAL 30V­2A with
±2 A and POT/GAL 15V­10A with
±10 A are available. Within the statedlimits, any combination of ac and dc
voltage or current is supported. Poten­
tial applications of such extended out­
put signals are● non linear dielectric, conductivity
and impedance spectroscopy;● test of materials under stress;

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Fig. 3. Principle set­up of a four elec­
trode impedance measurement forelectrode­sample interface and cableeffects compensation.
Fig. 2: Sample voltage with non­linear
response current, current harmonicbase wave and first harmonic.
● evaluation of extreme high or low
impedance materials, using highvoltages or currents, respectively;● special technical materials like e.g.
fuel cell characterization with the
POT/GAL 15 V­10 A interface.

Non linear dielectric, con­ductivity and impedance
spectroscopyWith the new Alpha­A series, Novo­
control introduced the first turnkey
commercial solution for non linear
dielectric, conductivity and impedance
spectroscopy. For this purpose, the Al­
pha­A mainframe and all test inter­faces (except G22) support
measurements of the sample voltage
and current in terms of dc compon­
ents, harmonic base waves and high­er harmonics up to the interface highfrequency limit.
Non linear evaluation is fully suppor­
ted by the Novocontrol WinDETA soft­
ware which reads and graphicallydisplays all voltage and current baseand higher harmonic components. In
addition, other parameters like dc ma­

terial parameters, linear impedance,
permittivity, conductivity and the cor­2

responding higher harmonic terms areprocessed.
Base wave I*1(ω) and higher har­monic current components I*n>1(ω) arecalculated by complex Fourier Trans­
form
from the sampled current i(t), where ndenotes harmonic n­1.

Polarization effects
In a measurement of a material pre­pared between parallel­plate elec­
trodes with spacing d, the complex
permittivity or conductivity is evaluatedfrom the phase­sensitive measure­ment of the electrodes voltage differ­ence US and current IS. This method
assumes that the applied voltage US
drops homogeneously within the ma­
terial by creating a constant electricfield E=US/d.
This assumption, however, does notalways hold. Electrically inhomogen­eous layers at the sample­electrodeinterface may create a significant
voltage drop and thus reduce the ef­
fective electric field in the sample.
Such layers may be due to, e.g.,● accumulation of ions at the elec­
trode for ion conductors like e.g.
electrolytes and many liquids (water,electrode polarization);● bad electrode­sample contact con­nections (contact impedance).
Similar effects may be created whenmeasuring low­impedance samples
due to non­negligible impedance ofTest Interfaces for the Alpha­A Analyzer

cables connecting the electrodes tothe analyzer voltage and current ter­minals, respectively.
These effects may be compensatedby using separate electrodes for the
sample current and voltage measure­ments, respectively, as shown in Fig­ure 3.

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impedance is higher than 1012 Ω par­allel to 10 pF. These parameters ex­
ceed the range of most competing
instruments by several orders of mag­nitude and therefore must be con­sidered as a major improvement inbroadband dielectric, conductivity and
impedance measurements using
three­ or four­wire configurations.
When measureing high impedance
samples at high frequencies, however,the 10 pF input capacity may be of thesame order of magnitude as the
sample capacity and may thus contrib­
ute to the measured result. Three­ andfour­electrode measurements there­

Fig. 4: Principle set­up of a threeelectrode electrochemical cell for
impedance measurement.
The outer two electrodes corres­
pond to the parallel plates of a stand­ard two­electrode configuration. The
voltage, however, is measured by two
additional (e.g. ring or needle) elec­
trodes in the inner sample area where
the electric field is homogenous since
there are no interface effects present.
If the two voltages are measured byan instrument with infinite input imped­
ance, no current flow appears in thevoltage electrodes, and thus no ionscan accumulate. Due to the negligible
current, contact or cable impedancecontributions cannot create a voltage
drop as well. The electrical paramet­ers of the material portion between thevoltage electrodes can thus be de­termined without contributions from in­
terface polarization and contact orcable effects, simply by measuring thevoltage between the inner electrodes
and the current flowing through theouter electrodes. The only, but in prac­
tice crucial and rarely well fulfilled pre­sumption is the sufficiently high input
impedance of the voltage channels.
Inn addition to the standard two­wire
set­up, the ZG4 and POT/GAL inter­faces can be configured for three­, orfour­wire measurements. Their input

Fig. 5: Principle of Potentiostat / Gal­
vanostat circuit with differential refer­ence voltage inputs.
fore in practice always require a de­tailed analysis of the currents flowing
into the voltage terminals and the re­lated voltage drop at contacts or elec­
trode interfaces.

Electrochemical characteriz­
ationsThree­ and four­electrode arrange­ments are often used for electrochem­
ical studies as well. Here we are
typically less interested in the bulk
electrolyte but rather in the propertiesof the polarization layer at the metal toelectrolyte or ion conductor interface
and the related chemical reactions.
This is just the opposite of typicaldielectric, conductivity and impedancematerial spectroscopy where these ef­
fects are cpnsidered as undesirable
electrode polarization which can besuppressed by using, e.g., four­elec­
trode arrangements and special cells.
The measurement set­up for a typic­
al electrochemical three­electrode3

measurement is shown in Figure 4. In
addition to the two parallel plate elec­
trodes (denoted as Counter and Work­ing electrodes, respectively), a third
voltage reference electrode is placed
close to the polarization layer andmeasures the voltage difference of thepolarization double layer capacity to
the working electrode. In contrast to
material spectroscopy where all elec­
trodes are made of inert metal as e.g.
gold, stainless steel or platinum, thisapplies for the electrochemical cellonly for the counter electrode feeding
current into the electrolyte.
The working electrode consists ofthe metal to be characterized in com­bination with the electrolyte. The refer­ence electrode is usually an open
tipped glass capillary filled with astandard electrolyte coupled to a
standard metal in order to create adefined electrochemical potential tothe electrolyte.
The total potential drop across thecell is summed up by all contributionsof the chemical process like masstransport, chemical and adsorption
steps, electron transfer, etc [2]. By
measuring the impedance spectrum
Vref*(ω)/Is*(ω) and fitting it using anequivalent circuit model, the several
process contributions can be separ­
ated from each other. The typical eval­uation includes determination of a
Warburg impedance related to masstransport, electron transfer resistance,electrolyte resistance and double layer
capacity [2].
As on the working electrodes anelectrochemical reaction takes place,
it is necessary to keep the dc potential
VRef at a defined value or alternatively
apply a constant dc current to the cell.
This can be achieved by a Potentio­
stat/Galvanostat dc circuit as shown in
Figure 5. In potentiostat mode, thevoltage amplifier connected to the CE
electrode compares the differential
voltage Vprc = VRE+ ­ VRE­ of both refer­ence electrodes with the intended
voltage Vsetdc. The amplifier adjusts its
output voltage until Vprc and Vsetdc
match resulting in a constant andsample impedance independent refer­ence voltage differential which can beTest Interfaces for the Alpha­A Analyzer

Novocontrol Technologies

adjusted by Vsetdc. In galvanostat
mode, Vprc is created proportional tothe measured cell current by a current
to voltage converter (V<­I), resulting inconstant sample cell current. In bothmodes, the variable capacitor Ct ad­
justs the control loop time constant inorder to avoid free high frequency os­
cillations caused by too high open
loop gain.
For impedance measurement anadditional small AC voltage Vac is su­
perimposed to Vsetdc and the ac re­sponse is measured according to
Figure 4.
The two POT/GAL interfaces are
optimized for impedance measure­ments of electrolytes with superim­
posed controlled voltage or current as
described above. The POT/GAL 15V­
10A provides up to ±10 A output cur­rent and thus is particulary well suitedfor fuel cell characterization. The
POT/GAL 30V­2A is a high quality
general purpose instrument. In addi­
tion to dc control, the dc voltages andcurrent at the four electrodes are con­tinuously measured and displayed.
In contrast to existing potentiostats
and galvanostats for impedance
measurement, the POT/GAL inter­faces are not restricted to electrolyte
characterization but can be used fornearly all other kind of materials as
well. Both interfaces, e.g., support thereference capacitor technique for ac­
curate and broadband measurementof high impedance low loss isolators.
For samples not requiring controlled
dc signals, a third direct voltage mode
is included which bypasses the control
amplifier and allows operation as astandard dielectric, conductivity and
impedance analyzer with extended
current and voltage range. As a further
improvement and new feature, thebandwidth for impedance measure­ment is not limited by the selected
time constant of the dc control amplifi­er (Fig. 5). Instead for any dc band­
width like e.g. 1 Hz, the full AC
impedance frequency range up to
1 MHz is available in both dc con­trolled modes. Finally, both POT/GAL
interfaces provide sophisticatedmeans of protecting sensitive (and po­

second. This allows process monitor­
ing on time scales below 10 ms. The
fast data rates are supported for all
test interfaces, but not available for all
operation modes like, e.g., reference
measurement mode or at frequencies
below 200 Hz.
For the mainframe standard version(without the fast option) the maximum
data rate is up to 10 data points per
second.

Two electrode standard con­figurations

Fig. 6: System topology for the Alpha­A series and a traditional PC ­ FRA ­interface system
tentially expensive) samples. This isaccomplished by voltage and current
limiters which are● operating independently of the dc
control loop
● fast and continuously adjustable● operative even in case of oscillation
or reference electrode cable dam­age.

Characterization of fast time­dependent processes
One major area of dielectric, con­ductivity and impedance spectro­
scopy is monitoring samples with time
variant properties which are usually
due to chemical reactions or crystalliz­
ation. Examples are measurementsof, e.g., epoxy curing or material age­ing. Most dielectric analysis systems
had data rates in the range of several
seconds. This limit is significantly re­duced by the new Alpha­A mainframe:
its fast data rate option can measure
up to 157 impedance data points per

4

For most dielectric, conductivity and
impedance measurements polariza­tion or contact effects as discussed
above are less prominent. In thiscase, the standard configuration withthe sample material prepared between
two parallel plate electrodes is mostadvantageous. This arrangement al­lows easy and flexible sample prepar­
ation. Nevertheless, the design
requirements for a suitable sample
cell, operating over wide frequency,
impedance and temperature ranges
without sacrificing the Alpha analyzer's
high accuracy are extraordinary de­manding.
Such a sample cell in realized as apart of the ZGS interface which is the
successor of the popular Alpha­S ana­lyzer active sample cell [1]. In addition
to the sample cell, the ZGS houses animpedance converter and reference
capacitors in its top part. This arrange­
ment avoids cables in the impedance
path between the sample electrodes
and analyzer input terminals. Cables
may limit the usable high frequency
range due to inductance and contrib­
ute low frequency noise for high im­pedance samples.
In contrast to other interfaces andsolutions from other manufactures, theZGS is specified at the sample elec­
trodes position: users do not have tocare about artefacts by cell contribu­
tions to the measured results. The
ZGS interface is thus the optimal andturnkey solution for dielectric, conduct­
ivity and impedance material meas­
urements for two­electrodeconfigurations.

Test Interfaces for the Alpha­A Analyzer

The ZG2 interface contains thesame impedance converter and refer­ence capacitors as the ZGS, but no in­tegrated sample cell. The ZG2 can beconnected by BNC terminals to any
passive sample cell like, e.g., the No­
vocontrol BDS 1200 or any imped­
ance under test. Compared to the
ZGS, the combination ZG2 + BDS
1200 is more flexible but not as accur­ate due to the additional cables
between the BDS 1200 and the ZG2.

New test interface concept
improves flexibility and per­formance
For the test interfaces, a new sys­
tem concept is realized, combining theadvantages of a stand alone dielectric,
conductivity and impedance analyzer
with the specialized functionality of
traditional combined analyzer ­ inter­face combinations.
Compared to traditional set­ups, the
new Alpha­A series has a different
system connection topology startingwith one out of a series of interfaces
which is connected to the Alpha­A
mainframe. The mainframe operates
the entire system including low levelinterface control and high level result
evaluation. To this end, the mainframe
is operated by a PC via a set of highlevel GPIB commands in a flexible
and simple fashion.
A typical command sequence could
look like this:● adjust AC voltage and frequency● start measurement● read result as complex impedanceor capacity.
Depending on the interface type, themainframe automatically adapts its
functionality and command set. The
voltage adjust command, e.g., will ac­
cept voltages up to ±500 V for a
HVB 1000 high voltage interface but
only ±40V for a ZG2 interface; special
commands for DC polarization control
will be available for the POT/GAL in­
terfaces.
The adaptive interface concept al­lows● fast low level data exchange andcontrol between the Alpha main­
frame and the interface;

Novocontrol Technologies● easy and straightforward integrationof the Alpha­A system into own writ­ten control software or system con­trol packages of othermanufacturers.
Though the Alpha­A and all inter­faces except G22 are completely in­tegrated in the Novocontrol WinDETA
software, operation by other software
may be required if the analyzer is tobe operated in combination with otherequipment (e.g., at a synchrotronring).
This option is an advantage overtraditional device combinations fordielectric or electrochemical imped­
ance measurements, where a fre­quency response analyzer and aninterface need to be controlled by a
dedicated PC software and the sys­
tem can not operate without this soft­
ware as shown in Figure 6.

Frequency response, gain
phase measurements
In impedance mode, typically used
for dielectric, conductivity and imped­
ance spectroscopy, the Alpha­A ana­lyzer measures the voltage andresponse current of a material sample
to an applied sine wave signal.
In gain phase mode, a second
voltage is measured instead of thecurrent. This allows to measure two
response voltages to an applied sine
wave driver signal at two arbitrary
points of a system under test. The twovoltages are measured with the Alpha­
A frequency response analyzer chan­nels CH1 and CH2. The applied sine
wave is created by the Alpha sine
wave generator.
Gain phase measurements are sup­ported by the Alpha­A mainframe bothstand­alone or in combination with any
test interface, except the three HVB
test interfaces which are for imped­
ance mode only. The G22 interface isfor gain phase measurements only
and optimized for those applications.
A typical application of a gain­phasemeasurement is, e.g., the transfer
function of an amplifier or transformer.
In this case, the Alpha generator out­
put and input CH1 have to be connec­
ted to the amplifier or transformer
input and CH2 to the amplifier ortransformer output. The complex
5transfer function defined by Vout*/Vin* isdetermined by measuring the voltages
at CH2 and CH1.
It should be emphasized that in gain
phase mode, the Alpha­A can be oper­
ated like a digital lock­in amplifier with
two input channels. The main functionof a lock­in amplifier is to apply a sig­
nal with a defined frequency to a sys­
tem under test and to measure a
response signal. As a further lock­inamplifier feature, only the frequency
component of the applied generator
signal is detected in the response sig­
nal. Since most of the signal noise
and DC errors appear at other fre­quencies, these contributions will be
suppressed with very high efficiency.
The Alpha­A uses the same principle,
but offers an additional voltage chan­nel, wider bandwidth and better accur­
acy than standard lock­in amplifiers.
Gain phase measurements are,therefore, not specifically related todielectric, conductivity and impedance
spectroscopy but may be of generalinterest if● a very small or noisy signal has tobe measured with high precision;● the response of any kind of system
to an applied signal in the frequency
domain has to be measured.

References[ 1 ] G. Schaumburg, Novocontrol,
Dielectrics Newsletter, Issue May
1999[ 2 ] Electrochemistry, Carl H. Ham­man et. al, Wiley­VCH, 1998, ISBN 3­
527­29096­6
Gerhard Schaumburg
Novocontrol Technologies GmbH &Co. KGTest Interfaces for the Alpha­A Analyzer

Novocontrol Technologies

Test Interfaces: Overview and Specifications

ZGS

ZG2

ZG4

HVB 300
HVB 1000
HVB 4000Dielectric or conductive samples
which can be prepared between
parallel plate electrodes like, e.g.,
polymers, semiconductors, glasses,
and liquids or powders with not toohigh ion conductivity (electrodepolarization).
Optimized for broadband
measurements of low loss dielectrics
over a huge temperature range. Most
accurate and straightforward solution
for parallel plate electrodeconfigurations.

Included active parallel
plate sample cell,
specification includes celleffects.

F 3 µHz ‒ 40 MHz
ZR
10 mΩ ‒ 1014 Ω
tan δ 3.10­5; Pa 2 m°
VAC
±4.3 VP
VDC ±40 VP,
70 mA max
ZO
50 Ω

General purpose interface for 2­wire
measurements of● dielectric or conductive material
samples in combinations with the
Novocontrol BDS 1200 parallel platesample cell;● passive customer own made sample
cells;● electronic components.

Fixed two­wire
measurement configuration.
Economical version of ZG4
without differential voltage
inputs for two­ or four­wire
measurements.

F 3 µHz ‒ 40 MHz
ZR
10 mΩ ‒ 1014 Ω
tan δ 3.10­5; Pa 2 m°
VAC
±4.3 VP
VDC ±40 VP,
70 mA max
ZO
50 Ω

Selectable two­, three­,or four­wire measurement
configuration withadditional high input
impedance and driven
shielded Vhigh and Vlow
differential voltage inputs.

F 3 µHz ‒ 40 MHz
ZR
0.1 mΩ ‒ 1014 Ω
tan δ 3.10­5; Pa 2 m°
VAC
±4.3 VP
VDC ±40 VP,
70 mA max
ZO
50 Ω

High AC and/or DC output
voltage. Protected against
sample breakdowns andpermanent shorts.

tanδ 3.10­5; Pa 2 m°
HVB 300:
F 3 µHz ‒ 1 MHz
ZR
1 Ω ‒ 1015 Ω
VAC+VDC ±150 VP
70 mA max
ZO
200 Ω
HVB 1000:F 3 µHz ‒ 10 kHz
ZR
100 Ω ‒ 1015 Ω
VAC+VDC ±500 VP,
3.3 mA max
ZO
150 kΩ
HVB 4000:F 3 µHz ‒ 10 kHz
ZR
1 k Ω ‒ 1015 Ω
VAC+VDC ±2000 VP,
2.7 mA max
ZO
750 kΩ

Dielectric or conductive samples with● significant electrode contact
impedance or electrode sample
interface polarization like, e.g.,
electrolytes, ion­conducting liquids(e.g. water based);● low impedance samples below 1 Ω
like, e.g,. strong electrolytes, heavily
doped semiconductors, metals,
superconductors;● electronic components or networks.
Dielectrics, semiconductors orelectronic components at high AC
and/or DC voltages:● non linear dielectric/impedance
spectroscopy● characterization of materials orcomponents under stress;● extreme high impedance samples
exceeding 1014 Ω
Optimized for broadband highvoltage measurements of low­loss
dielectrics. Operation with
Novocontrol High Voltage Sample
Cell recommended.

6

Test Interfaces for the Alpha­A Analyzer

Test Interface

POT/GAL 30 V­2A

POT/GAL 15 V­10A

Novocontrol Technologies

Recommended Applications

Special Features

Key Specifications● Electrochemical cell
reactions, metal electrolyte
interfaces, ion conductors ,conductive liquids for both
low and high impedance
samples up to 1013 Ω;● general purpose low
impedance samples orelectronic components athigh currents.

High power superimposed
fixed or controlled(Potentiostat) dc voltage orconstant dc current(Galvanostat).
Two­, three­, or four­wire
input configuration withdriven shields.

F 3 µHz ‒ 1 MHz
tan δ 10­4; Pa 6 m°
ZR
1 mΩ ‒ 1013 Ω

Simultaneous measurementof DC voltage and current at
the four sample terminals.
Continuously adjustable
output voltage and current
limit.

POT/GAL 15V­10A
VAC+VDC ±15 VP, ±10 AP
ZO
0.1 Ω‒ 1 kΩZVI1012 Ω|10 pF

Two highly sensitive voltage
channels with highimpedance driven shielded
differential inputs.
Not for impedance
measurements.

F 3 µHz ‒ 40 MHz
Pa
10 m°
VAC
±4.3 VP
VDC ±40 VP,
70 mA max
ZO
50 Ω
ZVI
1012 Ω║10 pF

Optimized for low
impedance samples withstrong electrode sample
interface polarization effects.

G22High accuracy frequency
response and gain phasemeasurements. Measures
the amplitudes and phaseshift V1high­V1low andV2high­V2low of two voltage
channels.
Similar functionality to adouble input channel lockin
amplifier with improved
accuracy.

POT/GAL 30V­2A
VAC+VDC ±30 VP, ±2 AP
ZO
1 Ω‒ 1 kΩ
ZVI1012 Ω║10 pF

Tab. 1: Alpha­A analyzer test interfaces overview. All test interfaces except the G22 support automatic reference capacitor
measurements and are suited for both dielectric and conductive samples but optimized for special applications. The Alpha­A
mainframe standalone and all interfaces except HVB support dual­channel high accuracy frequency response or gain phasemeasurements.
Ranges:
F: Frequency, ZR: Impedance, VAC: AC output voltage, VDC: DC output voltage, VAC+VDC: Any combination of |AC output
voltage| + |DC output voltage|
Absolute Accuracies: tanδ: loss factor, Pa: Phase angle
Other: ZVI: Differential voltage terminals input impedance, ZO: Power amplifier output impedance

7