CEN ISO/TR 5602:2022

Sources of error in the use of electrochemical impedance spectroscopy for the investigation of coatings and other materials (ISO/TR 5602:2021)

This document describes the main sources of error in the use of electrochemical impedance spectroscopy for the investigation of coatings and other materials. The sources of error listed here include all process steps from the set-up of the sample with the measuring cell right through to evaluation.
NOTE       The sources of error discussed here do not represent a complete list.

Fehlerquellen bei der Anwendung elektrochemischer Impedanzspektroskopie bei der Untersuchung von Beschichtungen und anderer Stoffe (ISO/TR 5602:2021)

Dieses Dokument beschreibt die wichtigsten Fehlerquellen bei der Anwendung der elektrochemischen Impedanzspektroskopie zur Untersuchung von Beschichtungen und anderen Materialien. Die hier aufgeführten Fehlerquellen umfassen alle Prozessschritte vom Probenaufbau mit der Messzelle bis hin zur Auswertung.
ANMERKUNG   Die hier erörterten Fehlerquellen stellen keine vollständige Liste dar.

Sources d'erreur dans l'utilisation de la spectroscopie d’impédance électrochimique pour l'étude des revêtements et autres matériaux (ISO/TR 5602:2021)

Le présent document décrit les principales sources d’erreur dans l’utilisation de la spectroscopie d’impédance électrochimique pour l’étude des revêtements et autres matériaux. Les sources d’erreur énumérées ici comprennent toutes les étapes du processus, de la mise en place de l’échantillon avec la cellule de mesure jusqu’à l’évaluation.
NOTE       Les sources d’erreur évoquées ici ne constituent pas une liste exhaustive.

Viri napak pri uporabi elektrokemijske impedančne spektroskopije pri preiskavah premazov in drugih materialov (ISO/TR 5602:2021)

Ta dokument opisuje glavne vire napak pri uporabi elektrokemijske impedančne spektroskopije pri preiskavah premazov in drugih materialov. Tukaj navedeni viri napak vključujejo vse korake postopka od nastavitve vzorca z merilno celico vse do ocene.

General Information

• Status: Published
• Publication Date: 22-Nov-2022
• ICS: 87.040 - Paints and varnishes
• Technical Committee: CEN/TC 139 - Paints and varnishes
• Drafting Committee: CEN/TC 139 - Paints and varnishes
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 23-Nov-2022
• Due Date: 04-Feb-2024
• Completion Date: 23-Nov-2022
• Ref Project: SIST-TP CEN ISO/TR 5602:2023 - Sources of error in the use of electrochemical impedance spectroscopy for the investigation of coatings and other materials (ISO/TR 5602:2021)

Overview

CEN ISO/TR 5602:2022 (adopted from ISO/TR 5602:2021) is a technical report that documents common sources of error in electrochemical impedance spectroscopy (EIS) when investigating coatings and other materials. The report covers the full workflow - from sample and measuring-cell set‑up through measurement, parameter selection and data evaluation - and explains how experimental and instrumental factors can bias EIS results. The document is informative (not normative) and explicitly notes that the listed errors are not exhaustive.

Key topics

The report organizes practical error sources and mitigation guidance across these technical areas:

• Measuring-cell make‑up
  • Surface roughness, O‑ring and exposed area definition, optically detectable and non‑detectable leaks
  • Reference and counter electrode positioning, shielding, bleeding, poisoning, gas inclusion
• Electronics and shielding
  • Use of Faraday cages, cable effects (shielding, extension, breaks), contact resistances, inductance
  • Power‑supply noise, insufficient signal‑to‑noise ratio, peripheral-device interference
• Parameter selection and measurement limits
  • Amplitude selection, frequency range limits, switching, open‑lead tests and dummy cells
• Non‑stationary conditions
  • Temperature fluctuations, changing electrolyte conductivity, swelling, drifting open‑circuit potential (OCP), corroding electrodes, gas formation
• Data modelling and interpretation
  • Choice and limitations of equivalent circuits (constant phase element, Warburg impedance)
  • Measurement uncertainty, plausibility checks and practical interpretation for coating systems
• Data presentation and annexes
  • Guidance on presenting results and annexes with capacitance calculations, double‑layer effects and corrosion‑related apparent capacitances

Applications and who uses it

This report is intended for professionals involved in EIS testing of coatings and materials, including:

• Corrosion scientists and electrochemists
• Coatings R&D and formulation engineers
• Quality‑control and test laboratories
• Materials scientists and surface analysts
• EIS instrument manufacturers and test-cell designers

Practical uses include troubleshooting inconsistent EIS data, designing robust measuring cells, defining measurement protocols (amplitude/frequency), improving signal‑to‑noise, selecting appropriate equivalent circuits, and assessing barrier properties and coating performance with greater confidence.

Related standards

• ISO/TR 5602:2021 (original ISO text)
• ISO 16773 series (EIS measurement methodology and dummy‑cell guidance)
• CEN/TC 139 and ISO/TC 35 background for paints and varnishes

Keywords: electrochemical impedance spectroscopy, EIS, coatings, sources of error, measuring cell, equivalent circuit, frequency range, signal‑to‑noise, corrosion, measurement uncertainty.

Standards Content (Sample)

SLOVENSKI STANDARD
01-februar-2023
Viri napak pri uporabi elektrokemijske impedančne spektroskopije pri preiskavah
premazov in drugih materialov (ISO/TR 5602:2021)
Sources of error in the use of electrochemical impedance spectroscopy for the
investigation of coatings and other materials (ISO/TR 5602:2021)
Fehlerquellen bei der Anwendung elektrochemischer Elektroimpdanzspektroskopie bei
der Untersuchung von Beschichtungen und anderer Stoffe (ISO/TR 5602:2021)
Sources d'erreur dans l'utilisation de la spectroscopie d’impédance électrochimique pour
l'étude des revêtements et autres matériaux (ISO/TR 5602:2021)
Ta slovenski standard je istoveten z: CEN ISO/TR 5602:2022
ICS:
87.040 Barve in laki Paints and varnishes
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN ISO/TR 5602
TECHNICAL REPORT
RAPPORT TECHNIQUE
November 2022
TECHNISCHER REPORT
ICS 87.040
English Version
Sources of error in the use of electrochemical impedance
spectroscopy for the investigation of coatings and other
materials (ISO/TR 5602:2021)
Sources d'erreur dans l'utilisation de la spectroscopie Fehlerquellen bei der Anwendung elektrochemischer
d'impédance électrochimique pour l'étude des Elektroimpdanzspektroskopie bei der Untersuchung
revêtements et autres matériaux (ISO/TR 5602:2021) von Beschichtungen und anderer Stoffe (ISO/TR
5602:2021)
This Technical Report was approved by CEN on 21 November 2022. It has been drawn up by the Technical Committee CEN/TC
139.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TR 5602:2022 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO/TR 5602:2021 has been prepared by Technical Committee ISO/TC 35 "Paints and
varnishes” of the International Organization for Standardization (ISO) and has been taken over as
which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
Endorsement notice
The text of ISO/TR 5602:2021 has been approved by CEN as CEN ISO/TR 5602:2022 without any
modification.
TECHNICAL ISO/TR
REPORT 5602
First edition
2021-11
Sources of error in the use of
electrochemical impedance
spectroscopy for the investigation of
coatings and other materials
Sources d'erreur dans l'utilisation de la spectroscopie d’impédance
électrochimique pour l'étude des revêtements et autres matériaux
Reference number
ISO/TR 5602:2021(E)
ISO/TR 5602:2021(E)
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO/TR 5602:2021(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Error in the make-up of the measuring cell . 1
4.1 Roughness of the surface . 1
4.2 O-ring — Considerations about the precise determination of the exposed area . 3
4.3 Faulty cell make-up . 7
4.3.1 Optically detectable leaks . 7
4.3.2 Optically non-detectable causes . 7
4.4 Reference electrodes . 9
4.4.1 General information on the distance between the reference and working
electrodes . 9
4.4.2 Shielding . 11
4.4.3 Air bubble in the reference electrode . 11
4.4.4 Poisoning of the reference electrode . 11
4.4.5 Bleeding of the reference electrode . 11
4.5 Counter electrodes . 11
4.5.1 Relative sizes . 11
4.5.2 Reactive counter electrodes . 11
4.6 Gas inclusions in the measuring cell . 11
5 Faults caused by electronics incl. shielding .12
5.1 Faraday cage .12
5.2 Extended cable (without active shielding) . 15
5.3 Cable breaks . 16
5.4 Contact resistances between metallic contacts and the working electrode/counter
electrode . 17
5.5 Inductivities . 18
5.6 Measurement range switching . 19
5.7 Scattering signals in power supply . 20
5.8 Insufficient signal-to-noise ratio . 22
5.9 Influence of peripheral devices . 22
6 Parameter selection, measurement range limits .24
6.1 Open-lead test. 24
6.2 Note on dummy cells – ISO 16773-3 . 24
6.3 Unsuitable amplitude . 24
6.4 Insufficient frequency range .26
6.5 Repetition rate for subsequent measurements . 27
7 Non-stationary measurement conditions .28
7.1 General .28
7.2 Temperature fluctuations . 29
7.3 Electrolytic conductivity . 31
7.4 Swelling . 31
7.5 Drifting OCP . 31
7.6 Corroding working electrode .33
7.7 Reactive counter electrodes . 33
7.8 Gas formation at the counter electrode . 33
8 Design and selection of equivalent circuit diagrams.34
8.1 Constant phase element .34
8.2 Multiple possibilities for the selection of equivalent circuits . 35
iii
ISO/TR 5602:2021(E)
8.3 Warburg impedance . 37
9 Significance of measurement values from equivalent circuits .37
9.1 Measurement uncertainty . . 37
9.2 Plausibility analysis .38
10 Interpretation of the measurement values of various coating systems .39
10.1 Pre-treatment . 39
10.2 Film thickness and measurement surface .40
10.3 Number of layers . 41
10.4 Conditioning. 45
10.5 Generic type of binder . . 45
11 Presentation of data .45
Annex A (informative) Calculation of the coating capacitance .48
Annex B (informative) Further information on the influence of the double-layer capacitance .49
Annex C (informative) Estimation of the order of magnitude of an apparent capacitance
caused by corrosion .50
Bibliography .52
iv
ISO/TR 5602:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee
SC 9, General test methods for paints and varnishes.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
ISO/TR 5602:2021(E)
Introduction
Electrochemical impedance spectroscopy is described in detail in ISO 16773-1 to ISO 16773-4. It
became apparent during use of these standards that sources of error and measurement artefacts that
lead to incorrect interpretations are not dealt with comprehensively. This document supplements the
ISO 16773 series of standards to deal with this issue.
vi
TECHNICAL REPORT ISO/TR 5602:2021(E)
Sources of error in the use of electrochemical impedance
spectroscopy for the investigation of coatings and other
materials
1 Scope
This document describes the main sources of error in the use of electrochemical impedance spectroscopy
for the investigation of coatings and other materials. The sources of error listed here include all process
steps from the set-up of the sample with the measuring cell right through to evaluation.
NOTE The sources of error discussed here do not represent a complete list.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4618, Paints and varnishes — Terms and definitions
ISO 16773-1, Electrochemical impedance spectroscopy (EIS) on coated and uncoated metallic specimens —
Part 1: Terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618, ISO 16773-1 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
limit impedance
minimum or maximum impedance that can be measured using the impedance spectrometer
3.2
limit frequency
minimum or maximum frequency that can be set on the impedance spectrometer
4 Error in the make-up of the measuring cell
4.1 Roughness of the surface
A wet and rough surface could conduct stray currents to a scratch or artificial defect, see Figure 1. This
could yield in a spectrum showing a much lower resistance than in reality. Examples of spectra are
shown in Figure 2.
ISO/TR 5602:2021(E)
Key
1 without UV-irradiation
2 after UV-irradiation
PMMA tube
seal
coating
electrolyte
steel
Figure 1 — Conductive path from counter electrode to scratch due to surface roughness
The rough surface was measured on the unscratched area. Although the rough surface was dried with
a tissue, the residual amount of water was sufficient to produce a conductive path via the scratch to the
substrate. As result, the spectrum of the sample resulted in the incorrect identification of a defective
coating. After 2 h of continuous immersion in the cell, the surface outside the cell had dried and the
conductive path was interrupted, which resulted in a typical spectrum of an intact coating.
ISO/TR 5602:2021(E)
Key
X frequency, f, in Hz
Y1 impedance, Z, in Ω
Y2 phase angle, φ, in degrees
2 h drying
wet
Figure 2 — EIS spectra of the initially wet coating and 2 h after drying
4.2 O-ring — Considerations about the precise determination of the exposed area
If an O-ring is used to seal the cell, the exposed area is smaller than the theoretically assumed area
because the O-ring will be compressed, and therefore, the exposed area will be reduced (see Figure 3).
a)  Ideal situation, uncompressed
ISO/TR 5602:2021(E)
b)  Real situation, compressed
Key
R radius of the uncompressed O-ring
a difference in the radius of the O-ring due to compression
Figure 3 — Uncompressed and compressed O-ring
This behaviour can be visualized easily by using two transparent PMMA (poly methylene methacrylate)
plates which were compressed with 4 screws. The screws were gently tightened only by hand and
without any tools.
Figure 4 shows the set-up and Figure 5 and Figure 6 show the compressed O-rings of 1,2 cm and 5 cm
diameter, respectively.
Figure 4 — Compression of O-ring using 4 screws
ISO/TR 5602:2021(E)
Figure 5 — Compressed O-ring of 1,2 cm diameter
Figure 6 — Compressed O-ring of 5 cm diameter
The exposed area can be calculated as illustrated in Figure 7.
SR=π ·
a)  O-ring not compressed — Contact surface of the specimen with testing solution
ISO/TR 5602:2021(E)
SR=−π · a
()
b)  O-ring compressed — Contact surface of the specimen with testing solution
2 2
ΔπSS=−SR=⋅ −⋅π Ra−
()
01 0 0
c)  Reduction of contact surface of specimen due to O-ring compression
Key
S geometric area with the O-ring uncompressed
S exposed area with the O-ring compressed
ΔS difference S − S
0 1
R radius of the uncompressed O-ring
a difference of the radius of the O-ring due to compression
Figure 7 — Calculation of the exposed area
The error dS between exposed area S and geometric area S can be approximated depending on the
1 0
O-ring radius, R , and the measured contact, 2a, using Formula (1):
2 ⋅⋅aR  ⋅ a
ΔS
d S =⋅ 100= ⋅ 100 (1)
S
R
Some examples for calculation of the error of the exposed area are shown in Table 1.
ISO/TR 5602:2021(E)
Table 1 — Approximate error estimation of contact surface of specimens in corrosion cells
Geometric area
Difference in Exposed area
Radius of the with the O-ring
the radius of the with the O-ring Error of the
uncompressed uncompressed
O-ring due to compressed exposed area
O-ring (theoretical
compression (real surface)
surface)
R a R − a S S dS
0 0 0 1
2 2
mm mm mm mm mm %
6 0,8 5,2 113 85 25
12 0,8 11,2 452 394 13
24 0,8 23,2 1 809 1 690 7
30 0,8 29,2 2 826 2 677 5
6 1 5 113 79 31
12 1 11 452 380 16
24 1 23 1 809 1 661 8
30 1 29 2 826 2 641 7
6 1,25 4,75 113 71 37
12 1,25 10,75 452 363 20
24 1,25 22,75 1 809 1 625 10
30 1,25 28,75 2 826 2 595 8
4.3 Faulty cell make-up
4.3.1 Optically detectable leaks
Optically detectable leaks in the measuring cell are obvious and are not dealt with here.
4.3.2 Optically non-detectable causes
The behaviour shown in Figure 8 was observed in a non-reproducible manner for a very well-
documented coating (cathodic e-coat) that is in familiar use in measurement technology. This behaviour
occurred with varying amounts of pressure on the measuring cell at different locations on the same
test panels; however, a direct relationship was not detected.
If the behaviour shown in Figure 8 is observed in a measuring cell, the measuring cell is not suitable.
Generally, every measurement set-up is tested for errors with a familiar system before this measuring
cell is used on an unfamiliar system.
ISO/TR 5602:2021(E)
a)  Magnitude of impedance as a function of frequency
b)  Phase angle as a function of frequency
Key
X logarithm of the frequency, log f, in Hz
Y1 logarithm of the modulus of the impedance, log |Z|, in Ω⋅cm
Y2 absolute value of the phase angle, φ, in degrees
wrong sealing
sealing correct
wrong sealing
sealing correct
Figure 8 — Possible influence of a faulty cell set-up
ISO/TR 5602:2021(E)
4.4 Reference electrodes
4.4.1 General information on the distance between the reference and working electrodes
RE1, RE2 and RE3 as shown in Figure 9 are the various positions where the reference electrode RE can
be placed to measure the potential. At distances very close to the working electrode, the equipotential
lines are close together and small variations in the position of the reference electrode can lead to
large variations in the ohmic drop. This applies in particular to uncoated samples. In some cases, it
is preferable not to use a Luggin capillary, and instead to place the reference electrode far from the
working electrode and measure and compensate for the ohmic drop.
Key
1 working electrode (WE)
2 reference electrode 1 (RE 1)
3 reference electrode 2 (RE 2)
4 reference electrode 3 (RE 3)
5 equipotential lines
Figure 9 — Equipotential lines shown at close proximity to the working electrode
The influence of the reference electrode distance is negligible for measurements on coated (high-
resistance) samples. See Figure 10.
ISO/TR 5602:2021(E)
a)  Three |Z| curves are shown here that were recorded with different distances between the
reference electrode and working electrode. The distances to the coated substrate are 37 mm
(top), 15 mm (middle) and 2 mm (bottom).
b)  Three phase angle curves are shown here that were recorded with different distances be-
tween the reference electrode and working electrode. The distances to the coated substrate are
37 mm (top), 15 mm (middle) and 2 mm (bottom).
Key
X1 frequency, f, in Hz
X2 frequency, f, in Hz
Y1 modulus of the impedance, |Z|, in Ω⋅cm
Y2 absolute value of the phase angle, φ, degrees
top (mostly invisible due to overlayings with the middle and bottom data points)
middle
bottom
Figure 10 — Spectra of coated (high-resistance) samples
ISO/TR 5602:2021(E)
4.4.2 Shielding
If the distance between the reference electrode and working electrode is too small, the electrical field
is shielded, and this leads to an undefined state. Shielding of the working electrode by the reference
electrode can only occur as a problem with the Haber-Luggin capillary, as there is a very small distance
between the capillary opening and working electrode in this case.
4.4.3 Air bubble in the reference electrode
An air bubble in the reference electrode leads to undefined potentials and can result in strong
oscillations in the phase.
4.4.4 Poisoning of the reference electrode
Poisoning of the reference electrode occurs when ions or molecules diffuse into the electrode and react
with the reference material. This results in a potential shift. This effect is less significant with a coated
electrode than with a metallic electrode.
Poisoning of the reference electrode can largely be prevented by hydrostatic effects and by correctly
positioning the electrode.
The use of a Haber-Luggin electrode can be effective in order to delay poisoning of the reference
electrode.
4.4.5 Bleeding of the reference electrode
Diffusion of ions from the reference electrode into the electrolyte is referred to as bleeding of the
reference electrode. These ions can alter the reaction at the working electrode.
The use of a Haber-Luggin electrode can be effective in order to delay bleeding of the reference
electrode.
4.5 Counter electrodes
4.5.1 Relative sizes
For coated samples, there are no known artefacts that can be ascribed to an unsuitable choice of relative
sizes of the working electrode and counter electrode. This can be explained by the very low currents
in the measurement of these high-resistance systems. However, the area of the counter electrode is
chosen as large as possible.
4.5.2 Reactive counter electrodes
As regards the make-up of measuring cells, the counter electrode consists of a material that is inert to
the electrolyte over the period of measurement. If there are doubts as to the suitability of the counter
electrode material, comparative measurements are carried out on different materials with a known
reference sample. Exposure experiments are also carried out.
4.6 Gas inclusions in the measuring cell
Despite the influence of gas bubbles in the measuring cell that is to be expected theoretically, this could
not be verified in a test experiment with gas bubbles on the counter electrode, see Figure 11. A single-
layer test coating was measured.
ISO/TR 5602:2021(E)
Key
X logarithm of the frequency, log f, in Hz
Y1 logarithm of the modulus of the impedance, log |Z|, in Ω⋅cm
Y2 absolute value of the phase angle, φ, in degrees
with air bubbles
without air bubbles
Figure 11 — Bode plots for two measurements with and without gas bubbles on the counter
electrode
The reduction of the effective area caused by gas-bubble absorption at the working electrode has an
influence on the measurement values of the layer capacitance and layer resistance.
5 Faults caused by electronics incl. shielding
5.1 Faraday cage
Any discontinuities in the phase angle plot at 50 Hz are probably due to insufficient shielding. See
Figure 12.
ISO/TR 5602:2021(E)
Key
X frequency, f, in Hz
Y1 modulus of the impedance, |Z|, in Ω⋅cm
Y2 absolute value of the phase angle, φ, in degrees
t = 0 h
t = 10 h
t = 20 h
t = 40 h
t = 70 h
Figure 12 — Dramatic grid frequency influence visible on a Bode plot
Figure 12 shows a dramatic example for grid frequency influences, whereas Figure 13 shows negligible
disturbance.
ISO/TR 5602:2021(E)
Key
X logarithm of the frequency, log f, in Hz
Y1 logarithm of the modulus of the impedance, log |Z|, in Ω⋅cm
Y2 absolute value of the phase angle, φ, in degrees
phase angle
impedance
Figure 13 — Negligible grid frequency influence visible on a Bode plot
Figure 14 shows a magnified representation of the phase plot; the phase plot reacts particularly
sensitively to grid frequency influences.
ISO/TR 5602:2021(E)
Key
X logarithm of the frequency, log f, in Hz
Y absolute value of the phase angle, φ, in degrees
Figure 14 — Magnified representation of the phase plot
5.2 Extended cable (without active shielding)
Figure 15 shows the phase plot of a measurement of a 330-pF capacitor. The yellow dots show the result
with shielded cables; the cables were extended without active shielding in the case of the red and green
curves, and the cables were also twisted in the case of the green curve. The amplitude was 10 mV. It
is observed that significantly more interference signals are received in the case of the extension with
unshielded cables.
ISO/TR 5602:2021(E)
Key
X frequency, f, in Hz
Y phase angle, φ, in degrees
result with shielded cables
result with unshielded cables
result with unshielded cables and twisted in comparison to the red curve
Figure 15 — Phase plot of a measurement of a 330-pF capacitor
5.3 Cable breaks
In Figure 16, deviations from the real state can be seen that are caused by a cable break. The same
dummy cell was measured in each case. After the measurement with the broken cable, the measurement
was repeated with a new cable.
ISO/TR 5602:2021(E)
Key
X logarithm of the frequency, log f, in Hz
Y1 logarithm of the modulus of the impedance, log |Z|, in Ω
Y2 absolute value of the phase angle, φ, in degrees
failure cable
efficient cable
Figure 16 — Measurement of a dummy cell with and without cable break
5.4 Contact resistances between metallic contacts and the working electrode/counter
electrode
The profile shown in Figure 17 can occur if corroded connections are used (e.g. alligator clamps).
ISO/TR 5602:2021(E)
Key
X logarithm of the frequency, log f, in Hz
Y1 logarithm of the modulus of the impedance, |Z|, in in Ω⋅cm
Y2 absolute value of the phase angle, φ, in degrees
impedance
phase angle
Figure 17 — Measurement with corroded connections
5.5 Inductivities
Inductivities can be caused by connection cables that are too long/twisted in the high-frequency range
above 10 000 Hz. This influence is shown in Figure 18. The inductivity can be observed from the change
in the sign of the phase. Because absolute values of the phase angle are plotted in the diagram, the
curve of the phase angle is reflected instead of crossing the x-axis at Y2 = 0.
ISO/TR 5602:2021(E)
Key
X logarithm of the frequency, log f, in Hz
Y1 logarithm of the modulus of impedance, log |Z|, in Ω
Y2 absolute value of the phase angle, φ, in degrees
phase angle
impedance
Figure 18 — Measurement with a cable that is too long between the measurement set-up and
measuring device
5.6 Measurement range switching
Commercially available impedance spectrometers require several current measurement ranges over
the entire frequency range. These current measurement ranges are automatically adapted by switching
during the measurement. If switching between measurement ranges is not perfectly coordinated or
if the calibration data are corrupt, a discontinuity in the phase plot can be observed. This is shown
in Figure 19 b). This phenomenon occurs almost exclusively in the case of very high-resistance, low-
capacitance systems.
ISO/TR 5602:2021(E)
a)  Despite calibration, measurement range switching can be detected by the jump in the phase
plot.
b)  In the case of a non-calibrated system, the measurement range switching is clearly
detectable in the phase plot.
Key
X frequency, f, in Hz
Y1 impedance, Z, in Ω
Y2 absolute value of the phase angle, φ, in degrees
impedance
phase angle
Figure 19 — Characteristics of measurement range switching for high-resistance,
low-capacitance systems (a section of the entire spectrum is shown)
5.7 Scattering signals in power supply
The quality of measurement depends on the quality of the power supply. If the grid frequency has other
frequencies, e.g. from generators or electromotive drives, superimposed on it, this can lead to impure
ISO/TR 5602:2021(E)
frequency signals in impedance spectroscopy. This can be rendered visible by carrying out a Fourier
transform of the measurement signal. See Figure 20 b).
a) Example of impedance spectra with scattered data due to the influence of the power supply
b) Fourier transform: harmonics of the 50 Hz disturbance are clearly detectable at 100 Hz,
250 Hz and 350 Hz
Key
X frequency, f, in Hz
Y1 impedance, Z, in Ω
Y2 absolute value of the phase angle, φ, in degrees
Y3 current, I, in A
impedance
phase angle
current
Figure 20 — Effects of a disturbance frequency (50 Hz)
ISO/TR 5602:2021(E)
5.8 Insufficient signal-to-noise ratio
If a measurement is carried out with an excitation amplitude that is too low, the signal-to-noise ratio
will be too high. This first becomes apparent in noise in the phase plot at low frequencies. See Figure 21.
Key
X frequency f, in Hz
Y1 magnitude of the impedance |Z|, in Ω ⋅ cm
Y2 absolute value of the phase angle φ, in degrees
t = 0 h
t = 2 h
t = 24 h
t = 168 h
t = 504 h
Figure 21 — Influence of too low amplitude leading to a phase plot with a lot of noise
5.9 Influence of peripheral devices
Stirrers, temperature sensors, pumps and measurement devices in the immediate vicinity of the
measurement equipment can transmit interference signals to the impedance spectrometer. The
antenna effect of a temperature sensor with a connection cable that is too long is shown in Figure 22.
ISO/TR 5602:2021(E)
Key
X logarithm of the frequency, f, in Hz
Y absolute value of the phase angle, φ, in degrees
Figure 22 — Influence of a temperature sensor with a connection cable that is too long due to
antenna effect
An additional influence caused by peripheral devices is shown in Figure 23. Phase plots when a
thermostat is switched on and off are shown here.
ISO/TR 5602:2021(E)
Key
X logarithm of the frequency, log f, in Hz
Y absolute value of the phase angle, φ, in degrees
thermostat on
thermostat off
Figure 23 — Influence of a thermostat that is switched on and off
6 Parameter selection, measurement range limits
6.1 Open-lead test
Carrying out an open-lead test in accordance with ISO 16773-2:2016, Annex A, provides information
about the maximum measurement range of a measurement set-up. Values in the upper limit range are
uncertain and associated with significant errors.
6.2 Note on dummy cells – ISO 16773-3
The calibration of the spectrometer is checked with dummy cells at periodic intervals. The resistors
and capacitors in the dummy cells correspond to real measurement conditions as closely as possible.
Commercially available dummy cells normally have a component tolerance of between 1 % and 5 %.
6.3 Unsuitable amplitude
Harmonics can occur at amplitudes that are too high. These can easily be identified in a Fourier
spectrum (see Figure 24). Nonlinearities can also be detected in a Lissajous figure (see Figure 25).
One can clearly recognize the nonlinear behaviour (asymmetry) at an excitation amplitude of 50 mV. A
software check for nonlinearities is also carried out, e.g. Kramers-Kronig.
ISO/TR 5602:2021(E)
Key
X frequency, in Hz
Y current in frequency domain
50 mV amplitude
10 mV amplitude
Figure 24 — Fourier spectrum with harmonics at 2 kHz, 3 kHz, 4 kHz, etc. (FFT analysis at
1 000 Hz; structural steel in a 1 M NaCl solution at room temperature)
ISO/TR 5602:2021(E)
Key
X potential (AC), in volts
Y current (AC), in amperes
50 mV amplitude
10 mV amplitude
Figure 25 — Lissajous figure for the same measurement at 0,1 Hz
6.4 Insufficient frequency range
If a frequency range that is too small is selected for the evaluation, misleading fit parameters can be
obtained. It can be seen in Figure 26 that an apparent resistance of around 800 MΩ (green line) is falsely
created when fitting up to 1 Hz as the lowest frequency. However, if the entire frequency measurement
range is fitted, the capacitive part is averaged. This can be seen from the significant deviation of the
phase angle from the measurement curve (blue line). In contrast, the overall resistance is represented
more accurately.
ISO/TR 5602:2021(E)
Key
X frequency, f, in Hz
Y1 impedance, Z, in Ω
Y2 phase angle, φ, in degrees
Z curve of a model paint “DTA”
(Y2) phase angle of a model paint “DTA”
fit of Z in the range of 30 µHz until 1 MHz
fit of Z in the range of 1 Hz until 1 MHz
fit of Z in the range of 100 Hz until 1 MHz
fit of φ in the range of 30 µHz until 1 MHz
fit of φ in the range of 1 Hz until 1 MHz
fit of φ in the range of 100 Hz until 1 MHz
Figure 26 — Measurement and three fit evaluations for different frequency ranges
6.5 Repetition rate for subsequent measurements
In the case of series of measurements over time, the time intervals between the individual measurements
is chosen to be appropriate for the kinetics of the system to be observed.
For the swelling kinetics of coatings, for example, impedance spe
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