ASTM G199-09(2014)
(Guide)Standard Guide for Electrochemical Noise Measurement
Standard Guide for Electrochemical Noise Measurement
SIGNIFICANCE AND USE
5.1 Use of this guide is intended to provide information on electrochemical noise to monitor corrosion on a continuous basis.
5.2 This guide is intended for conducting electrochemical noise measurements, both in the laboratory and in-service environments (36).
5.3 This technique is useful in systems in which process upsets or other problems can create corrosive conditions. An early warning of corrosive attack can permit remedial action before significant damage occurs to process equipment (37).
5.4 This technique is also useful when inhibitor additions are used to control the corrosion of equipment. The indication of increasing corrosion activity can be used to signal the need for additional inhibitor (38).
5.5 Control of corrosion in process equipment requires knowledge of the rate or mechanism of attack on an ongoing basis. This technique can be used to provide such information in a digital format that is easily transferred to computers for analysis (39) .
SCOPE
1.1 This guide covers the procedure for conducting online corrosion monitoring of metals by the use of the electrochemical noise technique. Within the limitations described, this technique can be used to detect localized corrosion activity and to estimate corrosion rate on a continuous basis without removal of the monitoring probes from the plant or experimental cell.
1.2 This guide presents briefly some generally accepted methods of analyses that are useful in the interpretation of corrosion test results.
1.3 This guide does not cover detailed calculations and methods; rather it covers a range of approaches that have found application in corrosion testing.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: G199 − 09 (Reapproved 2014)
Standard Guide for
Electrochemical Noise Measurement
This standard is issued under the fixed designation G199; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope G15 Terminology Relating to Corrosion and CorrosionTest-
ing (Withdrawn 2010)
1.1 This guide covers the procedure for conducting online
G16 Guide for Applying Statistics to Analysis of Corrosion
corrosion monitoring of metals by the use of the electrochemi-
Data
cal noise technique. Within the limitations described, this
G31 Guide for Laboratory Immersion Corrosion Testing of
techniquecanbeusedtodetectlocalizedcorrosionactivityand
Metals
to estimate corrosion rate on a continuous basis without
G46 Guide for Examination and Evaluation of Pitting Cor-
removal of the monitoring probes from the plant or experimen-
rosion
tal cell.
G59 Test Method for Conducting Potentiodynamic Polariza-
1.2 This guide presents briefly some generally accepted
tion Resistance Measurements
methods of analyses that are useful in the interpretation of
G61 Test Method for Conducting Cyclic Potentiodynamic
corrosion test results.
Polarization Measurements for Localized Corrosion Sus-
1.3 This guide does not cover detailed calculations and ceptibility of Iron-, Nickel-, or Cobalt-Based Alloys
G96 Guide for Online Monitoring of Corrosion in Plant
methods;ratheritcoversarangeofapproachesthathavefound
application in corrosion testing. Equipment (Electrical and Electrochemical Methods)
G102 Practice for Calculation of Corrosion Rates and Re-
1.4 The values stated in SI units are to be regarded as
lated Information from Electrochemical Measurements
standard. No other units of measurement are included in this
G106 Practice for Verification of Algorithm and Equipment
standard.
for Electrochemical Impedance Measurements
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions—The terminology used herein, if not spe-
priate safety and health practices and determine the applica-
cifically defined otherwise, shall be in accordance with Termi-
bility of regulatory limitations prior to use.
nology G15. Definitions provided herein and not given in
Terminology G15 are limited only to this guide.
2. Referenced Documents
2 3.2 Definitions of Terms Specific to This Standard:
2.1 ASTM Standards:
3.2.1 coupling current, n—measured current flowing be-
G1 Practice for Preparing, Cleaning, and Evaluating Corro-
tween two electrodes in an electrolyte coupled by an external
sion Test Specimens
circuit.
G3 Practice for Conventions Applicable to Electrochemical
3.2.2 current measuring device, n—device that is capable of
Measurements in Corrosion Testing
measuring the current flow across the electrode/electrolyte
G4 Guide for Conducting Corrosion Tests in Field Applica-
interface or the coupling current of a pair of electrodes, usually
tions
a zero resistance ammeter (ZRA) or current-to-voltage con-
G5 Reference Test Method for Making Potentiodynamic
verter.
Anodic Polarization Measurements
3.2.3 electrochemical current noise measurement,
n—electrochemical noise measurement using an electrochemi-
This guide is under the jurisdiction ofASTM Committee G01 on Corrosion of
cal current signal.
Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemical
Measurements in Corrosion Testing.
3.2.4 electrochemical noise measurement (ENM),
Current edition approved May 1, 2014. Published May 2014. Originally
n—technique involving the acquisition and analysis of electro-
approved in 2009. Last previous edition approved in 2009 as G199- 09. DOI:
10.1520/G0199-09R14. chemical current and potential signals.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G199 − 09 (2014)
3.2.5 electrochemical potential noise measurement, 4. Summary of Guide
n—electrochemical noise measurement using an electrochemi-
4.1 Electrochemical noise measurement is used for moni-
cal potential signal. 4
toring of localized corrosion processes such as pitting (1, 2).
3.2.6 Fourier transform, n—transformation of a time do-
4.2 Electrochemical noise measurement may be used to
main signal into the frequency domain.
estimate a general corrosion rate (3).
3.2.7 galvanostat, n—device used for automatically main-
4.3 Electrochemical noise measurement operates on the
taining a controlled current between two electrodes.
principle that fluctuations in potential and current occur as a
3.2.8 noise impedance, |Zn|, [Ω],n—ratio of the amplitude
result of spontaneous changes in the instantaneous corrosion
of potential noise to current noise, in the frequency domain, at rate (4). The fluctuations may be due to one or more of several
a specified frequency.
phenomena that include: initiation (5) and propagation of
localized corrosion (6), Faradaic currents (7), double-layer
3.2.9 noise resistance, R , [Ω],n—standard deviation of
n
capacitance discharge, gas bubble formation (8), adsorption/
potential noise divided by the standard deviation of current
desorption processes, surface coverage (9), diffusion (10),
noise.
variation of film thickness (11), mobility of charge carrier (12),
3.2.10 pit indicator, n—standard deviation of current noise
passivity breakdown (13), and temperature variations (14, 15).
divided by the mean of the coupling current.
4.4 The noise fluctuations associated with corrosion phe-
3.2.11 pitting factor, n—standard deviation of the current
nomena can usually be distinguished from thermal (white)
noise divided by the general corrosion current.
noise (caused by thermal effects in which noise power is
3.2.11.1 Discussion—The general corrosion current is nor-
directly proportional to the measured bandwidth), Johnson
mally estimated by a secondary electrochemical means.
noise (produced by the measurement instrumentation), and
3.2.12 pitting index, n—standard deviation of current noise shot noise (in electrical circuits caused by the quantized nature
oftheelectroniccharge) (16-18).However,theelectrochemical
divided by the root mean square of the coupling current
calculated over the same sample period. noise signals generated may have characteristics similar to
those stated in the preceding sentence.
3.2.13 potential measuring device, n—a high impedance
digital voltmeter or electrometer used to measure the potential 4.5 The electrochemical noise method of corrosion mea-
surement may help to evaluate the corrosion mechanism of
between two electrodes.
metals in electrolytes. Its particular advantage is in continuous
3.2.13.1 Discussion—Ideally, one of these electrodes is
monitoring without applying any external perturbation.
understudyandtheotherisareferenceelectrode;however,the
measurements may be made between two nominally identical
4.6 Method A—ZRA-Based Current and Potential
electrodes manufactured from the material being studied.
Measurement—Twonominallyidenticalelectrodesarecoupled
through a ZRA, which maintains a 0-V potential difference
3.2.14 potentiostat, n—device used for automatically main-
between them by injecting (measured) current. The potential
taining a controlled voltage difference between an electrode
between the couple and a third (reference) electrode is also
under study and a reference electrode in which a third
measured. The reference electrode may be either a conven-
electrode,thecounter(orauxiliary)electrode,isusedtosupply
tional reference electrode such as a saturated calomel electrode
a current path from the electrode under study back to the
(SCE) or simply be a third electrode identical in material to the
potentiostat.
coupled electrodes (19, 20).
3.2.15 sample interval, n—time delay between successive
4.7 Method B—Potentiostatic Current Measurement with
electrochemical noise measurements.
Standard Reference Electrode—Reference Test Method G5
3.2.16 sampleperiod,n—timebetweenthefirstandlastdata
provides practice for making potentiostatic measurements.The
collection during electrochemical noise measurement.
working electrode potential is controlled with respect to the
3.2.17 time domain analysis, n—direct evaluation of time
referenceelectrodeataprescribedvalue.Thecurrentmeasured
series data, for example, using statistical descriptions of the
(flowing between the working (Test 1) and auxiliary or counter
data.
(Test 2) electrodes) is that required to maintain potential
control (21, 22).
3.2.18 time record, n—dataset obtained over a sample pe-
NOTE1—Noiseonthereferenceelectrodewillresultinacorresponding
riod at a typical sample interval in electrochemical noise
current noise signal; therefore, the reference electrode needs to be
measurement.
relatively noise free. The potential measurement can only be made across
the auxiliary and working electrodes, as the potential between the
3.2.19 zero resistance ammeter (ZRA), n—electronic device
used to measure current without imposing a significant IR drop
by maintaining close to 0-V potential difference between the 4
The boldface numbers in parentheses refer to the list of references at the end of
inputs. this standard.
G199 − 09 (2014)
referenceandtheworkingisheldconstantbythepotentiostat.Thevoltage
lead to apparent electrical shorting of the probe elements
developed across the auxiliary and working electrodes is a function of the
leading to erroneous readings.
currentflowingthroughthecellandtheimpedancecausedbytheauxiliary
electrode, the working electrode, and the solution resistance.
7. Apparatus
4.8 Method C—Galvanostatic Potential Measurement—An
7.1 Electronics:
electrode is supplied with current from a galvanostat at a
7.1.1 The input impedance of the device should be high
prescribed current value. The potential difference between the
enough to minimize current drawn from the electrodes, such
electrode and a reference electrode is measured. An auxiliary
that the electrodes are not polarized by the measuring device.
electrode is used to carry the return current.
Practice G106 provides guidelines for verification of algorithm
and equipment for electrochemical impedance measurements.
4.9 There are several methods by which the electrochemical
7.1.2 The potential range of the device depends on the
noise data can be obtained (23-26) and analyzed, and some
maximum potential difference between the two electrodes
methods of interpreting the data are given in Appendix X1
(typically <1 V).
(27-35). These analyses are included to aid the individual in
7.1.3 The potential resolution of the device should be
understandingtheelectrochemicalnoisetechniqueandsomeof
adequate to discriminate the signal to within the required
its capabilities. The information is not intended to be all-
accuracy (typically 10 µV or lower).
inclusive.
7.1.4 The device should be capable of maintaining an offset
potential between the two electrodes of less than 1 mV.
5. Significance and Use
7.1.5 The frequency response of the device should be flat
5.1 Use of this guide is intended to provide information on
(within the desired accuracy) across the frequency range of the
electrochemical noise to monitor corrosion on a continuous
analysis.Thedeviceshouldhaveafastenoughresponsesothat
basis.
signal transients are not distorted. Note that the signal that one
5.2 This guide is intended for conducting electrochemical
is attempting to measure may be below the resolution of the
noise measurements, both in the laboratory and in-service instrument.
environments (36).
NOTE 2—The offset voltage will appear as a current offset in the
measurement with no electrodes connected.
5.3 This technique is useful in systems in which process
upsets or other problems can create corrosive conditions. An
7.1.6 The current range depends on the system being
early warning of corrosive attack can permit remedial action
measured. The wide dynamic ranges seen in passive-to-active
before significant damage occurs to process equipment (37).
transitions (nA to mA) may require auto-ranging circuits.
7.1.7 The bias current of the device should be within the
5.4 This technique is also useful when inhibitor additions
required accuracy of the measurement. Otherwise it may cause
are used to control the corrosion of equipment. The indication
an error in the measured current.
of increasing corrosion activity can be used to signal the need
7.1.8 The background noise of the device should be below
for additional inhibitor (38).
the electrochemical current or potential noise being measured.
5.5 Control of corrosion in process equipment requires
High-impedance reference electrode inputs may pick up extra-
knowledge of the rate or mechanism of attack on an ongoing
neous noise from the environment and shielding may be
basis. This technique can be used to provide such information
required. An independent measurement of the background
in a digital format that is easily transferred to computers for
noise level should be performed.
analysis (39).
7.1.9 The requirements in 7.1.1 – 7.1.8 do not include all
possible combinations of instrumentation and electrode ar-
6. Limitations and Interferences
rangements. The instrument, cell, and analysis requirements
should be determined by the particular test being undertaken.
6.1 Results are representative of the probe element (elec-
trode). When first introduced into a system, corrosion rates on
7.2 Test Cell—The test cell should be constructed to allow
a probe element may be different from that of the structure.
the following items to be inserted into the solution chamber:
7.2.1 Three identical electrodes, two of which comprise the
6.2 Noise can originate from thermal, electrical, and me-
coupled electrodes and the third electrode acts as a reference.
chanical factors. Since the interest is only on the noise from
Alternatively,insteadofthethirdidenticalelectrode,aLuggin-
Faradaic processes, care should be exercised to minimize noise
Haber capillary with salt bridge connection for a reference
from other sources.
electrode may be used.
6.3 Probe elements by their nature are consumable. Hazard-
7.2.2 An inlet and an outle
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G199 − 09 G199 − 09 (Reapproved 2014)
Standard Guide for
Electrochemical Noise Measurement
This standard is issued under the fixed designation G199; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide covers the procedure for conducting online corrosion monitoring of metals by the use of the electrochemical
noise technique. Within the limitations described, this technique can be used to detect localized corrosion activity and to estimate
corrosion rate on a continuous basis without removal of the monitoring probes from the plant or experimental cell.
1.2 This guide presents briefly some generally accepted methods of analyses that are useful in the interpretation of corrosion
test results.
1.3 This guide does not cover detailed calculations and methods; rather it covers a range of approaches that have found
application in corrosion testing.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
G1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
G3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
G4 Guide for Conducting Corrosion Tests in Field Applications
G5 Reference Test Method for Making Potentiodynamic Anodic Polarization Measurements
G15 Terminology Relating to Corrosion and Corrosion Testing (Withdrawn 2010)
G16 Guide for Applying Statistics to Analysis of Corrosion Data
G31 Guide for Laboratory Immersion Corrosion Testing of Metals
G46 Guide for Examination and Evaluation of Pitting Corrosion
G59 Test Method for Conducting Potentiodynamic Polarization Resistance Measurements
G61 Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of
Iron-, Nickel-, or Cobalt-Based Alloys
G96 Guide for Online Monitoring of Corrosion in Plant Equipment (Electrical and Electrochemical Methods)
G102 Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements
G106 Practice for Verification of Algorithm and Equipment for Electrochemical Impedance Measurements
3. Terminology
3.1 Definitions—The terminology used herein, if not specifically defined otherwise, shall be in accordance with Terminology
G15. Definitions provided herein and not given in Terminology G15 are limited only to this guide.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 coupling current, n—measured current flowing between two electrodes in an electrolyte coupled by an external circuit.
This guide is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemical
Measurements in Corrosion Testing.
Current edition approved March 15, 2009May 1, 2014. Published April 2009May 2014. Originally approved in 2009. Last previous edition approved in 2009 as G199-
09. DOI: 10.1520/G0199-09.10.1520/G0199-09R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G199 − 09 (2014)
3.2.2 current measuring device, n—device that is capable of measuring the current flow across the electrode/electrolyte interface
or the coupling current of a pair of electrodes, usually a zero resistance ammeter (ZRA) or current-to-voltage converter.
3.2.3 electrochemical current noise measurement, n—electrochemical noise measurement using an electrochemical current
signal.
3.2.4 electrochemical noise measurement (ENM), n—technique involving the acquisition and analysis of electrochemical
current and potential signals.
3.2.5 electrochemical potential noise measurement, n—electrochemical noise measurement using an electrochemical potential
signal.
3.2.6 Fourier transform, n—transformation of a time domain signal into the frequency domain.
3.2.7 galvanostat, n—device used for automatically maintaining a controlled current between two electrodes.
3.2.8 noise impedance, |Zn|, [Ω],n—ratio of the amplitude of potential noise to current noise, in the frequency domain, at a
specified frequency.
3.2.9 noise resistance, R , [Ω] , n—standard deviation of potential noise divided by the standard deviation of current noise.
n
3.2.10 pit indicator, n—standard deviation of current noise divided by the mean of the coupling current.
3.2.11 pitting factor, n—standard deviation of the current noise divided by the general corrosion current.
3.2.11.1 Discussion—
The general corrosion current is normally estimated by a secondary electrochemical means.
3.2.12 pitting index, n—standard deviation of current noise divided by the root mean square of the coupling current calculated
over the same sample period.
3.2.13 potential measuring device, n—a high impedance digital voltmeter or electrometer used to measure the potential between
two electrodes.
3.2.13.1 Discussion—
Ideally, one of these electrodes is under study and the other is a reference electrode; however, the measurements may be made
between two nominally identical electrodes manufactured from the material being studied.
3.2.14 potentiostat, n—device used for automatically maintaining a controlled voltage difference between an electrode under
study and a reference electrode in which a third electrode, the counter (or auxiliary) electrode, is used to supply a current path from
the electrode under study back to the potentiostat.
3.2.15 sample interval, n—time delay between successive electrochemical noise measurements.
3.2.16 sample period, n—time between the first and last data collection during electrochemical noise measurement.
3.2.17 time domain analysis, n—direct evaluation of time series data, for example, using statistical descriptions of the data.
3.2.18 time record, n—dataset obtained over a sample period at a typical sample interval in electrochemical noise measurement.
3.2.19 zero resistance ammeter (ZRA), n—electronic device used to measure current without imposing a significant IR drop by
maintaining close to 0-V potential difference between the inputs.
4. Summary of Guide
4.1 Electrochemical noise measurement is used for monitoring of localized corrosion processes such as pitting (1, 2).
4.2 Electrochemical noise measurement may be used to estimate a general corrosion rate (3).
4.3 Electrochemical noise measurement operates on the principle that fluctuations in potential and current occur as a result of
spontaneous changes in the instantaneous corrosion rate (4). The fluctuations may be due to one or more of several phenomena
that include: initiation (5) and propagation of localized corrosion (6), Faradaic currents (7), double-layer capacitance discharge,
gas bubble formation (8), adsorption/desorption processes, surface coverage (9), diffusion (10), variation of film thickness (11),
mobility of charge carrier (12), passivity breakdown (13), and temperature variations (14, 15).
4.4 The noise fluctuations associated with corrosion phenomena can usually be distinguished from thermal (white) noise
(caused by thermal effects in which noise power is directly proportional to the measured bandwidth), Johnson noise (produced by
The boldface numbers in parentheses refer to the list of references at the end of this standard.
G199 − 09 (2014)
the measurement instrumentation), and shot noise (in electrical circuits caused by the quantized nature of the electronic charge)
(16-18). However, the electrochemical noise signals generated may have characteristics similar to those stated in the preceding
sentence.
4.5 The electrochemical noise method of corrosion measurement may help to evaluate the corrosion mechanism of metals in
electrolytes. Its particular advantage is in continuous monitoring without applying any external perturbation.
4.6 Method A—ZRA-Based Current and Potential Measurement—Two nominally identical electrodes are coupled through a
ZRA, which maintains a 0-V potential difference between them by injecting (measured) current. The potential between the couple
and a third (reference) electrode is also measured. The reference electrode may be either a conventional reference electrode such
as a saturated calomel electrode (SCE) or simply be a third electrode identical in material to the coupled electrodes (19, 20).
4.7 Method B—Potentiostatic Current Measurement with Standard Reference Electrode—Reference Test Method G5 provides
practice for making potentiostatic measurements. The working electrode potential is controlled with respect to the reference
electrode at a prescribed value. The current measured (flowing between the working (Test 1) and auxiliary or counter (Test 2)
electrodes) is that required to maintain potential control (21, 22).
NOTE 1—Noise on the reference electrode will result in a corresponding current noise signal; therefore, the reference electrode needs to be relatively
noise free. The potential measurement can only be made across the auxiliary and working electrodes, as the potential between the reference and the
working is held constant by the potentiostat. The voltage developed across the auxiliary and working electrodes is a function of the current flowing
through the cell and the impedance caused by the auxiliary electrode, the working electrode, and the solution resistance.
4.8 Method C—Galvanostatic Potential Measurement—An electrode is supplied with current from a galvanostat at a prescribed
current value. The potential difference between the electrode and a reference electrode is measured. An auxiliary electrode is used
to carry the return current.
4.9 There are several methods by which the electrochemical noise data can be obtained (23-26) and analyzed, and some methods
of interpreting the data are given in Appendix X1 (27-35). These analyses are included to aid the individual in understanding the
electrochemical noise technique and some of its capabilities. The information is not intended to be all-inclusive.
5. Significance and Use
5.1 Use of this guide is intended to provide information on electrochemical noise to monitor corrosion on a continuous basis.
5.2 This guide is intended for conducting electrochemical noise measurements, both in the laboratory and in-service
environments (36).
5.3 This technique is useful in systems in which process upsets or other problems can create corrosive conditions. An early
warning of corrosive attack can permit remedial action before significant damage occurs to process equipment (37).
5.4 This technique is also useful when inhibitor additions are used to control the corrosion of equipment. The indication of
increasing corrosion activity can be used to signal the need for additional inhibitor (38).
5.5 Control of corrosion in process equipment requires knowledge of the rate or mechanism of attack on an ongoing basis. This
technique can be used to provide such information in a digital format that is easily transferred to computers for analysis (39).
6. Limitations and Interferences
6.1 Results are representative of the probe element (electrode). When first introduced into a system, corrosion rates on a probe
element may be different from that of the structure.
6.2 Noise can originate from thermal, electrical, and mechanical factors. Since the interest is only on the noise from Faradaic
processes, care should be exercised to minimize noise from other sources.
6.3 Probe elements by their nature are consumable. Hazardous situations may occur if probes are left in service for extended
periods beyond their probe life. In some configurations, crevice corrosion can cause damage or leaks at the interface between the
element and its sealing surface that can cause false readings.
6.4 Electrical contact between probe elements should be avoided. In certain situations (for example, sour corrosion in the
presence of hydrogen sulfide), the corrosion products can lead to apparent electrical shorting of the probe elements leading to
erroneous readings.
7. Apparatus
7.1 Electronics:
7.1.1 The input impedance of the device should be high enough to minimize current drawn from the electrodes, such that the
electrodes are not polarized by the measuring device. Practice G106 provides guidelines for verification of algorithm and
equipment for electrochemical impedance measurements.
7.1.2 The potential range of the device depends on the maximum potential difference between the two electrodes (typically <1
V).
G199 − 09 (2014)
7.1.3 The potential resolution of the device should be adequate to discriminate the signal to within the required accuracy
(typically 10 μV or lower).
7.1.4 The device should be capable of maintaining an offset potential between the two electrodes of less than 1 mV.
7.1.5 The frequency response of the device should be flat (within the desired accuracy) across the frequency range of the
analysis. The device should have a fast enough response so that signal transients are not distorted. Note that the signal that one
is attempting to measure may be below the resolution of the instrument.
NOTE 2—The offset voltage will appear as a current offset in the measurement with no electrodes connected.
7.1.6 The current range depends on the system being measured. The wide dynamic ranges seen in passive-to-active transitions
(nA to mA) may require auto-ranging circuits.
7.1.7 The bias current of the device should be within the required accuracy of the measurement. Otherwise it may cause an error
in the measured current.
7.1.8 The background noise of the device should be below the electroche
...
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