Ab etterw ay to deal with this problem, however, is to directly measure
and compensate for the solution resistance. In this method, ahigh-frequency
AC voltages ignali sa pplied betweent he electrodes short-circuiting
R p through the double-layer capacitance, thereby,d irectly measuring the
solutionr esistance. The state-of-the-art, patented SRC technology also
eliminates the need forathirdelectrode, even in low-conductivity solutions.
Consequently,t he two-electrode probes have become the standard with
the three-electrode probe available on special order only.T he above points
are clearly indicated in ASTM Standard Guide G96 that states:
3.2.8 Two-electrodep robes andt hree-electrodep robesw itht he
reference electrode equidistant from the test and auxiliary
electrode do not correct for effects of solution resistance without
special electronic solution resistance compensation. With high
to moderate conductivity environments, this effect of solution
resistance is not normally significant.
3.2.9 Three-electrode probesc ompensate fort he solution resistance R s
by varyingd egrees dependingo nt he positiona nd proximityo f
ther eference electrode to the test electrode. With ac lose-spaced
reference electrode,the effectsof R s canbereduced up to approximately ten-fold.Thisextends the operatingrange over that adequate
determinationofthe polarization resistance canbemade.
3.2.10 At wo-electrode probew ithe lectrochemicali mpedance measurement techniquea th ighf requency shortc ircuitst he double-layer
capacitance.C dl,s ot hatameasurement of solution resistance R s
canb em adef or application as ac orrection. This also extendst he
operatingr ange over which adequate determinationo fp olarization resistance canb em ade.
11.2 Comparison of CORROSOMETER (ER) andC ORRATER
(LPR) MeasurementT echniques
The CORROSOMETER (ER) and CORRATER (LPR)t echniques are both
extremely effective corrosion monitoring methods. The choice of which is
betteri sd ependent on the application. The principal attributesa nd limitations of each are briefly summarized below:
1. CORRATER systemsr equire as ufficientlyc onductive liquid;
CORROSOMETER systemsare suitablef or all environments.
2. CORROSOMETER systemsm easure metall ossd irectly, andt heir
accuracy is comparable to thecouponmethod. CORRATER systems
determine corrosionr ateb ased on electrochemicalt heory and
depend on averagecalibration constantstodetermine corrosionrate.
Corrosion Monitoring
545
CAT8247—CHAPTER 11—6/10/2006—12:56—SRIDHAR—XML MODEL B–pp. 533–547
and compensate for the solution resistance. In this method, ahigh-frequency
AC voltages ignali sa pplied betweent he electrodes short-circuiting
R p through the double-layer capacitance, thereby,d irectly measuring the
solutionr esistance. The state-of-the-art, patented SRC technology also
eliminates the need forathirdelectrode, even in low-conductivity solutions.
Consequently,t he two-electrode probes have become the standard with
the three-electrode probe available on special order only.T he above points
are clearly indicated in ASTM Standard Guide G96 that states:
3.2.8 Two-electrodep robes andt hree-electrodep robesw itht he
reference electrode equidistant from the test and auxiliary
electrode do not correct for effects of solution resistance without
special electronic solution resistance compensation. With high
to moderate conductivity environments, this effect of solution
resistance is not normally significant.
3.2.9 Three-electrode probesc ompensate fort he solution resistance R s
by varyingd egrees dependingo nt he positiona nd proximityo f
ther eference electrode to the test electrode. With ac lose-spaced
reference electrode,the effectsof R s canbereduced up to approximately ten-fold.Thisextends the operatingrange over that adequate
determinationofthe polarization resistance canbemade.
3.2.10 At wo-electrode probew ithe lectrochemicali mpedance measurement techniquea th ighf requency shortc ircuitst he double-layer
capacitance.C dl,s ot hatameasurement of solution resistance R s
canb em adef or application as ac orrection. This also extendst he
operatingr ange over which adequate determinationo fp olarization resistance canb em ade.
11.2 Comparison of CORROSOMETER (ER) andC ORRATER
(LPR) MeasurementT echniques
The CORROSOMETER (ER) and CORRATER (LPR)t echniques are both
extremely effective corrosion monitoring methods. The choice of which is
betteri sd ependent on the application. The principal attributesa nd limitations of each are briefly summarized below:
1. CORRATER systemsr equire as ufficientlyc onductive liquid;
CORROSOMETER systemsare suitablef or all environments.
2. CORROSOMETER systemsm easure metall ossd irectly, andt heir
accuracy is comparable to thecouponmethod. CORRATER systems
determine corrosionr ateb ased on electrochemicalt heory and
depend on averagecalibration constantstodetermine corrosionrate.
Corrosion Monitoring
545
CAT8247—CHAPTER 11—6/10/2006—12:56—SRIDHAR—XML MODEL B–pp. 533–547