1、Designation: D 5391 99 (Reapproved 2005)Standard Test Method forElectrical Conductivity and Resistivity of a Flowing HighPurity Water Sample1This standard is issued under the fixed designation D 5391; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of electricalconductivity and resistivity of
3、high purity water samples below10 S/cm (above 0.1 Mohm-cm). It is applicable to bothcontinuous and periodic measurements but in all cases, thewater must be flowing in order to provide representativesampling. Static grab sampling cannot be used for such highpurity water. Continuous measurements are m
4、ade directly inpure water process lines, or in side stream sample lines toenable measurements on high temperature or high pressuresamples, or both.1.2 The values stated in SI units are to be regarded as thestandard.1.3 This standard does not purport to address all of thesafety concerns, if any, asso
5、ciated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1066 Practice for Sampling SteamD 1125 Test Methods for
6、 Electrical Conductivity and Re-sistivity of WaterD 1129 Terminology Relating to WaterD 1192 Specification for Equipment for Sampling Waterand Steam in Closed Conduits3D 1193 Specification for Reagent WaterD 2186 Test Methods for Deposit-Forming Impurities inSteamD 2777 Practice for Determination of
7、 Precision and Bias ofApplicable Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3864 Guide for Continual On-Line Monitoring Systemsfor Water AnalysisD 4519 Test Method for On-Line Determination of Anionsand Carbon Dioxide in High Purity Water by CationExch
8、ange and Degassed Cation Conductivity3. Terminology3.1 Definitions:3.1.1 electrical conductivityrefer toTest Methods D 1125.3.1.2 electrical resistivityrefer to Test Methods D 1125.3.1.3 For definitions of other terms used in these testmethods, refer to Terminology D 1129.3.2 Definitions of Terms Sp
9、ecific to This Standard:3.2.1 cell constantthe ratio of the length of the path, L(cm) and the cross-sectional area of the solution, A (cm2),between the electrodes of a conductivity/resistivity cell, withunits of cm1. In high purity water measurements, the cellconstant is normally between 0.001 and 0
10、.1 cm1to preventelectrical interference. This is lower than the 1 cm1of thestandard centimetre cube and is taken into account by directreading instrument ranges that are matched with specific cellconstants.4. Summary of Test Method4.1 Conductivity or resistivity is measured with a cell andtemperatur
11、e sensor or compensator in a flowing, closed system1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.03 on Sampling of Water andWater-Formed Deposits, Surveillance of Water, and Flow Measurement of Water.Current edition app
12、roved April 1, 2005. Published April 2005. Originallyapproved in 1993. Last previous edition approved in 1999 as D 539199.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, ref
13、er to the standards Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.to prevent trace contamination from wetted surfaces and fromthe atmosphere. Specialized temperature compensation
14、cor-rects the measurement to 25C, taking into account thetemperature effects on the ionization of water, the contami-nants, and interactions between the two. In the absence ofspecialized temperature compensation, the sample temperatureis controlled to 25 6 0.2C.4.2 To determine the cell constant of
15、a high purity conduc-tivity cell with an instrument capable of accurate measurementover the range of pure water to 150 S/cm with a single cellconstant, Test Methods D 1125 are used directly. Manufactur-ers certification of cell constant traceability by this means is anacceptable alternative.4.3 To d
16、etermine the cell constant of a high purity conduc-tivity cell with an instrument which does not accurately coverthe range from pure water to 150 S/cm with a single cellconstant, a secondary standard cell is used that has an inter-mediate cell constant with precise value determined by TestMethods D
17、1125. That secondary standard cell is then used inlow conductivity water (not a standard) and readings arecompared with those of the low constant cell under test. In thismanner, the cell constant of the latter is determined. Manufac-turers certification of cell constant traceability by this means is
18、an acceptable alternative.5. Significance and Use5.1 Conductivity measurements are typically made onsamples of moderate to high ionic strength where contamina-tion of open samples in routine laboratory handling is negli-gible. Under those conditions, standard temperature compen-sation using coeffici
19、ents of 1 to 3 % of reading per degreeCelsius over wide concentration ranges is appropriate. Incontrast, this test method requires special considerations toreduce trace contamination and accommodates the high andvariable temperature coefficients of pure water samples thatcan range as high as 7 % of
20、reading per degree Celsius. Inaddition, measuring instrument design performance must beproven under high purity conditions.5.2 This test method is applicable for detecting traceamounts of ionic contaminants in water. It is the primary meansof monitoring the performance of demineralization and otherh
21、igh purity water treatment operations. It is also used to detectionic contamination in boiler waters, microelectronics rinsewaters, pharmaceutical process waters, etc., as well as tomonitor and control the level of boiler and power plant cyclechemistry treatment chemicals. This test method supplemen
22、tsthe basic measurement requirements for Test Methods D 1125,D 2186, and D 4519.5.3 At very low levels of alkaline contamination, for ex-ample, 01 g/L NaOH, conductivity is suppressed, and canactually be slightly below the theoretical value for pure water.(13,14)4Alkaline materials suppress the high
23、ly conductivehydrogen ion concentration while replacing it with less con-ductive sodium and hydroxide ions. This phenomenon is not aninterference with conductivity or resistivity measurement itselfbut could give misleading indications of inferred water purityin this range if it is not recognized.6.
24、Interferences6.1 Exposure of the sample to the atmosphere may causechanges in conductivity/resistivity due to loss or gain ofdissolved ionizable gases. Carbon dioxide, normally present inthe air, can reach an equilibrium concentration in water ofabout 1 mg/L and add approximately 1 S/cm to the condu
25、c-tivity due to formation of carbonic acid. Closed flow-throughor sealed in-line cell installation is required for this reason.6.2 Power plant installations utilizing long sample lines canexperience significant sampling problems. New sample linesnormally require longterm conditioning. Iron oxides an
26、d otherdeposits accumulate in slow flowing horizontal sample linesand can develop chromatograph-like retention of ionic species,resulting in very long delay times. Precautions are described inSection 9.6.3 Cell and flow chamber surfaces will slowly leach traceionic contaminants, evidenced by increas
27、ing conductivity read-ings with very low or zero flowrate. There must be sufficientflow to keep these contaminants from accumulating to the pointthat they affect the measurement. The high and convolutedsurface area of platinized cells precludes their use for highpurity measurements for this reason.6
28、.4 Capacitance of the cell and extension leadwire, espe-cially in high purity ranges can add significant positive error toconductance readings (negative error to resistance readings).The measuring instrument must be designed to accommodatecell and leadwire characteristics in high purity water asdesc
29、ribed in 7.1.1 and Annex A1. In addition, the instrumentmanufacturers recommendations on cell leadwire must becarefully followed.6.5 Conductivity and resistivity measurements are refer-enced to 25C. Either samples must be controlled to 25.0 60.2C or specialized temperature compensation must be em-pl
30、oyed that accounts for the characteristics of high purity waterwith specific contaminants, as described in 7.1.2.6.6 Samples containing dissolved gases must have sufficientflow through the cell that bubbles cannot accumulate andoccupy sample volume within the cell, causing low conductiv-ity (high re
31、sistivity) readings. This problem is typical inmakeup water treatment systems where water warms up, dropsin pressure, and is acidified by cation exchange operations.This releases dissolved air and converts carbonates to carbondioxide gas.6.7 High purity conductivity measurement must not bemade on a
32、sample downstream of pH sensors since theyinvariably contaminate the sample with traces of referenceelectrolyte salts. Use a dedicated sample line or place theconductivity cell upstream from the pH sensors.6.8 Conductivity cells mounted downstream from ion ex-changers are vulnerable to catching resi
33、n particles between thecell electrodes. Resin particles are sufficiently conductive toshort the cell and cause high off-scale conductivity or ex-tremely low resistivity readings. Resin retainers must beeffective and cells must be accessible for cleaning. Cell designswith electrode spacing greater th
34、an 0.06 in. (1.5 mm) havebeen found to be less likely to trap such particles.4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.D 5391 99 (2005)26.9 Conductivity cells, if subjected to demineralizer regen-eration reagents, would require excessive rinse
35、 time to obtainsatisfactory results. Therefore, locate cells where they will beisolated during regeneration cycles.7. Apparatus7.1 Measuring Instrument:7.1.1 The instrument shall be continuously reading in eitherconductivity or resistivity units. It shall be specifically de-signed to measure in high
36、 purity ranges, measuring with ac ofappropriate voltage, frequency, wave shape, phase correction,and wave sampling technique to minimize errors due to paralleland series capacitance of cell and leadwire as well as minimiz-ing electrode polarization errors and effects of small directcurrent (dc) pote
37、ntials.Acell simulation technique to verify theperformance of an unproven measuring circuit design underhigh purity conditions is provided in Annex A1.7.1.2 The measurement shall include algorithms to tempera-ture compensate conductivity or resistivity values to 25.0C.The algorithm shall compensate
38、for changes in water ionizationas well as for solute ion mobility for neutral salt contaminants.The conductivity of pure water has been documented with highaccuracy (15,1).7.1.3 In the case of samples containing acidic or basicsolutes (such as power plant treatment using ammonia, mor-pholine, etc.,
39、or acidic cation conductivity samples or micro-electronics acid etch rinse monitoring), special algorithms shallbe employed that account for the interaction of acids and baseswith the ionization of water (2, 3, 4). The user is cautioned thataccuracy of temperature compensation algorithms for theseso
40、lutes may vary significantly. The user must determine theapplicability and accuracy for a particular sample in theanticipated temperature range. Fig. 1 illustrates the variation intemperature effects on conductivity representative of neutralsalts, ammonia, morpholine, and acids. Where specialized hi
41、ghpurity temperature compensation algorithms are not providedto accurately compensate for these effects, sample temperatureshall be controlled to 25.06 0.2C. (Note that conductivitytemperature coefficients exceed 7 % of reading per degreeCelsius in the temperature range of 0 to 10C.)7.1.4 Output sig
42、nal(s) from the instrument, if provided,shall be electrically isolated from the cell and from the earthground to prevent ground loop problems when the instrumentis connected to grounded external devices.7.2 Cell:7.2.1 Flow-through or in-line conductivity/resistivity cellsshall be used to prevent con
43、tamination from the atmosphereand wetted surfaces as described in 6.1 and 6.3. Flowrates shallbe maintained within the manufacturers recommendations.The cell shall retain its constant calibration under the condi-tions of flowrate, temperature, and pressure of the installation.The cell shall incorpor
44、ate an integral precision temperaturesensor to ensure that it accurately senses the sample tempera-ture where the conductivity/resistivity is being detected toensure accurate temperature compensation.7.2.2 The cell for high purity water measurements shall notbe used for measuring higher ionic conten
45、t samples (greaterthan 20 S/cm, less than 0.05 Mohm-cm) since it would retainionic contaminants and require excessive rinse-down time forvalid measurements in high purity ranges. A high purity cell ina demineralizer system shall not be located where it can beexposed to regeneration reagents.7.2.3 El
46、ectrodes of the cell shall not be platinized for purewater measurements since the microscopically rough, poroussurface would retain ionic contaminants and produce excessivedownscale response times. Only a trace or flash of platinumblack is permissible on electrode surfaces. Electrodes oftitanium, ni
47、ckel, monel, stainless steel, or platinum are suitableNOTECurves represent concentrations of impurities given in Table 1.FIG. 1 Temperature Effects on the Conductivity of High PurityWaterTABLE 1 Concentrations of Trace Contaminants Plotted in Fig. 1ConductivityS/cm at 25CConcentration (g/L)NaCl HCl
48、NH3Morpholine5.00 2295 430 638 13 7552.00 903 172 177 26321.00 439 86 76 8370.500 207 42.6 34.4 2980.250 91 20.7 16.1 1170.100 21.0 6.5 5.4 34.60.055 0.0 0.0 0.0 0.0D 5391 99 (2005)3for high purity measurement. However, extra care must betaken using platinum cells not to exceed manufacturersrecommen
49、ded flowrate and not to permit rough handling thatcould bend the electrodes and change the cell constant.7.2.4 If the cell constant as checked does not fall withinacceptable limits of its nominal value, it is necessary to cleanor replace the cell. Even in pure water samples, coatings suchas iron oxide crud in power plant installations, resin fines, andother solids and films can develop. Insulating coatings overelectrode surfaces can cause negative conductivity errors.Conductive accumulations between electrodes can short themand cause positive errors. Mec
