1、Designation: D5391 99 (Reapproved 2009)D5391 14Standard Test Method forElectrical Conductivity and Resistivity of a Flowing HighPurity Water Sample1This standard is issued under the fixed designation D5391; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of electrical conductivity and resistivi
3、ty of high purity water samples below 10S/cm (above 0.1 Mohm-cm). It is applicable to both continuous and periodic measurements but in all cases, the water must beflowing in order to provide representative sampling. Static grab sampling cannot be used for such high purity water. Continuousmeasuremen
4、ts are made directly in pure water process lines, or in side stream sample lines to enable measurements on hightemperature or high pressure samples, or both.1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard
5、 does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM St
6、andards:2D1066 Practice for Sampling SteamD1125 Test Methods for Electrical Conductivity and Resistivity of WaterD1129 Terminology Relating to WaterD1192 Guide for Equipment for Sampling Water and Steam in Closed Conduits (Withdrawn 2003)3D1193 Specification for Reagent WaterD2186 Test Methods for D
7、eposit-Forming Impurities in SteamD2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3864 Guide for On-Line Monitoring Systems for Water AnalysisD4519 Test Method for On-Line Determination
8、 of Anions and Carbon Dioxide in High Purity Water by Cation Exchange andDegassed Cation Conductivity3. Terminology3.1 Definitions:DefinitionsFor definitions of other terms used in these test methods, refer to Terminology D1129.3.1.1 electrical conductivityrefer to Test Methods D1125.3.1.2 electrica
9、l resistivityrefer to Test Methods D1125.3.1.3 For definitions of other terms used in these test methods, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 cell constantconstant, nthe ratio of the length of the path, L (cm)(cm), and the cross-sectional area of the s
10、olution,A (cm (cm2), between the electrodes of a conductivity/resistivity cell, with units of cm cm1. In high purity water measurements,the cell constant is normally between 0.001 and 0.1 cm 1 to prevent electrical interference. This is lower than the 1 cm 1 of thestandard centimetre cube and is tak
11、en into account by direct reading instrument ranges that are matched with specific cell constants.1 This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-Formed Deposits, Analysis of Water for Powe
12、r Generation and Process Use, On-Line Water Analysis, and Surveillance of Water.Current edition approved May 1, 2009Feb. 1, 2014. Published June 2009February 2014. Originally approved in 1993. Last previous edition approved in 20052009 asD5391 99 (2005).(2009). DOI: 10.1520/D5391-99R09. 10.1520/D539
13、1-14.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard
14、is referenced on www.astm.org.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. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommend
15、s that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.1.1 Discussion
16、In high purity water measurements, the cell constant is normally between 0.001 and 0.1 cm1 to prevent electrical interference.This is lower than the 1 cm1 of the standard centimetre cube and is taken into account by direct reading instrument ranges thatare matched with specific cell constants.4. Sum
17、mary of Test Method4.1 Conductivity or resistivity is measured with a cell and temperature sensor or compensator in a flowing, closed system toprevent trace contamination from wetted surfaces and from the atmosphere. Specialized temperature compensation corrects themeasurement to 25C, taking into ac
18、count the temperature effects on the ionization of water, the contaminants, and interactionsbetween the two. In the absence of specialized temperature compensation, the sample temperature is controlled to 25 6 0.2C.4.2 To determine the cell constant of a high purity conductivity cell with an instrum
19、ent capable of accurate measurement overthe range of pure water to 150 S/cm with a single cell constant,Test Methods D1125 are used directly. Manufacturers certificationof cell constant traceability by this means is an acceptable alternative.4.3 To determine the cell constant of a high purity conduc
20、tivity cell with an instrument which does not accurately cover therange from pure water to 150 S/cm with a single cell constant, a secondary standard cell is used that has an intermediate cellconstant with precise value determined by Test Methods D1125. That secondary standard cell is then used in l
21、ow conductivitywater (not a standard) and readings are compared with those of the low constant cell under test. In this manner, the cell constantof the latter is determined. Manufacturers certification of cell constant traceability by this means is an acceptable alternative.5. Significance and Use5.
22、1 Conductivity measurements are typically made on samples of moderate to high ionic strength where contamination of opensamples in routine laboratory handling is negligible. Under those conditions, standard temperature compensation using coefficientsof 1 to 3 % of reading per degree Celsius over wid
23、e concentration ranges is appropriate. In contrast, this test method requiresspecial considerations to reduce trace contamination and accommodates the high and variable temperature coefficients of purewater samples that can range as high as 7 % of reading per degree Celsius. In addition, measuring i
24、nstrument design performancemust be proven under high purity conditions.5.2 This test method is applicable for detecting trace amounts of ionic contaminants in water. It is the primary means ofmonitoring the performance of demineralization and other high purity water treatment operations. It is also
25、 used to detect ioniccontamination in boiler waters, microelectronics rinse waters, pharmaceutical process waters, etc., as well as to monitor and controlthe level of boiler and power plant cycle chemistry treatment chemicals. This test method supplements the basic measurementrequirements for Test M
26、ethods D1125, D2186, and D4519.5.3 At very low levels of alkaline contamination, for example, 01 g/L NaOH, conductivity is suppressed, and can actuallybe slightly below the theoretical value for pure water. (11 and 2,2)4 Alkaline materials suppress the highly conductive hydrogenion concentration whi
27、le replacing it with less conductive sodium and hydroxide ions. This phenomenon is not an interference withconductivity or resistivity measurement itself but could give misleading indications of inferred water purity in this range if it isnot recognized.6. Interferences6.1 Exposure of the sample to
28、the atmosphere may cause changes in conductivity/resistivity due to loss or gain of dissolvedionizable gases. Carbon dioxide, normally present in the air, can reach an equilibrium concentration in water of about 1 mg/L andadd approximately 1 S/cm to the conductivity due to formation of carbonic acid
29、. Closed flow-through or sealed in-line cellinstallation is required for this reason.6.2 Power plant installations utilizing long sample lines can experience significant sampling problems. New sample linesnormally require longterm conditioning. Iron oxides and other deposits accumulate in slow flowi
30、ng horizontal sample lines andcan develop chromatograph-like retention of ionic species, resulting in very long delay times. Precautions are described in Section9.6.3 Cell and flow chamber surfaces will slowly leach trace ionic contaminants, evidenced by increasing conductivity readingswith very low
31、 or zero flowrate. There must be sufficient flow to keep these contaminants from accumulating to the point that theyaffect the measurement. The high and convoluted surface area of platinized cells precludes their use for high purity measurementsfor this reason.6.4 Capacitance of the cell and extensi
32、on leadwire, especially in high purity ranges can add significant positive error toconductance readings (negative error to resistance readings). The measuring instrument must be designed to accommodate cell and4 The boldface numbers in parentheses refer to a list of references at the end of this sta
33、ndard.D5391 142leadwire characteristics in high purity water as described in 7.1.1 and Annex A1. In addition, the instrument manufacturersrecommendations on cell leadwire must be carefully followed.6.5 Conductivity and resistivity measurements are referenced to 25C. Either samples must be controlled
34、 to 25.0 6 0.2C orspecialized temperature compensation must be employed that accounts for the characteristics of high purity water with specificcontaminants, as described in 7.1.2.6.6 Samples containing dissolved gases must have sufficient flow through the cell that bubbles cannot accumulate and occ
35、upysample volume within the cell, causing low conductivity (high resistivity) readings. This problem is typical in makeup watertreatment systems where water warms up, drops in pressure, and is acidified by cation exchange operations. This releases dissolvedair and converts carbonates to carbon dioxi
36、de gas.6.7 High purity conductivity measurement must not be made on a sample downstream of pH sensors since they invariablycontaminate the sample with traces of reference electrolyte salts. Use a dedicated sample line or place the conductivity cellupstream from the pH sensors.6.8 Conductivity cells
37、mounted downstream from ion exchangers are vulnerable to catching resin particles between the cellelectrodes. Resin particles are sufficiently conductive to short the cell and cause high off-scale conductivity or extremely lowresistivity readings. Resin retainers must be effective and cells must be
38、accessible for cleaning. Cell designs with electrode spacinggreater than 0.06 in. (1.5 mm) 1.5 mm have been found to be less likely to trap such particles.6.9 Conductivity cells, if subjected to demineralizer regeneration reagents, would require excessive rinse time to obtainsatisfactory results. Th
39、erefore, locate cells where they will be isolated during regeneration cycles.7. Apparatus7.1 Measuring Instrument:7.1.1 The instrument shall be continuously reading in either conductivity or resistivity units. It shall be specifically designed tomeasure in high purity ranges, measuring with ac alter
40、nating current (ac) of appropriate voltage, frequency, wave shape, phasecorrection, and wave sampling technique to minimize errors due to parallel and series capacitance of cell and leadwire as well asminimizing electrode polarization errors and effects of small direct current (dc) potentials. A cel
41、l simulation technique to verifythe performance of an unproven measuring circuit design under high purity conditions is provided in Annex A1.7.1.2 The measurement shall include algorithms to temperature compensate conductivity or resistivity values to 25.0C. Thealgorithm shall compensate for changes
42、 in water ionization as well as for solute ion mobility for neutral salt contaminants. Theconductivity of pure water has been documented with high accuracy (33-5,4).7.1.3 In the case of samples containing acidic or basic solutes (such as power plant treatment using ammonia, morpholine, etc.,or acidi
43、c cation conductivity samples or microelectronics acid etch rinse monitoring), special algorithms shall be employed thataccount for the interaction of acids and bases with the ionization of water (56-8, 6, 7). The user is cautioned that accuracy oftemperature compensation algorithms for these solute
44、s may vary significantly. The user must determine the applicability andaccuracy for a particular sample in the anticipated temperature range. Fig. 1 illustrates the variation in temperature effects onconductivity representative of neutral salts, ammonia, morpholine, and acids. Where specialized high
45、 purity temperaturecompensation algorithms are not provided to accurately compensate for these effects, sample temperature shall be controlled to25.0625.060.2C. (Note that conductivity temperature coefficients exceed 7 % of reading per degree Celsius in the temperaturerange of 0 to 10C.)7.1.4 Output
46、 signal(s) from the instrument, if provided, shall be electrically isolated from the cell and from the earth groundto prevent ground loop problems when the instrument is connected to grounded external devices.7.2 Cell:7.2.1 Flow-through or in-line conductivity/resistivity cells shall be used to prev
47、ent contamination from the atmosphere andwetted surfaces as described in 6.1 and 6.3. Flowrates shall be maintained within the manufacturers recommendations. The cellshall retain its constant calibration under the conditions of flowrate, temperature, and pressure of the installation. The cell shalli
48、ncorporate an integral precision temperature sensor to ensure that it accurately senses the sample temperature where theconductivity/resistivity is being detected to ensure accurate temperature compensation.7.2.2 The cell for high purity water measurements shall not be used for measuring higher ioni
49、c content samples (greater than20 S/cm, less than 0.05 Mohm-cm) since it would retain ionic contaminants and require excessive rinse-down time for validmeasurements in high purity ranges. A high purity cell in a demineralizer system shall not be located where it can be exposed toregeneration reagents.7.2.3 Electrodes of the cell shall not be platinized for pure water measurements since the microscopically rough, porous surfacewould retain ionic contaminants and produce excessive downscale response times. Only a trace or flash of platinum black ispermis
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