1、Designation: D1125 95 (Reapproved 2009)D1125 14Standard Test Methods forElectrical Conductivity and Resistivity of Water1This standard is issued under the fixed designation D1125; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 These test methods cove
3、r the determination of the electrical conductivity and resistivity of water.The following test methodsare included:Range SectionsTest Method AField and Routine Laboratory 10 to 200 000 12 to 18Test Method AField and Routine Laboratory 10 to 200 000 12 to 18Measurement of Static (Non-Flowing)SamplesS
4、/cmTest Method BContinuous In-Line Measure 5 to 200 000 19 to 23Test Method BContinuous In-Line Measure 5 to 200 000 19 to 23ment S/cmment S/cm1.2 These test methods have been tested in reagent water. It is the users responsibility to ensure the validity of these testmethods for waters of untested m
5、atrices.1.3 For measurements below the range of these test methods, refer to Test Method D5391.1.4 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 an
6、y, 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 Standards:2D1066 Practice for Sampling SteamD1129 Terminology Re
7、lating to WaterD1192 Guide for Equipment for Sampling Water and Steam in Closed Conduits (Withdrawn 2003)3D1193 Specification for Reagent WaterD2186 Test Methods for Deposit-Forming Impurities in SteamD2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19
8、on WaterD3370 Practices for Sampling Water from Closed ConduitsD4519 Test Method for On-Line Determination of Anions and Carbon Dioxide in High Purity Water by Cation Exchange andDegassed Cation ConductivityD5391 Test Method for Electrical Conductivity and Resistivity of a Flowing High Purity Water
9、SampleE1E2251 Specification for ASTM Liquid-in-Glass ThermometersLiquid-in-Glass ASTM Thermometers with Low-HazardPrecision Liquids3. Terminology3.1 Definitions:1 These test methods are under the jurisdiction of Committee D19 on Water and are the direct responsibility of Subcommittee D19.03 on Sampl
10、ingWater andWater-FormedDeposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water.Current edition approved May 1, 2009Feb. 1, 2014. Published June 2009March 2014. Originally approved in 1950. Last previous edition approved in 20052009 asD1125
11、 95 (2009). (2005). DOI: 10.1520/D1125-95R09.10.1520/D1125-14.2 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
12、.3 The last approved version of this historical standard 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
13、 adequately depict all changes accurately, ASTM recommends 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 Cons
14、hohocken, PA 19428-2959. United States13.1.1 electrical conductivityconductivity, nthe reciprocal of the a-c resistance in ohms measured between opposite faces ofa centimetre cube of an aqueous solution at a specified temperature.NOTE 1The unit of electrical conductivity is siemens per centimetre. (
15、The previously used units of mhos/cm are numerically equivalent to S/cm.)The actual resistance of the cell, Rx, is measured in ohms. The conductance, 1/Rx, is directly proportional to the cross-sectional area, A (in cm 2), andinversely proportional to the length of the path, L (in cm):1/Rx 5KA/L3.1.
16、1.1 DiscussionThe unit of electrical conductivity is siemens per centimetre. (The previously used units of mhos/cm are numerically equivalentto S/cm.) The actual resistance of the cell, Rx, is measured in ohms. The conductance, 1/Rx, is directly proportional to thecross-sectional area, A (in cm2), a
17、nd inversely proportional to the length of the path, L (in cm):1/Rx 5KA/LThe conductance measured between opposite faces of a centimetre cube, K, is called conductivity. Conductivity values areusually expressed in microsiemens/centimetre or in siemens/centimetre at a specified temperature, normally
18、25C.The conductance measured between opposite faces of a centimetre cube, K, is called conductivity. Conductivity values areusually expressed in microsiemens/centimetre or in siemens/centimetre at a specified temperature, normally 25C.3.1.2 electrical resistivityresistivity, nthe a-c resistance in o
19、hms measured between opposite faces of a centimetre cube ofan aqueous solution at a specified temperature.NOTE 2The unit of electrical resistivity is ohm-centimetre. The actual resistance of the cell, Rx, is measured in ohms, and is directly proportionalto the length of the path, L (in cm), and inve
20、rsely proportional to the cross-sectional area, A (in cm 2):Rx 5RL/A3.1.2.1 DiscussionThe unit of electrical resistivity is ohm-centimetre. The actual resistance of the cell, Rx, is measured in ohms, and is directlyproportional to the length of the path, L (in cm), and inversely proportional to the
21、cross-sectional area, A (in cm2):Rx 5RL/AThe resistance measured between opposite faces of a centimetre cube, R, is called resistivity. Resistivity values are usuallyexpressed in ohmcentimetre, or in megohm centimetre, at a specified temperature, normally 25C.The resistance measured between opposite
22、 faces of a centimetre cube, R, is called resistivity. Resistivity values are usuallyexpressed in ohmcentimetre, or in megohm centimetre, at a specified temperature, normally 25C.3.1.3 For definitions of other terms used in these methods, refer to Terminology D1129.3.2 Symbols:3.2.1 Symbols used in
23、the equations in Sections 14 and 16 are defined as follows:J = cell constant, cm cm1,K = conductivity at 25C, S/cm,Kx = measured conductance, S,K1 = conductivity of the KCl in the reference solution at the temperature of measurement (Table 1), S/cm,K2 = conductivity of the water used to prepare the
24、reference solution, at the same temperature of measurement, S/cm,Q = temperature correction factor (see Section 11),R = resistivity at 25C, ohm cm,Rx = measured resistance, ohm.4. Significance and Use4.1 These test methods are applicable for such purposes as impurity detection and, in some cases, th
25、e quantitative measurementof ionic constituents dissolved in waters. These include dissolved electrolytes in natural and treated waters, such as boiler water,boiler feedwater, cooling water, and saline and brackish water.4.1.1 Their concentration may range from trace levels in pure waters (2)4 to si
26、gnificant levels in condensed steam (see TestMethods D2186 and D4519, and Ref (3), or pure salt solutions.4.1.2 Where the principal interest in the use of conductivity methods is to determine steam purity, see Ref (4). These testmethods may also be used for checking the correctness of water analyses
27、 (5).4 The boldface numbers in parentheses refer to a list of references at the end of this standard.D1125 1425. Interferences5.1 Exposure of a sample to the atmosphere may cause changes in conductivity/resistivity, due to loss or gain of dissolved gases.This is extremely important in the case of ve
28、ry pure waters with low concentrations of dissolved ionized materials. The carbondioxide, normally present in the air, can drastically increase the conductivity of pure waters by approximately 1 S/cm. Contactwith air should be avoided by using flow-through or in-line cell where feasible. Chemically
29、pure inert gases, such as nitrogen orhelium, may be used to blanket the surface of samples.5.2 Undissolved or slowly precipitating materials in the sample can form a coating on the electrodes of the conductivity cellthat may cause erroneous readings. For example, biofouling of the cell or a build-up
30、 of filming amines may cause poor cellresponse. In most cases these problems can be eliminated by washing the cells with appropriate solvents.5.3 If an unshielded cell is used to measure the resistivity/conductivity of high resistivity water there is a possibility of electricalpickup causing erroneo
31、us reading. For this reason it is recommended that conductivity cells for this application be of coaxialshielded type or equivalent, and that the cables and instrument also be shielded.5.4 Formation of bubbles on the surfaces of conductivity cell electrodes will cause erroneously low conductivity re
32、adings andmust be prevented during calibration and measurement. Bubble formation can occur with measurements of water containingdissolved gases when the water is warming up or dropping in pressure or both. For laboratory samples, swirling or tapping thesensor on the bottom of the sample container ca
33、n dislodge bubbles. For continuous measurements, cell installation in a high flowvelocity location (within manufacturers recommendations) can prevent bubble adherence.6. Apparatus6.1 Measuring CircuitThe instrument may be a manually operated wheatstone bridge or the equivalent, or a direct readingan
34、alog or digital meter. Instruments shall energize the conductivity cell with alternating current and, together with the cell and anyextension leadwire, shall be designed to reduce errors from the following sources:6.1.1 In highly conductive solutionsHighly Conductive SolutionsUncompensated electrode
35、 polarization due to excessivecurrent density at the electrode surfaces can cause negative conductivity errors. Insufficient series capacitance at theelectrode/solution interface can allow charging effects to distort the a-c measurement and cause errors if not compensated.Leadwire resistance can add
36、 significantly to the measured resistance. Four-electrode type conductivity cells can reduce the effectsof polarization by energizing two or more electrodes to create an a-c field across the sensing area and measuring from another pairof electrodes within the field with minimal current flow.6.1.2 In
37、 low conductivity solutionsLow Conductivity SolutionsExcessive parallel capacitance in the cell and extensionleadwire can shunt the measurement and cause positive conductivity errors. Temperature compensation errors can be significantbelow 5 S/cm if variable coefficient algorithms are not employed a
38、s described in Test Method D5391.6.1.3 These sources of error are minimized by an appropriate combination of a-c drive voltage, wave shape, frequency, phasecorrection, wave sampling technique and temperature compensation designed in by the instrument manufacturer. The instrumentmanufacturers recomme
39、ndations shall be followed in selecting the proper cell constant, leadwire size, and length and maintenanceof the electrode surface condition for the range of measurement. Calibration may be in either conductivity or resistivity units.6.1.4 When an output signal is required from an on-line instrumen
40、t, it shall be electrically isolated from the cell drive circuitto prevent interaction between a solution ground at the cell and an external circuit ground.6.2 Cells:TABLE 1 Electrical Conductivity Values Assigned to the Potassium Chloride in the Reference Solution SolutionAcolwidth=“1.31in“/COLSPEC
41、ReferenceSolutionApproximateNormality ofSolutionMethod of Preparation Tempera-Temperature,ture, CElectricalConductivity,S/cmA 1 74.2460 g of KCl weighed in air per 1 L of 0 65 176solution at 20C 18 97 83825 111 342B 0.1 7.4365 g of KCl weighed in air per 1 L of 0 7 138solution at 20C 18 11 16725 12
42、856C 0.01 0.7440 g of KCl weighed in air per 1 L of 0 773.6solution at 20C 18 1 220.525 1 408.8D 0.001 Dilute 100 mL of Solution C to 1 L at 20C 0 77.69B18 127.54B25 146.93A Excluding the conductivity of the water used to prepare the solutions. (See 7.2 and Section 1414.).) These tabulated conductiv
43、ity values are in international units. Whenusing measuring instruments calibrated in absolute units, multiply the tabular values by 0.999505.B From Glasstone (1).CC The boldface numbers in parentheses refer to a list of references at the end of this standard.D1125 1436.2.1 Flow-through or in-line ce
44、lls shall be used for measuring conductivities lower than 10 S/cm (resistivities higher than100 000 ohm cm), to avoid contamination from the atmosphere. However, samples with conductivity greater than 10 S/cm mayalso be measured. In all other cases, pipet-type or dip cells can also be used. Pipet or
45、 dip cells may be used to measure samplesin the range of 1 to 10 S/cm if the sample is protected by an inert gaseous layer of nitrogen or helium.6.2.2 A cell constant shall be chosen which will give a moderate cell resistance, matching the instrument manufacturersrequirements for the range of measur
46、ement. For laboratory bridges, Table 2 provides conservative guidelines.6.2.3 Flow-through and in-line cells shall be mounted so that continuous flow of the sample through or past it is possible. Flowrate should be maintained at a constant rate consistent with the manufacturers recommendations for t
47、he cell being used,particularly at conductivities below 10 S/cm. The cell shall retain calibration under conditions of pressure, flow, and temperaturechange, and shall exclude the atmosphere and be constructed of corrosion resistant, chemically inert materials. The chamber or cellshall be equipped w
48、ith means for accurate measurement of the temperature.6.2.4 Platinized cells shall not be used for measurement of conductivities below 10 S/cm, except that a trace or flash ofplatinum black may be used on cells for measurements in the range of 0.1 to 10 S/cm (see 9.4). Because of the cost and fragil
49、ityof platinum cells, it is common practice to use titanium, monel, hastelloy, stainless steel and graphite electrodes for measurementswith accuracies on the order of 1 %. Note that these electrodes may require special surface preparation. Titanium and monelelectrodes are especially suitable for high resistance solutions such as ultrapure water, but may introduce a small surface resistancewhich limits their accuracy when the measured resistance is less than a few thousand ohms (2).6.2.5 It is recommended that cells
