Test Procedure: Astm D4940; Before You Start - Elcometer 138 Guia Del Usuario

3 TEST PROCEDURE: ASTM D4940

3.1 BEFORE YOU START

1 Calibrate the conductivity meter, see Sections 4.6 and 4.7 on
pages en-8 and en-12.
2 Determine the conductivity meter sensor cell constant, see
Section 3.2 below.
3 Rinse the beakers, stirring rod and funnel with pure water until
tests show the rinse water has a conductivity of 5µS/cm or less.
 Measure the conductivity of the rinse water using the Elcometer 138E
Conductivity Meter, see Section 4.9 on page en-14.
4 As the test is sensitive, we recommend that clean latex or nitrile
gloves are worn during the test procedure to prevent cross
contamination.
3.2 DETERMINING THE SENSOR CELL CONSTANT (K )
The conductivity meter sensor cell constant should be determined and
checked periodically using the procedure outlined below.
The Elcometer 138E Conductivity Meter and standard 1413 µS/cm
(1.413 mS/cm) calibration solution supplied in the kit can be used for
this purpose.
1 Using the Elcometer 138E Conductivity Meter, measure the
conductivity of the standard calibration solution at 25°C (77°F),
see Section 4.9 on page en-14.
 Rinse the sensor cell several times with the solution to be measured before
taking the reading.
2 Calculate the sensor cell constant (K ) using the following
formula:
K = (C / C )
25 s
where:
K = conductivity sensor cell constant
25
C = measured conductivity of the standard calibration solution
m
C = specific conductivity of the standard calibration solution
s
(1413 µS/cm if using the standard calibration solution supplied.)
Note: Users can prepare their own potassium chloride solution instead of using the
standard calibration solution supplied. Refer to the ASTM Standard for further
information.
b
Additional pouches of calibration solution are available to purchase from Elcometer or your local
Elcometer supplier, see Section 8.1 'Elcometer 138E Calibration Solutions' on page en-17.
en-3
R
m
b
25
25
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