Appendix C: Temperature Effects - Extech Instruments EC100 User Manual

Appendix C: Temperature Effects

Linear temperature correction
Calculating Temperature Coefficient ( )
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Conductivity measurements are temperature dependent; if the temperature increases, conductivity
also increases. For example, the conductivity measured in a 0.01 M KCL solution at 20°C is
1.273mS/cm, whereas, at 25°C, it is 1.409 mS/cm.
The concept of reference temperature (normalization temperature) was introduced to allow the
comparison of conductivity results obtained at different temperatures. The reference temperature is
usually 20°C or 25°C. This conductivity meter measures the actual conductivity and temperature
and then converts it to the reference temperature using a temperature correction function and then
displays the conductivity at the reference temperature. This meter uses linear temperature
correction.
In moderately and highly conductive solutions, temperature correction can be based on a linear
equation involving a temperature coefficient. The coefficient is usually expressed as a conductivity
variation in %/°C. Refer to the following formula:
Where:
K = Conductivity at Tref
Tref
K = Conductivity at T
T
T = Reference temperature
ref
T = Sample temperature
= Temperature coefficient
Note: The correction is accurate only within a limited temperature range near T1 and T2; the greater the
difference between T and Tref, the higher the risk of error.
Measuring the conductivity of a sample at temperature T1 close to Tref and another temperature
T2, the temperature coefficient can be calculated using the following equation:
T2 should be selected as a typical sample temperature and should be approximately 10°C different
from T1. The temperature coefficients of the following electrolytes generally fall into the ranges
shown below:
Acids: 1.0 – 1.6%/°C
Bases: 1.8 – 2.2%/°C
Salts: 2.2 – 3.0%/°C
Drinking water: 2.0%/°C
Ultrapure water: 5.2%/°C
Average temperature coefficients of standard electrolyte solutions expressed as %/C of the
conductivity value at 25C.
Temperature Range (°C) KCl 1 M
15 – 25 1.725
15 – 25 – 35 1.730 (15 – 27°C)
25 - 35 1.762 (25 – 27°C)
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KCl 0.1 M KCl 0.01 M
1.863 1.882
1.906 1.937 (15 – 34°C)
1.978 1.997 (25 - 34°C)
10
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Saturated NaCl
1.981
2.041
2.101
EC100-EU-EN v2.2 06/13
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