Calibration and Maintenance of Conductivity Meter

Calibration and Maintenance 

of Conductivity Meter 

Electrochemical Analysis Laboratory 

Department of Chemical Metrology and Biometry 

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Outline 

What is Conductivity? 

How is Conductivity Measured? 

What is Conductive solution? 

Conductivity Meter 

Traceability 

Standard method 

Rules for reliable measurement 

Calibration 

2 



Conductivity is the ability of a solution to pass an 

electric current. The current is carried by cations and 

anions. 

G 

1 

R 

The electrical conductance 

(G, Siemens) is the 

reciprocal of the resistance 

(R, Ohm). 

3 



G 

 

K 

A 

l 

l 

A 

 

1 

 

 

K is the cell constant (m -1 ) 

A 

l 

A is the electrode area (m 2 ) 

l is the electrode gap (m) 

is the specific conductivity (S/m) 

is the specific resistance (m) 

4 



Solution conducts electricity depends on 

• Concentration 

• Mobility of ions 

• Valence of ions 

• Temperature 

5 



Conductivity may be measured by applying an 

alternating electrical current (I) to two electrodes 

immersed in a solution and measuring the resulting 

voltage (V). 

6 



Conductivity is measured in aqueous solutions of 

electrolytes. 

Electrolytes are substances containing ions or 

compounds that ionise in solution. 

• Strong electrolytes: fully ionised in solution 

• Weak electrolytes: not fully ionised in solution 

7 



 

 

C C n 

is molar conductance (S cm 2 mol -1 ) 

is conductivity (S/m) 

C is concentration 

n is charge of ion 

 

 

 

 

 

is equivalent conductivity of ion 

 

8 



Equivalent conductivity of various ions at 25 o C 

9 


Conductivity value of solution 

10 



At the low electrolytic conductivity, the 

relationship between conductivity and concentration is 

linear. 

11 



The cell constant (K) cannot be determined by 

measuring the electrode gap and area. 

The cell constant is determined using a calibration 

solution with known conductivity (usually 0.01 mol/l 

KCl solution) 

12 



13 



The conductivity 

meter uses the conductance 

and cell constant to display 

the conductivity 

Conductivity = cell constant x conductance 

14 


Conductivity Cell 

• 2 – pole cell 



• Platinised cell 

• Flow through cell 

15 



• 2 – pole cell : universal used, interfere with 

polarization 

• 3 – pole cell: better reproducibility 

16 



• 4 – pole cell: should measure with outer tube 

to minimize volume effect 

17 



• Platinised cell: coated electrode 

with platinum black to increase 

surface area and decrease 

polarization effect. 

18 



• Flow through cell: designed for flow 

system or small volume sample, 

suitable for measurement of 

conductivity of pure water (avoid 

carbon dioxide) 

19 


Storage 

Before storing the cell, rinse with deionised water 

• Short-term : deionised water 

• Long-term : deionised water or store dry 

After long-term storage, condition the cell for 8 hours in 

deionised water before use. 

20 


Selection of Conductivity Meter 

• Factor affecting measurement accuracy 

• Formats and units of reports results 

• Suitability for the measuring environment 

• features assisting ease of use 

21 


Selection of Conductivity Cell 


Advantages 

Disadvantages 

- Easy to maintain - Field effect – cell must 

be positioned in the middle 

of measuring vessel 

- Economic - Polarization in high 

conductivity sample 

- Recommended for 

viscous sample with 

suspension 

22 


Selection of Conductivity Cell 


Advantages 

- Linear over a very large 

conductivity range 

- Calibration and 

measurement in different 

range 

- Ideal for high 

conductivity measurement 

Disadvantages 

- Unsuitable for micro 

samples 

23 


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24

Conductivity Measurement 

The accuracy of conductivity measurements can be 

influenced by 

• Polarization 

• Geometry 


25 



• Polarization 

Polarization occurs on the electrode surface, 

which leads to errors on result. 

26 



Preventing polarization 

• increasing the electrode area: coating platinum 

black on platinum electrode 

• Selecting 4 – pole conductivity cell 

27 



• Geometry related errors – field effect 

Field lines 

These field lines can effect the 

measurement if something 

interferes with the field lines 

such as the sample vessel 

wall. 

This effect can be minimized 

by using 4-pole conductivity 

cell 

28 




Conductivity measurements are the temperature 

dependent, varying from 1.5 to 5.5 %/ o C 

Temperature increasing - conductivity increasing 

Conductivity meter measures the actual 

conductivity and temperature and then converts 

it to reference temperature using temperature 

correction function 

29 




Temperature correction function 

• Linear function 

• Non-linear function 

• User-Definable temperature compensation 

30 



• Linear function 

31 


Determination of the temperature coefficient 

The temperature coefficients of some electrolytes 

32 



• Non-linear function 

Non-linear 

compensation data for 

variety of solutions is 

widely available such 

as ISO 7888-1985 

(natural waters) 

33 


Traceability 

= G K 

Primary reference solution 

Primary cell 

(defined dimension) 

Secondary cell 

Secondary reference solution 

Electrolytic conductivity meter 

34 


Standard method for Conductivity 

Measurement of Water 

• ASTM D1195 – 95 (Reapproved 1999) Standard 

Test Methods for Electrical 

Resistivity of Water 

Conductivity and 

• ISO 7888 – 1985 Water quality – Determination of 

electrolytic conductivity 

• OIML R 68 Calibration method for conductivity 

cells 

35 


Rules for reliable measurements 

• Calibrate frequently: cell constant is an important 

factor for conductivity measurement. Calibration 

interval for conductivity cell will depend on the 

application, sample and operating condition. 

• Temperature and stirring conditions: For accurate 

measurement, recommended to use thermostat bath 

36 



• Position of conductivity cell: All the pole of 

conductivity cell are covered by the sample and stand 

at the center of sample vessel. 

• Low conductivity measurement: 

• use a flow through cell, to avoid CO 2 from air 

• use non-platinised and low cell constant (< 1 cm -1 ) 

37 



• High conductivity measurement: 

• use platinised cells to prevent polarization error 

• use high cell constant (> 1 cm -1 ) 

• do not dilute sample (conductivity is not 

proportional to concentration at high levels) 

38 


General Condition 

• The conductivity of an electrolytic solution may be 

determined from the measured resistance of the cell, 

when it contains the solution, and the constant K of 

the cell 

• The value of the cell constant K depends on 

the construction of the cell 

the temperature and concentration of the 

solution 

the measuring frequency 

etc. 

39 


Preparation for Calibration 

check the rigidity of the fixing of the electrode and 

the state of their surface 

the cell shall be degreased with the appropriate 

solvent according to the materials of which the cell 

and electrode are made and then wash with distilled 

water 

the standard solution shall be prepared in quantity 

sufficient for calibration 

40 



the cell shall be washed with standard solution at 

least 5 times 

the solution of the last washing shall be left in the 

cell for 10 minutes 

the cell containing the solution shall be brought in 

thermostat bath at 25 0 C and maintain at thermal 

equilibrium 

41 



the cell shall be washed with standard solution at 

least 5 times 

the solution of the last washing shall be left in 

the cell for 10 minutes 

the cell containing the solution shall be brought 

in thermostat bath at 25 0 C and maintain at thermal 

equilibrium 

42 


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43

Calibration and Maintenance of Conductivity Meter

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