Conductivity measurement techniques include 2-electrode, 4-electrode, and inductive methods. Conductivity is a measure of a solution's ability to conduct electricity and is calculated using conductance, resistance, voltage, current, and cell constant. Factors like temperature, polarization, and contamination can affect conductivity readings so calibration is important. Conductivity is used in various applications like water treatment, leakage detection, and interface detection.

1. Conductivity measurement
By – Praful Hanmante

2. Contents
• Basics about conductivity
• Measurement techniques
• 2-cell
• 4-cell
• Inductive type
• Factors affecting conductivity
• Calibration
• Applications

3. Basics about conductivity
• R=V/I
• G=1/R
Where,
G=conductance( Siemens)
R=resistance(ohms)
V= voltage(volt)
I = current (ampere)
K = d/A
where,
K = cell constant
d =distance between two
electrodes
A = effective area of the
electrodes
Conductivity = cell constant × conductance

4. Typical Conductivity Values
0.055
0.5
1
50
50,000
355,000
0 1 100 10,000 1,000,000
Ultra Pure Water
Distilled Water
Boiler Feed Water
Mains Water Supply
Sea Water
10% NaOH

5. Measurement techniques
• Electrode Conductivity
i. 2 electrode type
ii. 4 electrode type
• Inductive conductivity

6. Electrode conductivity meter
• Applying AC current
across two electrode
• By measuring voltage ,
we can calculate
conductivity

7. 2 electrode type
• Easy to maintain
• Polarisation in high
conductivity samples
• Field effects - cell must
be positioned in the
centre of the measuring
vessel

8. 4 electrode
• a current is applied to
the outer rings
• Linear over a very large
conductivity range
• No polarisation effect

9. Platinised cells
• Covering the cell poles with a layer of
platinum black
• To minimise polarisation effects
• cell constant tends to drift faster than the
constant of non-platinised cells
• Recommended in non-viscous samples,

10. Inductive type
• Non contact type as
coils are encased in a
polymeric material
• Can be used in
aggressive environment
• Not recommended for
low conductivity
measurement

11. Factors affecting conductivity
• Polarization
• Temperature

12. Polarisation
• Polarization occurs because of migration of
the ions in the solution to the surfaces of the
electrodes.
• Leads to reduction in conductivity between
electrodes
• To reduce polarisation we use AC supply

13. Temperature effect
• As the temperature increases, conductivity
increases .
• reference temperature, typically 25°C .
• 2 algorithms commonly used
1. Linear temperature coefficient
2. High purity water or dilute sodium chloride

14. Linear temperature coefficient
• conductivity of an electrolyte changes by about the
same percentage for every °C change in temperature.
• C25=
𝐶𝑡
1+α(𝑡−25)
Where,
α = linear temperature coefficient
C25=calculated conductivity at 25°C,
Ct = raw conductivity at t°C,
Acid 1.0- 1.6% per ̊c
Base 1.0- 1.6% per ̊c
salts 1.0- 1.6% per ̊c

15. High purity water correction
• The high purity water
correction assumes the
sample is pure water
contaminated with (NaCl)
• Point 1 = the raw
conductivity.
• point 2 =the conductivity of
sodium and chloride.
• point 3= conductivity of
sodium and chloride at
25°C,
• point 4 =the corrected
conductivity at 25°C,

16. Calibration Methods
• By using solution of known conductivity
• By using previously calibrated sensor and
analyser

17. Calibration against a referee sensor
and analyser
• Both measuring and reference sensors are
placed in process flow
• Automatic temperature compensation is
turned off
• Output of measuring sensor is matched with
referee sensor

18. Calibration against a standard
solution
• calibration is performed without temperature
compensation
• Contamination error due to atmospheric CO2
• Standard solutions

19. Applications
• Water treatment
• Leakage detection
• Clean in place
• Interface detection