Conductivity Measurement

1
Conductivity Measurement
Dr. Edgar Ballin
2
Conductivity Measurement Principle
Aim of Measurement of Conductivity

• monitoring of the conductivity
• calculation of the conductivity for a reference
  temperature
• determination of concentration
• determination of salinity
• calculation of the retention in the osmosis
• calculation of the pH-value

- small values for e.g. bioler feed water, - for
detection of break through of ion exchanger-
Pharmaceutical Water USP
3
Conductivity Measurement Principle
Conductivity
c L / A
A
4
Conductivity Measurement Principle
5
Conductivity Measurement Principle
electrical potential
Help alternating anode /cathode
6
Conductivity Measurement Principle
SensoCheckâ
polarisation
u
meas.
0
t
-u
7
Conductivity Measurement Principle
polarisation
polarisation effects are eliminated by separating
current and voltage path
voltage path
8
Conductivity Measurement Principle
inductive principle
sender
receiver
e.g. 100 Ohm
9
Conductivity Measurement Principle
inductive principle
10
Conductivity Measurement Electrodes
Conductivity probes
11
Conductivity Measurement Electrodes
12
Conductivity Measurement Adjustment
C a l i b r a t i o n r e q u i r e d
metal
correct
too low
too high
13
Conductivity Measurement Adjustment
Calibration- via sample calibration- with
reference solution- with reference solution
in a calibration beaker
too low
14
Conductivity Measurement Adjustment
PortaSim Cond Afor 0.055 µS/cm, 25 CPortaSim
Cond Bfor 5 µS/cm, 100 C
15
Conductivity for Determination of Concentrations
Determination of concentration via
conductivityis possible for pure aqueous
solutions of - NaCl- HCl - NaOH - H2SO4 - HNO3
16
Conductivity for Determination of Concentrations
17
Conductivity for Determination of Concentrations
Isotherms of Conductivity over concentration
(here Sulfuric Acid)
18
Conductivity Temperature Compensation
Temperature compensation for conductivity
measurement Advantage- comparable
values Problem- very important reason for
wrong determination - temperature coefficient is
mostly unknown - the conductivity is very often a
non-linear function of the temperature -
dependance of the temperature function on the
concentration itself
19
Conductivity Temperature Compensation
Temperature compensation for conductivity
measurement
First approximation Linearity of the function
20
Conductivity Temperature Compensation
21
Conductivity Temperature Compensation
22
Conductivity Temperature Compensation
23
Conductivity Temperature Compensation
non - linear function for Conductivity
?/mScm -1
tc 3.6 /K
25
24
Conductivity Temperature Compensation
Non - linear function for Conductivity
?/mScm -1
tc 2.7 /K
25
Conductivity Temperature Compensation
Further non - linear function for Conductivity
26
Protos Special Feature
Calculation of pH based on the conductivity
measurement
conductivitymeasurement II
ion exchanger
SE604
27
Protos Special Feature
Calculation of pH based on the conductivity
measurement
28
Protos Special Feature

• Determination of the concentration of NaOH in
  boiler feed water NaCl , NaOH
  HCl, H2O

cation exchanger
Conductivity 2
Conductivity 1
Cond 1 - 1/3 Cond 2
mmol/l
c (NaOH)
243
Cond 1, 2 µS/cm
243 µS/cm per mmol/l NaOH
29
Protos Special Feature

• VGB directive 450 L for boiler feed water, boiler
  water and
• vapor by steam generator over 68 bar tolerable
  operating pressure
• 1. determination of the NaOH (2x Cond)2.
  calculation of the pH-value
• pH 11 log c(NaOH)
• assumptions
• for alkalisation NaOH is used, only (no Sodium
  Phosphate)
• operation range pH 7.5 to 10.5
• for pH-values less than pH 8 any impurifications
  have to be much less than the concentration of
  NaOH

in mmol/l
30
Practical Part

• Sensor settings
• cell constant
• temperature compensation
• Parameter Sets A/B