Transcript Document

pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
CONTROLS
An Overview of
Conductivity
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IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
What is Conductivity
Electrolytic conductivity is a measure of the ability of a
solution to carry a current.
It is defined as the reciprocal or resistance, in ohms, of a
1cm3 of liquid at a specified temperature which is expressed
as siemens/cm. As the range of the conductivity is very low
it is frequently expressed as millionths of a siemens or
microsiemens/cm (S/cm).
Current in liquid is carried by ions. Any change in
concentration of ions will change the conductivity of a
liquid. Ions are formed in a liquid when a solid, such as a
salt, is dissolved. NaCl (table salt) is dissolved to form Na+
and Cl- and will contribute to the overall conductivity of the
solution.
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IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
Conductivity Terminology
and Formulas
Conductivity = Kcell 100-TC(25.0-TTC)
R
100
Kcell = cell constant in cm-1
R = Measured resistance in ohms
TC = temperature compensation factor as % change per °C
TTC = measured temperature in °C
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IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
Conductivity Terminology
and Formulas
Kcell can range from 0.01 cm-1 to 50.0 cm-1
Conductance =
1
Resistance
Conductivity =
1
= Conductance/cm
Resistivity
Cell Constant = Kcell = L
A
L = distance in cm between electrodes
A = Area in cm2 of the electrodes
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IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
www.iccontrols.com
Conductivity Terminology
and Formulas
MEASUREMENT
UNITS
Resistance
Ohm
Conductance
siemens
Resistivity
Ohmcm
Conductivity
siemens/cm
IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
Conductivity for Commonly
Used Chemicals
Conductivity is an effective measurement of concentration
of pure chemicals.
As seen on the following graph, there are well know curves
that can be applied to specific chemicals.
However, these curves only work with pure chemicals. If
other chemicals are added to the process they will influence
the conductivity and the analyzer will not be able to track
concentration accurately.
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IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
Conductance Data for
Commonly Used Chemicals
900000
S odium Chloride
Potassium Chloride
800000
S odium Hydroxide
Hydrochloric Acid
S ulfuric Acid
700000
Conductivity (uS/cm)
Nitric Acid
600000
500000
400000
300000
200000
100000
0
0
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5
10 15 20
25 30 35 40 45 50 55 60 65 70
% by Weight
75 80 85 90 95 100
IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
Temperature Compensation
Temperature compensation is critical to conductivity
measurement. As you can see from the attached graph,
temperature has a significant effect of about 2% per °C.
Therefore, if a solution starts at a temperature of 25 °C and
a conductivity of 1000 µS/cm and the temperature rises to
75 °C the conductivity will double to 2000 µS/cm.
75 °C - 25 °C = 50 °C change x 2% per °C = 100% change
1000 µS/cm + 100% change = 2000 µS/cm
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IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
Temperature Compensation
2800.00
2600.00
Conductivity (microsiemens/cm)
2400.00
2200.00
2000.00
1800.00
1600.00
1400.00
1200.00
1000.00
800.00
600.00
400.00
0
10
20
30
40
50
60
70
80
90
100
110
T emperature (Celcius)
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IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
Temperature Compensation
Temperature compensation is also specific to different
types of chemicals. Even though 2% change per °C is a
good average, the table on the next slide shows the
variation between different chemicals.
IC Controls analyzers are programmed to allow the user to
change the % value in the configuration. This ensures
temperature changes will accurately be reflected in the
conductivity displayed and output from the transmitter or
analyzer.
For specific chemicals, like HCl and NaOH, IC Controls can
supply these curves pre-programmed into the model 455 so
concentration will be displayed very accurately.
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IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
www.iccontrols.com
Temperature Compensation
SUBSTANCE
% CHANGE PER °C
Acids
1.0 to 1.6
Bases
1.8 to 2.2
Salts
2.2 to 3.0
Neutral Water
2.0
IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
Temperature Compensation
2.35
2.25
2.15
2.05
1.95
1.85
1.75
1.65
1.55
1.45
1.35
1.25
1.15
NaCl
HCl
NaOH
-10
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0
10
20
30
40
50
60
70
80
90 100
IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
Cell Constants
To determine the amount of current that will flow through a
known amount of liquid, the volume between the two
electrodes must be exact and the current must be kept
consistent and moderate. This is known as the cell
constant. Any effective volume change alters the cell
constant and current; too much volume will result in noise
(low current) and too little volume results in electrolytic
effects (high current). Cell constant recommendations will
vary depending on the conductivity range of the solution.
High conductivity requires a high cell constant and low
conductivity requires a low cell constant.
Choosing the right cell constant will ensure accurate
conductivity.
The table on the next slide shows the best cell constants for
different application.
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IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
www.iccontrols.com
Cell Constants
Cell Constant
Design Range
Lowest Range
Highest Range
0.01/cm
10 µS/cm
0 µS/cm
100 µS/cm
0.02/cm
20 µS/cm
0 µS/cm
200 µS/cm
0.1/cm
100 µS/cm
10 µS/cm
1000 µS/cm
0.2/cm
200 µS/cm
20 µS/cm
2000 µS/cm
1.0/cm
1000 µS/cm
100 µS/cm
10,000 µS/cm
2.0/cm
2000 µS/cm
200 µS/cm
20,000 µS/cm
5.0/cm
5,000 µS/cm
500 µS/cm
50,000 µS/cm
20.0/cm
20,000 µS/cm
2000 µS/cm
1,000,000 µS/cm
IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS
pH / ORP
Conductivity
Dissolved Oxygen
Chlorine
Standards
www.iccontrols.com
IC Controls offers a wide variety of
sensor and analyzer styles to suit
your conductivity needs. Go to the
conductivity section of our website
www.iccontrols.com to find Quality
Water Solutions.
IC Controls Quality Water Solutions for Conductivity
R1.0 © 2004 IC CONTROLS