presentation thornton presentation conductivity measurement
TRANSCRIPT
Theory of Liquid MeasurementsConductivity/Resistivity pH ORP
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Ionic Conductance~
H+
O H
Na+
O H H
Cl-
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Cell Constant
1 cm
1 cm 1 cm
Conductivity Cell Constant =
Length Area
=
1 cm 1 cm2
= 1 cm-1
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Other Cell Constants
1cm 0.1cm 1cm
1cm 10cm 1cm
0.1constant
10.0constant
Cell Constant = Multiplier
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Resistivity/Conductivity CellConcentric Electrodes
OUTER ELECTRODE
INNER ELECTRODE
INSULATOR
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Units of Conductivity/ResistivityResistance Conductance Resistivity ohm mho, siemens = 1/ohm ohm-cm, megohm-cm, M-cm mho/cm, mho/cm siemens/cm, microsiemens/cm, S/cmTHORNTON / METTLER TOLEDO
Conductivity
Units of Conductivity/ResistivityIndustry Preferences:Resistivity - Semiconductor ultrapure water Conductivity - Power, Pharmaceutical, Pretreatment stages, Cooling towers, Wastewater Total Dissolved Solids (ppm TDS)
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Cell Constant Traceability
ASTM D1125 Primary Standard and Pure Water at 15, 25, 40C
Standards Lab Cell Constant
Production Cell Constant
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Ultrapure Water Sensor Calibration/ Certification System
Thornton Inc.
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Conductivity, Resistivity, TDS RangesResistivity 100M 10M 1M 100K 10K 1K 100 10 1 ohm-cm Ultrapure water Deionized water Distilled water Condensate Drinking water Cooling tower water Percentage of acids, bases and salt Waste water Brackish water, Sea water Water for Industrial Process 5% Salinity 2% NaOH 20% HCl Conductivity TDS 0.01 .1 0.021 1 0.4 10 4.6 100 46 1000 460 10k 4.6k 100k 1000k S-cm ppm
Conductivity and resistivity are measured at 25C; TDS is expressed as Sodium Chloride (NaCl)
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On-Line Conductivity Sensor Calibration/Verificationon-line instrument
in-line cell Process flow sample take-off calibrated reference instrument
factory-certified reference cell 200-500 mL/min sample flow flow chamber
to drain
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Temperature Effects on Conductivity
~
H+ O H H
O
H
Na+
Cl-
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Conductivity/Resistivity Temperature Coefficients
Natural waters, etc. (>2 S/cm)
~ 2 %/C
High purity water (0.055 S/cm or 18.2 Megohm-cm) 4 - 7 %/C
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Dissociation of WaterH+ H+ O2O2H+ H+
H2O
H+ + OHTHORNTON / METTLER TOLEDO
Conductivity of Pure Water vs. TemperatureResistivity (M -cm) Conductivity (S/cm)
100
0.01
10
0.1
1 0 10 20 30 40 50 60 70 80 90
1 100
Temperature (C)THORNTON / METTLER TOLEDO
Conductivity vs. Temperature10.00NaCl Concentration4390 ppb
C onductivity (S/cm)
1730 ppb
1.00840 ppb 395 ppb 129 ppb
0.1040 ppb
0 ppb
0.010 10 20 30 40 50 60 70 80 90 100
Temperature (C)
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Temperature Compensation Standard -- high purity water with mineral contamination Linear, %/C -- special applications with known coefficient Cation/Ammonia/ETA -- power plant cycle chemistry and semiconductor acid etch rinse operations Alcohol -- special semiconductor rinse operations Glycol -- semiconductor coolant monitoring Light 84 -- same as Standard but with 1984 pure water data(reads slightly higher resistivity)
Direct % Concentration Readout of HCl, H2SO4, NaOH automatically selects appropriate compensation
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Cell InstallationRecommended Cell Installation...OUTLET
INLET
Flow should be directed at the end of the sensor
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High Conductivity Measurements Applications Reverse Osmosis feedwater Acid/Base deionizer regenerant concentration Process fluids Recycle water Wastewater/effluent Cooling towers
Conductivity Measurement Technologies Two-electrode contact Four-electrode contact Inductive (non-contact, electrodeless, toroidal)
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Conductivity vs. Concentration0.9 0.8
0.7
HCl
H2SO4
Conductivity (S/cm)
0.6
0.5
0.4
NaOH
0.3
0.2
NaCl0.1
0 0 10 20 30 40 50 60 70 80 90 100
Concentration (% by weight)THORNTON / METTLER TOLEDO
Two-Electrode Conductivity Measurement
50/cm Constant Cell
Graphite Electrodes
Bottom view
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Two-Electrode Conductivity Measurement
10/cm Constant CellSheath Slot RTD
Graphite Electrodes
Bottom view
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Four-Electrode Conductivity MeasurementAC Current Source
Four-Electrode Measuring Instrument
AC Voltage Measurement
Measuring Electrodes
Four Electrode SensorDrive ElectrodesTHORNTON / METTLER TOLEDO
Four-Electrode Conductivity MeasurementFour-electrode sensors and instruments can tolerate poor measuring conditions due to three factors:1. Electrode metal surface condition is less important. 2. Electrode fouling or coating has much less effect. 3. Four-electrode sensors do not have the narrow channels of high, two-electrode cell constants. The resulting flat surface design is much less vulnerable to fouling.THORNTON / METTLER TOLEDO
Inductive Conductivity Measurement
Energized
Measured
Inductive (non-contact, electrodeless, toroidal) Conductivity SensorTHORNTON / METTLER TOLEDO
Inductive Conductivity Measurement Virtually non-fouling No metal/solution contact Reliable high conductivity measurements Relatively large sensor size Cell constant can be affected by surrounding pipe
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pH Range
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pH MeasurementDissociation of water
H2O
H+ + OH-
Kw =
[H+] [OH-]
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pH ScalepH ~ -log10 [H+] [H+] ~ 10-pH
0 1
2
3 4 5
6 7
8 9 10 11 12 13 14 pH [H+] [OH+]
10-0 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-1110-1210-1310-14
10-14 10-13 10-12 10-1110-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 10-0
at 25C
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Conductivity vs pH
Conductivity
Acid
Base
0.055 S/cm 18.2 M-cm 7
pHTHORNTON / METTLER TOLEDO
Conductivity vs pH
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pH vs. Temperature for Pure Waters11 10 9
pH8 7 6 0 10 20 30 40
0.5 ppm NH3
Pure Water
50
60
70
80
90
100
Temperature (C)
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pH Electrode SystemGlass pH Reference Temperature Compensator To Measuring Circuit
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Combination pH Electrode
Electrolyte
RTD (insulated)
Reference junction
Measuring membrane
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pH Electrode Output25C 50C 100C 0C
400 200
mV
0
-200
-400
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14
pH
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pH Temperature Compensation
Adder (standardize offset, asymmetry) Multiplier (slope)
Solution Temperature Coefficient
Electrode mV Temperature
Nernst Electrode Temperature Compensation
pHT
Solution Temperature Compensation
pH25C
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Detachable pH Electrode System
VP Preamplifier
VP pH Electrode
Housing
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High Purity pH Sensor AssemblyPreamp Electrolyte Reservoir to Instrument
Combination pH Electrode Buffer solution Calibration Funnel 3-way Valve Sample Inlet to drain RTD
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pH Standards NIST standards--materials to make up buffers at: 1.681, 3.557, 4.006, 6.863, 7.41, 9.180, 10.011, 12.46 pH Commercial standard buffer solutions NIST recipes Integral pH values
Have unique temperature dependence
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High Purity pH Measurement Equipment
Low volume, stainless steel flow chamber Low sample flowrate with atmospheric discharge Flowing junction reference electrode Solution temperature compensation as well as electrode temperature compensation Convenient disabling of Solution temperature compensation during buffer calibration NIST-traceable buffer solutions
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ORP:Oxidation-Reduction (redox) Potential Oxidation-reduction chemical reactions Oxidationloss of electrons, higher potential Reductiongain of electrons, reduced potential
Examples Chlorine, ozone, permanganate can oxidize organics (color, odor, bacteria) Bisulfite or carbon beds can reduce chlorine (protect RO membranes & DI resins); Hydrazine can reduce oxygen
ORP monitors the status of these reactionsTHORNTON / METTLER TOLEDO
ORP Response to Dechlorination
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ORP Electrode SystemTo Measuring Circuit
Measuring
Reference
Platinum Disk
Reference Junction
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