Presentation Thornton Presentation Conductivity Measurement

Theory of Liquid MeasurementsConductivity/Resistivity pH ORP

THORNTON / METTLER TOLEDO

Ionic Conductance~

H+

O H

Na+

O H H

Cl-


Cell Constant

1 cm

1 cm 1 cm

Conductivity Cell Constant =

Length Area

=

1 cm 1 cm2

= 1 cm-1


Other Cell Constants

1cm 0.1cm 1cm

1cm 10cm 1cm

0.1constant

10.0constant

Cell Constant = Multiplier


Resistivity/Conductivity CellConcentric Electrodes

OUTER ELECTRODE

INNER ELECTRODE

INSULATOR


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)


Cell Constant Traceability

ASTM D1125 Primary Standard and Pure Water at 15, 25, 40C

Standards Lab Cell Constant

Production Cell Constant


Ultrapure Water Sensor Calibration/ Certification System

Thornton Inc.


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)


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


Temperature Effects on Conductivity

~

H+ O H H

O

H

Na+

Cl-


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


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)


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


Cell InstallationRecommended Cell Installation...OUTLET

INLET

Flow should be directed at the end of the sensor


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)


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


Two-Electrode Conductivity Measurement

10/cm Constant CellSheath Slot RTD

Graphite Electrodes

Bottom view


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


pH Range


pH MeasurementDissociation of water

H2O

H+ + OH-

Kw =

[H+] [OH-]


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


Conductivity vs pH

Conductivity

Acid

Base

0.055 S/cm 18.2 M-cm 7

pHTHORNTON / METTLER TOLEDO

Conductivity vs pH


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)


pH Electrode SystemGlass pH Reference Temperature Compensator To Measuring Circuit


Combination pH Electrode

Electrolyte

RTD (insulated)

Reference junction

Measuring membrane


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


pH Temperature Compensation

Adder (standardize offset, asymmetry) Multiplier (slope)

Solution Temperature Coefficient

Electrode mV Temperature

Nernst Electrode Temperature Compensation

pHT

Solution Temperature Compensation

pH25C


Detachable pH Electrode System

VP Preamplifier

VP pH Electrode

Housing


High Purity pH Sensor AssemblyPreamp Electrolyte Reservoir to Instrument

Combination pH Electrode Buffer solution Calibration Funnel 3-way Valve Sample Inlet to drain RTD


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


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


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


ORP Electrode SystemTo Measuring Circuit

Measuring

Reference

Platinum Disk

Reference Junction


Documents

Presentation Thornton Presentation Conductivity Measurement