Theory of Liquid Measurements Theory of Liquid Measurements - - PowerPoint PPT Presentation

SLIDE 1

THORNTON / METTLER TOLEDO

Theory of Liquid Measurements Theory of Liquid Measurements

• Conductivity/Resistivity

Conductivity/Resistivity

• pH

pH

• ORP

ORP

SLIDE 2

THORNTON / METTLER TOLEDO

H H Na Na+

+

Cl Cl-

• H

H H H+

+

O O O O H H

• ~

~

Ionic Conductance Ionic Conductance

SLIDE 3

THORNTON / METTLER TOLEDO

1 cm 1 cm 1 cm 1 cm 1 cm 1 cm

Conductivity Cell Constant = Conductivity Cell Constant = Length Length Area Area 1 cm 1 cm 1 cm 1 cm2

2

= = = 1 cm = 1 cm-1

• 1

Cell Constant Cell Constant

SLIDE 4

THORNTON / METTLER TOLEDO

Other Cell Constants Other Cell Constants

1cm 0.1cm 1cm 1cm 10cm 1cm

.1constant 1 .0constant

Cell Constant = Multiplier

SLIDE 5

THORNTON / METTLER TOLEDO

Resistivity/Conductivity Cell Resistivity/Conductivity Cell

Concentric Electrodes

INSULATOR ELECTRODE ELECTRODE INNER OUTER

SLIDE 6

THORNTON / METTLER TOLEDO

Resistance Resistance

• hm
• hm

Conductance Conductance mho, siemens = 1/ohm mho, siemens = 1/ohm Resistivity Resistivity

• hm-cm,
• hm-cm,

megohm megohm-cm, M

• cm, MΩ

Ω Ω Ω Ω Ω Ω Ω-cm

• cm

Conductivity Conductivity mho/cm, mho/cm, µ µ µ µ µ µ µ µmho/cm mho/cm siemens/cm, siemens/cm, microsiemens microsiemens/cm, /cm, µ µ µ µ µ µ µ µS/cm S/cm

Units of Conductivity/Resistivity Units of Conductivity/Resistivity

SLIDE 7

THORNTON / METTLER TOLEDO

Industry Preferences: Industry Preferences:

Resistivity - Semiconductor ultrapure water Resistivity - Semiconductor ultrapure water Conductivity - Power, Pharmaceutical, Conductivity - Power, Pharmaceutical, Pretreatment stages, Cooling towers, Pretreatment stages, Cooling towers, Wastewater Wastewater Total Dissolved Solids (ppm TDS) Total Dissolved Solids (ppm TDS)

Units of Conductivity/Resistivity Units of Conductivity/Resistivity

SLIDE 8

THORNTON / METTLER TOLEDO

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

°C

C Standards Lab Standards Lab Cell Constant Cell Constant Production Cell Production Cell Constant Constant

Cell Constant Traceability Cell Constant Traceability

SLIDE 9

THORNTON / METTLER TOLEDO

Ultrapure Water Sensor Ultrapure Water Sensor Calibration/ Certification System Calibration/ Certification System

Thornton Inc.

SLIDE 10

THORNTON / METTLER TOLEDO

Conductivity, Resistivity, TDS Ranges Conductivity, Resistivity, TDS Ranges

100M 10M 1M 100K 10K 1K 100 10 1 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 0.01 .1 1 10 100 1000 10k 100k 1000k 0.021 0.4 4.6 46 460 4.6k Conductivity TDS ppm Conductivity and resistivity are measured at 25°

° ° °C; TDS is expressed as Sodium Chloride (NaCl)

Resistivity

• hm-cm

µS-cm

SLIDE 11

THORNTON / METTLER TOLEDO in-line cell sample take-off factory-certified reference cell to drain 200-500 mL/min sample flow Process flow flow chamber

• n-line

instrument calibrated reference instrument

On-Line Conductivity Sensor On-Line Conductivity Sensor Calibration/Verification Calibration/Verification

SLIDE 12

THORNTON / METTLER TOLEDO

H H Na Na+

+

Cl Cl-

• H

H H H+

+

O O O O H H

• ~

~

Temperature Effects on Conductivity Temperature Effects on Conductivity

SLIDE 13

THORNTON / METTLER TOLEDO

Natural waters, etc. Natural waters, etc. (>2 (>2 µ µ µ µ µ µ µ µS/cm) S/cm) ~ 2 %/°C ~ 2 %/°C High purity water High purity water (0.055 (0.055 µ µ µ µ µ µ µ µS/cm or 18.2 S/cm or 18.2 Megohm Megohm-cm)

• cm) 4 - 7 %/°C

4 - 7 %/°C

Conductivity/Resistivity Conductivity/Resistivity Temperature Coefficients Temperature Coefficients

SLIDE 14

THORNTON / METTLER TOLEDO

O O2-

2-

H H2

2O

O H H+

+ + OH

+ OH-

• H

H+

+

H H+

+

O O2-

2-

H H+

+

H H+

+

Dissociation of Water Dissociation of Water

SLIDE 15

THORNTON / METTLER TOLEDO

Conductivity of Pure Water vs. Temperature Conductivity of Pure Water vs. Temperature

Temperature (°C)

1 10 100 10 20 30 40 50 60 70 80 90 100 0.01 0.1 1

Conductivity (µS/cm) Resistivity (M

• cm)

SLIDE 16

THORNTON / METTLER TOLEDO

Conductivity vs. Temperature Conductivity vs. Temperature

0.01 0.10 1.00 10.00

10 20 30 40 50 60 70 80 90 100

Temperature (°C) Conductivity (µS/cm)

0 ppb 129 ppb 40 ppb 395 ppb 840 ppb 1730 ppb 4390 ppb

NaCl Concentration

SLIDE 17

THORNTON / METTLER TOLEDO

Temperature Compensation 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

SLIDE 18

THORNTON / METTLER TOLEDO

Cell Installation Cell Installation

Recommended Cell Installation...

OUTLET INLET Flow should be directed at the end of the sensor

SLIDE 19

THORNTON / METTLER TOLEDO

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)

SLIDE 20

THORNTON / METTLER TOLEDO

Conductivity vs. Concentration

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10 20 30 40 50 60 70 80 90 100

Concentration (% by weight) Conductivity (S/cm)

HCl H2SO4 NaOH NaCl

SLIDE 21

THORNTON / METTLER TOLEDO

Two-Electrode Conductivity Measurement

50/cm Constant Cell

Bottom view Graphite Electrodes

SLIDE 22

THORNTON / METTLER TOLEDO

Two-Electrode Conductivity Measurement

10/cm Constant Cell

Graphite Electrodes Bottom view Sheath Slot RTD

SLIDE 23

THORNTON / METTLER TOLEDO

AC Current Source AC Voltage Measurement Drive Electrodes Measuring Electrodes

Four Electrode Sensor Four-Electrode Measuring Instrument

Four-Electrode Conductivity Measurement

SLIDE 24

THORNTON / METTLER TOLEDO

Four-Electrode Conductivity Measurement

Four-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.

SLIDE 25

THORNTON / METTLER TOLEDO

Inductive (non-contact, electrodeless, toroidal) Conductivity Sensor

Inductive Conductivity Measurement

Energized Measured

SLIDE 26

THORNTON / 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

SLIDE 27

THORNTON / METTLER TOLEDO

pH Range pH Range

SLIDE 28

THORNTON / METTLER TOLEDO

H H2

2O

O H H+

+ + OH

+ OH-

• pH Measurement

pH Measurement

K Kw

w

= [H = [H+

+]

[OH ] [OH-

• ]

]

Dissociation of water Dissociation of water

SLIDE 29

THORNTON / METTLER TOLEDO

1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH

10 10-0

• 0 10

10-1

• 1 10

10-2

• 2 10

10-3

• 3 10

10-4

• 4 10

10-5

• 5 10

10-6

• 6 10

10-7

• 7 10

10-8

• 8 10

10-9

• 9 10

10-10

• 10 10

10-11

• 1110

10-12

• 1210

10-13

• 1310

10-14

• 14 [H

[H+

+]

]

10 10-14

• 14 10

10-13

• 13 10

10-12

• 12 10

10-11

• 1110

10-10

• 10 10

10-9

• 9 10

10-8

• 8 10

10-7

• 7 10

10-6

• 6 10

10-5

• 5 10

10-4

• 4 10

10-3

• 3 10

10-2

• 2 10

10-1

• 1 10

10-0

• 0 [OH

[OH+

+]

]

pH ~ -log pH ~ -log10

10 [H

[H+

+]

] [H [H+

+] ~ 10

] ~ 10-pH

• pH

at 25°C at 25°C

pH Scale pH Scale

SLIDE 30

THORNTON / METTLER TOLEDO

Conductivity Conductivity vs vs pH pH

Conductivity pH

0.055 µS/cm 18.2 MΩ Ω Ω Ω-cm 7 Acid Base

SLIDE 31

THORNTON / METTLER TOLEDO

Conductivity Conductivity vs vs pH pH

SLIDE 32

THORNTON / METTLER TOLEDO

Temperature (°C) pH

6 7 8 9 10 11 10 20 30 40 50 60 70 80 90 100 Pure Water 0.5 ppm NH3

pH vs. Temperature for Pure Waters pH vs. Temperature for Pure Waters

SLIDE 33

THORNTON / METTLER TOLEDO

To Measuring To Measuring Circuit Circuit Glass pH Glass pH Reference Reference Temperature Temperature Compensator Compensator

pH Electrode System pH Electrode System

SLIDE 34

THORNTON / METTLER TOLEDO

Measuring membrane Reference junction Electrolyte RTD (insulated)

Combination pH Electrode Combination pH Electrode

SLIDE 35

THORNTON / METTLER TOLEDO

1 2 3 4 5 6 7 8 9 10 11 12 13 14

pH

400 200

• 200
• 400

mV

0°C 25°C 50°C 100°C

pH Electrode Output pH Electrode Output

SLIDE 36

THORNTON / METTLER TOLEDO

pH Temperature Compensation pH Temperature Compensation

Electrode mV Temperature Nernst Electrode Temperature Compensation

pHT

Solution Temperature Compensation

pH25°C

Solution Temperature Coefficient

Adder (standardize

• ffset, asymmetry)

Multiplier (slope)

SLIDE 37

THORNTON / METTLER TOLEDO

Detachable pH Electrode System Detachable pH Electrode System

VP Preamplifier VP pH Electrode Housing

SLIDE 38

THORNTON / METTLER TOLEDO

High Purity pH Sensor Assembly High Purity pH Sensor Assembly

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

SLIDE 39

THORNTON / METTLER TOLEDO

pH Standards 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

SLIDE 40

THORNTON / METTLER TOLEDO

High Purity pH Measurement Equipment 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

SLIDE 41

THORNTON / METTLER TOLEDO

ORP: ORP:

O Oxidation- xidation-R Reduction ( eduction (redox redox) ) P Potential

• tential
• Oxidation-reduction chemical reactions
• Oxidation—loss of electrons, higher potential
• Reduction—gain of electrons, reduced potential
• Examples
• Chlorine, ozone, permanganate can oxidize
• rganics (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

reactions

SLIDE 42

THORNTON / METTLER TOLEDO

ORP Response to ORP Response to Dechlorination Dechlorination

SLIDE 43

THORNTON / METTLER TOLEDO

ORP Electrode System ORP Electrode System

To Measuring Circuit Measuring Reference Platinum Disk Reference Junction