What is pH?faculty.chemeketa.edu/csekafet/ELT291/14.pdf · All-Hands Meeting What is pH? pH is the...
Transcript of What is pH?faculty.chemeketa.edu/csekafet/ELT291/14.pdf · All-Hands Meeting What is pH? pH is the...
All-Hands Meeting
What is pH?What is pH?
pH is the measurement of the Hydrogen Ion concentration in a particular solution. Indicates the Acidity or Alkalinity of a solution.u Why is pH measured?
² Used as a process control parameter.² Most reliable specific Ion measurement.² Least maintenance intensive specific Ion
measurement.
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What is pH ?What is pH ?
•pH = - Log [H+]
100 10-1 10-2 10-3 10-4 10-10 10-13 10-1410-1210-5 10-6 10-7 10-8 10-9 10-11
10010-110-210-310-410-1010-1310-14 10-12 10-510-610-710-810-910-11OH-
H+
pH Scale
1 2 3 4 5 6 7 8 9 10 11 12 13 140
Acid Base
Neutral
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The pH MeasurementThe pH Measurement•pH Measuring Components
– Measuring Electrode– Reference Electrode– Temperature Compensator– Analyzer (Transmitter)
•How the Measuring System worksuThe glass electrode develops a potential directly related to the
Hydrogen Ion concentration of a solution. The potential is measured as (mV) across the glass membrane.
uThe Reference electrode is necessary as a constant potential for comparison against the measuring electrode. It also completes the electrical circuit - Provides liquid wire!
uThe change in voltage/Hydrogen Ion concentration will be directly proportional to the change in pH.
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pH Simplified!pH Simplified!• pH system works similar to battery -
The Glass electrode provides a constant voltage (steady state), while the reference builds resistance with time/usage.
• As Reference electrode ages the internal resistance (across Junction) increases
• Resistance across Junction increases until measurement signal lost - High Impedance!
• After initial calibration, 90% or more of calibration offset is due to reference deterioration.
V = Constant VoltagePotential
V = IR
V = Glass electrode output
R = Reference electrode
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Measuring ElectrodesMeasuring Electrodes
• Glass: Most Common - Used in 95% or more of all applications.
• Solid State - Utilizes a Solid State Chip rather than glass. Example: ISFET Technology - Currently used in 2%-3% of all applications
• Antimony - Silver white metal (Similar to Lead). Used in applications where glass will not! Example: (HF) Used in 1%-2% of all applications.
Antimony Electrode
Solid State Electrode
Glass Electrode
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Glass Measuring ElectrodeGlass Measuring Electrode
H+
KCl Electrolyte
Ag/AgCl Electrode
H+
Glass Membrane
High Impedance
Coaxial Cable
H+
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Durafet pH ElectrodeDurafet pH ElectrodeLow ImpedanceConnector
FastRespondingTemperatureSensor
ReplaceableCeramicReferenceJunction
QuickDisconnectCable
Ag/AgClElement
RefillableSaturatedKCl Gel
RuggedDurafetSensor
CounterElectrode
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Troubleshooting the Electrode Troubleshooting the Electrode SystemSystem
•Reference electrode is the weak link in the measurement system in 90% of all applicationsuReference open to the process - porous junctionuTypical modes of reference failure:
² Plugging² Fouling² Poisoning² Depletion² Pressure spikes
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Reference ElectrodesReference Electrodes• Diffusion (Slurry/Gel) - Used
in 95% or more applicationsuSingle JunctionuDouble JunctionuTriple Junction
• Flowing - Used in 5% or less applicationsuSalt BridgeuBellowmatic
• Solid State -Currently unavailable
Single Junction
Double Junction
Triple Junction
Ion Sensitive Coating
Non-Porous Reference
Ceramic body
Solution ground
l
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ProblemJunction Type
Plugging Fouling Poisoning Depleting Pressure InitialCost
Ease ofUse
LongTermCosts
DIFFUSION JUNCTION REFERENCE ELECTRODESingle Junction 2 3 3 2 3 1 1 3Double Junction 2 3 2 2 3 1 1 2Triple Junction 2 3 1 3 3 1 1 2
FLOWING JUNCTION REFERENCE ELECTRODESalt Bridge 1 1 1 1 2 2 3 1Bellomatic 1 1 1 1 1 2 2 1Solid State 1 2 1 1 1 3 1 1
RANKING:
1=GOOD
2= FAIR
3==POOR
l
Reference Electrode Selection GuideReference Electrode Selection Guide
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Reference Electrode Diffusion TypeReference Electrode Diffusion Type
KCl ElectrolyteSaturated
Gel
Standard Wire
Ag/AgCl Electrode
Porous Junction
K+
Cl-
K+ Cl- mVJunction Potential
offset during calibration(Asymmetry)
K+
Cl-
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Double Junction Double Junction Reference ElectrodeReference Electrode
Diffusion TypeDiffusion Type
KCl ElectrolyteSaturated
Gel
Standard Wire
KCl ElectrolyteSaturated
Gel
Ag/AgCl Electrode
Porous Junction
K+
Cl-
K+ Cl-
No Silver Ion
Internal Junction
K+ Cl-
Ag+
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Triple Junction Reference Triple Junction Reference Electrode Diffusion typeElectrode Diffusion type
K+ Cl-
K+Cl-
Ag/AgCl
K+ Cl-
K+
Cl-
K+Cl-
Cl-
Standard Wire
Saturated KCLElectrolyte Gel
No Silver Ion
Porous Junction
Internal Junction
Ag/AgCl Wire
Saturated KCL orAmmonium Nitrate
Electrolyte Gel
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Reference ElectrodeReference ElectrodeFlowing TypeFlowing Type
Ag/AgCl Electrode
Flowing Junction
Standard Wire
K+
Cl-
K+ Cl-
KCl Electrolyte2 Normal
To Reservoir
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Reference “ Rules of Thumb”Reference “ Rules of Thumb”•Typical Applications - Expect to replace (3)
Reference electrodes for every (1) Measuring•Harsh Applications - Expect to replace (10)
Reference electrodes for every (1) Measuring•Minimum Life expectancy - Junction Poisoning
uSymptoms to be aware of:² Severe discoloring of Junction
• Junction turns brown or black in color• Discoloration not removed when cleaned
•Remember - When in doubt think...........uReference!
² Reference!• Reference!
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The Bellowmatic electrodeThe Bellowmatic electrode
•Flowing JunctionuInternally pressurized by bellows assembly
•Pressure compensatinguBellows floats with process pressure changes
•Self containeduNo external connections/tubes/reservoirs
•Unique to the industryuOne of a Kind!
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The Bellowmatic SolutionThe Bellowmatic Solution•What problems can the Bellowmatic solve?
uPlugging ² Positive pressure prevents internal build-up.
uFouling² Positive pressure prevents external build-up.
uPoisoning² Positive pressure prevents process migration.
uDepletion² Positive pressure prevents dilution.
uPressure Spikes² Floating bellows compensates for process spikes.
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Where each Reference electrode Where each Reference electrode type type could could operateoperate
0
20
40
60
80
100
All pH Applications
(%)
Single
Double
Triple
Salt Bridge
Bellowmatic
Solid State
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Where each Reference electrode Where each Reference electrode type type shouldshould operateoperate
010
203040
506070
8090
100
All pH Applications
(%)
Solid State
Flowing - Salt Bridge
Flowing - Bellowmatic
Diffusion - All types
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Test QuestionsTest QuestionspH
1) What should the output (Millivolts) of a pH measuring electrode be in a 7 buffer?
2) What should the Asymmetry of a new reference electrode be after calibration?
3) In a typical application how many reference electrodes will be replaced per glass electrode?
4) What is the reference mode of failure that causes the junction to turn brown or black?
5) What company makes an electrode like the Bellomatic?
6) What are two applications ideal for using the Bellomatic?
CONDUCTIVITY7) What “Rule of Thumb” value (uS/cm) defines when
to use Inductive vs. Contacting conductivity?8) What factor is used to convert from uS/cm to
uMho/cm?9) What two industries were DC400 designed for?10) What other companies make Dual cell analyzers?11) How many bore sizes are available for the IC40
sensor?
12) Why is the IC40 stable with process temperature changes?
13) The 5X5 matrix is compensating for what effect on the solution?
• match the analyzer/measuring technology that should be used with the following applications: a = DC; b = SC; c = IC
14) Reverse Osmosis system15) Demineralizer Regeneration System16) Softener17) Demineralizer Outlet
ZIRCONIA OXYGEN18) Why is our cell resistant to attacks from flue
gases?19) How does the competition bond the platinum to
their ceramic cells.20) What are two advantages of using reference air as
one of the calibration gases?
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Test QuestionsTest QuestionspH
1) What should the output (Millivolts) of a pH measuring electrode be in a 7 buffer? (Zero Millivolts)
2) What should the Asymmetry of a new reference electrode be after calibration? ( + or - 20 Millivolts)
3) In a typical application how many reference electrodes will be replaced per glass electrode? (3 to 1)
4) What is the reference mode of failure that causes the junction to turn brown or black? (Poisoning)
5) What company makes an electrode like the Bellomatic? (None)
6) What are two applications ideal for using the Bellomatic? (Students Choice)
CONDUCTIVITY7) What “Rule of Thumb” value (uS/cm) defines when to use
Inductive vs. Contacting conductivity? (100 uS/cm)8) What factor is used to convert from uS/cm to uMho/cm?
(None - both units have same value)9) What two industries were DC400 designed for? (Power &
Semiconductor)10) What other companies make Dual cell analyzers?
(Rosemont, L&N, Thornton, Foxboro, Signet)11) How many bore sizes are available for the IC40 sensor?
(One)
12) Why is the IC40 stable with process temperature changes? (Matched Coils)
13) The 5X5 matrix is compensating for what effect on the solution? (Temperature)
• match the analyzer/measuring technology that should be used with the following applications: a = DC; b = SC; c = IC
14) Reverse Osmosis system (DC or a)15) Demineralizer Regeneration System (IC or C)16) Softener (DC or a)17) Demineralizer Outlet (SC or b)
ZIRCONIA OXYGEN18) Why is our cell resistant to attacks from flue gases?
(Molecular Bonding)19) How does the competition bond the platinum to their
ceramic cells. (Adhesive Bonding)20) What are two advantages of using reference air as one of
the calibration gases? (Cost and true zero of cell output)