Process Instrument Verification for Drinking Water
2014 Plant Operations Conference
http://www.vaawwa.org/�
PIV for Drinking Water
• Overview of Operation, Calibration, Verification • Chlorine Analyzer • Turbidimeter • pH Sensor • Hands-On Lab
Operation, Calibration, and Performance Verification of
CL17 Chlorine Analyzer and 1720 Series Turbidimeters
Take-Home Messages
• Do NOT calibrate the CL17 analyzer unless required by regulatory agencies. – DO verify performance of unit regularly.
• DO calibrate 1720 Series turbidimeters at
least quarterly. – DO verify performance regularly.
Course Outline
• Process Monitoring • Key Differences (color and turbidity) • Operation of (colorimetric) CL17 • Operation of (turbidimetric) 1720 Turbidimeters • Calibration and Verification Strategies • Hands-On Lab
Process Monitoring
• Key to cost control • Key to regulatory compliance • Key to process control
Laboratory vs On-line Monitoring
• Laboratory monitoring consists of collecting grab or composite samples and then analyzing them in the laboratory. – Time and labor intensive – Variations in technique at time of sampling and/or
analysis may cause inconsistent results
Laboratory vs On-line Monitoring
• Automated analysis (on-line) is key to solving critical water problems and reducing labor requirements.
• Fast detection and correction in each unit process can cut treatment costs and keep a plant’s process in control.
Laboratory vs On-line Monitoring
• In addition to monitoring, on-line instrumentation can also be used to control chemical feed, process automation
Laboratory vs On-line Monitoring
• Laboratory analysis can (and should) be used to supplement the on-line instrumentation – Parameters not needing constant measurement or
control – Problem solving – Checking calibration of on-line instruments
Process Monitoring
• Process instruments automate analytical tests for on-line, continuous monitoring and control.
Advantages to Process Monitoring
• Detect process problems as they happen • Save operator time • May be used for process automation
Selecting an Instrument
• Considerations in selecting a process instrument – Maintenance requirements – Does it meet the needs of the users? – Reliability – Ease of operation – Features – Cost
Course Outline
• Process Monitoring • Key Differences (color and turbidity) • Operation of (colorimetric) CL17 • Operation of (turbidimetric) 1720D • Calibration and Verification Strategies • Hands-On Lab
Color Measurement
• Chlorine Analyzer uses Color Measurement • Measure the intensity of light passing through
a colored sample • Convert light intensity measurements to
concentration
Color Measurement
In this case, the sample absorbs very little of the incident light.
It is a low concentration sample.
Color Measurement
In this case, most of the incident light is absorbed by the sample.
It is a high concentration sample.
Lamp Monochromator or Filter
Lens Sample Detector
Basic Spectrophotometer
What is Turbidity?
• A measure of relative water clarity • An indirect measure of suspended
solids – Measured by light scattering
• An indicator of water quality
Basic 90o Turbidimeter
Key Differences
• CL17 measures dissolved substance – Color formed is proportional to concentration. – Turbidity is potential interference.
• 1720 Turbidimeters measure suspended matter
– Scattered light is proportional to concentration. – Color is an interference.
Key Differences
• CL17 measures transmitted light at 180 degrees to light source.
• 1720 Turbidimeters measure scattered light at 90 degrees to light source.
Key Differences
• CL17’s analysis is a two-step process, that can compensate for aging light source.
• 1720 Turbidimeter analysis is a single-step process which cannot compensate for aging light sources.
Course Outline
• Process Monitoring • Key Differences (color and turbidity) • Operation of (colorimetric) CL17 • Operation of (turbidimetric) 1720 Turbidimeters • Calibration and Verification Strategies • Hands-On Lab
Operation of (colorimetric) CL17 • Colorimetry is the measurement of color. • The intensity of the color relates to the chlorine
concentration, based on the instrument calibration. • The CL17 measures transmitted light at 180 degrees
to the light source. • Two complimentary colors involved (green light and
reacted pink color)
Lamp Filter Sample Detector
Old Model CL17
New Model CL17
Sample Detector LED
Operation of (colorimetric) CL17
• Analysis is a two-step, comparative process. – ZERO then READ
• The final results are displayed as mg/L. (milligrams/Liter)
CL17 Chlorine Analyzer
Colorimeter
Pump Module
Keypad Wiring
Operation of (colorimetric) CL17 • “ZERO”
– Sample cell flushed with fresh sample. – Flow stops and instrument “zeroes out” any color
or turbidity. • “READ”
– Reagents added, mixed, and allowed to react. – The pink color formed is measured and compared
to calibration to determine chlorine concentration.
CL17 CHLORINE ANALYZER
SAMPLE INLET SAMPLE VALVE
UNDER PRESSURE
LIGHT SOURCE TO WASTE
DETECTOR GLASS CELL
MAGNETIC STIRRER PINCHERS
INDICATOR
BUFFER SOLUTION
CL17 Operation - Zero
Sample line opens
Colorimeter cell flushes with sample.
CL17 Operation - Zero
Sample line closes and flow through colorimeter stops.
CL17 Zeros on the blank with clear solution (sample) in cell.
CL17 Operation - Read
Sample line closed.
Reagents dispensed through middle tubes.
CL17 Operation - Read
Reagents mix with sample in sample cell.
If chlorine is present, pink color forms and persists for ~1 minute.
CL17 reads sample.
CL17 Operation - Read
CL17 uses factory programmed calibration curve to convert absorbance measurement into mg/L chlorine reading.
Light Source Detector
% Transmittance Absorbance
100
10
0.00
1.00
“ZERO”
60 0.22 “READ”
40 0.40 “READ”
“READ”
(Abs = -log T)
Absorbance
Concentration (m
g/L) 0.88
1.60
4.00
0.22 0.40 1.00
Slope or gain of
calibration
Operation of (colorimetric) CL17
• What happens when light source fades? - Is the accuracy of the reading affected?
• No. The instrument response is a comparative process. The transmitted light is proportional to incident light, therefore %T is unaffected.
Light Source Detector
% Transmittance Absorbance
100
60
40
10
0.00
0.22
0.40
1.00
“ZERO”
“READ”
“READ”
“READ”
(Abs = -log T)
Light Source
Detector
% Transmittance Absorbance
100
60
40
10
0.00
0.22
0.40
1.00
“ZERO”
“READ”
“READ”
“READ”
(Abs = -log T)
Faded Light Source
The amount of light differs, but not the percent transmittance!
Common Mistakes (CL17)
• Incorrect Flow Rate (300 mL/min ideal) – Low flow causes low readings due to incomplete
cell flushing – High flow causes low readings due to constant
flushing (color never develops)
Common Mistakes (CL17)
• Reagents/Mixing – DPD powder not used (mix entire bottle of
powder into indicator solution) – No stir bar, 2 stirbars, stir bar upside down (old) – Failure to change tubing regularly – Failure to prime reagents after tubing change
Common Mistakes (CL17)
• Reagents/Mixing – Use stir bar retriever to remove stir bar from
sample cell
Common Mistakes (CL17)
• Reagents/Mixing – Use caution not to lose stir bar after removal
Common Mistakes (CL17)
• Problem with optics – Dirty sample cell – Faulty interference filter (old design) – Problem with lamp or photocell
Common Mistakes (CL17)
• “Wrong” Reading – Improper (lab) comparison calibration
• Check your GAIN – should be 1.00
Common Mistakes (CL17)
Press MENU and scroll to SETUP
Scroll to GAIN and hit ENTER
Common Mistakes (CL17)
Optimal gain!
Common Mistakes (CL17)
• To check the gain on an old CL17 – Hit the STD key – Gain of 1.00 is optimal
Absorbance
Concentration (m
g/L) 0.40
0.10
(1.00) (2.00)
(0.50)
It’s not 0.40 mg/L, it should be 0.20mg/!
Absorbance
Concentration (m
g/L)
0.20
0.10
(1.00) (2.00)
(0.50)
It’s not 0.40 mg/L, it should be 0.20mg/!
Gain adjusted to “calibrate”
reading
Course Outline
• Process Monitoring • Key Differences (color and turbidity) • Operation of (colorimetric) CL17 • Operation of (turbidimetric) 1720 Turbidimeters • Calibration and Verification Strategies • Hands-On Lab
Operation of 1720 Turbidimeters
• Turbidity relates to the suspended matter in a liquid, but is not a direct measurement of it.
• Suspended matter causes light to scatter or be redirected upon contact.
• Instruments measure scattered light at 90 degrees to light source
Operation of 1720 Turbidimeters
• A one-step process – Turbidimeters don’t have a ZERO key! – Zero turbidity does not exist.
• Results are displayed as NTU. – Nephelometric Turbidity Units
1720E
SAMPLE IN
SAMPLE OUT
1720D/E Flow Diagram
Sample In
Sample Out
Basic 90o Nephelometer
90ø DETECTOR
LAMP
LENS
APERATURE
WATER LEVEL
Lamp
Lens
Aperture
Water Level
90o detector
Turbidimeter Principle of Operation
Operation of 1720 Turbidimeters
DETECTOR DETECTOR DETECTOR
LIGH
T SOU
RC
E
Amount of Light Scattered
Turbidity (NTU
)
0.20
0.40
0.80
Slope or gain of
calibration
Operation of 1720 Turbidimeters
• What happens as light source ages and fades - Is the accuracy of the reading affected?
• Yes! The amount of light scattered is directly related to the calculated turbidity, based on the calibration.
• An aging bulb causes low readings.
Operation of 1720 Turbidimeters
New Lamp
0.20 NTU 0.40 NTU 0.80 NTU
DETECTOR
LIGH
T SOU
RC
E
DETECTOR DETECTOR
Operation of 1720 Turbidimeters
0.20 NTU 0.40 NTU 0.80 NTU
LIGH
T SOU
RC
E
Aged Lamp
DETECTOR DETECTOR DETECTOR
Amount of Light Scattered
Turbidity (NTU
) 0.20
0.40
0.80
Slope or gain of
calibration
Amount of Light Scattered
Turbidity (NTU
)
0.20
0.40
0.80
Slope or gain of
calibration
0.12
0.48
0.24
Amount of Light Scattered
Turbidity (NTU
) 0.20
0.40
0.80
Original Gain
Adjusted Gain
Operation of 1720 Turbidimeters
• Measurement is a single step process, and is unable to account for light decay.
• Periodic calibration corrects the problem by adjusting the relationship between scattered light and corresponding turbidity(calibration gain).
Common Mistakes 1720Turbidimeters
• Improper (lab) comparison calibration – Can cause large errors, since it is usually
performed at low concentrations – Some state guidelines (CA) do not recommend
comparison calibration
1720D/E Turbidimeter Calibration
• User-Prepared Standards – Dilution water and 20 NTU
Formazin • StablCal Standards
– 20 NTU Standard Solution • Comparison with Lab Reading
– not recommended (Hach)
Proper Technique For Lab Turbidity Measurements
• Clean sample cells • Use silicone oil • Degas sample • Maintain instrument • Follow proper calibration procedure
Common Mistakes 1720Turbidimeters
• Improper Maintenance – Replace lamp annually – Clean turb body, bubble trap
• What can scale do to turbidity values? – Keep optics (lamp, lens, photocell) clean
• Before calibration, not after!
1720D/E Lamp
• Instrument provides a warm environment for biological growth, as evidenced below!
Common Mistakes 1720Turbidimeters
• Error in calibration procedure – Contamination – Inaccurate measurement of formazin – Bubbles in dilution water – Failure to clean photodetector – Failure to zero electronics
Course Outline
• Process Monitoring • Key Differences (color and turbidity) • Operation of (colorimetric) CL17 • Operation of (turbidimetric) 1720 Turbidimeters • Calibration and Verification Strategies • Hands-On Lab
Calibration/Verification Strategies • CL17 Chlorine Analyzer
– Calibration not recommended (by Hach) – Verification with lab DPD analysis
• Lab analysis verified with standard solutions
• 1720 Turbidimeters – Multiple choices for Calibration – Verification
• Lab comparison or Ice-Pic Verification Module
CL17 Calibration • Calibration/Verification kit
• Cat # 544900 Complete Kit • Cat # 2835900 Reagents Only
• Comparison to Laboratory Instrument • Not Recommended by Hach
CL17 Verification – Periodically verify lab
measurement with standard solutions or standard additions
– Collect grab sample from CL17 – Perform lab analysis on grab
sample – Compare results – Acceptance +/- 10%
1720D/E Turbidimeter Calibration
• User-Prepared Standards – Dilution water & 20 NTU
Formazin • StablCal Standards
– 20 NTU Standard Solution • Comparison with Lab Reading
– not recommended (Hach)
1720D/E Turbidimeter Verification • Lab Comparison Method
– Calibrate lab turbidimeter – Verify lab technique/analysis with 0.5
or 1.0 NTU StablCal – Collect grab sample from turbidimeter
body – Measure grab with lab instrument – Compare results – Acceptance +/- 10% or 0.05 below 0.5
NTU
1720D/E Turbidimeter Verification
• Use of Ice-Pic Verification Module – Silence alarms, hold outputs – Thoroughly dry turb head – Place module inside turb body – Place turb head inside module, let
reading stabilize – Compare readings with stored value – Acceptance +/- 10%
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Course Outline
• Process Monitoring • Key Differences (color and turbidity) • Operation of (colorimetric) CL17 • Operation of (turbidimetric)1720 Turbidimters • Calibration and Verification Strategies • Hands-On Demonstration
Operation, Calibration, and Performance Verification of CL17 Chlorine Analyzer and
1720 Series Turbidimeters
Chris Griffin [email protected]
804-513-6731
2014 Plant Operations Conference
mailto:[email protected]�http://www.vaawwa.org/�
Operation, Calibration and Verification for pH
http://www.hach.com/fmmimghach?CODE:NGMP-PHC101-PRBESTND9156|1�
pH Theory
• pH is a measurement of the relative acidity of an aqueous solution
• pH is a measurement of hydrogen ion concentration
pH Theory
• Acid - increases the hydrogen ion (H+) concentration in a solution
• Base - increases the hydroxide ion (OH-) concentration in a solution
pH Scale
7 14 0 Acid Base
Neutral
Vinegar pH 3
Ammonia pH 11.5
pH Scale
• pH is a negative logarithmic function • Each decrease in pH unit = 10X increase in acidity
– Solution at pH4 is 10X more acidic than solution at pH5 – Solution at pH 4 is 100X more acidic than pH6 solution
7 14 0 6 5 4
10X
100X
Measuring pH
How Does a pH Probe Work?
• Probe measures hydrogen ion concentration – Two electrodes in probe - sensing half-cell, reference
half-cell
Half-Cells
• Ion sensing pH half cell – Glass bulb that is sensitive to H+.
• Reference half-cell – Glass tube filled with salt solution to complete circuit.
METER
Ion Sensing Half-Cell
Reference Half-Cell
Ag/AgCl Wire
Internal Filling Solution
Reference Electrolyte
Salt Bridge Junction
Reference Half-Cell
• Dispenses reference solution which completes circuit for meter
Sensing Half-Cell
H+ H+
H+ H+
H+
H+
H+ H+
H+
H+ H+
H+ H+
H+ H+
H+
Hydrogen ion concentration fixed at
pH 7
pH 7 Solution
H+ conc the same both inside and outside glass bulb
*No potential develops
Sensing Half-Cell
0mV
pH 7 Solution
H+ conc the same both inside & outside glass bulb
*No Potential develops
Sensing Half-Cell
H+ H+
H+ H+
H+
H+
H+ H+
1000H+
Hydrogen ion concentration fixed at
pH 7
pH 4 Solution
H+ conc 1000x greater outside glass bulb
*Potential develops
1000H+ 1000H+
1000H+ 1000H+
1000H+ 1000H+
Sensing Half-Cell
pH 4 Solution
H+ conc 1000x greater outside glass bulb
*Potential develops
180mV
Sensing Half-Cell
1000 H+ 1000 H+
1000H+ 1000H+
Hydrogen ion concentration fixed at
pH 7
pH 10 Solution
H+ conc 1000x greater inside glass bulb
*Potential develops
H+
H+
H+
H+
Sensing Half-Cell
-180mV
pH 10 Solution
H+ conc 1000x greater inside glass bulb
*Potential develops
Calibration
• A calibration curve allows the meter to convert a measured millivolt potential into a pH reading.
pH
mV
Calibration
• The optimal slope for pH is –59.16 /decade * • Acceptance criteria = +/- 5% or 3 mV
* at 25 degrees Celsius
Calibration
mV
pH
0
+180
-180 4 7 10
Calibration
• -180mV difference measured between pH4 and pH7 • pH4 to pH7 (3 pH units) is 1000x concentration
change • Decade = 10-fold concentration change = 1pH unit • -180/3 = -60 ≈ -59.16 mV/decade
Probe Care and Maintenance
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Maintenance
• New probe • Calibration • Measurement/Storage • Troubleshooting • Cleaning
New Probe
• Condition new pH probe in pH 7 buffer for approximately 30 minutes before initial use
Calibration
• Use fresh calibration solutions • Use temperature compensation • Allow enough time for meter to stabilize on both
Temp and pH reading • Record mV readings to determine drift in sensor
Calibrate
• Calibrate bench pH meters each shift using two or three fresh buffer solutions
4.0 7.0 10.0
Calibration and Verification
• On-line sensors comparison check daily – Agreement to (+/-) 0.20 pH units with a calibrated
laboratory meter • On-line sensors monthly calibrate linearity or per
regulatory schedule
Measurement
• Place probe into sample, stir, and wait for readings to stabilize
• Rinse and dry between measurements • Storage between measurements
– Sample or solution of similar ionic strength to sample – pH4 buffer – Electrode storage solution (i.e. 3M KCl)
Troubleshooting
• mV reading in pH 7 buffer – Should read 0 ± 30 mV in pH 7 buffer
• Response time – May require cleaning if slow (2 min) in buffered solution
• Slope – Optimal slope is –59.16 ± 3 mV/decade (+/- 5%)
Cleaning
• Slow response may indicate need for cleaning – Longer than 2 minutes – Immerse and agitate in a warm dilute mild detergent
solution for a few minutes. Rinse with DI and blot dry before use.
– Alternate soaking in dilute hydrochloric acid and dilute sodium hydroxide. Rinse with DI water and condition in pH 7 buffer before use.
pH - Take Home Messages
• pH is an electrochemical measurement, useful in many applications.
• As with many electrochemical analyses, pH requires frequent calibration to achieve accurate results.
• Proper probe maintenance is essential.
Chris Griffin [email protected]
804-513-6731
2014 Plant Operations Conference
mailto:[email protected]�http://www.vaawwa.org/�
2 PIV Verification of CL17 and 1720 TurbProcess Instrument Verification�for Drinking Water���2014 Plant Operations Conference�PIV for Drinking WaterOperation, Calibration, and Performance Verification of�CL17 Chlorine Analyzer and 1720 Series TurbidimetersTake-Home MessagesCourse OutlineProcess MonitoringLaboratory vs On-line MonitoringLaboratory vs On-line MonitoringLaboratory vs On-line MonitoringLaboratory vs On-line MonitoringProcess MonitoringAdvantages to Process MonitoringSelecting an InstrumentSlide Number 14Course OutlineColor MeasurementColor MeasurementColor MeasurementSlide Number 19What is Turbidity?Basic 90o TurbidimeterKey DifferencesKey DifferencesKey DifferencesCourse OutlineOperation of (colorimetric) CL17Slide Number 27Operation of (colorimetric) CL17CL17 Chlorine AnalyzerOperation of (colorimetric) CL17Slide Number 31CL17 Operation - ZeroCL17 Operation - ZeroCL17 Operation - ReadCL17 Operation - ReadCL17 Operation - ReadSlide Number 39Slide Number 40Operation of (colorimetric) CL17Slide Number 42Slide Number 43Common Mistakes (CL17)Common Mistakes (CL17)Common Mistakes (CL17)Common Mistakes (CL17)Common Mistakes (CL17)Common Mistakes (CL17)Common Mistakes (CL17)Common Mistakes (CL17)Common Mistakes (CL17)Slide Number 54Slide Number 55Course OutlineOperation of 1720 Turbidimeters Operation of 1720 Turbidimeters 1720ESlide Number 61Basic 90o NephelometerSlide Number 63Operation of 1720 TurbidimetersSlide Number 66Operation of 1720 TurbidimetersOperation of 1720 TurbidimetersOperation of 1720 TurbidimetersSlide Number 70Slide Number 71Slide Number 72Operation of 1720 TurbidimetersCommon Mistakes 1720Turbidimeters1720D/E Turbidimeter CalibrationProper Technique For Lab Turbidity Measurements Common Mistakes 1720Turbidimeters1720D/E LampCommon Mistakes 1720TurbidimetersCourse OutlineCalibration/Verification StrategiesCL17 CalibrationCL17 Verification1720D/E Turbidimeter Calibration 1720D/E Turbidimeter Verification1720D/E Turbidimeter VerificationCourse OutlineOperation, Calibration, and Performance Verification of�CL17 Chlorine Analyzer and �1720 Series Turbidimeters�����Chris Griffin�[email protected]�804-513-6731���2014 Plant Operations Conference�
4 PIV pHOperation, Calibration and Verification for pH�pH TheorypH TheorypH Scale pH Scale Slide Number 26How Does a pH Probe Work?Half-CellsSlide Number 29Reference Half-CellSensing Half-CellSensing Half-CellSensing Half-CellSensing Half-CellSensing Half-CellSensing Half-CellCalibrationCalibrationCalibrationCalibrationProbe Care and MaintenanceMaintenanceNew ProbeCalibration CalibrateCalibration and VerificationMeasurementTroubleshootingCleaningpH - Take Home Messages�����Chris Griffin�[email protected]�804-513-6731���2014 Plant Operations Conference�