Process Instrument Verification for Drinking Water Operations...Process Instrument Verification for Drinking Water 2014 Plant Operations Conference . PIV for Drinking Water ... (color

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


• 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.


• In addition to monitoring, on-line instrumentation can also be used to control chemical feed, process automation


• 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


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.


Reagents mix with sample in sample cell.

If chlorine is present, pink color forms and persists for ~1 minute.

CL17 reads sample.


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


100

60

40

10

0.00

0.22

0.40

1.00

“ZERO”

“READ”

“READ”

“READ”

(Abs = -log T)

Light Source

Detector


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)


• 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


• Reagents/Mixing – Use stir bar retriever to remove stir bar from

sample cell


• Reagents/Mixing – Use caution not to lose stir bar after removal


• Problem with optics – Dirty sample cell – Faulty interference filter (old design) – Problem with lamp or photocell


• “Wrong” Reading – Improper (lab) comparison calibration

• Check your GAIN – should be 1.00


Press MENU and scroll to SETUP

Scroll to GAIN and hit ENTER


Optimal gain!


• 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


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


• A one-step process – Turbidimeters don’t have a ZERO key! – Zero turbidity does not exist.

• Results are displayed as NTU. – Nephelometric Turbidity Units

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


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


• 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.


New Lamp

0.20 NTU 0.40 NTU 0.80 NTU

DETECTOR

LIGH

T SOU

RC

E

DETECTOR DETECTOR


0.20 NTU 0.40 NTU 0.80 NTU

LIGH

T SOU

RC

E

Aged Lamp

DETECTOR DETECTOR DETECTOR


Turbidity (NTU

) 0.20

0.40

0.80

Slope or gain of

calibration


Turbidity (NTU

)

0.20

0.40

0.80

Slope or gain of

calibration

0.12

0.48

0.24


Turbidity (NTU

) 0.20

0.40

0.80

Original Gain

Adjusted Gain


• 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


• 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!


• Error in calibration procedure – Contamination – Inaccurate measurement of formazin – Bubbles in dilution water – Failure to clean photodetector – Failure to zero electronics

Course Outline


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


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+


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+


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

http://www.hach.com/fmmimghach?CODE:NGMP-PHC101-PRBESTND9156|1�

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


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�

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Process Instrument Verification for Drinking Water Operations...Process Instrument Verification for Drinking Water 2014 Plant Operations Conference . PIV for Drinking Water ... (color