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Quality Control for PH of Tea

Final Presentation

YU Jiayi, CUI Liwen, CHEN Rui, GUO Dingcheng, CAO Qing

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Project Overview

DefineMeasureAnalyzeImproveControl

PH value

Gage R&R

Off-line Experiments

DOE

Suggestions

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Project Overview

DefineMeasureAnalyzeImproveControl

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Define (1/3)

• Study Problem– As the PH value of tea beverage is an important

quality index, we would like to study the factors that would affect the PH value through off-line experiments.

– We expect to obtain the recommended values of the related influence factors to obtain the recommended PH value, thus guiding the real production of tea beverage.

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Define (2/3)

• Response (y)– PH value of tea beverage• Green Tea: PH value of 6.2 recommended

• Factors (x)– Temperature– Time– Percentage of Tea– Container (stainless steel, glass, ceramic, etc.)

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Define (3/3)

• Methodology: Design of Experiment– Off-line experiments– Gage R&R study– GLM• Identify significant factors• Specify relationships between x and y

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Project Overview

DefineMeasureAnalyzeImproveControl

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Measurement Instruments

Electronic PH-meter

Measuring Cup

Temperature-control Pot

Electronic Scale

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Gage R&R (1/6)

• Experiment setting– pH meter– 3 operators– 3 cups of tea– 3 replicates– Parameters• 3g tea• 200 mL water• 8 min

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Gage R&R (2/6)

• Experiment without SOP– Effect of operator is significant– Contributions of total Gage R&R: nearly 100%• Repeatability: 62.57%• Reproducibility: 37.43%

Source DOF SS MS F PPart 2 0.01982 0.009911 1.5971 0.309Operator 2 1.01682 0.508411 81.9284 0.001Part*operator 4 0.02482 0.006206 0.0647 0.992Repeatability 18 1.7272 0.095956Total 26 2.78867

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Gage R&R (3/6)

• Experiment without SOP

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Gage R&R (4/6)

• Experiment with SOP– Effect of part and interaction are significant– Contributions of total Gage R&R: 35.21%• Repeatability: 14.72%• Reproducibility: 20.49%

Source DOF SS MS F PPart 2 0.005341 0.00267 15.1789 0.014Operator 2 0.001252 0.000626 3.5579 0.129Part*operator 4 0.000704 0.000176 2.7941 0.058Repeatability 18 0.001133 0.000063Total 26 0.00843

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Gage R&R (5/6)

• Experiment with SOP

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Gage R&R (6/6)

• The gage has acceptable repeatability and reproducibility– Different operations of operators have large

influence in R&R– A proper SOP is required to improve the

performance of operators

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Project Overview

DefineMeasureAnalyzeImproveControl

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Design of Experiment (1/2)

• fractional factorial design• Response variable: pH value (using pH meter)• Tea: 憩园甘露• Initial model:

Factor Level

A Temperature (C) 60 80 98

B Time (min) 2 5 8

C Volume of water (ml) 50 100 200

D Material of cup Glass Ceramic Stainless steel

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Design of Experiment (2/2)

• Sequence of experiment– Three cups of tea are tested in the same period. – The cups are made of different materials. – The total time of each cup is different.– Measure their PH at their own time point.

• Control of factors– Temperature: air-conditioner, thermos– Volume of water: measuring glass– Weight of tea: electronic balance

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Design of Experiment

不锈钢 陶瓷 玻璃

0 min 2 min 4 min

6 min7 min8 min

8-0=8 min 7-2=5 min 6-4=2 min

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Experiment process (1/4)

• Experiment notes– Cleaning acidometer & container everytime after

reading PH value to get accurate data– Put acidometer into tea at least 1 min before

reading to get stable PH value– To save time, we compress 3 experiments into one

8 min cycle, with same water temperature

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Experiment process (2/4)

• Preparation– Make sure the 3 experiments’ parameter

combination (3g tea-leaf, same temperature)• 2min, A mL water, B1 container• 5min, A mL water, B2 container• 8min, A mL water, B3 container

– Measuring required water & three 3g tea-leaf– Put tea-leaf into 3 container

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0 min 1 min 2 min 3 min 4 min 5 min 6 min 7 min

Pour A mL water into B3 container

• Read PH value• Wash acidometer• Put acidometer into B2 container• Wash B3 container

Measuring A mL water

Put acidometerinto B1 container

8 min

Pour A mL water into B2 container

Measuring A mL water

• Pour A mL water into B1 container• Wash acidometer

• Read PH value• Wash acidometer• Put acidometer into B1 container• Wash B2 container

• Read PH value• Wash acidometer• Wash B1 container

Experiment process (3/4)• Experiment cycle

8 min

5 min

2 min

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Experiment process (4/4)

All experiment instruments

Measure 3g tea

Read PH value

3 cups per cycle

Experiment

Snapshots

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Design of Experiment (1/9)

• Result of the initial model– All main effects are significant– Three interactions are not significant

Source DOF Seq SS Adj SS Adj MS F PTemperature 2 0.110289 0.110289 0.055144 10.48 0.011Time 2 0.298689 0.298689 0.149344 28.38 0.001Volume 2 0.877222 0.877222 0.438611 83.34 <0.001Material 2 0.097356 0.097356 0.048678 9.25 0.015Temperature*Time 4 0.019822 0.019822 0.004956 0.94 0.5Temperature*Volume 4 0.018889 0.018889 0.004722 0.9 0.52Time*Volume 4 0.015422 0.015422 0.003856 0.73 0.602Residual 6 0.031578 0.031578 0.005263Total 26 1.469267

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Design of Experiment (2/9)

• Residual plot

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Design of Experiment (3/9)

• Mean of main effect

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Design of Experiment (4/9)

• Interaction

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Design of Experiment (5/9)

• Result of model without interaction

Source DOF Seq SS Adj SS Adj MS F P

Temperature 2 0.11029 0.11029 0.05514 11.58 0.001

Time 2 0.29869 0.29869 0.14934 31.36 <0.001

Volume 2 0.87722 0.87722 0.43861 92.11 <0.001

Material 2 0.09736 0.09736 0.04868 10.22 0.001

Residual 18 0.08571 0.08571 0.00476

Total 26 1.46927

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Design of Experiment (6/9)

• Residual plot

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Design of Experiment (7/9)

• Mean of main effect

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Design of Experiment (8/9)

• Residual vs. sequence

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Design of Experiment (9/9)

• Recommended parameter– Time: 2min– Volume of water: 200ml– Material of cup: Ceramic– Temperature: 98C– Estimated pH: 6.231

• Limitation: no consideration on the effect of– Reusing tea– Type of tea

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Project Overview

DefineMeasureAnalyzeImproveControl

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Improve & Control

• Improvements can be made to the production line to obtain a recommended PH value– Temperature: 98 ℃ recommended – Time: 2 minutes– Tea/water ratio: 3g tea/200 ml water

recommended– Container: change the original stainless steel

container to the porcelain container

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Thanks

2014/06/13