DOE Multi level Taguchi - I am doing a Capstone Project

T

tmf8985

#1
Hi I am doing a Capstone Project at a company, we will just call it company X.
I have to find the best location to find the worst possible solution in a tank with acidic solution. I take samples and titrate them to find the acidity level and if solutions acidity drops, I can add more acid to strengthen the acidity to the required level. The goal is again to find the best location and volume to fins the worst sample. This will perform as an early detection system to keep the acidity to required strength.

The factors I have decided for this DOE are listed with their respective levels
1. Water type ( to rinse sample cup) water and RO water 2 levels
2. Time 6am when machine starts and 10 am 4hrs after the machine has started and the solution has been kept agitated 2 levels
3. Location front of tank and back of tank 2 levels
4. Size or volume 10ml 55ml and 100ml 3 levels
5. Depth of sample surface, 18 inches and bottom of tank 3 levels

By the hand work i figured the following for degrees of freedom for truth table

3 factors at 2 level = 3 * (2-1)= 3
2 factors at 3 level = 2 * (3-1)= 4
miu = 1
error = 1

DOF = 9

The problem with L9 table is that it does not incorporate level 3 settings

So i use Minitab to form a multi level taguchi design with 5 factors and L36 with 2**3 and 3**2 settings, i get a 36 experiment table, 12 of which are repeats so i am left with 24 experiments, the problem is when i perform the analysis the S/N ratio is wrong and way off compared to hand calculations. What am I doing wrong? Can some one please help. i can provide the data and the Minitab file. Thanks

Tina

EDIT: I have attached the files. the files were done in version 15 of minitab. also for analysis i was using larger the better option.
 

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Miner

Forum Moderator
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Admin
#4
When you add files using the Edit option, it does not show up as a new post in the "Post Last 24 Hours" or "Since Last Visit" searches. We did not realize that you had added the files.
 

Miner

Forum Moderator
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#5
Which response are you using, conductivity or pH? Why did you choose to use S/N ratio rather than analyze the response directly?
 
T

tmf8985

#6
I am using Conductivity as the main response. Analyzing directly how would I do that?
 

wang1568

Starting to get Involved
#7
Your design is only a simple factorial design and designed by taguchi orthogonal array, not a taguchi design - need noise factors
The correct method to analyze experimental data is GLM in ANOVA
 
T

tmf8985

#8
Using GLM that doesn't tell me which settings for factor to use to get worst sample and if i use the Taguchi analysis Larger the better option I get wrong values for S/N ratio, compared to if I do this by hand.

Wang1568, when you mentioned noise factor, what can they be in this case? any ideas?

Tina
 

Miner

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Staff member
Admin
#9
Attached is an analysis of the conductivity using a General Factorial DOE. Two factors were significant, depth and size of sampling container. Deeper depths increased conductivity, which makes physical sense as you would expect contaminants to settle. The sampling container size did not make physical sense because the medium size container had the lowest conductivity.
 

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wang1568

Starting to get Involved
#10
Miner had work out the analysis of DOE data.
I was wondering about the two factors water type and size of sampling cotainer.
The water type and size of sampling were used to titrate them and calculate the acidity level, not the cause of acidity, and may be as noise factors.
there was another wondering, why the reponse was conductivity, not ph value?
 
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