(signal to noise ratio).pdf

8/14/2019 (SIGNAL TO NOISE RATIO).pdf

1/24

SIGNAL TO NOISE S/N) RATIO

GROUP-2ANKIT SAXENA (PGMSE 136013)

VIVEK GUPTA (PGMSE136016)

ANAND PRAKASH (PGMSE136021)

VAIBHAV SHARMA (PGMSE136024)

SHEM DEBBARMA (PGMSE136027)

Submitted to :- DR. JAGTAR SINGH


2/24

INTRODUCTION Taguchi has proposed various performance measures known as

Signal-to-Noise (S/N) ratio for evaluating the performance of

engineering systems.

The concept of signal (S) to noise (N) ratios has high visibility in

design of experiment circles due to the work of Taguchi to carry out

complete analysis.

The signal is what you are measuring that is the result of the

presence of your action.

Noise is extraneous information that can interfere with or alter thesignal.

It can not be completely eliminated, but hopefully reduced. Noise is

considered random.


3/24

EnergyTransformation

Noise

Squeal

Wear

Heat

Signal Slow Car

Fig. 1 Block diagram showing concept of S/N ratio


4/24

Since noise can not be eliminated (it is random), we are more

interested in the S/N ratio than the intensity of the noise.


5/24

S/N OBJECTIVE?

Reduce as much of the noise as possible by carefully controlling

conditions

Temperature, power supply variations, etc.

Increase the signal to noise ratio

More signal vs. noise means a lower Standard Deviation.

More precise measurement

Lower St. Deviation means a better LOD

Lower limits of detection


6/24

TYPESOFNOISE..

Chemical Noise:

Undesired chemical reactions.

Reaction/technique/instrument specific.

Instrumental Noise:

Affects all types of instruments.

Can often be controlled physically (e.g. temp) orelectronically (software averaging).


7/24

Thermal (Johnson) Noise:

Thermal agitation of electrons affects their smooth flow.

Due to different velocities and movement of electrons in

electrical components.

Dependent upon both temperature and the range of

frequencies (frequency bandwidths) being utilized.

Can be reduced by reducing temperature of electrical

components.

Eliminated at absolute zero.


8/24

Flicker Noise:

Frequency dependent.

Magnitude is inversely proportional to frequency.

Significant at frequencies less than 100 Hz.

Results in long-term drift in electronic components.

Can be reduced by using resisters that are metallic, wire

wound.


9/24

Environmental noise: Unlimited possible sources.

Can often be eliminated by eliminating the source.Other noise sources can not be eliminated.

Methods of eliminating it

Moving the instrument somewhere else.

Isolating /conditioning the instruments power source.Controlling temperature in the room.

Control expansion/contraction of components ininstrument.

Eliminating interferences

Stray light from open windows, panels oninstrument.

Turning off radios, TVs,other instruments.


10/24

There are many different S/N Ratios. The important

S/N ratios are:

Nominal the Best

Target the Best

Smaller the BetterLarger the Better

Dynamic

Classified Attribute.


11/24

NOMINAL-THE-BEST :

This case arises when a specified value is MOST desired,

meaning that neither a smaller nor a larger value is desirable.

n = 10 log10(square of mean/ variance)

Examples are;

(i) most parts in mechanical fittings have dimensions which

are nominal-the-best type.

(ii) Thickness should be uniform in deposition /growth

/plating /etching.


12/24

Fig. 2 Robust Design without noise


13/24

Fig. 3 Robust Design with noise


14/24

SMALLERTHEBETTER:

This is usually the chosen S/N ratio for all undesirable

characteristics like " defects " etc. for which the ideal value is

zero.

n = -10 Log10[ mean of sum of squares of measured data ]

Also, when an ideal value is finite and its maximum or

minimum value is defined (like maximum purity is 100% or

maximum Tc is 92K or minimum time for making a telephone

connection is 1 sec) then the difference between measured

data and ideal value is expected to be as small as possible. Thegeneric form of S/N ratio then becomes

n = -10 Log10[ mean of sum of squares of {measured -

ideal} ]


15/24

Fig. 4 Automotive emission

The S/N ratio for

smaller the better is

used for the situations

where the target value

is zero, such ascomputer response

time, automotive

emission or corrosion.

S/N= -10 Log10(MSD)


16/24

The negative sign is used to ensure that the largest value

gives the optimum value for the response variable and ,

therefore, Robust design.

Mean standard deviation is given to show the

relationship to the loss function.

Loss function is an ideal measure for quality of products

as it is shipped by the supplier to the customer.

Minimizing loss function leads to quality improvement.


17/24

Larger the Better :-

It is used where the largest value is desired such

as weld strength, gasoline mileage or yield.

Mathematically the largest value is 00 like thelost function. It is the reciprocal of smaller the

better .

n = -10 Log10[mean of sum squares ofreciprocal of measured data]


18/24

S/N RATIOS FOR DYNAMIC PROBLEMS

Types of Dynamic Problems:

Continuous - Continuous type ( C - C )

Continuous - Digital type ( C - D ) Digital - Continuous type ( D - C )

Digital - Digital type ( D - D )


19/24

CONTINUOUS - CONTINUOUS

TYPE PROBLEM

Both signal factor and quality characteristics take

positive or negative values.

When signal m = 0,Quality characteristic = 0,

Ideal function y = m

Scaling factor exists to adjust slope (proportionality

constant) between y and m.


20/24

CONTINUOUS- DIGITALTYPE( C- D)

temperature controller

input temperature setting - continuous

output of heating unit - ' on ' or ' off

divide into two separate problemsone for ' on ' function

other for ' off ' function

each one continuous - continuous type or nominal

- the - best type problem


21/24

DIGITAL - CONTINUOUS TYPE ( D - C )

digital to analog converter

conversion to ' 0 ' and ' 1

divide into two separate problems

one for ' 0 ' functionother for ' 1 ' function

each one continuous - continuous type or nominal

- the - best type problem


22/24

CONCLUSION

Signal-to-Noise ratio is also one more contribution of

Taguchi.

We came across different types of noise which affect the

performance of the system.

Thermal noise can only be eliminated if temperature is

absolute zero.

Environmental noise can be eliminated by certain

methods as explained.

Nominal-the-best is used when a specified value is

MOST desired.


23/24

Smaller-the-better is used for undesirable values such as

defects, automotive emission, corrosion etc.

Larger the better is used where the largest value isdesired such as weld strength, gasoline mileage or yield.

Taguchi strongly recommended this approach for

multiple runs.


24/24

(signal to noise ratio).pdf

Documents