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Understand MSA in brief before getting in the depths

What is MSA? A Measurement system is a process by which we assign a number to a characteristic of a product or service.The_ first step in assessing a system is to understand this process, and determine whethe_r it will satisfy our requirements.

Measurement System Analysis, often referred to as MSA, is used to assess the_ statistical properties of process measurement systems.

• MSA primarily deals with analyzing the_ effect of the_ measurement system on the_ measured value in

quantifiable terms

• mphasis is on the_ effect due to equipment and personnel

• !e test the_ system to determine the_ numerical values of its statistical properties and compare the_m to

accepted standards. "t is a process used to standardize the_ methods of analysis to ensure anddemonstrate that your measuring systems have adequate resolution, do not e#cessively bias results, andpossess a small variability in comparison with specified tolerances. "t helps you assess, monitor, andreduce measurement system variation. The_ ob$ective of a measurement system analysis study is toma%e sure that your measurement system & gages, methods, and procedures are stable and capable ofmeasuring data, before continuing with your process improvement efforts. "t ensures that your measuringprocedures and systems provide'

• Adequate resolution

• (esults that are not unduly biased, and

• )ittle variability in comparison with specified tolerances

Fundamental IssuesTo evaluate a measurement system determine'

• "f it has adequate discrimination

• "f it is statistically stable over time

• "f statistical properties are consistent over the_ e#pected range and acceptable for process analysis or

control

• "f the_ sum of all variables is an acceptable level of measurement uncertainty

Overall Objective of MSA*ncertainty of Measurement

"t is the_ range within which the_ true value of a characteristic is estimated to lie. Such data can be e#pressedas the_ statistical distribution of a series of measurements, standard deviations, probability, percentages, anderror as the_ difference between actual value minus the_ true value, as points on a control chart or diagram.

Bestin!lass Approach• +etermining the_se fundamental issues are most meaningful if made relative to process variation

• (eporting measurement error as only percent of tolerance is inadequate for the_ worldwide mar%et where

emphasis is on continual process improvement

Use of "ata in Measurement S#stem StudiesThe_ data collected using a measurement system is used'

•

To control process• "n estimating the_ e#istence of relationship between variables that can affect the_ outcome of a process

• To conduct analytical studies to increase the_ %nowledge about the_ system of causes and its effect on

processes

• To focus on measurement systems where readings can be repeated on each part, and reproduced by

different operators. A measurement is not always e#act. Measurement system variation affects individual measurements anddecisions based on data. Measurement system errors are classified into five categories' bias, repeatability,reproducibility, stability, and linearity. ou need to %now the_ e#tent of variation before deciding on the_ following applications.

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MSA Applications• stablish criteria for suitability and acceptability of new measuring equipment

• -ompare one measuring device against anothe_r 

• valuate suspect equipment

• -ompare the_ performance of an equipment before and after its repair 

• -alculate measurement system variation

•

stablish acceptability of manufacturing process• Manage improve the_ measurement process

Where to start?• valuate the_ components of the_ measuring system, and control the_ variation in the_m as much as

possible to ensure that an item of measuring equipment complies with the_ requirements for its intendeduse

• #pand your consideration of Measurement /rocess 0ariation to Measurement System Statistical /roperties

Measurement *ncertainty.

• 1ollow the_ basics of S/-.

$rocess Accurac# Measurements

Stabilit#

Stability 2or drift3 is total variation in measurements obtained with a measurement system on same master or parts when measuring a single characteristic over an e#tended time period 2a time period is days, not hours3.Stability is the_ %ey to predictability. Stable processes are those that are free from special cause variation. "nterms of measuring equipment, stability is determined by using a control chart. As measurements are ta%en,points within the_ limits indicate that the_ process has not changed and the_ prediction is made that it is notli%ely to change in the_ future. Statistical process control 2S/-3, scatter plots, or othe_r forms of statisticalanalysis are used to measure process stability.

%inearit#)inearity is the_ difference in the_ accuracy values through the_ e#pected operating range of the_ equipment.Selecting the_ parts throughout the_ operating range of the_ instrument can determine the_ linearity. The_ accuracy of the_se parts is determined by the_ difference between the_ master measurement and the_ observed average measurement.

Bias

+ifference between observed average of measurements and reference value. The_ reference value, also%nown as accepted reference value or master value, is a value that serves as an agreed upon reference for measured values. A reference value can be determined by averaging several measurements with a higher levelof measuring equipment.

$rocess $recision Measurements

&age '('4age (( statistically isolates different types of variation in the_ measurement process. The_se types of variation include'

• (epeatability 5 equipment variation 5 within variation

• (eproducibility 5 appraiser variation 5 between variation

• (esidual or pure error 

• 0ariation due to interaction effects. 1or e#ample, out of several inspectors, one might have a tendency to

read one gage differently than othe_rs.4age ((& 4age (epeatability and (eproducibility can be applied to any %ind of measurement 2attribute or variables, indeterminate or determinate3. The_ two most common methods used and supported by statisticalsoftware are the_ A670A method 2Analysis 7f 0ariance3 and the_ average and range method.

(epeatability refers to the_ variation in measurements obtained with one measurement instrument when usedseveral times by one assessor while measuring the_ identical characteristics on the_ same part.

(eproducibility refers to the_ variation in the_ average of measurements made by different assessors usingthe_ same measuring instrument while measuring the_ identical characteristics on the_ same part.

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(( is the_ combination of repeatability and reproducibility variation, and is considered as the_ totalmeasurement variation e#cluding within part variation and variation in central location.

'eference Material A material or substance with one or more properties, which are sufficiently well established to be used for the_ calibration of an apparatus, assessment of a measurement method, or for assigning values to materials.

Measurement Uncertaint#• Measurement *ncertainty is the_ sum of all the_ probabilities 2percents3 assigned to the_ variables that

ma%e up the_ measurement system.

• The_ total of the_se probabilities should be weighed, and carry importance in proportion to the_

seriousness, and criticality of the_ measurements being made.

• +ecisions resulting from measurement system analysis include'

o*sing the_ system as is, ta%ing into account its uncertainty.o "mproving the_ system to control the_ variation in the_ contributing factors.o-onsidering othe_r measurement systems of higher levels of discrimination and capability.

/roduct and process conformance are determined by the_ measurements ta%en by a measurement system. "f the_ measuring process is changing over time, the_ ability to use the_ data gathe_red in ma%ing decisions isreduced. "n essence, establishing the_ adequacy of your measurement system using a measurement systemanalysis process is fundamental to measuring your own business process capability, and meeting the_ needs of your customer.