IPC-TM-650 EN 2022 试验方法.pdf - 第31页

1 Scope Tests performed on presumably identical samples under seemingly identical conditions do not always yield iden- tical results. This is due in part to errors inherent in every measurement. During the development of…

Measurement Systems Analysis For Binary Data

Test Effectiveness Calculator

Version 1.0, August 2002

Introduction

Welcome to the Measurement Precision Calculator. This utility is intended to

perform the calculations for Measurement Precision Studies as described

in the IPC test method IPC-TM 1.8.

This unility is useful for situations where the measurement data is recorded

in binary format,, such as pass/fail or go/no-go.

Please refer to the test method before beginning the measurement precision study.

The test method defines the terms and equations used in detail.

Refer to the User Guide for further detailed instructions.

This workbook includes the following

- A blank spreadsheet to enter measurements

- A spreadsheet with example data

- A form for manual data entry, if desired.

The test data should be entered into the yellow areas on the

data entry spreadsheet. Code results as "A" and "R".

This is a beta version of this software.

Your comments and suggestions would be appreciated.

If you have any questions, please contact:

Scope

Tests

performed on presumably identical samples

under seemingly identical conditions do not always yield iden-

tical results. This is due in part to errors inherent in every

measurement. During the development of a new test proce-

dure or use of an existing test procedure, this variability must

be understood and precautions taken to ensure that it is con-

trolled to within necessary limits. Performance of this test

method will help to estimate measurement error and trouble-

shoot possible causes. It can provide evidence that a new test

procedure is suitable for use when submitted for review, or an

existing test procedure is capable of measuring the applicable

parameter.

This method provides a simple, easy to use, standard proce-

dure for determining the precision of a test method using the

average and range method. It can be used on tests that

involve measurements that yield continuous data. The calcu-

lations shown in this procedure are streamlined versions; use-

ful for situations where up to five repeated readings are taken

on each of up to 10 samples by up to 10 test laboratories,

operators or test conditions.

This procedure is not useful for measurements which result in

binary data, such as pass-fail or go-no go results, or where

more than five repeated measurements or more than ten labo-

ratories or conditions are used. These situations are covered

under other methods. (see 6.3)

1.1

Definitions

Accuracy

(Bias) –

The

difference between an observed

measurement and the true (but perhaps unknown) value being

measured (see Figure 1).

Continuous

Data –

Numerical

data that can take any con-

ceivable value within an observed range and forms a distribu-

tion about a mean value.

Precision

–

The

closeness to each other of repeated mea-

surements of the same quantity.

Repeatability

–

Variation

of a measurement system that is

obtained by repeating measurements on the same sample(s)

by the same procedure under the same measurement condi-

tions (see Figure 1).

Reproducibility

–

Variation

among the averages of measure-

ments made under different measurement conditions such as

different

operators, equipment, and/or locations (see Figure 1).

Resolution

–

The

size of the smallest increment on the mea-

surement instrument under examination. This value is fre-

quently used in the advertising literature to classify the instru-

ment.

IPC-19-1

Figure

1 Measurement Repeatibility and Reproducibility

Repeatibility

Reproducibility

Accuracy

Reproducibility

Repeatibility

How close is the

measurement to the

true value?

True

value

How close are a series of

measurements by several

people on the same part on

the same equipment?

True

value

True

value

How close is a series of

measurements on one

part by one person?

Operator A

Operator C

Operator

2215

Sanders Road

Northbrook, IL 60062-6135

IPC-TM-650

TEST METHODS MANUAL

Number

1.9

Subject

Measurement

Precision Estimation for Variables

Data

Date

01/03

Revision

Originating Task Group

Measurement Precision Task Group (7-11a)

Material

in this Test Methods Manual was voluntarily established by Technical Committees of IPC. This material is advisory only

and its use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this

material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement.

Equipment referenced is for the convenience of the user and does not imply endorsement by IPC.

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ASSOCIATION CONNECTING

ELECTRONICS INDUSTRIES

2 Applicable Documents

The applicable document will be

the test procedure under evaluation.

Test Specimens

The test specimens used will be as

specified in the test procedure under investigation.

The number and types of test materials to be used will

depend on the range of levels in the class of materials to be

tested. If it is known that precision is worse at one end of the

range, evaluations could be limited to that end of the range. In

general, evaluations should be performed on all combinations

of materials, levels, test set-ups, and test conditions. If

resources are limited, begin the study with those combina-

tions deemed to be the most critical, or where measurement

error is likely to be greatest.

The number of samples will also depend on the difficulty

involved in obtaining, processing, and distributing the test

specimens, the difficulty, length of time required for, and

expense of performing the test, and other prior known infor-

mation.

This test method will assume that measurements can be

repeated on the same sample. For situations where this is not

possible or the sample is consumed during the test, see 6.3.

Apparatus

The apparatus used will be as specified by

the test procedure under investigation.

The resolution of the measurement apparatus should be suf-

ficient to achieve the desired accuracy of the measurement.

For example, if you were to measure mass, and expect to

measure it to 1 gm, the balance should be able to measure to

at least 0.1 gm.

Procedure

5.1 Planning the Evaluation

Keep

the evaluation as

simple as possible to obtain estimates of within and between

tester variability that are free of unintended secondary effects.

A particular test condition could be different combinations of

laboratories, operators, equipment, etc.

Be sure the procedure under evaluation is complete and

describes the test parameters as well as recommended tech-

niques for controlling variability. Include known best practices

and draw extensively on the experience of test users.

The method used in this procedure allows for up to ten test

conditions. Solicit participants from among the community of

facilities with the proper test equipment, competent operators

and familiarity with the test. In order to obtain representative

precision estimates, do not select only from a small group of

users who are considered exceptionally qualified. Be sure to

specify any special calibration procedures or material prepara-

tion requirements.

The analysis method used in this procedure allows up to five

repeated measurements per sample. The test samples should

be carefully prepared in order to be as consistent and homo-

geneous as possible. Try to limit the lots of raw materials and

processing facilities used. Randomize the samples prior to

dividing into test groups. Prepare more than the material

required to ensure adequate amount is available for the study

in case of lost or damaged specimens, errors, test set-up, etc.

Carefully package and label the samples. Assign serial num-

bers, if possible. Identify the version of the test procedure and

specify care and handling procedures. Provide a data sheet,

and describe any documentation required. Require a test log,

and insist that all observations of any unusual events be

recorded.

5.2

Conducting the Evaluation

Ensure

the samples are

inspected on receipt. Send replacement units if damaged or

tests are performed improperly. Follow the documented test

procedure carefully to ensure no unusual variation is intro-

duced.

Inspect the data sheets when returned. Review the test logs

for unusual events. Review the measurements for level and

consistency. Question unusual data points. Incorrect readings

and typographical errors must be corrected prior to analysis.

5.3

Analyzing the Data

Analysis

may be performed on the

Measurement Precision data sheet or on other applicable

software. A Measurement Precision Calculator has been pre-

pared to perform the calculations using the equations shown

below (see 6.5).

This evaluation technique is called the Average and Range

Method and partitions the total measurement precision (S

R&r

)

into

two portions: the with-in test condition variation, called

repeatability (S

)

and between test condition variation, called

reproducibility (S

The method does this by calculating an

estimate of the standard deviation of the measurement

repeatability by using the range of the repeated measure-

ments with-in each test condition, and by calculating an esti-

mate of the standard deviation of the reproducibility by using

the range between different test condition averages.

For normally distributed parameters, these two standard

deviations are combined to estimate the total measurement

precision by taking the square root of the sum of the squares.

IPC-TM-650

Number

1.9

Subject

Measurement

Precision Estimation for Variables Data

Date

01/03

Revision

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