form 8a: committee decision for dis iso/tc 131 · comment2 comments proposed change observations of...

Form 8A: Committee decision for DIS

Secretariat:

ANSI

ISO/TC 131

N 623

Project number and title:

ISO 19973-2:2015/CD Amd 1 - Pneumatic fluid power -- Assessment of component reliability by testing -- Part 2: Directional control valves -- Amendment 1

This form should be sent to the ISO Central Secretariat (http://isotc.iso.org/livelink/si/), together with thedraft of the project, by the secretariat of the technical committee or subcommittee concerned.

The accompanying document is submitted for circulation to member body vote:

As a DIS

Consensus has been obtained from the P-members of the committee:

on 2017-05-18

At the meeting of ISO/TC 131. See Resolution number . In document N .

By ballot initiated on

Please attach a copy of the ballot results (if applicable)

Listing of the P-members (NWIP, CD or Resolution)

P-members in favour:

Brazil (ABNT), China (SAC), Germany (DIN), Italy (UNI), Japan (JISC), Korea, Republic of (KATS),Netherlands (NEN), Poland (PKN), Turkey (TSE), United Kingdom (BSI), United States (ANSI)

11

P-members voting against:

France (AFNOR)

1

P-members abstaining:

India (BIS), Sweden (SIS)

2

FORM 8A – Committee decision on

1 of 5

http://isotc.iso.org/livelink/si/

P-members who did not vote: 1

Russian Federation (GOST R)

Remarks:

I hereby confirm that this draft meets the requirements of Part 2 of the ISO/IEC Directives:

Secretariat:

ANSI

Date:

2017-11-07

Name/Signature of TC/SC Secretary:

Rockhill, Denise Ms

FORM 8A – Committee decision on

2 of 5

http://isotc.iso.org/livelink/livelink/open/10562502

Result of voting

Ballot Information

Ballot reference ISO 19973-2:2015/CD Amd 1

Ballot type CD

Ballot title Pneumatic fluid power -- Assessment ofcomponent reliability by testing -- Part 2:Directional control valves -- Amendment 1

Opening date 2017-01-31

Closing date 2017-03-28

Note

Member responses:

Votes cast (14) Brazil (ABNT)China (SAC)France (AFNOR)Germany (DIN)India (BIS)Italy (UNI)Japan (JISC)Korea, Republic of (KATS)Netherlands (NEN)Poland (PKN)Sweden (SIS)Turkey (TSE)United Kingdom (BSI)United States (ANSI)

Comments submitted (2) Australia (SA)Belgium (NBN)

Votes not cast (1) Russian Federation (GOST R)

Questions:

Q.1 "Do you approve the circulation of the draft as a DIS?"

Votes by members Q.1

Brazil (ABNT) Approval

China (SAC) Approval

France (AFNOR) Disapproval

Germany (DIN) Approval withcomments

India (BIS) Abstention

Italy (UNI) Approval

3 of 5

Japan (JISC) Approval withcomments

Korea, Republic of(KATS)

Approval

Netherlands (NEN) Approval withcomments

Poland (PKN) Approval

Sweden (SIS) Abstention

Turkey (TSE) Approval

United Kingdom (BSI) Approval withcomments

United States (ANSI) Approval withcomments

Answers to Q.1: "Do you approve the circulation of the draft as a DIS?"

6 x Approval Brazil (ABNT)China (SAC)Italy (UNI)Korea, Republic of (KATS)Poland (PKN)Turkey (TSE)

5 x Approval withcomments

Germany (DIN)Japan (JISC)Netherlands (NEN)United Kingdom (BSI)United States (ANSI)

1 x Disapproval France (AFNOR)

2 x Abstention India (BIS)Sweden (SIS)

Comments from Voters

Member: Comment: Date:

France (AFNOR) Comment File 2017-03-2714:01:02

Germany (DIN) Comment File 2017-03-2717:11:05

Japan (JISC) Comment File 2017-03-2701:59:59

Netherlands (NEN) Comment File 2017-03-2012:15:27

United Kingdom (BSI)

Comment File 2017-03-2809:48:08

United States (ANSI) Comment File 2017-03-1419:52:12

4 of 5

Comments from Commenters

Member: Comment: Date:

Australia (SA) Comment 2017-03-2102:18:11

Abstain.

Belgium (NBN) Comment 2017-03-2210:43:15

No comments

5 of 5

Collated comments Date: 2017-05-18 Document: comments on ISO/CD 19973-2 Amd 1

Project: ISO 19973-2_A1

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Comments Proposed change Observations of the

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1 MB = Member body / NC = National Committee (enter the ISO 3166 two-letter country code, e.g. CN for China; comments from the ISO/CS editing unit are identified by **)

2 Type of comment: ge = general te = technical ed = editorial

page 1 of 17 ISO/IEC/CEN/CENELEC electronic balloting commenting template/version 2012-03

NL-01

Whole docume

nt

All parts ed What means the term "return-OFF shifting time"?

Is it the same as shifting off-time in ISO 12238.

Use the same wording or explain the difference in the clause ―Terms and definitions‖.

Accepted.

The same wording as in

ISO 12238 will be used.

DE-

01

Whole

document

All parts ed In this draft, the term "return-OFF shifting time" is

used, while the term "shifting off-time" is used in ISO 12238.

Use the same term as in ISO 12238:

Shifting off-time

Accepted.

See NL-01

FR-01

Title Te The title so-called ―Estimating B10D for valves used in safety controls circuits‖ limits the perimeter of the annex on safety control circuits. It is partly true for ISO 13949 or IEC 62061. Otherwise, introduction B.1 defines a few standards based on risk assessment (ISO 12100) and on general requirements for safety in fluid power technologies (ISO 4413 and ISO 4414). Considering ISO 4414, safety pneumatics can be split into two general fields: fundamental principles (ISO 13849-2- annex.B - E.g. Pressure limitation, unexpected start-up) and appropriate protective measures for pneumatic drives (E.g. control technology solutions that move a cylinder in accordance with a desired behaviour).

Protective measures for safety-related pneumatics describe circuit-based solutions.

These include:

Protection against uncontrolled movement

Ventilation and venting

Braking the movement

Blocking the movement

Reversing the movement

Free movement option

Balancing forces on the drive

For instance, annex V of Machinery Directive indicates the list of safety components referred in

Change the tile into: ‖Estimating B10D for valves

used in functional safety applications‖

Accepted.

The title to be changed to read

―Estimating B10D for valves in functional safety applications‖.

ISO/TC 131/WG 4 N 332



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article 2(c). These component may have reliability requirement (B10d for instance) but are not necessary used in SRCS (1).

(1) Energy limiters as pressure limiters can be used to guaranty, without any control circuits, the limitation of the pressure to lower a force in accordance with ISO 12100.

Therefore, it is important to relate B10d values for valves for applications defined in the general sense of functional safety.

FR-02

B.1 2nd

§ - from 2

nd

sentence to end of §.

Te ―For pneumatic valves, shifting time failures for the return-OFF function are considered dangerous failures; shifting time failures for the shift-ON function is not considered a dangerous failure because, according to the basic safety principle (―use of de-energization principle‖ of ISO 13849-2, Table B.1), that is not the action typically required for implementing a safety function.‖

―Leakage is a performance failure and not considered a dangerous failure (unless it is so severe as to prevent a return shift). Minimum shifting pressure is not considered a dangerous failure because it is typically much lower than the operating pressure of a system. If additional failure types (based on a specific application) lead to a dangerous failure, these failure mechanisms shall be considered as well. But, this shall clearly be based on agreement between supplier and user.‖

The writing of the introduction creates a misunderstanding on classification between so-called ―defined failures‖ and ―dangerous failures‖.

In functional safety, reliability data of a directional

This formulation cannot be fully applied because:

- Table B1 – ISO 13849-2 is included in annex B which is only informative

- Table B1 gives caution on the ―use of de-energization principle‖:

―This principle shall not be used in applications, e. g. where the loss of pneumatic pressure will create an additional hazard.‖ See ISO 12100 - § 6.2.11.3 (normative).

Mean that Shift-ON may be dangerous or not. Same for leakage (could be defined as a dangerous failure when trapped pressure requested for safety).

Identification of failures is requested in order to collect data during testing time. Some failure modes may be dangerous, others not dangerous. But the answers of these questions should not be in this annex because the final choice (is or is not dangerous) depends on application (even if it is for functional safety) and not on testing conditions as defined in part 2 (ISO 19973).

The sentence ―But, this shall clearly be based on agreement between supplier and user.‖ highlights the difficulty to define in a standard (even more in

Paragraph 1 of the

comment.

Not accepted.

A system shall turn into a safe state when there is a

power loss. This is a basic safety principle.

Therefore, it is not relevant that Table B1 - ISO 13849-

2 is an informative Annex.

Paragraph 2 of the

comment.

Not accepted.

It is true that it depends on the application whether a

specific failure leads to a hazard or not. If a valve

does not return to the basic position, this is in

contradiction to the basic safety principles. Other

failures can also lead to a safety risk in certain



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control valve are given by tests procedure. The starting point to define a procedure is the knowledge of the failure modes of the component.

Therefore, what is important is to provide a clear table on which each expected failure mode is defined separately with its proper characteristics that permit to identify its occurrence in normal conditions of use.

an annex) what is dangerous and what is not.

Re-write this 2nd § to point out this:

Provision of data is optional and at the discretion of the manufacturer.

Scope and object focused on testing procedure to get reliability data in functional safety applications

Requirements based on a table with the failure modes of directional control valves, testing conditions and statistical analysis of tests results.

applications. Since the application is only known to

the user, the user has to carry out a risk analysis

and make appropriate arrangements with the

valve manufacturer.

See the last sentence of

B.1, paragraph 2.

Paragraph 3 of the

comment.

Accepted in principle.

To avoid a misunderstanding on the

classification between ―defined failures‖ and

―dangerous failures‖, the first sentence of paragraph

2 will be changed to read:

―...obtained from a Weibull

plot using all defined failures from ISO 19973-2,

Clause 8.

Paragraph 4 and 5 of the

comment.

Comment noted

On the one hand, the various design types of

valves must be considered, e.g. poppet valves, hard

spool valves, soft seal valves and others. On the

other hand, the failure rate differs for different valve



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functions, e.g. 3/2 valves, 5/2 valves, 5/3 valves and

others. Manufacturers also offer various quality levels

(e.g., low-cost products, high-performance products

and others).

For all these variants, it does not seem possible to provide failure characteristics for each failure mode.

General:

WG4 by majority vote (Yes: CN, JP, DE, KR, US; NO: FR) agreed to only use shifting-off time and leave other potential dangerous failures to be an item to be agreed upon between supplier and user.

Note for sec: check "between supplier and user" for consistency with other standards…

FR-03

B.1 3rd

§ Te The method is based on Weibull modelling. First termination failure in a sample of 7 test units is requested. This assumption is supposed to be helped by MRR.

The number of seven test units creates uncertainties. A minimum of 10 relevant failures is necessary to compare MLE and MRR.

Change 7 to 10.

Not accepted.

The method described in Annex B is not based on Weibull modelling, it is called ―SUCCESS RUN method‖ for estimating the B10D value. Therefore, it is not necessary to calculate the Weibull parameters, but only to observe the first



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failure. In a sample size of 7 test units the first failure is related to a failure probability of 9,4%. (See tables for the Median rank or use the Bernard’s approximation, both are described in IEC 61649: 2008 - Weibull Analysis or in technical literature).

7 Samples is the minimum sample size to get a B10 value.

FR-04

B.1 3rd

§ Te ―The cumulative failure for that first of seven test

units is 9.4 % (from a Median Rank table). This is close to the 10% level on which the B10D life is

defined, and the first failure life is considered to be an acceptable estimate for the B10D. Thus, it

is not necessary to continue the test after the first termination failure. If there is one suspension in

the sample of 7 test units, before a first failure occurs, the cumulative failure is 11.4 % at the first

failure life. This is still considered to be an acceptable estimate of the B10D life.‖

The % values are not justified with equations. Benard’s approximation should be used: with i = 1 and N = 7 to reach the % value of 9,4. But Medium Rank table is not referred or available. Therefore, the % value 11, 4 (when one suspension occurs) is not easy to calculate because no adjusted rank equation is defined. Which values are available with a sample of more than 7 test units to estimate B10d?

Provide more justification to define B10d with sample of more than 7 units.

Comment noted.

Median rank tables are given in IEC 61649:2008. The Bernard’s approximation is obviously well known. It is not necessary calculate the Median rank, but only to observe the first failure.

Equations for calculating the median rank for sample sizes with suspensions are also given in IEC 61649:2008. Clause 7.2.3: This method is also called the Johnson’s estimation. Clause 7:3: This calculation method is



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known as Nelson’s estimation. See also technical literature.

FR-04 (last question): Which values are available with a sample size of more than 7 test units to estimate B10D?

In principle accepted: in the next revision of ISO 19973-1 it should be discussed whether more explanation and clarification on the application of IEC 61649 should be given.

If the sample size is greater than 7, a lower failure probability is assigned to the first failure. Example: For a sample size of 10, the median rank for the first failure (Bernard's approximation) is 6,7%. In order to keep the process simple, the time of the first dangerous failure should be considered as a B10 value. This is a conservative assumption on the ―save side‖. See the DE-03 proposed NOTE in B.6.



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FR-05

B.1 3rd

§ Te Goodness test is not available.

How can we choose between a log-normal distribution and a Weibull distribution?

Define specific test (Hypothesis testing Kolmogorov-Smirnov).

Comment noted.

Can be discussed again in

a possible revision of ISO 19973-1 (also see FR-04).

It is a fundamental

definition in all parts of ISO 19973 that the evaluation

of the life time data shall be done according to a

Weibull distribution. See ISO 19973-1, Clause 7.

There are also other reasons, why a Kolmogorov-Smirnov test cannot be applied: The sample sizes are too small. In IEC 61649:1997 is written: ―The statistical procedures for the goodness-of-fit test, Weibull parameter confidence intervals, and reliability lower confidence limits of this standard are valid when at least 10 relevant failures are recorded.‖ Other literature about statistics says that a sample size should be at least 30, to use Kolmogorov-Smirnov tests, Anderson-Darling tests, Chi-Squared tests or others.



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FR-05 06

B.1 3rd

§ Te It is very important to be compliant with existing components standard dealing with reliability methods for functional safety (see annex K of CEI 60947-4-1).

Rebuild this annex to include clear reference to annex K of CEI 60947-4-1 (§ K3.4 Weibull Modelling for instance).

Not accepted.

IEC 60947-4-1, ―Low-

voltage switchgear and controlgear‖ is a Standard

on electronic devices.

IEC 61649:2008 seems to be well suited and is already listed under ―Normative references‖ in ISO 19973-1.

US-01

B.1 2 Clause B.1, 2nd paragraph, last sentence Modify the beginning of the last sentence as follows: "If these, or additional, failure types....

Accepted (but it is the second last sentence).

It will be modified as follows:

"If these, or additional failure types (based on a specific application) lead to a dangerous failure, these failure mechanisms shall be considered as well."

US-02

B.1 and

B.4.3

The term "rest period" (appearing in the first paragraph and NOTE of clause B.4.3) could lead to confusion as it may imply a state of zero-gauge pressure to some readers.

It would be better to simply refer to it as the "24-hour period" or "energized period".

Accepted.

The term ―rest period‖ will be replaced in B.4.3 and in the NOTE by ―24-hour period‖.

DE-

02

B.4.3 te Germany suggests that only the immediate

return-OFF switching times be measured to determine the B10D value. The determination of

the 24h value should be omitted.

Reason: The 24h measurement is very error-

prone. The test units must not be exposed to strong vibrations (eg volume assembly) before

measurement. Also even minimal changes in the

Delete clause B.4.3 Withdrawn



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supply pressure can lead to small movements of the valve piston, which leads to incorrect

measured values. Repeating the measurement is very time-consuming. With the ILT performed so

far, it could not be observed that the measurement leads to more failures after 24h

than the immediate return-OFF measurement.

NL-

02

B.6 te How to determine a B10D value, when no shifting

off-failure will be observed?

Please add a description or explanation. See DE-03.

A new clause B.6.4 is proposed there.

GB1 page 3 B.6 B.6.3 te The clause states that only one suspension is allowed otherwise the test is invalid. In B.1 it is stated that the first failure is to be considered an acceptable estimate. However, there is no mention of what happens if there are 2 simultaneous failures. Due to the testing intervals during life testing, there is a chance this could happen. If 2 failures happen simultaneously, then this method is not valid. See Images 1 to 3.

Add the following: "B.6.4

If the first return-OFF shift failure is experienced by two test units simultaneously (which is plausible due to testing intervals), then the test is invalid or additional test specimen need to be added to the test."

Not accepted.

According to ISO 19973-1, clause 10.3, and B.6.1 of

this draft, the termination life is the last time at which

the three-point moving average did not exceed the

threshold, or the time preceding a catastrophic

failure.

This is also in accordance with the SUCCESS RUN procedure. In this case it does not matter, whether one or even all test units fail between two test intervals.

GB2 B.6 B.6.5 te The assumption made in this Annex does not show good results for low Beta values (shape factor/slope). There should be a comment making this known. See Images 4 to 6.

Add the following: "B.6.5

Due to the assumptions made in this Annex, there will be some error between the estimated B10D using this method compared to the actual B10D if testing were to continue. This error is increased for lower Beta values."

Not accepted.

Looking at the first failure for B10D different Beta

values make no difference.

The target of Annex B is, to

estimate a B10D value and not a βD value.



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GB3 Image 1 This plot shows the first failure occurring at 1000 hrs

The test is then stopped and all other valves are treated as suspensions

Assuming a Beta of 1 B10 is ~738 hrs (compared with the

assumption that would be 1000 hrs)

Comments noted.

All the data analysis done

by GB have need for an assumption of a βD value.

But a βD value is not available at this state of

testing and it is also not needed. Therefore these

analyses are not needed/not required.

Please refer to the success run method. See also observation on GB-01.

GB4 Image 2 This plot shows the first failure occurring at 1000 hrs with 1 suspension before it (at 800 hrs). The test is then stopped and all other valves are treated as suspensions

B10 is ~719 hrs (compared with the assumption that would be 1000 hrs)

Note: there is not much difference between these results and result in Image 1

See GB3.



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GB5 Image 3 This plot shows the first failure occurring at 1000 hrs on two valves simultaneously. The test is then stopped and all other valves are treated as suspensions

B10 is ~373 hrs (compared with the assumption that would be 1000 hrs)

The method is no longer valid in this situation.

See GB3.



Assuming a Beta of 0.5 B10 is ~547 hrs (compared with the


See GB3.



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Assuming a Beta of 1 B10 is ~738 hrs (compared with the


See GB3.

JP-01

21 Annex B B.1 Introduction

…, it is not necessary to continue the test …

te How do you know you have got the "first" termination failure among 7 if you do not conduct tests on 7 specimens? Unless all the tests of, say, 7 specimens start at the same time, the life estimation by using only one termination failure is dangerous and may lead to a too conservative or a too unconservative estimate; i.e., an estimated life becomes much shorter or much longer than real B10D life.

Tests shall be done on at least 7 specimens. Accepted.

The test has to be done with at least 7 test units. Nothing else is written in B.1.

JP-02

B6.3 te No description can be found concerning the number of the additional specimens. How many specimens can be added to the test? If the number is large, the test is also invalid.

Suspended data shall not be ignored.

There are many statistical methods that can deal

with suspended data. Among them, the adjusted rank methods is recommended [1].

[1] e.g., R. B. Abernethy: "The New Weibull Handbook (4th ed.)," SAE (2000)

Accepted in principle:

Suspensions will not be ignored. See B.1, 3

rd

paragraph. See also observations on FR-04.

Statistical methods how to deal with suspended data are also given in IEC 61649:2008.



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DE-03

B6 te Clause B.6 does not describe how to proceed when no failure is observed. Therefore, a new sub-clause B.6.4 should be inserted.

New sub-clause B.6.4:

B.6.4 If the testing is stopped and no failure

from a return-OFF shift has been observed, the test termination time shall be the value of B10D.

NOTE If the sample size exceeds 7 test units, the true B10D value is larger than determined

according to clauses B.6.3 and B.6.4. This estimation is therefore a conservative

assessment.

Accepted.

"return-OFF shift" to be changed in " shifting off-time "

DE-04

New B.7 ed te Some examples could be helpful for the users of this Annex.

Insert a new clause B.7 and renumber the old clauses B.7 and B.8 to B.8 and B.9.

See Annex to DE-04

Accepted.

Check for wording:

"return-OFF shift" to be changed in " shifting off-time "



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Annex to DE-04

B.7 Examples

B.7.1 B10D testing with or without suspensions

Consider a test run on a sample of 7 test units and parameters related to three failure modes (leakage, shifting pressure and return-OFF shift) are measured during a reliability test. Raw data from each parameter are collected as the test progresses. When a failure has occurred (either by no longer being able to perform a required function, or by exceeding the threshold in a 3PMA), the cycle count at which the test unit was last observed in satisfactory condition is recorded as the termination life.

The target of the test is to determine the B10D value of the test units.

See Table B.1 for an example of the data collected during such a test. The data for the test units are recorded from the observations when a unit fails by any failure mode for the first time. In case of the failure modes ―leakage‖ and ―shifting pressure‖ the exceeding of threshold levels was recorded, but the test was continued. For example, test unit number 3 reaches a threshold level for a return-OFF shift failure at the cycle count of 69 million (shaded cells). After this observation, the test was ended.



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Table B.1 — Example of test-unit cycle counts and failure modes for a sample that contains no suspended test units

termination life from 3PMA

Failure mode leakage

Failure mode shifting

pressure

Failure mode return-OFF shift

Note

33 x 106 Test unit No. 3 — — Test continued

48 x 106 — Test unit No. 7 — Test continued


67 x 106 Last time no dangerous failures observed (termination life)

69 x 106 — — Test unit No. 3 Dangerous failure

69 x 106 Test ended – all other test units still operating.

Test result: The B10D life is 67 x 106 cycles.

NOTE Only one suspension, as described in ISO 19973-1, Clause 10.4, is permissible before the first dangerous failure (return-OFF shift) occurs.

B.7.2 Termination of testing without return-OFF shift failure

Consider a test run on a sample of 7 test units as described in B.7.1.

During the test the failure modes ―leakage‖ and ―shifting pressure‖ occurred, but no ―return-OFF shift‖ failure. The manufacturer decided to end the test at 160 million test cycles. There were no suspensions up to this cycle count.



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Table B.2 — Example of test-unit cycle counts and failure modes for a sample that contains no return-OFF shift failures

termination life from 3PMA

Failure mode leakage

Failure mode shifting

pressure

Failure mode return-OFF shift

Note








160 x 106 Test ended – no return-OFF shift failure occurred.

Test result: The B10D life is 160 x 106 cycles.



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FR-04 (proposal) If a sample size is greater than 7, the number of permissible suspensions can be calculated according to Johnson’s Method. The Equation is shown below, where N is the sample size.

Some calculations lead to the following results:

N = 7 8 9 10

Failure rate for 1. failure*

0,094 0,083 0,074 0,067

With 1 suspension before the first failure

Adjusted rank 1,143 1,125 1,111 1,100

Median rank* 0,114 0,098 0,086 0,077

With 2 suspensions before the first failure

Adjusted rank 1,333 1,286 1,250 1,222

Median rank* 0,140 0,119 0,101 0,089


Adjusted rank 1,429 1,375

Median rank* 0,120 1,103


Adjusted rank 1,667 1,571

Median rank* 0,145 0,122

* Bernard’s approximation

If the exceeding of the 10% value by 2% is acceptable, as agreed at the last WG meeting, then the following figures apply for suspensions (see shaded cells in the table above).

SUSPENSION LIMITS

N = 7 8 9 10

LIMIT 1 2 3 4

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