IEC 61810-2:2017

IEC 61810-2 ®
Edition 3.0 2017-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electromechanical elementary relays –
Part 2: Reliability
Relais électromécaniques élémentaires –
Partie 2: Fiabilité
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IEC 61810-2 ®
Edition 3.0 2017-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electromechanical elementary relays –

Part 2: Reliability
Relais électromécaniques élémentaires –

Partie 2: Fiabilité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.120.70 ISBN 978-2-8322-4388-6

– 2 – IEC 61810-2:2017 © IEC 2017
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
3.21 Terms and definitions related to tests . 10
4 General considerations . 10
5 Test conditions . 11
5.1 Sample items . 11
5.2 Environmental conditions . 12
5.3 Operating conditions . 12
5.4 Test equipment . 13
6 Failure criteria . 13
7 Output data . 13
8 Analysis of output data . 13
9 Presentation of reliability measures . 13
Annex A (normative) Data analysis . 15
A.1 General . 15
A.2 Abbreviations . 15
A.3 Symbols and definitions . 15
A.4 Weibull distribution . 16
A.5 Procedure . 17
A.5.1 Graphical methods . 17
A.5.2 Numerical methods . 22
A.5.3 Confidence Intervals . 23
A.5.4 WeiBayes Approach . 25
Annex B (informative) Example of data analysis . 28
B.1 Graphical methods case study (cumulative hazard plot) . 28
B.1.1 General . 28
B.1.2 Procedure of cumulative hazard plot . 28
B.1.3 Example applied to life test data . 30
B.2 Numerical methods case study (Weibull probability) . 33
B.2.1 General . 33
B.2.2 Distribution parameters . 33
B.2.3 Mean cycles to failure (MCTF) . 33
ˆ
B.2.4 Value of B . 34
B.2.5 Mean time to failure (MTTF) . 34
B.3 Confidence intervals case study . 34
B.3.1 General . 34
B.3.2 Interval estimation of β . 34
B.3.3 Interval estimation of η. 35
B.3.4 Lower confidence limit for B10 . 35
B.3.5 Lower confidence limit for R . 36
B.4 WeiBayes case study . 36
Annex C (informative) Statistical tables . 38

C.1 Table of gamma function . 38
C.2 Fractiles of the normal distribution . 38
Annex D (informative) Success run – Test without failures . 40
D.1 General . 40
D.2 Confidence level and minimum reliability . 40
D.3 Example. 41
Bibliography . 42

Figure A.1 – An example of Weibull probability paper . 18
Figure A.2 – An example of cumulative hazard plotting paper . 20
Figure A.3 – Plotting of data points and drawing of a straight line . 20
Figure A.4 – Estimation of distribution parameters . 21
Figure B.1 – Estimation of distribution parameters . 30
Figure B.2 – Cumulative hazard plots . 32
Figure B.3 – Type test versus WeiBayes analysed periodic test . 37

Table A.1 – Confidence levels for WeiBayes without failures . 26
Table B.1 – Worksheet for cumulative hazard analysis . 28
Table B.2 – Example worksheet . 31
Table B.3 – First twenty failures in this example . 33
Table C.1 – Values of the gamma function . 38
Table C.2 – Fractiles of the normal distribution . 39
Table D.1 – Number of samples and life cycles . 41

– 4 – IEC 61810-2:2017 © IEC 2017
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROMECHANICAL ELEMENTARY RELAYS –

Part 2: Reliability
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61810-2 has been prepared by IEC technical committee 94: All-or-
nothing electrical relays.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) not only graphical but also numerical methods are added;
b) reduction of number of samples in specified cases;
c) new subclauses of confidence intervals are added;
d) the WeiBayes approach is added to facilitate compliance tests (routine test) with lower
effort;
e) annexes have been restructured into an Annex A for data analysis (normative) and
Annex B (informative) where various examples of the data analysis are given;
f) the former Annex C has been incorporated into the modified Annex B;
g) a new Annex C replaces the old Annex D.
The text of this International Standard is based on the following documents:
FDIS Report on voting
94/415/FDIS 94/418/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
This International Standard is to be used in conjunction with IEC 61649:2008.
A list of all parts in the IEC 61810 series, published under the general title Electromechanical
elementary relays, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 61810-2:2017 © IEC 2017
INTRODUCTION
Within the IEC 61810 series of basic standards covering elementary electromechanical relays,
IEC 61810-2 is intended to give requirements and tests permitting the assessment of relay
reliability. All information concerning endurance tests for type testing have been included in
IEC 61810-1.
NOTE According to IEC 61810-1, a specified value for the electrical endurance under specific conditions (e.g.
contact load) is verified by testing 1 or 3 relays. None is allowed to fail. Within this document, a prediction of the
reliability of a relay is performed using statistical evaluation of the measured cycles to failure of a larger number of
relays (generally 10 or more relays).
This document is the base for IEC 61810-2-1 to determine reliability values for relays where
enhanced requirements for the verification of reliability (B and B ) apply.
10 10D
The technical committee responsible for dependability has developed IEC 61649 dealing with
Weibull-distributed test data. It contains both numerical and graphical methods for the
evaluation of Weibull-distributed data as well as WeiBayes estimation.
On the basis of this basic reliability standard, this document was developed. It comprises test
conditions and an evaluation method to obtain characteristic reliability values for
electromechanical elementary relays. The life of relays as non-repairable items is primarily
determined by the number of operations. For this reason, the reliability is expressed in terms
of mean cycles to failure (MCTF).
Commonly, equipment reliability is calculated from mean time to failure (MTTF) figures. With
the knowledge of the frequency of operation (cycling rate) of the relay within a piece of
equipment, it is possible to calculate an effective MTTF value for the relay in that application.
Such calculated MTTF values for relays can be used to calculate respective reliability,
probability of failure, and availability (e.g. MTBF (mean time between failures)) values for
equipment into which these relays are incorporated.
Generally, it is not appropriate to state that a specific MCTF value is “high” or “low”. The
MCTF figures are used to make comparative evaluations between relays with different styles
of design or construction, and as an indication of product reliability under specific conditions.

ELECTROMECHANICAL ELEMENTARY RELAYS –

Part 2: Reliability
1 Scope
This part of IEC 61810 covers test conditions and provisions for the evaluation of endurance
tests using appropriate statistical methods to obtain reliability characteristics for relays.
This document applies to electromechanical elementary relays considered as non-repaired
items (i.e. items which are not repaired after failure).
The lifetime of a relay is usually expressed in number of cycles (CTF). Therefore, whenever
the terms “time” or “duration” are used in IEC 61649, they carry the meaning “cycles”.
However, with a given frequency of operation, the number of cycles can be transformed into
respective times (e.g. times to failure (TTF)).
The failure criteria and the resulting characteristics of elementary relays describing their
reliability in normal use are specified in this document. A relay failure occurs when the
specified failure criteria are met.
As the failure rate for elementary relays cannot be considered as constant, particularly due to
wear-out mechanisms, the cycles to failure of tested items typically show a Weibull
distribution. This document provides numerical and graphical methods to calculate
approximate values for the two-parameter Weibull distribution, as well as lower confidence
limits and a method for confirmation of reliability values with the WeiBayes method.
This document does not cover procedures for electromechanical elementary relays where
enhanced requirements for the verification of reliability apply.
NOTE 1 Such reliability test procedures are specified in IEC 61810-2-1. In particular, when electromechanical
elementary relays are intended to be incorporated in safety-related control systems of machinery in accordance
with IEC 62061 and ISO 13849-1, IEC 61810-2-1 defines procedures for the manufacturer to provide B values.
10D
NOTE 2 Electromechanical elementary relays with forcibly guided (mechanically linked) contacts according to
IEC 61810-3 offer the possibility of a high diagnostic coverage according to 4.5.3 of ISO 13849-1:2015.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 61649:2008, Weibull analysis
IEC 61810-1:2015, Electromechanical elementary relays – Part 1: General and safety
requirements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

– 8 – IEC 61810-2:2017 © IEC 2017
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
item
any component that can be individually considered
Note 1 to entry: For the purpose of this document, items are electromechanical elementary relays.
3.2
non-repaired item
item which is not repaired after a failure
3.3
sample
one or more sampling items intended to provide information on the population
[SOURCE: IEC 60050-151:2001, 151-16-19, modified – The words "or on the material" have
been deleted from the definition.]
3.4
sample item
one of the individual items in a population of similar items and taken from one place and at
one time
[SOURCE: IEC 60050-151:2001, 151-16-18, modified – The words "or a portion of material
forming a cohesive entity" have been deleted from the definition.]
3.5
cycle
operation and subsequent release/reset
[SOURCE: IEC 60050-444:2002, 444-02-11]
3.6
frequency of operation
number of cycles per unit of time
[SOURCE: IEC 60050-444:2002, 444-02-12]
3.7
reliability
ability of an item to perform a required function under given conditions for a given number of
cycles or time interval
Note 1 to entry: It is generally assumed that the item is in a state to perform this required function at the
beginning of the time interval.
Note 2 to entry: The term “reliability” is also used as a measure of reliability performance (see
IEC 60050-312:2001, 312-07-06).
[SOURCE: IEC 60050-395:2014, 395-07-131, modified – The words "number of cycles or"
have been added to the definition, and the second note has been replaced by a new note.]

3.8
reliability test
experiment carried out in order to measure, quantify or classify a reliability measure or
property of an item
[SOURCE: IEC 60300-3-5:2001, 3.1.27, modified – The notes have been deleted.]
3.9
life test
test with the purpose of estimating, verifying or comparing the lifetime of the class of items
being tested
[SOURCE: IEC 60300-3-5:2001, 3.1.17, modified – The note has been deleted.]
3.10
cycles to failure
CTF
total number of cycles of an item, from the instant it is first put in an operating state until
failure
3.11
mean cycles to failure
MCTF
expectation of the number of cycles to failure
3.12
time to failure
TTF
total time duration of operating time of an item, from the instant it is first put in an operating
state until failure
3.13
mean time to failure
MTTF
expectation of the time to failure
[SOURCE: IEC 60050-192:2015, 192-05-11, modified – The word "operating" has been
deleted from the term and the definition, and the notes have been deleted.]
3.14
useful life
number of cycles or time duration until a certain percentage of items have failed
Note 1 to entry: In this document, this percentage is defined as 10 %.
3.15
failure
termination of the ability of an item to perform a required function as defined in the failure
criteria
[SOURCE: IEC 60050-603:1986, 603-05-06, modified – The words "as defined in the failure
criteria" have been added to the definition.]
3.16
malfunction
event when an item does not perform an expected function

– 10 – IEC 61810-2:2017 © IEC 2017
3.17
contact failure
occurrence of break and/or make malfunctions of a contact under test, exceeding a specified
number
3.18
failure criteria
specified conditions to judge if a fault or malfunction is a failure
3.19
contact load category
classification of relay contacts dependent on wear-out mechanisms
Note 1 to entry: Various contact load categories are defined in IEC 61810-1.
3.20
fault
deviation of the existing condition from the expected condition
3.21 Terms and definitions related to tests
3.21.1
type test
conformity test made on sample relays representative of the production to get basic
performance data or to verify that these relays comply with the specified requirements
3.21.2
routine test
conformity test made on sample without any modifications and specification changes during or
after mass production with specified repetition
4 General considerations
The provisions of this document are based on the relevant publications on dependability. In
particular, the following documents have been taken into account: IEC 60050-191,
IEC 60300-3-5 and IEC 61649.
The aim of reliability testing as given in this document is to obtain objective and reproducible
data on reliability performance of relays representative of standard production quality. The
tests described and the related statistical tools to gain characteristic reliability values can be
used for the estimation of such characteristic reliability values, as well as for the verification
of stated characteristic values.
NOTE 1 Examples for the application of characteristic reliability values are:
• establishment of characteristic reliability values for a new relay type;
• comparison of relays with similar characteristics, but produced by different manufacturers;
• evaluation of the influence, on a relay, of different materials or different manufacturing processes;
• comparison of a new relay with a relay which has already worked for a specific period of time;
• calculation of the reliability of an equipment or system incorporating one or more relays.
According to Clauses 8 and 9 of IEC 60300-3-5:2001, for non-repaired items showing a non-
constant failure rate, the Weibull model is the most appropriate statistical tool for evaluation
of reliability measures. This analysis procedure is described in IEC 61649.
Relays within the scope of this document are considered as non-repaired items. They
generally do not exhibit a constant failure rate but a failure rate increasing with number of

cycles, being tested until wear-out mechanisms become predominant. The cycles to failure of
a random sample of tested items typically show the Weibull distribution.
NOTE 2 In cases where no wear-out mechanisms prevail, random failures with constant failure rate can be
assumed. Then the shape parameter β of the Weibull distribution equals 1, and the reliability function becomes the
well-known exponential law.
The first step in the analysis of the recorded cycles to failure (CTF) of the tested relays is the
determination of the two distribution parameters of the Weibull distribution. In a second step,
the mean cycles to failure (MCTF) is calculated as a point estimate. In a third step, the useful
life is determined as the lower confidence limit of the number of cycles by which 10 % of the
relay population will have failed (B ) (see 10.5 and 10.6 of IEC 61649:2008).
With a given frequency of operation, these reliability measures expressed in number of cycles
(MCTF) can be transformed into respective times (MTTF); see Annex B for an example.
The statistical procedures require some appropriate computing facility. Software for
evaluation of Weibull-distributed data is commercially available on the market. Such software
may be used for the purpose of this document provided it shows equivalent results when the
data given in Annex B are used.
Since the number of cycles to failure highly depends on the specific set of test conditions
(particularly the electrical loading of the relay contacts), values for MCTF and useful life
derived from test data apply only to this set of test conditions, which have to be stated by the
manufacturer together with the reliability measures.
Upon explicit specification of the manufacturer, the test may be performed with even less than
10 relays, provided the uncertainty of the estimated Weibull parameters is acceptable to him.
In such a case, the minimum number of tested relays shall be specified; this number then
replaces the minimum number of 10 relays wherever prescribed in this document. This
reduction of relay specimens is acceptable in both numerical and graphical methods. Here,
the number of failures or specimens may be determined, being concerned with confidence
interval, which can be calculated by A.5.3. On the other hand, the reduction due to WeiBayes
approach shown in A.5.4 is also acceptable if the shape parameter, β, is assumed from
historical data from prior experiments, or from engineering knowledge of the physics of the
failure.
However, the WeiBayes approach applies only for routine test.
5 Test conditions
5.1 Sample items
For useful life estimation, a minimum of 10 failures need to be recorded to perform the
analysis described in this document, 10 or more items (relays) should be submitted to the
test. However, at least 2/3 of the tested relays shall fail physically. This allows the test to be
carried out with 10 relays only, even when the test is stopped before all relays have physically
failed (with a minimum of 7 physical failures recorded). When the test is stopped at a specific
number of cycles, all relays that have not yet failed shall be considered as suspended or
censored at that number of cycles.
Upon explicit specification of the manufacturer, less than 10 items can be tested to determine
the basic Weibull parameters (B and β), but the minimum number of samples to be tested is
5. The requirement to truncate a test still remain with 2/3 of the number of samples. The
results with less than 10 samples shall be published in conjunction with the confidence level
and number of samples. The evaluation method in this specific case shall be the numeric
method.
– 12 – IEC 61810-2:2017 © IEC 2017
For a WeiBayes test, the number of samples and failures shall be selected according to the
desired confidence level.
The items shall be selected at random from the same production lot and shall be of identical
type and construction. No action is allowed on the sample items from the time of sampling
until the test starts.
Where any particular burn-in procedure or reliability stress screening is employed by the
manufacturer prior to sampling, this shall apply to all production. The manufacturer shall
describe and declare such procedures, together with the test results.
Unless otherwise specified by the manufacturer, all contacts of each relay under test shall be
loaded as stated and monitored continuously during the test.
The test starts with all items and is stopped at a certain number of cycles. At that instant, a
certain number of items have failed. The number of cycles to failure of each of the failed items
is recorded.
Items failed during the test are not replaced once they fail.
5.2 Environmental conditions
The testing environment shall be the same for all items.
– The items shall be mounted in the manner intended for normal service; in particular, relays
for mounting onto printed circuit boards are tested in the horizontal position, unless
otherwise specified.
– The ambient temperature shall be as specified by the manufacturer.
– All other influence quantities shall comply with the values and tolerance ranges given in
Table 1 of IEC 61810-1:2015, unless otherwise specified.
5.3 Operating conditions
The set of operating conditions
– rated coil voltage(s),
– coil suppression (if any),
– frequency of operation,
– duty factor,
– contact load(s),
shall be as specified by the manufacturer.
Recommended values should be chosen from those given in Clause 5 of IEC 61810-1:2015.
The test is performed on each contact load and each contact material as specified by the
manufacturer.
All specified devices (for example, protective or suppression circuits), if any, which are part of
the relay or stated by the manufacturer as necessary for particular contact loads, should be
operated during the test.
The contacts shall be continuously monitored to detect malfunctions to open and malfunctions
to close, as well as unintended bridging (simultaneous closure of make and break side of a
changeover contact).
The contacts are connected to the load(s) in accordance with Table 12 of IEC 61810-1:2015
as specified and indicated by the manufacturer.
5.4 Test equipment
The test circuit described in Annex C of IEC 61810-1:2015 shall be used, unless otherwise
specified by the manufacturer and explicitly indicated in the test report.
6 Failure criteria
Whenever any contact of a relay under test fails to open or fails to close or exhibits
unintended bridging, this shall be considered as a malfunction.
Three severity levels are specified:
– severity A: the first detected malfunction is defined as a failure;
– severity B: the sixth detected malfunction or two consecutive malfunctions are defined as
a failure;
– severity C: as specified by the manufacturer.
The severity level used for the test shall be as prescribed by the manufacturer and stated in
the test report.
Faults occurring during test like insulation fault, dielectric test fault, thermal deformation of
enclosure, burning and others, shall be judged as failure.
7 Output data
The data to be analysed consists of cycles to failure (CTF) for each of the items put on test.
These CTF values have to be known exactly. However, it is not necessary to gather the CTF
values for all items under test, under the conditions described under 5.1.
8 Analysis of output data
The evaluation of the CTF values obtained during the test shall be carried out in accordance
with the procedures given in Annex A.
9 Presentation of reliability measures
The basic reliability measures applicable to relays as described in this document and obtained
from the data analysis shall be provided.
However, since the values obtained for these reliability measures using the procedures of
Annex A depend to a great extent on the basic design characteristics of the relay, on the test
conditions of Clause 5 and on the failure criteria of Clause 6, the following information shall
also be provided together with the test results:
– relay type for which the results are valid:
a) contact material;
b) deviations from standard types (if any);
c) type of termination.
– set of operating conditions (see 5.3):
a) rated coil voltage(s);
– 14 – IEC 61810-2:2017 © IEC 2017
b) coil suppression (if any);
c) frequency of operation;
d) duty factor;
e) contact load(s);
f) ambient conditions.
– test schematic selected (see Clause C.3 of IEC 61810-1:2015, or test circuit details, if
different from the circuit described in Clause C.1 of IEC 61810-1:2015);
– severity level (see Clause 6).
In addition, basic data of the test and the related analysis (see Annex A) shall be given in the
test report:
– analysis method;
– number of items (n) on test;
– number of failed items (r) registered during the test;
– time (given in number of cycles) when the test was stopped (T);
– confidence level, if less than 90 %.
The test results are applicable to the samples specifically tested and variants, as stipulated by
the manufacturer, provided that the relevant design characteristics remain the same.
NOTE Acceptable examples are coil variants with the same ampere-turns. Unacceptable examples are variants
with AC in place of DC coils, or different contact dynamics.
When test results for various operating conditions (for example, contact loads) are available,
they may be compiled as a family of curves or in suitable tables. However, it shall be ensured
that a sufficient number of points are determined when plotting such curves.

Annex A
(normative)
Data analysis
A.1 General
This annex has been derived from the reliability standard IEC 61649:2008 with certain
modifications necessary to adopt the procedures to elementary relays. The distribution
considered in the reliability standard is of the Weibull type, which has been empirically
recognized to correspond to an appropriate data analysis for elementary relays.
The graphical method as well as the numerical method are covered in IEC 61649. In addition,
not only the Weibull probability analysis but also the Weibull hazard analysis is taken up in
the graphical method. Here, Weibull hazard and Weibull probability analyses are applied to
complete and incomplete data, respectively. The latter is especially useful for the reliability
analysis of relays because many data sets obtained from life tests are incomplete (censored
tests).
NOTE 1 Incomplete data are the data sets obtained from the test after either a certain number of failures or a
certain number of cycles, when there are still items functioning, whereas complete data are the data sets without
censoring.
This annex deals with the Weibull probability plot and the Weibull hazard plot for the graphical
method based upon median rank regression (MRR) principles, and the maximum likelihood
estimation (MLE) for the numerical method in accordance with the provisions of IEC 61649.
When more in-depth information is required, IEC 61649 is to be consulted.
The concept “time” is to be understood as “cycles” in the case of relays. However, with a
given frequency of operation, the values indicated in numbers of cycles can be transformed
into respective times.
NOTE 2 Whereas the variable “time” (symbol: t) is used within IEC 61649, this document is based on the variable
“cycles” (symbol: c).
For the sake of consistency, the following symbols and equations are reproduced in
accordance with IEC 61649.
A.2 Abbreviations
CDF cumulative distribution function
MRR median rank regression
MLE maximum likelihood estimation
MCTF mean cycles to failure
PDF probability density function
A.3 Symbols and definitions
The following symbols are used in this Annex A, and in both Annex B and Annex C. Auxiliary
constants and functions are defined in the text.
f(c) probability density function
F(c) cumulative distribution function (failure probability)
h(c) hazard function (or instantaneous failure rate)

– 16 – IEC 61810-2:2017 © IEC 2017
H(c) cumulative hazard function
R(c) reliability function of the Weibull distribution (survival probability)
B expected time at which 10 % of the population have failed
(10 % fractile of the lifetime)
c cycle – variable
mˆ mean cycles to failure (MCTF)
β Weibull shape parameter (indicating the rate of change of the instantaneous failure rate
with time)
η Weibull scale parameter or characteristic life (at which 63,2 % of the items have failed)
σ standard deviation
A.4 Weibull distribution
The fundamental Weibull formulae are defined as follows.
NOTE For more information, reference is made to IEC 61649.
The probability density function (PDF) of the Weibull distribution is:
β
 c
 
β−1 −
 
c
η
 
f (c)=β
...