Characteristics and Ratings –by terms and definitions

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Characteristics and Ratings –by terms and definitions

A recent working group dialog revealed that there was some confusion over what a product characteristic is and what a product family rating is. One approach to resolve this matter is to consult the definition for these terms in a dictionary or glossary created by a standards development organisation (SDO).

Finding definitions for terms

My favourite reference work is the IEC Glossary. The Glossary is the collected terms and definitions taken from IEC standards published since 2002. The ISO/IEC Directives require that the definition formulation shall be able replace the term in a sentence. This means the definition shall be a phrase and any definition starting with, for example, “the” shows the formulation group didn’t understand the rules and the ISO/IEC editors were asleep at the wheel when the document was edited at central office. Being a phrase is limiting, meaning that usually there is only room for the essential elements of the term to appear. Informative information can be relegated to additions like notes or examples.

The IEEE doesn’t have the phrase constraint allowing some IEEE definitions to look more like a chapter of a book. May be the IEEE-SA should apply the Twitter tweet restriction of no more than 140 characters.

Because many standards use the same term, the glossary contains many entries for a given term. For example the term “routine test” occurs 81 times in the Glossary at the time of writing this document. This means routine test is defined in at least 81 IEC standards. In the perfect world all the definitions would be the same, but the world isn’t perfect and people inadequately formulate, tweak and customise definitions.

Here is an example of a (claimed) customisation of the “term” definition in IEC 60050-151 by IEC SC37A WG5

routine test: test made on each SPD or on parts and materials as required to ensure that the product meets the design specifications
Published in:   IEC 61643-11, ed. 1.0 (2011-03)
Source:            IEC 60050-151:2001, 151-16-17 (modified)

Customisation proliferates definition variances, restricts usage of what should be generic item into a specific one with the potential of causing confusion. As terms and definitions are shown without the rest of the standard they occur in, the acronym SPD should have been explained by writing “surge protective device” in full. Likewise references to figures and clauses in a standard should be avoided.

What does the referenced IEC 60050-151 source definition look like?

routine test: conformity test made on each individual item during or after manufacture

Quite how IEC SC37A WG5 justifies their definition is a modification of the IEC 60050-151 one is an interesting debate. The IEC 60050-151 definition is an example of daisy chaining as you now need to find out what a conformity test is.

conformity test (compliance test): test for conformity evaluation

OK, one last time

conformity evaluation: systematic examination of the extent to which a product, process or service fulfils specified requirements

Bearing in mind the term can be replaced by its definition we have:

routine test:  test for systematic examination of the extent to which a product, process or service fulfils specified requirements made on each individual item during or after manufacture

The two substitutions don’t quite work and that’s the problem with daisy chaining definitions, you need to check that replacement works.

When using the IEC Glossary it is important to pick the most relevant definition for your purpose with an emphasis on a generic definition rather than a customised definition. Next time we’ll get down to the business of looking up the definition of the term “characteristic”.

 

Edited by: admin on 9 Feb 2014 - 09:03
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Characteristics and Ratings – characteristic definition

Characteristic

The IEC Glossary returns seven definitions for the term “characteristic”. The most suitable definitions found were:

characteristic: inherent and measurable property of a device
Published in:   IEC 61643-341, ed. 1.0 (2001-11)

characteristic: a physical, chemical, visual or any other measurable property of a product or material
Published in:   IEC 62680-4, ed. 1.0 (2010-10)

The IEC 61643-341 definition restricts the item concerned to a “device” (81 IEC Glossary entries) a term that can interpreted in many ways. The most suitable definition for our use is:

device: combination of components having a given function, forming part of a piece of equipment, apparatus, or system
Published in:   IEC 61000-5-6, ed. 1.0 (2002-06)

IEC 62680-4 uses the more generic “product” term (33 IEC Glossary entries) rather than “device”.

product: thing or substance produced by a natural or artificial process
Published in:   IEC 61360-2, ed. 3.0 (2012-10)

Some other useful definitions are:

product family: group of products each of which contains the same substances or material at a similar concentration level
Published in:   IEC 62474, ed. 1.0 (2012-03)

product specification: document which defines the parameters that are used for determining the expected performance of a product
Published in:   IEC 62059-11, ed. 1.0 (2002-01)

specification: document that specifies, in a complete, precise, verifiable manner, the requirements, design, behaviour or other characteristics of a system or component and, often, the procedures for determining whether these provisions have been satisfied
Published in:   IEC 61513, ed. 2.0 (2011-08)

The IEC 61513 definition could be made more generic by replacing “system or component” by “product”.

From the above one could simply state that a characteristic is an inherent product property that can be measured.

The procedure of checking or establishing parameter values is termed characterisation.

characterisation: process of testing a sample of components to determine the key electrical parameter values that can be expected of all produced components of the type tested
Published in:   IEC 62396-1, ed. 1.0 (2012-05)

Next time we’ll start looking up the complicated definition of the term "rating".

 

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Characteristics and Ratings – rating definition

Rating

The IEC Glossary returns twenty-four definitions for the term “rating”. The most suitable definitions found were:

rating: value that establishes either a limiting capability or a limiting condition for a semiconductor device
Published in: IEC 62240-1, ed. 1.0 (2013-04)

rating: set of rated values and operating conditions
Published in: IEC 62850, ed. 1.0 (2013-02)
Source: IEC 60050-151:2001, 151-16-11

The IEC 62240-1 definition is specific but could be changed to generic by replacing “semiconductor device” with“product”.

A English language reference dictionary for IEC definitions is the Oxford English Dictionary (OED). There we have:

capability: the power or ability to do something

condition: the state of something with regard to its appearance, quality, or working order

My interpretation is that the IEC 62240-1 rating definition covers two attributes; firstly what the product characteristic limits are e.g. maximum limiting voltage and second what are the maximum stresses that can be imposed on the product e.g. maximum surge current.

The IEC 62850 definition is generic, two attributes again and we need to clarify  the meaning of “rated values”and “operating conditions”.

For “rated values” one can find:

rated value: value of a quantity used for specification purpose, established for a specific set of operating conditions
Published in: IEC 62246-1, ed. 2.0 (2011-02)

rated value: value of a quantity used for specification purposes, established for a specified set of operating conditions of a component, device, equipment, or system
Published in: IEC 61236, ed. 2.0 (2010-10)
Source: IEC 60050-151:2001, 151-16-08

rated value: assigned value, generally by the manufacturer, for a specified operating condition of a component, device or equipment
Published in: IEC 60974-1, ed. 4.0 (2012-06)

For “operating conditions” one can find:

operating limit: stress level above which the product no longer functions nominally.
Published in:   IEC 62500, ed. 1.0 (2008-07)

absolute maximum ratings: limiting values of operating and environmental conditions applicable to any semiconductor device of a specific type as defined by its published specification data, which should not be exceeded under the worst possible conditions
Published in: IEC 62240-1, ed. 1.0 (2013-04)
Source: IEC 60134:1961, Clause 4

The IEC 62240-1 and IEC 62850 definitions each have two attributes which can have equivalence if we say:

Attribute 1: product characteristic limits (IEC 62240-1) is the same as rated value (IEC 62850)

Attribute 2: maximum stresses that can be imposed (IEC 62240-1) is the same as stress level above which the product may no longer functions nominally (IEC 62850)

Attribute 1 is the one that causes confusion as it may be stated in the product specification either as maximum or minimum limits of the characteristics or as a rated value in the ratings. Both of these can be measured as a characteristic.

Here’s an example for cable current carrying capacity:

current carrying capacity: maximum current a cable circuit (one or several conductors) can support resulting in a specified increase of the surface temperature of the conductor beyond the ambient temperature, not exceeding the maximum allowed operating temperature of the cable
Published in: ISO/IEC 29125, ed. 1.0 (2010-09)
Source: IEC 61156-1:2007, 3.24

The test procedure here is to apply the specified maximum current to the cable and measure the temperature at thermal equilibrium at the specified ambient. The measured value should not exceed the maximum cable operating temperature. This could be expressed in characteristics as a maximum cable temperature value for a specified ambient temperature and applied current. Alternative it could be expressed as a rated current value for a specified ambient temperature and maximum temperature rise.

Attribute 2 is definitely only a rating as the test procedure is to apply the maximum stress given in product specification and then measure specified product characteristics to verify the product has withstood the stress without specified degradation.

The rule is Absolute Maximum Ratings are verified and Characteristics are measured.

Here’s an Absolute Maximum Rating example for a GDT:

Durability:

10 applications of 50 Hz, 1 s, 2 A

10 applications of 8/20, 1 kA

100 applications of 10/1000, 10 A

After a stress test the product characteristics shall be

DC spark-over voltage 400 V ±30%, initial value was 400 V ±25%

Impulse spark-over voltage at 100 V/µs < 900 V, initial value was < 800 V

Impulse spark-over voltage at 1 kV/µs < 1050 V, initial value was < 950 V

Insulation resistance at 100 V DC > 108 Ohm, initial value was > 109 Ohm

The conundrum here is whether to specify a limit characteristic value as max. or min. or a rated value of the applied test condition, e.g. the current in the cable case above.

Personally I prefer to put it in the characteristics list, leaving the option of adding a typ. value. This would then leave ratings as purely absolute maximum ratings.

The figure below summarizes these postings to date.

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Free Access to the IEEE Standards Definition Database

Both the IEC and ITU have had free term definition dictionaries for years. The IEEE has now realised that being able to find term definitions on the internet propagates those definitions. Hence the IEEE announced on 2014-02-20 that access to the on-line IEEE Standards Definition Database would be free provided you give the IEEE some personal details to create a (free) IEEE Account. Those who already have IEEE Accounts can skip the account creation step.

IEEE Account Creation
Browse to: https://www.ieee.org/profile/public/createwebaccount/showRegister.html
Complete the form and you will get a user name and password.

IEEE Standards Definition Database access
Browse to: http://dictionary.ieee.org and login with your IEEE Account user name and password.

Obviously there haven't been any dictionary additions in 2014 as the copyright currently reads: