Ins umen a ion Viewpoin 8 4
m1
The usual no a ion o unce ainly is shown in equa ion 1.
Y = X ± U
Equa ion 1. Typical no a ion o he unce ainly in a esul
T aceabili y
Acco ding o he de ini ion o CEM [1].” A aceabili y chain, see Fig.2., is a unb o-
ken chain o compa isons, had es ablished all unce ain ies. This ensu es ha a
measu emen esul o alue o pa e n is associa ed wi h e e ences o highe
le els, up o p ima y s anda d.”
CONFORmITY OF THE QUALITY IN THE mEASURES
(1) Labo a o io de me ologia y Calib ación. Uni e sidad Poli écnica de Ca alunya. Vilano a i la Gel ú
(2) Depa amen o de Elec ónica. Escola Poli écnica Supe io d’Enginye ia de Vilano a i la Gel ú.
Abs ac - We’ll wan o implan he awa eness o he impo ance a measu emen ’s
quali y ha mus ha e wi h sys ems acquisi ion o own design. The choice o sys em
acquisi ion will be e y impo an because his sys em will mus ul ill ou expec a-
ions.
Keywo ds- acquisi ion’s sys em, aceabili y, unce ainly, accu acy
I. INTRODUCTION
In any me hod o acquisi ion’s sys em we mus hink he nex ques ion: “ he
da a ha we’ll wan o acqui e ha e he su icien accu acy ha we wish?”. No -
mally his concep is e y clea o he designe howe e we mus ha e answe
ano he ques ion: “ he unce ainly o my sys em o measu e will be su icien ly
small in o de ha om he da a acquisi ion could ex ac conclusions?”.
II. BASIC CONCEPTS
Unce ainly acco ding o he de ini ion o CEM [1] “The unce ainly is a quan i a-
i e measu e o he quali y measu emen esul , which allows ha he measu e-
men esul s should be compa ed wi h o he esul s, wi h e e ences, speci ica-
ions o s anda ds”. The unce ainly is calcula ed by p obabili y
Some he p obabili y dis ibu ion mo e used a e he no mal dis ibu ion and
he uni o m dis ibu ion. A Fig. 1. We can see g aphically heses p obabili y dis-
ibu ions calcula ed wi h a his og am:
Albe Ga cia1,Da id Palme o1,E a Vaqué1,An oni mánuel2
p essu e a ia ions and I´ll need e alua e a ia ions a ound o 1 a m, and he
esolu ion o he equipmen used is 0,5 a m, i can hink ha sys em is good
o make he wo k. Such an analysis is no alid, because we mus calcula e he
unce ainly sys em. In ac is possible ha he unce ain y’s sys em can be o e
1 a m and my acquisi ion sys em isn´ good o he wo k.
Equa ion 2, acco ding o UNE-EN 30012 [2] we can ela e he expanded unce -
ainly (U) o he equipmen wi h he alue o Tole ance (T) o he measu emen
we wan o do. In ou case he ole ance is he minimum alue ha we wan o
see, in he p e ious example is 1 a m.
The alues 3 and 10 ha e he nex explica ion:
The alue 3 indica e ha he sys em has he op alue o unce ainly compa ed
o ole ance. In his case ou sys em has he minimum equi emen s o ha e an
alue accep able.
The alue 10 indica e ha ou sys em has a lowes alue o unce ainly com-
pa ed o ole ance. This is an ideal case, bu i we wan o ge 10 usually he
equipmen s ha we need a e e y expensi e.
Fo his is eason, all equipmen s o sys ems mus pass a calib a ion by he
manu ac u e , which will gi e he accu acy, by ou sel es h ough some in e nal
me hod. The mos impo an is main enance he aceabili y chain.
IV. TOLERANCE´S MODIFICATION
One ime ha we calcula ed he unce ainly o ou measu e’s sys em, we mus
know ha he minimum alue ha we wan o see no longe co esponds o he
ini ial alue, because has been al e ed by unce ainly. Now ou ole ance (T) will
ha e been modi ied and will become (T’). This a ia ion is showed in he Fig. 3.:
III. SYSTEM ANALYSIS
Be o e beginning he design o he sys em we mus e alua e he unce ainly
ha mus ha e he sys em. Fo example i we choose a sys em o acqui ing o
Fig.3. Tole ance’s modi ica ion o he p ocess
V. SYSTEMATIC
To de e mine he bes equipmen o he pu pose ha we wish, we mus choose
ha equipmen o measu emen sys em. In he nex diag am, Fig. 4.,we can see
he s eps o ollow o a good choice:
Fig. 4. Diag ama de sis emá ica del p oceso
VI. CONCLUSIONS
We ca ied ou a sys ema ic s udy o make a choice acco ding o ou needs. In
his way we can educe he pu chase p ice o equipmen and gi e a alida ion
o he alue ha we wan o analyze.
REFERENCES
[1] Edición del Cen o Español de Me ología (CEM). “ la me ología ab e iada”. M-20557-2005.
[2] No ma UNE-EN 30012.” equisi os de asegu amien o de la calidad de los equipos de medida.
Pa e 1: Sis ema de con i mación me ológica de los equipos de medida (ISO 10012-1:1992).
(Ve sión o icial EN 30012-1:1993)”
Fig. 1. His og ams ep esen ing he no mal dis ibu ion and he uni o m dis-
ibu ion espec i ely
Equa ion 2. Rela ion be ween Tole ance (T) and expanded
Unce ainly (U)
Fig.2. La cadena de azabilidad