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EAL-G20 Z C AL IB R A T IO N O F S T YL U S IN S T R U M E N T S F O R M E A S U R IN G R O U G H N E S SEALEuropean cooperation for
Accreditation of Laboratories
EAL-G20Publication Reference
P U R P O S E
Calibra t ion of Stylus
Inst ruments for Measur ingSurface Roughness
This document has been produced by EAL to improve the harmonisation in surface roughness
measurement. It provides guidance to national accreditation bodies to set up minimum requirements
for the calibration of stylus instruments and gives advice to calibration laboratories to establish practical
procedures.
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E D I T I O N 1 ZZ A U G U S T 1 9 9 6P AG E 2 O F 9
Authorship
This publication has been written by EAL Committee 2 (Calibration and Testing activities).
Official language
The text may be translated into other languages as required. The English language version remainsthe definitive version.
Copyright
The copyright of this text is held by EAL. The text may not be copied for resale.
Guidance Publications
This document represents a consensus of EAL member opinion and preferred practice on how therelevant clauses of the accreditation standards might be applied in the context of the subject matterof this document. The approaches taken are not mandatory and are for the guidance of accreditationbodies and their client laboratories. Nevertheless, the document has been produced as a means of
promoting a consistent approach to laboratory accreditation amongst EAL member bodies,particularly those participating in the EAL Multilateral Agreement.
Further information
For further information about this publication, contact your National member of EAL:
Calib National member Testing National member
Austria BMwA BMwA
Belgium BKO/OBE BELTEST
Denmark DANAK DANAK
Finland FINAS FINAS
France COFRAC COFRAC
Germany DKD DAR
Greece Ministry of Commerce ELOT
Iceland ISAC ISAC
Ireland NAB NAB
Italy SIT SINAL
Netherlands RvA RvA
Norway NA NA
Portugal IPQ IPQ
Spain ENAC ENAC
Sweden SWEDAC SWEDAC
Switzerland SAS SAS
United Kingdom UKAS UKAS
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EAL-G20 Z C AL IB R A T IO N O F S T YL U S IN S T R U M E N T S F O R M E A S U R IN G R O U G H N E S S
1 Introduct ion 4
2 Scope and field of applica t ion 4
3 Terminology 4
4 Reference standards 5
5 Example of a ca libra t ion procedure 5
6 Uncer ta in ty of measurement 7
7 Calibra t ion cer t ifica te 8
8 References 9
Section Page
Contents
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1 In t r od u c t ion
1.1 The purpose of this technical guideline is to improve the harm onisation within
EAL for surface roughness measurement. It provides guidance to nationalaccredita tion bodies to set u p minim um requirem ents for t he calibra tion of stylus
instruments and gives advice to calibration laboratories to establish practical
procedures. The guideline is based on a national calibration guideline [ref. 1].
In the first part (sections 2, 3 and 4), the general definitions, the reference
sta nda rds t o be used a nd t he t echn ical requirem ents for t he calibrat ion of stylus
measurement instruments are given. The second part of this guideline is of
procedural na ture and g ives pract ica l advice to ca l ibra t ion and tes t ing
laboratories. In section 5 an example of a typical calibration procedure is
present ed. It m ay be am ended or modified to meet t he specific requirem ents of
accreditation.
2 Scop e a n d fie ld o f a p p lica t ion
2.1 T h is gu i de li n e a p p li es t o t h e ca l ib r a t i on of s t yl u s i n st r u m e n t s for t h e
mea sur emen t of sur face roughness by th e profile met hod as defined in ISO 3274
[ref. 2]. The calibrat ion sha ll be car ried out with th e aid of reference sta nda rds.
The guideline is intended only for inst ru ment s with pick-ups with independent
datum.
2.2 Com p on e n t s : The stylus inst rum ent comprises th e basic equipment (indicat or,
evaluat ion a nd cont rol units), a t ra verse unit , a probe (pick-up) with t he st ylus
an d a pr ofile recorder. Only complet e combin at ions of inst ru men ts a re qua lified
for calibration. If the basic equipment is used with several traverse units and
pick-ups, each of th ese instr um ent combina tions sha ll be calibrat ed separ at ely.
2.3 S it e o f ca lib r a t ion : The stylus instrum ent shall be calibrat ed at the place of
use, so that all the ambient conditions which will influence the instrument in
service, are ta ken into considera tion.
No te : Genera l r equ i r emen ts fo r the acc red i t a t ion o f l abo ra to r ie s and
o r g a n i s a t i o n s p e r f o r m i n g s i t e c a l i b r a t i o n s a r e g i v e n i n P u b l i c a t i o n
EAL-R3 [ref. 3].
3 Te r m in o logy
3.1 The surface roughness parameters are defined in ISO/DIS 4287-1.2 [ref. 4]:
P t tota l height of pr ofile over evalu at ion lengt h
R a ar ith met ical mea n deviat ion of roughn ess profile over five samplin g lengt hs
R z aver age height of rough ness pr ofile over five sam pling length s
R z1max ma ximum h eight of roughness profile over one sam pling length
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The measuring conditions are described in ISO/DIS 4287-1.2 [ref. 4] and ISO
4288 [ref. 5] usin g a pr ofile filter accordin g t o ISO 11562 [ref. 6].
4 R e fe r e n ce s t a n d a r d s
4.1 The s tylus ins t rument shall be ca l ibra ted by means of reference standards .
Among other sta nda rds of similar type, the following proved to be appr opriat e:
(a) Optical flat. Reproduces th e residual profile; th e effects of externa l datu m
stra ightness , environmenta l condi t ions and ins t rument noise can be
established.
(b) Depth m easu rem ent st an dar d, type A1 or A2 according to ISO 5436 [ref. 7]
(Fig.1): Reproduces the profile depth Pt ; ensures the traceability of the
vert ical pr ofile component to th e un it of lengt h.
(c) Roughness measur ement st anda rds, preferably type D according to ISO 5436
[ref. 7] (Fig. 2): Reproduce the arithmetic mean deviation R a a n d t h e
ma ximu m height of profile R z and R z1max establishing an overall check of
the ins trument.
4 .2 Dependent on the type and the metrological character is t ics of the ins t rument
to be calibra ted, th e following sta nda rds m ay be used a s well:
(a) inclination s tandard
(b) s ph er e
(c) wavelength m easuremen t st anda rd t ype C according to ISO 5436 [ref. 7].
4 .3 The depth and roughness measurement standards should be ca l ibra ted by a
na tional met rology inst itut e or an accredited la bora tory capable of delivering
th e measu rem ent un certa inty required for t he specific applicat ion in quest ion.
The calibra tion inter val should not exceed 5 years.
5 E xa m p le o f a ca lib r a t ion p r oc e d u r e
5.1 The following procedure is taken from a nat ional calibrat ion guideline [ref. 1].
It refers to specific reference sta nda rds. Both th e guideline a nd th e reference
standards have proven to be very useful and to lead to excellent agreement
am ong accredit ed labora tories [ref. 8, 9]. Other sta nda rds of similar or differen t
type are available from several manufacturers.
5.2 P rep a r a ti on f or ca l ibr a t i on
5.2 .1 Before ca libra t ion , check t hat the s ty lus ins t rument opera tes cor rect ly as
described in th e ma nu factur er's opera ting inst ru ctions. Additional inform at ion
can be t ak en from [ref. 8] if necessar y.
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5.2.2 Before calibrat ion th e following prepara tions ha ve to be made:
(a) Es t abl ish the effects of ex terna l da tum s t r a ightn ess , environm enta l
conditions and instrument noise by measuring Ra
and Rz
of an optical flat .
The measuring conditions are in accordance with those applied for the
corresponding roughness standards (usually five sampling lengths over a
total evaluation length of ln = 4 mm and a cut-off wavelength of lc = 0,8
mm for t he filter ). The measu red R a and Rz values must be indicated in the
calibration certificate.
(b) Align the plane of the depth m easuremen t sta ndar d to the dat um a xis in
the best possible way, al ign the plane of the roughness measurement
stan dard to within 10 % of the mea suring range.
(c) Always select t he sma llest possible mea sur ing ran ge.
(d) Take measur ements in th e middle of the m easuring ran ge each time.
5.3 Ca l ib ra t ion by m ea n s of a d ep t h m ea su r em en t s ta n d a r d
5.3.1 Measu re each groove in five profile sections (Fig. 5.1). Probe th e grooves
individua lly in succession an d deter mine t he Pt value of the unfiltered profile
(without automatic al ignment) . Indicate the deviation of the mean value
(obtained from t he 5 m easur ed Pt values) from th e value given in t he calibrat ion
cert ificat e of th e depth measu rem ent st an dar d, in percent a nd in micrometers.
5.4 Ca l ib ra t i on b y m ea n s of rou g h n e ss m ea s u r em en t
s t a n d a r d s .
5 .4 .1 C a r r y ou t 1 2 m e a su r e m e n t s on e a ch r ou g h n e ss m e a s u r em e n t s t a n d a r d ,
distributed over the measur ement surface as shown in the measur ement locat ion
pattern (Fig.5.2) . Measuring condit ions: 5 sampling lengths over a total
evaluat ion length ofln = 4 an d a cut -off wavelengt h oflc = 0,8 mm for t he filter .
Calculat e the ar ithm etical mean a nd th e standa rd deviat ion for each roughness
parameter. The deviations (in percent and in micrometers) of the mean from
the value sta ted in th e calibrat ion certificat e of the standa rd a nd th e stan dard
deviat ions a re t o be indicated in t he certificat e.
Figure 5.1. Depth setting standard (type A2) with enlarged area of measurement
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Figure 5.2. Roughness standard (type D) with enlarged area of measurement(above) and measurement location pattern with starting points andmeasurement lengths (below).
6 Un ce r t a in t y o f m ea su r em en t
6.1 The uncertainty of measurement shall be calculated according to EAL-R2 [ref.
10] . This means that al l quanti t ies ( input es t imates) contr ibuting to the
measurement resu l t a re t rea ted as random var iab les . The square of the
combined standard uncertainty is obtained by summing the variances of the
input es t imat es . The expan ded un cer ta in ty is g iven wi th a coverage fac tor
k = 2.
6 .2 The uncer ta in ty of the sty lus inst rument ca l ibra t ion cons is ts main ly of the two
components un and u e :
(a ) un is the stan dard u ncerta inty of the m easured value of the st anda rd a s it is
taken from the calibration cert if icate of the s tandard. I t contains the
un iform ity of the reference sta nda rd.
(b) u e is the st anda rd uncertainty estimat ed by experience for tra nsferring the
measur ed value of the standa rd to the stylus instr umen t. It conta ins the
instrum ent's repeata bility on th e same measur ement length.
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6 .3 The tota l expanded uncerta in ty is given by:
U u un e
= +2 2 2
The va lues rounded to an in tege r pe rcen t fo r the meas u red roughnes s
parameters and rounded to integer hundredths of a micrometer for the groove
depth s ar e to be indicated in t he calibra tion cert ificat e.
Note: Since the su rface of the roughness mea sur ement sta nda rd is not perfectly
uniform, the results of the measurements will scatter, resulting in a random
component of th e uncerta inty, expressed by its experiment al sta nda rd deviation.
This ra ndom component , which is cau sed by th e roughness sta nda rd, is already
included in t he un certaint y un of the roughness stan dard. It must th erefore not
be added to the component u e once more , though th is sca t ter ing of the
measur ement r esults is found a gain when the st ylus instru ment is calibrat ed.
7 Ca lib r a t ion c e r t i fica t e
7.1 The certificate of calibrat ion shall be in conforma nce with EAL-R1 [ref. 11]. In
par ticular it ha s t o cont ain th e following inform at ion:
(a) Identificat ion of all relevan t component s of th e complete instr um ent
combin at ion a ccording to section 2 of th is docum ent .
(b) Site of calibrat ion.
(c) Method of calibrat ion.
d) Type of stan dards used, including their calibrat ion value.
(e) Measur ing conditions (measu ring ran ge, tr averse speed applied, length
probed, wavelength cut off, filter type, stylus t ip ra dius).
(f) Results of the R a a nd R z mea sur ement s on th e optical flat.
(g) The mean measu red profile depth for each groove of the depth measu rement
sta nda rd an d the deviations from th eir calibrat ion values.
(h) The mean measured R a and R z values for each roughness measurement
stan dard, their experimental sta ndar d deviation and the deviations from
th eir calibrat ion values.
(j) Each result h as to be given with i ts uncertainty of measurement.
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8 R e fe r e n ce s
1. DKD - R 4 - 2 . Richt l in ie zum Kalibr ieren von Tas tschnit tger ten im Deutschen
Kalibrierdienst, PTB-Mitteilungen , 102(1992), Nr.1, pp.23-26.
2. ISO 3274 : 1995. Geometrical Product Specification (GPS) - Surface texture
Profile method - Nom inal characteristics of conta ct (stylus) instru m ents
3. E AL -R 3 : 1996. R equirem ents for the Accredita tion of Laboratories and
Organisations Perform ing S ite Calibrations
4. ISO/DIS 4287 - 1.2 : 1995. Geometrical Produ ct Sp ecification (GPS) - S urface
texture - Profile m ethod. Part 1: T erm s, definitions an d param eters of surface
texture.
5. ISO 4288 : 1995. Geometrical Product Specification (GPS) - Surface textureProfile method - Rules and procedures for the assessment of surface texture.
6. ISO 11562 : 1995. Geometrical Product Specification (GPS) Surface texture
Profile m ethod - Metrological characteristics of ph ase correct filters.
7 ISO 5436 : 1985. Calibration specim ens - S tylus instru m ents - Types, calibration
and use of specim ens.
8. Hillmann,W. Komm enta r zur Richtlinie zum Kalibrieren von Tastschn ittgerten
im Deut schen Kalibrierdiens. PTB-Bericht: PTB - F-8, Dezember 1991.
9. Hillmann, W. Calibration of contact stylus instrum ents with in th e DeutscherKalibrierdienst. Techn ische Un iversit t Chem nitz, VIII. Inter na tionales
Oberflchenkolloquium, Chemnitz, 3. - 5. Februar 1992, Band 2, S. 58 - 65.
10. EAL-R2 : 1996.Expression of th e Uncertaint y of Measurement in Calibration.
11. E AL-R1 : 1995. Requirements Concerning Certificates Issued by Accredited
Calibration Laboratories.
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