DKD-R 4-2 Calibration of Devices and Standards for Roughness Metrology Sheet 2: Calibration of the vertical measuring system of stylus instruments

Transcription

1 DKD-R 4- Calibration of Devices and Standards for Roughness Metrology Sheet : Calibration of the vertical easuring syste of stylus instruents

2 DKD-R 4- Sheet.7 DKD-R 4- Calibration of Devices and Standards for Roughness Metrology Sheet : Calibration of the vertical easuring syste of stylus instruents. Purpose and field of application.... Ters and sybols.... Measuring devices Abient conditions Calibration Plane glass plate Depth setting standard type A, (DIN EN ISO 546-) Roughness standard type D (DIN EN ISO 546-) Measureent uncertainty Joint odel in Directive DKD-R Device calibration ith depth setting standards Device calibration ith roughness standards Adissibility for calibration Calibration certificate Recalibration, interediate test.... Literature.... Purpose and field of application In this sheet of the Directive, the calibration of the vertical easuring syste of stylus instruents (DIN EN ISO 74) is described. The basic regulations of DIN EN ISO 79 are taken into account. Procedures for calculation of the easureent uncertainty in the calibration of stylus instruents ith depth setting standards and roughness standards are stated. The calibration ith depth setting standards establishes traceability to the national length standard, the calibration ith roughness standards validates the function of the coplete transission chain of the stylus instruent.. Ters and sybols Here, only the ters and sybols hich are specific for this sheet are explained. Generally valid ters are entioned in the surface standards stated in chapter. Rz Wt U n Basic noise of the device Straightness deviation of the guidance Uncertainty of the reference standard Pt Mean value of Pt of the currently easured profile depth Nuber of repetition easureents perfored at the sae probing place Nuber of repetition easureents for changed probing places t Indices: t Due to topography Due to repetition easureent pl Due to plastic deforation sp Due to stylus tip DKD-R 4. Sheet /

3 DKD-R 4- Sheet.7. Measuring device The stylus instruent in accordance ith DIN EN ISO 74 consists of a basic unit, a feed device (ith a guidance of its on) and a probing syste. If different device coponents are cobined, each device cobination ust be calibrated separately. Before calibration is carried out, correct functioning of the stylus instruent is checked in accordance ith its operating instructions. Feed device and surface of the standards are to be aligned in parallel to each other. 4. Abient conditions The stylus instruent should be calibrated at is place of use. This guarantees that the influences of the abient conditions, hich also prevail in the later use of the stylus instruent, are taken into account for the calibration. Teperature gradients, e.g. by direct sun light, ust be avoided. 5. Calibration For a calibration, the folloing three types of standards are used: Plane glass plate Depth setting standard, type A in accordance ith DIN EN ISO 546- Roughness standard, type D in accordance ith DIN EN ISO 546- Table shos a survey of their use in the calibration activities to be perfored. Objective Design Chapter Deterination of the basic noise Deterination of the guidance deviation Deterination of the vertical aplification 5x easureent of Rz on plane glass plate 5x easureent of Wt on a plane glass plate Measureent of the depth of different grooves on a depth setting standard Deterination of the repeatability 5x easureent of the depth of a groove at the sae place on a depth setting standard Checking of the transission chain function Monitoring of the device proper ties Table : Suary of the calibration activities 5. Plane glass plate Measureent of roughness paraeters on a roughness standards Regular calibration and docuentation On a plane glass plate, Rz is deterined in five surface profiles under the easureent conditions used for the calibration of the device ith roughness standards. The ean value is to be indicated in the calibration certificate as s Rz DKD-R 4. Sheet /

4 DKD-R 4- Sheet.7 On the plane glass plate, Wt is deterined in five surface profiles for the area of the guidance hich ill later be used for the easureents. The ean value is required as Wt for the calculation of the easureent uncertainty of paraeters hich are evaluated at the unfiltered profile (see chapter 6.). 5. Depth setting standards, type A (DIN EN ISO 546-) The easureents on the depth setting standard ust be carried out for the profile depths hich ill be iportant for the later use. The sallest possible easureent range hich suits the profile depth ust be selected. The groove of a depth setting standards is to be easured five ties in the sae position at a calibrated place (for deterination of s ( ) ) and in five profile sec- Pt tions hich are close to one another (for deterination of Pt ). A plan of easureent points in accordance ith Fig. has proved its orth. Tiefen- Einstellnoral XXX PTB xx 4x je,5 Mittellinie Rillen-Nuer Fig. : Exaple of a plan of easureent points for calibration of the stylus instruent ith a depth setting standards (here: type A). For calibration of the device, five easureents are carried out in the centre of the groove of this standard and five easureents for a range of µ around the centre. The evaluation of the profile depth Pt on a depth setting standard is described in Directive DKD-R 4-, sheet, Annex B. Before the evaluation is realized, the reference level of the standard is to be aligned horizontally ith the aid of to partial ranges on the left and on the right of the groove by eans of the least squares ethod. The deviation of the ean value Pt (hich has been obtained by five easureents) fro the calibration certificate of the device is indicated in percent fro the easureent value and in icroeters. For evaluation of the groove depth D (in accordance ith DIN EN ISO 546-) described in Directive DKD-R 4-, sheet, in Annex B, the sae procedure is valid. DKD-R 4. Sheet 4 /

5 DKD-R 4- Sheet.7 5. Roughness standard, type D (DIN EN ISO 546-) On a roughness standard ith an irregular profile, profile sections are recorded on the easureent face. The sallest possible easuring range suiting the roughness is to be selected (DIN EN ISO 488). For the liiting avelength λ c =.8, the plan of easureent points according to Fig. has proved its orth. PTB Mess- richtung Mittellinie syetry line Startlinie starting line Fig. : Exaple of a plan of easureent points on a roughness standard ith λ c =.8 ; indicated are the starting points of the easureent sections (each 4 in length). Fro this, the probing sections are obtained in accordance ith the filter properties of the device. Fro the profile sections, the arithetic ean of the desired roughness paraeters is calculated in accordance ith DIN EN ISO 487 or DIN EN ISO 565-,. The deviations of the currently deterined values fro the values stated in the calibration certificate of the standard are to be indicated in the calibration certificate of the device in percent of the easureent value and in icroeters. 6. Measureent uncertainty 6. Joint odel in Directive DKD-R 4- The calculation of the easureent uncertainty in Annex A of Directive DKD-R 4- is based on the generally valid odel of the probing process of the stylus instruent on a echanical surface. Fro this odel, the quantities hich affect the calibration of stylus instruents ith depth setting standards and ith roughness standards are copiled. In accordance ith GUM, the standard uncertainties of the influence quantities are quadratically added, and the su is ultiplied by the coverage factor K. This guarantees for the result a coverage probability of 95%. As soe of the influence quantities have a sall degree of freedo, the value of K ust be calculated fro the effective degree of freedo of the overall uncertainty. A concrete description of the procedure can be found in DKD-. DKD-R 4. Sheet 5 /

6 DKD-R 4- Sheet.7 6. Device calibration ith depth setting standards The odel of the interaction during the easureent on depth setting standards is described in Directive DKD-R 4-, sheet, Annex B. On the basis of this odel, the uncertainty coponents, hich are influenced by the device properties and the calibration process, are taken into account hen the easureent uncertainty is deterined during the calibration of the devices ith depth setting standards in accordance ith DIN EN ISO 79. The odel: U Gerät (Pt) = [ u n + st ( Pt) + s ( ) Pt + ( Wt ) t + ( Rz ) ] eq. u n st t ( Pt ) Standard uncertainty of the reference standard used for the device calibration. un = U n / K. The expanded uncertainty U n and the coverage factor K are taken fro the calibration certificate of the reference standard. Influence, hich results in the disseination fro the topography of the reference standard by an inexact localization of the probing place. As estiated value serves the standard deviation s of the ean value of the currently easured profile depth Pt of the reference standard for t easureents and for a slight variation of the probing place. s ( Pt) Probing repeatability of the device to be calibrated. The standard deviation s of the ean value of the currently easured profile depth Pt of the reference standard serves as an estiated value for easureents hen the easureents are carried out at the sae probing place. ( Wt ) Straightness deviations of the guidance of the device to be calibrated ( Rz ) Noise of the device to be calibrated t Table shos a survey of the influence quantities for a device calibration in accordance ith equation on the basis of paraeter Pt. The nubers of the chapters in the table relate to the chapters in Annex A of Directive DKD-R 4- sheet. Chapter Input quantity keyord Calculation of the input quantity Exaple value for Pt=µ Sensitivity coeff. Method of deterination, distribution Variance/ n. Reference standard 4 U n Un = 5 n (Cal. certificate) B Gaussian 56 DKD-R 4. Sheet 6 /

7 DKD-R 4- Sheet.7 Chapter Input quantity keyord. Difference beteen easureent place and calibration place. Repeatability Calculation of the input quantity st t ( Pt.5 Guidance deviation ( ).6 Basic noise ( ) ) Exaple value for Pt=µ s t ( Pt ) = 6 n (t=5) s( Pt) s = 5 n, = 5 Sensitivity coeff. Method of deterination, distribution B Gaussian A Gaussian Wt Wt = 5n B equal Rz Rz = n A equal Variance/ n Device, totally Su colun above u device ( Pt) 9, Zelle oberhalb u device (Pt) 8 n K = U device (Pt) 6 n U Gerät ( Pt) / Pt U rel (device, Pt), % 7, 5 8 Table : Calculation of the easureent uncertainty of the device calibration in the easureent of the profile depth Pt ith exaple values The sae procedure can also be applied hen the easureent uncertainty of the device calibration is deterined during the easureent of the groove depth D (DIN EN ISO 546-). 6. Device calibration ith roughness standards Based on the odel shon in Directive DKD R 4-, sheet, Annex A, the uncertainty coponents hich are influenced by the device properties and the calibration process are taken into account for the deterination of the easureent uncertainty hen stylus instruents are calibrated ith roughness standards in accordance ith DIN EN ISO 79. The odel: u gerät ( Rz) = [ u RN + s ( Pt ) + ( Rz ) + DKD-R 4. Sheet 7 / a pl u( r sp ) + ( ) ] eq. u RN Standard uncertainty of the easurand on the reference standard (RS) used for device calibration. urn = U RN / K. Die uncertainty U RN and the coverage factor K are taken fro the calibration certificate of the roughness standard. This also includes the deterination of a possible aplification deviation.

8 DKD-R 4- Sheet.7 a pl ( Rz ) s ( Pt ) Probing repeatability of the device to be calibrated. The standard devia- tion s of the ean value of the currently easured profile depth of the reference standard serves as an estiated value for easureents of the profile depth Pt of the reference depth setting standard hen the easureents are carried out at the sae probing place. Noise of the device to be calibrated Plastic deforation on the standard by stylus tip ( u( r )) sp Influence of the deviation of the stylus tip fro the noinal radius Table shos a survey of the influence quantities for device calibration in accordance ith equation on the basis of roughness paraeter Rz. The nubers of the chapters in the table relate to the chapters in Annex A of Directive DKD-R 4-, sheet. Chapter Input quantity keyord Calculation of the Input quantity DKD-R 4. Sheet 8 / Exaple value for Rz = µ. Traceability u U ( Rz) = % RN RN fro the cal. cert. of RS u = 45 n. Repeatability.6 Basic noise ( ).7 Plast. defor..8 Stylus tip s( Pt) s = 5 n, = 5 repeat easureents Sensitivity coeff. Method of deter., distribution B Gaussian B Gaussian Rz Rz = n A equal a a pl pl = 5 n B equal ( u( )) r sp u(r sp ) =.5 µ - n/µ B equal Variance [n ] 5 Device, totally Su colun above u device ( Rz) 4 Zelle oberhalb u device (Rz) 46 n K = U device (Rz) 9 n U device ( Rz) / Rz U rel (device, RN) % Table : Calculation of the easureent uncertainty of the device calibration for deterination of the roughness paraeter Rz ith exaple values. As a ave filter is used, guidance deviations do not exert any influence in the case of roughness standards. 5 8

9 DKD-R 4- Sheet.7 Note Consequently, the device calibration is ainly deterined by the uncertainty of the reference roughness standard, hose uncertainty is in turn ainly deterined by its standard deviation during its calibration. As, according to DIN EN ISO 79, the influences due to the iperfection of the standards do not have to be taken into account for the uncertainty of the device calibration, this suand ould actually have to be oitted. As the influence of the topography is, hoever, unavoidably connected ith the calibration, it ust reain included. 7. Adissibility for calibration The adissibility for calibration is deterined in to steps. First, the calibration is carried out ith a depth setting standard (reference standard) in accordance ith chapter 5.. If - after an adjustent of the device - the deviations of the results are still larger than the expanded easureent uncertainty plus a constant aount (for DKD laboratories, an aount of. µ has proved its orth), the device is regarded as not adissible for calibration. If the deviation is saller, the easureent uncertainty of the device calibration can be deterined ith depth setting standards in accordance ith chapter 6.. If this requireent is et, calibration ith a roughness standard is carried out in the second step in accordance ith chapter 5.. The device is suitable for roughness easureents if the results of the easureent of the roughness paraeters on the reference standards deviate by less than their expanded easureent uncertainty plus a constant aount (for DKD laboratories, an aount of % of the calibrated paraeters has proved its orth). If the deviation is saller, the easureent uncertainty of the device calibration can be deterined ith roughness standards in accordance ith chapter Calibration certificate The calibration is docuented in the calibration certificate. It shall contain the folloing inforation: Place of the calibration Coponents of the calibrated device cobination (anufacturer, type, serial nuber) Standards used (identification nuber, official ark and date of the latest calibration) Description of the calibration procedure, possibly also ith reference to standards, directives or relevant scientific texts Measureent conditions (teperature, easureent range, feed velocity, probing section, liit avelength, filter type, stylus radius) Measureent result of Rz on the plane glass plate Measureent results hose easureent uncertainty and deviations (in µ and percent) deviate fro the calibrated values of the depth setting standard and the roughness standard. DKD-R 4. Sheet 9 /

10 DKD-R 4- Sheet.7 9. Recalibration, interediate test The calibration is to be repeated at regular intervals. Depending on the easureent task, recalibration periods beteen onth and years are usual. The recalibration period is influenced by the stability of the environental conditions change of coponents of the device frequency of the use requireents for the uncertainty For interi checks of the functional capacity of the device, it has proved its orth to easure the paraeters Rz and RS at shorter intervals on a roughness standard ith a regular profile (type C in accordance ith DIN EN ISO 546-) and to docuent the deviations of the displayed values.. Literature DIN EN ISO 74 (4/998): Geoetrical Product Specifications (GPS) - Surface texture: Profile ethod - Noinal paraeters of contact (stylus) instruents DIN EN ISO 79 (/): Geoetrical Product Specifications (GPS) - Surface texture: Profile ethod - Calibration of contact (stylus) instruents DIN EN ISO/IEC 75 (5): All General requireents for the copetence of testing and calibration laboratories DIN EN ISO 487 (/998): Geoetrical Product Specifications (GPS) - Surface texture: Profile ethod ; Ters, definitions and surface texture paraeters DIN EN ISO 546- (998): Geoetrical Product Specifications (GPS) - Surface texture: Profile ethod ; Standards; part : Material easures DIN EN ISO 488 (/998): Geoetrical Product Specifications (GPS) - Surface texture: Profile ethod ; Rules and procedures for the assessent of surface texture DIN 4768 (5/99) Deterination of the roughness paraeters R a, R z, R ax ith electrical stylus instruents; ters, easureent conditions Note: This ithdran standard is entioned here due to the definition of the idely-used paraeter Rax. Directive DKD-R 4-: Calibration of easuring instruents and standards for roughness etrology; sheet : Calibration of standards for roughness etrology DKD-R 4. Sheet /

11 DKD-R 4- Sheet.7 EN 49 (6): Measureent of roughness average Ra and peak count RPc on etallic flat products DKD- (edition, ) Expression of the easureent uncertainty in calibrations Published by the Accreditation Body of the Geran Calibration Service (DKD), DKD-R 4. Sheet /