1

Practical Interpretation of Unbroken Chain in Metrological Traceability

as to VIM 3

Center for Measurement Standards (CMS)Industrial Technology Research Institute

(ITRI)

Authors: Yi-Ting Chen, Lung-Hen Chow, Liang-Hsing Chen, and Gwo-Sheng Peng

2

Outline

1. Introduction

2. Definition of “Metrological traceability” in VIM 3

3. Typical Metrological Traceability Diagram

4. Additional Mathematical Description

5. Case study - Gauge Block Measurement

6. Discussion and Conclusion

3

Introduction

4

Introduction• Clear the addresses of VIM

– ISO/IEC Guide 99:2007, “International vocabulary of metrology — Basic and general concepts and associated terms” cancels and replaces the old VIM:1999 .

• The term “Traceability” is replaced by “Metrological traceability” – a new definition as property of a measurement result whic

h can be related to a reference – an evidence of measurands tracing to the primary standar

ds which can realize the SI units

– a documented unbroken chain of calibrations

5

Introduction• National Measurement Laboratory (NML, the NMI

in Taiwan) has operated its mission since 1987. Effective knowledge transfer has become an essential issue.

• Gauge block measurement is demonstrated for such purpose at NML.

• In dealing with definition of “metrological traceability” in VIM 3, additional mathematical description is taken to enhance the practical interpretation of the definition.

6

Definition of “Metrological traceability” in VIM 3

7

Definition of metrological traceability in VIM 3 Definition of this term in VIM 3 :2.41 metrological traceability

Property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.

2007

8

Metrological traceabilityProperty of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.

Unbroken chain of calibrations

Metrological traceability

Metrological traceability

Measurement result

Calibration

Calibration

CalibrationMeasurement

Result

Measurand

Reference

Measurement standard

Measurement procedure

Measurement unit

Measurement uncertainty

Measured quantity value&

document

document

document

9

Six important elements in ILAC P-10

1. an unbroken chain2. uncertainty of measurement3. documentation4. competence5. reference to SI units6. calibration intervals

The International Laboratory Accreditation Cooperation (ILAC) also proposed six important elements to confirm the definition of “metrological traceability” :

2.41 Metrological Traceability :Property of a measurement result whereby the result can be related to a reference5 through a documented3 unbroken chain1 of calibrations6, each contributing to the measurement uncertainty2.

10

Typical metrological traceability diagram

11

Typical metrological traceability diagram• Hardness traceability chain in Metrologia 47(2010) S59–S66

(Traceability in hardness measurements: from the definition to industry)

12

• For a specific measured quantity of calibration at NML, there will be two documents: – Instrument Calibration Technique (ICT)– Measurement System Validation Procedure

(MSVP).

Typical approach of NML’s metrological Traceability Diagram

Gauge block comparator measurement traceability diagram

Mass measurement system traceability diagram

• Measurement System Validation Procedure (MSVP).• The traceability illustration in figures cannot fully cover the

aforementioned six important elements of metrological traceability.

13

Additional MathematicalDescription

14

Additional Mathematical Description• Combine “mathematical measurement equation”

with typical metrological traceability diagram to reinforce the evidence of “unbroken chain of calibrations”.

• In order to really focus on the property of measurement result as metrological traceability defined in VIM 3 ,

we shall emphasize the output

quantity in the measurement

model or equation.

15

Case study - Gauge Block Measurement

16

Gauge Block Comparator

calibration system

Metrological traceability of gauge block measurement

ncalculatio fromnumber stripe ceinterferen:tmeasuremen fromnumber stripe ceinterferen:

h wavelengtumlaser vacu:eterinterferomblock gauge from deviation:

(3) )(2

2

2

d

d

SI unitlength (m)

Gauge Block Interferometer calibratio

n system

Frequency Stabilized Lasers calibration

systemFequency stabilized laser,

f λ, wavelength：632.990 904 4 nm

Standard gauge block, Lr

0.5 mm to 100 mm

Gauge blockmeasurement

result

Gauge blockmeasurement

result

Measured difference, d1 (m)

Gauge block, LX

0.5 mm to 100 mmcomparatorblock gauge from differencet measuremen

block gauge standard ofresult t measuremen block gauge calibrated ofresult t measuremen

(1)

r

x

x

：：：

dLL

dLL r

1

1

eterinterferom block gauge from deviation comparator block gauge from difference mesurement

block gauge standard of value nominal block gauge calibrated of result tmeasuremen x

x

：：：：

2

1

N

21N

ddLL

ddLL

eterinterferomblock gauge from deviation block gauge standard of valuenominal

block gauge standard ofresult t measuremen (2)

2

r

2r

：：：

dLL

dLL

N

N Deviation, d2 (m)

The left-hand parameter of the equation is unknown and the right-hand parameters are known. In mathematical approach, an unbroken chain is demonstrated and measurement result of each step traced to the measurand of the previous step.

MeP Fequency Stabilized laser,fr , (Iodine stabilized He-Ne laser )

vacuuminlight of velocity cindex refractive n

tmeasuremenfrequency beat of deviationfrequency laser standard of valuefrequency laser calibrated of valuefrequency

(4) Δ , n

c

0

r

r0

：：：：：

f

ff

ffff

SI unit : length (m)

Frequency deviation, f △ (kHz)

1. an unbroken chain5. reference to SI units

17

SI units

platinum resistance thermometer

dew point hygrometer

U = 0.20 ℃

B970682B970683

C970446

Metrological traceability of auxiliary parameters Metrological traceability of auxiliary parameters

NML the fixed-point calibration system for platinum

resistance thermometers

(T05)

NML two- pressure humidity

generator calibration

system (H01)

K K Pa

standard resistor

digital pressure gage

U = 20 µ U = 0.010 kPa

C970374A980021

Electricitystandard

NML gas lubricated

piston gauge calibration

System (P04)

NML direct resistance calibration

system (E13)

Pa

digital thermometer

U = 0.029 ℃

B980642

NML resistance

temperature detectors calibration syste

m (T04)

Temperaturestandard

KSI unit

length (m)

Gauge Block Interferometer calibratio

n system (D02)

Frequency Stabilized Lasers calibration

system (D16)

Comparator calibration system

(D01)

Standard gaugeblock

Stabilized laser

Gauge blockmeasurement

result

Gauge blockmeasurement

result

Gauge block

Temperaturestandard

Pressurestandard

Temperature、pressure standard

The triple point of water： U = 0.21 mK

Ga melting point： U = 0.40 mK The laboratories operating calibrations of relevant

auxiliary parameters are all inner labs of NML and accredited by TAF. Calibration intervals indicate on their calibration certificates issued by the laboratories.

MeP Stabilized laser

(Calibration certificate)

4. competence6. calibration intervals

18

20 kHz

Expanded uncertaintyDocument No.

20 nm to 33 nm

28 nm to 57 nmICT:07-3-86-0034MSVP:07-3-86-0028

ICT:07-3-93-0141 MSVP:07-3-93-0132

ICT:07-3-85-0051MSVP:07-3-85-0033

SI unitlength (m)

Gauge Block Interferometer calibratio

n system (D02)

Frequency Stabilized Lasers calibration

system (D16)

Comparator calibration system

(D01)

Fequency stabilized laser,f λ, wavelength：

632.990 904 4 nm

Standard gauge block, Lr

0.5 mm to 100 mm

Gauge blockmeasurement

result

Gauge blockmeasurement

result

Measured difference, d1

(m)

Gauge block, LX

0.5 mm to 100 mm

Deviation, d2

(m)

MeP Fequency Stabilized laser,fr , (Iodine stabilized He-Ne laser )

Note:1. Instrument Calibration Technique, ICT:

documented calibration procedure used in NML2. Measurement System Validation Procedure, MSVP:

calibration system evaluation report used in NML, within which the claimed uncertainty is recorded

Metrological traceability of gauge block measurement

- Complementary illustration in documentation

It shows complementary illustration including documented expanded uncertainties associated with documented ICT and MSVP in each traceability step at NML.

2. uncertainty of measurement3. documentation

19

Discussion & Conclusion

20

Discussion & Conclusion• Through the study activities for drawing metrological

traceability diagrams combined with mathematical description, we will assure ourselves on knowledge transfer of gauge block and the other measurement systems with sufficient metrological know-how at NML.

• We will keep elaborating to further and deepen the concept of unbroken chain in metrological traceability to every measurement system of any kind quantities operating at NML.

• Since “reference to the SI units” is one of metrological traceability elements, derived quantity would be more complex than base quantity.

21

Thanks for your attention

~The End~