© NMISA 2010 Dissemination of Mass Standards from the National Prototype by Thomas Mautjana.

© NMISA 2010

Dissemination of Mass

Standards from the

National Prototype

by

Thomas Mautjana

© NMISA 2010

Presentation overview

• Introduction

• Method description

• Traceability

• Conclusion

© NMISA 2010

Introduction

• Kg is the only SI unit that is still an artefact

• Our mandate is to maintain and disseminate the value

of the kilogram

© NMISA 2010

How do we disseminate the value of kg?

• Weighing design is used to calibrate a set of weights

using one reference standard

• Subdivision and multiplication method

• Calibrate in decades :D1 500, 200, 200*,100

D2 50, 20, 20*,10

D3 5, 2, 2*, 1

etc D 6

© NMISA 2010

Weighings with 5221 structure

(10) + d1 vs (5) + (2) + (2)* + (1)

(10) + d2 vs (5) + (2) + (2)* + (1)*

(5) vs (2) + (2)* + (1) + d3

(5) vs (2) + (2)* + (1)* + d4

(2)+(1) vs (2)* + (1)* + d5

(2)+(1)* vs (2)* + (1) + d6

(2) vs (1) + (1)* + d7

(2)* vs (1) + (1)* + d8

© NMISA 2010

Method description

• To determine the values of all the unknown

weights the normal equations would have to be

orthogonal (i.e. without variances)

• To ensure orthogonality some of the equations

may be omitted and some used more than

once

• Reference standard should be the defining (Head)

weight

© NMISA 2010

Orthogonal design: 5221

(10) = (5) + (2) + (2)* + (1) - d1

(10) = (5) + (2) + (2)* + (1)* - d2

(5) = (2) + (2)* + (1) + d3

(5) = (2) + (2)* + (1)* + d4

(2)+(1) = (2)* + (1)* + d5

(2)+(1) = (2)* + (1)* + d5

(2)+(1)* = (2)* + (1) + d6

(2)+(1)* = (2)* + (1) + d6

(2) = (1) + (1)* + d7

(2) = (1) + (1)* + d7

(2)* = (1) + (1)* + d8

(2)* = (1) + (1)* + d8

© NMISA 2010

Calculation: Equations

© NMISA 2010

Calculation: Equations continues

© NMISA 2010

Method: Advantages and Disadvantages

• Advantages:

Less use of reference weights

Use check weights

Produces no variances or co-variances

Lead to higher accuracies

• Disadvantage:

Placing several weights on a pan

© NMISA 2010

Traceability Copy 56

1kgTransfer Standards

E1 set of Transfer

StandardsE1 Working Standards

E2 Working Standards

Customer Standards

© NMISA 2010

Conclusion

• Orthogonal system produces no variances or co-

variances

• The most accurate method with self check

• Customer standards are compared against the

working standards and never and never will be

compared against the national standard.

© NMISA 2010 Dissemination of Mass Standards from the National Prototype by Thomas Mautjana.

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Transcript of © NMISA 2010 Dissemination of Mass Standards from the National Prototype by Thomas Mautjana.