Required skills

Required skills include

gathering information on uncertainty components from calibration reports or reference material report

making logical assumptions based on experience or experimental data

calculating sensitivity coefficients either experimentally or by partial differentiation

calculating a combined standard uncertainty using rootsumofsquares accounting for correlations where necessary

calculating expanded uncertainty

using spreadsheets to calculate uncertainties

deciding if the uncertainty is suitable for the accuracy required for the test and establishing whether it is fitforpurpose using the tolerance to uncertainty ratio TUR

Required knowledge

Required knowledge includes

knowledge of the steps in the measurement test or calibration involved

evaluation of formulae containing powers exponents logarithms functions

use of scientific notation correct units and correct number of significant figures

preparation and interpretation of linear graphs

mean standard deviation standard deviation of the mean and degrees of freedom

significance tests such as ttest ftest and analysis of variance ANOVA variances standard deviation of prediction and linear regression for chemical industry sector

the difference between errors corrections and uncertainties

uncertainty in the uncertainty estimation process

uncertainty components that are common to the use of an instrument

uncertainty components that arise due to the instrument being used under different conditions to those when it was calibrated

procedures for determining the uncertainty components associated with each of the inputs and whether they are significant and for applying appropriate corrections

manufacturers specifications eg instrument drift specification and reference materials

procedures for determining uncertainty components from quality control data

normal rectangular triangular distributions and the factors used to reduce each to a standard uncertainty

the concept of degrees of freedom and how to allocate degrees of freedom to each uncertainty component including use of the WelchSatterthwaite equation

use of the students ttable to get a coverage factor for a particular level of confidence

the characteristics of a valid measurement

relevant reporting requirements such as the GUM National Association of Testing Authorities NATA or other applicable reference material

The Evidence Guide provides advice on assessment and must be read in conjunction with the performance criteria required skills and knowledge range statement and the Assessment Guidelines for the Training Package

Overview of assessment

Critical aspects for assessment and evidence required to demonstrate competency in this unit

Assessors should ensure that candidates can

prepare a realistic uncertainty budget that is appropriate for the application

fully document the uncertainty budget

report results and uncertainties in the required formats

Context of and specific resources for assessment

This unit of competency is to be assessed in the workplace or simulated workplace environment

This unit of competency may be assessed with

MSLA Perform standard calibrations

MSL904001A Perform standard calibrations

MSLA Perform nonstandard calibrations

MSL905001A Perform non-standard calibrations.

Resources may include

data sets and records

test methods and description of test setup

computer and relevant software or laboratory information system

relevant workplace procedures

Method of assessment

The following assessment methods are suggested

review of data worksheets calculations computer files such as spreadsheets and databases statistical analysis graphs andor tables prepared by the candidate

questions to assess understanding of relevant procedures trends in data and sources of uncertainty

review of reports prepared by the candidate

feedback from supervisors and peers regarding the candidates ability to estimate uncertaintyin accordance with enterprise procedures

In all cases practical assessment should be supported by questions to assess underpinning knowledge and those aspects of competency which are difficult to assess directly

Where applicable reasonable adjustment must be made to work environments and training situations to accommodate ethnicity age gender demographics and disability

Access must be provided to appropriate learning andor assessment support when required

The language literacy and numeracy demands of assessment should not be greater than those required to undertake the unit of competency in a work like environment

This competency in practice

Industry representatives have provided the case studies below to illustrate the practical application of this unit of competency and to show its relevance in a workplace setting

Manufacturing

Production workers in a water meter manufacturing company are required to batch test water meters Twenty meters are connected together and tested at the same time using a test rig that collects the water in a tank that sits on top of a weighing instrument The companys production technician needs to ensure that each water meter meets its maximum permissible error and that all measurements have a maximum permissible uncertainty that is below that specified by the regulator The technician needs to consider the calibration uncertainty of the weighing instrument any drift in it over time the resolution of the meters under test and other factors relating to the temperature of the water its effect on its density and the buoyancy correction for the weighing instrument

There are a number of corrections that need to be applied in order to achieve an uncertainty less than the maximum permissible uncertainty Production workers enter readings from the meters into a palmheld device This data is then downloaded to a computer which uses a spreadsheet program to make the required corrections tabulate the readings calculate the uncertainties and determine compliance of each meter with the regulations and produce a report Uncertainty components may change for different models of water meters that have different flowrates readability and minimum deliveries To cope with this the technicians spreadsheet program has lookup tables for these components according to the water meter model Once this system was setup there is no ongoing overhead costs for uncertainty estimation The calibration uncertainty may have to be updated when the weighing instrument is recalibrated Estimating uncertainties have highlighted which uncertainty components have the biggest effect on the final uncertainty This tells the technician which components to focus on and which have little effect

Chemical

A consulting laboratory analyses beef fat for a meat export company to determine the concentration of the pesticide residue Dieldrin prior to export The maximum residue limit for Dieldrin in beef fat is mgkg The technician analyses the sample using a validated gas chromatography GC method To estimate the measurement uncertainty of the analysis heshe needs to take into account such things as the

uncertainty from the GC calibration

uncertainty associated with the reference materials used

homogeneity of the sample

calibration of the glassware used for the analysis

the repeatability

reproducibility of the method

uncertainty of the method recovery

The technician calculates a result and uncertainty of mgkg The reported uncertainty suggests to the meat export company that the concentration of Dieldrin in the meat products could be above the residue limit They can now make informed decisions about whether to sell the meat or not and possibly avoid exporting meat with excessive levels of pesticide residue which could cost the exporter millions of dollars in lost revenue

Calibration

Technicians in a commercial calibration laboratory routinely calibrate digital multimeters including digit handheld multimeters and high accuracy digit bench mounted multimeters From experience they know that there are some uncertainty components common to each calibration such as the

uncertainty of the calibration of their reference instrument a calibrator

drift over time of their reference which they establish from its yearly calibrations over the last years

repeatability of their measured results at each test point from which they calculate a standard deviation of the mean

resolution of the multimeter being calibrated

Because of the higher accuracy of the digit multimeter the technicians know that for these instruments they must also consider additional uncertainty components such as the input impedance of cables together with thermal and capacitive effects These components may be insignificant in terms of the accuracy of a digit multimeter The uncertainty estimation and the rigour required relates to the accuracy required The tolerance in electrical calibrations is typically the manufacturers specification and the uncertainty needs to be smaller than that so that they can decide whether an instrument is within specification A tolerancetouncertainty ratio TUR is typical The technicians thorough understanding of uncertainty estimation enables the laboratory to optimise their measurement effort to ensure they achieve the ratio in an efficient manner The laboratory has NATA accreditation which lists not only what calibrations they can perform but their best accuracy least uncertainties of measurement As part of the process of gaining accreditation they need to submit to NATA for review their uncertainty estimations to justify the uncertainties that appear in their scope of accreditation and which they report on appropriate instruments

Codes of practice

Standards, codes, procedures and/or enterprise requirements

Data

Calculations

Statistical analysis

Records

Uncertainty components

Confidence level

Occupational health and safety (OHS) and environmental management requirements