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Te Reo SI
The Measurement Standards Laboratory has prepared a translation of the BIPM’s Concise Summary of the SI in te reo Māori. We are making this resource available to support the teaching and learning of science in te reo Māori.
NZ Standard Time
MSL maintains New Zealand's time standard. You can find more information about the Time Standard here.
Technical Guides are published by the Measurement Standards Laboratory to provide assistance with measurement techniques and support best practice.
Technical Guide 8
How to obtain a traceable calibration of a stopwatch using the MSL talking clock. Includes details on the use of the clock and the uncertainty to be expected.
Technical Guide 9
This guide describes the uncertainty calibrations made for the measurements reported in the MSL time and frequency bulletins and recommends a method for users of the bulletins to calculate the uncertainty in the frequency of their remote oscillator.
Technical Guide 27
The ac measurement of resistors, inductors and capacitors (R, L and C) requires a clear understanding of exactly what is being measured. This guide aims to help owners of impedance standards make the best use of their equipment. Part I explains the information provided in a typical calibration certificate for an impedance standard and Part II gives general advice on using the impedance standards.
Technical Guide 28
The relationship between voltage and current in a system being metered can be expressed in several ways, e.g., by a power factor, a phase angle, or by describing the load as inductive or capacitive. This is straightforward when the system being metered is a net consumer of power and the phase angle is between +90° and −90°. It is less clear when the system is generating power and the phase angle exceeds 90°.
Technical Guide 33
The Electricity Authority has specified the requirements for electricity metering in Part 10 of the Electricity Industry Participation Code. Class B Approved Test Houses have many responsibilities placed on them by the code to assure the trustworthiness of the metering that they install and maintain. This guide offers practical advice on how to manage measurement uncertainty from design to installation without needing to carry out specialist in-depth uncertainty calculations.
Technical Guide 34
Illuminance meters are commonly used in industry to ensure lighting is at an appropriate level to demonstrate compliance for purposes such as health and safety and inspection. They can be purchased relatively cheaply but how good an instrument are they? This technical guide explains one of the most critical components of illuminance meter characteristics, the spectral mismatch, and the likely magnitude of error this effect can lead to in common commercial light meters.
Technical Guide 38
This guide provides information about reference materials that can be used when calibrating or checking the performance of a UV/visible light spectrophotometer. The known absorbance of reference materials at particular wavelengths can be used to validate the scale of absorbance (photometric accuracy), the wavelength accuracy of a spectrometer and identify stray light problems.
Technical Guide 6
An introduction to magnetic effects in weighing and how to avoid them. Includes a description of MSL’s facility for measuring the magnetic properties of weights. Suitable for anyone using or calibrating balances, or calibrating weights.
Technical Guide 7
How to calibrate standard weights to a best accuracy of 1 part per million. Suitable for weight calibration laboratories and for anyone using or calibrating balances.
Technical Guide 12
This technical guide covers quality assurance aspects of the use of electronic balances and other weighing devices, including calibration, in-service checks and acceptance criteria, control charts, and check weights.
Technical Guide 13
This technical guide outlines a method to calibrate a pressure gauge and calculate the uncertainty of the gauge corrections. The method is suitable for gauge calibration laboratories accredited to ISO 17205 and can be applied to any pressure gauge or transducer calibration.
Technical Guide 16
Deadweight testers, also known as pressure balances or piston gauges, are stable instruments, with long recalibration intervals, that can reliably generate pressures with a small uncertainty. To assure this stable behaviour between calibrations the deadweight tester has to be operated correctly and looked after well.
Technical Guide 17
This guide describes a method for measuring the volume of a vessel by weighing the water it can contain (or deliver). The method is suitable for vessels such as burettes and pipettes, and can also be applied to the calibration of water flowmeters. The guide covers the necessary calculations, measurement uncertainties with an emphasis on repeatability, and some practical details.
Technical Guide 19
This guide explains how to use a digital barometer to measure atmospheric pressure in a laboratory or industrial setting. It starts with a brief discussion of the atmosphere and then talks about barometers, their stability and calibration requirements, along with how to work out the uncertainty of an air pressure measurement.
Technical Guide 25
A method for calibrating balances is described in this technical guide. It includes pre-calibration steps, the measurements to be recorded and their analysis, the evaluation of measurement uncertainties and the reporting of results. This method, which is taught in the MSL Balances and Weighing workshop, is focused on electronic top-loading balances but applies to most modern weighing devices.
Technical Guide 30
This technical guide describes a method for calibrating both fixed volume and variable volume piston pipettes with volumes from below 1 µL to above 10 mL. The guide covers the necessary equipment, the method and how it relates to ISO Standards for piston pipettes, the necessary calculations and the measurement uncertainties. It also addresses the method uncertainty associated with calibrating pipettes to ISO 8655.
Technical Guide 36
This technical guide describes how to calculate pressures generated by a deadweight tester, or pressure balance, for use in calibrating pressure-measuring instruments. It is applicable to hydraulic and pneumatic deadweight testers that generate gauge pressure (including negative gauge pressure), where a relative uncertainty in pressure of 0.003 % (30 ppm) or greater is required.
Technical Guide 1
How to make a simple temperature reference at 0 °C accurate to 0.01 °C. Suitable for anyone using liquid-in-glass thermometers, thermocouples, thermistors or platinum resistance thermometers.
Technical Guide 2
A simple procedure for checking low-temperature radiation thermometers at 0 ºC.
Technical Guide 3
The MSL technical guide TG3: "Propagating uncertainties in the SPRT subranges of ITS-90" has been superceded by the more helpful document Uncertainties in the realisation of the SPRT subranges of ITS-90 published by the BIPM's Consultative Committee for Thermometry (BIPM, Interntional Bureau of Weights and Measures, www.bipm.org ). The guide explains all of the sources of uncertainty in the use and calibration of standard platinum resistance thermometers (SPRT), and gives the expressions for total uncertainty for a wide range of measurement senarios.
Technical Guide 4
How to construct a simple single point humidity generator using MSL Technical Guide 1 (The Ice Point) as the saturator temperature controller. Useful for routine spot checks of dew point meters and relative humidity hygrometers.
Technical Guide 5
For those who own a Leeds & Northrup 8078 resistance bridge, some tips on how to reduce the uncertainty in the readings.
Technical Guide 10
This technical guide describes a simple circuit that provides a voltage proportional to temperature difference. The circuit is linear within 0.1 ºC over ranges of up to ±10 ºC, capable of accuracies of a few millikelvin, and will resolve temperature differences below 50 K.
Technical Guide 11
This technical guide provides users with a simple method for assessing the quality of thermometer immersion in dry-block calibrators. Although the test method describes the testing of dry-block calibrators, it can also be used to assess the quality of immersion in any furnace, calibration bath, oven, etc.
Technical Guide 14
Thermocouples are the most widely used of all temperature sensors. The simplicity of two wires connected to a meter has an obvious appeal. However, when high confidence is required, thermocouples can be a liability. Unlike other temperature sensors, thermocouple faults are often not obvious and calibration of thermocouples can be a waste of time.
Technical Guide 15
Reflection errors occur in most practical applications of radiation thermometry. This guide describes the development of a simple graphical method (called a nomogram) for calculating reflection corrections, and gives instruction on its use.
Technical Guide 18
Platinum resistance thermometers (PRT), also known as resistance-temperature detectors (RTD) and PT100 sensors (100 Ω platinum sensors), are a workhorse of both industrial and laboratory temperature measurement.
Technical Guide 20
One of the most common reasons for measuring temperature is to control it. This applies not only to industrial processes but also to many laboratory tests and experiments. To the uninitiated, control systems seem to exhibit confusing and sometimes peculiar behaviour. The purpose of this guide is to help users understand the behaviour and to obtain the best performance from temperature controllers.
Technical Guide 21
Standard platinum resistance thermometer (SPRT) calibration certificates typically report measurements as resistance ratios with respect to the SPRT resistance at the triple point of water and give the uncertainties in these measured resistance ratios. This guide explains how to use the certificate with the SPRT to measure temperature, and how to calculate the uncertainty in the measured temperature caused by the calibration uncertainties.
Technical Guide 22
The advent of low-cost handheld infrared thermometers, which make non-contact measurements in the range –50 °C to 500 °C, has led to a proliferation of the thermometers in the food, building, and low-temperature processing industries. However, these instruments are not as simple to use as they first appear due to systematic effects related to emissivity, reflections, and the temperature of the thermometer itself. This guide explains how to calibrate low-temperature infrared thermometers and gives methods for correcting for the systematic effects.
TG22 Spreadsheet Download
In addition to Technical Guide 22, you can download the excel spread sheet to assist with your calculations.
Technical Guide 23
Industrial platinum resistance thermometers, also known as Pt100s or RTDs, are very widely used in industry where accuracies of 1 °C or better are required. With a little care, they can also be used to obtain accuracies of 0.01 °C; this guide explains how.
Technical Guide 24
Chilled mirror hygrometers provide accurate measurements of humidity as long as the state of the condensate (frost or dew) is known. Large errors are common when the mirror temperature lies between 0 °C and ‑25 °C, since the condensate can be frost or supercooled dew, or even a mixed state. This technical guide explains how to account for, and partially correct, the error in a chilled-mirror hygrometer measurement, when it is not possible to unambiguously identify the condensate.
Technical Guide 26
The accuracy of most handheld infrared thermometers is severely limited by a phenomenon known as the size-of-source effect (SSE), which arises from scattering and diffraction of radiation within the optical system of the device. The error caused by the SSE can be many times larger than the accuracy quoted in the device's specifications. This guide explains how a calibration laboratory can characterise the SSE and provide information on a calibration certificate to enable users to correct for the SSE and achieve the best accuracy in their measurements.
Technical Guide 29
Thermal imagers are being increasingly used quantitatively to make absolute temperature measurements, and thus require calibration by an accredited laboratory. However, calibration of these instruments is complicated by the fact that, for some thermal imagers, the radiometric accuracy is not retained when the focusing lens is adjusted. This impacts on the user, as the temperature readings will only be accurate if the focus setting matches that used by the calibration laboratory. This technical guide describes the origin of this focus effect, and gives advice to the calibration laboratory on how to identify whether the problem exists and what steps to take to deal with it if it does.
Technical Guide 35
Blackbodies are commonly used as a transfer medium for the calibration of radiation thermometers. While the emissivity of such cavities is generally close to 1, for high-accuracy calibrations it is important that the actual emissivity is known. This emissivity will depend on the geometry of the cavity, the emissivity of the material it is made from, and the field of view of the radiation thermometer viewing the cavity. Additionally, the emissivity will vary with any temperature non-uniformities that exist along the cavity length. Methods to calculate the cavity emissivity are highly mathematical and require sophisticated computer programs to implement them. This guide provides a brief overview on how to calculate cavity emissivity and is accompanied by a software application (Microsoft Windows compatible) that implements the method and illustrates the concepts graphically.
Technical Guide 35
In addition to the Technical Guide download providing a brief overview on how to calculate cavity emissivity, it is accompanied by a software application (Microsoft Windows compatible) that implements the method and illustrates the concepts graphically. Click Order Now to connect to our contact form and request the software for this TG.
Technical Guide 39
This technical guide provides users of noble-metal thermocouples with the knowledge required to ensure both good accuracy and longevity of reference thermocouples. The guide focuses on alumina-sheathed bare-wire noble-metal thermocouples of Types B, R, and S. It describes how to prevent contamination, re-annealing, calibration intervals, and reversible causes of drift.
Technical Guide 40
This technical guide describes two methods for calculating the values for corrections and uncertainties between entries reported in a calibration certificate, and gives advice on the required conditions for obtaining meaningful interpolated values.
Technical Guide 41
This technical guide describes an electrical-analogue model of Peltier devices as an aid for the design of small refrigeration and temperature control systems. The model is easily incorporated into spreadsheets, where the performance of a system under different operating conditions can be explored easily.
MSL staff have written technical books to assist with measurement practice. Currently available books are:
Authors: J V Nicholas and D R White
This book is a little different to most other measurement texts; it explains what goes wrong with temperature measurements, how to recognise when something is wrong, and how to fix it. Sections include operating principles, sources of error, choosing and using instruments, and calibration methods for each type of thermometer. It also provides the background material on measurement, uncertainty, calibration, accreditation, and the international measurement system, to support the understanding of the instruments and their use in making traceable temperature measurements.
Author: Peter Saunders
This tutorial text provides an introduction to the subject of radiation thermometry, focusing on sources of measurement error and giving advice on methods for minimizing or eliminating these errors. Topics covered include: blackbody radiation, emissivity, reflection errors, and atmospheric absorption and emission; commonly used radiation thermometer types; uncertainty calculation; and procedures for in-house calibration of radiation thermometers. Included is a chapter containing detailed measurement examples for a variety of furnace types and operating conditions found in the methanol, ammonia, and refining industries.
Authors: B D Hall and D R White
This introduction to measurement uncertainty is intended for metrology professionals working in calibration laboratories and metrology institutes, as well as students in tertiary-level science and engineering programmes. The subject matter is presented with an emphasis on developing models of the physical measurement process. The level of mathematics and statistics used is basic and is typically covered by high school studies.
Software for Data Processing
The Measurement Standards Laboratory has developed several tools for data-processing that automatically propagate measurement uncertainty.
These software tools are based on the notion of an uncertain number, an abstract data-type that encapsulates a value and an associated uncertainty. Uncertain-number data processing simultaneously evaluates the value and an associated uncertainty.
The MSL Uncertainty Calculator is an Excel spreadsheet that provides an uncertainty table suitable for summarising an uncertainty calculation. It automatically highlights the components that contribute significantly to the total uncertainty. Each component is entered in the table using one of three convenient ways of expressing degrees of freedom. The total uncertainty is calculated together with the effective degrees of freedom and coverage factor. This tool is recommended when the equation for propagating uncertainty can easily be reduced to a sum of uncertainty terms in a common unit (e.g all in volt or all in milliohm). If offers the convenience of being able to take input data from other parts of the spreadsheet including linking the input for one uncertainty component to the output of another uncertainty table. The calculation in the table can be repeated for multiple calibration points by using Excel’s Data Table feature under the What-If Analysis option in the Data Tools group. The spreadsheet should first be downloaded and saved locally before opening and clicking on ‘Enable Content’ to allow the macros to operate (it relies on Visual BASIC functions). The template on the ‘Calculator’ sheet is protected so that only the cells for data entry can be modified. This protection is for convenience only and the sheet can be unprotected by right-clicking the sheet tab and choosing ‘Unprotect sheet …’ with no need for a password.
The GUM Tree Calculator (GTC) is a data processing tool with full support for uncertainty calculations involving real and complex quantities. GTC is a stand-alone executable for Windows. It can handle instructions typed at the command prompt or evaluate text files containing instructions. It is closely integrated with the Windows Explorer for ease of use and does not depend on any other software. GTC can be used on small problems, or as a sophisticated data processing tool for more demanding tasks. Instructions use the Python programming language. An integrated development environment, with syntax highlighting and on-line help, is distributed with the calculator.
An Excel add-in available for real-valued quantities is available called SGUM. SGUM provides a suite of worksheet functions that can be used to manipulate uncertain numbers referenced to Excel cells. Documentation and examples are provided. Important note about Office 2007 and 2010: The SGUM add-in was developed before the release of Office 2007. We believe that spreadsheets written with earlier Excel versions still execute correctly when opened with Excel 2007 and 2010. However, SGUM will not work properly if worksheets exceed the size limits imposed by earlier Excel versions, or use features not supported in earlier versions