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Technical Guides are published by the Measurement Standards Laboratory to provide assistance with measurement techniques.

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Electrical and RF

Technical Guide 8 - Calibration of Stop-watches (PDF 180KB)

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 - Uncertainty Calculations for Remote Clocks (PDF 206KB)

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. This version is a draft for comment.

Technical Guide 27 Impedance (RLC) Standards (PDF 226KB)

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.  The guide applies to impedance standards used typically between 20 Hz and 1 MHz, but does not cover RF impedance standards.

Technical Guide 28 Phase and Sign Conventions for Energy Meters (PDF 171KB)

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 straight-forward 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°.  Different conventions are in use around the world and this guide describes the international conventions adopted by MSL for four quadrant metering, covering phase angles from −180° to +180°.

Technical Guide 31 - Using calibrated RF power sensors (PDF 175KB)

The measurement of power at radio and microwave frequencies using a calibrated power sensor is explained. Factors that can influence a measurement, such as mismatch, zero setting, noise and drift are discussed and a simple measurement model is developed which can be used to evaluate the measurement uncertainty. Consideration of some engineering units commonly encountered in manufacturer specifications is given and an example uncertainty calculation is provided.

Technical Guide 32 -   An accurate RF reference signal for testing power measuring instruments (PDF 158KB)

A simple method of providing an accurate RF reference signal for calibrating or testing power measuring instruments is described. A resistive power splitter and a pair of power sensors is used to improve the raw performance of a signal generator and to remove the undersirable effects of an arbitrary interconnecting network. For best results, the power splitter and one of the power sensors should be calibrated, but a traceable signal reference can still be obtained if only the power sensor has been calibrated. A simpler implementation of the technique can be used to monitor the performance of a suite of power measuring instruments over time.

Technical Guide 33Electricity Metering: Advice for Class B Approved Test Houses (PDF 573KB)

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. While the Code is clear on the need for Class B Approved Test Houses to manage measurement uncertainty, it can be difficult to interpret how this is done in practice.

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Photometry and Radiometry

Technical Guide 34 - Spectral Mismatch of Illuminance Meters (PDF 478)

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.

Mass and Pressure

Technical Guide 6 - Magnetic Effects in Weighing  (PDF 237KB)

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 - Calibrating Standard Weights  (PDF 475KB)

How to calibrate standard weights to a best accuracy of 1 part in 106. Suitable for weight calibration laboratories and for anyone using or calibrating balances.

Revised version with improved examples.

Technical Guide 12 - Assuring the Quality of Weighing Results  (PDF 206KB)

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.

NEW: Version 3, revised following user feedback and for consistency with Technical Guide 25.

Technical Guide 13 - Pressure Gauge Calibration  (PDF 352KB)

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 - Care and Use of a Deadweight Tester  (PDF 341KB)

Deadweight testers, also know 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.

This guide describes some simple procedures for the care and use of both gas and oil operated deadweight testers. Maintenance of the operating fluid and weights are covered along with procedures for regular performance testing of the instrument spin and fall rates.

Technical Guide 17 - Measuring Volume by Weighing Water  (PDF 427KB)

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.  A worked example is included.

Technical Guide 19 - Measuring Atmospheric Pressure with a Barometer  (PDF 595KB)

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 - Calibrating Balances (PDF 764KB)

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 & Weighing workshop, is focussed on electronic top-loading balances but applies to most modern weighing devices.

NEW: Version 4 with minor revisions.

Technical Guide 30 - Calibrating Piston Pipettes  (PDF 382KB)

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.  An example is included and a spreadsheet for the calculations is available on request.  For larger volumes, see MSL Technical Guide 17: Measuring volume by weighing water.

Technical Guide 36Calculating deadweight tester pressures  (PDF 241KB) (draft for comment )

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. In particular, guidance is given throughout on minimizing the effort required in calculating pressure and associated uncertainty. Several worked examples are included.

Temperature and Humidity

Technical Guide 1 - The Ice Point  (PDF 811KB)

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 - Infrared Thermometry Ice Point  (PDF 190KB)

A simple procedure for checking low temperature radiation thermometers at 0 ºC.

Technical Guide 3 - Uncertainties in the realisation of the SPRT subranges of ITS-90  (PDF 929KB)

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 BIPMs Consultative Committee on 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 - Icepoint Humidity Generator  (PDF 225KB)

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.  (This procedure makes use of an assembled saturator coil which is sold by MSL.  Click here for further information on this product.)

Technical Guide 5 - Using the Leeds & Northrup 8078 Bridge  (PDF 177KB)

For those who own a Leeds and Northrup 8078 resistance bridge, some tips on how to reduce the uncertainty in the readings.

Technical Guide 10 - A simple, narrow-band, thermistor thermometer  (PDF 231KB)

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 - Thermometer immersion and dry-block calibrators  (PDF 219KB)

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 - Making Sense of Thermocouples  (PDF 216KB)

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.

The purpose of this guide is to provide thermocouple users with a simple explanation of how thermocouples really work, their problems, and how to get the best from thermocouple measurements.

Technical Guide 15 - Correcting Radiation Thermometers for Reflection Errors  (PDF 208KB)

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.

The nomogram is applicable to both high-temperature and low-temperature thermometers, and enables operators to make corrections rapidly without the need for calculators or spreadsheets. It is also a useful tool for describing the impact of measurement uncertainty on temperatures corrected for reflection errors.

Technical Guide 18 - Resistance Measurement for Thermometry  (PDF 241KB)

Platinum resistance thermometers (PRT), also known as resistance-temperature detectors (RTD) and PT100 sensors (100 W platinum sensors), are a workhorse of both industrial and laboratory temperature measurement.

This guide describes the different measurement methods and indicate the advantages and disadvantages of each method. We begin with the simple dc methods typically used for industrial thermometry, and progress to the high-accuracy ac methods typically used in calibration laboratories.

Technical Guide 20 - Introduction to Temperature Control  (PDF 432KB)

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 - Using SPRT Calibration Certificates  (PDF 235KB)

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. For simplicity, the guide covers only the temperature ranges from 84 K to 660 °C, but the principles are the same for other Temperature ranges. Further detail can be found in the references. 

Technical Guide 22 - Calibration of Low-Temperature Infrared Thermometers  (PDF 327KB)

Blackbody Correction Spreadsheet

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.

Technical Guide 23 - Using Industrial Platinum Resistance Thermometers for Laboratory Thermometry  (PDF 595KB)

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 - Dew-Frost Error and the Chilled-Mirror Hygrometer  (PDF 246KB)

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 26Size-of-Source Effect in Infrared Thermometers  (PDF 670KB)

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  - Focus effect in Thermal Imagers  (PDF 400KB)

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 35Emissivity of Blackbody Cavities  (PDF 620KB)

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. The software can be requested by clicking here .