Calibration Technology verlag moderne industrie Calibration Technology Basics, reference instruments for pressure and temperature, professional calibration

verlag moderne industrie Calibration Technology Basics, reference instruments for pressure and temperature, professional calibration Christian Elbert

This book was produced with the technical collaboration of WIKA Alexander Wiegand SE & Co. KG. Christian Elbert is head of the Calibration Technology Product Unit at WIKA in Klingenberg, Germany. He is a member of the board of directors of the German Calibration Service (DKD) and chairman of the associated Technical Committee for Pressure. His special thanks go to Danica Schwarzkopf for the expert support in the key topic of temperature and to the marketing team of André Habel Nunes. Translation: RKT Übersetzungs- und Dokumentations-GmbH, Schramberg © 2012 All rights reserved with Süddeutscher...

Contents Introduction 4 Traceability and calibration hierarchy Professional calibration Reference instruments Calibration characteristics Measurement uncertainty Trends 66 Technical terms The company behind this book

Every measuring instrument is subject to ageing as a result of mechanical, chemical or thermal stress and thus delivers measured values that change over time. This cannot be prevented, but it can be detected in good time by calibration. The Egyptians already knew this almost 5000 years ago. The workers calibrated their yardsticks by comparing them with a “royal cubit” (approx. 52.36 cm) made of stone and thus managed to achieve, for example, side lengths on the Cheops pyramid of 230.33 m which differ from each other by only about 0.05 per cent. In the process of calibration, the displayed value...

Introduction  5 Fig. 1: Accredited calibration laboratory for the measurement par­ameter “temperature” instructions, requirements of a quality assurance standard or in-house and customerspecific regulations. Calibration must also be carried out when the measuring instrument is used for the preparation of products which are subject to official supervision such as drugs or foodstuffs. As part of a survey of 100 management executives of international companies, the Nielsen Research Company established in 2008 that due to faulty calibrations, manufacturing companies were losing more than 1.7 million...

Fig. 2: Calibration of pressure measuring instruments with a portable calibrator amount of oxygen during a chemical reaction. The calibration of measuring instruments can sometimes also be relevant to safety: if pressure or temperature sensors (in the chemical industry, for example) do not provide correct values, the incorrect control of chemical processes may even result in a risk of explosion (Fig. 2). At the very least, the importance of calibration can be seen in everyday examples such as in household gas or water meters and in fuel gauges at petrol pumps. In this book, the basics of calibration...

Traceability and calibration hierarchy To be able to compare measuring results, they must be “traceable” to a national or inter­ national standard via a chain of comparative measurements. To this end, the displayed values of the measuring instrument used or a measurement standard are compared over one or several stages to this standard. At each of these stages, calibration with a standard previously calibrated with a higher-ranking standard is carried out. In accordance with the ranking order of the standards – from the working standard or factory standard and the reference standard to the national...

8  Traceability and calibration hierarchy Traceability in practice The German Calibration Service DKD (Deutscher Kalibrierdienst) designates the following as essential elements of traceability: • The chain of comparison must not be interrupted. • In each stage of the calibration chain, the measurement uncertainty must be known so that the total measurement uncertainty can be calculated. As a rule, a higher-ranking measuring instrument should have a measuring accuracy three to four times higher than the instrument calibrated by it. • Each stage of the calibration chain must be documented as must...

National metrological institutes  9 tatives of those 26 associated member states without full voting rights. National metrological institutes On a national level, institutes are responsible in most cases for metrology. They maintain the national standards to which all calibrated measuring instruments can be traced and ensure that these primary standards are comparable on an international level. In most countries, the top metrological institutes are state agencies or authorities. Thus, the national metrology institute of the Federal Republic of Germany PTB (Physikalisch Technische Bundesanstalt)...

10  Traceability and calibration hierarchy serve among other things as the basis for the time signal in radio clocks and watches (Fig. 4). As the national metrological institute, the PTB also has the legislative mandate to offer scientific and technical services in the area of calibration to science and commerce. For this, it uses a network of accredited institutions. Accredited calibration laboratories Accredited calibration laboratories often take on calibration as external service providers for those companies that do not have the required equipment themselves. However, they themselves can...

In-house calibration  11 exclusively on specialist grass-roots projects such as the development of standards and directives (Fig. 5). DAkkS carries out a complete evaluation of every accredited calibration laboratory every five years and also pays monitoring visits every 18 months, to ensure that the high demands of measuring processes are met. In addition to the described process monitoring of laboratories, there are also expert committees to ensure technical development and knowledge transfer. Since all European bodies that accredit calibration laboratories collaborate in the EA, the work procedures...