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CALIBRATION HANDBOOK OF MEASURING INSTRUMENTS
Alessandro Brunelli
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FIRST EDITION Notice The information presented in this publication is for the general education of the reader. Because neither the author nor the publisher has any control over the use of the information by the reader, both the author and the publisher disclaim any and all liability of any kind arising out of such use. The reader is expected to exercise sound professional judgment in using any of the information presented in a particular application. Additionally, neither the author nor the publisher has investigated or considered the effect of any patents on the ability of the reader to use any of the information in a particular application. The reader is responsible for reviewing any possible patents that may affect any particular use of the information presented. Any references to commercial products in the work are cited as examples only. Neither the author nor the publisher endorses any referenced commercial product. Any trademarks or tradenames referenced belong to the respective owner of the mark or name. Neither the author nor the publisher makes any representation regarding the availability of any referenced commercial product at any time. The manufacturer’s instructions on the use of any commercial product must be followed at all times, even if in conflict with the information in this publication. Copyright © 2017 International Society of Automation (ISA) All rights reserved. Printed in the United States of America. 10 9 8 7 6 5 4 3 2 ISBN: 978-1-945541-57-5 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher. ISA 67 T. W. Alexander Drive P.O. Box 12277 Research Triangle Park, NC 27709 Library of Congress Cataloging-in-Publication Data in process
Disclaimer: Neither the Author nor the Publisher are responsible for the results obtained by the use or possible misuse of the spreadsheets used in this handbook or on the CD. The literary property and all rights of the series of ISA Publications are reserved to the Publisher. The graphical structure, the editorial content, and illustrations in this volume cannot be reported, translated, or stored, even partially, without the permission of the Publisher.
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TABLE OF CONTENTS Preface
5
Part I – Requirements and General Guidelines for Management of Instruments and Measurements
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1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
International System of Units (SI) International Calibration System (ILAC) European Calibration System (EA) Traceability and Compatibility of the Measures Measurement Uncertainty Calibration of Measuring Instruments Requirements in the Quality Management Systems ISO 9001, 14001, 16949, and EN 9100 Requirements in the Measurement Management Systems ISO 10012 Criteria for Instrument Selection in Relation to the Measurement Requirements Criteria for Conformity Evaluation of the Measuring Instrument Notes to Legislative Requirements for Initial and Periodic Calibration Checks Notes to Technical Requirements on Document Management According to FDA 21 CFR Part 11
9 15 17 21 23 29 35 39 49 53 59 65
Part II – Requirements and Criteria for the Management and Calibration of Measuring Instruments
71
1.
73
Physical Quantities 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
2.
3.
4.
5.
Pressure Flow Level Temperature Humidity Viscosity Density Mass
75 87 113 119 143 153 163 175
Chemicals for Liquids
191
2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8
pH Redox Turbidity Conductivity Dissolved Oxygen Dissolved Ions Colorimetry Refractometry
193 199 205 211 217 223 229 235
Chemicals for Gases
241
3.1 3.2 3.3 3.4 3.5 3.6
Infrared Analyzers Ultraviolet Analyzers Comburent Gases Combustible Gases Chromatography Spectrometry
243 247 251 255 261 267
Mechanical Quantities
273
4.1 4.2 4.3 4.4 4.5 4.6
275 287 291 295 299 305
Length Force Torque Velocity (and Rotation) Vibration (and Acceleration) Sound and Noise
Electrical Quantities
315
5.1 5.2 5.3 5.4 5.5 5.6
317 321 325 329 333 337
Indicators Oscilloscopes Transformers Energy Meters Clamp Meters Multimeters
Analytical Index for Acronyms, Terms, and Instruments to be Calibrated Copyrighted Material
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Dedication To my learned readers, this book combines my so-called HME versus HMS, or How Much is Enough versus How Much it Serves, in compliance with metrological requirements imposed by the reference normatives for calibrating and confirming measuring instruments. In loving memory of my beloved wife, Romanella, who always encouraged me to give the best of myself.
PREFACE The Calibration Handbook of Measuring Instruments was commissioned by the Association for the Instrumentation, Control and Automation Company in Italy (GISI) to meet the needs of instrumentation technicians, who strongly requested a handbook that clearly and completely explained calibration procedures and periodic metrological confirmation for all the instruments for measurement in industrial applications: chemical, petrochemical, pharmaceutical, food, energy, and custody and transfer for water, oil, and gas. Published first in the Italian language in 2012, it was outstandingly successful; many companies, professionals, and training centers have found this calibration handbook a valuable reference.
FOREWORD The handbook is mainly dedicated to operators involved in the verification and calibration of measuring instruments used in ISO 9001 – Quality management systems, ISO 14001 – Environment applications, ISO 16949 – Automotive industry, and EN 9100 – Aviation industry to be a reference and consultation handbook in the main topics for the assurance and management of industrial process measurement, such as: • • • •
The general concepts for managing the measurement equipment according to ISO 10012 concerning the management system of instruments and measurements The ability of the instrument to perform accurate measurements, by controlling the drift to maintain the quality of the measurement process The criteria and procedures for acceptance, management, and verification of the calibration of the main industrial measuring instruments The provisions of law and regulations for production and the European marking, CE, of metrological instruments used in commercial transactions and for their periodic verification
The handbook consists of two main parts: •
•
Part I illustrates the International System of Units (SI) and the international, European, and national calibration services (ILAC, EA, and others) and then the performance requirements of the instruments for measuring and the criteria for assessing the traceability and uncertainty of the measurements. It also covers the technical and regulatory requirements relating to the management of instruments and measurements. Part II describes the problems of calibration, verification, and metrological confirmation for the main families of instruments for measuring physical, chemical, mechanical, and electrical quantities. Then, for each quantity, it describes the specific concepts of the measure and the main reference standards, and then presents the most common types of instruments, simple calibration procedures, and metrological confirmation. This is accompanied by the format for collecting and processing experimental data, suitable for recording and editing the calibration report of metrological confirmation.
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GENERAL GUIDELINES
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For the most common measurement instruments, it is possible to determine the best practices for calibration procedures suitable for industrial applications, with procedures harmonized on the following points: • • • • • • • • •
Scope and purpose Identification and classification Normative references Ambient conditions Initial checks Calibration method Calibration verification Calibration results Metrological confirmation
Practical report templates useful for recording both the recorded instrument data and the experimental calibration data, to evaluate the conformity of the instrument, are available on the enclosed CD for practical usage. The report templates are reported in “white” on the enclosed CD for a practice specific use. Furthermore, the CD contains various spreadsheets in Excel (Reports Calibration) that automatically calculate errors and the relative uncertainty of measurement. They directly determine the compliance of the calibrated instrument according to the two methods mentioned in this calibration handbook: as a practical method, according to the error approach, or an analytical method, according to the uncertainty approach. Therefore, once again, the author aims to develop and promote the culture of instrumentation in its metrological and application aspects, currently the cornerstone of a company’s production as traceability and compatibility ensure measurements in the global market.
ABOUT THE AUTHOR Alessandro Brunelli has worked for more than 40 years in the field of training and certification in industrial instrumentation at an experimental laboratory. He graduated from the Higher Institute of Industrial Technology Mechanical of the Polytechnic (University) of Milan in 1974 and later became a professor of mechanical and thermal measurement at the Polytechnic of Milan. As a technologist, Brunelli participates in the activities of National, European, and International standardization for mechanical and electronic equipment. He is responsible for the Italian National Unification (UNI) commission on “Metrology of Pressure and Temperature” and is secretary of the technical committee Italian Electrotechnical Committee (CEI) on “Industrial-Processes Measurement, Control and Automation.” During his career, Brunelli published many papers in the areas of measurement and automation of industrial processes. He published two monographs relating to humidity and flow measurement, a series of five volumes on measurement and control in industrial applications, a specific volume titled Industrial Measurements: Physical & Mechanical, and a two-volume Instrumentation Handbook series.
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PART I
Requirements and General Guidelines for Management of Instruments and Measurements 1. International System of Units (SI) 2. International Calibration System (ILAC) 3. European Calibration System (EA) 4. Traceability and Compatibility of the Measures 5. Measurement Uncertainty 6. Calibration of Measuring Instruments 7. Technical Requirements in Quality Management Systems ISO 9001, 14001, 16949, and EN 9100 8. Technical Requirements in Measurement Management Systems ISO 10012 9. Criteria for Instrument Selection in Relation to the Measurement Requirements 10. Criteria for Conformity Evaluation of the Measuring Instruments 11. Notes to Legislative Requirements on Initial and Periodic Calibration Checks 12. Notes to Technical Requirements on Document Management according to FDA 21 CFR Part 11
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1
International System of Units (SI)1
1.1
Introduction
INTERNATIONAL SYSTEM OF UNITS (SI)
The International System of Units (in French: Système International d’unité), abbreviated SI, is the international reference system for expressing measurement results all over the world. The International System was established in 1960 as a result of the Metre Convention of 1875, which sought to coordinate all metrological activities at all levels: • •
Scientific and diplomatic International and national
It did this through the General Conference on Weights and Measures (Conférence Générale des Poids et Mesures [CGPM]), which was formed by the delegates of the member states to the Metre Convention and still has these tasks (see figure 1-1): • • • •
Discuss and promote the necessary measures to spread and refine the SI system Recognize the results of new fundamental metrological determinations Issue scientific resolutions of international scope Approve the definition of the SI units
The CGPM uses the work of the International Committee for Weights and Measures (Comité International des Poids et Mesures [CIPM]), composed of members appointed by the same CGPM. Their task is to carry out the decisions of the CGPM and oversee the activities of the International Bureau of Weights and Measures (Bureau International des Poids et Mesures [BIPM]). This latter institution is an international metrological laboratory based in Sèvres near Paris. It is the permanent scientific body of the CGPM and has the following tasks: • • •
Preserve the international prototypes of measurement standards Carry out and coordinate the determination of fundamental physical constants Make the necessary comparisons to ensure the uniformity of international measures
The units, terminology, and International System recommendations are established by the General Conference of Weights and Measures, the diplomatic body that is connected with the BIPM. The International System of quantities and units has thus developed over time: • • • • •
1889: the “MKS system” with only three units (meter, kilogram, second), approved by the first CGPM 1935: the “MKSΩ system” with a fourth unit (ohm) dedicated to electrical resistance, on the proposal of the Italian physicist Giovanni Giorgi 1946: the “MKSA system” with a variation of the fourth unit: ampere electric current, based on the Giorgi proposal and therefore also commonly called the “Giorgi system” 1954: the “SI system” with the addition of kelvin and candela, approved by the 10th CGPM 1971: the “SI system” included a seventh unit, the mole, approved by the 14th CGPM
Therefore, currently the International System: • • •
1.
Is based on seven fundamental quantities (with the respective units of measurement) (see table 1-1) Is made up of other so-called derived quantities (and their units) (see table 1-2 for the variables that have proper names and table 1-3 for other units.) Includes prefixes to identify the different sizes of the various units of measurement (see table 1-4)
The measurement units of the International System (SI) are currently regulated by the International Standards ISO/IEC 80000 series, replacing the previous standard ISO 31 and IEC 60027 series.
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GENERAL GUIDELINES
The International System is therefore a coherent system in that its magnitudes and derived units are derived as a product of magnitudes and fundamental units.
METRE CONVENTION
CGPM Diplomatic Level Technical Level
CIPM
ADVISORY COMMITTEES (quantities of competence)
1 – 2 – 3 – 4 – 5 – 6 – 7 – 8 – 9 – 10 – i i
Electricity and Magnetism Photometry and Radiometry Thermometry Length Time and Frequency Ionizing Radiation Units of Measurement Mass and Related Quantities Quantities of Substance Acoustics, Ultrasound, and Vibration
NATIONAL LABORATORY CGPM = Conférence Génerale des Poids et Mesures (General Conference of Weights and Measures) CIPM = Comité International des Poids et Mesures (International Committee of Weights and Measures) BIPM = Bureau International des Poids et Mesures (International Bureau of Weights and Measures) Figure 1-1. International Organization of Metrology
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BIPM
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1.2
INTERNATIONAL SYSTEM OF UNITS (SI)
Writing Rules Used in the International System
To standardize the writing and avoid misinterpretation, the SI provides some rules for writing units of measurement and their symbols: a) Units writing A unit of measure should be written: • •
In full and without accents or diacritical marks if it is introduced in a discursive text (e.g., leakage current of a few milliamperes and not a few mA) With the symbol if included in a formulation with quantitative rather than qualitative value (e.g., 10 mA and not 10 milliamperes)
b) Symbols writing Units of measurement symbols are identified as follows: • •
With a small letter, if the unit is derived from the name of a unit (e.g., m for meter, cd for candela) With a capital letter, if the unit is derived from the name of a person (e.g., A for Ampere, V for Volta, W for Watt)
The only exception is for liter, where both the symbols l and L are acceptable. c) Quantities writing Regarding quantities detected or identified by units of measure, SI symbols: • • • •
Should never be followed by a period (e.g., write 10 mm and not 10 mm.) Should be placed after the numeric value (e.g., write 10 mm and not mm 10) Must be separated from the numeric value by a space (e.g., write 10 mm and not 10mm) Can be derived quantities written without spaces or interposed by “.” or “/” (e.g., Nm or N.m, ms-2 or m/s2)
d) Numbers writing Finally, regarding separating the numbers of the quantity values: • •
Use a space to separate them with the whole numbers in groups of three (no points or commas); for example, 1 000 000 and not 1.000.000 or 1,000,000. Use a comma as the separator between the whole numbers and decimal ones, except for using the decimal point in English-language texts (CGPM of 2003).
The SI should be used in each country. In some of them, such as in Italy, their use is mandatory, in compliance with the EEC Council Directive 18 October 1971 (71/1354/ EEC), as amended on 27 July 1976 (76/770/EEC). Its use is mandatory in drafting acts and documents with legal value, and therefore the failure to comply with the above rules of writing could invalidate such documents.
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CALIBRATION OF MEASURING INSTRUMENTS
6
Calibration of Measuring Instruments
6.1
Introduction
The control of measuring instruments, namely: • •
Measuring equipment in the ISO 9001 – Quality management systems Surveillance equipment in the ISO 14001 – Environmental management systems
ensures, where necessary for valid results, that the measuring instruments are: • •
Calibrated and verified, at specified intervals or prior to use, against measurement standards traceable to international or national measurement standards. Where no such standards exist, they must be registered with the criteria used for calibration or verification. Adjusted or regulated again, when necessary.
Therefore, all management systems provide the initial calibration and any periodic “adjustment or metrological confirmation” (according to ISO 10012 – Measurement management systems) of the measuring instruments to validate the various measurement processes to ensure proper traceability of measurements to the International System (SI) (for terminology, see table 6-1).
6.2
General Calibration Conditions
To correctly perform a calibration, one must have infrastructure, means, methods and procedures, and appropriate staff, or possess the four fundamental pillars: Ambient Conditions If the measurement ambient is industrial, it is appropriate that the measures are carried out within these maximum limits: • •
Temperature Relative humidity
: 20 ± 5°C (or 25 ± 10°C) : 50 ± 25%
This contains the thermal drift of the standard and calibration instruments. If, however, the measurement is made in a laboratory, it is appropriate that the measures are carried out in controlled conditions, within these maximum limits: • •
Temperature Relative humidity
: 20 ± 2°C for mechanical measurements, 23 ± 3°C for electrical measurements : 50 ± 10% (or ± 20%)
This gives better uncertainty, and therefore traceability, of the measuring process. Measurement Equipment Use appropriate equipment for the measuring ranges and the desired levels of uncertainty, traceable to the SI units (see point 1) by: • •
National calibration laboratories (NCL): o European cooperation for Accreditation (EA) (or extra-European) o International Laboratory Accreditation Cooperation (ILAC) National metrological institutes (NMI)
The reference standard instrument should still have a measurement uncertainty of typically better than one-third of the nominal uncertainty of the calibrated instrument (see point 10).
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GENERAL GUIDELINES
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Technical Personnel Technical personnel should be specifically trained and operating under the technical and management procedures regarding the quality manual of the company or the laboratory. Operating Procedures The operating calibration procedures should be specifically drawn up: • •
For each type of provided measurement For each type of instrumentation with respect to any applicable normatives
In the absence of specific reference normatives, it is good practice to follow the generic operating procedures described in table 6-1.
6.3
Generic Operational Procedures3
Among the various international normatives available in the field of instrumentation, reference is made hereinafter to IEC 61298 concerning the methods and procedures to evaluate process instrumentation. It provides for the accuracy determination, namely the error indication, of industrial measurement instrumentation (i.e., pressure, flow, level, temperature). There are essentially two main procedures: calibration and verification.
6.3.1 Calibration Procedure (or Initial Characterization) This is applicable to new instrumentation, and typically also to the standard instrumentation. This first procedure consists initially in performing three full excursions of the measuring signal up and down, and then follow this methodology: a. With input signal of 0%, adjust the initial scale of the instrument being calibrated. b. With input signal equal to 100%, adjust the full scale of the instrument being calibrated. c. Return the input signal to 0%, and check the instrument’s output signal. If this error is more than one-quarter error of the nominal value specified by the manufacturer or the user of the instrument, readjust the initial scale to fall within the tolerance above. d. Return the input signal to 100% and check the instrument’s output signal. If this error is more than one-quarter error of the nominal value specified by the manufacturer or the user of the instrument, readjust the full scale up to fall within the tolerance above. e. Repeat steps (c) and (d) until the initial and the full scale are within the tolerance of one-quarter specified nominal value. f. Perform the measuring cycle every 20–25% by detecting the instrument output signal, after a sufficient period of stabilization, in the following modes: • 20/40/60/80/100/80/60/40/20/0% • 25/50/75/100/75/50/25/0% Usually the complete measuring cycle up and down is expected for instrumentation using sensors at “elastic deformation” (and therefore with displacement: type dial manometers or dilatation thermometers) while a measuring cycle is carried out up (preferentially) or down for the instrumentation using sensors at the “solid state” (and thus using sensors without moving, electric type: digital multimeters and sensor thermoelectrics as resistance thermometers and thermocouples that don’t have inherent hysteresis phenomena).
3. 30
See also table 6-3
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CALIBRATION OF MEASURING INSTRUMENTS
Table 6-1. Main Terms Relating to Measurement Processes (ISO-VIM) Measurand: Quantity intended to be measured. Measurement: Process of experimentally obtaining one or more quantity values that can reasonably be attributed to a quantity. Error: Measured quantity value minus a reference quantity value. Accuracy: Closeness of agreement between a measured quantity value and a true quantity value of a measurand. Accuracy class: Class of measuring instruments or measuring systems that meet stated metrological requirements that are intended to keep measurement errors or instrumental measurement uncertainties within specified limits under specified operating conditions. Measurement accuracy: Closeness of agreement between a measured quantity value and a true quantity value of a measurand. International measurement standard: Measurement standard recognized by signatories to an international agreement and intended to serve worldwide. Reference measurement standard: Measurement standard designated for the calibration of other measurement standards for quantities of a given kind in a given organization or at a given location. Traveling measurement standard: Measurement standard, sometimes of special construction, intended for transport between different locations. Primary measurement standard: Measurement standard established using a primary reference measurement procedure, or created as an artifact, chosen by convention. Secondary measurement standard: Measurement standard established through calibration with respect to a primary measurement standard for a quantity of the same kind. Material measure: Measuring instrument reproducing or supplying, in a permanent manner during its use, quantities of one or more given kinds, each with an assigned quantity value. Reference material: Material, sufficiently homogeneous and stable with reference to specified properties, that has been established to be fit for its intended use in measurement or in examination of nominal properties. Measuring instrument: Device used for making measurements, alone or in conjunction with one or more supplementary devices. Metrological traceability: Property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty (see point 4.2). Metrological traceability chain: Sequence of measurement standards and calibrations used to relate a measurement result to a reference (see figure 4-1). Measurement uncertainty: Nonnegative parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the information used (for more details, see point 5 and table 5-1). Measurement method: Generic description of a logical organization of operations used in a measurement. Measurement methods may be qualified in various ways, such as: • •
Direct measurement method (e.g., manometer calibration with pressure balance) Indirect measurement method (e.g., manometer calibration with reference manometer)
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6.3.2 Verification Procedure (or Metrological Confirmation) The verification procedure is applicable to instrumentation in operation and therefore particularly suitable for the metrological confirmation of instrumentation in production processes. This second procedure also begins by executing three complete excursions of the measurement signal up and down; expected, however, only for mechanical-type instrumentation with displacement sensors. Subsequently, however, it only provides for the execution of the measuring cycle according to the method described in the preceding calibration procedure in step (f), since the aim of this procedure is to be seen during the metrological confirmation in subsequent times, if the error or uncertainty detected on the instrumentation of the production process is better than the limit expected for the “correct control” of the quality of the “measurement process.”
6.4
General Index of the Operational Procedures
Each operating procedure should be structured on the following points: 1. 2. 3. 4. 5. 6. 7. 8. 9.
Scope and purpose Identification and classification Normative references Ambient conditions Initial checks Calibration method Calibration verification Calibration results Metrological confirmation
The last point is required only in the case of procedures aimed at metrological confirmation.
6.5
General Index of the Calibration Report or Metrological Confirmation4
Following the calibration procedure or metrological confirmation, note and record the results and further elaborations, on a specific report that must contain at least the following information (see also ISO 10012): a. b. c. d. e. f. g. h. i. j. k. l.
Applicant (if applicable) Subject of the report (calibration or confirmation) Name or symbol of the instrument Reference standards and calibration certificates Procedures used Ambient conditions Reference values and measured errors Measurement uncertainty resulting Uncertainties of measurement requests The result of the declaration of conformity Execution date of the calibration or confirmation and date of the next confirmation Signature executor and the person responsible for the calibration or confirmation reports
For an example of procedures and reports of calibration or confirmation, see Part II.
4. 32
See also table 6-3
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CALIBRATION OF MEASURING INSTRUMENTS
6.6 Examination of Internal or External Calibration Feasibility of Measuring Instruments In order to properly calibrate instruments at home, in the first analysis, a company must have at least the following elements: • • • • •
A metrological chain, composed of at least one standard, for each type of instrument Any ancillary equipment, according to requirements (e.g., generators, furnaces) A local or a work area with suitable environmental conditions to the needs Designed and tested calibration procedures Trained and qualified personnel
All this represents a significant cost that can be justified by the amount of equipment to be calibrated, and therefore a cost/benefit analysis on the convenience of equipping a laboratory or on delegating calibration to an external laboratory must be done. Generally, for instruments such as manometers, thermometers, hygrometers, micrometers, calipers, and analog and digital multimeters, internal calibration is convenient when the group of instruments is referable to a single reference standard that exceeds at least 10 units. For lesser quantities, it may be more beneficial to contact an external laboratory. These figures and tables provide examples: • • •
Figure 6-1 shows a possible suitable framework to analyze the possibility of internal or external calibration. Table 6-2 shows the possible advantages and disadvantages of internal and external calibration. Table 6-3 shows some considerations for the procedures and results of related expressions.
DEFINITION OF THE QUALITY PLAN AND PRODUCT CHARACTERISTICS TO CHECK
IDENTIFICATION OF THE INSTRUMENTS THAT MUST BE CALIBRATED
YES
Calibration in the internal metrological laboratory
NOT
Calibration inside the Fompany ?
YES
Accredited Falibration Fenter?
Calibration at a Falibration Fenter: ILAC, EA, etc.
Qualify the Falibration Fenter NOT
Calibration at a qualified outside center
RESULTS CONTROL (MADE IN COMPANY) x
check that the results are within acceptance criteria
x
indicate the controller (Oaboratory or Tuality Uesponsible)
Figure 6-1. Sequential Scheme of Analysis for Choice of the Internal or External Calibration
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Table 6-2. Evaluation of the Advantages and Disadvantages of Internal and External Calibration Evaluation
Internal Calibration
External Calibration
Purchase costs of the reference standards Calibration of the reference standards Cost for personnel training Cost of procedures Locations for the laboratory Unavailability time of the instrument Costs to ship the instrument Possibility of damage during transport Possibility of immediate verifications Possibility of checks on the processes
Yes Yes Yes Yes Yes hour No No Yes Yes
No No No No No 2-30 days Yes Yes No No
Laboratory qualification
No
Yes, if it is not ILAC
Table 6-3. Common Terms Relating Procedures and Results of Expressions (ISO and Others) Operational procedure: Procedure that tends to define and characterize the metrological characteristics of an instrument, or to adjust or restore the functional and metrological characteristics of an instrument or a measuring apparatus. Note: The operational procedure should be specified: measurement, calibration, verification, etc. Measurement procedure: Detailed description of a measurement according to one or more measurement principles and to a given measurement method, based on a measurement model and including any calculation to obtain measurement results. Calibration procedure: Procedure performed under the specified conditions that establishes the relationship between the values of a quantity related with the associated measurement uncertainties and the reading of a measuring instrument, which can be expressed by means of a table or calibration curve, usable for the eventual measurement results correction conducted with the calibrated instrument. Note: This procedure should not be confused with the procedures described below! Verification procedure: Operation that provides evidence that an instrument meets the specified requirements. (Note: This procedure is normally used in the sense of “metrological confirmation.”) Adjustment procedure: Set of operations carried out (of zero and span adjustments) on an instrument so that it provides prescribed information (specified) in relation to the measured value. Note: This procedure is commonly used before the “calibration procedure.” Maintenance procedure: Process conducted in a systematic manner or as necessary to return the instrument to its normal functional conditions. (Note: This procedure is performed periodically according to the manufacturer’s specifications.) Calibration curve: Expression of the relation between indication and corresponding measured quantity value (and relative measurement uncertainty). Calibration certificate: Document that provides a calibration curve of an instrument, issued by a laboratory or an accredited organization (e.g., accredited ISO 17025: ILAC, EA). Calibration report: Document that provides a calibration curve of an instrument, issued by a laboratory or an organization that is not accredited for calibration (e.g., accredited only ISO 9001). As found report/certificate: Document that provides a calibration curve for an instrument, as found, or as presented to the calibration or metrological confirmation. As left report/certificate: Document that provides a calibration curve for an instrument, as left, or after making an adjustment procedure (because it was found out of the specifications).
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REQUIREMENTS IN THE QUALITY MANAGEMENT SYSTEMS ISO 9001, 14001, 16949, AND EN 9100
7
Requirements in the Quality Management Systems ISO 9001, 14001, 16949, and EN 9100
7.1
Introduction
The main international normative requirements on calibration of measuring instruments in the quality management systems, in the environmental management system, and in the automotive and aeronautic industries are provided.
7.2
ISO 9001 Requirements
ISO 9001:2015 on quality management systems (QMS) states in point 7.1.5:
7.1.5 Monitoring and measuring resources 7.1.5.1 General The organization shall determine and provide the resources needed to ensure valid and reliable results when monitoring or measuring is used to verify the conformity of products and services to requirements. The organization shall ensure that the resources provided: a) Are suitable for the specific type of monitoring and measurement activities being undertaken b) Are maintained to ensure their continuing fitness for their purpose The organization shall retain appropriate documented information as evidence of fitness for the purpose of monitoring and measurement resources. 7.1.5.2 Measurement traceability When measurement traceability is a requirement, or is considered by the organization to be an essential part of providing confidence in the validity of measurement results, measuring equipment shall be: a) Calibrated or verified, or both, at specified intervals, or prior to use, against measurement standards traceable to international or national measurement standards; when no such standards exist, the basis used for calibration or verification shall be retained as documented information b) Identified in order to determine their status c) Safeguarded from adjustments, damage, or deterioration that would invalidate the calibration status and subsequent measurement results The organization shall determine if the validity of previous measurement results has been adversely affected when measuring equipment is found to be unfit for its intended purpose, and shall take appropriate action as necessary.
7.3
ISO 14001 Requirements
ISO 14001:2015 on environmental management systems (EMS) states in point 9.1.1:
9.1 Monitoring, measurement, analysis, and evaluation 9.1.1 General The organization shall monitor, measure, analyze, and evaluate its environmental performance. The organization shall determine: a) What needs to be monitored and measured b) The methods for monitoring, measurement, analysis, and evaluation, as applicable, to ensure valid results c) The criteria by which the organization will evaluate its environmental performance, and appropriate indicators d) When the monitoring and measuring shall be performed e) When the results from monitoring and measurement shall be analyzed and evaluated
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Part II
Requirements and Criteria for the Management and Calibration of Measuring Instruments Part II describes the requirements and operating procedures for the management and calibration of measuring instruments for the following measurement quantities: 1.0 Physical quantities: Pressure, flow, level, temperature, etc. 2.0 Chemicals for liquids: pH, redox, turbidity, conductivity, etc. 3.0 Chemicals for gases: Infrareds, ultraviolets, gas chromatographs, etc. 4.0 Mechanical quantities: Length, speed, acceleration, etc. 5.0 Electrical quantities: Indicators, oscilloscopes, multimeters, etc. For the main types of measuring instruments, the operating procedures of calibration and metrological confirmation for managing the quality of the measurements is presented. They are accompanied by the registry and metrology card, suitable for recording the instrument identification and the registration of subsequent verification checks and metrological confirmation implemented with the two methods explained in Part I, 10.2.1 and 10.2.2: •
•
Verify that the Maximum Relieved Error (MRE) of the instrument is less than or equal to the Maximum Tolerated Error (MTE). This is generally recommended when using references with uncertainty less than or equal to one-third of that of the instrument to be calibrated. Verify that the Maximum Relieved Uncertainty (MRU) of the instrument is less than or equal to the Maximum Tolerated Uncertainty (MTU). This is particularly recommended when using references with uncertainty greater than one-third of that of the instrument to be calibrated.
Obviously, this must always be done in compliance with any applicable normative references. At the same time, note that errors and uncertainties are generally expressed: • •
In absolute terms in the case of temperatures (°C), lengths (mm), etc. In relative terms (e.g., percent of full scale for pressure or percent of reading for flow)
Also note that for editorial convenience, all metrological confirmation intervals of different measurement instruments have been set at one year, without regard to the course management criteria of the intervals reported in Part I in: • • •
8.5 Definition of Metrological Confirmation Intervals 8.6 Review of the Metrological Confirmation Intervals 8.7 Examples of Definition of Metrological Confirmation Intervals
This is unless otherwise specified in any technical requirements or related legislations. In addition, it points out the importance of reviewing the metrological confirmation intervals with the scale method provided by the international document OIML D 10, which in principle should lead to: • •
An increase in the interval for the most stable instruments (or scarcely used), type: manometers, thermocouples, etc. A decrease in the interval for the most critical instruments (or continuous use), type: analyzers, gas chromatographs, etc.
This is unless otherwise specified in the technical requirements and/or related legislations. Finally, note that for uniformity in the various operating procedures, the document has highlighted the environmental conditions in terms of temperature, relative humidity, and atmospheric pressure. This is a practice for a proper independent laboratory. For an industrial laboratory, always specify the temperature, and specify humidity and pressure if they are influential or prescribed by applicable normative references.
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INTRODUCTION
1. Physical Quantities This first section of Part II describes the requirements and specific criteria for managing and calibrating measuring instruments of physical quantities: 1.1 Pressure 1.2 Flow 1.3 Level 1.4 Temperature 1.5 Humidity 1.6 Viscosity 1.7 Density 1.8 Mass For each quantity, the International System (SI) of units, any specific definitions, the main operating principles, and any reference tables will be succinctly presented. In addition to the main types of instruments, the handbook will present the relative operating procedure of calibration and metrological confirmation articulated on the following points: 1. 2. 3. 4. 5. 6. 7. 8. 9.
Scope and Purpose Identification and Classification Normative References Ambient Conditions Initial Checks Calibration Method Calibration Verification Calibration Results Metrological Confirmation
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PRESSURE
1.1 Pressure Units of Measurement and Definitions The pressure P is defined as the ratio between the force F acting on a surface and its area A: P=F/A The pressure unit in the International System is pascal (Pa): 1 Pa = 1 N / 1 m2 The pressure unit bar is also accepted: 1 bar = 105 Pa For the relationship with other units, see table 1. Table 1. Conversions of the Different Units of Pressure Pa
bar
Atm
kg/cm2
mm H2O @ 4°C
mm Hg @ 0°C
psi
in H2O @ 4°C
in Hg @ 0°C
1 Pa
1
0.00001
0.0000099
0.000010
0.101972
0.00750
0.000145
0.004015
0.000295
1 bar
100000
1
0.986923
1.01972
10197.2
750.062
14.5038
401.463
29.530
1 Atm
101325
1.01325
1
1.03323
10332.3
760
14.6959
406.78
29.921
1 kg/cm2
98066.5
0.980665
0.967841
1
10000
735.559
14,2233
393.701
28.959
1 mm H2O
9.80665
0.000098
0.000097
0.0001
1
0.07355
0.001422
0.03937
0.002896
1 mm Hg
133.322
0.001333
0.001316
0.001359
13.595
1
0.019337
0.53524
0.03937
1 psi
6894.76
0.068947
0.068046
0.070307
703.07
51.715
1
27.68
2.03602
1 in H2O
249.089
0.002491
0.002458
0.002540
25.4
1.86832
0.03613
1
0.073556
1 in Hg
3386.39
0.038639
0.033421
0.034532
345.316
25.4
0.491154
13.5951
1
Notes: The standard reference atmospheric pressure at sea level is 1013.25 mbar (101325 Pa). The air pressure decreases by about 1 mbar for every 10 m above sea level (valid until 4000 m). The concepts related to the type of the relative and absolute pressures are shown in figure 1.
Pressure [bar]
Absolute pressure above atmospheric P
Related pressure above atmospheric P (pressure)
Atmospheric pressure 1.013 Limits of variation of atmos pheric pressure
Abs olute pressure below atmospheric P
Related pressure below atmospheric P (depression)
0
Figure 1. Concepts Related to the Type of Pressure Measurement
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Main Instruments for Pressure Measurement The main instruments and most common pressure measurements are as follows: • •
Manometers or pressure gauges, according to European standard EN 837 Transmitters or pressure transducers, according to international standard IEC 60770
As an example, the following tables show the features provided by the European standard EN 837 for manometers (i.e., pressure gauges or dial gauges), which standardizes the use of Bourdon tubes, membranes, and capsules: table 2 for standard ranges, table 3 for standard nominal diameters, and table 4 for standard accuracy classes. Table 2. Standard Measuring Ranges for Manometers (EN 837) Instrument
Measuring Ranges (1)
Manometers or Pressure Gauges
Measuring ranges in bar (2) 0 – 0.6 0–1 0 – 10 0 – 1.6 0 – 16 0 – 2.5 0 – 25 0–4 0 – 40 0–6 0 – 60
0 – 100 0 – 160 0 – 250 0 – 400 0 – 600
Measuring ranges in mbar (3) 0–1 0 – 10 0 – 1.6 0 – 16 0 – 2.5 0 – 25 0–4 0 – 40 0–6 0 – 60
0 – 100 0 – 160 0 – 250 0 – 400 0 – 600
Vacuum Gauges
Measuring ranges in bar –0.6 – 0 –1 – 0 Measuring ranges in mbar (3) –1 – 0 –10 – 0 –1.6 – 0 –16 – 0 –2.5 – 0 –25 – 0 –4 – 0 –40 – 0 –6 – 0 –60 – 0
Pressure and Vacuum Gauges
Measuring ranges in bar –1 – 0.6 –1 – 3 –1 – 1.5 –1 – 5
–100 – 0 –160 – 0 –250 – 0 –400 – 0 –600 – 0
–1 – 9 –1 – 15
Notes: (1) The preferred units are the bar and mbar. (2) The maximum measuring range is 25 bar for diaphragm and capsule manometers. (3) Measuring ranges are in mbar only for diaphragm and capsule manometers.
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0 – 1000 0 – 1600
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–1 – 24
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PRESSURE
Table 3. Standard Nominal Diameters DN for Manometers (EN 837) DN
Nominal Diameters (1)
(mm)
40
50
63
80
100
150
160
250
Note: (1) The minimum nominal diameter is 50 for diaphragm and capsule manometers.
Table 4. Standard Accuracy Classes for Manometers (EN 837) Cl
Accuracy Classes (1)
(%)
0.1
0.25
0.6
1
1.6
2.5
4
Note: (1) The minimum accuracy class is 0.6 for diaphragm and capsule manometers. Calibration and Metrological Confirmation Procedures 1.1.1 Pressure indicators (manometers)
: PI
: EN 837
1.1.2 Pressure transmitters
: PT
: EN 60770
1.1.3 Electromechanical manometers
: PE
: EURAMET 17
1.1.4 Pressure balances
: PB
: EURAMET 3
For Other Pressure Gauges • • • • •
Manometers for extinguishers use Manometers for welding use Manometers for medical use Manometers for tires use (1) Manometers for pressure blood (2)
: EN 3-5 with accuracy class 6% : EN 562 with accuracy class 2.5% : EN 738 with accuracy class 2.5% : EN 12645 according to EC Directive 86/217 (with MTE ≤ 2.5%) : EN 1060 according to EC Directive 93/42 (with MTE ≤ 3 mm Hg)
For the latter pressure gauges, generally follow the procedure for manometers EN 837 (1.1.1) with calibration points at least every 20% (15% for EN 562); however, follow the specific method described in the relevant technical normative references or legal regulations. Notes: (1) There is also a similar international recommendation, OIML R 23: Tire pressure gauges for motor vehicles. (2) There is also a similar international recommendation, OIML R 16: Sphygmomanometers.
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PHYSICAL QUANTITIES
1.1.1 Pressure Indicators 1. Scope and Purpose This procedure applies to all types of pressure indicators or dial manometers with Bourdon tubes or membranes and capsules, with measuring ranges between –1 and 1600 bar (or greater). 2. Identification and Classification Before information about the new instrument is used in the application, it must be filed in accordance with the instrument card at the right, defining the procedures, the normative references, and the required checks and results. The instrument must be confirmed metrologically for the application, including the instrument’s recalibration, if necessary. 3. Normative References • EN 472 (1995) : Pressure gauges – vocabulary • EN 837-1-2-3 (1996) : Pressure gauges – Bourdon tube, membrane, capsule pressure gauges 4. Ambient Conditions Temperature: (20 ± 2)°C, Relative humidity: (50 ± 25)%, Atmospheric pressure: (1000 ± 25) mbar 5. Initial Checks Before starting any operation, check that the instrument does not indicate traces of rupture, wear, or alteration of parts, such as measuring scale and fittings. Then install the instrument in the measuring circuit, ensure that there are no leaks, and make three preload cycles on the whole verification range. 6. Calibration Method Perform calibration methods by comparing with standard instruments: • For laboratory manometers, by pressure balance with standard masses (figure A) • For industrial manometers with accuracy class more than 1, with standard manometer (figure B) • For industrial manometers with accuracy class less than 1, with standard calibrator (figure C) It has a lower measurement uncertainty, possibly one-fourth of that of the manometer in calibration (according to the normative references). Mass
Manometer in calibration 3 2
Ma no me ter i n cal ibr atio n Standard manometer
Manometer in calibration
4
1
5 0
kPa
6
Fluid reservoir Δh = 0
Δh ≠ 0
2.500 bar
Variable volume
Fluid filling valve
Figure A
Manual pump or pressure reducer
Figure B
S ta nd ar d ca libr ato r
Refe re nce l eve l
Figure C
If there is a different level Δh between the intake of the standard manometer and the manometer in calibration, it is necessary to correct the pressure difference ΔP between the two levels, through the relation: ΔP = ρ ⋅ g ⋅ Δh [Pa], where ΔP = differential pressure in pascal (1 Pa = 10-5 bar), ρ = density of the measurement fluid (for water ≈ 1000 kg/m3), g = local gravitational acceleration (or standard = 9.80665 m/s2), and Δh = different level between the two manometers in meters 7. Calibration Verification The verification should be carried out with increasing/decreasing pressure (i.e., at least every 25% of scale): 25 – 50 – 75 – 100 – 75 – 50 – 25 – 0% Reach every point of measurement without going over, and wait for the indication that the standard and instrument in calibration are perfectly stable. Then read and detect the standard and the instrument indications. 8. Calibration Results Report the calibration results in an instrument card to first be processed and then valued against the Maximum Tolerated Error (MTE) or Maximum Tolerated Uncertainty (MTU): • Verify that the Maximum Relieved Error (MRE) of the instrument is less than or equal to MTE. • Verify that the Maximum Relieved Uncertainty (MRU) of the instrument is less than or equal to the MTU. If the check is not positive, it will be necessary to recalibrate the instrument, and then repeat the calibration verification (point 7), or downgrade or alienate the instrument. 9. Metrological Confirmation Record on the side of the instrument card: • The results of the metrological confirmation (positive, negative: declassification or alienation) • The signature of those who made the verification and the next verification date Also, fill out and attach the positive confirmation label on the instrument, indicating at least the number of the verification/calibration report, the instrument serial number, and the next verification date. 78
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Metrological Laboratory
PRESSURE
Pressure Indicators (pressure gauges or dial manometers)
Card Number XX-PI
IDENTIFICATION AND METROLOGICAL DATA Instrument identification Instrument classification Instrument denomination Manufacturer Model Serial number Date of acquisition Location of installation Installation conditions Utilization conditions
PI 11 Process Manometer ABC DN 100 XYZ 01.02.2010 Process PI 11 Vertical Eventual
Measuring range Calibration range Accuracy class Measure resolution (Eres) Max Tolerated Error (MTE) Max Tolerated Uncertainty (MTU) Reference standard uncertainty (Uref) Certificate number of standard Fluid exercise/calibration Fluid filling
0–10 bar 0–10 bar 1% 0.05 bar 0.10 bar 0.15 bar 0.01 bar 1111 Air/air Eventual
APPLICABLE PROCEDURES AND NORMATIVES Calibration procedure Confirmation procedure
PP-PI PP-PI
Maintenance procedure Normative reference
Manufacturer spec. EN 837
REQUIRED CONTROLS Calibration
Confirmation
YES
NO
YES
Certification NO
YES
Body Control Internal External
NO
TRACEABILITY OF MEASUREMENT Calibration and Confirmation Internal traceability to reference standard PS 11
Certification External traceability of certification body
INTERVAL OF METROLOGICAL CONFIRMATION 3 months
6 months
1 year
2 years
RESULTS OF CONFIRMATION Date of Control
Body Control
Number of Report
Results of Confirmation
Drift MRE/bar
Signature Vision
Deadline
01.06.2017
Internal
XX-PI
Positive
0.05
White
01.06.2018
Notes
RESULTS OF LAST CONFIRMATION Was the adjustment made before the verification? Pressure Reference
RELIEVED VALUES
YES RELIEVED ERRORS
Increasing
Decreasing
Increasing
Decreasing
(bar)
(bar)
(bar)
(bar)
(bar)
0 2 4 6 8 10
– 1.95 3.95 5.95 7.95 9.95
0.05 2.05 4.05 6.05 8.05 –
– –0.05 –0.05 –0.05 –0.05 –0.05
0.05 0.05 0.05 0.05 0.05 –
NO
Max Relieved Error Emax (bar)
0.05
RESULTS OF METROLOGICAL CONFIRMATION MRE < MTE MRU < MTU
0.05 bar < 0.10 bar OR ALTERNATIVELY 2
2
2
2
2
2
E max Eres 0.05 Uref 0.01 0.05 + = 2 ⋅ MRU = 2 ⋅ = 0.06bar < 0.15bar + + + 3 2 2 1.73 3, 46 2. 3
THE NEXT VERIFICATION MUST BE CARRIED OUT WITHIN Metrological Function
EXECUTOR SIGNATURE
YES
NO
YES
NO
01.06.2018 RESPONSIBLE SIGNATURE
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LEVEL
1.3 Level Units of Measurement and Definitions The level of liquid and solid products (such as powders, mixtures, and granules) in containers (such as tanks, silos, and vessels) is measured in height in meters. In the case of liquids, the level or height measurement is always the effective real average height of the liquid content. In the case of solids, the level or height measured is the punctual real actual height of the solid content, a height which is substantially a function of the measuring point (figure 1).
1
2
3
1
2
h1 h2 h3
h
(a)
3
(b)
Figure 1. Level Measurement of Products in Containers with Sensors (1-2-3) Mounted on Top of the Tank a. Level measurement of liquids: The sensors always detect the same level h (h1 = h2 = h3) given the horizontal liquid level. b. Level measurement of solids: The sensors detect various levels (h1 ≠ h2 ≠ h3) as a function of the content solid surface.
Calibration and Metrological Confirmation Procedures 1.3.1 Pressure (Hydrostatic)
: LP: IEC 60770
1.3.2 Reflection (Sonar and Radar) : LX: IEC 60770
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1.3.1 Measurers at Pressure (Hydrostatics) 1. Scope and Purpose This procedure applies to the types of pressure level meters, otherwise called hydrostatic, that use relative (for vessels open to the atmosphere) or differential (for pressure vessels) pressure measuring instruments with an analog (mA or mV) or digital (HART or Bus) output signal. 2. Identification and Classification Before information about the new instrument is used in the application, it must be filed in accordance with the instrument card at the right, defining the procedures, the normative references, and the required checks and results. The instrument must be confirmed metrologically for the application, including the instrument’s recalibration, if necessary. 3. Normative References • IEC 60770-1 (2010) • IEC 60770-2 (2010) • IEC 60770-3 (2014)
: Industrial transmitters – Part 1: Methods for performance evaluation : Industrial transmitters – Part 2: Methods for inspection and routine : Industrial transmitters – Part 3: Methods for performance evaluation of intelligent transmitters
4. Ambient Conditions Temperature: (20 ± 2)°C, Relative humidity: (50 ± 25)%, Atmospheric pressure: (1000 ± 25) mbar 5. Initial Checks Before starting any operation, check that the instrument does not indicate traces of rupture, wear, or alteration of parts, such as casings, fittings, and the optional indicator. Then install the instrument in the measuring circuit and ensure that there are no leaks. Make three preload cycles on the whole verification range. 6. Calibration Method Since the principle of hydrostatic measurement precisely uses the pressure generated by the liquid level in the vessel bottom (according to the note and detailed formula at the bottom of a typical installation in figure A) to perform the calibration locally (by intercepting the transmitter) or elsewhere (by removing the transmitter) for comparison with a standard instrument (calibrators or pressure balances): • For analog instruments with a pressure calibrator measuring the output signal (figure B) • For digital instruments with a pressure calibrator and digital communicator or configurator (figure C) In any case, it has a lower measurement uncertainty possibly of one-fourth of that of the instrument in calibration (according to the normative references).
Load 250 Ω
Transmitter or Transducer
Figure A
Figure B
Output 4-20 mA Supply Connection
Communicator or Configurator
Figure C
The hydrostatic pressure exerted by the liquid level of the tank bottom is given by the following relation: P = ρ ⋅ g ⋅ h [Pa], where P = pressure exercised in pascal (1 Pa = 10-5 bar), ρ = density of the measurement fluid (for water ≈ 1000 kg/m3), g = local gravitational acceleration (or standard = 9.80665 m/s2), h = level height to be measured in meters 7. Calibration Verification The verification should be carried out with increasing/decreasing pressure (i.e., at least every 20% of scale): 20 – 40 – 60 – 80 – 100 – 80 – 60 – 40 – 20 – 0% Reach every point of measurement without going over, wait for the indication that the standard and instrument in calibration are perfectly stable, then read and detect the standard and the instrument output or indications. 8. Calibration Results Report the calibration results in an instrument card to first be processed and then valued against the Maximum Tolerated Error (MTE) or Maximum Tolerated Uncertainty (MTU): • Verify that the Maximum Relieved Error (MRE) of the instrument is less than or equal to the MTE. • Verify that the Maximum Relieved Uncertainty (MRU) of the instrument is less than or equal to the MTU. If the check is not positive, it will be necessary to recalibrate the instrument, then repeat the calibration verification (point 7), or downgrade or alienate the instrument. 9. Metrological Confirmation Record on the side of the instrument card: • The results of the metrological confirmation (positive, negative: declassification or alienation) • The signature of those who made the verification and the next verification date Also, fill out and attach the positive confirmation label on the instrument, indicating at least the number of the verification/calibration report, the instrument serial number, and the next verification date. 114
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LEVEL
Metrological Laboratory
Measurers at Pressure Card Number XX-LP (Hydrostatics) IDENTIFICATION AND METROLOGICAL DATA Instrument identification LP 11 Measuring range (0–10m H2O) 0–100 kPa Instrument classification Process Calibration range (0–10m H2O) 0–100 kPa Instrument denomination Transmitter Accuracy class 0.05% Manufacturer ABC Measure resolution (Eres) 0.01% Model LP Max Tolerated Error (MTE) 0.05% Serial number XYZ Max Tolerated Uncertainty (MTU) 0.10% Date of acquisition 01.02.2010 Reference standard uncertainty (Uref) 0.01% Location of installation Process LP 11 Certificate number of standard 1111 Installation conditions Vertical Fluid exercise/calibration Water/air Supply conditions Nominal ± 1% Output load 250 Ω ± 0.1% APPLICABLE PROCEDURES AND NORMATIVES Calibration procedure PP-LP Maintenance procedure Manufacturer spec. Confirmation procedure PP-LP Normative reference IEC 60770 REQUIRED CONTROLS Calibration Confirmation Certification Body Control YES NO YES NO YES NO Internal External TRACEABILITY OF MEASUREMENT Calibration and Confirmation Certification Internal traceability to reference standard PS 11 External traceability of certification body INTERVAL OF METROLOGICAL CONFIRMATION 3 months 6 months 1 year 2 years RESULTS OF CONFIRMATION Date of Body Number of Results of Drift Signature Deadline Notes Control Control Report Confirmation MRE/% Vision 01.06.2017 Internal XX-LP Positive 0.03 White 01.06.2018
Pressure Reference (%) 0 20 40 60 80 100 MRE < MTE MRU < MTU
RESULTS OF LAST CONFIRMATION Was the adjustment made before the verification? RELIEVED VALUES RELIEVED ERRORS Increasing Decreasing Increasing Decreasing (%) (%) (%) (%) – 19.99 39.98 59.97 79.98 99.99
0.00 – 20.01 – 0.01 40.00 – 0.02 59.99 – 0.03 80.00 – 0.02 – – 0.01 RESULTS OF METROLOGICAL CONFIRMATION 0.03% < 0.05% OR ALTERNATIVELY 2
E max Uref MRU = 2 ⋅ + 3 2
2
2
2
2
0 0.01 0.00 – 0.01 0.00 –
2
Eres 0 .01 0 .03 0 .01 = 2 ⋅ + + + = 0 .04 % < 0 .10 % 2 1 .73 3 .46 2. 3
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YES NO Max Relieved Error Emax (%)
0.03
YES
NO
YES
NO
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PHYSICAL QUANTITIES
1.3.2 Measurers at Reflection (Sonar and Radar) 1. Scope and Purpose This procedure applies to all the types of level measurers at reflection (sonar and radar) with an analog (mA or mV) or digital (HART or Bus) output signal and a measurement range to 50 m (or more). 2. Identification and Classification Before information about the new instrument is used in the application, it must be filed in accordance with the instrument card at the right, defining the procedures, the normative references, and the required checks and results. The instrument must be confirmed metrologically for the application, including the instrument’s recalibration, if necessary. 3. Normative References • IEC 60770-1 (2010) • IEC 60770-2 (2010) • IEC 60770-3 (2014)
: Industrial transmitters – Part 1: Methods for performance evaluation : Industrial transmitters – Part 2: Methods for inspection and routine : Industrial transmitters – Part 3: Methods for performance evaluation of intelligent transmitters
4. Ambient Conditions Temperature: (20 ± 2)°C, Relative humidity: (50 ± 25)%, Atmospheric pressure: (1000 ± 25) mbar 5. Initial Checks Before starting any operation, check that the instrument does not indicate traces of rupture, wear, or alteration of parts, such as casings, fittings, and the optional indicator. Then install the instrument in the measurement system and check the electrical functionality. 6. Calibration Method Since the measuring principle of the transmitters in question uses the reflection of waves, use, respectively: • Sonic for sonar, with propagation velocity of about 300 m/s • Electromagnetic for radar, with velocity of propagation of about 300 • 106 m/s Therefore, it must be prepared in a “variable level” calibration system in order to verify the measurements obtained by the transmitters with respect to the calibration system, or between the probe and the level surface. The calibration, therefore, can be practically performed (see the figure) locally, by intercepting the transmitter, or remotely, by removing the transmitter. This is provided that this last condition is representative of the process (type of gas, pressure, and temperature) in terms of the wave propagation speed of measurement and the quality of the reflection, for comparison with standard systems consisting of ribs or reference lasers, having in each case a lower measurement uncertainty possibly of ¼ of that of the instrument being calibrated (according to the normative references). Max level (100%) Measure wave
Reflected wave
Depth of the level to be measured
Variable level to be measured
Reference level to be measured by comparison with rib metric or laser device
Min level (0%)
7. Calibration Verification The verification must be carried out with progressive levels every 20% of the measuring scale, namely: 0 – 20 – 40 – 60 – 80 – 100%. 8. Calibration Results Report the calibration results in an instrument card to first be processed and then valued against the Maximum Tolerated Error (MTE) or Maximum Tolerated Uncertainty (MTU): • Verify that the Maximum Relieved Error (MRE) of the instrument is less than or equal to the MTE. • Verify that the Maximum Relieved Uncertainty (MRU) of the instrument is less than or equal to the MTU. If the check is not positive, it will be necessary to recalibrate the instrument, then repeat the calibration verification (point 7), or downgrade or alienate the instrument. 9. Metrological Confirmation Record on the side of the instrument card: • The results of the metrological confirmation (positive, negative: declassification or alienation) • The signature of those who made the verification and the next verification date Also, fill out and attach the positive confirmation label on the instrument, indicating at least the number of the verification/calibration report, the instrument serial number, and the next verification date. 116
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LEVEL
Metrological Laboratory
Measurers at Reflection Card Number XX-LR (sonar and radar) IDENTIFICATION AND METROLOGICAL DATA Instrument identification LR 11 Measuring range (0–10m H2O) 0–10 m Instrument classification Process Calibration range (0–10m H2O) 0–10 m Instrument denomination Transmitter Accuracy class 0.05% Manufacturer ABC Measure resolution (Eres) 0.01% Model LR Max Tolerated Error (MTE) 0.05% Serial number XYZ Max Tolerated Uncertainty (MTU) 0.10% Date of acquisition 01.02.2010 Reference standard uncertainty (Uref) 0.01% Location of installation Process LR 11 Certificate number of standard 1111 Installation conditions Vertical Fluid exercise/calibration Water/water Supply conditions Nominal ± 1% Output load 250 Ω ± 0.1% APPLICABLE PROCEDURES AND NORMATIVES Calibration procedure PP-LR Maintenance procedure Manufacturer spec. Confirmation procedure PP-LR Normative reference IEC 60770 REQUIRED CONTROLS Calibration Confirmation Certification Body Control YES NO YES NO YES NO Internal External TRACEABILITY OF MEASUREMENT Calibration and Confirmation Certification Internal traceability to reference standard LS 11 External traceability of certification body INTERVAL OF METROLOGICAL CONFIRMATION 3 months 6 months 1 year 2 years RESULTS OF CONFIRMATION Date of Body Number of Results of Drift Signature Deadline Notes Control Control Report Confirmation MRE/% Vision 01.06.2017 Internal XX-LR Positive 0.03 White 01.06.2018
Level Reference (m) 0 2 4 6 8 10 MRE < MTE MRU < MTU
RESULTS OF LAST CONFIRMATION Was the adjustment made before the verification? RELIEVED VALUES RELIEVED ERRORS (m)
(%)
0.000 0.00 1.999 – 0.01 3.998 – 0.02 5.997 – 0.03 7.998 – 0.02 9.999 – 0.01 RESULTS OF METROLOGICAL CONFIRMATION 0.03% < 0.05% OR ALTERNATIVELY 2
2
2
2
2
2
E max Eres 0 .01 0 .03 0 .01 Uref MRU = 2 ⋅ + = 2⋅ = 0 .04 % < 0 .10 % + + + 3 3 .46 1 .73 2 2 2. 3
THE NEXT VERIFICATION MUST BE CARRIED OUT WITHIN Metrological EXECUTOR SIGNATURE RESPONSIBLE SIGNATURE Function
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YES NO Max Relieved Error Emax (%)
0.03
YES
NO
YES
NO
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TEMPERATURE
1.4 TEMPERATURE Units of Measurement and Definitions The kelvin is the fraction 1/273.16 of the temperature interval from the triple point of water to absolute zero, and can be formulated as follows: 1 K = 1/273.16
Thermodynamic temperature of the triple point of water
For conversion to other units still in use and for the evolution of the temperature scale, see table 1 and table 2. (Please note that for temperature intervals, the kelvin K corresponds to the °C.)
Table 1. Conversion for Temperature Measurement Units
• • • •
Temperature
tC
tK
tF
tR
tC
1
tK – 273.15
5/9 (tF – 32)
5/9 tR – 273.15
tK
tC + 273.15
1
5/9 tF + 255.37
5/9 tR
tF
9/5 tC + 32
9/5 tK – 459.67
1
tR – 459.67
tR
9/5 tC + 491.67
9/5 tK
tF + 459.67
1
tC = Relative temperature in Celsius degrees (°C): Scale that assigns 0°C and ≅ 100°C at the fusion and boiling point of the water tK = Absolute temperature in kelvin (K): Scale that assigns 0 K = –273.15°C at zero absolute temperature tF = Relative temperature in Fahrenheit degrees (°F): Scale that assigns 32°F and ≅ 212°F at the fusion and boiling point of the water tK = Absolute temperature in Rankine degrees (°R): Scale that assigns 0°R = –459.67°F at zero absolute temperature
Table 2. Fixed Points of the International Temperature Scales Substance Element Hydrogen Hydrogen Hydrogen Neon Neon Oxygen Oxygen Argon Mercury Water Water Gallium Water (2) Indium Tin Zinc Antimony (2) Aluminum Silver Gold Copper
IPTS 68
ITS 90
Symbol
Fixed Points (@ 101325 Pa)
(K)
(°C)
(K)
(°C)
H2 H2 H2 Ne Ne O2 O2 Ar Hg H2O H2O Ga H2O In Sn Zn Sb Al Ag Au Cu
Triple point Liquefaction point Boiling point Triple point Boiling point Triple point Boiling point Triple point Triple point Fusion point Triple point Fusion point Boiling point Fusion point Solidification point Solidification point Solidification point Solidification point Solidification point Solidification point Solidification point
13.81 17.042 20.282 (1) 27.102 54.361 90.188 (1) (1) 273.15 273.16 (1) 373,15 (1) 505.118 692.73 903.89 (1) 1235.93 1337.58 (1)
-259.34 -256.108 -252.868 (1) -246.048 -218.789 -182.962 (1) (1) 0 0.01 (1) 100 (1) 231.968 419.58 630.74 (1) 961.93 1064.43 (1)
13.803 17.036 20.271 24.556 (1) 54.358 (1) 83.806 234.316 273.15 273.16 302.915 373.124 426.749 505.078 692.677 (1) 933.473 1234.93 1337.33 1357.77
-259.347 -256.114 -252.879 -248.594 (1) -218.792 (1) -189.344 -38.834 0 0.01 29.765 99.974 156.599 231.928 419.527 (1) 660.323 961.78 1064.18 1084.62
(1) Primary fixed point not provided (2) Secondary fixed point provided For the old International Practice Temperature Scale, IPTS 68 (1968) For the new International Temperature Scale, ITS 90 (1990)
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PHYSICAL QUANTITIES The Most Widely Used Temperature Sensors
Standardized Types of Resistance Thermometers (table 3): • Platinum resistance thermometers: According to technical standard IEC 60751 • Nickel and copper resistance thermometers: According to legal standard OIML R 84 For the characteristics of standardized resistance thermometers (or thermoresistances), also see table 4 for the tolerance classes and table 5 for the resistance values for the various types of standardized resistance thermometers.
Table 3. Temperature Limits and Interpolating Polynomials for Normalized Resistance Thermometers Material Type
Temperature Limits (°C)
Temperature Coefficient (/°C)
Interpolating Polynomial (3) Rt = Ro (1 + A•t + B•t2 + C•t3) (Ω)
– 200 / +850
3.85 • 10-3
A = 3.9083 • 10 –3 B = – 5.7750 • 10 –7 C = – 4.1830 • 10 –12
Platinum (1)
Nickel (2)
– 60 / +180
6.17 • 10-3
A = 5.485 • 10 –3 B = 6.650 • 10 –6 C = 2.805 • 10 –11
Copper (2)
– 180 / +200
4.26 • 10-3
A = 4.260 • 10 –3
(4)
(1) According to international technical standard IEC 60751 (2) According to international legal standard OIML R 84 (3) Temperature value with sign (t) (4) Coefficient C applicable only under 0° C and multiplied by the factor (t – 100°C)
Table 4. Temperature Ranges and Tolerance Classes of Standardized Resistance Thermometers (Thermoresistances) Thermoresistance Type (0)
Commercial Denomination (4)
Tolerance Classes
Temperature Ranges (°C)
Tolerance Values (°C)
Platinum – Pt (1)
PRT
AA A B C
– 50 / + 250 – 100 / + 450 – 200 / + 600 – 200 / + 600
± (0.10°C + 1.7•10-3t) (3) ± (0.15°C + 2.0•10-3t) (3) ± (0.30°C + 5.0•10-3t) (3) ± (0.60°C + 10.0•10-3t) (3)
Nickel – Ni (2)
NRT
C C
0 / + 180 – 60 / 0
± (0.20°C + 8.0•10-3t) (3) ± (0.20°C + 16.5•10-3t) (3)
Copper – Cu (2)
CRT
B C
–50 / + 200 –50 / + 200
± (0.25°C + 3.5•10-3t) (3) ± (0.50°C + 6.5•10-3t) (3)
(0) Or more precisely, resistance thermometer detectors (RTD) (1) According to international technical standard IEC 60751 (2) According to international legal standard OIML R 84 (3) Temperature module without sign t (4) Equivalent to the drop cap of the type of material followed by the acronym RT (resistance thermometer)
Table 5. Resistance Values of the Standardized Resistance Thermometers with 100 Ω @ 0°C: Values Ω versus °C in the range –200 to 600°C Type
–200
–150
–100
–50
PRT
18.52
39.72
60.26
80.31
100.00 119.40 138.51 157.33 175.86 194.10 212.05 229.72 247.09 264.18 280.98 313.71
NRT
74.21
100.00 129.17 161.72 198.68
CRT
78.70
100.00 121.30 142.60 163.90 185.20
120
0
50
100
150
200
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250
300
350
400
450
500
600
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TEMPERATURE
Standardized Types of Thermocouples (TC) (table 6): • •
Thermocouples of metals in alloy: According to International Electrotechnical standard IEC 60584 Thermocouples of pure metals: According to International Electrotechnical standard IEC 62460
For the characteristics of standardized thermocouples see: • • • •
Table 7 for the tolerance classes of thermocouples alloy Table 8 for the tolerance classes of extension and compensating cables Table 9 for the connecting cables in accordance with international standard IEC and national standards Table 10 for the values of the electromotive force for various thermocouples standardized by IEC
Table 6. Temperature Limits of Standardized Thermocouples (IEC 60584-1) Thermocouple Type (1) T E J K N S R B C A
Thermocouple Materials Positive Conductor Copper Nickel – Chromium Iron Nickel – Chromium Nickel – Cr – Si Platinum – 10% Rh Platinum – 13% Rh Platinum – 30% Rh Tungsten – 5% Re Tungsten – 5% Re
Negative Conductor Copper – Nickel Copper – Nickel Copper – Nickel Nickel – Aluminum Nickel – Silicon Platinum Platinum Platinum – 6% Rhodium Tungsten – 26% Rhenium Tungsten – 20% Rhenium
Temperature Range – 270 / 400 – 270 / 1000 – 210 / 1200 – 270 / 1300 – 270 / 1300 – 50 / 1760 – 50 / 1760 0 / 1820 0 / 2315 0 / 2500
Commercial Denomination (2) Copper Constantan Chromel Constantan Iron Constantan Chromel Alumel Nicrosil Nisil
(1) Thermocouples in pure metals (IEC 62460) have no identifying letter, but rather the component metals symbols (2) The Copper-Nickel alloy is commonly called Constantan
Table 7. Tolerance Classes of Standardized Thermocouples (IEC 60584-2) Thermocouple Type
Positive Conductor T E J K N S R B C A
Tolerance Classes (1)
Thermocouple Materials
Copper Nickel – Chromium Iron Nickel – Chromium Nickel – Cr – Si Platinum – 10% Rh Platinum – 13% Rh Platinum – 30% Rh Tungsten – 5% Re Tungsten – 5% Re
Negative Conductor Copper – Nickel Copper – Nickel Copper – Nickel Nickel – Aluminum Nickel – Silicon Platinum Platinum Platinum – 6% Rhodium Tungsten – 26% Rhenium Tungsten – 20% Rhenium
1
2
0.5°C or 0.4% 1.5°C or 0.4% 1.5°C or 0.4% 1.5°C or 0.4% 1.5°C or 0.4% 1.0°C or 0.2% 1.0°C or 0.2% (2) (2) (2)
1.0°C or 0.75% 2.5°C or 0.75% 2.5°C or 0.75% 2.5°C or 0.75% 2.5°C or 0.75% 1.5°C or 0.25% 1.5°C or 0.25% 1.5°C or 0.25% 1.0% > 425°C 1.0% > 1000°C
(1) Tolerance values are always worth the greater value. (2) For types A, B, C, the Tolerance Class 1 is not foreseen.
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PHYSICAL QUANTITIES
Table 8. Tolerance Classes of Extension (X) and Compensation (C) Cables for Thermocouples (IEC 60584-3) Cable Type EXTENSION (1)
COMPENSATION (2)
Tolerance Classes 2
Cable Temperature Range
Measure Junction Temperature
± 30 μV (0.5°C) ± 120μV (1.5°C) ± 85μV (1.5°C) ± 60μV (1.5°C) ± 60μV (1.5°C)
± 60 μV(1.0°C) ± 200 μV(2.5°C) ± 140 μV(2.5°C) ± 100 μV(2.5°C) ± 100 μV(2.5°C)
– 25°C / +100°C – 25°C / +200°C – 25°C / +200°C – 25°C / +200°C – 25°C / +200°C
300°C 500°C 500°C 900°C 900°C
– – – –
± 100 μV(2.5°C) ± 100 μV(2.5°C) ± 100 μV(2.5°C) ± 30 μV (2.5°C) ± 60 μV (5.0°C)
0°C / +150°C 0°C / +150°C 0°C / +100°C 0°C / +100°C 0°C / +200°C
900°C 900°C 900°C 1000°C 1000°C
Cable Symbol
1
TX EX JX KX NX NC KCA KCB RCA/SCA RCB/SCB
–
(1) The extension cable is of the same constituents as the thermocouple materials, used for common thermocouples: T, E, J, K, N. (2) The compensation cable is made of other materials than those constituting the thermocouple, used for precious thermocouples: R, S, B (for the latter, they are usually used for normal copper cables with typical maximum error of 3.5° C).
Table 9. Matching the Colors of Thermocouple Wires between IEC 60584-3 and Other National Standards Cable for Thermocouple Type
T
E
J
K
N
R/S
B (*)
Colors of Sheath and Cables According to: (INTERNAT.) IEC
(U.S.) ANSI
(U.K.) BS
(D) DIN
(F) NFE
(J) JIS
(S)
Brown
Brown
Blue
Brown
Blue
Brown
(+)
Brown
Blue
White
Red
Yellow
Red
(–)
White
Red
Blue
Brown
Blue
White
(S)
Violet
Brown
Brown
Black
Violet
Violet
(+)
Violet
Violet
Brown
Red
Yellow
Red
(–)
White
Red
Blue
Black
Violet
White
(S)
Black
Brown
Black
Blue
Black
Yellow
(+)
Black
White
Yellow
Red
Yellow
Red
(–)
White
Red
Blue
Blue
Black
White
(S)
Green
Brown
Red
Green
Yellow
Blue
(+)
Green
Yellow
Brown
Red
Yellow
Red
(–)
White
Red
Blue
Green
Violet
White
(S)
Pink
Brown
Orange
(+)
Pink
Orange
Orange
(–)
White
Red
Blue
(S)
Orange
Green
Green
White
Green
Black
(+)
Orange
Black
White
Red
Yellow
Red
(–)
White
Red
Blue
White
Green
White
(S)
Grey
Grey
(+)
Grey
Grey
Red
Red
(–)
White
Red
Grey
White
Grey
(*) For type B thermocouples, common copper cables in the range up to 100°C are usually used. (+) Conductor + (–) Conductor – (S) Outer Sheath
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TEMPERATURE
Table 10. Values of the Various Types of Normalized Thermocouples Consisting of Alloy Metals (IEC 60584) and Pure Metals (Au-Pt and Pt-Pd: IEC 62460) Type
– 200 – 100
0
100
200
T
–5.603 –3.379
0
4.279
9.288
E
–8.825 –5.237
0
6.319
13.421 21.036 28.946 37.005 45.093 53.112 61.017 68.787 76.373
J
–7.890 –4.633
0
5.269
10.779 16.327 21.848 27.393 33.102 39.132 45.494 51.877 57.953 63.792 69.553
K
–5.891 –3.554
0
4.096
8.138
12.209 16.397 20.644 24.905 29.129 33.275 37.326 41.276 45.119 48.838
N
–3.990 –2.407
0
2.774
5.913
9.341
12.974 16.748 20.613 24.527 28.455 32.371 36.256 40.087 43.846
S
0
0.646
1.441
2.323
3.259
4.233
5.239
6.275
7.345
8.449
9.587
R
0
0.647
1.469
2.401
3.408
4.471
5.583
6.743
7.950
9.205
10.506 11.850 13.228
B
0
0.033
0.168
0.431
0.787
1.242
1.792
2.431
3.154
3.957
4.834
C
0
1.451
3.090
4.865
6.732
8.657
10.609 12.559 14.494 16.398 18.260 20.071 21.825
A
0
1.336
2.871
4.512
6.203
7.908
9.605
11.283 12.933 14.549 16.127 17.662 19.150
Au-Pt
0
0.778
1.845
3.142
4.633
6.301
8.135
10.132 12.291 14.609 17.085
Pt-Pd
0
0.569
1.208
1.933
2.781
3.787
4.974
6.352
300
400
500
600
700
800
900
1000
1100
1200
14.862 20.872
7.917
9.657
10.757 11.951
5.780
6.786
11.557 13.601 15.772
Values in mV versus °C, in the range –200 to 1200°C, with thermocouple reference junction @ 0°C
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PHYSICAL QUANTITIES
Standardized Types of Thermometers to Radiation (also called pyrometers): • •
Pyrometers operating in the red radiation: OIML R18 Pyrometers operating in the red and infrared radiation: IEC 62492
For the measuring characteristics of pyrometers and relative sensors, see respectively: • •
Table 11 for the accuracy classes depending on the measurement temperature Table 12 for the applicable sensors in relation to the measuring range to be detected
For the operating characteristics of pyrometers related to the emissivity of the bodies to be measured and the transmissivity of the interposed media, see respectively: • •
Table 13 for the emissivity (ε) of the bodies to be measured (for black body coinciding with 1) Table 14 for the transmissivity (τ) of the interposed medium (for pure air N2+O2 coinciding with 1)
Table 11. Standardization of Monochromatic Pyrometers Operating @ 0.65 µm (OIML R 18) Maximum Permissible Errors (1)
Temperature Range (°C)
Deviation (2) (%)
Repeatability (3) (%)
Normal
400 – 800 800 – 1400 1400 – 2000 2000 – 3200 3200 – 6000
± 1.5 ± 1.5 ± 1.5 ± 2.5 ± 4.0
1 1 1 2 3
Special
400 – 800 800 – 1400 1400 – 2000 2000 – 3200 3200 – 6000
± 1.0 ± 0.6 ± 0.6 ± 1.2 ± 2.0
0.50 0.25 0.25 0.50 1.00
Accuracy Class
(1) Maximum permissible errors in % of the upper limit of the temperature measurement range of the pyrometer (2) Mean deviation values tolerated for five measures between the indicated temperature and the reference (3) Maximum repeatability values tolerated in five measures to the same reference temperature
Table 12. Measuring Spectral Bands of Infrared Pyrometers with Various Sensors Sensor
Minimum Temperature Measurable
Spectral Band (μm)
(°C)
(K)
0.38 – 0.76
> 600
> ≈ 900
0.5 – 1.0
> 400
> ≈ 700
PbS
1–3
> 200
> ≈ 500
Human eye Si PbSe
2–4
> 100
> ≈ 400
InAs
2–4
> 100
> ≈ 400
InSb
2–5
>0
> ≈ 300
HgCdTe
5 – 15