Principles and Practices of Traceability and Calibration
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The document provides an overview of measurement units, calibration standards, and traceability principles, aimed at educating readers on the essential concepts of measurement practices. It covers base and derived SI units, types of measurement standards, common measurement techniques, and the importance of traceability in ensuring measurement accuracy. Additionally, it outlines procedures for substituting calibration standards when necessary.
Principles and Practices of Traceability and Calibration
- 1. Welcome! PRINCIPLES AND PRACTICES OF TRACEABILITY AND CALIBRATION 1 By: Jasmin NUHIC
- 2. OBJECTIVE 2 • To learn and understand different types of measurements units, measurement constants, calibration and measurement standards as well as principles and practices of treaceability.
- 3. AGENDA 3 • Introduction • Base SI Units • Derived SI Units • SI Multipliers and Conversions • Fundamental Constants • Common Measurements • Principles and Practices of Traceability • Types of Measurement Standards • Substitution of Calibration Standards • Sample Questions • Q & A Session
- 4. BASE SI UNITS 4 Characteristic Fundamental Unit Description Length Meter (m) Path of light traveling in vacuum during 1/299,792,458 of a second Time Second (s) Duration of 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of ground state of the cesium atom Mass Kilogram (kg) Equal to international prototype platinum-iridium alloy cylinder Electric Current Ampere (A) Constant flow that produces 2X10^-7 Newtons per each meter of length between two straight conductors
- 6. BASE SI UNITS (cont’d) 6 Characteristic Fundamental Unit Description Temperature Kelvin (K) Fraction of 1/273.16 of the thermodynamic temperature of the triple point of water (0.01 C) NOTE: know how to convert from Kelvin to Celsius and vice-versa Light Candela (cd) Luminous intensity of a source that emits monochromatic radiation of frequency 540x10^12 hertz and has radiant intensity in the same direction of 1/683 watt Amount of Substance Mole (mol) Amount of substance of a system which contains many elementary entities as there are atoms in 0.012 kilogram of carbon 12
- 7. DERIVED SI UNITS 7 Characteristic Fundamental Unit Description Area m^2 Length multiplied by length Volume m^3 Length multiplied by length multiplied by length Frequency Hz Time inverted Density kg / m^3 Mass divided by volume Velocity m / s Length divided by time Acceleration m / s^2 Length divided by squared time Force N Mass multiplied by acceleration
- 8. DERIVED SI UNITS (cont’d) 8 Characteristic Fundamental Unit Description Pressure Pa Newton divided by volume Kinematic Viscosity m^2 / s Squared length divided by time Work (energy) J Newton multiplied by length Power W Power divided by time Electric Charge C Amperes multiplied by time Voltage (electromotive force) V Power divided by amperes Electric Resistant Ω Voltage divided by amperes
- 9. DERIVED SI UNITS (cont’d) 9 Characteristic Fundamental Unit Description Electric Capacitance F Amperes multiplied by time divided by voltage Magnetic Flux Wb Voltage multiplied by time Inductance H Voltage multiplied by time divided by amperes Magnetic Flux Density T Magnetic flux divided by area Magnetic Field Strength A/m Amperes divided by length Magnetomotive Force A Amperes Luminance cd / m^2 Candela divided by area
- 10. DERIVED SI UNITS (cont’d) 10 Characteristic Fundamental Unit Description Luminance flux Im Candela multiplied Illuminations Lx Luminance flux divided by area
- 12. FUNDAMENTAL CONSTANTS 12 Speed of light in vacuum; unchanging in space or time Not dependent on time or place; gravitational attraction of matter Varies by place; within the US, it varies 0.2% (scales should be calibrated at point of use) Relationship between pressure, volume and temperature in an ideal gas Relationship between amount of substance and number of molecules in that amount Back body used in calibration; temp of black body measured by its color
- 13. COMMON MEASUREMENTS 13 • Inspection, Measurement, and Test Equipment (IM&TE) • To calibrate any equipment, it is necessary to generate a known amount of the variable to be measured and apply it to the unit under test. • Variable can be generated by using known generator (i.e. gage block) or unknown generator (in the case it must be measured simultaneously with calibrated device). • Where IM&TE is also a generator then the output must be known.
- 14. COMMON MEASUREMENTS (cont’d) 14 • Laboratory Measurement of Temperature: – Liquid-in-glass thermometers must be immersed in the calibration bath to a predefined depth. – Resistance-Temperature-Devices work on the basis of temperature versus resistance characteristics. – Thermocouples work the basis of temperature versus voltage characteristics. – Optical Pyrometer is used to measure temperatures above 200 C by measuring the color of the object from the distance.
- 15. COMMON MEASUREMENTS (cont’d) 15 • Laboratory Measurement of Humidity: – Humidity is best measured using a chilled mirror hydrometer. – Psychrometer measures humidity by comparing the temperature near a dry bulb with that of a wet bulb (the lower the humidity the greater the cooling)
- 16. COMMON MEASUREMENTS (cont’d) 16 • Laboratory Measurement of Pressure: – The most accurate way to measure pressure is to generate it (weight divided by the area). – Low pressures can be measured using manometer (column of liquid responds to positive and negative pressures). – The Bourdon gage measures pressure by mechanical means of elasticity (elastic element used). – The Quartz Bourdon gage measures pressure by means of electronic transducer.
- 17. COMMON MEASUREMENTS (cont’d) 17 • Laboratory Measurement of Torque: – Torque is difficult to generate and measure. – Greatest uncertainty, when it comes to measuring torque, is the distance from the center of the mass to the center of the ratating lever arm.
- 18. COMMON MEASUREMENTS (cont’d) 18 • Laboratory Measurement of Force: – Force is generate by hanging calibrated weights on the unit under test (requires correction to local gravity).
- 19. COMMON MEASUREMENTS (cont’d) 19 • Laboratory Measurement of Mass: – Masses are calibrated by comparison to known and traceable reference standards. – Gravity correction required????? • No, if the materials of the standard are the same as of the unit under test. • Yes, where there is difference in materials.
- 20. COMMON MEASUREMENTS (cont’d) 20 • Laboratory Measurement of Electrical Quantity: – Electronic Calibrators, Capacitors and Inductors, Digital Multimeters, Null Indicators, Bridges and Transfer Standards. – Number of digits on the display does NOT mean that the same level of accuracy has been achieved. – In case where DC is used, special attention should be paid to high and low voltage (potential results distortion)
- 21. COMMON MEASUREMENTS (cont’d) 21 • Laboratory Measurement of Electrical Calculations: – Calibration technician is expected to perform simple calculations when it comes to electronics and their properties. – Electric Current is measured in amperes – Electronic Potential or electromotive force is measured in volts – Electrical resistance is measured in ohms next slide – Electrical Power is measured in Watts
- 22. COMMON MEASUREMENTS (cont’d) 22 • Ohm’s Law: E = iR or i = E/R or R = E/I R – resistance i – current E – voltage
- 23. COMMON MEASUREMENTS (cont’d) 23 • Laboratory Measurement of Time and Frequency: – GPS (Global Positioning System) signal is considered traceable to national standards and has output of about 10MHz (at full capacity). When it comes to length measurements, the most important fact to remember is that the temperature for dimensional measurements shall be 20 C!
- 24. PRINCIPLES AND PRACTICES OF TRACEABILITY 24 • Traceability is defined as ability to link the results of the calibration and measurement to related standard and/or reference (preferably national or international standard) through an unbroken chain of comparisons. • Calibration is typically performed by measuring a test unit against a known standard or reference. • Master standard (i.e. gages) are kept by National Measurement Institute (NMI) of each country.
- 25. PRINCIPLES AND PRACTICES OF TRACEABILITY (cont’d) 25 • National Institute of Standards and Technology (NIST) provides internal tracking numbers, which are often used as evidence of traceability. • WARNING! NIST does not certify or guarantee that calibration and measurements are correct, nor does it provide any kind of certification of accuracy and calibration and the internal number does mean that the test unit calibrated is indeed valid. NIST only provides certifications for the work performed by them.
- 26. TYPES OF MEASUREMENT STANDARDS 26
- 27. TYPES OF MEASUREMENT STANDARDS (cont’d) 27 • International Standard – Highest level of reference standards agreed by multiple countries for the common purpose (kept at Bureau of Weights and Measures in Sevres, France). • Intrinsic Standard – If properly maintained they provide standards based on laws of physics, fundamentals of nature, invariant properties of materials. • National Standard – In US, it is maintained by NIST, and it is a standard formed by one or many groups within one country (or only few countries = adapted).
- 28. TYPES OF MEASUREMENT STANDARDS (cont’d) 28 • Reference Standard – Item of highest metrological quality located at a site where calibration is being conducted. • Master Standard – Lower level of Reference Standard and used for calibration of lower level calibration requirements measuring devices. • Working Standard (working master) – Should be compared to Master Standard or Reference Standard on regular basis; Used for daily checks / comparisons of the calibrated devices.
- 29. TYPES OF MEASUREMENT STANDARDS (cont’d) 29 • Derived Standard – Combination of two or more standards for the sake of fulfilling traceability requirements. • Consensus Standard – Example of such standard is Rockwell Hardness; This standard is used when no traceability to a known standard can be established, but rather an agreement of all parties is considered the standard. • Transfer Standard – This standard is actually an artifact designed to be calibrated at one location and transferred to another location without its impact to validity of calibration (deviation ranges due to transportations acceptable). – NOTE: Sometimes Transfer Standard is used to describe transferring values from a NIST standard to a local standard.
- 30. SUBSTITUTE OF CALIBRATION STANDARDS 30 • When no valid standard is available at point of use, a technician can: – Postpone the calibration until the standard becomes available, or – Identify suitable substitute standard • If substitute standard is to be used then: – Procedure must allow it – Substitute standard must be available at point of use – Substitute standard must be of equal or better specifications – The uncertainty of standard must be equal or better than required to calibrated the test unit
- 31. SUBSTITUTE OF CALIBRATION STANDARDS (cont’d) 31 • ISO standard for calibration laboratories is: – ISO 17025 – This standard is NOT procedure heavy • ANSI standard for calibration is: – ANSI Z540-1 Remember: Not all procedures and practices allow substitutions of standards and sometimes they might be test unit specific Remember: Substitution is a “judgment call” made by a technician (where no documented procedure and/or practice exists)
- 32. THANK YOU! 32 Presented By: Jasmin NUHIC