CE738_Lecture_03_MeasurementSystem_6a26584a-7179-4a48-b966-f4b5d951f503.pdf

CE 738A : Hydrometry Standards and Measurement System 1  Recap Measurement Metrology and Hydrometry & Importance of measurements Four scales / levels of measurements Standards for measurements – d...

CE 738A : Hydrometry Standards and Measurement System 1  Recap Measurement Metrology and Hydrometry & Importance of measurements Four scales / levels of measurements Standards for measurements – definition & desired characteristics International System of Units – Set-up & history 7 base units, Derived units, Prefixes, Non-SI units and Formatting guidelines 2 Hierarchy of Measurement Standards 3 Source: National Physical Laboratory of India  Standards for Water Isotopes Isotopes: same number of protons but a different number of neutrons in their nucleus. Stable isotopes of hydrogen and oxygen Isotopologues: molecules that differ only in their isotopic composition Isotopolgues of water: o H216O (~ 99.731%), o HD16O (~ 0.003789%), o H217O (~0.037%) o H218O (~ 0.2%) Isotopic compositions (R): relative abundance of a heavier (HD16O or H218O) to the lighter H216O isotope 𝑅𝑠𝑎𝑚𝑝𝑙𝑒 𝛿= − 1 × 1000 𝑅𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 4  Standards for Water Isotopes Vienna Standard Mean Ocean Water (VSMOW):Primary standard Standard Light Antarctic Precipitation (VSLAP):Complementary standard VSMOW o Prepared by International Atomic Energy Agency (IAEA) in 1966 o Supply dwindled by mid-1990s VSMOW2 o Prepared in 1999 o 300 litre o 20 ml ampoules once in 3 years Need for working standards 5 Source: U. S. Geological Survey  Measurement System A collection of instruments and components arranged to measure physical variable and convert them into readable, interpretable data for analysis and control. 6 Source: Dunn and Davis (2017)  Transducers, Sensors and Actuators Transducer: o Devices that convert one form of energy or physical quantity into another o Conversion o Bidirectional transducers & transceivers Sensor: o Devices that receives and responds to a signal or stimulus from a physical system o Input o Temperature and humidity sensors, microphone Actuator: o Devices that convert electrical signals into a physical action or change o Output o Electric motors, loudspeakers 7 Temperature Measurement System Resistance Temperature Detector (RTD) 8 Mercury Thermometer – Is this a measurement system? 9 Source: itoldya420  Classification of Sensors Active Sensors: Require external power (e.g., RTD, photodiodes) Passive Sensors: Generate their own power (e.g., piezoelectric sensors, thermocouples) Analog Sensors: Continuous output signal proportional to signal (e.g., thermocouples, RTD) Digital Sensors: Discrete output signal (e.g., proximity sensors) Invasive Sensors: Direct contact with the object being measured (e.g., RTD) Non-invasive Sensors: No physical contact with the object being measured (e.g., Infrared thermometers, optical & acoustic sensors) 10