Principles of Measurement INTRODUCTION TO MEASUREMENT 1 Measurement

Principles of Measurement • • • INTRODUCTION TO MEASUREMENT 1 Measurement units 2 Measurement system applications 3 Elements of a measurement system 4 Choosing appropriate measuring instruments

Measurement ● ● Measurement of a given quantity (measured variable) is essentially an act or result of comparison between the quantity and predetermined or predefined standards. ﺇﻳﺠﺎﺩ ﻣﻘﺪﺍﺭ ﻛﻤﻴﺔ ﻓﻴﺰﻳﺎﺋﻴﺔ ﺃﻮ ﻣﺘﻐﻴﺮ ﻓﻴﺰﻳﺎﺋﻲ ﺃﻮ ﺗﻘﺪﻳﺮ ﺣﺎﻟﺔ ﻣﺎ ﺑﺎﺳﺘﺨﺪﺍﻡ ﺟﻬﺎﺯ

Instruments and Measurement Systems • Measurement involves the use of instruments as a physical means of determining the quantities or variables. • Because of modular nature of the elements within it, it is common to refer the measuring instrument as a measurement system. • A measurement system is a tool used for quantifying the measured variable. As such, a measurement system is used to extend the abilities of the human senses that, while they can detect and recognize different degrees of roughness, length, sound, color, and smell, are limited and relative; they are not very adept at assigning specific values to sensed variables.

Methods of Measurement • Direct Methods: In these methods, the unknown quantity (called the measured ) is directly compared against a standard (e. g. rulers) • Indirect Methods: Measurements by direct methods are not always possible, feasible and practicable. In engineering applications measurement systems are used which require need of indirect method for measurement purposes.

Standards • When a measurement system is calibrated, its indicated value is compared directly with a reference value. • This reference value forms the basis of the comparison and is known as the standard. • This standard may be based on the output from a piece of equipment, from an object having a well defined physical attribute to be used as a comparison, or from a well-accepted technique known to produce a reliable value.

Factors affects your Measurements

Unites and dimensions • Standard units (basic quantities) units( length – mass – time) dimensions (meter-kilogramsecond) • Cgs unit (cm-gram-sec. ) • Mks unit (m-kg-sec. ) • Fbs unit (ft-lb-sec. ) • SI unit (m-kg-sec. )

Fundamental SI units • • • Length Mass Time Electric current Temperature Luminous intensity Matter Plane angle Solid angle meter kilogram second ampere Kelvin candela mole radian steradian m kg s A K cd mol rad sr

Derived units • • • Area Volume Velocity Acceleration Angular velocity Density Mass flow rate Volume flow rate force

Derived units • • Pressure Torque Power Work Kinematics viscosity Dynamic viscosity Volt emf pot diff Thermal conductivity

Power unit 1/10 ﺩﻳﺴﻲ 1/100 ﺳﻨﺘﻲ 1/1000 ﻣﻴﻠﻠﻲ 1/1000000 ﻣﻴﻜﺮﻭ 1/100000 ﻧﺎﻧﻮ 1/1000000 ﺑﻴﻜﻮ ﻓﻴﻤﺘﻮ 1/100000000 ﺃﺘﻮ 1/1000000000 d c mm µ n p f a • • • •

units • • • Mile = 1. 609 km=1760 yard 1 yard=3 ft 1 ft=12 inch 1 inch = 2. 54 cm 1 g= 9. 81 m/s. s 1 g=32. 2 ft/s. s

Closed loop control system

Open loop control system