MEASUREMENT

S.I. UNITS system International units A modification of the older French metric system.

Base Units Base units they are not derived from any pre-existing number or formula. like distance, temperature and time, and we do so by agreeing to a reliable definition of some basic facts.

Base Units Length

Base Units Length Meter

Base Units Length Meter (m)

Base Units Mass

Base Units Mass Kilogram

Base Units Mass Kilogram (kg)

Base Units Time

Base Units Time Seconds

Base Units Time Seconds (s)

Base Units Temperature

Base Units Temperature Kelvin

Base Units Temperature Kelvin (K)

Base Units Amount of Substance

Base Units Amount of Substance mole

Base Units Amount of Substance mole (mol)

Base Units Electric Current

Base Units Electric Current Ampere

Base Units Electric Current Ampere (A)

Base Units Luminous Intensity

Base Units Luminous Intensity candela

Base Units Luminous Intensity candela (cd)

Derived Units Area

First Derivative Area length squared

Derived Units Area length squared (m 2 )

Second Derivative Volume

Second Derivative Volume length cubed

Second Derivative Volume length cubed (m 3 )

Derived Units Density

Derived Units Density mass per unit volume

Derived Units Density mass per unit volume (kg/m 3 )

First Derivative Speed (velocity)

Derived Units Speed (velocity) distance traveled per unit time

Second Derivative Speed (velocity) distance traveled per unit time (m/s)

Third Derivative Acceleration

Third Derivative Acceleration speed changed per unit time

Derived Units Acceleration speed changed per unit time (m/s 2 )

Derived Units Force

Derived Units Force mass times acceleration of an object

Derived Units Force mass times acceleration of an object (kg m/s 2 )

Derived Units Force Note: (kg m/s 2 ) = Newton (N)

Derived Units Pressure

Derived Units Pressure Force per unit area

Derived Units Pressure Force per unit area (kg /m s 2 ) or N/m 2

Derived Units Pressure Note: (kg /m s 2 ) = N/m 2 = Pascal (Pa)

Derived Units Energy

Derived Units Energy Force times distance traveled

Derived Units Energy Force times distance traveled (kg m 2 /s 2 )

Derived Units Energy Note: (kg m 2 /s 2 ) = Joule (J)

Other Units to Know About Length –Angstrom (Å) = m

Other Units to Know About Temperature 3 common scales Fahrenheit Celsius Kelvin

Temperature Freezing Pt Boiling Pt 32 °F 212 °F 0 °C 100 °C K K

Temperature Formulas for converting scales °C = K 1.8(°C ) + 32 = °F

Other units to know about Volume Liter (l) = 1 dm 3 1 ml = 1 cm 3

STANDARDS OF MEASUREMENT The standards of measurements are very useful for calibration of measuring instruments. They help in minimizing the error in the measurement systems.

The difference types of standards of measurement and classified by their function and application in the category : 1. Primary Standards 2. Secondary standards 3. Working standards

Primary Standard A primary standard quantity will have only one value and it is fixed. An instrument which is used to measure the value of primary standard quantity is called primary standard instrument. It gives the accurate value of the quantity being measured. No pre-calibration is required for this instrument. It is used to calibrate the instruments having less accuracy. By comparing the readings of the two instruments, the accuracy of the second instrument can be determined.

Secondary Standard The value of the secondary standard quantity is less accurate than primary standard one. It is obtained by comparing with primary standard. For measurement of a quantity using secondary standard instrument, pre-calibration is required.

Without calibration, the result given by this instrument is meaningless. Calibration of a secondary standard is made by comparing the results with a primary standard instrument or with an instrument having high accuracy or with a known input source. In practical fields, secondary standard instruments and devices are widely used.

Working standards: These standards are similar in design to primary & secondary standards. But being less in cost and are made of low grade materials, they are used for general applications in metrology laboratories.