measurement week 5

8/11/2019 Measurement Week 5

1/17

MEASUREMENT

Week 5


2/17

The science of measurement

Metrology.Accuracy.- How close a measurement is to its

true value.

Precision.- How close measurements are to eachother.


3/17

The five main physicall quantities used in

engineering are

- length (metre),

- mass (kilogram,

- time (second),

- electric current (ampere),- and temperature (kelvin).


4/17

Together with

- light intensity (candela) and

- the mole, the amount of a substance used inchemistry,

the seven units are the base units of the

International System of Units (SI units).


5/17

Other units are derived from these base units,

for example

- speed (length and time) and

- force (length, time and mass).


6/17

Note.- SI units have been adopted throughout

the world in science and engineering except in

the USA where a system based on the imperial

units of inches, pounds, and degrees

Fahrenheit is still used, and still survives in

other countries in everyday use.


7/17

Measurement is a fundamental requirement for

ensuring quality.

Two techniques are used together:

- Quality Control

- Quality Assurance


8/17

Quality Control is a reactive process of

inspection which uses measurement ro find

and eliminate defects in products.

Quality Assurance uses proactive

management systems to prevent errors

occurring.


9/17

Many different instruments are used for

inspection. They need to be calibrated against

standards to ensure accuracy and precision.

Inspection areas are located in temperature-

controlled rooms to eliminate errors in length

measurement due to thermal expansion of

metals in instruments and products.


10/17

Economic manufacture and the

interchangeability of parts such as screw threads

require a system of tolerances that allow a

defined error in accuracy for an acceptable

product. Where two parts fit together, there is a

standard system of limits and fits which defines

the tolerances that allow parts such as holes andshafts to have clearance, transition, or

interference between them depending on the

function.


11/17

This ensures that any part from a batch can

mate with any other part from a batch so that

parts do not have to be specially made to fit

together.

AE American English

BE British English


12/17

Metre (BE) Meter (AE)

Odometer.- An instrument used for measuring

the distance travelled in a vehicle. (AE)

Milometer (BE)

Tachometer.- An instrument which measuresthe working speed of an engine, usually in

revolutions per minute.


13/17

Imperial measurements: (UK and USA)

Inches, feet, yards

Ounces, pounds Cups, pints, quarts, gallons

Farenheit scale:(water freezes at 32 and boils at 212)


14/17

Micrometer.- A gauge which measures small

distances or thicknesses between two faces,

one of which can be moved away from or

toward the other by turning a screw with a

fine thread.

Dial gauge.- An instrument which measures

small linear distances.


15/17

Callipers (calipers).- An instrument for

measuring external or internal dimensions,

having two hinged legs resembling a pair of

compasses and in-turned or out-turned

points.

Depth.- The distance down from the top

surface of something and


16/17

Depth.- The distance down from the top

surface of something and also the distance

from the front to the back of something. The swimming pool is 10 metres deep

The shelf is 40 centimetres deep


17/17

Micrometre.- The SI term for one millionth of

a metre. This shouldntbe confused with the

instrument micrometer discussed earlier in

the unit, though the pronunciation is the

same. Micron.- A non-SI term used for micrometre.

In AE this helps differentiate between the gauge and the measurement, which

have the same spelling.

measurement week 5

Documents