EME revision points for Unit 1

 Hints for Quick recall/revision

Unit 1

1. Metrology : Science of Measurement with agreed units and methods

2. Types of metrology :  use short form LIDS  to recall types

LIDS means

L : legal metrology    I : Industrial metrology  D : Deterministic  metrology  S : Scientific metrology

3. Instrument characteristics :   use short form APSC  to recall types

Accuracy : Closeness with true value of measurement

Precision : Repeatability of  same measurement in  similar conditions of measurement

Sensitivity : Ability to detect small input variations by instrument

Calibration : Checking instrument scale with certified standards.  Slip gauges are used as a standards for calibration of vernier, micrometer

4. Errors :

Types : Systematic or controllable errors   and Random( Accidental errors)

Reading error : Parallax error

 Observer's direction should be proper to read the correct reading.

Loading error or contact pressure Error:

More force or pressure applied during measurement

Instrumental error :  faulty or defective instrument , pointer bend, loose joints,etc

Calibration error : Instrument not calibrated properly. Standard not used to check accuracy

Random error: Accidental and can not controlled , no causes can be detected

Least count : minimum measurement of an instrument

Vernier caliper :

LC = Value of smallest div on Main scale/ Total No of divisions on Vernier scale

LC = 1/ 50 = 0.02 mm

Micrometer:

LC = Pitch of the screw/ Total No of divisions on Circular scale

 LC = 0.5/50 = 0.01 mm

Factors for selection of an Instrument

1. Dimension to be measured Like length, diameter, depth

2.Range of an instrument 

3. Accuracy /LC of an instrument

4. Sensitivity 

5. Cost of an instrument