Chapter I:Metrology and

Control

1

មាត្រ�សាត្រ�្តនិងការត្រ��ួពិនិ�្យ

Prepared by: SRY Vannei

I. Definition of MeasureI.1. Notion of measure: All most of the work pieces have neither exactly dimension value nor perfect surface. The dimension values are function with tolerances, correction geometric of the surface, surface condition and so on.

The purposes of metrology are measurement and verification or comparison work pieces for assure the condition function.

Metrology is used with all the mechanical work, optic, pneumatic, or electric that can be assure the control.

2

3

I.2. Quality of instruments in measurement:I.2.1. Control range:Control is the range of the biggest measure for work piece. It indicates in measurement instrument that doesn’t have high error and maximum tolerance.

I.2.2. Sensitivity of instrument in measure:Sensitivity (or resolution) is the coefficient made by the proportion of needle displacement(de) with the real changing of measurement work piece(dg). It is the smallest difference in dimension that the instrument can detect or distinguish. Ex. A wooden yardstick has far less sensitivity than a finely graduated steel rule.

4Sensitivity(k) =

5

I.2.3. Fidelity:The quality of apparatus is the accurate value of the measurement. However, the exact value dimensions can not be get. There is fidelity errors which are sum of many errors such as error parallel and a long position.

e = vmax - vmin

6

I.2.4. Justice:It is sum of error systematic on instrument measurement (ex. Error zero, graduation …).

Where, vm is value measurev is the real value

c = vm - v

7

I.2.5. Precision: (not accuracy)It is the degree to which the instrument gives repeated measurements of the same standard. It is the error that get from error justice and error fidelity. Ex. A common wooden or aluminum ruler, will expand or contract, depending on the environmental temperature, thus giving different measurements. I.3. Errors of measurement:It is the different result from different readers that is different from the exact value of measure. The smallest error, the greatest precision measure.Ex. The real dimension of the work piece is 50mm and the value from reader is 50.02mm. The precision of this measure is 0.02mm. We also call error absolute. Other error call error relative which is error in percentage. [(50.02-50)/50]×100 = 0.04%.

8

I.4. Causes of errors metrologyThe causes of those errors are originally from: Apparatus Operators Atmosphere I.4.1. Errors of apparatus-The constant fault of origin position on the apparatus.Ex. Caliper, zero position is not at the close position.Because of:• Unequal of the intervals graduations.• Slip of guiding.• Surface of the contact incorrect.

9

10

I.4.2. Errors of operators

Fault appreciation of the correct mark. For prevent this fault, the operators need to see in the position of perpendicular to the mark point.

Fault in manipulation:Use to much force on the contact

apparatus.Fault of presentation of the apparatus.

11

12

I.4.3. Errors of varies temperatures:Environment temperature in the room measure is important for the measurement. In general, the temperature using of the apparatus is the same as work piece temperature. In opposite, dilating of equipment with the work piece creates fault in measure.II. Units of the length and angle in SI system:The units of the length in SI system is metre (m) [mètre]. In fabrication, unit measure is mm.

13

Symbols nm μm mm cm dm m km

1nm 1 10-3 10-6 10-7 10-8 10-9 10-12

1μm 103 1 10-3 10-4 10-5 10-6 10-9

1mm 106 103 1 10-1 10-2 10-3 10-6

1cm 107 104 10 1 10-1 10-2 10-5

1dm 108 105 102 10 1 10-1 10-4

1m 109 106 103 102 10 1 10-3

1km 1012 109 106 105 104 103 1

Table of Length Unites

14

By Measure

By Plug Gages (gauges)

15

Unit of measure angles in system SI is radian (rad). Ex. Angle of 900 = π/2 rad, angle of 1800 = π rad.In fabrication, the unit measure is degree ( 0 ).

III. Class of the control way:

In metrology, the dimensions of the control are obtained by two ways, measurement and calibration.