Week 2 - Eng metrology and instrumentation

Question 1

Measurement Standard

Answer 1

• Inch, foot; based on human body
• 4000 B.C. Egypt; King’s Elbow=0.4633 m, 1.5 ft, 2 handspans, 6 hand-widths, 24 finger-thickness
• AD 1101 King Henry I ->yard (0.9144 m) from his nose to the tip of his thumb
• 1872, Meter (in Greek, metron to measure)- 1/10 of a millionth of the distance between the North Pole and the equator
• Platinum (90%)-iridium (10%) X-shaped bar kept in controlled condition in Paris->39.37 in
• In 1960, 1,650,763.73 wave length in vacuum of the orange light given off by electrically excited krypton 86.

Question 2

MEASUREMENT AND INSPECTION

Answer 2

1. Metrology
2. Inspection Principles
3. Conventional Measuring Instruments and Gages
4. Measurement of Surfaces
5. Advanced Measurement and Inspection Techniques

Question 3

Measurement

Answer 3

Procedure (unknown quantity is compared to a known standard, using an accepted and consistent system of units

• May involve a simple linear rule to scale the length of a part
• Or it may require a sophisticated measurement of force vs deflection during a tension test
• Provides a numerical value of the quantity of interest, within certain limits of accuracy and precision

Question 4

Metrology

Answer 4

-science of measurement
7 Quantities
1. Length(m)
2. Mass (kg)
3.Time(s)
4.Electric current(A)
5. Temperature(K)
6.Light intensity (candela)
7. Matter (mole)

Question 5

Metrology (derived from basic quantities)

Answer 5

• Area
• Volume
• Velocity and acceleration
• Force
• Electric voltage
• Heat energy

Question 6

Manufacturing metrology

Answer 6

Measures:

• Length and width
• Depth
• Diameter
• Straightness, flatness, and roundness, etc.
• Surface roughness

Question 7

Selection of Measuring Instruments

Answer 7

• Accuracy
• Precision
• Magnification (amplification)
• Sensitivity (Resolution);
• Rules of 10
• Stability (drift);
• Standard measuring -temperature 20C

Question 8

Accuracy

Answer 8

closeness of agreement between an observed value and a standard

Question 9

Precision

Answer 9

closeness of agreement between randomly selected individual measurements

Question 10

Sensitivity (Resolution)

Answer 10

the smallest difference in dimensions that the instrument can detect or distinguish

Question 11

Rules of 10 (gage maker’s rule)

Answer 11

At least 10 times more accurate than the tolerance

Question 12

Stability (drift)

Answer 12

capability to maintain calibrated status

Question 13

Repeatability (equipment variation)

Answer 13

Variation in multiple measurements by an individual using the same instrument.

Question 14

Reproducibility (operator variation)

Answer 14

Variation in the same measuring instrument used by different individuals

Question 15

Calibration

Answer 15

Comparing a measurement device or system to one having a known relationship to national standards

Question 16

Repeatability and Reproducibility Studies

Answer 16

Quantify and evaluate the capability of a measurement system

• Select m operators and n parts
• Calibrate the measuring instrument
• Randomly measure each part by each operator for r trials
• Compute key statistics to quantify repeatability and reproducibility

Question 17

Accuracy

Answer 17

• Degree to which a measured value agrees with the true value of the quantity of interest
  
  • A measurement procedure is accurate when it is absent of systematic errors
  • Systematic errors: positive or negative deviations from true value that are consistent from one measurement to the next

Question 18

Precision

Answer 18

• Degree of repeatability in the measurement process

- Good precision means that random errors in the measurement procedure are minimized

Question 19

Accuracy vs precision

Answer 19

slide 15 pic

Question 20

Dominant systems of units

Answer 20

1. U.S. customary system (U.S.C.S.)

2. SI (for Systeme Internationale d’Unites) - the “metric system”

Question 21

Product quality for manufacturing importance

Answer 21

• For interchangeable manufacture
• Standardization and mass production
• Product components must fit/assemble properly and be replaceable
• Prevention of defect

To verify quality-requires inspection

Question 22

High product quality:

Answer 22

Reliable performance

Cost is high

Question 23

Low quality product

Answer 23

Less reliable/fails after short time
Low cost
Difficult to use

Question 24

Inspections

Answer 24

Inspection involves the use of measurement and gaging techniques to determine whether a product, its components, subassemblies, or materials conform to design specifications

Question 25

Types of Inspections

Answer 25

• By variables: product or part dimensions of interest are measured by the appropriate measuring instruments
• By attributes:product or part dimensions are gaged to determine whether or not they are within tolerance limits