Factors affecting the accuracy of the Measuring System
The basic components of an accuracy evaluation are the five elements of a measuring system such as:
• Factors affecting the calibration sta
• Factors affecting the work piece.
• Factorsngthe inherentaffecticharacteristics of the instrument.
• Factors affecting the person, who car
• Factors affecting the environment.
1. Factors affecting the Standard: It may be affected by:
-Coefficient of thermal expansion
-Stability with time
2. Factors affecting the Work piece: These are: -Cleanliness
-Surface finish, waviness, scratch, surface defects etc., -Hidden geometry
-Elastic properties,-adequate datum on the work piece -Arrangement of supporting work piece
-Thermal equalization etc.
3. Factors affecting the inherent characteristics of Instrument: -Adequate amplification for accuracy objective
-Effect of friction, backlash, hysteresis, zero drift error
-Deformation in handling or use, when heavy work pieces are measured -Calibration errors
-Mechanical parts (slides, guide ways or moving elements) -Repeatability and readability
-Contact geometry for both work piece and standard.
4. Factors affecting person:
-Sense of precision appreciation
-Ability to select measuring instruments and standards -Sensible appreciation of measuring cost
-Attitude towards personal accuracy achievements
-Planning measurement techniques for minimum cost, consistent with precision requirements etc.
5. Factors affecting Environment:
-Temperature, humidity etc.
-Clean surrounding and minimum vibration enhance precision -Adequate illumination
-Temperature equalization between standard, work piece, andinstrument -Thermal expansion effects due to heat radiation from lights
-Heating elements, sunlight and people
-Manual handling may also introduce thermal expansion.
Higher accuracy can be achieved only if, ail the sources of error due to the above five elements in the measuring system are analyzed and steps taken to eliminate them. The above analysis of five basic metrology elements can be composed into the acronym SWIPE, for convenient reference where,
S –STANDARD W –WORKPIECE I –INSTRUMENT
P –PERSON E –ENVIRONMENT