MEASUREMENT AND ITS TYPE
MEASUREMENT:
MEASUREMENT
IS USED TO TELL US THE LENGTH, THE WEIGHT, THE TEMPERATURE, OR A CHANGE IN ONE
OF THESE PHYSICAL ENTITIES OF A MATERIAL. IT IS THE RESULT OF AN OPINION FORMED
BY ONE OR MORE OBSERVERS ABOUT THE RELATIVE SIZE OR INTENSITY OF SOME PHYSICAL
QUANTITY. THE OPINION IS FORMED BY THE OBSERVER AFTER COMPARING THE OBJECT WITH
A QUANTITY OF SAME KIND CHOSEN AS A UNIT, CALLED STANDARD.
THE
RESULT OF MEASUREMENT IS EXPRESSED BY A NUMBER REPRESENTING THE RATIO OF THE
UNKNOWN QUANTITY TO THE ADOPTED STANDARD.
FOR EXAMPLE,
10 CM LENGTH OF AN OBJECT IMPLIES THAT THE OBJECT IS 10 TIMES AS LARGE AS 1 CM;
THE UNIT EMPLOYED IN EXPRESSING LENGTH.
TYPE OF MEASUREMENT
MEASUREMENTS
ARE DIVIDING IN TO THREE CATEGORIES
DIRECT AND INDIRECT MEASUREMENTS
DIRECT MEASUREMENTS
THE VALUE
OF THE PHYSICAL PARAMETER (MEASURAND) IS DETERMINED BY COMPARING IT DIRECTLY
WITH REFERENCE STANDARDS. THE PHYSICAL QUANTITIES LIKE MASS, LENGTH, AND TIME
ARE MEASURED BY DIRECT COMPARISON.
INDIRECT MEASUREMENTS:
THE VALUE
OF THE PHYSICAL PARAMETER (MEASURAND) IS MORE GENERALLY DETERMINED BY INDIRECT
COMPARISON WITH SECONDARY STANDARDS THROUGH CALIBRATION.
PRIMARY, SECONDARY AND TERTIARY MEASUREMENTS
PRIMARY:
IN
PRIMARY MODE, THE SOUGHT VALUE OF A PHYSICAL PARAMETER IS DETERMINED BY
COMPARING IT DIRECTLY WITH REFERENCE STANDARDS. THE REQUISITE INFORMATION IS
OBTAINABLE THROUGH SENSES OF SIGHT AND TOUCH. E.G. ARE MATCHING OF TWO LENGTHS
WHEN DETERMINING THE LENGTH OF AN OBJECT WITH A RULER.
SECONDARY:
THE
INDIRECT MEASUREMENTS INVOLVING ONE TRANSLATION ARE CALLED SECONDARY
MEASUREMENTS. THE CONVERSION OF PRESSURE INTO DISPLACEMENT
TERTIARY:
THE
INDIRECT MEASUREMENTS INVOLVING TWO CONVERSIONS ARE CALLED TERTIARY
MEASUREMENTS. THE MEASUREMENT OF THE SPEED OF A ROTATING SHAFT BY MEANS OF AN
ELECTRIC TACHOMETER IS THE EXAMPLE OF THE TERTIARY MEASUREMENTS.
CONTACT AND NON-CONTACT TYPE MEASUREMENTS
CONTACT MEASUREMENT: - WHERE THE SENSING ELEMENT OF THE MEASURING DEVICE HAS
A CONTACT WITH THE MEDIUM WHOSE CHARACTERISTICS ARE MEASURED.
NON-CONTACT: - WHERE THE
SENSOR DOES NOT COMMUNICATE PHYSICALLY WITH THE MEDIUM.
References:
- Measurement & Control By Dr. D.S. Kumar
very useful information
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