MEASUREMENT AND ITS TYPE

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