SELECTING AN MEASURING INSTRUMENT

SELECTING AN MEASURING INSTRUMENT

THE SELECTION OF AN INSTRUMENT FOR A SPECIFIC MEASUREMENT APPLICATION REQUIRES THE CONSIDERATION OF SEVERAL FACTORS THE FOLLOWING BEING CERTAINLY FUNDAMENTAL TO ENTIRE PHILOSOPHY OF MEASUREMENT AND INSTRUMENT SELECTION.

MAXIMUM AND MINIMUM VALUES THE INPUT VARIABLES ARE EXPECTED TO ASSUME -

THE INSTRUMENT RANGE MUST EQUAL TO THE EXPECTED RANGE OF VARIABLE TO BE MEASURED. EXCESSIVE INSTRUMENT RANGE MEANS A LOT OF READABILITY.FOR A WIDE RANGE IN THE VARIABLE, MULTIPLE RANGE OF INSTRUMENT ARE DESIRED.

NATURE OF THE INPUT SIGNAL - 

IS IT CONSTANT OR TIME DEPENDENT? IF TIME VARIANT, THEN WHETHER VARIATION IS PERIODIC, TRANSIENT OR RANDOM. FOR TRANSIENT MEASUREMENT, IT IS TO BE ENSURED THAT NATURAL FREQUENCIES AND TIME CONSTANTS ARE PROPERLY SELECTED.

NON INTERFERENCE WITH MEASURING SYSTEM -

THE BASIC PRINCIPAL OF MEASURING IS THAT THE ACT SHOULDN'T AFFECT THE QUANTITY BEING MEASURED. OUR JOB IS TO SEE THAT THE INSTRUMENT OFFERS MINIMUM INTERFERENCE.

COST CRITERION –

THE DEMAND FOR A HIGH ACCURACY WOULD REQUIRE THE USE OF HIGHLY SOPHISTICATED AND SPECIALIZED INSTRUMENTS HAVING SPECIAL ANCILLARIES TO COMPENSATE FOR AMBIENT CONDITION. THE MORE ACCURATE INSTRUMENTS ARE MORE DIFFICULT TO OPERATE.

NEVER DEMAND AN ACCURACY OF MEASUREMENTS HIGHER THAN THAT WHICH IS REALLY NEEDED, AND NEVER FORGET THAT EACH DEGREE OF ACCURACY, IF DEMANDED, IS LIKELY TO HAVE A DIS PROPORTIONATE EFFECT ON THE COMPLEXITY AND COST F THE MEASURING APPARATUS

EASY CALIBRATION -

THE INSTRUMENT SHOULD BE EASY TO CALIBRATE AND CALIBRATION CURVE MUST BE STABLE FOR TIME REQUIRE TO COMPLETE A TEST.

CONVENIENCE AND EASE IN READING THE INSTRUMENT – 

SCALES THAT ARE PROPERLY RULED AND NUMBERED FOR EASY LEGIBILITY, PROPER ILLUMINATION, AND READING STRAIGHT DIALS ARE FEATURE THAT WILL HAVE A DECISIVE INFLUENCE ON THE SELECTION OF AN INSTRUMENT.      OFTEN ENGINEER RELIES WITH EXPERIENCE, WHEN MAKING A COMPARISON OF MANY FACTORS IN THE COURSE OF PROPER SELECTION OF INSTRUMENTS.