static characteristics in instrumentation and metrology
TRANSCRIPT
STATIC CHARACTERISTICS
Faizan AliRoll No. 33
STATIC CHARACTERISTICS:9 Calibration10Repeatability11Reproducibility12Linearity13Sensitivity
1 Accuracy2 Precision3 Resolution4 Threshold5 Hysteresis6 Dead zone7 Drift8 Backlash
ACCURACY• The closeness of the instrument output to the
true value of the measured quantity.
•It is specified as the percentage deviation from the true value.
•It depends on the inherent limitations of the instrument as well as on the shortcomings in the measurement process.
•It depends on the various systematic errors involved in the measurement process.
•For example, if a chemical balance reads 1g with an error of .001g, the accuracy of the measurement would be specified as 1%
PRECISION• The ability of the instrument to reproduce a
certain set of readings within a given accuracy.
•It depends on the repeatability.
•It depends on the factors that cause random errors.
•A highly precise instrument is one that gives the same output information, for a given input information when the reading is repeated a large number of times.
• For example, if a particular transducer is subjected to an accurately known input and if the repeated read outs of the instrument lie within say +_1%, then the precision or alternatively the precision error of the instrument would be stated as +_1%
RESOLUTION
•It is the degree of fitness with which a measurement can be made.
•The smallest increment in the measured value that can be detected with certainity by the instrument.
•The least count of any instrument is taken as the resolution of the instrument.
•A high resolution instrument is one that can detect smallest possible variation in the input.
•For example, a ruler with a least count of 1mm maybe used to measure 0.5mm by intepolation. Hence its resolution is 0.5mm
REPRODUCIBILITY• The degree of
closeness with which a given value of quantity can be repeatedly measured.
•Perfect reproducibility means that the instrument has no drift.
•For example, a psychologist who found that aggression in children under the age of five increased if they watched violent TV, could generalize that all children under five would display the same condition.
•Reproducibility is different to repeatability, where the researchers repeat their experiment to test and verify their results.
REPEATABILITY
•The ability of the instrument to reproduce a group of measurements of the same measured quantity, made by the same observer, using the same instrument, under the same conditions.
•The deviations in repeatability is caused due to random or accidental errors.
•A measurement may be said to be repeatable when this variation is smaller than some agreed limit.