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STATIC AND DYNAMIC CHARACTERISTIC OF INSTRUMENTS (ERROR (Error can be…
STATIC AND DYNAMIC CHARACTERISTIC OF INSTRUMENTS
Sensitivity
as the ratio of the output to the magnitude of the input signal
Static sensitivity,k=change of output signal/change in input signal
Accuracy-precision
Accuracy of an instrument indicates how closely the reading of the instrument approaches the true value
Accuracy=(result-actual value)/actual value x 100%
How closely the instrument measure the actual value
Precision is the ablity of the instrument to reproduce a certain set of readings within a given accuracy
The ability of measurement to produce the same output value on every time
ERROR
Error=Vi(indicated value)-Va(actual value
no measurement can be made with perfect accuracy and perfect precision
Error can be classified by
Systematic/Cumulative Error
Have the same magnitude & sign
Example
Instrument error
Loading error
Environmental error
Accidental/Random Error
Random variations in the parameter od the system of measurement(by lack of consistency in the measured values)
Presence of certain system defects(change the tolerance)
Miscellaneous error
systematic/random error
human error-observe/read
Improper appication of the instrument
Faulty component/adjustment
Dead zone
the largest change in input quantity for which a noticeable change in the output from zero
due to friction in the instrument
Drift
the variation of output for a given input caused due to change in the sensititivity of instruement due to interfering inputs
zero drift
sensitivity drift
Reproducibility
is the degree of closeness with which a given value is repeatedly measured within a close range
the difference between the largest and the smallest result
Selection of the instrument
Instrument's qualities,value guided
accuracy & precision characteristics
nature & type of data avaible
Futher data computation
dynamis responce characteristic
Convenoence aspects,value judged
Safety in use
Maintenance,repair,steady delivivery
Material durability & Non-faouling design
Cost,initial and cumulative total
Initial cost
Running cost
Expected lifetime
Types of dynamic input signal
periodic signals with time
varying cyclicaly with time or repeating itself after a constant interval
Transient signal
varying non-cyclically with time
Somwtimes,the signal becomes zero after a certain period of time
Random signal
varying randomly with time,with no definite period and amplitude
may be continues but not cyclic