Instrument Characteristics
The function of a scientific instrument, therefore, is primarily to convert the quantitative aspect of some natural phenomenon into a series of recognizable coincidences in time and space.
Therefore, no statement of the result of a measurement is complete unless it includes an estimate (necessarily in statistical terms) of the probable magnitude of the uncertainty. The uncertainty is the interval within which the true value of a quantity can be expected to lie with a stated probability.
Characteristics of Instruments
Static Characteristic Determinations
The better the secondary inputs are understood, the better the response of the instrument to the primary input and the instruments measurement ability can be understood.
Input-Outpud Diagram
Static Performance Characteristics
Correction
Accuracy
Error
PPT Slide
Precision
Repeatability
Time interval is short enough for real differences to be unable to develop.
Stability/Reproducibility
Resolution
Representativeness
Sensitivity
Zero Effect / Bias
Zero Drift
Range
Span
Linearity
Non-linearity can be important for some instruments.
Hysteresis
Threshold
Dead Band
Traceability
Uncertainty
Those uncertainties which may be evaluated by other means:
Upon examining the various static response characteristics, it is evident that not all are of equal significance or importance. An instrument must be chosen that has values of those properties suitable for a particular scientific use.
Dynamic Performance Characteristics
Evaluation is by use of differential equations; as above:
Rearranging
Integrating
Integrating between the limits gives:
Time Response
Time Response for liquid thermometers
Standardization of Instruments
Standard Instrument -
Primary Standard -
Reference Standard -
International Standard
Regional Standard
End
Email: alcorn@ariel.met.tamu.edu
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