Page 14 - Mechanical Engineers' Handbook (Volume 2)

Mechanical Engineers’ Handbook: Instrumentation, Systems, Controls, and MEMS, Volume 2, Third Edition.

Edited by Myer Kutz

Copyright  2006 by John Wiley & Sons, Inc.

CHAPTER 1
INSTRUMENT STATICS
Jerry Lee Hall
Department of Mechanical Engineering
Iowa State University
Ames, Iowa
Sriram Sundararajan
Department of Mechanical Engineering
Iowa State University
Ames, Iowa
Mahmood Naim
Union Carbide Corporation
Indianapolis, Indiana
1 TERMINOLOGY 3 3.4 Propagation of Error or
1.1 Transducer Characteristics 3 Uncertainty 10
1.2 Definitions 4 3.5 Uncertainty Interval 12
3.6 Amount of Data to Take 14
2 STATIC CALIBRATION 6 3.7 Goodness of Fit 15
2.1 Calibration Process 6 3.8 Probability Density Functions 16
2.2 Fitting Equations to Calibration 3.9 Determination of Confidence
Data 6 Limits on 17
3.10 Confidence Limits on
3 STATISTICS IN THE Regression Lines 18
MEASUREMENT PROCESS 9 3.11 Inference and Comparison 22
3.1 Unbiased Estimates 9
3.2 Sampling 9 REFERENCES 31
3.3 Types of Errors 10

1 TERMINOLOGY
1.1 Transducer Characteristics
A measurement system extracts information about a measurable quantity from some medium
of interest and communicates this measured data to the observer. The measurement of any
variable is accomplished by an instrumentation system composed of transducers. Each trans-
ducer is an energy conversion device and requires energy transfer into the device before the
variable of interest can be detected.
The Instrument Society of America (ISA) defines transducer as ‘‘a device that provides
usable output in response to a specified measurand.’’ The measurand is ‘‘a physical quantity,
property or condition which is measured.’’ The output is ‘‘the electrical quantity, produced
by a transducer, which is a function of the applied measurand.’’ 1
It should be made very clear that the act of measurement involves transfer of energy
between the measured medium and the measuring system and hence the measured quantity

3