MECHANICAL MEASUREMENT

The essential purpose and basic function of all branches of engineering is to design.

Design begins with the recognition of a need and the conception of an idea to meet

that need. One may then proceed to design equipment and processes of all varieties

to meet the required needs. Testing and experimental design are now considered a

necessary design step integrated into other rational procedures. Experimentation is

often the only practical way of accomplishing some design tasks, and this requires

measurement as a source of important and necessary information.  

Valid data are defined as those data which support measurement of the most representative value of the desired quantity and its associated precision or uncertainty. When calculated quantities employ measured parameter.

One must naturally ask how the precision or uncertainty is propagated to any calculated quantity. Use of appropriate propagation-of-uncertainty equations can yield a final result and its associated precision or uncertainty. Thus the generalized measurement problem requires consideration of the measuring system and its characteristics as well as the statistical analysis necessary to place confidence in the resulting measured quantity. The considerations necessary to accomplish this task  

STANDARDS OF MEASUREMENT  

The defined standards which currently exist are a result of historical development,
current practice, and international agreement. The System International d'Unites (or SI system) is an example of such a system that has been developed through international agreement and subscribed to by the standard laboratories throughout the world, including the National Institute of Standards and Technology of the United States. The SI system of units consists of seven base units, two supplemental units, a series of derived units consistent with the base and supplementary units, and a series of prefixes for the

formation of multiples and sub multiples of the various units  

CALIBRATION  

The process of calibration is comparison of the reading or output of a measuring system to the value of known inputs to the measuring system. A complete calibration of
a measuring system would consist of comparing the output of the system to known
input values over the complete range of operation of the measuring device. For
example, the calibration of pressure gauges is often accomplished by means of a
device called a dead-weight tester where known pressures are applied to the input of
the pressure gauge and the output reading of the pressure gauge is compared to the
known input over the complete operating range of the gauge.  

Sensitivity  

The sensitivity is defined as the change in the output signal relative to the change in

the input signal at an operating point k. Sensitivity S is given by

                                                                                                                                              Resolution

       

The resolution of a measuring system is defined as the smallest change in the input
signal that will yield an interpretable change in the output of the measuring system

at some operating point. Resolution R is given by  

     

Response  

When time-varying signals are to be measured, the dynamic response of the measuring system is of crucial importance. The components of the measuring system must be
selected and/or designed such that they can respond to the time-varying input signals
in such a manner that the input information is not lost in the measurement process 

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