In these slides you will be able to learn characteristics of measurement,analysis of measurement.methods of measurement etc.Its base on the subject Transducers and instrumentation.

1. Transducers and Instrumentation
Lecture 1

2. Measurement
• Measurements provide us with a means of
describing various phenomena in quantitative
terms.
• "whatever exists, exists in some amount".
• The determination of the amount is
measurement all about.

3. Physical Quantities
• Quantities like
– pressure, temperature, displacement, fluid flow,
acoustics , and fundamental quantities like mass,
length, and time
• within the scope of mechanical measurements
• But often, measured by electrical means
– transducing them into an analogous electrical
quantity.

4. Fundamental Measuring Process

5. Measurement System
• Measurement systems are used for many
detailed purposes in a wide variety of
application areas.
• The term “measurement system” is meant to
include all components in a chain of hardware
and software that leads from the measured
variable to processed data.

6. Measured Value versus True Value
• Measured Value
– Numerically value obtained by instrument after
measurement
• True Value- Unknown and Unknowable
– Perfectly exact definition of physical quantities are
impossible
• Example: Length of a cylindrical rod
– Are the two ends of the rod plane?
– If they are plane, are they parallel?
– If they are not plane, what sort of surfaces are they?
– What about surface roughness?

7. Reference Value
• Exemplar Method
– The method agreed on by experts as being
sufficiently accurate for the purposes to which the
data will ultimately be put.
• True value is then referred to as Reference
Value when measured by an exemplar method

8. Nature of Measurement Process
• Measurement process, with assumed identical
conditions, repeated over and over, will not
produce the same output(s) always.
– Never possible to ensure identical conditions for each
trial
• Random Sequence-in state of statistical control
• For future use, numerical estimates of error
associated with collected data set can be
calculated

9. Statistical Control
• Instrument accuracy is always subjected to its
environment and method of use
– Instruments plus inputs
• Every instrument has infinite number of inputs
• Inputs with severe effects
– can be held constant during calibration
• Remaining infinite number of inputs
– left uncontrolled
• Aggregate effect of uncontrolled inputs is of
random nature.

10. Bias and Uncertainty in Measurement

11. Performance Characteristics
• Selection of most suitable instrument
– (proposed measurement)
• Design of Instrument
– (For specific measuring tasks)
• Performance Criteria
– Quantitative bases for comparing one instruments
with possible alternatives

12. Static Characteristics
• Static characteristics of a measurement
system are, in general, those that must be
considered when the system or instrument is
used to measure a condition not varying with
time.

13. Static Characteristics
• Accuracy
– closeness of the instrument output to the true
value of the measured quantity
– 1 g with an error of 10-2g
– inherent limitations of the instrument
– shortcomings in the measurement process
– systematic or cumulative errors

14. Static Characteristics
• Precision
– ability of the instrument to reproduce a certain set
of readings within a given accuracy
– Repeatability of same measured quantity, made
by the same observer, using the same instrument,
under the same conditions.
– Random or accidental errors
– Determine extent of random errors using
Statistical analysis

15. Accuracy vs. Precision

16. Static Characteristics
• Resolution
– smallest increment in the measured value detected with
certainty by the instrument.
– Degree of fineness with which a measurement
• Threshold
– minimum value of input below which no output can be detected.
– friction between moving parts
– looseness in joints (more correctly termed as backlash),
– inertia of the moving parts
– length of the scale,
– spacing of graduations,
– size of the pointer, etc.

17. Static Characteristics
• Static Sensitivity (Gain/Scale factor)
– determined from the results of static calibration
– sensitivity is represented by the slope of the
input-output curve
– sensitivity of a typical linear spring 400N/mm
– Deflection factor

18. Static Sensitivity

19. Drift
• It is defined as the variation of output for a
given input caused due to change in the
sensitivity of the instrument due to certain
interfering inputs like temperature changes,
component instabilities, etc.

20. Linearity
• Desirable Feature
– Linear indicating scale
• Departure from linearity
• Independent of input
• Proportional to input

21. Linearity

22. Range and Span
• The range of the
instrument is specified
by the lower and upper
limits
• Designed to operate for
measuring, indicating or
recording the measured
variable
• Unidirectional
• Bidirectional
• The algebraic difference
between the upper and
lower range values is
termed as the span of
the instrument

23. Hysteresis
• Magnitude of error caused in the output for a
given value of input, when this value is
approached from opposite directions
– From ascending order and then descending order
– Loading then unloading
• Backlash
• Elastic deformation
• Magnetic characteristics
• Frictional effects

24. Hysteresis

25. Hysteresis
• Dead Band
– It is defined as the largest change of the
measurand to which the instrument does not
respond
• Backlash
– It is defined as the maximum distance or angle
through which any part of the mechanical system
may be moved in one direction without causing
motion of the next part