2. ⦁ Basics of Measurements and
Instrumentation
Electrical measurement and
Instrumentation 2
3. Measurement
⦁ An act or result of comparison between an Unknown
quantity with a predefined standard and after the
comparison results are expressed in numerical values
What is Instrumentation?
An art of measurement or use of measuring instrument to
serve the desired functions of Indicating, Recording &
Controlling actions.
Electrical measurement and
Instrumentation 3
5. Measurement standards are defined in four (4)
categories
1.International Standard
2.Primary Standard
3.Secondary Standard
4.Working Standard
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Instrumentation 5
13. Two requirements to make measurement meaning full
⦁ The standards used must be accurately defined and
universal accepted
⦁ The apparatus & method for measurement should be
provable
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Instrumentation 13
15. ⦁ The measurand ( unknown qty) is directly compared
against a standard, & results is in terms of numbers and
units
⦁ Not possible
⦁ Not feasible
⦁ Not practicable
⦁ Egs:
◦ Length
◦ Mass
◦ Time
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Instrumentation 15
16. ⦁ Effect of the measurand on another known characteristics
or element is measured as a new quantity
⦁ direct methods are not possible for measurement
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Instrumentation 16
17. Measurement by conversion
⦁ the measurand is converted into directly measurable
quantity
Measurement by substitution
⦁ The element carrying the measurand is placed into the
measuring device, and then substituted by some
accurately known standard.
The application of null method.
⦁ Bridges method uses the null method which has a high
degree of accuracy.
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Instrumentation 17
18. Purpose in industrial manufacturing and processing
⦁ Improve the quality of the product
⦁ Improve the efficiency of production
⦁ Maintain the proper operation
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Instrumentation 18
20. SENSING ELEMENT:
⦁ This is in contact with the process and gives an output
which depends in some way on the variable to be measured.
Examples
⦁ Thermocouple where millivolt e.m.f. depends on
temperature
⦁ Strain gauge where resistance depends on mechanical strain
Electrical measurement and
Instrumentation 20
21. SIGNALCONDITIONING ELEMENT:
⦁ This takes the output of the sensing element and converts it
into a form more suitable for further processing, usually a
d.c. voltage, d.c. current or frequency signal.
⦁ Examples
⦁ Deflection bridge which convert an impedance change into
a voltage change
⦁ Amplifier which amplifies millivolts to volts
Electrical measurement and
Instrumentation 21
22. Signal processing element:
⦁ This takes the output of the conditioning element and
converts it into a form more suitable for presentation
Example
⦁ Analogue-to-digital converter (ADC) which converts a
voltage into a digital form for input to a computer.
⦁ Computer which calculates the measured value of the
variable from the incoming digital data.
Electrical measurement and
Instrumentation 22
23. Data presentation element:
⦁ This presents the measured value in a form which can
be easily recognized by the observer.
Examples
⦁ Alphanumeric display
⦁ Chart recorder
⦁ Visual display unit (VDU).
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Instrumentation 23
25. ⦁ VERY STA
TICAND STABLE
⦁ NOT FOR DYNAMICAPPLICATIONS
⦁ They have moving parts, and hence Inertia
problems arises
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Instrumentation 25
27. ⦁ Devices that used to describe physical properties of
electricity.
⦁ eg,. Electric current, voltage, etc
⦁ Output is generally a mechanical movements
⦁ limited time of response
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Instrumentation 27
28. ⦁ Devices consisting of a large number of small complex
parts of that utilize electricity.
Eg. Electronic computers or microchip
⦁ More reliable
⦁ Higher sensitivity
⦁ Recording capabilities
⦁ Measured and monitored even in remote locations
⦁ Lower weight
⦁ Lesser power consumption
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Instrumentation 28
30. STATIC
CHARACTERISTICS
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Instrumentation 30
DYNAMIC
CHARACTERISTICS
⦁ When measurand is either
constant or slow varying
⦁ A set of criteria that gives
meaningful description of
the quality of measurement
⦁ Instruments and
measurements involved in
rapidly varying quantities
⦁ To establish a relation b/w
the input and output in
terms of mathematical
equations
31. ⦁ The process of checking the instrument against a
known standard and………………….
⦁ Subsequently to find
ERRORS
ACCURACY
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Instrumentation 31
32. ⦁ Accuracy
⦁ Precision
⦁ Sensitivity
⦁ Dead Zone
⦁ Resolution
⦁ Repeatability
⦁ Static Error
⦁ Stability
. Reproducibility
. Linearity
.Dead Time
.Drift
. Threshold
.Hysteresis
.Range or Span
.Tolerance
Electrical Measurement &
Instrumentation 32
33. ⦁ Accuracy : - Closeness with which an instrument
reading approaches true value of the quantity being
measured
⦁ Sensitivity : - Infinitesimal change in o/p
◾Infinitesimal change in I/p
⦁ Linearity : When the o/p is proportional to i/p
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Instrumentation 33
34. ⦁ Dead time : - The time required by a measurement
system to begin to respond to change in the measurand
⦁ Dead Zone : - Largest change of input quantity for
which there is no output of the instrument
⦁ Reproducibility :- degree of closeness with which a
given value may be repeatedly measured
⦁ Drift :- a slow variation to output of measuring system
which is not due to any change with the input quantity.
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Instrumentation 34
35. ⦁ Drift may be classified into three categories:
a) zero drift
If the whole calibration gradually shifts due to slippage,
permanent set, or due to undue warming up of electronic
tube circuits
b) span drift or sensitivity drift
If there is proportional change in the indication all along
the upward scale
c) Zonal drift
In case the drift occurs only a portion of span of an
instrument
Range or span
The minimum & maximum values of a quantity for which an
instrument is designed to measure is called its range or span.
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Instrumentation 35
36. ⦁ Resolution
If the input is slowly increased from some arbitrary input value, it will
again be found that output does not change at all until a certain
increment is exceeded. This increment is called resolution.
Threshold:
If the instrument input is increased very gradually from zero there will
be some minimum value below which no output change can be
detected
Stability:
It is the ability of an instrument to retain its performance throughout is
specified operating life.
Tolerance
The maximum allowable error in the measurement is specified in
terms of some value
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Instrumentation 36
37. ⦁ Repeatability
It is defined as the variation of scale reading & random in
nature Drift
⦁ Precision
it is the measure of Reproducibility of the measurement that is
given a fixed value of variable.
⦁ Hysteresis
⦁ When the input of an instrument varied from zero to its full scale
and then if the input is decreased from its full scale to zero, the
output varies.
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Instrumentation 37
38. ⦁ Speed of Response
⦁ Measuring Lag
⦁ Fidelity
⦁ Dynamic error
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Instrumentation 38
39. Rapidity with which
a measurement
system responds to
changes in the
measured quantity
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Instrumentation 39
40. ⦁ Retardation type
⦁ Response of the
measurement systems
begins immediately
after a change in
measured quantity has
occured
⦁ Time Delay type
⦁ The response of the
system begins after a
dead time
even after the
application of input
Electrical measurement and
Instrumentation 40
41. ⦁ FIDELITY
⦁ Ability of the measuring
system to indicate the
changes in the measured
quantity without any
dynamic error
⦁ DYNAMIC ERROR
⦁ Difference between the
true value and the
quantity under
measurement changing
with time
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Instrumentation 41
47. ⦁ Deviations from the nominal value ( specified Value)
of a particular quantity
⦁ Aa =As + δA
⦁ or
⦁ Aa =As - δA
⦁ Aa =Assured V
alue
⦁ As = Nominal value
⦁ δA= error
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Instrumentation 47
48. ⦁ Ԑr =Aa –AS/AS
⦁ Defined as the ratio of the ERROR to the specified
magnitude of the quantity
⦁ Aa –AS = Error
⦁ AS= Nominal value or magnitude of the qty
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Instrumentation 48
49. Gross Errors : - By human
mistakes in reading,
recording , calculations,
observing measurements
Systematic Errors
1. Instrumental Errors 2. Environmental Errors 3. Observational Errors
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Instrumentation 49
50. ⦁ It is because of
◦1. Inherent short comings in the
Instrument
◦2. Misuse of the Instrument
◦3. Loading Effect
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Instrumentation 50
51. ⦁ Errors because of
◦ 1.Un known happenings
◦ 2. Unaware disturbances
◦ 3. Very small factors
◦ Lumped together to give this errors
◦ Also called as RESIDUAL ERRORS
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Instrumentation 51
52. RANDOM ERROR :- Analysis
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Instrumentation 52
53. ⦁ Repeated measurements of given quantity are done by
using different
◦A. Test conditions
◦B. Instruments
◦C. Different methods and ways
◦D. Different Observers
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Instrumentation 53
54. ⦁ HISTOGRAM
⦁ ARITHMETIC MEAN
⦁ STANDARD DEVIATION
⦁ DISPERSION
⦁ RANGE
⦁ Statistical approach
⦁ are used to optimize errors
Electrical measurement and
Instrumentation 54
55. DUMB INSTRUMENTATION
⦁ the conventional instrumentation system the data should be
processed by the observer
INTELLIGENT INSTRUMENTATION
⦁ Use of digital computer for evaluating physical variables in
instrumentation system
⦁ After measurement of physical variable further
processing is carried out.
Electrical measurement and
Instrumentation 55
