Unit 01 introduction to measurements

Unit – 01
Introduction to
MEASUREMENTS
PROF. WAGHMODE D R
1
K. B. P. POLYTECHNIC, SATARA

COURSE OUTCOMES
a. Use relevant instrument for
measuring displacement.
2

UNIT OUTCOMES
1a. Identify different characteristics of the given
instruments.
1b. Identify the error in the given instrument.
1c. Classify the transducers for the given application.
1d. Identify the given contact and non-contact
transducer with justification.
3

What is Measurement ?
Measurement is the process of determining the value of
magnitude of an Unknown quantity by comparing it with
similar quantity whose magnitude is known.
4

Measurement is the process of determining the value of magnitude of an
Unknown quantity by comparing it with some predetermine standard of
reference.
OR
5

BASIC REQUIREMENT
A)A piece of equipment having known measure
of physical quantity.
6

TYPE OF MEASUREMENTS
TYPES OF
MEASUREMENTS
1. Direct Measurement
2. Indirect
Measurement
7

1. Direct Measurement
The Measurand (unknown quantity) is directly compared with a
standard
E.g - weight, distance, Length etc
8

2. Indirect Measurement
It is Measuring Something by measuring another
or
measurement is converted into analogous signal
which is processed & fed to the end device that
represent the result of measurement
9

K. B. P. POLYTECHNIC, SATARA 10

Indirect Measurement
Primary measurement- that made by direct
observation without involving any conversion.
Secondary measurement - that involve one
translation are called
Tertiary measurement- involving two conversion

Also Classified as
1. Contact Type
Sensing Element of Measuring Device has Contact with medium
whose parameters are to be measured.
2. Non- Contact Type
Sensing Doesn’t Contact Physically with Medium
12

Instruments
It is device which senses a physical parameter, processes and translates it
into a final result
Or
Which allow the observer to observe & measure aspect of physical
quantity
13

CLASSIFICATION OF INSTRUMENTS
• Contact Type
• Non Contact Type
I) Method
of Contact
• Manual Operated Instrument
• Automated Operated instrument
ii) Mode of
Operation
• Self-operated instrument or
active instrument
• Power operated instrument
iii) Source
of Energy
14

• Mechanical Type
Instruments
• Electrical Type
Instruments
iv)
Application
• Analog Instruments
• Digital Instruments
v) Output
Signal
15

I) Method of Contact
a) Mercury Thermometer
b) Infrared Thermometer
a) Contact Type
A Contacting type of instrument is one which m
akes a physical contact with the whole magnitu
de is to be determined
b) Non Contact Type
These Instruments are placed remotely i.e away
from the measuring Medium
16

ii) Mode of Operation
a) Manual Operated Instrument
It Requires the service of an operator
b) Automated Operated instrument
These Devices do not require manual help for their
Running
b)
a)
17

iii) Source of Energy
a) Self-operated instrument or active instrument
These Instruments do not require any outside
power in performing its function.
b) Power operated instrument
These Instruments require external power
source such as electricity, Compressed air etc
for their operation.
18

v) Output Display
a) Null Type Instruments
In these types of instruments , Deflection is made
ZERO by applying an effect opposing that
generated by the measured quantity.
b) Deflection Type Instruments
In these type of instruments, the measurement is
done by relative displacement between pointer and
dial.
19

vi) Output Signal
a) Analog Instruments
In these type of instruments , signal can
take infinite Number of values and vary in a
continuous fashion
b) Digital Instruments
In these type of instruments, signal varies
in discrete steps and take finite number of
values in given range
20

STATIC TERMS AND CHARACTERISTICS
21

Range –
It is Defined as region between lower limit to upper limit of an
instrument , within which it is designed to operate.
E.g: If thermometer is used to measure temperature between 0º C to
100º C.
Then Range is 0º C to 100º C
Span –
It is Algebraic Difference between the upper and lower limits of instrument
E.g: If thermometer is used to measure temperature between 35º C to 42º C.
Then SPAN = 42º C - 35º C
= 07º C
1) Range and Span
22

Accuracy
It is Defined as Conformity with or Closeness to an accepted value
(standard)
Precision
It is defined as the repeatability of measuring process.
High accuracy
High precision
Low accuracy
High precision
High accuracy
Low precision
Low accuracy
Low precision
2) Accuracy and Precision
23

24

Iv) Reliability
The reliability of instrument is defined as the possibility that it will
perform its assigned functions for a specific period of time
under given conditions
v) Calibration
Calibration is the process of establishing the reliability of a
Measuring instrument.
25

VII) Dead Time
Dead time is defined as the time required for an instrument
To begins to respond to a change in the measurand Quantity.
VIII) Dead Zone
Dead Zone defines the largest change of the input quantity to
which the instrument does not respond.
26

ix) Drift
a) It is an undesired gradual departure of an instrument output over a
period of a time that is unrelated to changes in input, operating
condition or load.
b) An instrument is said to have no drift if it reproduces same reading at
different times for same variation in measured variables.
x) Sensitivity
Sensitivity of an instrument is defined as the ratio of its
magnitude of the response and the magnitude of the quantity
being measured.
Sensitivity (K)
Change in Output
Change in Input
27

xiii) Linearity
Linearity is defined as the ability to reproduce the input
characteristics symmetrically and linearly.
xiv) Repeatability
Repeatability is the property of instrument to give the same output
value each time the measurement of a given quantity is repeated,
under the same conditions
28

xv) Reproducibility
Closeness bet successive measurement of the same
measured quantity where measurement made by
different operator, location with different measuring
instrument.
29

xi) Threshold
When the input signal to an instrument is gradually increased
from zero, there will be some minimum value input before
which the instrument will not detect any output change. This
minimum value is called the threshold of the instrument.
xii) Resolution
The resolution is defined as the smallest change of input
for which there will be a change of output.
30

Dynamic Terms and CHARACTERISTICS
31

Dynamic Characteristics
1) Speed of response
2) Fidelity
3) Overshoot
32

I) Speed of Response
Measuring instrument the speed of response is defined as
the value of the rapidity with which an instrument
responds to a change in the value of the quantity being
measured.
ii) Fidelity
Degree to which measurement system indicate change in
measured quantity without any error.
33

ii) Overshoot
The overshoot is defined as the maximum amount by which the pointer
moves beyond the steady state.
34

Desirable Characteristics
Accuracy Precision
Calibration
Sensitivity Linearity
Repeatability
Reproducibility Speed of Response Fidelity
Undesirable Characteristics
Hysteresis Dead time and Zone Drift
35

ERROR
It is the difference between the true value of the size
being measured and the value found by measurement.
36

Sources of Error
1. Defect in instrument.
2. Adjustment of an instrument.
3. Imperfection in instrument design.
4. Method of location of instrument.
5. Environmental effects.
6. Observation error.
7. Error caused by measuring forces of instruments.
37

Measurement of Error
Static error-
The difference between the measured value and the true value of
the quantity represents static error.
38

Classification of errors
1. Instrument error.
2. Environmental error.
3. Observation error.
4. Operational error.
5. System, Random, residual error.
6. Translation and signal transmission error.
39

(a) Instrument Errors
1. Improper selection, poor maintenance of the instrument.
2. Fault in construction of instrument.
3. Mechanical friction wear, backlash and hysteresis.
4. Assembly error.
(b) Environmental Errors
1. Different condition for manufacturing and use.
2. Different condition of temperature, pressure, humidity.
(c) Observation Errors
1. Parallax Unit Conversion
2. Personal bias Estimate
3. Wrong Scale reading.
40

(d) Operational Errors
1. The differential type of flow meter will read inaccurately if it is placed immediately after valve or
a bend.
2. A thermometer will not read accurately if the sensitive portion is not properly installed.
41

(f) Translation and signal transmission error.
1. The instrument may not sense or translate the measurement effect with complete fidelity
2. The error also include the non capability of instrument to follow effects
3. The error may also result from unwanted disturbances such as noise,ripple etc.
42

Transducers
Transducer is defined as conversion of a physical phenomenon or chemical
properties into an electrical form.
OR
It is devices , which converts energy from one form to another
43

Classification of Transducers
1. Resistance transducer.
2. Capacitive transducer.
3. Inductive transducer.
4. Strain gauge transducer.
5. Photoelectric transducer.
6. Piezoelectric transducer.
44

Also Classified as
1. Primary / Secondary Transducers.
2. Active / Passive Transducers.
3. Analog / Digital Transducers.
4. Mechanical- electrical Transducers.
45

Primary / Secondary Transducers
• The mechanical device converts the physical quantity to be
measured into a mechanical signal. Such mechanical device are
called as the primary transducers, because they deal with the
physical quantity to be measured.
• The electrical device then convert this mechanical signal into a
corresponding electrical signal. Such electrical device are
known as secondary transducers.

For example, in pressure measurement, as shown in the above figure,
Bourdon’s tube acts as a primary transducer which converts pressure into
displacement and LVDT acts as a secondary transducer which converts this
displacement into an equivalent quantity of electrical signal

ACTIVE TRANSDUCERS
These transducers do not need any external source of power for
their operation. Therefore they are also called as self generating
type transducers
The active transducer are self generating devices which operate
under the energy conversion principle.
As the output of active transducers we get an equivalent electrical
output signal e.g. temperature or strain to electric potential,
without any external source of energy being used.

Passive Transducer
These transducers need external source of power for their operation. So they
are not self generating type transducers.
A DC power supply is used as an external power source.
These transducers produce the output signal in the form of variation in
resistance, capacitance, inductance or some other electrical parameter in
response to the quantity to be measured.

Mechanical Transducer- like as dial gauge, Bourdon tube pressure
gauge
Commonly used sensing elements- spring, bellow, torsion bar,
bimetallic strip
Electrical Transducer- in which sensing device which convert a
physical quantity into an equivalent electrical signal.

ANALOG & DIGITAL
TRANSDUCERS
Analog transducers converts input signal into output signal, which is a
continuous function of time such as THERMISTOR ,strain gauge, LVDT ,
thermocouple etc.
Digital transducers converts input signal into the output signal in the form
of pulses e.g. it gives discrete output

1. Observational Error due to
a) Parallax
b) Improper selection and poor maintenance of instrument
c) Excessive friction at the mating parts
d) None of above

2. The desirable static characteristics of a
measuring system are
a) Accuracy and reproducibility
b) Accuracy, sensitivity and reproducibility
c) Drift and dead zone
d) Static error.

3. Function of transducer is to convert
a) Electrical signal into non electrical quantity
b) Non electrical quantity into electrical signal
c) Electrical signal into mechanical quantity
d) All of these

A null type instrument compared to a
deflection type instrument has
a) A higher accuracy
b) A lower sensitivity
c) A faster response
d) All of above

Error of measurement =
True value – Measured value
Precision – True value
Measured value – Precision
None of the above

The ability by which a measuring device can detect small
differences in the quantity being measured by it, is called its
Damping
Sensitivity
Accuracy
None of the above

The following term(s) is (are) associated with
measuring devices
A Sensitivity
B Damping
C Both ‘a’ and ‘b’
D None of the above

The degree of closeness of the measured value of a certain
quantity with its true value is known as
Accuracy
Precision
Standard
Sensitivity

Self generating type transducers are _____ transducers.
a) Active
b) Passive
c) Secondary
d) Inverse

Difference bet the upper and lower range value of the instrument called
as
Range
Span
Accuracy
Precision

Ratio of change in o/p to change in i/p
signal called as
Reliability
Sensitivity
Linearity
Reproducibility

Largest change of measured quantity to which
the instrument does not respond called as
Dead time
Dead one
Drift
overshoot

Instrumental errors due to
Wear of part
Friction
Improper calibration
All of above

Which measurement method does not involve any conversion
of measured quantity
Secondary measurement
Tertiary measurement
Primary measurement
None of above

Unit 01 introduction to measurements

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