EKT 314
ELECTRONIC INSTRUMENTATION
Elektronik Instrumentasi
Semester 2 2012/2013
Chapter 1
Introduction to Electronic Instrumentation
Session 2
Mr. Fazrul Faiz Zakaria
school of computer and communication engineering. universiti malasia perlis
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Error in measurement
Measurement always introduce error
Error may be expressed either as absolute or
percentage of error
Yn − X n
Absolute error, e =
where, Yn -expected value
X n -measured value
Yn − X n
×100
% error =
Yn
2
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Error in measurement
Y
−
X
n
n
relative accuracy, A = 1 −
Yn
% Accuracy, a = 100% - % error
= A ×100
Xn − Xn
precisions, P= 1 −
Xn
where,
X n - value of the n th measurement
X n - average set of measurement
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Wednesday, March 6, 13
Review Exercise 1.1
a measurement using a ammeter give a reading of 5.2 mA at Io, calculate
I.Expected value of Io
II.The absolute error
III.The % of error
IV.The relative accuracy
V.The % of accuracy
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Wednesday, March 6, 13
Review Exercise 1.2
a measurement using a ammeter give a reading of 0.2 A at iR3, calculate
I.Expected value of iR3
II.The absolute error
III.The % of error
IV.The relative accuracy
V.The % of accuracy
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Review Exercise 1.3
in a laboratory experiment, you had measured the value of RAB =6 k ohm from the
above circuit. To verify your measurement please calculate:
I.The expected value of RAB
II.The absolute error
III.The % of error
IV.The relative accuracy
V.The % of accuracy
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Review Exercise 1.4
in Ops Sikap, AES (Automated Enforcement System) had spotted an orange
Lamborghini exceeding the speed limit. The AES reading shows that the orange
Lamborghini speeding at 220 Km/h, if that Lamborghini had drove 556 kilometers
on north-south highway in 2 hours and 30 minuets, evaluate the performance of the
AES by calculating:
I.The absolute error
II.The % of error
III.The relative accuracy
IV.The % of accuracy
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Review Exercise 1.5
No.
1
2
3
4
5
6
Diameter
(mm)
2.21
2.18
2.2
2.21
2.17
2.19
The diameter of a copper wire has uneven measurements and has
been recorded as shown in the table, calculate
I.The precision of each measurement
II.The precision average
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Wednesday, March 6, 13
Limiting error
The accuracy of measuring instrument is
guaranteed within a certain percentage (%) of
full scale reading
E.g manufacturer may specify the instrument
to be accurate at 2 % with full scale deflection
For reading less than full scale, the limiting
error increases
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Example 1.3
Given a 600 V voltmeter with accuracy 2% full scale.
Calculate limiting error when the instrument is used to
measure a voltage of 250V?
solution
The magnitude of limiting error, 0.02 x 600 = 12V
Therefore, the limiting error for 250V = 12/250 x 100 = 4.8%
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Wednesday, March 6, 13
Example 1.3
Given for certain measurement, a limiting error for
voltmeter at 70V is 2.143% and a limiting error for
ammeter at 80mA is 2.813%. Determine the limiting error
of the power.
solution
The limiting error for the power = 2.143% + 2.813%
= 4.956%
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Wednesday, March 6, 13
Review Exercise
A voltmeter is accurate 98% of its full scale reading.
I. If the voltmeter reads 200V on 500V range, what is the
absolute error?
II. What is the percentage error of the reading in (i).
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Type of Static Error
Gross error/human error
Systematic Error
Random Error
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Type of Static Error
Gross Error
cause by human mistakes in reading/using instruments
may also occur due to incorrect adjustment of the instrument and the
computational mistakes
cannot be treated mathematically
cannot eliminate but can minimize
Eg: Improper use of an instrument.
This error can be minimized by taking proper care in reading and recording
measurement parameter.
In general, indicating instruments change ambient conditions to some
extent when connected into a complete circuit.
Therefore, several readings (at three readings) must be taken to minimize
the effect of ambient condition changes.
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Type of Static Error
Systematic Error
due to shortcomings of the instrument (such as defective or
worn parts, aging or effects of the environment on the
instrument)
In general, systematic errors can be subdivided into static
and dynamic errors.
Static – caused by limitations of the measuring device or
the physical laws governing its behavior.
Dynamic – caused by the instrument not responding very
fast enough to follow the changes in a measured variable.
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Type of Static Error
Systematic Error
3 types of systematic error :Instrumental error
Environmental error
Observational error
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Type of Static Error
Systematic Error
:Instrumental error
inherent while measuring instrument because of their
mechanical structure (eg: in a D’Arsonval meter, friction in
the bearings of various moving component, irregular spring
tension, stretching of spring, etc)
error can be avoid by:
selecting a suitable instrument for the particular
measurement application
apply correction factor by determining instrumental
error
calibrate the instrument against standard
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Type of Static Error
Systematic Error
:Environmental error
due to external condition effecting the
measurement including surrounding area condition
such as change in temperature, humidity, barometer
pressure, etc
to avoid the error :use air conditioner
sealing certain component in the instruments
use magnetic shields
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Type of Static Error
Systematic Error
: Observational error
introduce by the obser ver
most common : parallax error and
estimation error (while reading the
scale)
Eg: an observer who tend to hold his
head too far to the left while reading the
position of the needle on the scale.
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Type of Static Error
Random Error
due to unknown causes, occur when all
systematic error has accounted
accumulation of small effect, require at high
degree of accuracy
can be avoid by
increasing number of reading
use statistical means to obtain best
approximation of true value
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Statistical Analysis
can be used to determine the
uncertainty of the test results.
the analysis requires a large number
of measurement (data) to be taken
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Statistical Analysis
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Statistical Analysis
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Statistical Analysis
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Statistical Analysis
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Example 1.4
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Classification of instrument
Absolute
Provide
magnitude of the
quantity under
measurement in
terms of physical
constant of the
instrument.
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Secondary
Provide magnitude
of the quantity
under measurement
only from the
obser vation of the
output from the
instrument.
Most instrument in
used are secondary.
Operation Mode
Operation Type
Deflection
Only one source of input
required.
Output reading is based
on the deflection from
the initial condition of
the instrument.
The measured value of
the quantity depends on
the calibration of
instrument.
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Null
Requires t wo inputs –
measurand and balance
input
Must have feedback
operation that compare
measurand and the
standard value.
More accurate and sensitive
compared to deflection type
of instrument.
Operation Mode
Analog
Signal Type
Digital
Produce the signal
that vary in
continuous way.
Produce the signal
that vary in
discrete steps.
Infinite range of
value in any given
range.
Finite different
values in a given
range.
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Instrument Element
3 model of Instrument
Model
Block Diagram
Subsystem
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Instrument Element
Model
Sensor is the important element which can convert the
physical variable into signal variable.
Signal variable can be displayed, recorded or integrated into
secondary instrument system
Signal variable also can be used as an input signal of a
control system
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Instrument Element
Block Diagram
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Instrument Element
Block Diagram
simplified
Tranducers
Subsystem
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Signal
Conditioner
Subsystem
Filter/Amplifier
Subsystem
Data Processors/
Process Controller/
Command Generator
Subsystem
Recorder
Subsystem
Elements of Electronic Instrumentation
Transducers
Device that converts a change in physical quantity into a
change of electrical signal magnitude.
Power Supply
Provide energy to drive the transducer.
Signal Conditioning Circuit
Electronics circuit that convert the output from transducer
into a more usable electrical signal.
Amplifiers
Amplify low voltage signal from transducers or signal
conditioning circuit.
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Elements of Electronic Instrumentation
Recorders
Used to display the measurement for easy reading and
interpretation.
Data processors
Can be a microprocessor or microcontroller.
Process Controllers
Used to monitor and adjust any quantity of the specified level
or value.
Command Generator
Provide control voltage that represents the difference of the
parameter of a given process.
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Application Area
Engineering Analysis
To validate new design of structure, component or system by theoretical
and experimental approach.
Process Control
Monitoring Process – provide real-time data that allow operator to react.
Automatic Process – provide real-time feedback data to the control system
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