Introduction to Instrumentation

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Chapter 01

• Introduction to Instrumentation Measurements (3
  Hours)

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Objectives

• At the end of this chapter, you should be able
  to
• explain units and quantities in electrical
• discuss and calculate various types of error in
  measurement
• explain the meaning of some terms in
  instrumentation field

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Chapter outline

• The outline of this chapter is as follows
• 1.1 Principles of instrumentation and
• measurements
• 1.2 Error in measurement
• 1.3 Measurement standard

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1.1 Principle of Instrumentation
Measurements

• Instrumentation
• is a technology of measurement which serves not
  only science but all branches of engineering,
  medicine, and etc
• instrumentations serve three (3) basic functions
  -
• indicating
• recording
• controlling
• the knowledge of any parameter largely depends on
  the measurement

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1.1 Principle of Instrumentation
measurements
3 basic functions of instrument
Controlling
Indicating
Recording
General-purpose electrical electronics test
instruments
Industrial-process
Control / automated system
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1.1 Principle of Instrumentation
Measurements

• Measurement
• A process to present an observer with a numerical
  value corresponding to the variable being
  measured by using appropriate instrument
• Basically used to monitor a process or operation,
  or as well as the controlling process
• Eg thermometers, multimeter, etc

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1.1 Principle of Instrumentation
measurements

• The major problem encountered with any measuring
  instrument is the error
• Therefore, it is necessary to select the
  appropriate measuring instrument measurement
  method which minimises error
• To avoid errors in any experimental work, careful
  planning, execution evaluation of the
  experiment are essential

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1.1 Principle of Instrumentation
Measurements

• Before measurement process we have to
• ensure
• Methods/procedures of measurement
• Characteristics of the parameter
• Quality time and cost, instrument capabilities,
  knowledge of measurement, acceptable result
• What instrument to use

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1.1 Principle of Instrumentation
Measurements

• During the measurements we have to ensure
• Quality- best instrument chosen, suitable
  position when taking the data, etc..
• Safety- electric shock, overloaded, instrument
  limits, read instrument manual
• Sampling observe parameter changing, taking
  enough sample
• After measurement
• Analyse the data mathematically/statistically
• Full result must be reported completely and
  accurately

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1.1 Principle of Instrumentation
Measurements

• Electrical Units
• i) Fundamental Quantity

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1.1 Principle of Instrumentation
Measurements

• ii) Derived Quantity

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1.2 Error in Measurement

• Error
• is defined as the difference between the
  measured value and the expected value (true
  value) of the measured parameter
• Various types of error in measurement
• i) absolute error
• ii) gross error
• iii) systematic error
• iv) random error
• v) limiting error
• static error numerical difference between the
  true value of a quantity and its value as
  obtained by measurement (i.e. repeated
  measurement of the same quantity gives different
  indications.

Static errors
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1.2 Error in Measurement

• i) Absolute error
• The difference between the expected value of the
  variable and the measured value of the variable,
  ore Yn Xn
• where
• e absolute error
• Yn expected value
• Xn measured value

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1.2 Error in Measurement

• To express error in percentage
• error , e Yn - Xn
• We also derived relative accuracy, A

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1.2 Error in Measurement

• Percentage accuracy, a

a 100 - error
or
a A x 100
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Example 1.1

• The expected value of the voltage across a
  resistor is 5.0 V. However, measurement yields a
  value of 4.9 V. Calculate
• a) absolute error
• b) error
• c) relative accuracy
• d) accuracy

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1.2 Error in Measurement

• ii) Gross Error
• Due to human mistakes
• Example incorrect reading, incorrect recording,
  improper use of instruments, etc
• To minimize
• take at least 3 separate reading
• take proper care in reading recording

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1.2 Error in Measurement
Instrumental errors

• iii) Systematic Error
• due to instruments problem or environmental
  effects or observational errors
• example???
• defective or worn parts
• ageing
• parallax error
• wrong estimation reading scale

Environmental errors
Observational errors
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1.2 Error in Measurement

• Instrumental errors
• due to friction in the bearings of the meter
  movement, incorrect spring tension, improper
  calibration, or faulty instruments
• can be reduced by proper maintenance, use, and
  handling of instruments

• Environmental errors
• due to external condition of the measuring
• eg effects of change in temperature, humidity,
  barometric pressure, electrostatic fields etc
• can be avoided by air conditioning,
  hermetically sealing certain components in the
  instrument and using magnetic shields

• Observational errors
• Errors that introduced by the observer
• The two most common observational errors are
  probably the parallax error introduced in reading
  a meter scale and the error of estimation when
  obtaining a reading from a meter scale

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1.2 Error in Measurement

• iv) Random Errors
• Errors that remain after gross and systematic
  errors have been substantially reduced
• Are generally the accumulation of a large number
  of small effects
• May be of real concern only in measurements
  requiring a high degree of accuracy
• such errors can only be analyzed statistically
• Due to unknown causes

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1.2 Error in Measurement

• v) Limiting Errors
• Most manufacturers of instruments state that an
  instrument is accurate within a certain
  percentage of a full-scale reading
• Eg a voltmeter is accurate within 2 at
  full-scale deflection (limiting errors)
• however, with reading less than full-scale, the
  limiting error will increase
• therefore, it is important to obtain measurements
  as close as possible to full scale

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Example 1.2

• A 300-V voltmeter is specified to be accurate
  within 2 at full scale. Calculate the limiting
  error when the instrument is used to measure a
  120-V source?

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Example 1.2

• Solution
• The magnitude of the limiting error is
• 2/100 x 300 6V
• Therefore, the limiting error at 120 V is
• 6/120 x 100 5
• (reading lt full scale, limiting error increased)

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Example 1.3

• A voltmeter and an ammeter are to be used to
  determine the power dissipated in a resistor.
  Both instruments are guaranteed to be accurate
  within 1 at full scale. If the voltmeter reads
  80V on its 150-V range and the ammeter reads 70mA
  on its 100-mA range, calculate the limiting error
  for the power calculation.

The limiting error for the power calculation
is the sum of individual limiting errors involved
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1.2 Error in Measurement

• Precision of measurement
• A measure of the consistency or repeatability of
  measurements

where Xn the value of the nth measurement Xn
the average of the set of n measurements sum
of the nth measurement values / nth
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Example 1.4

• Table below gives the set of 10 measurement that
  were recorded in the laboratory. Calculate the
  precision of the 6th measurement.
• ??
• Precision ??

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1.2 Error in Measurement

• STATISTICAL ANALYSIS OF MEASUREMENT DATA
• Important because it allows an analytical
  determination of the
  uncertainty of the final
  result
• A large number of measurements is usually
  required
• can be divided into 4
• Arithmetic mean / average
• deviation
• average deviation
• standard deviation

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1.2 Error in Measurement

• Arithmetic mean/average
• - the most probable value of measured variable

n total number of reading xn nth reading
taken xi set of number
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1.2 Error in Measurement
ii) Deviation - The difference between each
piece of data and arithmetic mean
- Algebraic sum of deviation,
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1.2 Error in Measurement
iii) Average deviation (D) - precision of a
measuring instrument - high D ?low precision -
low D ? high precision
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1.2 Error in Measurement
iv) Standard deviation - also known as root
mean square deviation - the most important
factor in statistical analysis - reduction
means improvement in measurement
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Example 1.5
For the following data compute (a) The
arithmetic mean (49.9) (b) The deviation of each
value (0.2,-0.2,-0.3,0.3) (c) The algebraic sum
of the deviation (0) (d) The average deviation
(0.25) (e) The standard deviation (0.294) x1
50.1 x2 49.7 x3 49.6 x4 50.2
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1.3 Measurement Standards

• Standards are defined in 4 categories
• i) international standards
• ii) primary standards
• iii) secondary standards
• iv) working standards

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1.3 Measurement Standard

• i) International Standards
• Defined by international agreements
• These standards are maintained at the
  International Bureau of Weight and Measures in
  Paris, Frances
• They are periodically evaluated and checked by
  absolute measurements in term of the fundamental
  units of physics
• They represent certain units of measurement to
  the closest possible accuracy attained by the
  science and technology of measurement and used
  for comparison with primary standards

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1.3 Measurement Standard

• ii) Primary Standard
• Are maintained at institution in various
  countries around the world, such as the National
  Bureau of Standard on Washington D.C, SIRIM in
  Malaysia
• The primary standards are not available for use
  outside the national laboratories
• Their principle function is to calibrate and
  verify the secondary standards
• Also known as National Standard

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1.3 Measurement Standard

• iii) Secondary Standard
• Used as the basic reference standards used by
  measurement calibration laboratories in the
  industry
• Each industrial laboratory is completely
  responsible for its own secondary standards
• Each laboratory sends its secondary standards to
  the national standards ( primary standards)
  laboratory for calibration
• After calibration, the secondary standards are
  returned to the industrial uses with the
  certification and checked periodically

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1.3 Measurement Standard

• iv) Working Standard
• Working standard is the principle tools of a
  measurement laboratory and the lowest level of
  standards
• Used to check and calibrate the instruments used
  in the laboratory or to make comparison
  measurement in industrial application
• Example the standard resistor, capacitors,
  inductor which usually found in an electronics
  laboratory are classified as working standards.

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Summary

• Some terms definitions are as below
• Error ---???
• Accuracy The degree of exactness of a
  measurement compared to the expected value
• Precision A measure of consistency, or
  repeatability of measurements.

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Summary

• Instrument a device or mechanism used to
  determine the present value of a quantity
• Measurement a process of comparing an unknown
  quantity with an accepted standard quantity.
• Standard an instrument or device having a
  recognized permanent (stable) value that is used
  as a reference.

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Summary

• expected value the most probable value we
  should expect to obtain.
• deviation the difference between any piece of
  data in a set of numbers and the arithmetic mean
  of the set of numbers.
• transducer a device that converts one form of
  energy into another form

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Evaluation

• Electrical Quantity

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• THANK U FOR YOUR ATTENTION!!?