Introduction to Instrumentation

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Chapter 01

• Introduction to Instrumentation Measurements.

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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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Outlines

• The outline of this chapter is as follows
• Principles of instrumentation and measurements
• Electrical Units
• Error in measurement
• Some terms definitions in instrumentations.

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Introduction

• Why learning BEE1313?
• What is the main role/ purpose of
  instrumentation?
• Give Example of applications?

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Introduction

• Instrumentations serve three (3) basic functions
  -
• indicating
• recording
• controlling

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Function Characteristics of Instruments
3 basic functions
Indicating
Recording
Controlling
General-purpose electrical electronics test
instruments
Industrial-process
Control / automated system
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Electrical Units

• Fundamental Quantity

Quantity Symbol Unit Unit Abbre.
Length l meter m
Mass m kilogram kg
Time t second s
Temperature T Kelvin oK
Electric current I Ampere A
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Electrical Units

• Derived Quantity

Quantity Symbol Unit Unit Abbre.
emf/ voltage V volt V
charge Q coulomb C
resistance R Ohm ?
capacitance C farad F
inductance L hendry H
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Measurement Standards

• Standards are defined in 4 categories
• international standards.
• primary standards.
• secondary standards.
• working standards.

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Measurement Standard (International Standard)

• Are defined by international agreements. These
  standards are maintained at the International
  Bureau of Weight and Measures in Paris, France.
  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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Measurement Standard (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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Measurement Standard(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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Measurement Standard(working standard)

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

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Error in Measurement
Measurement
The process of comparing an unknown quantity with
an accepted standard quantity
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Error in Measurement

• There are various types of error in measurement
• absolute error
• gross error
• systematic error
• random error
• limiting error

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Error in Measurement

• What is the meaning of error?
• Please define.
• --------------------------------------------------
  ----

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Error in Measurement

• Error - The deviation of a reading or set of
  readings from the expected value of the measured
  variable.

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Error in Measurement

• Absolute error.
• Absolute error maybe defined as 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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Error in Measurement

• to express error in percentage
• error
• we also derived relative accuracy, A

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Error in Measurement
Percent accuracy, a
a 100 - Percent error
or
a A x 100
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Error in Measurement

• 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
• absolute error
• error
• relative accuracy
• accuracy

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Error in Measurement
Precision of measurement A quantitative, or
numerical, indication of the closeness with which
a repeated set of measurements of the same
variable agrees with the average of the set of
measurements.
where Xn the value of the nth measurement Xn
the average of the set of n measurements
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Error in Measurement

• Errors are generally categorized under the
  following three (3) major headings
• Gross Errors
• Systematic Errors
• Random Errors

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Error in Measurement

• Gross Error
• generally the fault of the person using the
  instruments
• such as incorrect reading, incorrect recording,
  incorrect use etc.

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Error in Measurement
Instrument errors
Environmental errors

• Systematic Error
• due to problems with instruments/ environmental
  effects/ or observational errors.
• Example???
• parallax error
• wrong estimation reading scale

Observational errors
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Error in Measurement
Instrument errors Instrument errors may be due
to friction in the bearings of the meter
movement, incorrect spring tension, improper
calibration, or faulty instruments. Instrument
error can be reduced by proper maintenance, use,
and handling of instruments.
Environmental errors Environmental conditions
in which instruments are used may cause errors.
Subjecting instruments to harsh environments such
as high temperature, pressure, or humidity, or
strong electrostatic or electromagnetic fields,
may have detrimental effects, thereby causing
error.
Observational errors Observational errors are
those errors 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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Error in Measurement

• Random Errors
• generally the accumulation of a large number of
  small effects
• maybe of real concern only in measurements
  requiring a high degree of accuracy.
• such errors can only be analyzed statistically.

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Error in Measurement

• Limiting Errors
• manufacturers of instruments state that an
  instrument is accurate within a certain
  percentage of a full-scale reading.
• example is a voltmeter is accurate within 2 at
  full-scale deflection.
• this specification is called the limiting errors.

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Error in Measurement

• 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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Error in Measurement

• 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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• Solution Example 1-2
• 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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Error in Measurement

• 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
3.304
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STATISTICAL ANALYSIS OF ERROR IN MEASUREMENT
1) Arithmetic mean/average
n total number of piece of data xn the
value of the nth measurement xi set of number
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STATISTICAL ANALYSIS OF ERROR IN MEASUREMENT
2) Deviation the difference between each piece
of data and arithmetic mean
Note
algebraic sum of deviation
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STATISTICAL ANALYSIS OF ERROR IN MEASUREMENT
3) Average deviation (D) - precision of a
measuring instrument - high D ?low precision -
low D ? high precision
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STATISTICAL ANALYSIS OF ERROR IN MEASUREMENT
4) Standard deviation the degree to which the
value vary about the average value
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STATISTICAL ANALYSIS OF ERROR IN MEASUREMENT
Example 1-4 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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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

Quantity Symbol Unit Unit Abbre.
l meter
Capacitance F
Time second
T Kelvin oK
Charge