EMT 462EMT 462ELECTRICAL ELECTRICAL

SYSTEM SYSTEM TECHNOLOGTECHNOLOG

YYPart 2:Part 2:InstrumentatInstrumentationion

By:En. Muhammad Mahyiddin Ramli

Part 2: Instrumentation 2

Syllabus

Chapter 4: DC and AC Motors

Chapter 5: DC and AC Bridges

Chapter 6: Sensors and Transducers

Instrumentation

Part 2: Instrumentation 3

Basic Concept of Instrumentation and Measurement Instrument is a device that transform a

physical variable of interest (measurand) into a form that is suitable for recording (measurement).

Part 2: Instrumentation 4

Introduction

3 Basics Function of Instrument

•Indicating•Recording•Controlling

Classification of Instruments•Analog Instrument•Digital Instrument

Part 2: Instrumentation 5

Simple Instrument Model

Part 2: Instrumentation 6

Instrumentation System

Physical Parameter:• Temperature• Pressure• Velocity• Force• etc.

Sensor / Transducer

• Bridge• Amplifier• Filter

Signal Converter:• ADC• DAC• FVC• etc.

Display:• OSC• Meter• Plotter• Computer

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Two Basic Characteristic of an Instrument

Static characteristic – in generally for instrument which are used to measure an unvarying

process condition.

Dynamic characteristic

Part 2: Instrumentation 8

Two Basic Characteristic of an InstrumentSeveral terms of static characteristic:Instrument - A device or mechanism used to determine the

present value of a quantity under observation.Measurement - The process of determining the amount, degree,

capacity by comparison (direct or indirect) with the accepted standards of the system units being used.

Accuracy - The degree of exactness (closeness) of a measurement compared to the expected (desired) value.

Resolution - The smallest change in a measured variable to which instrument will response.

Precision - A measure of consistency or repeatability of measurements, i.e. successive readings do not differ or the consistency of the instrument output for a given value of input.

Expected value - The design value that is “most probable value” that calculations indicate one should expect to measure.

Sensitivity - The ratio of the change in output (response) of the instrument to a change

Part 2: Instrumentation 9

Error In MeasurementError: The difference between the true value (expected value) of the

measurand and the measured value indicated by the instrument

Error may be expressed either as a absolute error or as percentage of error.

Absolute errors:

e = |Yn - Xn|

Where Yn = expected value

Xn = measured value

Part 2: Instrumentation 10

Error In MeasurementAbsolute ErrorExpected Value

X 100 %

Yn – Xn

Yn

X 100 %

or

Percentage Error:

Relative Accuracy, A:

A = 1 -

Yn – Xn

Yn

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Error In Measurement

Percentage relative accuracy, a = 100 % - Percentage Error

= A x 100 %

Part 2: Instrumentation 12

Example 1

The expected value of the voltage across a resistor is 90 V. However, the measurement gives a value of 89 V.

Calculate:a) Absolute errorb) Percentage errorc) Relative accuracyd) Percentage of accuracy

Part 2: Instrumentation 13

SolutionExpected value of voltage across a resistor, Yn = 90 VMeasured value of voltage across a resistor, Xn = 89 V

a) Absolute error, e = Yn – Xn = 90 – 89 = 1V

b) Percentage error, e =

=

Yn – Xn

Yn

X 100 %

90 – 89 90 X 100

% = 1.1111 %

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Solution

c) Relative accuracy, A = 1 -

Yn – Xn

Yn

= 1 – 0.0111= 0.9889

d) Percentage of accuracy, a = 100 x 0.9889 = 98.8900 %

ora = 100 % - 1.1111 % = 98.8889 %

Part 2: Instrumentation 15

Types of Error Gross Errors - Are generally the fault of the person using instruments

and are due to such things as incorrect reading of instruments, incorrect recording of experimental data or incorrect use of instrument.

Systematic Errors - Are due to problems with instrument, environment effects or observational errors. Instrument Errors - May be due to friction in the bearings of the

meter movement, incorrect spring tension, improper calibration or faulty instruments.

Environmental Errors – Environmental conditions in which instrument are used may cause errors. Subjecting instruments to harsh environment such high temperature, pressure, humidity, strong electrostatic or electromagnetic fields, may have detrimental effects, thereby causing error.

Observational Errors – Are those errors introduced by observer. Two most common observational errors are probably the parallax error introduced in reading a meter scale and errors of estimation when obtaining a reading from a scale meter.

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Types of Error

Random Errors – the accumulation of a large number of small effects and may be of real concern only in measurements requiring a high degree of accuracy. Such errors can be analyzed statistically. 

Part 2: Instrumentation 17

Standard and Calibration

4 types of standards of measurement: International standards – British Standard Institution (BSI),

International Electrotechnical Commission (IEC), International Organization for Standardization (ISO).

Primary standards – SIRIM, Local University, Industry Secondary standards – SIRIM Working standards – SIRIM, Local University, Industrial

Calibration: the act or result of quantitative comparison between a known standard and the output of measuring system measuring the same quantity.