1. Introduction to Instrumentation Engineering
Universität Karlsruhe
Institut für Telematik
Mobilkommunikation
SS 1998
Introduction to Instrumentation Engineering
Chapter 1: Fundamental Concepts
By Sintayehu Challa
Changes to previous year:
Prof. Dr. Dr. h.c. G. Krüger
E. Dorner / Dr. J. Schiller

2. Universität Karlsruhe Institut für Telematik
Mobilkommunikation
SS 1998
Goals of this chapter
Give an overview of fundamental concepts and terminologies in instrumentation and measurement systems
Discuss system of units
Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
Prof. Dr. Dr. h.c. G. Krüger
E. Dorner / Dr. J. Schiller

3. Universität Karlsruhe Institut für Telematik
Mobilkommunikation
SS 1998
Overview
Definition of Instrumentation System
General Instrumentation system
Applications of Instrumentation Systems
Systems of Units and Standards of measurement
Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
Prof. Dr. Dr. h.c. G. Krüger
E. Dorner / Dr. J. Schiller

4. Instrumentation System - Definition
An assembly of various instruments and/or components interconnected to measure, analyze and control various physical quantities (variables)
Physical quantities can be classified in a number of ways
Electrical-quantities: Voltage, current, resistance, inductance, capacitance, electrical power, electrical energy
Non-electrical quantities: Pressure, displacement, torque, temperature, illumination, etc
Instrument is a device for determining the value or magnitude of a quantity or variable
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5. Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
Definition …
Measurement: Act or the result of a quantitative comparison between a predefined standard and an unknown magnitude
Direct comparison with either a primary or a secondary standard
Indirect comparison with a standard through the use of a calibrated system
E.g., water level by a capacitor, temperature by a resistor
An empirical relation is established between the measurement actually made and the results that are desired
There are two requirements that must be met
Standard which is used for comparison must be accurately defined and commonly accepted
Procedure and apparatus employed for obtaining the comparison must be provable
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6. Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
Overview
Definition of Instrumentation system
General Instrumentation system
Different types of measurement systems
Systems of Units and Standards of measurement
Introduction to Instrumntaion - Ch. 1 Fundamental Concepts

7. General Instrumentation System
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General Instrumentation System
The purpose of an instrumentation (measurement) system is to present an observer with a numerical value corresponding to the variable being measured
Most general instrumentation systems consists of four distinct functional elements
Input
variable
Output variable
System being
measured
Measurement
system
Observer Or
True value of a variable
Measured value of variable
Introduction to Instrumntaion - Ch. 1 Fundamental Concepts

8. Functional Elements of Instrumentation System
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9. Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
Contd.
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10. General Instrumentation …
Sensing element
Signal conditioning element
Signal conversion/processing element
Output presentation
Non-electrical quantity
Electrical
signal
Description of the block diagram
Sensing element: Called transducer or sensor and is useful if the quantity is non-electrical
Signal conditioner: Example are amplifiers, bridges, attenuation
Signal conversion: A/D and D/A converters
Output presentation: Recorder (graphic, magnetic, digital) or indicators (pointer-scale, alpha numeric, graphic)
Each functional element may have one or more components in the same instrument
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11. Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
Sensing Element
Sensing element also called sensor or transducer
Is a primary sensing element which receives energy from the measured medium and produces an output
Converts non-electrical quantity to a corresponding electrical quantity
If there are more than one sensing elements in a system, the element in contact with the process (input) is termed the primary sensing element, the other is the secondary sensing element
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12. Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
Sensing Element …
Usually the input physical effect is transformed into another physical output, in most cases to electrical signals
Sensing element is required when measurement of a non-electrical quantity is made
Generate voltage/current variation in response to variation of the quantity under interest
Examples:
Thermocouple: input of temperature and an output of a small e.m.f.
Resistance thermometer : input of temperature and an output of a resistance change
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13. Sensing Element – Examples
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Sensing Element – Examples
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14. Signal Conditioning Element
In most cases, the output of the sensor or the element quantity to be measured is so small
Not suitable to the output presentation section
The signal conditioning element converts the signal into a form matching the characteristics of the output device (or more suitable for further processing)
Example
Bridges: Convert an impedance change into a voltage change
Amplifiers: Converts mille volt to volts
Oscillators: Impedance change into a variable frequency voltage
Filters: Filters unwanted frequency range
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15. Signal Conversion Element
Converts the output of the signal conditioning element into a form more suitable for presentation
Signal conversion is necessary only when digital techniques are required
Example: Analog-to-digital converter
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16. Data Presentation Element
This presents the measure value in a form which can be easily recognized by the observer
For presentation as an indication on an instrument or recording in a graphical presentation
Example:
Pointer-scale indicator
Chart recorder
Visual display unit
In a typical system, one part may be missing or may occur more than once
The final terminating stage may also include data-transmission element for storage/playback
Introduction to Instrumntaion - Ch. 1 Fundamental Concepts

17. Example: Piston Pressure Gage
Piston: Primary sensing element and variable conversion element
Piston rod: Data transmission element
Spring: Variable conversion element
Linkage: Variable manipulation element
Pointer and Scale: Data presentation element
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18. Example: Pressure Thermometer
Bulb: Primary sensing element and variable conversion element
Tubing: Data transmission Bourdon Tube: Variable conversion element
Linkage and gear: Variable manipulation element
Scale and Pointer: Data presentation
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19. Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
Overview
Definition of Instrumentation system
General Instrumentation system
Applications of measurement systems
Monitoring of processes and operations
Control of processes and operations
Experimental analysis
Systems of Units and Standards of measurement
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20. Applications of measurement
Applications of measurement systems includes
Monitoring (or measurement ) of processes and operations
Control of processes and operations (i.e., system control)
Experimental analysis
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21. Monitoring of Processes and Operations
Instruments that measure physical quantities such as length, volume and mass in terms of standard units
E.g., in weather bureau, instruments such as thermometers, barometers and anemometers are used to serve the purpose of monitoring
E.g., water and electric meters for domestic use have similar functions (allows the company to determine the charge)
Measurement system displays or records a quantified output corresponding to the variable input quantity
They simply indicate the condition of the environment and the readings do not serve any control function
If action is taken based on this measurements, then the measurement serves a control function
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22. Processes and Operations Control
Measuring instrument serves as a component of an automatic control system
Basically in a control system
To control the variable, it is first necessary to measure it
Measurement provides information that enables human beings to take some prescribed action accordingly
Control action
Open-loop control
Closed-loop control
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23. Processes and Operations …
Open-loop system
The basis of open-loop control is that the system is controlled by a signal which is a pre-set value (reference value)
Signal: In electrical engineering could mean voltage or current
Controller are required to
Compare the output variable with the desired value of the controlled variable and
Reacts by sending message to the control element to take corrective action
Controller
System under control
Output signal (required signal)
Input signal (Preset value or reference value)
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24. Processes and Operations …
Close-loop system
Measures the value of the parameter being controlled at the output of a system and compares to a desired signal
Automatic feedback control system
Example:
Greenhouse: A thermometer is used to determine whether a heat should be turned on or open windows
Controller
System under control
Output signal
Desires signal
Measurement system
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25. Processes and Operations …
Example: A temperature control system
Temperature Ta (i.e., controlled variable) of a room is maintained at a reference value Td
Ta, as determined by a temperature-measuring device, is compared with Td, and the difference is applied as an error signal to the heater
The heater then modifies the room temperature until Ta = Td
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26. Experimental Analysis
To solve engineering problems two general methods are available: theoretical and experimental
Many problems require the application of both methods
Normally, they complement each other
Complex situations are often dealt by experimental methods, e.g., convection heat transfer relations
Frontier knowledge often require very extensive experimental studies since adequate theories are not available yet
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27. Experimental Analysis …
Types of Experimental-Analysis Problems
Testing the validity of theoretical predictions
Formulation of generalized empirical relationships
Determination of material, component, and system parameters, variables, and performance indices
Study of phenomena with hopes of developing a theory
Solution of mathematical equations by means of analogies
For any successful experiment, it has to be designed carefully and this requires specifying the physical variables to be investigated and their role in later analytical works
This will help to procure appropriate instrumentation
It is here where a thorough knowledge of the governing principles of instruments will be required
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28. Experimental Analysis …
In all the above three processes, accurate measurement will include the specification of the degree of accuracy
This indicates the limitations of the instruments that account for certain random and/or regular errors which may be present in the experimental data
Statistical techniques are used for analyzing data to determine expected errors and deviations from the true measurements
Discussed in Chapter latter
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29. Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
Overview
Definition of Instrumentation System
General Instrumentation system
Applications of measurement systems
Systems of Units and Standards of measurement
System of Units
Standard of measurement system
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30. Introduction to Instrumntaion - Ch. 1 Fundamental Concepts
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Systems of Units
Fundamental units: The smallest set of quantities that are accepted by definition
Example: In mechanical system, length, mass and time
Derived units: Units expressed in terms of the fundamental units
Each derived unit originates from some physical law which defines that unit
Example: Velocity = d/ t has unit m/s or ms-1
A derived unit is recognized by the dimensions and can be defined as the complete algebraic formula for the derived unit
Dimensional symbols for the fundamental units for the fundamental units of length, mass, & time are L, M, & T
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Systems of Units …
In general, system of units in engineering are divided into
Foot-Pound-Second (FPS)
Foot-Slug-Second (FSS)
Centimeter-Gram-Second (CGS)
Meter-Kilogram-Second (MKS)
English System of Units: FPS and FSS
Mechanical System of Units: CGS and MKS
System of International (SI) unit: The most recent and widely accepted system of unit
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Systems of Units …
The SI system of units with seven Fundamental quantities are defined as
All other quantities defined by the basic SI unit are called Derived quantities
Quantity
Unit
Symbol
Length
Meter M
Mass
Kilogram Kg
Time
Second S
Current
Ampere A
Temperature
Kelvin 0k
Illumination
Candela Cd
Amount of substance
Mole
mol
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Systems of Units …
Conversion of Units: It is often necessary to convert physical quantities from one system of unit into another
Example: The floor area of a class-room measures 30ft by 24ft. Calculate the floor area in m2
Solution
We find that 1cm= ft or 1m = 3.28ft
A=30ft X 24 ft = 720 ft2
Or A = 720 ft2 X (1/3.28ft)2 = 67.3 m2
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34. Standard of Measurement System
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Standard of Measurement System
The standard is the physical representation of the units defined in the system of units
Different standards of measurement exist
Differ in their functional and hierarchy
Have different levels of accuracy
International standard (IS)
Defined by international agreement
Represent certain units of measurements to the closest possible accuracy that the production and measurement technology allow
IS are the highest accuracy standards
Primary standards (PS)
Maintained by International standard laboratories in different part of the world
Used for verification and calibration of secondary standards
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35. Standard of Measurement …
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Standard of Measurement …
Secondary standards
Are the basic reference standards in industrial measurement laboratories
Working standards are
Principal tools of a measurement laboratory
Used to check and calibrate general laboratory instruments for accuracy
All standards are checked by the highest or greater standard
The better instrument is checked by 10:1 accuracy ratio
Introduction to Instrumntaion - Ch. 1 Fundamental Concepts