1. Measurement And Instrumentations DR. Eng. Samir Elshamy

2. Measurements and Measurement Systems
Measurements provide us with a means of describing various phenomena in quantitative terms.
The measurements are not necessarily carried out by purely mechanical means.
Quantities like pressure, temperature, displacement, fluid flow and associated parameters, acoustics and related parameters, and fundamental quantities like mass, length, and time are typical of those which are within the scope of mechanical measurements.
However, in many situations, these quantities are not measured by purely mechanical means, but more often are measured by electrical means by transducing them into an analogous electrical quantity.
DR. Eng. Samir Elshamy

3. it is more appropriate to use the term Measurement of Mechanical Quantities rather than mechanical measurements .
All mechanical quantities are not measured by mechanical means.
And, measurement of mechanical quantities, in modern technology, involves the use of electrical and electronic techniques.
The Measurement of a given quantity is essentially an act or result of comparison between a quantity whose magnitude (amount) is unknown, with a similar quantity whose magnitude (amount) is known, the latter quantity being called a Standard.
DR. Eng. Samir Elshamy

4. Process of Comparison (Measurement)
Standard
(Known quantity)
Result
(Numerical Value)
Measured
(Unknown quantity)
Fundamental Measuring Process.
DR. Eng. Samir Elshamy

5. In order that the results of measurement are meaningful, the basic requirements are:
The standard used for comparison purposes must be accurately defined and should, be commonly acceptable.
The standard must be of the same character as the measured (the unknown quantity or the quantity under measurement) and usually, but not always, is prescribed and defined by a legal or recognized agency or organization like Indian Bureau of Standards (IBS) or the International Organization of Standards (ISO).
The apparatus used and the method adopted for the purposes of comparison must be provable.
DR. Eng. Samir Elshamy

6. METHODS OF MEASUREMENT
1. Direct Methods. the unknown quantity is directly compared against a standard. The result is expressed as a numerical number and a unit. The standard, in fact, is a physical embodiment of a unit. Direct methods are quite common for the measurement of physical quantities like length, mass and time.
DR. Eng. Samir Elshamy

7. 2. Indirect Methods. Measurements by direct methods are not always possible, feasible and practicable. These methods in most of the cases, are inaccurate because they involve human factors. They are also less sensitive. Hence direct methods are not preferred and are less commonly used.
In engineering applications Measurement Systems are used. These measurement systems use indirect methods for measurement purposes.
A measurement system consists of a transducing element which converts the quantity to be measured into an analogous signal. The analogous signal is then processed by some intermediate means and is then fed to the end devices which present the results of the measurement.
DR. Eng. Samir Elshamy

8. PRIMARY, SECONDARY AND TERTIARY MEASUREMENTS
1. Primary Measurements. A primary measurement is one that can be made by direct observation without involving any conversion, (translation) of the measured quantity into length.
In this case, the change in the measured quantity stimulates a set of the observer's nerve endings, so that he can see or sense the change directly.
Typical examples of primary measurements are:
the matching of two lengths, such as when determining the length of an object with a meter rod,
the matching of two colors, such as when judging the color of red hot metals and
the counting of strokes of a clock chime to measure the time.
DR. Eng. Samir Elshamy

9. 2. Secondary Measurements
2. Secondary Measurements. A secondary measurement involves only one translation (conversion) to be done on the quantity under measurement to convert it into a change of length. The measured quantity may be pressure of a gas, and therefore, may not be observable. Therefore, a secondary measurement requires.
An instrument which translates pressure changes into length changes, and.
A length scale or a standard which is calibrated in length units equivalent to known changes in pressure.
Therefore, in .a pressure gauge, the primary signal (pressure) is transmitted to a translator and the secondary signal (length) is transmitted to observer's eye.
DR. Eng. Samir Elshamy

10. 3. Tertiary Measurements
3. Tertiary Measurements. A tertiary measurement involves two translations. A typical example of such a measurement is the measurement of temperature of an object by thermocouple. The primary signal (temperature. of object) is transmitted to a translator which, generates a voltage which is a function of the temperature. Therefore, first translation is temperature to voltage. The voltage, in turn, is applied to a voltmeter through a pair of wires. The second translation is then voltage into length. The tertiary signal (length change) is transmitted to the observer's brain. This tertiary measurement is depicted in Figure
DR. Eng. Samir Elshamy

11. Atypical tertiary measurement
DR. Eng. Samir Elshamy

12. ANALOG AND DIGITAL OF OPERATION
Secondary instruments work in two modes:
(i) Analog mode, and (ii) Digital mode.
Signals that vary in a continuous fashion and take on an infinite number of values in any given range are called analog signals. The devices which produce these signals are called analog devices.
In contrast, the signals which vary in discrete steps and thus take up only finite different values in a given range are called digital signals. The devices that produce such signals are called digital devices.
DR. Eng. Samir Elshamy

13. FUNCTIONS OF INSTRUMENTS AND MEASUREMENT SYSTEMS.
There is another way in which instruments or measurement systems may be classified.
This classification is based upon the functions they perform.
The three main functions are explained below:
Indicating Function.
Recording Function.
Controlling Function.
DR. Eng. Samir Elshamy

14. APPLICATIONS OF MEASUREMENT SYSTEMS.
Monitoring of processes and operations.
Control of processes and operations.
and Experimental Engineering analysis.
DR. Eng. Samir Elshamy

15. The Generalized Measurement System
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The Generalized Measurement System
Most measurement systems may be divided into three parts:
A detector-transducer stage, which detects the physical variable and performs either a mechanical or an electrical transformation to convert the signal into a more usable form.
Some intermediate stage, (Signal conditioning)which modifies the direct signal by amplification, filtering, or other means so that a desirable output is available.
A final or terminating stage, which acts to indicate, record, or control the variable being measured. The output may also be digital or analog.
DR. Eng. Samir Elshamy

16. Bourdon-tube pressure gage
The bourdon tube is the detector-transducer stage because it converts the pressure signal into a mechanical displacement of the tube.
The intermediate stage consists of the gearing arrangement, which amplifies the displacement of the end of the tube so that a relatively small displacement at that point produces as much as three-quarters of a revolution of the center gear.
The final indicator stage consists of the pointer and the dial arrangement, which, when calibrated with known pressure inputs, gives an indication of the pressure signal impressed on the bourdon tube.
DR. Eng. Samir Elshamy

17. DR. Eng. Samir Elshamy

18. 1.8. INPUT-OUTPUT CONFIGURATIONS OF MEASURING INSTRUMENTS AND MEASUREMENT SYSTEMS.
A generalized configuration in instruments and measurement systems which brings out a significant input-output relationship present in them is shown in Figure. Input quantities are classified into three categories:
Desired inputs.
Interfering inputs.
Modifying inputs.
DR. Eng. Samir Elshamy

19. Desired inputs. Desired Inputs are defined as quantities for which the instrument or the measurement system is specifically designed to measure and respond.
Interfering inputs. Represent quantities to which an instrument or a measurement system becomes unintentionally عن غير قصد sensitive. The instruments or measurement systems are not desired to respond to interfering inputs but they give an output due to interfering inputs on account of their principle of working, design many other factors like the environments in which they are placed.
Modifying Inputs. This class of inputs can be included among the interfering inputs. However, a separate classification is essential since such a classification is more significant. Modifying Inputs are defined as inputs which cause a change in input-output relationships for either desired inputs or interfering inputs or for both.
DR. Eng. Samir Elshamy

20. Generalized input-output configuration of measurement systems.
DR. Eng. Samir Elshamy

21. Measurement of different pressure with manometer
Acceleration as an interfering input
Angle of tilt as an interfering input
DR. Eng. Samir Elshamy

22. METHODS OF CORRECTION FOR INTERFERING AND MODIFYING INPUTS.
Method of Inherent Insensitivity
Method of high gain Feedback
Method of calculated output corrections
Method of Signal Filtering
Method of opposing Inputs
DR. Eng. Samir Elshamy

23. Thanks for your kind attention
DR. Eng. Samir Elshamy