What is Measurement?
Measurement:-
Measurement is the process that determining the value of the magnitude of an unknown quantity with some predetermined standards of references.In order that the result of the measurement is meaningful, there are two basic requirements:
1. Standard used for comparison must be accurately defined and should be commonly accepted.
2. The apparatus used for measurement and procedure of measurement must be proven.
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| define Measurement |
There are two major functions of all branches of engineering:
1. Design of equipment and process.
2. Proper operation and main trance of equipment and process.
Measurement is useful and important for:
1. Controlling some variables in the process within its specified limits.
2. To monitor some certain quantity that is the Diameter rod.
3. To study and analyze different elements of machine structure.
4. To check the validity of the design and different laws of physics, mechanics, etc.
5. Testing the quantity of product.
Common function/applications of instrument systems are :
• Measurement of system parameters.
• Control of the process of operation.
• To Simulation of system conditions.
• Experimental design studies.
• To perform various manipulation.
• Testing of material, maintenance, and specification of product.
• Verification of physical phenomenon or scientific theories.
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| what is measurement |
Classification of mechanical measurement :
1. Mechanics type measurement:
• Empirical method:
The empirical method is based on intuition and good engineering judgments. The designer max judgments based on his past experience. design data available in the form of ‘Thumb rule’ helps the designer to develop his design. The method of design is based on the judgment which, may prove to be wrong.• Rational design method:
It is based on well-established scientific laws and relationships. These laws and relations are mainly available in the area of thermodynamics, mechanics. This area has a limited scope of design.• Experimental method:
This method is based on co-related measurements of all physical quantity involved. The results are scientifically analyzed and errors are calculated. Then by trial and error method, all the parameters are adjusted till the product gives the desired performance or result.2. Power type measurement.
i) Application:
a) Mechanical instruments.b) Electrical instruments.
c) Electronic instruments.
ii) Mode of operation:
a) Manual operated: Null type potentiometer.
b) Automatic operated: Mercury in glass thermometer.
iii) Method of energy conversion:
a) Self-operated: Dial thermometer
b) Power-operated : Wheatstone bridge
iv) Nature of output signal:
a) Null type: Weighing balance.
b) Deflection type: Bourdon pressure gauge.
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| mechanics type measurement |
Methods of measurement
1. Direct method :
This type of method is the quantity yo be measured is directly compared with known as standard. The direct method of measurement is very common for the measurement of physical quantities such as time, length, mass.
Example :
a) To measure the length of steel bar by comparing it with a steel rule.
b) Determination of weight by balance.
c) Measuring the speed of the shaft by the tachometer.
Advantages of measurement by the direct method:
1. Measurement can be done quickly.
2. The complicated mechanism and processes is eliminated.
3. It is the simplest method of measurement.
Disadvantages of measurement by direct methods:
1. This method all quantities can not be measure.
2. The result of the measurement may not be accurate.
3. The method is limited within human capabilities and the chance of error is more.
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| method measurement |
2. Indirect method :
Measurements by the direct method are always not possible. In indirect method of measurement, measurand is converted into some effect which can be measured. The method makes comparison with standard through the use of a calibrated system that is an Empirical relation is established between the measurement actually made and the results that are desired.i) Primary measurement:
Primary measurement is one that can be made by direct observation without involving any conversion or translation of measure quantity.
Examples,
a) Measurement of length by meter rod.
b) Matching of two colors when judging the temperature of red hot steel.
b) Matching of two colors when judging the temperature of red hot steel.
c) Measurement of time by counting the number of strokes of the clock.
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| primary measurement |
ii) Secondary measurement:-
The indirect measurement involving one translation is called secondary measurement.
Example,
(a) The conversation of pressure into displacement by means of bellows, and conversion of force into displacement buy means of springs are examples of secondary measurements.
(b) Temperature measurement by mercury in glass thermometer: In this, the temperature sensed by the bulb is converted into the displacement of mercury in capillary and its height indicates temperature.
(c) Force measurement by using spring balance: forced gives Deflection of spring and defalcation of spring gives the value of force to be measured.
(iii) Tertiary measurement :
Those measurements involving two conversions are allied Tertiary measurement.
Example,
(a) Measurement of pressure by Bourdon pressure gauge.
(a) Measurement of pressure by Bourdon pressure gauge.
(b) Measurement of speed by the electric tachometer.
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| indirect type of measurement |
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