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  1. MODULE 4 DEFINITIONS MEASUREMENT : It is the act of result of quantity comparison between a pre- determined standard and unknown magnitude. For comparison we should have proper operation and procedure and it must be reliable. Measurement provides us with a means of describing various phenomenon in quantitative terms. The result is expressed in terms of numerical value. In order that the result of a measurement are meaningful and these are two basic requirements 1. The standard used for comparison purpose must be accurately defined and should be universally and commonly accepted. 2. The apparatus used and method adopted for the purpose of comparison must be provable.
  2. SIGNIFICANCE OR AIMS OF MEASUREMENT (RESEARCH & DEVELOPMENT (R &D) In the engineering field R & D program, measurement and its interpretation is of great importance. Measurement is a vast field which embraces detection, acquisition, control and analysis of data. It involves the measurement of physical, electrical, mechanical, optical and chemical quantities and plays a very significant role in every branch of scientific research and engineering processes, which include control systems, process instrumentation and data reduction. Measurement and Instrumentation in every field from machine to satellite.
  3. Mechanical Measurements The measurement involved in the field engineering and technology are classified into 2 broad categories 1. Mechanics type of measurements 2. Power type of measurements 1. Mechanics type of measurements: Mechanics type of measurements are used as a design tool for experiment, research and developmental programs. Complete solution of any mechanical engineering design problem of any mechanical engineering design problem requires the following 3 methods (i) Empherical method (ii) Rational method (iii) Experimental method
  4. .  The Empherical design method is based upon INTUTION and good engineering judgement on the part of the designer. The designer usually makes this judgement, that is an outcome of his or other designer’s past experience of working similar designs. Since this method of design is mainly based upon the judgement of the designer, which may prove wrong, it cannot be relied upon especially in the case of design of complete systems.
  5. . The rational design method is strictly based upon well established scientific laws and relationships. These laws are mainly available in the areas of mechanics and thermodynamics. While in other areas of mechanical engineering their availability is rather therefore in areas othrerthan mechanics and thermodynamics. The use of rational design method has a very limited scope. In the experimental method, the product based upon an initial design tested. Accurate and corrected measurements of all physical quantities involved are done. The results are scientifically analyzed and process are interpreted. Then by TRIAL AND ERROR method the parameters are adjusted till the product or system design gives the desired performance.
  6. 2. Power type of measurement These are operational measurements which are usually a part of a control system for example: in order that a steam power plant operates reliably and economically many quantities have to be continuously monitored, some of the quantities are steam pressure, temperature, flow rate along with speed of the turbine, quantities of coolant etc., these are compared with the corresponding reference quantities and the error signal that are generated.
  7. FUNDAMENTAL METHOD OF MEASUREMENT The fundamental method of measurement is classified into two types 1. Direct Method : In these methods the unknown quantity is directly compared against the standard. The result is expressed as a numerical number or unit. Direct methods are common for the measurement of length, mass and time. Although the measurement of length and time is easier than measurement of mass. 2. Indirect Method : Measurement of direct methods are not always possible, feasible and practicable which may be inaccurate because they involve human factors. A measuring system consists of a transducing element which converts the quantity to be measured into analogous signal. The analogous signal is then proceeded by some intermediate means and it then fed to the end devices which present the results of the measurement.
  8. 1. CALIBRATION: Every measuring system must be provable i.e it must prove its ability to measure reliably. The procedure for this is called calibration. It consists of determining the system’s scale, at some point during the preparation of the system for measurement, known magnitude of the basic input quantity must be fed into the detector-transducer and the system behavior must be observed. Calibration is usually carried out by making adjustments such that readout device produces zero-output for zero-measured input and similarly it should display an output equivalent to the known measured input near the full scale input value. It is important that any measuring system calibration should be performed under environmental conditions that are as close as possible to those conditions under which actual measurements are to be made.
  9. . It is also important that the reference measured input should be known to much greater degree of accuracy, usually the calibration standard for the system should be atleast one order of magnitude more accurate than the desired measurement system accuracy i.e accuracy ratio of 10:1. The static and dynamic calibration systems are used in calibration of measuring system.
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