Production Technology - Lect. 10: Measurements PDF

Mechanical Engineering Dept. Production Technology Lect. 10: Measurements Associate Prof. Mohamed A. Bhlol  Topics Definition of measurement and instrumentation Significance of measurement Important Characteristics of Instruments Mai...

Mechanical Engineering Dept. Production Technology Lect. 10: Measurements Associate Prof. Mohamed A. Bhlol  Topics Definition of measurement and instrumentation Significance of measurement Important Characteristics of Instruments Main types of Instruments -Direct Measuring Instruments - Indirect Measuring Instruments  Definition of measurement and instrumentation Measurement Measurement is the art of assigning a specific value to a physical variable detected by a sensor. A measurement tells us about a property of something. It might tell us how heavy an object is, or how hot, or how long it is. The result of a measurement is normally in two parts: a number and a unit of measurement, e.g. ‘How long is it?... 2 metres.’  Definition of measurement and instrumentation Instrumentation Measurements are always made by using an instrument (tool) of some kind. Rulers, stopwatches, weighing scales, and thermometers are all measuring instruments. Iinstrument is a device that transforms a physical variable of interest into a form that is suitable for recording. Some Tools for Measurement  Definition of measurement and instrumentation ❑ Examples of Measurements What kinds of measurements did you make today? You are making a measurement when you: Check your weight. Read your watch. Take your temperature. Read the speed indicator of your car.  Significance of measurement ❑ Why measurement? To estimate the size/amount of things To monitor devices and industrial processes To control process and systems To verify laws of nature To establish standards To design and build systems To improve the quality of the product To improve the efficiency of production  Important Characteristics of Instruments Accuracy of measurement is one consideration in the choice of instrument for a particular application. Other parameters such as range, sensitivity, linearity and the reaction to ambient temperature changes are further considerations. ❑ Range: The range is the minimum and maximum values of a quantity for which an instrument is designed to measure. Example: the range of steel ruler may be 0-150, 0-300, or 0-500 mm.  Important Characteristics of Instruments ❑ Accuracy: Accuracy of an instrument is a measure of how close the output reading of the instrument is to the correct value. It is measured in terms of the measurement error. Less the error more accurate is the measurement. ❑ Precision: Precision is the repeatability of the measuring process. Precision refers to the degree of agreement within a group of measurements or instruments.  Important Characteristics of Instruments Distinction between Accuracy and Precision  Important Characteristics of Instruments ❑ Resolution of the measuring instrument is the ability of a measuring device to detect small differences in the quantity being measured. Example: the resolution of the ruler is 1mm and the resolution of steel ruler is 0.5 mm.  Main types of Instruments Instruments Direct Indirect These are instruments which These are instruments which have do not enable us to read a scale that enables us to read directly the measurement, directly or determine the but require the individual to measurement. transfer the measurement to Examples: scales, micrometers, a direct reading instrument. Verniers, ….etc. Examples: dividers, telescopic gauges,….etc.  Main types of Instruments ❑ Direct measuring Instruments Steel Ruler: A steel ruler is a direct reading measuring instrument with resolution of 0.5mm. Available in various lengths, widths and thickness with several graduations. They are made from high carbon steel, spring steel, stainless steel and various alloy steel.  Main types of Instruments ❑ Direct measuring Instruments Folding ruler: The folding ruler is very helpful in measuring and laying out large work, the resolution being 0.5mm.  Main types of Instruments ❑ Direct measuring Instruments Steel circumference ruler: This is used to find out directly the circumference of a cylinder.  Main types of Instruments ❑ Direct measuring Instruments Vernier caliper : is a versatile instrument with which both outside and inside measurements may be made accurately. These instruments may have provision for depth measurement also. Measuring range: 0-100, 0-125, 0-150,…, 2000 mm. Resolution: 0.1, 0.05, and 0.02 mm.  Main types of Instruments ❑ Direct measuring Instruments Micrometers: Outside and inside micrometers are used for measuring components where greater accuracy is required. Measuring range: 0-25, 25-50, 50-75,…, 500-600 mm. Resolution: 0.01 mm.  Main types of Instruments ❑ Direct measuring Instruments Dial indicator: a tool which is like a small clock, used to true and align machine tools, fixtures and work. Resolution: 0.01 mm or 0.001 mm.  Main types of Instruments Vernier instruments All instruments employing a Vernier consist of two scales: one moving and one fixed. The fixed scale is graduated in millimetres, every 10 divisions equaling 10 mm. The moving or Vernier scale is divided into 50 equal parts which occupy the same length as 49 divisions or 49 mm on the fixed scale. This means that the distance between each graduation on the Vernier scale is 49 ⁄ 50 mm = 0.98 mm, or 0.02 mm.  Main types of Instruments Vernier instruments Vernier caliper :  Main types of Instruments Vernier instruments Vernier caliper : Vernier caliper uses :  Main types of Instruments Vernier instruments Vernier caliper :  Main types of Instruments Vernier caliper readings:  Main types of Instruments Vernier instruments Vernier height gage :  Main types of Instruments Vernier instruments Vernier hight gage : Main types of Instruments Micrometer instruments  Main types of Instruments Micrometer instruments Example for reading the micrometer scale: On a 0–25 mm micrometer, the sleeve around which the thimble rotates has a longitudinal line graduated in mm from 0 to 25 mm on one side of the line and subdivided in 0.5 mm intervals on the other side of the line. The edge of the thimble is graduated in 50 divisions numbered 0, 5, 10, up to 45, then 0. Since one revolution of the thimble advances the spindle 0.5 mm, one graduation on the thimble must equal 0.5/50 mm = 0.01 mm.  Main types of Instruments Micrometer instruments Reading the micrometer scale:  Main types of Instruments Micrometer instruments Other types of micrometers: Internal micrometers depth micrometer  Main types of Instruments Dial indicators Dial indicators magnify small movements of a plunger or lever and show this magnified movement by means of a pointer on a graduated dial. Dial indicators are used to check the dimensional accuracy of workpieces in conjunction with other equipment such as gauge blocks, to check straightness and alignments of machines and equipment, to set workpieces in machines to ensure parallelism and concentricity. Main types of Instruments Dial indicators Main types of Instruments Dial indicators  Main types of Instruments ❑ Indirect measuring Instruments Calipers: are the very simple tools used together with a steel rule for the measurement or comparison of linear dimensions. Calipers are classified into two types: Outside calipers are used for measuring external dimensions such as the length, diameter, or even the thickness of a solid. Inside calipers are used for measuring internal dimensions such as the diameter of a hole, or the width of a slot etc.  Main types of Instruments ❑ Indirect measuring Instruments Thank you