Dimension measurement By Mr.Vuttichai Sittiarttakorn 1
LECTURE OUTLINE 1. Introduction 2. Standards and Calibration 3. Relative displacement : Translational and Rotational 4. displacement transducers Potentiometers displacement sensors Inductive displacement sensors Capacitive displacement sensors Eddy current displacement sensors Piezoelectric displacement sensors Ultrasonic displacement sensors Optical encoder displacement sensors Strain Gages displacement sensors 2
Introduction In physics and mathematics, the dimension of a mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any point within it. Thus a line has a dimension of one because only one coordinate is needed to specify a point on it. A surface such as a plane or the surface of a cylinder or sphere has a dimension of two because two coordinates are needed to specify a point on it. The inside of a cube, a cylinder or a sphere is three-dimensional because three coordinates are needed to locate a point within these spaces. 3
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In classical mechanics, space and time are different categories and refer to absolute space and time. That conception of the world is a four-dimensional space but not the one that was found necessary to describe electromagnetism. The four dimensions of space-time consist of events that are not absolutely defined spatially and temporally, but rather are known relative to the motion of an observer. A well dimensioned part will communicate the size and location requirements for each feature. Communications is the fundamental purpose of dimensions. Parts are dimensioned based on two criteria: Basic size and locations of the features. Details of a part's construction and for manufacturing. 5
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Time Time is a necessary component of many mathematical formulas and physical functions. It is one of several basic quantities from which most physical measurement systems are derived. Others are length, temperature, and mass. We can see distance and we feel weight and temperature, but we cannot apprehend time by any of the physical senses. WHAT IS TIME? Time is a physical quantity that can be observed and measured with a clock of mechanical, electrical, or other physical nature. 8
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Time measuring Instruments Sundial Clock Sand Clock Water Clock Mechanical Clock 10
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DATE, TIME INTERVAL AND SYNCHRONIZATION We obtain the date of an event by counting the number of cycles, and fractions of cycles, of periodic events, such as the Sun as it appears in the sky and the Earth s movement around the Sun, beginning at some agreedupon starting point. The important thing about measurement is that there be general agreement on exactly what the scale is to be and how the basic unit of that scale is to be defined. In other words, there must be agreement upon the standard against which all other measurements and calculations will be compared. 12
UNITS OF TIME The basic unit for measuring time is the second. The second multiplied evenly by 60 gives us minutes, or by 3600 gives us hours. The length of days, and even years, is measured by the basic unit of time, the second. Time intervals of less than a second are measured in l0 ths, 100 ths,1000 ths-on down to billionths of a second and even smaller units. Each basic unit of measurement is very exactly and explicitly defined by international agreement; each nation directs a government agency to make standard units available to anyone who wants them. 13
Standard Clock Caesium-133 : Frequency = 9,192,631,770 Hz National standards agencies in most industrialized and semiindustrialized countries maintain an accuracy of 10-9 seconds per day
Deep Space Atomic Clock NASA s Deep Space Atomic Clock (DSAC) project is developing a reduced size mercury ion atomic clock that is as stable as a ground clock, small enough to be hosted on a spacecraft, and able to operate in deep space. 15
IEEE 1588 Standard for a Precision Clock Synchronization Protocol and Synchronous Ethernet Distribution of frequency and time over a packet network (main focus on Ethernet) 16
IEEE 1588 offers high accuracy (< 100 ns) over a data network but requires hardware assistance is designed for well-controlled LAN environment. Application of synchronized Clocks 17
The Length Measurement Standard The Length - Evolution from Measurement Standard to a Fundamental Constant explains the evolution of the definition of the meter. From the meter, several other units of measure are derived such as the: unit of speed is the meter per second (m/s). The speed of light in vacuum is 299 792 458 meters per second. unit of acceleration is the meter per second per second (m/s 2 ). unit of area is the square meter (m 2 ). unit of volume is the cubic meter (m 3 ). The liter (1 cubic decimeter), although not an SI unit, is accepted for use with the SI and is commonly used to measure fluid volume. 18
Unit definition The meter was intended to equal one ten-millionth of the length of the meridian through Paris from pole to the equator. However, the first prototype was short by 0.2 millimeters because researchers miscalculated the flattening of the earth due to its rotation. In 1927, the meter was more precisely defined as the distance, at 0, between the axes of the two central lines marked on the bar of platinum-iridium kept at the BIPM, and declared Prototype of the meter by the 1st CGPM, this bar being subject to standard atmospheric pressure and supported on two cylinders of at least one centimeter diameter, symmetrically placed in the same horizontal plane at a distance of 571 mm from each other. 19
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The 1889 definition of the meter, based upon the artifact international prototype of platinumiridium, was replaced by the CGPM in 1960 using a definition based upon a wavelength of krypton-86 radiation. This definition was adopted in order to reduce the uncertainty with which the meter may be realized. In turn, to further reduce the uncertainty, in 1983 the CGPM replaced this latter definition by the following definition: The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. 21
Relative displacement Calibration -Static calibration via micrometers 0.01 mm gauge blocks 12 micro-m laser interferometer 0.6 nm 22
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Gauge Blocks 25
Laser interferometer 26
Displacement Sensors types Potentiometers displacement sensors Inductive displacement sensors Capacitive displacement sensors Eddy current displacement sensors Piezoelectric displacement sensors Ultrasonic displacement sensors Optical encoder displacement sensors Strain Gages displacement sensors 27
Potentiometers displacement sensors 28
Resistive Potentiometers (single-turn, multiturn, linear and rotating translation) 29
Potentiometer loading effect (Linearity, power loss) 30
Construction of wire-wound resistance (resolution) 31
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Linear variable differential transformer (LVDT) 35
Differential Transformers 36
Methods for Null Reduction 37
LVDT
Strain gauge displacement transducers and extensometer 39
Industrial type LVDT 40
LVDT Application 41
Application 42
Eddy current non-contact transducers 43
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Target-Material Effect on Eddy- Current Transducer 45
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(a) Capacitance will vary with variation in dielectric constant, (b) gap between plates and (c) area of capacitor's plates. 47
Differential-Capacitor Pressure Pickup 48
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Piezoelectric Transducer 50
Piezoelectric displacement sensors Piezoelectricity the ability of certain materials to develop an electric charge that is proportional to a direct applied mechanical stress. The effect is reversible. Piezoelectric materials will deform (strain) proportionally to an applied electric field. The effect is of the order of nanometers. 51
Laser Dimensional Gauge 52
Self-Scanning Diode Arrays and Cameras 53
Translational and Rotary Encoders 54
Schematic diagram 55
Translational and Rotary Encoders.. 56
Disk image form 57
Translational and Rotary Encoders.. 58
Translational and Rotary Encoders 59
Output wave form of incremental encoder 60
Ultrasonic Displacement Transducer 61
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Average Velocity Measurement from x/ t : Hall-Effect Proximity Pickup 63
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