Mechatronics Engineering Lecture Notes (OFRME200) PDF

Mechatronics Engineering (OFRME200) LEC. 5 Level 2- Fall Semester By: Walaa Shoeib Faculty of Electronic Engineering, Menoufia University.  CHAPTER 2 Sensors & Transducers Electronic Measurements- By/ Walaa Shoeib 2 Linear Variable Different...

Mechatronics Engineering (OFRME200) LEC. 5 Level 2- Fall Semester By: Walaa Shoeib Faculty of Electronic Engineering, Menoufia University.  CHAPTER 2 Sensors & Transducers Electronic Measurements- By/ Walaa Shoeib 2 Linear Variable Differential Transformer or Linear Variable Differential Transducer (LVDT) 3 Linear Variable Differential Transformer Electronic Measurements- By/ Walaa Shoeib 4 Linear Variable Differential Transformer The LVDT consists of three individual coils wound sequentially around a hollow, non-magnetic insulated tube. One coil of magnetic wire is classed as the primary coil and the other coils forming two identical secondaries. The two secondary coils are connected together in a series-opposing configuration, that is they are electrically 180o out-of-phase with each other. Hence the Differential part if its name. When the moveable soft iron ferromagnetic core in positioned in the center of the two secondary coils, “null position”, the amount of primary magnetic flux induced into each of the two secondary coils is exactly the same. 5  Linear Variable Differential Transformer Advantages of LVDT (Linear variable differential transformer) Frictional loss reduced. Low power consumption. Direct conversion into electrical signals. Smooth operation. Greater sensitivity. Disadvantages of LVDT (Linear variable differential transformer) Need for extra setup: Extra setup is necessary because the LVDT is delicate to stray magnetic fields. Large displacement for little output: One of the disadvantages of LVDT is that it requires measuring a huge number of displacements to produce a small output. Demodulator use: Since the LVDT is an AC signal, a demodulator network is required to provide a DC output. 6 Sensors Capacitive sensor Piezoelectric sensor 7 Capacitive sensor Capacitive displacement sensor The capacitive transducer is used for measuring the displacement, pressure and other physical quantities. It is a passive transducer that means it requires external power for operation. The capacitive transducer works on the principle of variable capacitances. The capacitance of the capacitive transducer changes because of many reasons like overlapping of plates, change in distance between the plates and dielectric constant. 8 Capacitive sensor Capacitive displacement sensor The capacitive transducer contains two parallel metal plates. These plates are separated by the dielectric medium which is either air, material, gas or liquid. In the normal capacitor the distance between the plates are fixed, but in capacitive transducer the distance between them are varied. Electronic Measurements- By/ Walaa Shoeib 9 Basic capacitive theory 10  Advantage of Capacitive Transducer The capacitive transducer is very sensitive. It requires small output power for operation. Disadvantages of capacitive Transducer 1.The metallic parts of the transducers require insulation. 2.The cable connecting across the transducer causes an error. 11  Uses of Capacitive Transducer 1.The capacitive transducer uses for measurement of both the linear and angular displacement 2.It is used for the measurement of the force and pressures. The force or pressure, which is to be measured is first converted into a displacement, and then the displacement changes the capacitances of the transducer. 3.The humidity in gases is measured through the capacitive transducer. 4.The transducer uses the mechanical modifier for measuring the volume, density, weight etc. 12 Piezoelectric sensor Certain material are characterized that they generate electric voltage when they are deformed by subjecting to mechanical force or stress. The best-known material is quartz crystal. 13 Application of Piezoelectric sensor Vibration Monitoring Pressure Sensing Force Measurement Structural Health Monitoring 14 Advantage and Disadvantages of piezo electric sensor The sensors are simple to construct and can be made from inexpensive materials. They function over a wide range of pressures and temperatures The sensors are sensitive to vibration or acceleration, which may be common in the applications where they are used. The main limitation of piezoelectric sensors is that they can only be used for dynamic pressure measurement. Output is low 15 Photoelectric sensor (Photo eye) Discover the distance, absence, presence of an object. Using light transmitter, infrared, photoelectric receiver. Opposed (through beam), retro-reflective, and proximity- sensing (diffused) Requires only power source. Remote sensing as fiber optics. 16 Sensing mode A through-beam arrangement consists of a receiver located within the line-of- sight of the transmitter. In this mode, an object is detected when the light beam is blocked from getting to the receiver from the transmitter. A retroreflective arrangement places the transmitter and receiver at the same location and uses a reflector to bounce the inverted light beam back from the transmitter to the receiver. An object is sensed when the beam is interrupted and fails to reach the receiver. 17  A proximity-sensing (diffused) arrangement is one in which the transmitted radiation must reflect off the object in order to reach the receiver. In this mode, an object is detected when the receiver sees the transmitted source rather than when it fails to see it. The emitter sends out a beam of light (most often a pulsed infrared, visible red, or laser) that diffuses in all directions, filling a detection area. Detection occurs and output is turned on or off when sufficient light falls on the receiver. 18 Light sensor measuring the radiant energy that exists in a very narrow range of frequencies basically called “light”, and which ranges in frequency from “Infra-red” to “Visible” up to “Ultraviolet” light spectrum. The light sensor is a passive devices that convert this “light energy” whether visible or in the infra-red parts of the spectrum into an electrical signal output. Light sensors are more commonly known as “Photoelectric Devices” or “Photo Sensors” because the convert light energy (photons) into electricity (electrons). 19 The Photoconductive Cell as a Light Sensor light sensor does not produce electricity but simply changes its physical properties when subjected to light energy. The commonly used Photoconductive Cell is called the Light Dependent Resistor or LDR. The net effect is an improvement in its conductivity with a decrease in resistance for an increase in illumination. Also, photoresistive cells have a long response time requiring many seconds to respond to a change in the light intensity. 20 The Photoconductive Cell as a Light Sensor 21 Infrared (IR) sensor An IR sensor consists of two parts, the emitter circuit, and the receiver circuit. The emitter is an IR LED and the detector is an IR photodiode. The IR photodiode is sensitive to the IR light emitted by an IR LED. The photodiode’s resistance and output voltage change in proportion to the IR light received. The type of incidence can be direct incidence or indirect incidence. 22 Encoder Types and Technologies There are many different types of encoders but they basically fall into two main sensing techniques. Those being: – Linear – Rotary Within those categories, there are differing encoder measurement types such as: – Absolute – Incremental There are also various electromechanical technologies such as: – Magnetic – Optical – Inductive – Capacitive – Laser 23 Encoder Types and Technologies 24 Encoder Types and Technologies Encoders are a type of sensor that measures the movement of a mechanical parts. For example, a rotary encoder can measure the rotation of a motor. A linear encoder could measure the position of a piston in a robot. can easily be coupled to a motor shaft. Encoders are often used in control systems, as a type of feedback to ensure that a mechanical part is moving exactly as much as planned. An encoder has two major components: a disk, and a detector. The disk is covered with a unique pattern that the detector will be able to read when it moves across them. 25 To Chapter 3 26  Check Attendance ! 27