Sensors and its classification 1
- 1. Module 1-Introduction Lecture 3 of 4 –Potentiometer, LVDT, Capacitance sensors and Strain gauges Prepared by Mr.M.Mani Vannan Assistant Professor Department of Mechanical Engineering 1
- 2. UNIT I INTRODUCTION Introduction to Mechatronics – Systems – Concepts of Mechatronics approach – Need for Mechatronics – Emerging areas of Mechatronics – Classification of Mechatronics. Sensors and Transducers: Static and dynamic Characteristics of Sensor, Potentiometers – LVDT- Capacitance sensors – Strain gauges – Eddy current sensor – Hall effect sensor – Temperature sensors – Light sensors. Pot , LVDT, Capacitance sensors and Strain gauges 2
- 3. Potentiometers A potentiometer is also commonly known as pot. The Potentiometer is an electric instrument that used to measure the EMF (electro motive force) of a given cell, the internal resistance of a cell. And also it is used to compare EMFs of different cells. Although their most obvious use must be for volume controls on radios and other electronic equipment used for audio. Types of Potentiometers 1.Linear Potentiometers 2.Rotary Potentiometers Pot , LVDT, Capacitance sensors and Strain gauges 3
- 4. Types of Rotary Potentiometers 1.single turn Potentiometers -Single rotation of approximately 270 degrees or ¾ of a full turn 2.Multi turn potentiometers -Multiple rotations for increased precision 3.Dual gang Potentiometers -Two potentiometers combined on the same shaft ,enabling the parallel setting of two channels. 4.Servo Potentiometers -A motorized potentiometer which can also be automatically adjusted by a servo motor. 5.Concentric Potentiometers -Two potentiometers are individually adjusted by means of concentric shafts. Enables use of two control on one unit. Pot , LVDT, Capacitance sensors and Strain gauges 4
- 5. Construction A linear potentiometer transducer consists of a potentiometer, which is short circuited by a slider. The other end of the slider is connected to a slider arm. The force summing device on the slider arm causes linear displacement of the slider causing the short circuit of a certain portion of the resistance in the potentiometer. Pot , LVDT, Capacitance sensors and Strain gauges 5
- 6. Working Principle Let the whole resistance positions on the potentiometer be ABC. Let the resistance position caused by the slider movement be BC. As the movement of the slider moves further to the right, the amount of resistance increases. This increase in resistance value can be noted according to the corresponding change in the linear displacement of the slider. The change in resistance can be calculated with the help of a Wheatstone bridge. Pot , LVDT, Capacitance sensors and Strain gauges 6
- 7. Advantages 1.Cost-effective 2.Simple design and simple working 3.Can be used for measuring even large displacements. 4.Can produce a high electrical efficiency. 5.All devices other than wire-wound potentiometer can be used for a large frequency range. Disadvantages 1.A huge force may be required for the slider movement. 2.Can produce unwanted noise due to alignment problems, wear and tear of the sliding contact. This may also affect the total life of the device. Pot , LVDT, Capacitance sensors and Strain gauges 7
- 8. Rotary Potentiometers One terminal connected to a sliding contact called wiper and the other two terminals are connected to a fixed resistance track. The wiper can be moved along the resistive track either by use of a linear sliding control or a rotary “wiper” contact. Different materials are used to construct potentiometers, including carbon composition, cermet, conductive plastic, and the metal film. Pot , LVDT, Capacitance sensors and Strain gauges 8
- 9. Application of potentiometers 1.Used as Voltage Controllers/Dividers 2.Used as controllers are in audio systems 3.Used as measuring devices 4.Used as tuners and calibrators Pot , LVDT, Capacitance sensors and Strain gauges
- 10. LVDT(Linear Variable Differential Transformer) Pot , LVDT, Capacitance sensors and Strain gauges 10
- 11. LVDT(Linear Variable Differential Transformer) LVDTs operate on the principle of a transformer. LVDT consists of a coil assembly and a core. The coil assembly is typically mounted to a stationary form, while the core is secured to the object whose position is being measured. The coil assembly consists of three coils of wire wound on the hollow form. A core of permeable material can slide freely through the center of the form. The inner coil is the primary, which is excited by an AC source as shown. Magnetic flux produced by the primary is coupled to the two secondary coils, inducing an AC voltage in each coil. Pot , LVDT, Capacitance sensors and Strain gauges 11
- 12. Advantages: 1.The LVDT has low power consumption. 2.It has higher sensitive. 3.It has ruggedness. 4.It has wide range. 5.It has low hysteresis. Disadvantages: 1.It has large primary voltage produce distortion in output. Temperature affects the performance. 2.Sensitive to stray magnetic field. Applications: 1.It act as a secondary transducer, it is used to measure force, weight and pressure. 2.The LVDT can be used for displacement measurement ranging from fraction of mm to few cm. Pot , LVDT, Capacitance sensors and Strain gauges 12
- 13. Capacitance sensors Capacitive sensors are able to detect different objects and media without contact and regardless of shape. With these sensors, the fill levels of liquids or bulk materials can also be detected in direct contact with the medium or through a non- metallic container wall. Pot , LVDT, Capacitance sensors and Strain gauges 13
- 14. Capacitor A capacitor is a device that consists of two electrodes separated by an insulator. Capacitors are generally composed of two conducting plates separated by a non-conducting substance called dielectric (ɛ 𝑟). The dielectric may be air, mica, ceramic, fuel, or other suitable insulating material . The electrical energy or charge is stored on these plates. Pot , LVDT, Capacitance sensors and Strain gauges 14
- 15. Capacitance Capacitance is the electrical property of capacitors. It is the measure of the amount of charge that a capacitor can hold at a given voltage . The capacitance phenomenon is related to the electric field between the two plates of the capacitor Capacitance is measured in Farad (F) and it can be defined in the unit coulomb per volt C = Q/V where, C is the capacitance in farad (F), Q is the magnitude of charge stored on each plate (coulomb), V is the voltage applied to the plates (volts). Pot , LVDT, Capacitance sensors and Strain gauges 15
- 16. Capacitance The capacitance of a capacitor can be expressed in terms of its geometry and dielectric constant as C = ɛ 𝑟 ɛ 𝑜 𝑑 A where, C is the capacitance in farads (F), ɛ 𝑟is the relative static permittivity (dielectric constant) of the material between the plates, ɛ 𝑜is the permittivity of free space = 8.854 10-12(F/m) A is the area of each plate, (m2) and d is the separation distance (in meters) of the two plates.(m) 16Pot , LVDT, Capacitance sensors and Strain gauges
- 17. Capacitance Proximity Sensor The capacitive proximity sensor consist a high- frequency oscillator along with a sensing surface formed by two metal electrodes. When an object comes near the sensing surface, it enters the electrostatic field of the electrodes and changes the capacitance of the oscillator. As a result, the oscillator circuit starts oscillating and changes the output state of the sensor when it reaches certain amplitude. As the object moves away from the sensor, the oscillator’s amplitude decreases, switching the sensor back to its initial state. Pot , LVDT, Capacitance sensors and Strain gauges 17
- 18. Capacitive Sensor Applications 1.Proximity Sensing i)Spacing ii)Thickness measurement iii)Pressure sensing 2.Position Sensing i)Liquid level sensing ii)Shaft angle or linear position iii)Flow meter 3.Humidity Sensing 4.Tilt Sensing Pot , LVDT, Capacitance sensors and Strain gauges 18
- 19. Strain gauges A Strain gauge is a sensor whose resistance varies with applied force; It converts force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured. Pot , LVDT, Capacitance sensors and Strain gauges 19
- 20. Types of Strain Gauges 1. Unbounded metal strain gauges 2. Bonded metal wire strain gauges 3. Bonded metal foil strain gauges Pot , LVDT, Capacitance sensors and Strain gauges 20
- 21. 5. Bonded semiconductor strain gauges 7. Diffused metal strain gauges. Pot , LVDT, Capacitance sensors and Strain gauges 21
- 22. Advantages: 1. Strain gauge comes in large variety or shapes and sizes. 2. They are inexpensive and affordable. 3 Their configurations are extremely accurate. Disadvantages: 1. The installation of strain gauge is tricky and requires professional assistance. 2. Once the strain gauge is installed, it could only be used for a particular specimen. It cannot be removed or reused. Applications: It is used to measure force, pressure, tension, weight. Pot , LVDT, Capacitance sensors and Strain gauges 22
- 23. THANK YOU Pot , LVDT, Capacitance sensors and Strain gauges 23