PPT on sensors electronics and electrical.pptx

Sensor PPT

1. Types of Force Sensors Load Cells:  Predominantly used in weighing systems, load cells convert a load acting upon them into electrical signals. The strain gauges embedded within them deform when force is applied, resulting in voltage changes. Pressure Sensors:  Pressure sensors are designed to measure the force exerted over a surface area. This could be atmospheric pressure, fluid/gas pressure, etc. The pressure sensor readings are often presented in PSI (pounds per square inch). Torque Sensors:  Torque sensors measure the torsional force that causes an object to rotate. Applications of these sensors are frequently found in automotive systems, including electric power steering and engine monitoring.

2. Force sensors can operate on various technological principles, including strain gauge technology, piezoresistance, capacitance, optical, and Hall Effect among others. The choice of technology significantly influences the sensor’s sensitivity, response time, and other performance parameters. Strain Gauge Technology:  The strain gauge is a classic sensor type, where force is detected through the deformation of a strain-sensitive substrate. The strain causes the resistance of the substrate to change, thus enabling force measurement. Piezoresistive Force Sensors:  These sensors operate on the principle that the resistance of a material changes when a mechanical force or pressure is applied. Silicon, due to its piezoresistive properties, is commonly used in these sensors. Capacitive Force Sensors:  Capacitive force sensors operate by measuring changes in an electrical property called capacitance. When force is applied, the sensor deforms, causing a change in its capacitance.

3. Selecting the Right Force Sensor Force Range:  Force sensors are designed to operate within a specific range. Exceeding this can lead to inaccurate readings or even damage the sensor. Hence, it’s crucial to select a sensor with a suitable force range for the application. Sensitivity:  Some applications require highly accurate measurements, necessitating sensors with high sensitivity. Sensitivity is the minimum change in force that the sensor can detect. Environmental Conditions:  Factors such as temperature, humidity, and presence of corrosive substances can affect a sensor’s performance. Depending on the application, you may need a sensor with specific environmental resistances. Physical Constraints:  In some cases, the sensor’s size or shape may be a critical factor. Compact and flexible force sensors have been developed for use in such constrained environments.

4. Piezoelectric Effect Piezo  is a Greek term signifying “press” or “squeeze”.  Piezoelectricity  (also called the piezoelectric effect) is the presence of an electrical potential across the sides of a crystal when mechanical stress is applied by squeezing it. In working system, the crystal acts like a tiny battery with a positive charge on one face and a negative charge on the opposite face. To make it as a complete circuit, two faces are connected together and current is passed through it.

5. Inverse Piezoelectric Effect The effect is reversible. Whenever an electric field is applied onto crystal terminals, it undergoes mechanical stress and results in shape change. This is known as Inverse Piezoelectric Effect.

6. Working of a Piezoelectric Sensor can be summarized as, In a piezoelectric crystal the charges are exactly balanced in unsymmetrical arrangement also. The effect of the charges cancel out with each other and hence no net charge will be found on the crystal faces. When the crystal is squeezed, the charge in the crystal becomes unbalanced. Hence, from now on the effect of charge does not cancel with each other which make net positive and negative charge to appear on the opposite faces of the crystal. Therefore, by squeezing the crystal, voltage is produced across the opposite face and this is known as piezoelectricity.                                                                                                                                                                        

7. Piezoelectric Sensor Circuit The piezoelectric sensor circuit is shown below. It consists of internal Resistance R i  which is also known as insulator resistance. An inductor is connected which produces inductance due to inertia of sensor. The value of capacitance C e  is inversely proportional to the elasticity of the sensor material. To obtain the complete response of the sensor, load and leakage resistance should be larger enough such that low frequency is maintained.                                                                        

8. Applications of Piezoelectric Sensors: Piezoresistive Pressure Sensors: They are used to measure dynamic pressure. Dynamic pressure measurements include turbulence, engine combustion, etc. The pressure changes in liquids and gases in cylinder pressure measurements, hydraulic process can be measured using piezoresistive pressure sensors. When a force is applied to the piezoelectric diaphragm, it generates electric charge across the crystal faces. The output is measured as voltage which is proportional to the applied pressure.

9. Ultrasound Transducer and Piezoelectric Crystals: Ultrasound sensors generate ultrasonic waves. When transducer is held on one hand, its position is kept varying such that the ultrasound wave passes through the body parts to be analyzed and visualized. Sound waves are sent through the body tissue. The waves are reflected back to create the image of the tissue. This is the working principle of an Ultrasound Imaging System. In this, piezoelectric crystals are attached to the front of the transducer, which helps to generate ultrasonic waves. Electrodes act as connecting node between crystals and machine. When electric signal is applied to crystal, due to vibration it generates ultrasound wave of frequencies between 1.5 and 8 MHz In Industrial Applications piezoelectric sensor is used in engine knock sensors, pressure sensors, Sonar Equipment, etc. Piezoelectric actuators are applied in Diesel fuel injectors, optical adjustment, Ultrasonic cleaning and welding. Sensor is used in electrical appliances like dot matrix printer, inkjet printer, Piezo speaker, buzzers, humidifiers, etc. In musical instruments like Instrument pickups and microphone