TO- ROHIT KUMAR NIRALA
Question 1: Explain piezoelectric transducer in detail.
Answer: The Piezoelectric transducer is an electro acoustic transducer use for conversion of pressure or mechanical stress into an alternating electrical force. It is used for measuring the physical quantity like force, pressure, stress, etc., which is directly not possible to measure.
The piezotransducer converts the physical quantity into an electrical voltage which is easily measured by analogue and digital meter.
It is a reversible effect and the various material that exihibit this property are quartz crystal which is made from silicon and oxygen arranged in crystal structure. Piezoelectric crystal is electrically neutral. It does not require electric voltage source for operation. The electric voltage produced by piezoelectric transducer is linearly varies to applied stress or force.
It works on the principal of piezoelectric effect.It has high sensitivity so it also work as sensor in accelerometerfor excellent frequency response.
Advantages of Piezoelectric Transducer
No need of external force.
Easy to handle and use as it has small dimensions.
High frequency response it means the parameters change very rapidly.
Disadvantages of Piezoelectric Transducer
It is not suitable for measurement in static condition.
It is affected by temperatures.
Output is low so some external circuit is attached to it.
It is very difficult to give desired shape to this material and also desired strength.
Question 2: Explain about presser sensor.
Answer: Pressure sensor is an instrument consisting of a pressure sensitive element to determine the actual pressure applied to the sensor and some components to convert this information into an output signal. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area.
A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed.
Application of pressure sensor:-
1. Pressure sensing: – weather instrument, aircraft, automobiles and other machinery that has pressure function
2. Altitude sensing: – aircrafts, rockets, satellite, weather balloon
3. Flow sensing
4. Level/Depth sensing:-submarine or diver
5. Leak testing
Question 3: Explain about temperature sensor.
Answer: A temperature sensor is a device, typically, a thermocouple or RTD that provides for temperature measurement through an electrical signal. A thermocouple (T/C) is made from two dissimilar metals that generate electrical voltage in direct proportion to changes in temperature. An RTD (Resistance Temperature Detector) is a variable resistor that will change its electrical resistance in direct proportion to changes in temperature in a precise, repeatable and nearly linear manner.
Principles of Operation
A thermocouple is made from two dissimilar metal wires. The wires are joined together at one end to form a measuring (hot) junction. The other end, known as the reference (cold) junction, is connected across an electronic measurement device (controller or digital indicator). A thermocouple will generate a measurement signal not in response to actual temperature, but in response to a difference in temperature between the measuring and reference junctions. A small ambient temperature sensor is built into the electronic measuring device near the point where the reference junction is attached. The ambient temperature is then added to the thermocouple differential temperature by the measuring device in order to determine and display the actual measured temperature. Only two wires are necessary to connect a thermocouple to an electrical circuit; however, these connecting wires must be made from the same metals as the thermocouple itself. Adding wire made from other materials (such as common copper wire) will create new measuring junctions that will result in incorrect readings.
To greater or lesser degrees, all electrical conducting materials have some amount of resistance to the flow of electricity. When a known electric voltage passes through a conductor, the resistance varies based on the temperature of the conductor. This resistance can be measured and will correspond to a specific temperature. While various elements are affected by temperature in different ways, platinum is commonly used in an RTD due to its purity, linearity and stability over a wide range of temperatures. An electronic readout device, such as a controller or digital indicator designed to measure resistance, is required for use with RTD sensors.
Question 4: Explain optical sensors.
Answer: An optical sensoer is a device which is used to converts light rays into electrical signal . it measure physical quantity of light and then translaste it into a form readable by an instrument. An optical sensor is generally a part of a large system that integrates a source of light. An optical sensor can measure the changes from one or several light beams. When a change occurs, the light sensor operates as a photoelectric trigger and therefore either increases or decreases the electrical output.
Application of optical sensor:
1.It is used in mobilephones to adjust screen brightnes
2.It is used to connect one circuit to another.
3.It is perfect for oil and gas application.
Question 5: Explain electrostatic actuator.
Answer: An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a “mover”.
An actuator requires a control signal and a source of energy. The control signal is relatively low energy and may be electric voltage or current, pneumatic or hydraulic pressure, or even human power. Its main energy source may be an electric current, hydraulic fluid pressure, or pneumatic pressure. When it receives a control signal, an actuator responds by converting the signal’s energy into mechanical motion.
An actuator is the mechanism by which a control system acts upon an environment. The control system can be simple (a fixed mechanical or electronic system), software-based (e.g. a printer driver, robot control system), a human, or any other input.
An actuator is a motor that converts energy into torque which then moves or controls a mechanism or a system into which it has been incorporated. It can introduce motion as well as prevent it. An actuator typically runs on electric or pressure (such as hydraulic or pneumatic). The control system can be controlled mechanically or electronically, software driven or human operated.
What makes motors work? The rotor and stator assemblies. These are commonly known as the primary and secondary windings within the motor. Voltage is applied to the stator assembly – the primary winding – which results in inducing the flow of current to the rotor assembly, or the secondary winding. The interaction of these two creates a magnetic field which results in motion. There are two types of motors: AC motors, which commonly move at a constant speed; and DC motors, which move at variable speeds.
The speed of an AC motor is determined by the frequency of voltage applied by the number of magnetic poles. Within the AC motor are the stator assembly and the rotor assembly. If the AC motor is an induction motor, the rotor rotates slower that the stator’s field. If it is a synchronous motor, the rotor and the stator move in synchronization.
In DC motors, the rotor assembly rotates in an attempt to align itself with the stator assembly but is prevented by a part known as the commutator. At the precise moment, the commutator switches the rotor field while the stator assembly remains stationary. This provides the means to control speed and positioning.
There are several types of actuators, each of which function somewhat differently from the other.
Pneumatic motors are air driven, using either vacuum or compressed air, which converts energy into linear or rotary motion. Air pressure and flow determine both speed and torque. These are used in applications in which positional accuracy is not a requirement.
Hydraulic motors move a piston through a tube using pressurized fluid. The higher the fluid pressure, the higher the torque produced. Hydraulic motors output linear, rotary, or oscillating motion but acceleration is limited. Hydraulic motors are typically inefficient, can be a fire hazard and require more than usual maintenance.
Clutch/Brake motor functions by coupling a continuously rotating shaft with a load, stopping only when the load is uncoupled. While this motor is easy to apply, relatively inexpensive, and great for light loads, its acceleration is uncontrolled as well as inaccurate.
Stepper motors (DC motor) are electromechanical, converting a digital pulse into rotational movement or displacement. While stepper motors are not good for varying loads and are typically not energy efficient, they are great for constant loads and positional accuracy.
AC Motors (induction type) use electric starters to provide connections, startup, and/or overload protection. While Induction motors are more commonly thought of as having constant speeds, the introduction of microprocessor technology provides some variable speed capabilities.
Servo motors (DC motor) are extremely high performing with few weaknesses. Servos provide speed control and position accuracy due to its feedback device, are small, and priced relatively low.