Que1.25. bandy piezoelectric detector or transducer with suitable illustration.
Answer 1. A piezoelectric transducer( also known as a piezoelectric detector) is a device that uses the piezoelectric effect to measure changes in acceleration, pressure, strain, temperature or force by converting this energy into an electrical charge.
2. When pressure is applied to a demitasse, it’s elastically misshaped. This distortion results in a inflow of electric charge( which lasts for a period of a many seconds).
3. The performing electric signal can be measured as an suggestion of the pressure which was applied to the demitasse.
4. These detectors can not descry static pressures, but are used to measure fleetly changing pressures performing from blasts, explosions, pressure beatings( in rocket motors, machines, compressors) or other sources of shock or vibration.
5. Piezoelectric detector is used for the dimension of pressure, acceleration and dynamic- forces similar as oscillation, impact, or high speed contraction or pressure.
6. It contains piezoelectric ionic demitasse accoutrements similar as Quartz as shown inFig.1.25.1. On operation of force or pressure these accoutrements get stretched or compressed.
7. During this process, the charge over the material changes and redistributes. One face of the material becomes appreciatively charged and the other negatively charged.
8. The net charge q on the face is commensurable to the quantum x by which the charges have been displaced. The relegation is commensurable to force. thus we can write, q = kx = SF.(1.25.1) where k = Constant S = Constant nominated the charge perceptivity.
Que1.26. Give the advantages, disadvantages and operations of piezoelectric detector or transducer.
Answer Advantages 1. No need for an external force. 2. Easy to handle and use as it has small confines.
3. High- frequence response it means the parameters change veritably fleetly.
Disadvantages 1. It isn’t suitable for dimension in static condition. 2. It’s affected by temperatures.
3. The affair is low so some external circuit is attached to it.
4. It’s veritably delicate to give the asked shape to this material and also asked strength. Applications
1. In microphones, the sound pressure is converted into an electric signal and this signal is eventually amplified to produce a louder sound.
2. machine seat belts lock in response to a rapid-fire retardation is also done using a piezoelectric material.
3. It’s also used in medical diagnostics. 4. It’s used in electric lighter used in kitchens. The pressure made on piezoelectric detector creates an electric signal which eventually causes the flash to fire over. 5. They’re used for studying high- speed shock swells and blast swells. 6. It’s used gravidity treatment. 7. It’s used in inkjet printers.
Que1.27. Explain the parcels of piezoelectric demitasse.
Answer parcels 1. The desirable parcels of piezo- electric accoutrements are stability, high affair, moisture and the capability to be formed into utmost desirable shape.
2. Quartz is the most stable piezo- electric material. still, its affair is relatively small. On the other hand, Rochelle swab provides the loftiest affair but it can be worked over a limited moisture range and has to be defended against humidity. The loftiest temperature is limited to 45 °C.
Que2.1. Explain the construction and characteristics of thermistor.
1. A thermistor( or thermal resistor) is defined as a type of resistor whose electrical resistance varies with changes in temperature.
2. Although all resistors ’ resistance will change slightly with temperature, a thermistor is particularly sensitive to temperature changes.
3. Thermistors follow the principle of drop in resistance with adding temperature.
4. The material used in thermistor is generally a semiconductor material similar as a sintered essence oxide( fusions of essence oxides, chromium, cobalt, iron, manganese and nickel) or unravel polycrystalline ceramic containing barium titanate( BaTiO3) and other composites.
5. As the temperature of semiconductor material increases the number of electrons suitable to move about increases which results in further current in the material and reduced resistance.
6. Thermistors are rugged and small in confines. They parade nonlinear response characteristics.
7. Thermistors are available in the form of a blob( pressed slice), inquiry or chip.Fig.2.1.1 shows the construction of a blob type thermistor.
8. It has a small blob of dimension from0.5 mm to 5 mm carpeted with ceramic or glass material.
9. The blob is connected to an electric circuit through two leads. To cover from the terrain, the leads are contained in a pristine sword tube. Thermistor characteristics 1. The relationship between temperature and resistance is given as where, R1 = Resistance of the thermistor at absolute temperature T1( K). R2 = Resistance of the thermistor at temperature T2( K). = Constant depending upon the material of the transducer.
2. As we can see in the eq.(2.1.1) the relationship between temperature and resistance is largely nonlinear.
3. A standard NTC thermistor generally exhibits a negative thermal resistance temperature measure of about0.05/ °C.
Que2.2. bandy the working principle of thermistor.
Answer Working principle 1. The working principle of a thermistor is that its resistance is dependent on its temperature. We can measure the resistance of a thermistor using an ohmmeter.
2. As we’ve relationship between the temperature and the resistance of the thermistor by measuring the thermistor’s resistance we can decide its temperature. R1 = 1 2 1 1 2 T T R e
3. Change in resistance depends on the type of material used in the thermistor.
4. The relationship between a thermistor’s temperature and resistance is non-linear. A typical thermistor graph is shown inFig.2.2.1. Resistance() Temperature( °C) 2.2.1. Applications of thermistors 1. To cover the coolant temperature and/ or oil painting temperature inside the machine. 2. To cover the temperature of an incubator.
3. Thermistors are used in ultramodern digital thermostats.
4. To cover the temperature of battery packs while charging.
5. To cover temperature of hot ends of 3D printers.
6. To maintain correct temperature in the food running and processing assiduity accoutrements .
7. To control the operations of consumer appliances.
Que2.3. Describe the construction and working of thermocouple.
Answer Principle 1. The introductory principle of thermocouple is grounded on a law called Seebeck effect.
2. Seebeck effect states that when two different essence are in contact, a implicit difference or a voltage is generated. That voltage is a function of temperature.
3. The device with two different essence is called thermocouple and the voltage is known as Seebeck voltage. It’s substantially used for dimension of temperature.
1. For the construction of thermocouple, a brace of two different essence is welded together at the junction point to form a thermocouple.
2. The junction J1 and junction J2 must be at different temperature. Working 1. InFig.2.3.1, when heat is applied to any one junction J1 or J2, of two different essence an emf or voltage is produced which is to be measured at the another junction.
2. These two different essence make an electric circuit, due to this implicit difference, and a voltage is generated in the circuit.
3. Hence, a current( I) flows in the circuit. This current overflows in the circuit as long as T1> T2. The T1 and T2 are the temperatures at the junctions.
4. The voltage produced is a function of difference in temperature of the two junctions J1 and J2 and is given by, V = a where, = Temperature difference of two functions a = Constant. Advantages Active transducer
iii. They’re accessible to measure the temperature at one particular point in a piece of outfit. Disadvantage Low delicacy.