Sensors & Transducers: Piezoelectric sensor or transducer Unit 1 Part 4

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. 

Answer  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 

ii. Cheaper 

iii. They’re accessible to measure the temperature at one particular  point in a piece of  outfit.  Disadvantage  Low  delicacy.

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