HPCL Electrical Engineering Important Questions for Practice

TRANSDUCERS

1. Transducers are a devices which converts non electrical quantities into  electrical quantities
2. Transducer convert any form of energy to electrical energy . 
Classifications

• Active and Passive transducers

• Primary and Secondary transducers

• Transducers and inverts transducers

• analog and digital transducers

   ACTIVE AND PASSIVE TRANSDUCERS

Active Transducer   - there are a transducers which do not required external source of energy for their operation 

• For  Example - Thermocouple , piezo - electric transducer , photo voltaic cell

Passive Transducer -  There are the transducer which draw power from external source for their operation . 

• For Example - Linear variable Differential Transformer (LVDT) cAPACTIVE TRANSDUCER THERMISTOR , STRAIN GUADGE , et

PRIMARY AND SECONDARY TRANSDUCER

Primary transducer - there are the transducer which are in direct contact with quantity under measurement . there output may not be electrical signal there are also called as sensors  

• e.g bourden tube , bellows 

Secondary Transducers - secondary transducer which are connected at the output of primary transducer . their output is electrical signal 

• for example - LDVT , Use for mesurement of pressure with bourden tube as primary transducer . 

ANALOG AND DIGITAL TRANSDUCER 

Analog Transducer -  which transducer has analog signal is called analog signal . 

• example -  LVDT , thermistors , thermocouple etc . 

Digital Transducer -  output is digital signals 

• example - digital encoder ( shaft encoder )
• Note - Optical Encoder used for measurement of speed of shaft has gray code 
  

Strain Gauge Transducer strain gauge works on the principle of piezo resistive effect . the resistive of a conductor increase with increase in strain in the conductor 

 piezo electric Transducer 

it is based on the piezo - electric effect . according to this effect  , a piezo - electric material gets polarised when it is subjected to a mechanical stress and vice versa 

• for example Quartz , Rochelle salt , Ammonium Dihydrogen phosphate ( ADP ) , etc 

VOLTAGE SENSITIVITY OF A CRYSTAL 

g = (Electric field induced )/ (stress) 
g = (E / P ) in Vm/N
where P = pressure of stress in N/m^2

CHARGE SENSITIVITY 

d = e0erg C/N
output voltage V = gtp
where , 
t = thickness of crystal in m