What is RVDT?

 

RVDT is an acronym for Rotary Variable Differential Transformer and is a common type of electromechanical sensor that can convert the rotary motion of an object around an axis into a corresponding electrical signal.


Construction:

  • An RVDT consists of a hollow cylinder with a ferromagnetically conducted core rotating in clockwise and anticlockwise direction freely between the hollow cylinder. 
  • A primary coil is wrapped around in the hollow cylinder and is energized by constant amplitude AC source known as the primary excitation.
  • Two secondary coils having an equal number of turns are wrapped on either side of the primary coil at equal distances from the primary coil.  
  • The two secondary coils are connected in the series generating AC output voltage. 
  • A signal conditioning circuit that is housed inside the RVDT structure and is required to convert the output to either 5V dc or 4-20 mA’s whichever format is compatible with your data acquisition system. 

Working:

  • When the core is at the center, called a null point, no voltage appears at the secondary output.
  • But as soon as the core rotates by even the smallest amount, a differential voltage is induced at the secondary output. 
  • The phase of the output voltage is determined by the direction of the core’s displacement, while the amplitude is determined more or less radially by the magnitude of the core’s displacement from the center. 

RVDT characteristics:

  • The magnitude of the differential output voltage varies with the core position. 
  • The value of output voltage at maximum core displacement from null depends upon the amplitude of the primary excitation voltage and the sensitivity factor of the particular RVDT but is typically several volts RMS.





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