Page 296 - Electrician - TT (Volume 1)
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ELECTRICIAN - CITS





             Fig 1



















           Digital Volt Meter (DVM)


           Objectives: At the end of this lesson you shall be able to:
           •  distinguish between analogue and digital voltmeter
           •  list out the advantage of DVM
           •  explain the working principle of DVM.


           Digital Volt Meter (DVM) :

           The  Digital  Volt  Meter(DVM)  is  an  electrical  measureing  instrument  which  is  used  to  measure  line  potential
           difference (P.D) between two points. The voltage to be measured may be AC or DC.
           Digital voltmeters display the value of AC or DC voltage being measured directly as discrete numerical instead of
           a pointer deflection on a continuous scale as in analog instruments.
           Advantages of Digital Voltmeters:
           •  Read out of DVMs is easy as it eliminates observational errors in measurement

           •  Parallax error is eliminated
           •  Reading can be taken very fast
           •  Output can be fed to memory devices for storage and future computations
           •  More versatile and accurate
           •  Compact portable and cheap
           •  Requires low power

           Working Principle of Digital Voltmeter:
           The block diagram of a simple digital voltmeter is shown in the Fig 1 It consists the following blocks
           1  Input signal
           2  Pulse generator
           3  AND gate:
           4  Decimal Display
           Working (Fig 2)
           •  Unknown voltage signal is fed to the pulse generator which generates a pulse whose width is proportional to
              the input signal.
           •  Output of pulse generator is fed to one leg of the AND gate.
           •  The input signal to the other leg of the AND gate is a train of pulses.
           •  Output of AND gate is positive triggered train of duration same as the width of the pulse generated by the pulse
              generator.

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 CITS : Power - Electrician & Wireman - Lesson 50-53  CITS : Power - Electrician & Wireman - Lesson 50-53
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