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R.N.G.P.I.T, Bardoli �Electrical Engineering Department

Subject: EMMI

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Prepared By:

Dr. Shaikh Mohammed Suhel

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Prepared By:

  • Name: Dr. Shaikh Mohammed Suhel

(Assistant Professor RNGPIT, Surat)

  • Former Assistant Professor in SCET, SNPIT&RC, VIT
  • Qualification: PhD (Power- Electronics & Drives, NIT, Surat), M.Tech (Industrial Electronics, NIT-Surat), Gate, B.E. (Electrical Engineering., VNSGU-Surat).
  • Experience: 13 Years.

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CH: Basic DC Potentiometer

  • This Lecture contain
  • Methods for measurement of (DC Potentiometer)Voltages

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  • Potentiometer:
  • It is instrument used to measure the unknown voltage by comparing with a standard known voltage source.
  • The accuracy does not depends on the accuracy of instrument and only depends on accuracy of reference standard voltage source.
  • As it is a null detection method it does not take any power from the unknown voltage source under balanced condition.
  • No loading on the circuit under measurement

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  • Determination of voltage is independent of the source resistance.
  • It can be used for measuring the current also by passing the unknown current through a known resistance and measure the voltage across the resistor.
  • The process of adjusting the working current by adjusting Rh So as to match the voltage drop across the portion of slide wire against the standard reference source is known as standardizations

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(a) Standardization : Keep the sliding contact at 101.86 cm mark on slide wire keep S in calibrate position and close the key (K).

  • Now adjust Rh to set balance i.e. zero reading in galvanometer
  • Now 101.86 cm corresponds to 1.0186V=> 1cm 0.01V=10mV

And working current is 1.018/101.86=10mA

(b) Measurement: Now change the switch to operate position and move the sliding contact to set the balance.

  • Let the balance is obtained at 131.46cm

Unknown voltage=

131.46*10mA=1.3146V

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  1. A basic slide wire potentiometer has a working battery voltage of 3V with negligible internal resistance. The resistance of slide wire is 400Ω and its length is 200cm. The slide wire has 1mm scale division and is possible to read up to 1/5 of a division. The instrument is standardize with 1.018 V standard cell with sliding contact at the 101.8 cm mark on scale.

(a)Calculate working current, (b) the resistance of the series resistance (c) the measurement range and (d) the resolution of the instrument

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End

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THANK YOU