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Measurement of Voltage and Current using CRO

  • (a) Voltage Measurement using CRO :

    Both d.c and a.c can be measured on CRO. The CRO will be switched on and a horizontal line is obtained using the internal sweep. The unknown d.c voltage is applied to the vertical input terminals placing the input switch to d.c mode. On application of the voltage the horizontal line shifts. This displacement is measured using the scale marking on the graticule. The magnitude of the unknown voltage can be calculated, by multiplying the displacement obtained in meters with deflection factor.

    Unknown voltage = deflection factor x displacement in m. To measure the magnitude of alternating voltage, the CRO is switched on and the horizontal line is obtained. The unknown voltage is applied to the vertical deflecting plates. Now the sweep is withdrawn. A vertical line is displayed by the CRO. The length of this line is measured using the scale marking on the graticule. This length I multiplied by the deflection factor gives the peak to peak voltage of the applied voltage. 1/2 deflection factor gives the peak amplitude of the unknown voltage. 

    (b) Measurement of Current using CRO : 

    Measurement of current is an indirect method. The unknown current is allowed to flow through a known value of resistance R. The voltage developed across this resistance is applied to the vertical deflection plates of CRO. The displacement obtained is measured and the voltage drop across the known value of resistance is estimated. Now the ratio of the voltage drop across the resistor and its resistance gives the magnitude of current.



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