Electrical and Electronics Instruments

Analog & Digital Voltmeter & Ammeter

  1. Analog Ammeter and voltmeter

    1. Ammeter is connected in series because objects in series having the same current passing through them, whereas the voltmeter are connected in parallel because objects in parallel having same potential difference.

    2. The range of Ammeter can be altered by using shunt coil with moving coil, whereas the range of voltmeter is altered by connecting a resistance in series with the coil.

  2. Errors in Ammeter and voltmeter
    Errors in Ammeter and Voltmeter is caused due to following parameters

    1. Errors due to deflecting torque

    2. Errors due to heat generated in the instrument or change in ambient temperature which is due to the change in resistance of the working coil. Hence it is necessary that the resistance of the instrument remain constant so that power loss should be less.

    3. Error produced due to the variation in frequency which results in change of reactance of coil.

    4. Errors due the friction of the instrument must be kept as small as possible because the torque to weight ratio must be large.