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Study Operation and Technical Specification of Multimeter



Theory

A Multimeter is basically a PMMC meter .To measure D.C current the meter acts as an ammeter with low series resistance .Range changing is accomplished by shunt in such a way that the current passing through the meter does not exceed the maximum rated value. A Multimeter consists of an ammeter, voltmeter and ohmmeter combined, with a function switch to connect the appropriate circuit to the D Air son Val .movement.

To Measure:

  1. DC Voltage DC Voltage of different rating are measured using networking of resistance of different value.
  2. AC Voltage To measure the AC Voltage first the appropriate range is selected using resistance divider network and the AC input voltage is rectified by the use of a half wave rectifier, before current passes through the meter .
  3. Resistance: To measure the resistance the unknown resistance is connected in series with an internal battery and the meter simply measure the voltage drop across the unknown resistance. A resistance divider network is used to select different resistance.
  4. DC Current: To measure DC current, the meter acts as an ammeter with low series resistance. Range changing is obtained by using shunt in such a manner that the current passing through the meter doesn’t exceed the maximum rated value.

Digital multi meter:

A digital multimeter has resistance divided network it contains following elements.

  1. Balance bridge DC amplifier and indicating meter.
  2. Input attenuator or range switch to limit the magnitude of input voltage of the desired Value.
  3. Input battery and additional circuit to provide the capacity of resistance.
  4. Deductions switch to select the various measurement junction of the instrument.

Operating instructions:

  1. To prevent meter overloading and possible damage when checking voltage or current Start with the highest range of the instrument and move down the range successively
  2. For higher accuracy, the range selected should be such that the deflection falls in the upper half on the meter scale.
  3. Take extra precautions when checking high voltage and checking current in high Voltage circuits.
  4. Verify the circuit polarity before making a test particularly when measuring dc current or voltages.
  5. When checking resistance in circuits, be sure power to the circuit is switched off, otherwise the voltage across the resistance may damage the meter.

Viva-Voice Question:-

  1. What is the mean of Multimeter
  2. Why Multimeter is used?