Measuring instruments used in electrical field

Ammeter

Ammeter is an instrument used  to measure the current in a circuit in amperes.The ammeter is connected in series in the circuit.The ammeter must have low resistance so presence of ammeter should not decrease the current in circuit.

Voltmeter

Voltmeter is an instrument used to measure the voltage across two points in an electrical circuit in volts.voltmeter have high resistance. The voltmeter is connected in parallel in the circuit.Its construction is similar to ammeter.

Multimeter

The word multy means many ie;it is used for many applications. Multimeter is an electronic equipment used to measure current,voltage and resistance.multimeters are classified into two types they are analog and digital multimeters.

Analog multimeter

Analog meter is a moving coil galvanometer.It consist of a copper wire wound over a rectangle metal frame.It is placed between permanent magnets.One spring is attached to the top of coil and the other to bottom.It will help to restoring couple.they act input and output terminals.and along pointer is attached to the coil moves over the scale.when a direct current pasing the coil deflects that deflection helps ponter deflection.

Advantages

  1. Accuracy of the measurement is satisfactory

  2. Resistance ,voltage and current can be measured

  3. It is handy and compact

Disadvantage

  1. It lose some current from the circuit

  2. It is not highly sensitive

  3. Care should be taken for the proper selection of range

  4. It is not external accessories ,the values of capacitance and inductance cannot be measured.

Digital multimeter

A  digital Multimeter  has no moving coil meter.liquid crystal display is used in digital multimeter.The display unit consists  of seven segment display.In these meter electrical quantities such as resistance,voltage,current are converted to +ve dc voltage which quantity is varying.

 

ADVATAGES

  1. Digital multimeter have automatic polarity and zero adjustment

  2. The values of electrical quantity can be read of directly from the display in numerical form

  3. Voltages can be accurately measured

  4. Ac voltages can be directly read from the display of the multimeter

Disadvantages

  1. While measuring ac voltage ,the display may flicker

  2. Cost is high

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