Conversion Of Galvanometer To Voltmeter

A galvanometer is an excellent device for detecting even the slightest electrical impulses in an electrical circuit. A coil is placed or rotated between the concave pole sides of a powerful laminated horseshoe magnet. The galvanometer displays the deflection whenever an electric charge is sent via the coil.

The deflection is proportional to the amount of current passed. A voltmeter is a device that measures the electric potential between the two locations in an electrical circuit. This article will cover the basic conversion of galvanometer to voltmeter questions and the conversion of galvanometer to voltmeter examples with detailed concepts. 

What Is a Galvanometer? 

A galvanometer is an ‘electromechanical current’ measurement device. Original ‘galvanometers were uncalibrated’, but later versions, known as ammeters, were regulated and could measure current flow more precisely. A galvanometer operates by bending a pointer in the application of an electric current running throughout a coil in a magnetic field that is always present. Galvanometers are similar to actuators.

Galvanometers were inspired by Hans Christian Oersted’s finding, made in 1820, that the needle of a magnetic compass deflects when it comes into contact with an electric current-carrying wire. They were the first instruments for detecting and measuring small amounts of electricity. André-Marie Ampère, who mathematically expressed Oersted’s discovery, titled the instrument after the Italian electrical researcher Luigi Galvani, who established the “principle of the frog galvanoscope” that an electric current would cause the legs of a dead frog to jerk – in 1791.

Modern galvanometers of the ‘D’Arsonval or Weston type’ are built using a small pivoting wire coil called a spindle in the area of a magnet. The coil is connected to a narrow pointer that moves along a calibrated scale. The coil and needle are pulled to zero by a small torsion spring. A direct current is passed through the coil producing a magnetic field. This field opposes the permanent magnet—the coil twists, pressing against the spring and causing the pointer to move. The hand is pointing to a scale that represents the electric current.

The pole pieces are carefully designed to guarantee that the ‘magnetic field’ is uniform, such that the horizontal deviation of the pointer is proportional to the current. A helpful metre will usually have a facility for reducing the mechanical resonance of the moving pointer and coil so that the pointer returns to its original position fast and without oscillation.

What Is a Voltmeter? 

A voltmeter is an instrument used to measure straight or alternate electric charge voltages on a scale often graded in volts, millivolts as 0.001 volts or kilovolts as 1,000 volts. Several voltmeters are digital, with numerical displays that show readings. The devices described above can also offer analogue readings by rotating a pointer that displays voltage on a scale; however, digital voltmeters have greater accuracy than analogue instruments. A standard analogue voltmeter, for example, is likely to use an electromechanical system in which current passing via coils of wire gets converted into a voltage reading.

A ‘moving coil galvanometer’ can be used as a voltmeter by connecting a resistor to the instrument. A fine wire coil hung in a high magnetic field powers the galvanometer. When such an electrical current passes, the combination of the magnetic fields of the coil and the stationary magnet produces torque, which causes the coil to rotate. Torque is related to the current flowing through the coil. The coil rotates, squeezing a spring that rotates in the opposite direction. Therefore, the coil’s deflection equals the current, which is proportional to the voltage, as represented by a point on a scale.

One of the instrument’s design goals is to cause as little disruption to the circuit as feasible; therefore, the instrument should take as little current as possible. This is accomplished by connecting a delicate galvanometer with a ‘high resistance’ and then connecting the complete instrument in parallel connection under investigation.

How Does The Conversion Of the Galvanometer To Voltmeter Take Place? 

To create an ammeter, a small resistance known as shunt resistance is connected in parallel with a galvanometer so that greater current flows through the shunt resistance, which can be used as an ammeter while the total net resistance is zero. To produce a voltmeter, a significant resistance value is connected in series with a galvanometer such that electricity does not pass through the total combination because its net resistance is high, allowing it to be used as a voltmeter.

A galvanometer can be transformed into a voltmeter by attaching resistance in series with the galvanometer. The simple formula and calculation is below,

Let’s suppose G is the galvanometer’s resistance. IG denotes the current that flows through the galvanometer. R denotes the high resistance in series with the galvanometer.  Let V denote the galvanometer’s potential difference.

Therefore, we can present, V = IG (R + G),

Therefore = (V/IG)- G;

Resistance of the voltmeter will be Rs = R + G;

Therefore, we can say that the resistance of the voltammeter will be infinite for an ideal voltmeter. 

Conclusion

Suppose we attach an ordinary galvanometer in parallel to the circuit. In that case, this will take some current, causing the potential difference of the circuit to shift and the measurement to be inaccurate. It is critical to precisely measure a potential difference that the current between the two sites remains constant after attaching measuring equipment. This is feasible if the device’s resistance is infinite.