Other Apps Ballistic Galvanometer Ballistic galvanometers are the measuring instruments which are used for measuring the quantity of electric charges obtained from magnetic flux. Its construction is similar to the moving coil galvanometer and it consists of two additional properties. It consists of extremely small electromagnetic damping. It consists of undamped oscillations. So, the coil starts moving. When the charge flows through the coil, it gives rise to a current due to the torque produced in the coil.
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In this article, we shall study principle, construction, working, sensitivity and accuracy of the moving coil galvanometer Principle: When a current-carrying coil is suspended in a uniform magnetic field it is acted upon by a torque. Under the action of this torque, the coil rotates and the deflection in the coil in a moving coil galvanometer is directly proportional to the current flowing through the coil.
Construction of Suspended Type Moving Coil Galvanometer: The suspended type consists of a rectangular coil of thin insulated copper wires having a large number of turns. The coil is suspended between the poles of a powerful horseshoe magnet by a suspension fibre of phosphor-bronze.
A spring is attached to the other end of the coil. The current enters the coil through the fibre and leaves the coil through the spring. The upper end of the suspension fibre is connected to a rotating screw head so that the plane of the coil can be adjusted in any desired position.
The horseshoe magnet has cylindrically concave pole-pieces. Due to this shape, the magnet produces radial magnetic field so that when coil rotates in any position its plane is always parallel to the direction of the magnetic field. When current flows through the coil it gets deflected. A soft iron cylinder is fixed inside the coil such that the coil can rotate freely between the poles and around the cylinder. Due to the high permeability, the soft iron core increases the strength of the radial magnetic field.
A small plane mirror M is fixed to the suspension fibre. The sides PS and QR being parallel to the magnetic field do not experience any force, but the sides PQ and RS being perpendicular to the magnetic field experience force.
As these two forces are equal and opposite they form what is called as a couple and due to which a torque acts on the coil which tries to deflect the coil. Due to the radial magnetic field, the plane of the coil is always parallel to the direction of the magnetic field. Thus at any position, the deflecting torque has constant magnitude. When the coil comes to rest i.
Advantages of Moving Coil Galvanometers: They are not affected by a strong magnetic field. They have a high torque to weight ratio. They are very accurate and reliable. Their scales are uniform. Restoring torque cannot be easily changed. There is a possibility of damage to the phosphor bronze fibre or helical restoring spring due to severe stresses. Such instruments can only be used for measurement of direct current quantities and can not be used for measurement of alternating current quantities.
Pivoted Type Moving Coil Galvanometer: Construction : The rectangular coil of thin insulated copper wires having a large number of turns is pivoted between the poles of a powerful horseshoe magnet. The coil is mounted on a pivot between two supports. The supports are bearings with almost no friction. Two hairsprings are attached one above the coil and other below the coil which controls the rotation of the coil.
The two coils are spiralled in opposite directions. Current enters through one coil and leaves through the other. A long pointer is attached to the coil which directly moves over a graduated scale. The whole assembly is fitted in a box with a window through which deflection can be observed.
Note: The principle, working and theory of pivoted type moving coil galvanometer is the same as suspended type moving coil galvanometer. Sensitivity of Moving Coil Galvanometer: The sensitivity of moving coil galvanometer is defined as the ratio of the change in deflection of the galvanometer to the change in the current.
The current in moving coil galvanometer is given by Thus the sensitivity of moving coil galvanometer can be increased by Increasing the number turns n of the coil, Increasing the area A of the coil, increasing the magnetic induction B and Decreasing the couple per unit twist k of the suspension fibre.
Limitations to Increase in Sensitivity of Moving Coil Galvanometer: If the turns of the coil are increased the length of wire and hence the resistance of the coil increases.
Increasing the area of the coil beyond limit makes the instrument bulky. Increase in the number of turns and area of the coil increases the load on suspension fibre. Hence spring higher value of k should be used which decreases the sensitivity of the galvanometer. Increasing the strength of magnetic induction leads to an increase in the weight of the apparatus. Decreasing the couple per unit twist of the spring leads to a decrease in the strength of the spring.
It is small when the deflection is large. Thus for greater accuracy, the deflection in the galvanometer should be large for small current in it. As the expression of accuracy does not contain the terms n, A, B and k the accuracy is independent of the number of turns of the coil, the area of the coil, the magnetic induction and constant for the spring.
Circuit Globe Electrical Measurement Galvanometer Galvanometer Definition: The galvanometer is the device used for detecting the presence of small current and voltage or for measuring their magnitude. The galvanometer is mainly used in the bridges and potentiometer where they indicate the null deflection or zero current. Principle of Galvanometer The potentiometer is based on the premise that the current sustaining coil is kept between the magnetic field experiences a torque. Construction of the Galvanometer The construction of the potentiometer is shown in the figure below. The moving coil, suspension, and permanent magnet are the main parts of the galvanometer. It is rectangular or circular and has the number of turns of fine copper wire.
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In this article, we shall study principle, construction, working, sensitivity and accuracy of the moving coil galvanometer Principle: When a current-carrying coil is suspended in a uniform magnetic field it is acted upon by a torque. Under the action of this torque, the coil rotates and the deflection in the coil in a moving coil galvanometer is directly proportional to the current flowing through the coil. Construction of Suspended Type Moving Coil Galvanometer: The suspended type consists of a rectangular coil of thin insulated copper wires having a large number of turns. The coil is suspended between the poles of a powerful horseshoe magnet by a suspension fibre of phosphor-bronze. A spring is attached to the other end of the coil.
Photo by nimrlondon Posted By: Tony Onwujiariri July 25, The charge which flows round a given circuit is directly proportional to the change of flux linkage. Ballistics is the study of the motion of a body, such as a projectile , which is set off by a blow, and then allowed to move freely. By freely, we mean without friction. A ballistic galvanometer is one used to measure an electrical blow, or impulse: for example, the charge Q which circulates when a capacitor is discharged through it. A galvanometer which is intended to be used ballistically has a heavier coil than one which is not; and it has as little damping as possible —- an insulating former, no short-circuited turns, no shunt. The mass of its coil makes it swing slowly; for instance, when a capacitor is discharged, and the charge has finished circulating, while the galvanometer coil is just beginning to turn.
The coil is attached to a thin pointer that traverses a calibrated scale. A tiny torsion spring pulls the coil and pointer to the zero position. When a direct current DC flows through the coil, the coil generates a magnetic field. This field acts against the permanent magnet. The coil twists, pushing against the spring, and moves the pointer.