mention any one use of printer galvonemeter?
Answers
Probably the largest use of galvanometers was the D'Arsonval/Weston type movement used in analog meters in electronic equipment. Since the 1980s, galvanometer-type analog meter movements have been displaced by analog to digital converters (ADCs) for some uses. A digital panel meter (DPM) contains an analog to digital converter and numeric display. The advantages of a digital instrument are higher precision and accuracy, but factors such as power consumption or cost may still favor application of analog meter movements.
Answer:
Galvanometer
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A galvanometer is an electromechanical instrument used for detecting and indicating an electric current. A galvanometer works as an actuator, by producing a rotary deflection of a pointer, in response to electric current flowing through a coil in a constant magnetic field. Early galvanometers were not calibrated, but improved devices were used as measuring instruments, called ammeters, to measure the current flowing through an electric circuit.
Types
A tangent galvanometer is an early measuring instrument used for the measurement of electric current. It works by using a compass needle to compare a magnetic field generated by the unknown current to the magnetic field of the Earth. It gets its name from its operating principle, the tangent law of magnetism, which states that the tangent of the angle a compass needle makes is proportional to the ratio of the strengths of the two perpendicular magnetic fields. It was first described by Johan Jacob Nervander in 1834 (see J.J. Nervander, “Mémoire sur un Galvanomètre à châssis cylindrique par lequel on obtient immédiatement et sans calcul la mesure de l’intensité du courant électrique qui produit la déviation de l’aiguille aimantée,” Annales de Chimie et de Physique (Paris), Tome 55, 156–184, 1834. and J. Venermo and A. Sihvola, "The tangent galvanometer of Johan Jacob Nervander," IEEE Instrumentation & Measurement Magazine, vol. 11, no. 3, pp. 16-23, June 2008.) and in 1837 by Claude Pouillet.[7]
A tangent galvanometer consists of a coil of insulated copper wire wound on a circular non-magnetic frame. The frame is mounted vertically on a horizontal base provided with levelling screws. The coil can be rotated on a vertical axis passing through its centre. A compass box is mounted horizontally at the centre of a circular scale. It consists of a tiny, powerful magnetic needle pivoted at the centre of the coil. The magnetic needle is free to rotate in the horizontal plane. The circular scale is divided into four quadrants. Each quadrant is graduated from 0° to 90°. A long thin aluminium pointer is attached to the needle at its centre and at right angle to it. To avoid errors due to parallax, a plane mirror is mounted below the compass needle.
In operation, the instrument is first rotated until the magnetic field of the Earth, indicated by the compass needle, is parallel with the plane of the coil. Then the unknown current is applied to the coil. This creates a second magnetic field on the axis of the coil, perpendicular to the Earth's magnetic field. The compass needle responds to the vector sum of the two fields and deflects to an angle equal to the tangent of the ratio of the two fields. From the angle read from the compass's scale, the current could be found from a table.[8] The current supply wires have to be wound in a small helix, like a pig's tail, otherwise the field due to the wire will affect the compass needle and an incorrect reading will be obtained.
Tangent Galvanometer
An 1850 Pouillet Tangent Galvanometer on display at Musée d'histoire des sciences de la Ville de Genève
Tangent galvanometer made by J. H. Bunnell Co. around 1890.
Top view of a tangent galvanometer made about 1950. The indicator needle of the compass is perpendicular to the shorter, black magnetic needle.
Theory
The galvanometer is oriented so that the plane of the coil is vertical and aligned along parallel to the horizontal component BH of the Earth's magnetic field (i.e. parallel to the local "magnetic meridian"). When an electric current flows through the galvanometer coil, a second magnetic field B is created. At the center of the coil, where the compass needle is located, the coil's field is perpendicular to the plane of the coil. The magnitude of the coil's field is:
where I is the current in amperes, n is the number of turns of the coil and r is the radius of the coil. These two perpendicular magnetic fields add vectorially, and the compass needle points along the direction of their resultant BH+B. The current in the coil causes the compass needle to rotate by an angle θ:
From tangent law, B = BH tan θ, i.e.
or
or I = K tan θ, where K is called the Reduction Factor of the tangent galvanometer.
One problem with the tangent galvanometer is that its resolution degrades at both high currents and low currents. The maximum resolution is obtained when the value of θ is 45°. When the value of θ is close to 0° or 90°, a large percentage change in the current will only move the needle a few degrees.[9]
Geomagnetic field measurement
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