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Encyclopedia > Galvanometer
Wire carrying current to be measuredRestoring springN and S are poles of magnet
Wire carrying current to be measured
Restoring spring
N and S are poles of magnet

A galvanometer is a type of ammeter — an instrument for detecting and measuring electric current. It is an electromechanical transducer that produces a rotary deflection, through a limited arc, in response to electric current flowing through its coil. The name galvanometer has been applied to devices used in measuring, recording, and positioning equipment. Diagram showing the basic internal workings of a coil galvanometer. ... Wire carrying current to be measured Spring providing restoring force An ammeter is a measuring instrument used to measure the flow of electric current in a circuit. ... Electric current is the flow (movement) of electric charge. ... A transducer is a device, usually electrical or electronic, that converts one type of energy to another. ... Electric current is the flow (movement) of electric charge. ... A coil is a series of loops. ...

Contents

History

The term "galvanometer" derives from the surname of Luigi Galvani. Many early applications of galvanometers for measuring and recording are associated with William Thomson (Lord Kelvin). The earliest galvanometer was reported by Johann (Johan) Schweigger of Nuremberg at the University of Halle on 16th September 1820. André-Marie Ampère also contributed to the development of the galvanometer. Luigi Galvani - Italian physician famous for making frogs legs twitch. ... For other persons named William Thomson, see William Thomson (disambiguation). ... Johann (Johan) Salomo Christoph Schweigger, (April 8, 1779-September 6, 1857) was a chemist, physicist, and professor of mathematics at the Gymnasium of Bayreuth in 1803, at the Polytechnic School of Nuremberg in 1819, and the University of Halle, Germany, sometime in 1820. ... The Martin-Luther-University of Halle-Wittenberg is located in the German cities of Halle, Saxony-Anhalt and Wittenberg. ... André-Marie Ampère (January 20, 1775 – June 10, 1836), was a French physicist who is generally credited as one of the main discoverers of electromagnetism. ...


Operation

The most familiar use is as an analog measuring instrument, often called a meter. It is used to measure the direct current (flow of electric charges) through an electric circuit. Such devices are constructed with a small pivoting coil of wire in the field of a permanent magnet. 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. In some meters, the magnetic field acts on a small piece of iron to perform the same effect as a spring. Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... For other uses, see Magnet (disambiguation). ... This article or section does not adequately cite its references or sources. ... For other uses, see Iron (disambiguation). ...


When a direct current (DC) flows through the coil, the coil generates a magnetic field. This field acts with or against the permanent magnet. The coil twists, pushing against the spring, and moves the pointer. The hand points at a scale indicating the electric current. A useful meter generally contains provision for damping the mechanical resonance of the moving coil and pointer so that the pointer position smoothly tracks the current without excess vibration. Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ...

An automatic exposure unit from an 8 mm movie camera, based on a galvanometer mechanism (center) and a CdS photoresistor in the opening at left.
An automatic exposure unit from an 8 mm movie camera, based on a galvanometer mechanism (center) and a CdS photoresistor in the opening at left.

The basic sensitivity of a meter might be, for instance, 100 microamperes full scale (with a voltage drop of, say, 50 millivolts at full current). Such meters are often calibrated to read some other quantity that can be converted to a current of that magnitude. The use of current dividers, often called shunts, allows a meter to be calibrated to measure larger currents. A meter can be calibrated as a DC voltmeter if the resistance of the coil is known by calculating the voltage required to generate a full scale current. A meter can be configured to read other voltages by putting it in a voltage divider circuit. This is generally done by placing a resistor in series with the meter coil. A meter can be used to read resistance by placing it in series with a known voltage (a battery) and an adjustable resistor. In a preparatory step, the circuit is completed and the resistor adjusted to produce full scale deflection. When an unknown resistor is placed in series in the circuit the current will be less than full scale and an appropriately calibrated scale can display the value of the previously-unknown resistor. Image File history File links Download high resolution version (2048x1536, 181 KB)An automatic exposure meter with a galvanometer and a CdS photoresistor. ... Image File history File links Download high resolution version (2048x1536, 181 KB)An automatic exposure meter with a galvanometer and a CdS photoresistor. ... A Video8 cassette The 8mm video format refers informally to three related videocassette formats for the NTSC and PAL/SECAM television systems. ... The Arricam ST, a popular 35 mm film camera currently used on major productions. ... Cadmium sulfide (UK English sulphide), the mineral greenockite, is an hexagonal, yellowish crystal with specific gravity of 4. ... LDR The internal components of a photoelectric control for a typical American streetlight. ... See: Sensitivity (electronics) Sensitivity (human) Sensitivity (tests) For sensitivity in finance, see beta coefficient This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... For other uses, see Ampere (disambiguation). ... 50A shunt resistor In electronics, a shunt is a device which allows electrical current to pass around another point in the circuit. ... Resistor symbols (non-European) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ...


Because the pointer of the meter is usually a small distance above the scale of the meter, parallax error can occur when the operator attempts to read the scale line that "lines up" with the pointer. To counter this, some meters include a mirror along the markings of the principal scale. The accuracy of the reading from a mirrored scale is improved by moving the head while reading the scale so that the pointer and the reflection of the pointer are aligned; at this point, the operator's eye must be directly above the pointer and any parallax error has been minimized. For other uses, see Parallax (disambiguation). ... For other uses, see Parallax (disambiguation). ...


Types

Extremely sensitive measuring equipment once used mirror galvanometers that substituted a mirror for the pointer. A beam of light reflected from the mirror acted as a long, massless pointer. Such instruments were used as receivers for early trans-Atlantic telegraph systems, for instance. The moving beam of light could also be used to make a record on a moving photographic film, producing a graph of current versus time, in a device called an oscillograph. A mirror galvanometer A mirror galvanometer is a mechanical meter that senses electric current, except that instead of moving a needle, it moves a mirror. ... An oscillograph is an instrument for measuring alternating or varying electric current in terms of current and voltage. ...


Galvanometer mechanisms are used to position the pens of analog chart recorders such as used for making an electrocardiogram. Strip chart recorders with galvanometer driven pens might have a full scale frequency response of 100 Hz and several centimeters deflection. In some cases (the classical polygraph of movies or the electroencephalograph), the galvanometer is strong enough to move the pen while it remains in contact with the paper; the writing mechanism may be a heated tip on the needle writing on heat-sensitive paper or a fluid-fed pen. In other cases (the Rustrak recorders), the needle is only intermittently pressed against the writing medium; at that moment, an impression is made and then the pressure is removed, allowing the needle to move to a new position and the cycle repeats. In this case, the galvanometer need not be especially strong. “QRS” redirects here. ... Polygraph results are sometimes recorded on a chart recorder A polygraph (commonly yet incorrectly referred to as a lie detector) is a device that measures and records several physiological variables such as blood pressure, pulse, respiration and skin conductivity while the subject is asked and answers a series of questions. ... “EEG” redirects here. ...


Tangent galvanometer

A tangent galvanometer is a measuring instrument used for the measurement of electric current. It works on the basis of the tangent law of magnetism. It was first described by Claude Servais Mathias Pouillet in 1837. Captain Nemo and Professor Aronnax contemplating measuring instruments in Twenty Thousand Leagues Under the Sea In physics and engineering, measurement is the activity of comparing physical quantities of real-world objects and events. ... Electric current is the flow (movement) of electric charge. ... Claude Servais Mathias Pouillet. ...


A tangent galvanometer consists of a circular coil of insulated copper wire wound on a circular non-magnetic frame. The wire connected to the tangent galvanometer has to be wound, otherwise the field due to the wire will affect the deflection and an incorrect reading will be obtained. The frame is mounted vertically on a horizontal base provided with levelling screws on the base. 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. The compass box is circular in shape. 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.[1]


Theory

When current is passed through the tangent galvanometer a magnetic field is created at its corners given by B={mu_0 nIover 2r} where I is the current in ampere, n is the number of turns of the coil and r is the radius of the coil. Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ...


If the TG is set such that the plane of the coil is along the magnetic meridian i.e., B is perpendicular to BH (BH is the horizontal component of the Earth's magnetic field), the needle rests along the resultant. From tangent law, B = BHtanθ, i.e. Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ...

{mu_0 nIover 2r} = B_H tantheta

or

I=left(frac{2rB_H}{mu_0 n}right)tantheta

or I = Ktanθ, where K is called the Reduction Factor of the tangent galvanometer.


The value of θ is taken at 45 degrees for maximum accuracy.


Geomagnetic field measurement

A tangent galvanometer can also be used to measure the magnitude of the horizontal component of the geomagnetic field. When used in this way, a low-voltage power source, such as a battery, is connected in series with a rheostat, the galvanometer, and an ammeter. The galvanometer is first aligned so that the coil is parallel to the geomagnetic field, whose direction is indicated by the compass when there is no current through the coils. The battery is then connected and the rheostat is adjusted until the compass needle deflects 45 degrees from the geomagnetic field, indicating that the magnitude of the magnetic field at the center of the coil is the same as that of the horizontal component of the geomagnetic field. This field strength can be calculated from the current as measured by the ammeter, the number of turns of the coil, and the radius of the coils. The cause of Earths magnetic field (the surface magnetic field) is not known for certain, but is possibly explained by dynamo theory. ... schematic symbol for a potentiometer In this article: Rheostat and potentiometer. ... Wire carrying current to be measured Spring providing restoring force An ammeter is a measuring instrument used to measure the flow of electric current in a circuit. ...


Uses

Use of galvanometers declined late in the 20th century, largely replaced by time-domain reflectometers for finding faults in telecommunications cables. In telecommunication, a time-domain reflectometer (TDR) is an electronic instrument used to characterize and locate faults in metallic cables ( twisted pair, coax). ...


Mirror galvanometer systems are used as beam positioning elements in laser optical systems. These are typically high power galvanometer mechanisms used with closed loop servo control systems. They can have frequency responses over 1 kHz.


Galvanometers have been replaced as measuring instruments by analog to digital converters (ADC) for most uses. There are, for instance, self contained digital measuring systems, called digital panel meters (DPMs), available to replace most traditional analog meter functions. This article or section should include material from AD converters In electronics, an analog-to-digital converter (abbreviated ADC, A/D, or A to D) is a device that converts continuous signals to discrete digital numbers. ...


A galvanometer appeared in an episode (#12, season 2) of the television medical drama House to function as an electrocardiogram for a patient whose severe and extensive burns prevented use of the normal electrodes. House, also known as House, M.D., is an American medical drama television series created by David Shore and executive produced by Shore and film director Bryan Singer. ... “QRS” redirects here. ...


References

  1. ^ http://physics.kenyon.edu/EarlyApparatus/Electrical_Measurements/Tangent_Galvanometer/Tangent_Galvanometer.html

External links


  Results from FactBites:
 
Galvanometer - LoveToKnow 1911 (2114 words)
A ray of light being thrown on the mirror from a lamp the deflexions of the needle were observed by watching the movements of a spot of light reflected from it upon a fixed scale.
The movable coil galvanometer has the great advantage that it is not easily disturbed by the magnetic fields caused by neighbouring magnets or electric currents, and thus is especially useful in the electrical workshop and factory.
In the construction of a movable coil galvanometer, it is usual to intensify the magnetic field by inserting a fixed soft iron core in the interior of the movable coil.
Spartanburg SC | GoUpstate.com | Spartanburg Herald-Journal (1394 words)
The earliest galvanometer was reported by Johann (Johan) Schweigger of Nuremberg at the University of Halle on 16th September 1820.
In some cases (the classical polygraph of movies or the electroencephalograph), the galvanometer is strong enough to move the pen while it remains in contact with the paper; the writing mechanism may be a heated tip on the needle writing on heat-sensitive paper or a fluid-fed pen.
A galvanometer appeared in an episode (#12, season 2) of the television medical drama House to function as an electrocardiogram for a patient whose severe and extensive burns prevented use of the normal electrodes.
  More results at FactBites »

 
 

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