GALVANOMETRIC RECORDERS PDF

A galvanometer is an electromechanical instrument used for detecting and indicating an . Strip chart recorders with galvanometer driven pens may have a full scale frequency response of Hz and several centimeters of deflection. A chart recorder is an electromechanical device that records an electrical or mechanical input trend onto a piece of paper (the chart). Chart recorders may record. Galvanometer Type Recorder:The D’Arsonval movement used in moving coil indicating instruments can also provide the movement in a Galvanometer Type.

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A galvanometer is an electromechanical instrument used for detecting and indicating an electric current. A galvanometer works as an actuatorby 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 their later developments were used as measuring instruments, called ammetersto measure the current flowing through an electric circuit.

They were the first instruments used to detect and measure small amounts of electric currents. Sensitive galvanometers have been essential for the development of science and technology in many fields.

Galvanometer Type Recorder

For example, they enabled long range communication through submarine cables, such as the earliest Transatlantic telegraph cablesand were essential to discovering the galvanometroc activity of the heart and brainby their fine measurements of current. Galvanometers also had widespread use as the visualising part in other kinds of analog meters, for example in light metersVU metersetc. The coil is attached to a thin pointer galvanonetric 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. The hand points at a scale indicating the electric current.

Careful design recorers the pole pieces ensures that the magnetic field is uniform, so that the angular deflection of the pointer is proportional to the current. A useful meter generally contains provision for damping the mechanical resonance of the moving coil and pointer, so that the pointer settles quickly to its position without oscillation.

The basic sensitivity of a meter might be, for instance, microamperes full scale with a voltage drop of, say, 50 millivolts at galvanomettic 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 shuntsallows 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.

GALVANOMETRIC RECORDER

In a preparatory step, the circuit galvanomerric 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. These capabilities to translate different kinds of electric quantities, in to pointer movements, make the galvanometer ideal for turning output of other sensors that outputs electricity in some form or anotherinto something that can be read by a human.

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 galvanometrlc by positioning one’s 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. Since the s, galvanometer-type analog meter movements have been displaced by analog to digital converters ADCs for many uses.

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A digital panel meter DPM contains an analog to digital converter and numeric display. Decorders advantages of a digital instrument are higher precision and accuracy, but factors such as power consumption or cost may still favour application of analog meter movements.

Most modern uses for the galvanometer mechanism are in positioning and control systems. Galvanometer mechanisms are divided into moving magnet and moving coil galvanometers; in addition, they are divided into closed-loop and open-loop – or resonant – types.

Mirror galvanometer systems are used as beam positioning or beam steering elements in laser scanning systems. For example, for material processing with high-power lasers, closed loop mirror galvanometer mechanisms are used with servo control systems. Closed-loop mirror galvanometers are also used in similar ways in stereolithographylaser sinteringlaser engravinglaser beam weldinglaser TVslaser displays and in imaging applications such as retinal scanning with Optical Coherence Tomography OCT.

Almost all of these galvanometers are of the moving magnet type. The closed loop is obtained measuring the position of the rotating axis with an infrared emitter and 2 photodiodes. This feedback is an analog signal.

Open loop, or resonant mirror galvanometers, are galvaometric used in some types of laser-based bar-code scanners, printing machines, imaging applications, military applications and space systems. Their non-lubricated bearings are especially of interest in applications recordsrs require functioning in a high vacuum. A major early use for galvanometers was for finding faults in telecommunications cables.

They were superseded in this application late in the 20th century by time-domain reflectometers. Galvanojetric mechanisms were also used to get readings from photoresistors in the metering mechanisms of film cameras as seen in the adjacent image.

In analog strip chart recorders such as used in electrocardiographselectroencephalographs and polygraphsgalvanometer mechanisms were used to position the pen. The deflection of a magnetic compass needle by current in a wire was first described by Hans Oersted in The phenomenon was studied both for its own sake and as a means of measuring electric current.

The earliest galvanometer was reported by Johann Schweigger at the University of Halle on 16 September Early designs increased the effect of the magnetic field generated by the current by using multiple turns of wire. The instruments were at first called “multipliers” due to this common design feature.

Originally, the instruments relied on the Earth’s magnetic field to provide the restoring force for the compass needle. These were called “tangent” galvanometers and had to be oriented before use.

Later instruments of the ” astatic ” type used opposing magnets to become independent of the Earth’s field and would operate in any orientation.

The most sensitive form, the Thomson or mirror galvanometerwas patented in by William Thomson Lord Kelvin as an improvement of an earlier design invented in by Johann Christian Poggendorff.

Thomson’s design was able to detect very rapid current changes by using small magnets attached to a lightweight mirror, suspended by a thread, instead of a compass needle. The deflection of a light beam on the mirror greatly magnified the deflection induced by small currents.

Alternatively, the deflection of the suspended magnets could be observed directly through a microscope. The ability to measure quantitatively voltage and current allowed Georg Ohminto formulate Ohm’s Law — that the voltage across a conductor is directly proportional to the current through it.

The early moving-magnet form of galvanometer had the disadvantage that it was affected by any magnets or iron masses near it, and its deflection was not linearly proportional to the current.

An iron tube between the magnet’s pole pieces defined a circular gap through which the coil rotated. This gap produced a consistent, radial magnetic field across the coil, giving a linear response throughout the instrument’s range. A mirror attached to the coil deflected a beam of light to indicate the coil position.

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The concentrated magnetic field and delicate suspension made these instruments sensitive; d’Arsonval’s initial instrument could detect ten microamperes. Edward Weston extensively improved the design.

He replaced the fine wire suspension with a pivot, and provided restoring torque and electrical connections through spiral springs rather like those of a wristwatch balance wheel hairspring. He developed a method of stabilizing the magnetic field of the permanent magnet, so the instrument would have consistent accuracy over time. He replaced the light beam and mirror with a knife-edge pointer that could be read directly.

A mirror under the pointer, in the same plane as the scale, eliminated parallax observation error. To maintain the field strength, Weston’s design used a very narrow circumferential slot through which the coil moved, with a minimal air-gap. This improved linearity of pointer deflection with respect to coil current. Finally, the coil was wound on a light-weight form made of conductive metal, which acted as a damper. ByEdward Weston had patented and brought out a commercial form of this instrument, which became a standard electrical equipment component.

It was known as a “portable” instrument because it was affected very little by mounting position or by transporting it from place to place.

This design is almost universally used in moving-coil meters today. Initially laboratory instruments relying on the Earth’s own magnetic field to provide restoring force for the pointer, galvanometers were developed into compact, rugged, sensitive portable instruments essential to the development of electro-technology. The taut-band movement is a modern development of the D’Arsonval-Weston movement. The jewel pivots and hairsprings are replaced by tiny strips of metal under tension.

Such a meter is more rugged for field use. Some galvanometers use a solid pointer on a scale to show measurements; other very sensitive types use a miniature mirror and a beam of light to provide mechanical amplification of low-level signals.

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 Claude Pouillet in 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.

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 galvanometrid to an angle equal to the rfcorders of the reorders of the two fields. From the angle read from the compass’s scale, the current could be found from a table.

Top view of a tangent galvanometer made about The indicator needle of the compass is perpendicular to the shorter, black magnetic needle.