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for Mechanical watch:

Contents

[edit] History

Watches evolved from portable spring driven clocks, which first appeared in the 15th century. Portable timepieces were made possible by the invention of the mainspring. Although some sources erroneously credit locksmith Peter Henlein (or Henle or Hele) of Nürnberg with inventing the mainspring around 1511, many references to 'clocks without weights' and two surviving examples show that spring powered clocks appeared in the 1400s. The earliest existing spring driven clock is the chamber clock given to Peter the Good, Duke of Burgundy, around 1430, now in the Germanisches Nationalmuseum.

These portable clocks appealed as toys and novelties for the very wealthy. Over the 1500s, they were made smaller and began to be worn, evolving into pocketwatches by 1600.

[edit] Clock-watches: 1500

The first timepieces to be worn were transitional in size between clocks and watches. These 'clock-watches' were fastened to clothing or worn on a chain around the neck. They were heavy drum shaped cylindrical brass boxes several inches in diameter, engraved and ornamented. They had only an hour hand. The face was not covered with glass, but usually had a hinged brass cover, often decoratively pierced with grillwork so the time could be read without opening. The movement was made of iron or steel and held together with tapered pins and wedges, until screws began to be used after 1550. Many of the movements included striking or alarm mechanisms.

The shape evolved into a rounded , these were called Nürnberg eggs Later in the century there was a trend for unusually shaped watches, and watches shaped like crosses, and even skulls (Death's head watches)

It should not be thought that the reason for wearing these early clock-watches was to tell the time. The accuracy of their verge and foliot movements was so poor, perhaps several hours per day, that they were practically useless. They were jewelry and novelties, valued for their fine ornamentation, unusual shape, or intriguing mechanism, and accuracy in timekeeping was of very minor importance.

[edit] Pocketwatches: 1600

Styles changed around 1600 and watches began to be worn in pockets.

The timekeeping mechanism was the same as in all timepieces since the invention of clocks in the 13th century; the verge escapement which drove a foliot, a small bar with weights on the ends, to oscillate back and forth. However, the mainspring introduced a source of error not present in weight-powered clocks. The force provided by a spring is not constant, but decreases as the spring unwinds. The rate of all timekeeping mechanisms is affected by changes in their drive force, and this problem, called lack of isochronism, plagued mechanical watches throughout their history. The verge and foliot mechanism was especially sensitive to these changes in drive force, so early watches slowed down during their running period as the mainspring ran down.

Efforts to improve the accuracy of watches prior to 1650 focused on evening out the steep torque curve of the mainspring. Two devices to do this appeared in the first spring driven clock-watches: the stackfreed and the fusee. The stackfreed was a spring-loaded cam on the mainspring shaft. It added a lot of friction and was abandoned after about a century. The fusee was a much more lasting idea. A curving conical pulley with a chain wrapped around it attached to the mainspring barrel, it continuously changed the leverage as the spring unwound, equalizing the drive force. Fusees became standard in all verge watches, and were used until the early 1800s.

[edit] The balance spring: 1657

[edit] Lever escapement: 1800

[edit] Temperature compensation: 1850?

[edit] Better materials: 1900

[edit] Tuning fork watches: 1950

[edit] Quartz watches: 1970

Perez, Carlos (November 23, 2001). Prometheus Bound: The final paradigm of horological evolution. Carlos' Journal. TimeZone. Retrieved on April 23, 2008.





[edit] Terminology

Mechanical watches are a mature technology with a long history, and a number of specialized terms are used to describe them:

  • Adjusted - high quality mechanical watches are made more accurate by a process of adjusting the balance wheel and balance spring to eliminate errors due to temperature changes, and the effects of gravity on the balance wheel when the watch is in different positions. The usual adjustments are: heat, cold, isochronism, dial up, pendant up, pendant right, pendant left, pendant down.
  • Arbor - the axle or shaft of a watch's gear wheel.
  • Automatic or self-winding watch – a watch in which the mainspring is automatically wound using the natural motions of the wearer’s wrist, to make manual winding unnecessary.
  • Baguette - a watch in which the length of the case is at least three times its width; a long, narrow, diamond shaped watch.
  • Banking or knocking - an abnormal running condition in which the balance wheel rotates too far in each direction, causing the impulse pin to strike the back of the pallet fork. This is usually caused by too much drive force from the mainspring, and makes the watch gain time.
  • Barrel - a cylindrical box in a watch movement in which the mainspring is coiled, with gear teeth around the circumference to drive the wheel train.
  • Breguet key - a winding key with an attached ratchet allowing winding in only one direction.
  • Breguet spring or overcoil spring - a type of balance spring in which the end is bent up over the plane of the spiral, to increase accuracy.
  • BPH - beats per hour.
  • Bumper - a watch with an early type of self-winding mechanism in which a pivoted weight bumps back and forth between spring stops.
  • Calendar watch – a watch that displays the date, and often the day of the week.
  • Chronograph – a watch with additional stopwatch functions. Buttons on the case start and stop the second hand and reset it to zero, and usually several subdials on the face display the elapsed time in larger units.
  • Chronometer – a watch that has met the high standards of accuracy of the Controle Officiel Suisse des Chronometeres (COSC) of Switzerland.
  • Click - the pawl which stops the mainspring from turning backward and unwinding. It makes the 'clicking' sound when the watch is wound.
  • Complication – additional functions on a watch besides the basic display of time
  • Crown - knob on the outside of the case used to wind the watch, and usually to set the time.
  • Damaskeening - a decorative pattern of wavy parallel lines often used on the plates of watch movements. An American term, in Europe it was called Fausse Cotes or Geneva stripes.
  • Ebauche (ay-boesh) - an unfinished watch movement, lacking the balance, balance cock, mainspring, and with the plates unpolished. This is the form in which watch movements are sold by movement manufacturers. Watch manufacturers buy them, finish them, and put their own name on them.
  • Equation of time - a dial which displays the difference between the time kept by clocks and the time as indicated by the position of the sun, which varied during the year. This rare complication originated when watches had to be set by the passage of the sun overhead.
  • Escape wheel -
  • Flyback - a type of chronograph, in which pushing the stopwatch button successively causes the seconds hand to start, stop, and then return to zero. Also used more generally for a hand on the face that doesn't rotate continuously, but traverses a scale and then jumps back to the beginning of the scale.
  • Fusee - a conical pulley with a chain wound around it, used in the earliest pocketwatches to equalize the force of the mainspring.
  • Going barrel - the type of mainspring barrel used in modern watches, with a ring of teeth around it to drive the gear train.
  • Going train - the part of the gear train that transmits power from the mainspring to the balance wheel
  • Grande sonnerie (grand strike) - a repeater watch that chimes the hours and quarter hours at the press of a button.
  • Hacking or hack set - a feature that stops the second hand while the watch is being set, enabling the watch to be synchronized to the precise second. Mostly seen in military watches.
  • Hairspring - the balance spring of a watch.
  • Hunter case - a pocketwatch case with a hinged metal lid to protect the face that must be opened to see the time. The term originated with pocketwatches made to be carried on horseback by hunters.
  • Incabloc - trade name for a patented Swiss shockproof mounting system for balance wheel pivots.
  • Isochronism - means that a watch runs at the same rate regardless of the drive force; that is regardless of whether the mainspring is fully wound up or almost run down. The term is also used for the adjustments to the balance spring to achieve isochronism.
  • Jewels - bearings made from synthetic rubies or sapphires for the pivots in a watch, to reduce friction.
  • Jump hour watch - a mechanical watch which indicates the time with digits displayed in windows, instead of rotating hands.
  • Key set - an older pocketwatch in which the time had to be set with a key.
  • Key wind - an older pocketwatch in which the watch was wound with a key.
  • Keyless work - the mechanism used to set the time in a modern watch, so called because it doesn't use a key as in older watches.
  • Lever - 'T' shaped lever in the lever escapement. It has jewelled pallets on the arms that engage the escape wheel, and a fork on the end which gives impulses to the impulse pin on the balance wheel.
  • Lever escapement - the type of escapement used in modern watches. It has a 'T' shaped lever which is pushed by the escape wheel, which in turn gives pushes to the balance wheel to keep it oscillating.
  • Ligne - an old French measure used to express the size of watch movements. 2.256 millimeters.
  • Lugs - projections on a wristwatch case used to attach the strap.
  • Minute repeater - a watch that chimes the time audibly to the minute at the press of a button. This rare complication was originally used by blind people.
  • Moon phase dial - a complication that displays the phase of the moon on a dial with a painted moon face on a rotating disk.
  • Movement - the mechanism inside the watch case that keeps time and moves the hands.
  • Pallets -
  • Pair case - a pocketwatch that has two cases, an outer decorative one and an inner plain one to protect the movement. Needed because the outer case had to be opened frequently to wind the watch.
  • Perpetual calendar - a calendar mechanism which automatically adjusts for the different length of the months and for leap years.
  • Power reserve indicator or wind indicator - a dial that shows how much power is left in the watch's mainspring, usually graduated in hours the watch has left to run.
  • Rattrapante - a feature on chronographs to measure split or lap times. The watch has two second hands which start the timing interval moving together. A second push of the timing button stops the lap hand, so the lap time can be read, while the other second hand continues. Another push of the button causes the lap hand to catch up to the second hand again.[1]
  • Regulator - lever in the watch movement on the balance spring which is used to adjust the watch's rate.
  • Remontoire - in some antique watches, a small secondary spring which is wound up repeatedly by the mainspring, and in turn runs the movement. Its purpose is to even out the force of the mainspring.
  • Repeater - a watch that chimes the hours audibly at the press of a button. This rare complication was used before electric lighting to check the time in the dark, and by the blind.
  • Shockproof - watch company terminology for any of several systems for mounting the balance wheel pivots with springy mountings that absorb shock, to prevent the pivots from breaking if the watch is dropped.
  • Skeleton watch - a watch with the plates and bridges of the movement decoratively carved and cut away to allow the works to be seen. The face and/or the back is transparent to allow this decoration to be seen.
  • Stackfreed - a cam device used occasionally in the earliest watches to equalize the force of the mainspring.
  • Stopwork - devices used on the mainspring barrel of early watches to stop the spring from being wound all the way up, to prevent the mainspring from being broken by careless winding.
  • Tank watch - a watch with
  • Tonneau watch - a watch shaped like a barrel, rectangular with convex sides.
  • Tourbillon - an expensive elaborate complication that was originally designed to make the watch more accurate. The effect of gravity on the balance wheel makes watches run at slightly different rates when in different positions. In a tourbillon, the balance wheel and escapement are mounted in a cage that rotates slowly to eliminate the errors due to gravity. Usually the tourbillon is exposed on the watch's face to show it off.
  • Train - the gear train of a watch.
  • Transition watch - an early wristwatch converted from a pocketwatch. When wristwatches became popular in the early 1900s, the only movements that were available were pocketwatch movements. They are larger than later wristwatches and the crown is at the 12 o'clock position as in pocketwatches, not at the normal 3 o'clock position.
  • Trench watch - An early style of wristwatch worn by soldiers during World War 1. They typically had wire lugs that the strap was threaded through, and often had a metal shrapnel guard or a leather pocket on the strap to protect the face.


for Crookes tube

A Crookes tube. The electrons travel in straight lines from the cathode on the left, shown by the shadow cast by the cross on the fluorescence on the righthand wall. The anode is at bottom.
A Crookes tube. The electrons travel in straight lines from the cathode on the left, shown by the shadow cast by the cross on the fluorescence on the righthand wall. The anode is at bottom.

A Crookes tube is an early experimental discharge tube, invented by British physicist William Crookes around 1875, in which cathode rays, that is electrons, were discovered.[2] An evolution of the Geissler tube, it consists of a partially (but not completely) evacuated glass cylinder of various shapes, with two metal electrodes at either end. When a high voltage is applied between the electrodes, electrons travel in straight lines from the cathode to the anode. It was used by Crookes, Johann Hittorf, Juliusz Plucker, Eugen Goldstein, Heinrich Hertz, Philipp Lenard and others to discover the properties of cathode rays, culminating in J. J. Thompson's 1897 identification of cathode rays as the particles carrying the negative charge of atoms, which he named electrons.

Wilhelm Rontgen discovered x-rays with the Crookes tube in 1895. The term is also used for the first generation, cold cathode x-ray tubes, which evolved from the experimental Crookes tubes and were used until about 1910.



[edit] How it works

Crookes tubes were cold cathode tubes, meaning they didn't have a heated filament in them to generate electrons like later electronic vacuum tubes. The electrons in them were generated by ionization of the residual air by a high DC potential applied between the electrodes, usually by an induction coil (Ruhmkorff coil).

When high voltage is applied to the tube, it accelerates the small number of ions always present in the gas, created by natural processes like radioactivity. These collide with other gas molecules, knocking electrons off them and creating more positive ions in a chain reaction. All the positive ions are attracted to the cathode or negative electrode. When they strike it, they knock large numbers of electrons out of the surface of the metal, which in turn are repelled by the cathode and attracted to the anode. These are the cathode rays.

Enough of the air has been removed from the tube that most of the electrons can travel the length of the tube without striking a gas molecule. The high voltage accelerates them to a high velocity. When they get to the anode end of the tube, they have so much momentum that, although they are attracted to the anode, many fly past it and strike the end wall of the tube. When they strike atoms in the glass, they knock their orbital electrons into a higher energy level. When the electrons fall back to their original energy level, they emit light. This process, called florescence, enabled researchers to see where the electron beam was striking the tube. Later researchers painted the back wall of the tube with a fluorescent chemical such as _____ to make the glow more visible.

The above is The details of what goes on in an operating Crookes tube are complicated, because it contains a nonequilibrium plasma of positively charged ions, electrons, and neutral atoms which are constantly interacting. This creates different colored glowing regions in the gas, depending on the pressure in the tube. The details were not fully understood until the development of plasma physics in the mid 20th century.

[edit] History

Crookes tubes evolved from the earlier Geissler tubes, experimental tubes which are similar to modern neon lights. Geissler tubes had only a low vacuum, and the electrons in them could only travel a short distance before hitting a gas molecule. So the current of electrons moved in a slow diffusion process, constantly colliding with gas molecules, never gaining much energy. These tubes didn't create beams of cathode rays, only a pretty glow discharge that filled the tube as the electrons struck the gas molecules and excited them, producing light.

Crookes was able to evacuate his tubes to a lower pressure, 10-6 - 5x10-8 atm, using an improved Sprengel mercury vacuum pump made by his coworker Charles A. Gimingham. He found that as he pumped more air out of his tubes, a dark area in the glowing gas formed next to the cathode. As the pressure got lower, the dark area, called the Crookes dark space, spread down the tube, until the inside of the tube was totally dark. However, the glass envelope of the tube began to glow at the anode end.

What was happening was that as more air was pumped out of the tube, there were fewer gas molecules to obstruct the motion of the electrons, so they could travel a longer distance, on average, before they struck one. By the time the inside of the tube became dark, they were able to travel in straight lines from the cathode to the anode, without a collision. They were accelerated to a high velocity by the electric field between the electrodes, both because they didn't lose energy to collisions, and also because Crookes tubes required a higher voltage. By the time they reached the anode end of the tube, they were going so fast that many flew past the anode and hit the glass wall. The electrons themselves were invisible, but when they hit the glass walls of the tube they excited the atoms in the glass, making them give off light or fluoresce, usually yellow-green. Later experimenters painted the back wall of Crookes tubes with fluorescent paint, to make the beams more visible.

This accidental fluorescence allowed researchers to notice that metal objects in the tube, such as the anode, cast a shadow on the tube wall. They realized that something must be travelling down the tube from cathode to anode, to cast the shadow. Eugen Goldstein named them cathode rays, since they came from the cathode.

At the time, atoms were the smallest particles known, the electron was unknown, and what carried electric currents was a mystery. These high energy beams of pure electrons could be experimented on, and revealed the electron's properties far more clearly than when they were part of an atom. Many ingenious types of Crookes tubes were built to determine the properties of cathode rays (see below). The colorful glowing tubes were also popular in public lectures to demonstrate the mysteries of the new science of electricity.

In 1895, Wilhelm Rontgen discovered x-rays emanating from Crookes tubes. The medical use of x-rays for taking pictures of the inside of the body was immediately apparent, the first practical application for Crookes tubes. Researchers built tubes with heavy angled metal anodes which generated more x-rays; the first x-ray tubes, which were used until about 1920.

Crookes tubes were unreliable and tempramental. Both the energy and the quantity of cathode rays produced depended on the amount of residual gas in the tube. Over time the gas was adsorbed by the walls of the tube, reducing the pressure in the tube. This reduced the amount of cathode rays produced and caused the voltage across the tube to increase, creating 'harder' more energetic cathode rays. Soon the pressure got so low the tube stopped conducting entirely.

The electronic vacuum tubes invented later around 1906 operate at a still lower pressure, at which there are so few gas molecules that they don't conduct by ionization. Instead, they use a more reliable and controllable source of electrons, thermionic emission by a heated filament.

The technology of creating and manipulating electron beams pioneered in Crookes tubes was applied practically with the invention of the cathode ray tube by Ferdinand Braun in 1897.

[edit] Experiments with Crookes tubes

Crookes tubes were mainly used in dozens of experiments to try to find out what cathode rays were. There were two theories: Crookes and Cromwell Varley believed they were 'corpuscles', particles of 'radiant matter'. German researchers E. Wiedemann, Heinrich Hertz, and Eugen Goldstein believed they were some new form of electromagnetic waves, The debate continued until J. J. Thompson measured their mass, proving they were energetic negative particles, which he named electrons.

[edit] Maltese cross

Juliusz Plucker in 1869 built an anode shaped like a Maltese Cross in the tube. It was hinged, so it could fold down against the floor of the tube. When the tube was turned on, it cast a sharp cross-shaped shadow on the fluorescence on the back face of the tube, showing that the rays moved in straight lines. After a while the fluorescence would get 'tired' and decrease. If the cross was folded down out of the path of the rays, it no longer cast a shadow, and the previously shadowed area would fluoresce stronger than the aread around it.

[edit] Deflection by electric fields

Heinrich Hertz built a tube with a second pair of metal plates to either side of the cathode ray beam, a crude CRT. If the cathode rays were charged particles, their path should be bent by the electric field of the plates. He didn't find any bending, but it was later determined that his tube was insufficiently evacuated, causing accumulations of surface charge which masked the electric field. Later Arthur Shuster repeated the experiment with a higher vacuum. He found that the rays were attracted toward a positively charged plate and repelled by a negative one, bending the beam. This was evidence they were negatively charged, and so not electromagnetic waves.

[edit] Deflection by magnetic fields

Crookes put a magnet across the neck of the tube, so that the N pole was on one side of the beam and the S pole was on the other, and the beam travelled through the magnetic field between them. The beam was bent by the magnetic field, but not toward or away from the magnet; up perpendicular to the magnetic field. This was similar to the behavior of electric currents in an electric generator and showed that the cathode rays obeyed Faraday's law like electric charges.

[edit] Paddlewheel

Crookes put a tiny vaned turbine or paddlewheel in the path of the cathode rays, and found that it rotated when the rays hit it. The paddlewheel turned in a direction away from the cathode side of the tube, confirming that the rays were coming from the cathode. It was generally believed at the time that this showed that cathode rays had momentum, so the rays were likely matter particles. But in 1903 J. J. Thompson proved that the paddlewheel wasn't turned by the force of the cathode rays hitting it, but by the radiometric effect. When the rays hit a paddle, they heated the side they hit. The air next to that side of the paddle expanded, pushing the paddle away. All this experiment really showed was that cathode rays could heat objects.

[edit] Charge

Jean Perrin wanted to determine whether the cathode rays actually carried negative charge, or whether they just accompanied the charge carriers, as the Germans thought. He constructed a tube with a 'catcher', a closed aluminum cylinder with a small hole in the end facing the cathode, to collect the cathode rays. The catcher was attached to an electroscope to measure it's charge. The electroscope showed a negative charge, proving that cathode rays really carry negative electricity.

[edit] Perpendicular emission

Eugen Goldstein found that cathode rays were always emitted perpendicular to the cathode's surface. If the cathode was a flat plate, the rays were shot out in straight lines perpendicular to the plane of the plate. This was evidence that they were particles, because a luminous object, like a red hot metal plate, emits light in all directions, while a charged particle will be repelled by the cathode in a perpendicular direction. If the electrode was made in the form of a concave spherical dish, the cathode rays would be focused to a spot in front of the dish. This could be used to heat samples to a high heat.

[edit] Doppler shift

Eugen Goldstein figured out a method of measuring the speed of cathode rays. If the the glow discharge in Crookes tubes was produced by the moving cathode rays, the light radiated from them in the direction they were moving, down the tube, would be shifted in frequency due to the Doppler effect. This could be detected because the emission line spectrum would be shifted. He built a tube shaped like an 'L', with a spectroscope pointed through the glass of the elbow down one of the arms. He measured the spectrum of the glow when the spectroscope was pointed toward the cathode end, then switched the power supply connections so the cathode became the anode and the electrons were moving in the other direction, and again observed the spectrum looking for a shift. He didn't find one, which he calculated meant that the rays were travelling slower than ____. It is now recognized that the glow in Crookes tubes is emitted from gas atoms hit by the electrons, not the electrons themselves. Since the atoms are thousands of times more massive than the electrons, they move much slower, accounting for the lack of doppler shift.

[edit] Lenard window

Philipp Lenard wanted to see if cathode rays could pass out of the Crookes tube into the air. He built a tube with a 'window' in the glass envelope made of aluminum foil just thick enough to hold the pressure out (later called a Lenard window) facing the cathode so the cathode rays would hit it. He found that something did come through. Holding a fluorescent screen up to the window caused it to flouresce, even though no light reached it. A photographic plate held up to it would be darkened, even though it wasn't exposed to light. The effect had a very short range of about 2 inches. He measured the ability of cathode rays to penetrate sheets of material, and found they could penetrate much farther than moving atoms could. Since atoms were the smallest particles known at the time, this was first taken as evidence that cathode rays were waves. Later it was realized that electrons were much smaller than atoms, accounting for their greater penetration ability. Lenard received the first Nobel Prize in physics for this work.

[edit] Thompson's experiment

[edit] Discovery of x-rays

When the voltage applied to a Crookes tube is high enough, around 5,000 volts or greater, it can accelerate the electrons to a fast enough velocity to create x-rays when they hit the anode or the glass wall of the tube. In fact, the fluorescence of the tube's wall which revealed cathode rays may be partly caused by low energy x-rays created in the glass. Earlier researchers such as Hittorf had noticed that operating Crookes tubes could make foggy marks on nearby covered photographic plates. On November 8, 1895, Wilhelm Rontgen was operating a Crookes tube covered with black cardboard when he noticed a nearby fluorescent screen faintly glowing. Peters, Peter (1995). W. C. Roentgen and the discovery of x-rays. Ch.1 Textbook of Radiology. Medcyclopedia.com, GE Healthcare. Retrieved on 2008-05-05.</ref> He realized that some invisible rays from the tube were able to pass through the cardboard and make the screen fluoresce. He found that they could pass through books and papers on his desk. Roentgen began to investigate the rays full time, and on _______ published

The medical uses for x-rays were immediately apparent. X-ray generation provided the first practical application for Crookes tubes, and


[edit] External links

[edit] Footnotes

  1. ^ Rochkind, Mark. Flyback vs. Rattrapante.
  2. ^ {{cite journal |last=Crookes |first=William |month=December |year=1878 |title=On the illumination of lines of molecular pressure, and the trajectory of molecules |journal=Phil. Trans. |volume=170 |pages=135-164 }



[edit] Did Crookes tubes ever use a filament?

I can't find any reference to Crookes tubes using a heated cathode, as the article shows. These references describe Crookes tubes as cold cathode tubes: 1 2 3 4 5 Crookes Tube, 6 7 Crookes 8 9 10 11 12 13 14 15 16 17 18 19 The line of experimenters using Crookes tubes: Hittdorf, Crookes, Goldstein, Plucker, Lenard, Rontgen, and J. J. Thompson (1897), as far as I can tell, seem to have used cold cathode tubes. Although thermionic emission, the 'Edison effect', was descovered by Edison in 1880, and so theoretically could have been used, it was a curiosity and not understood. It is understandable that filaments weren't used: the effects being researched in Crookes tubes, glow discharges, the 'dark space', cathode rays, x-rays, fluorescence, all required high voltage, and high voltage tubes didn't need heated cathodes to produce electrons, since they could operate by ionization of the residual gas. Thermionic emission was not used practically until John Fleming's diode in 1904.







[edit] For Oudin coil

Oudin coil used for medical 'electrotherapy', 1907.
Oudin coil used for medical 'electrotherapy', 1907.

An Oudin coil, also called an Oudin oscillator or Oudin resonator, is a disruptive discharge coil, that is a transformer designed to produce high voltage electrical arcs and discharges. It is very similar to a Tesla coil, with the difference originally being that the Oudin coil was an autotransformer. It was invented by French physician Paul Marie Oudin and physicist Jacques d'Arsonval around 1899, and used for medical electrotherapy[1] and other quack medical devices until perhaps the 1940s.

Oudin and Tesla coils are both air-core transformers that use resonance to generate very high voltage high frequency alternating current, at low current levels. The primary circuit of the coil has one or more capacitors which combine with the primary winding of the coil to make a tuned circuit. The primary circuit also has a spark gap, or in later versions vacuum tubes, powered by a high voltage transformer or induction coil, to excite oscillations. The secondary winding is open circuited, attached to the output electrodes of the device. Although it doesn't include a capacitor, the secondary winding is also a tuned circuit; the parasitic capacitance between the ends of the secondary coil combine with the large inductance of the secondary. When the two tuned circuits are adjusted to resonate at the same frequency, the large turns ratio of the coil, aided by the high Q of the tuned circuits, steps up the primary voltage to hundreds of thousands of volts at the secondary.

[edit] The difference between Oudin and Tesla coils

The distinction between Oudin and Tesla coils was never great, and has changed over the years. [2] Originally it was that the Oudin was an autotransformer,[3] that is the primary winding was a part of the secondary winding, wound on the bottom of the secondary coil with coarser wire. The bottom of the primary was grounded and the output voltage taken across both windings in series. In the Tesla coil the primary and secondary were separate windings, with the output taken across the secondary only. The primary current was applied to the Oudin coil with an adjustable tap that could be moved up or down the windings to 'tune' the primary circuit to the resonant frequency of the secondary, which varied with capacitive loading as the device was used.[4]


[edit] Footnotes

  1. ^ Rochkind, Mark. Flyback vs. Rattrapante.
  2. ^ {{cite journal |last=Crookes |first=William |month=December |year=1878 |title=On the illumination of lines of molecular pressure, and the trajectory of molecules |journal=Phil. Trans. |volume=170 |pages=135-164 }

[edit] History

The device is a high frequency current generator which uses the principles of electrical resonant circuits. It produces an antinode of high potential. The high-voltage, self-regenerative resonant transformer has the bottom end of the primary and secondary coils connected together and firmly grounded.

Oudin coils generate high voltages at high frequency. Oudin coils produce smaller currents than other disruptive discharge coils (such as the later version of the Tesla coil). The Oudin coil is modified for greater safety.