Paschen's law

Paschen's law

Paschen's Law, named after Friedrich Paschen, was first stated in 1889. [cite journal
title = Ueber die zum Funkenübergang in Luft, Wasserstoff und Kohlensäure bei verschiedenen Drucken erforderliche Potentialdifferenz
author = Friedrich Paschen
journal = Annalen der Physik
volume = 273
issue = 5
pages = 69–75
year = 1889
url =
doi = 10.1002/andp.18892730505
] He studied the breakdown voltage of parallel plates in a gas as a function of pressure and gap distance. The voltage necessary to arc across the gap decreased up to a point as the pressure was reduced. It then increased, gradually exceeding its original value. He also found that decreasing the gap with normal pressure caused the same behavior in the voltage needed to cause an arc.

Paschen curve

Paschen found that breakdown voltage was described by the equation

: V=frac{a(pd)}{ln (pd)+b} .

Where "V" is the breakdown voltage in Volts, "p" is the pressure, "d" is the gap distance. The constants "a" and "b" depend upon the composition of the gas. For air at standard atmospheric pressure of 760 Torr, "a" = 43.6*106 and "b" = 12.8 , where "p" is the pressure in atmospheres and "d" is the gap distance in meters. [ [http://www.ece.rochester.edu/courses/ECE234/MEMS_ESD.pdf Rochester University, Course Handout] ] The graph of this equation is the Paschen curve. By differentiating it with respect to (pd) and setting the derivative to zero, the minimum voltage can be found. This yields

: pd=e^{1-b}

and predicts the occurrence of a minimum breakdown voltage for (pd)=7.5*10-6 meter atmospheres. This is 327 Volts in air at standard atmospheric pressure at a distance of 7.5 micrometers. The composition of the gas determines both the minimum arc voltage and the distance at which it occurs. For argon, the minimum arc voltage is 137 Volts at a larger 12 micrometers. With sulfur dioxide, the minimum arc voltage is 457 volts at only 4.4 micrometers.

For air at STP, the intensity of the electric field needed to arc the minimum voltage gap is much greater than that necessary to arc a gap of one meter. For 7.5 micrometers, the field is 43 Megavolts per meter and for one meter it is only 3.4 Megavolts per meter. This is about 13 times greater. The phenomenon is well verified experimentally and is referred to as the Paschen minimum. The equation fails for gaps under a few micrometers in air at one atmosphere and incorrectly predicts an infinite arc voltage at a gap of about 2.7 micrometers.

Early vacuum experimenters found a rather surprising behavior. An arc would take place in a long irregular path rather than at the minimum distance between the electrodes. For example, at 1 Torr, the distance for minimum breakdown voltage is 5.7 millimeters or about 0.22 inch. The voltage required to arc that distance is 327 Volts and is greater for gaps above and below that point. For a 2.85 mm gap, the required voltage is 533 Volts, nearly twice as much. If 500 Volts were applied, it would not be sufficient to arc at the 2.85 mm distance, but would arc at a 5.7 mm distance.

References

External links

* [http://home.earthlink.net/~jimlux/hv/paschen.htm High Voltage Experimenter's Handbook]
* [http://www.duniway.com/images/pdf/pg/Paschen-Curve.pdf Breakdown Voltage vs. Pressure]
* [http://www.stthomas.edu/physics/files/2005-Summer-Paschen-Mike_Cook.pdf Pachen Equation]
* [http://www.physics.csbsju.edu/370/jcalvert/dischg.htm.html Electrical Discharges]


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • paschen's law — noun Usage: usually capitalized P Etymology: after Friedrich Paschen : a statement in electronics: the breakdown voltage between electrodes in a gas is a function of the product of the distance and the pressure so that if the distance is doubled… …   Useful english dictionary

  • Paschen — may refer to:* Friedrich Paschen (1865 1947), German physicist ** Paschen (crater) ** Paschen Back effect ** Paschen series ** Paschen s law …   Wikipedia

  • Friedrich Paschen — Louis Karl Heinrich Friedrich Paschen (January 22, 1865 February 25, 1947), was a German physicist, known for his work on electrical discharges. He is also known for the Paschen series, a series of hydrogen spectral lines in the infrared region… …   Wikipedia

  • University of Cincinnati College of Law — Motto Juncta Juvant ( Strength in Unity ) Established 1833 Type Public (state university) …   Wikipedia

  • Microplasma — A microwave microplasma jet Microplasmas are plasmas of small dimensions, ranging from tens to thousands of micrometers. They can be generated at a variety of temperatures and pressures, existing as either thermal or non thermal plasmas. Non… …   Wikipedia

  • Закон Пашена — Кривые Пашена для гелия, неона, аргона, водорода и азота. Закон Пашена, назван в честь Фридриха Пашена, сформулировавшего …   Википедия

  • Nitrogen laser — A 337nm wavelength and 170 µJ pulse energy 20 Hz cartridge nitrogen laser A nitrogen laser is a gas laser operating in the ultraviolet range[1] (typically 337.1 nm) using molecular nitrogen as its gain medium, pumped by an electrical… …   Wikipedia

  • Electrostatic discharge — (ESD) is the sudden and momentary electric current that flows between two objects at different electrical potentials. The term is usually used in the electronics and other industries to describe momentary unwanted currents that may cause damage… …   Wikipedia

  • Sulfur hexafluoride — Chembox new Name = Sulfur hexafluoride ImageFile = Sulfur hexafluoride 2D dimensions.png ImageSize = 100px ImageName = Structure and dimensions of the sulfur hexafluoride molecule ImageFile1 = Sulfur hexafluoride 3D balls.png ImageSize1 = 100px… …   Wikipedia

  • Gas-filled tube — See also: Gas discharge lamp A gas filled tube, also known as a discharge tube, is an arrangement of electrodes in a gas within an insulating, temperature resistant envelope. Although the envelope is typically glass, power tubes often use… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”