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Bot: Removing Orphan Tag (Nolonger an Orphan) (Report Errors)

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	~~Royal Votaw~~ is ~~my name but I~~ by ~~no means truly liked that title~~. [~~http://Www~~.~~ncdoj.gov/Consumer/Automobiles/Extended~~-~~Car~~-~~Warranties~~.~~aspx Delaware~~] is the ~~place I~~ [http://www.~~farebook~~.us/~~index.php?do=~~/~~profile-7229~~/~~info/ extended auto warranty~~] ~~extended [http:~~/~~/panda-craft~~.~~eu/index.php?mod=users&action=view&id=17668 car warranty~~] ~~adore most but I need to transfer for my family members~~. ~~To perform croquet~~ is the ~~hobby I will by no means stop performing. auto warranty The job I~~'~~ve been occupying~~ for ~~many years~~ is a ~~bookkeeper but extended auto warranty I~~'~~ve currently applied for an~~ [http://~~Www~~.~~kbb~~.com/~~extended-auto-warranty~~/ ~~additional~~] ~~one.<br><br>Here is my blog;~~ [http://~~yardleyvashon~~.~~com~~/~~abig~~/~~ActivityFeed~~/~~MyProfile~~/~~tabid~~/~~381~~/~~UserId~~/~~1767~~/~~Default~~.~~aspx yardleyvashon~~.com]		{{Confusing\|reason=the diagram in the article doesn't match the one in the cited reference\|date=June 2012}}

			[[File:Mostek_Kelvina.svg\|thumb\|Kelvin bridge]]
			[[File:Kelvin bridge by RFT.png\|right\|thumb\|220px\|Kelvin bridge]]
			{{about\|a measuring instrument\|the bridge across the river Kelvin\|Kelvinbridge}}

			A '''Kelvin bridge''' (also called a '''Kelvin double bridge''' and in some countries a '''Thomson bridge''') is a [[measuring instrument]] used to measure an unknown [[electrical resistance]] below 1 [[Ohm]]. It was invented by [[William Thomson, 1st Baron Kelvin]].

			==Accuracy==

			There are some commercial devices reaching accuracies of 2% for resistance ranges from 0.000001 to 25 Ω. Some [[ohmmeter]]s include Kelvin bridges in order to obtain large measurement ranges.

			The instruments for measuring sub-ohm values are often referred to as [[low-resistance ohmmeters]], milli-ohmmeters, micro-ohmmeters, etc.

			==Principle of operation==

			Its operation is similar to the [[Wheatstone bridge]] except for the presence of additional resistors. These additional low value resistors and the internal configuration of the bridge are arranged to substantially reduce measurement errors introduced by voltage drops in the high current (low resistance) arm of the bridge.<ref>[http://www.allaboutcircuits.com/vol_1/chpt_8/10.html All About Circuits]</ref> It consists of two ratio arms. The outer ratio arm contains the known resistors and the inner ratio arm helps to connect the one terminal of the [[galvanometer]] at the appropriate point (which was the disadvantage of the first Kelvin bridge).

			The measurement is made by adjusting some resistors in the bridge, and the balance is achieved when:
			::<math>R_x=R_2 \cdot \frac{R_3}{R_4}+R \cdot \frac{R_3 \cdot R'_4 - R'_3 \cdot R_4}{R_4 \cdot \left( R+R'_3 + R'_4\right)}</math>

			Resistance ''R'' should be as low as possible (much lower than the measured value) and for that reason is usually made as a short thick rod of solid [[copper]]. If the condition ''R''<sub>3</sub>·''R''`<sub>4</sub> = ''R''`<sub>3</sub>·''R''<sub>4</sub> is met (and value of ''R'' is low), then the last component in the equation can be neglected and it can be assumed that:

			::<math>R_x \approx R_2 \cdot \frac{R_3}{R_4}</math>

			Which is equivalent to the [[Wheatstone bridge]].

			==See also==
			{{Portal\|Electronics}}
			* [[Bridge circuit]]
			* [[Ohmmeter]]
			* [[Carey Foster bridge]]

			==References==
			{{Reflist}}

			==External links==
			*[http://www.tpub.com/content/neets/14193/css/14193_94.htm Kelvin Bridge]
			*[http://www.cropico.co.uk/images/uploads/KB3_20Handbook.pdf Kelvin Bridge KB3 Data Sheet]
			*[http://www.uiitraining.com/b51a/200/25138measuring_system.htm# Valhalla 4100 ATC Low-Range Ohmmeter specifications]
			*[http://books.google.com/books?id=z3lKAAAAMAAJ Methods of Measuring Electrical Resistance - Edwin F. Northrup, 1912, full-text on Google Books] - see chapter 6

			[[Category:Electrical circuits]]
			[[Category:Electrical engineering]]
			[[Category:Measuring instruments]]
			[[Category:English inventions]]

			{{Link FA\|hu}}

			[[pl:Mostek (elektronika)#Mostek Thomsona (mostek Kelvina)]]

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