Talk:Wheatstone bridge

need to discuss the concept of balance

The concept of a balanced bridge is central to many practical uses of bridges. Someone needs to explain this. Is this a good place? As a measurement tool, we adjust the bridge to balance, or null, to establish the unknown value by comparison with the known arm. However the balance concept is fundamental to many applications of bridges that are not measurement related, and is a key idea used by circuit designers. It allows the currents flowing across the horizontal paths to be independent of the voltage imposed on the vertical paths.

--AJim (talk) 20:26, 29 October 2008 (UTC)

In my experience use of an unbalanced Wheatstone bridge is as common as use of a balanced one. For example, in some strain gauge measurements both R3 and Rx (and sometimes R1 and R2 as well) are unknown, being the strain gauges themselves. Instead of trying to determine these resistances, the objective is to measure the potential difference, which is proportional to the strain. The article doesn't really cover this class or applications.

-- Mermaldad (talk) 18:01, 29 October 2013 (UTC)

A very important aspect of the Wheatstone bridge is that, when the bridge is at balance, the condition is independent of the precise voltage source applied. In practical terms, especially with technology available at the time, it was far easier to create relatively stable and well-known resistors than it was to create a stable voltage source. This is not brought out in the article as it stands as of September 2021. BoomerVet46 (talk) 01:17, 3 September 2021 (UTC)

Precision needed

Concerning the circuit diagram of Wheastone bridge, it would be nice to add the orientation of currents and voltages in the branches. It is easy to find out which conventions/orientations have been taken with the equations displayed below but it would be easier to make it to appear explicitely on the diagram. I didn't add any modification as I dont know how to do it :). That was just a remark to help improving the article.

Kumar maman

Misc. comments

Can't we tell how it was used? This is in the bowels of the technology and does a great disservice to the fact that it was the first piece of network management gear. - carl ford cford@imhocorp.com —Preceding unsigned comment added by 67.80.28.24 (talk) 11:06, 28 October 2008 (UTC)

See also has a link to E-meter, does that have any place on a page about a high precision electronic circuit? —Preceding unsigned comment added by 138.16.39.141 (talk) 03:08, 22 October 2007 (UTC)

Wheatstone did NOT invent the Wheatstone bridge (see any full biography of him).

S. Chomet

Updated with the correct inventor -- DrBob 18:54 30 May 2003 (UTC)

Should we add the balance conditions for the wheatstone bridge? mickpc

I added the voltage divider equation used to detect resistance changes. Should we start a related discuss on RTD's? Three vs 4 wire?--Kdcarver 21:32, 11 October 2005 (UTC) kdcarver

James Kuo

It seem that the formula to calculate the Equivalent Resistance RE has a little error

(R1*R2)(R3*R4) should be replaced by (R1+R2)(R3+R4). Please verify my suggestion. Tks.

what about the emeter in referance to scientologys use of this type device?

I kindly request a brief discussion of how AC measurements are made with a Wheatstone... and/or how to measure inductance and capacitance (or a link to said information). If anyone is familiar with that, thanks in advance. Catapultsam 11:15, 15 April 2007 (UTC)

Confusion?

The maths seem to start of with R1, R2, R3 and Rx, which are defined. Later on R4 appears without explanation

R4 should be changed into Rx since the picture above is taking Rx as an unknown resistor --besterer

Diagram

In the article, they say that the first set of equations are for B and D. I believe the author meant B and C as current I1 does not feed into D.—The preceding unsigned comment was added by ZaydHammoudeh (talk • contribs) 22:09, May 31, 2006 (UTC).

Current article is wrong. Someone changed the image without checking definitions in the article.Orz.(Sorry, I don't have enough time to correct it now.)—The preceding unsigned comment was added by 155.230.100.86 (talk • contribs) 04:11, June 7, 2006 (UTC).

I restored the original diagram and adjusted some of the changes that had been made since it was replaced on May 22. The newer diagram, while perhaps nicer-looking, uses different numbering of the resistors and junctions. This change in numbering left the mathematical derivation incorrect. Several editors had made changes to individual sentences where they noted a discrepancy with the diagram, but this was not sufficient to fix the problem. I have reverted those changes, so the article should now be in accord with the diagram.

If the consensus is that the other diagram is better, someone needs to go over the article carefully and rework the derivation so that it is in accord with the new diagram. Alternatively, someone could relabel the new diagram so it matches the old one's numbering.--Srleffler 17:18, 23 August 2006 (UTC)

Text / Diagram Agreement

Please verify that my suggestion is a correct one. In order to have the text agree with the diagram, I feel that the following sentence, which constitutes the fourth paragraph:

"If the bridge is balanced, which means that the current through the galvanometer Rg is equal to zero, the equivalent resistance of the circuit between the source voltage terminals is:"

should be changed in this way:

"through the galvanometer Vg is equal to zero,"

since the label "Vg" appears on the diagram and the label "Rg" appears nowhere on the diagram.

I hope that this helps. Sincerely, Gallion620 (talk) 20:16, 9 January 2008 (UTC)

The whole sentence is irrelevant; we're not interested in the resistance presented to the source. I shall delete it.

Incidentally, I notice that in the diagram R2 is no longer shown as adjustable. Is this a mistake? --catslash (talk) 22:56, 9 January 2008 (UTC)

Question..

Does any one have a pic on one of these? And a common way it would be in use? This is just for personal not article use. 17:46, 17 July 2008 (UTC) Rippey574 (talk) 17:08, 25 July 2008 (UTC)Rippey574

Still no response? Rippey574 (talk) 07:16, 22 August 2008 (UTC)

In my contribution of the German article for the Thomson Bridge[1] you may find a picture, which you may use.

But I am not shure what you want, if you would try to explain it in more detail, you might get more response.

Rainglasz 18:44, 3 September 2008 (UTC)

I couldn't get the link to work from the de.wiki site so I added a link from the Scientology section. If someone thinks it isn't PC, feel free to find a better pic. Canoe1967 (talk) 19:44, 29 December 2011 (UTC)

please elaborate

It's a good start, but needs more :) For instance, the circuit on the page is specifically a quarter-bridge set up. A good site to refer to for more info is [2] though the focus there is more on strain gauges. Try [3] too. Happy editing :) —Preceding unsigned comment added by Cirmae (talk • contribs) 23:53, 11 May 2009 (UTC)

Equation for Rg

Replacing V_g with R5 and Rx with R4, and solving in terms of conductance (G1=1/R1, etc) I came up with this:

                   (G1*G4-G2*G3)
V5 = Gs *          ------------- 
          (G1+G2)(G3+G4) + G5(G1+G2+G3+G4) 

This seems right, but then I work a problem like this once every five years or so. The sign of V5 is a matter of convention. My diagram was D-B but I think the equations in this article use B-D. I would have liked to find this in the article rather than work it myself, but then this is no longer a balanced bridge so perhaps it doesn't belong. — MaxEnt 11:30, 8 July 2013 (UTC)

Uncertainty in measured voltage or current

The article contradicts itself as talking about the measured current vs. voltage. I know they can be derived from each other, but what is more common measurement? Sam-2727 (talk) 02:07, 16 March 2019 (UTC)

Which aspect? I'm not seeing an obvious problem in the article.

The bridge (in most uses) doesn't quantitatively measure anything, other than balancing the resistances in the legs, then comparing the current through the meter to zero (in either direction).

There is a note at the end of §Operation about them being read directly. But the point here is that the behaviour is linear and so voltage and current are directly related. The meter (like most voltmeters) will actually be measuring current, albeit current through a known and fixed load. Andy Dingley (talk) 12:48, 16 March 2019 (UTC)

Accuracy of Unbalanced Bridges

I'm not sure about the claim at the beginning that Wheatstone bridge is more accurate than a voltage divider at measuring resistances, well at least for the unbalanced bridge which is the only thing talked about in the citation #1 that follows its. Furthermore, this citation actually doesn't compare the bridge with a voltage divider, just it just compares it with using a voltmeter & current meter method instead so this is not a great source for this claim.

From my current understanding, the unbalanced Wheatstone bridge is simply two voltage dividers (since the middle is open circuited). Thus, I would expect the accuracy to be the same; the output voltage is sensitive to changes in the supply voltage or temperature coefficient differences between the reference and unknown resistors. It seems like the only advantage of the Wheatstone bridge in this circumstance is that can add a DC offset (approximately) to the output measurement to make the output more convient in circumstances were the change is small relative to the absolute value. For example, if you have a PRT with a 1000 ohm resistance at 0 C and 1100 at 25 C, you could set the resistor appropriately such that you get 0 V at 0 C.

I don't see where the accruacy improvement comes from for the unbalanced bridge (I agree the balanced bridge is more accurate). Does anyone agree/disagree? Nate266 (talk) 01:09, 19 August 2021 (UTC)

I agree that to make the article clearer we need a current application for the circuit and to be fair I do not know of any. 2001:8F8:1761:8F2D:FC48:CC11:82A7:9741 (talk) 03:28, 5 May 2022 (UTC)