The Kelvin Bridge
- 1. Gema Cabrera Gonzalo Valdivieso Jose Miguel Ruiz
- 2. Choosing a Term Initially we proposed three possible terms to update: Topology, Temperature Coefficient and Kelvin Bridge. Topology and Temperature Coefficient are very complete articles, so they are difficult to update. Kelvin Bridge was a very short one, so we thought that it would be very easy to find information, and that it wouldn’t be rejected.
- 3. Updating The term consisted in a very short definition, so we all agreed that a deeper description was needed. Some images were added to help us to describe it. This is its electrical circuit.
- 4. Text added When using a Wheatstone bridge to measure the low resistor, Rx, the non-perfect wires resistances can’t be ignored and substantially affect the measurement. To avoid this, some modifications must be introduced. If the ratios R3/R4 and R1/R2 are equal and the bridge gets balanced, the Wheatstone condition is again accomplished. Rx = Ra · R1 /R2
- 5. Text added As a result of this modification a new measuring instrument, the Kelvin Bridge, is achieved. There are some commercial devices reaching accuracies of 2% for resistance ranges from 0.001 to 25 ohms. Often, ohmmeters include Kelvin bridges, amongst others measuring instruments, in order to obtain large measure ranges, for example, the Valhalla 4100 ATC Low-Range Ohmmeter.
- 6. URL We can find the complete information in the following link: http://en.wikipedia.org/wiki/Kelvin_bridge
- 7. We have had some problems at finding quality sources. This term is a very specialized device, belonging to the Electronics Engineering, and only a few sites talk about it. Most of the sites where we had found information are copyrighted or non-free access. Problems
- 8. Problems It has been very difficult to summarize the idea because we wanted to explain the electrical description of a complex device using very short paragraphs. Decisions making has been solved by voting.
- 9. Bibliography http://www.allaboutcircuits.com/vol_1/chpt_8/10.html http://www.uch.ceu.es/principal/eponimos_cientificos/escala_kelvin.asp http://www.tpub.com/content/neets/14193/css/14193_94.htm