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Wheatstone Bridge Variations

June 28th Fact-of-the-Day

From DC up to about 150 MHz Wheatstone bridges, or other bridges that are merely modified forms of a Wheatstone bridge, provide the most accurate method of measuring resistance or impedance. The original Wheatstone bridge has four resistance arms and is used to measure resistance. The bridge is balanced when no voltage exists between center terminals. Bridge arms can have complex impedance quantities (various combinations of R, L and C) instead of only resistance, to measure complex impedance. Bridges with various arrangements of complex impedance arms are commonly identified by the names of developers who popularized them. For example, a Wien bridge is a special case of a Wheatstone bridge that allows the capacitance of two capacitors to be compared if the resistance values are known. A Schering bridge is a variation of a Wien bridge that provides a convenient way to measure capacitance and capacitor dissipation factor. Maxwell and Hay bridges allow comparisons of impedance with unlike reactances. Other named variations exist. ©2005 Martek International All rights reserved.

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