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In electronics, the Carey Foster bridge is a bridge circuit used to measure low resistances, or to measure small differences between two large resistances. It was invented by Carey Foster as a variant on the Wheatstone bridge. He first described it in his 1872 paper "On a Modified Form of Wheatstone's Bridge, and Methods of Measuring Small Resistances" (''Telegraph Engineer's Journal'', 1872–1873, 1, 196). ==Use== In the diagram to the right, X and Y are resistances to be compared. P and Q are nearly equal resistances, forming the other half of the bridge. The bridge wire EF has a jockey contact D placed along it and is slid until the galvanometer G measures zero. The thick-bordered areas are thick copper busbars of almost zero resistance. # Place a known resistance in position Y. # Place the unknown resistance in position X. # Adjust the contact D along the bridge wire EF so as to null the galvanometer. This position (as a percentage of distance from E to F) is . # Swap X and Y. Adjust D to the new null point. This position is . # If the resistance of the wire per percentage is , then the resistance difference is the resistance of the length of bridge wire between and : :: To measure a low unknown resistance X, replace Y with a copper busbar that can be assumed to be of zero resistance. In practical use, when the bridge is unbalanced, the galvanometer is shunted with a low resistance to avoid burning it out. It is only used at full sensitivity when the anticipated measurement is close to the null point. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Carey Foster bridge」の詳細全文を読む スポンサード リンク
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