Key, Bridge

A key for use with a Wheat stone Bridge, q.v. It is desirable to first send a current through the four arms of the bridge in using it for testing resistances and then through the galvanometer, because it takes a definite time for the current to reach its full strength. This is especially the case if the element being measured has high static capacity, as a long ocean cable. If the galvanometer connections were completed simultaneously with the bridge connections a momentary swing would be produced even if the arms bore the proper relation to each other. This would cause delay in the testing. A bridge key avoids this by first connecting the battery circuit through the arms of the bridge, and then as it is still further depre ed the galvanometer circuit is completed. 314   STANDARD ELECTRICAL DICTIONARY. IMG:8956969607833025625_313F206.jpg: Fig. 206. CHARGE AND DISCHARGE KEY