ABSTRACT
The majority of well known a.c. bridges are classified as four-arm bridges and consist of an arrangement of four impedances (in complex form, Z D Rš jX) as shown in Figure 27.1. As with the d.c. Wheatstone bridge circuit, an a.c. bridge is said to be ‘balanced’ when the current through the detector is zero (i.e., when no current flows between B and D of Figure 27.1). If the current through the detector is zero, then the current I1 flowing in impedance Z1 must also flow in impedance Z2. Also, at balance, the current I4 flowing in impedance Z4, must also flow through Z3.
