1-21MAXWELL BRIDGEThe Maxwell bridge, shown in view C of figure 1-14, measures inductance by comparing it with acapacitance and (effectively) two resistances.] This bridge circuit is employed for measuring inductanceshaving losses greater than 0.05 (expressed by the D dial reading). For such inductors it is necessary tointroduce, in place of the series control (D dial), a new loss control (Q dial), which shunts the standardcapacitor. This control, which becomes effective when the FUNCTION switch is turned to the L(Q)position, is conveniently calibrated in values of Q, the storage factor of the inductor under measurement.The balance for inductance is the same for either bridge circuit. This permits the use of the same markingson the RANGE switch for both the L(D) and L(Q) positions of the FUNCTION switch.REACTANCE MEASURING EQUIPMENTThe reactance type of inductance measuring equipment makes use of the following principle: If an acvoltage of fixed frequency is applied across an inductor (and a resistor in series), the voltage dropproduced across the reactance of the inductor by the resulting current flow is directly proportional to thevalue of the inductance. An inductance measurement using the reactance method is identical tocapacitance measurements using the same method, except that current flow is directly proportional to thevalue of inductance, rather than inversely proportional as in the case of capacitance. It follows then that ifa reactance-type capacitance measuring equipment is provided with a chart that converts the capacitancereadings to equivalent inductance values and a proper range multiplying factor, the same test setup can beused to measure both capacitance and inductance. In practice, test equipment using the reactance methodfor capacitance measurements usually provides an inductance conversion chart. Because the currentflowing through the inductance under test is directly proportional to the value of inductance, thereciprocals of the capacitance range multipliers must be used; for example, a multiplier of 0.1 becomesand a multiplier of 100 becomesThe reactance-type equipment gives approximate values only. Like the analog multimeter, it is usedonly when portability and speed are more important than precision. If the ohmic resistance of the inductoris low, the inductance value obtained from the conversion chart can be used directly. If the ohmic value(as measured with an ohmmeter) is appreciable, a more accurate value of inductance can be obtained byuse of the following formula: