1-22Q-16.Is the current flow through an inductor directly proportional or inversely proportional to itsinductance value?MEASUREMENT OF INDUCTANCE USING THE VTVMIf you do not have a 250DE+1325 at your disposal, the inductance of a coil can be determined byusing a vtvm and a decade resistance box, as shown in figure 1-15. In the following example theinductance of an unknown coil in the secondary winding of a 6.3-volt filament transformer will bedetermined with a vtvm and decade resistance box. The unknown coil must be connected in series withthe decade resistance box. The voltage across the decade box and across the coil must be monitored as thedecade box is adjusted. When equal voltages are reached, read the resistance of the decade box. Since thevoltage across the inductor equals the voltage across the decade box, the XL of the coil must be equal tothe resistance read on the decade box. For example, assume that the resistance reading on the decade boxis 4 kilohms and the frequency is 60 hertz. This must mean that the XL of the coil is also equal to 4,000ohms. The inductance formula L = XLI FDQ EH XVHG WR ILQG WKH LQGXFWDQFH RI WKH FRLO LQ KHQULHV Figure 1-15.—Determining inductance with a vtvm and decade resistance box.
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