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