1-24
With the ac signal applied to the bridge, R1 and R2 are varied until a zero reading is seen on the
meter. Zero deflection indicates that the bridge is balanced. (NOTE: In actual practice, the variables are
adjusted for a minimum reading since the phase difference between the two legs will not always allow a
zero reading.)
CAPACITANCE BRIDGE.—Because current varies inversely with resistance and directly with
capacitance, an inverse proportion exists between the four arms of the bridge in figure 1-7; the right side
of our expression is inverted from the resistance bridge expression as follows:
or
Figure 1-7.—Capacitance bridge.
Q-18. What effect does an increase in capacitance have on a capacitor’s opposition to current flow?
Because R1 and R2 are expressed in the same units, the equation R1/R2 becomes a simple
multiplication factor. This equation provides a numerical value for Cx and will be in the same units as Cs
(farad, microfarad, and so forth).
