This bridge is intended to inductance measurements and the standard is a capacitance. This makes it ideal to practical applications as when using inductances as standard the costs are higher. The basic circuit of a Maxwell Bridge is shown in figure bellow. The bridge uses a signal source with frequency determined by the magnitude of the measured inductance. See that the balance point independs of the frequency.
Formula:
When balanced:
L4 = R1 x R2 X C
and
R4 = (R1 / R2) X R3
Where:
L4 is the inductance to be measured in henry (H)
R1, R2, R4 and R4 are the resistance in the arms in ohm (Ω)
C is the capacitance in farads (F)
Application example:
In the Maxwell Bridge shown in figure the balance is found when: R1 = R2 = 100 Ω, R3 = 200 Ω and C = 0.1 F. Determine L and R4. (R4 is the resistance associated to the coil winding).
Data:
R1 = R2 = 100 Ω
R3 = 200 Ω
C = 0.1 µF (using C in µF the result is found in µH)
Using formula:
a) L4 = 100 x 200 x 0.1 = 2000 µH = 2 mH
b) R4 = (100 / 100) x 200 = 200 Ω
