Inductance transmissions consist of a metal rod inside an electrical coil. The position of the rod in the coil depends on the degree of movement of measuring element. As the metal rod moves, it changes the current passing through the coil. The transmitting coil and rod can be duplicated in the receiving instrument and combined with the receiving coil into an inductance bridge circuit. The inductance bridge is generally supplied for use with alternating current power supply (AC).
When the measuring element moves the metal rod in the transmitting coil the bridge balance is upset. The unbalance is then corrected by a movement of the metal rod in the receiver coil. Usually there is an amplifier and a motor in such a system. The unbalance is fed into the amplifier which provides a strong enough electrical impulse to cause the motor to run. The motor then moves the metal rod in the receiving coil to a position which restores bridge balance.
