Induction voidmeter

An induction voidmeter for detecting voids in a conductive fluid such as liquid sodium is disclosed. The device may comprise: a four arm bridge circuit having two adjustable circuit elements connected as opposite arms of the bridge, an input branch, and an output branch; two induction coils, bifilarly wound together, connected as the remaining two opposing arms of the bridge circuit and positioned such that the conductive fluid passes through the coils; means for applying an ac excitation signal to input branch; and means for detecting the output signal generated in response to the excitation signal across the output branch. The induction coils may be located outside or inside a nonmagnetic pipe containing the conductive fluid.