US Patent 9228878 Dual beam non-contact displacement sensor

This disclosure describes systems, methods, and apparatus for remotely monitoring an elevation, or change in elevation, of a fluid surface, such as that of molten sapphire. The remote monitoring can be performed by measuring positions of a pair of reflected laser beams off the fluid surface as detected on an imaging sensor. As the surface elevation falls, the positions of the pair of reflected laser beams move relative to each other, and this positional change can be converted into a change in the fluid surface elevation.