Melt view camera

Abstract

A method and apparatus for continuously monitoring a melt surface is provided. The camera includes a CCD detector array, electronic shutter, and associated optical train mounted within a water cooled enclosure, all mounted within close proximity to the melt. Radiation shields surround the enclosure in order to attenuate the heat radiated from the melt to manageable levels. To minimize damage to the electro-optical components of the camera due to melt vapors and other contaminants, the camera enclosure includes a small viewing pinhole through which an inert gas is directed. The pinhole is small enough to minimize the gas flow rate while avoiding noticeable image diffraction. The small pinhole also provides a large depth of field, rendering high quality images of the melt. A compound lens system focuses the image into the CCD array to produce a near diffraction limited image over the angles of interest. The lens system contains a ninety degree turning element to protect the CCD array from direct exposure to x-rays produced at the melt surface. The electronic shutter, in combination with the pinhole, is used to reduce the incident intensity and to prevent CCD saturation during normal use. The shutter speed may be sufficiently lowered to allow alignment in ambient light. A neutral density filter may also be used in combination with the electronic shutter to avoid saturation.