An optical alarm for vacuum traps

An optical alarm for large industrial vacuum systems has been developed to prevent overflow of vacuum filters and traps. The alarm prevents two problems: (1) nuclear reactions when the dirt contains both radioactive materials and water and (2) overload of the vacuum system. The level of dirt in the trap is detected by the attenuation of light across the trap. Water in the trap is detected by light refraction at large angles of incidence to the water surface. To minimize sensitivity to dirty trap walls, a second detector measures light attenuation across the empty section of the trap, and the results are used to normalize the first detector output. Logic circuits minimize sensitivity to large chunks of dirt moving in the trap.<>