Have a couple of dead nuclear source level detectors measuring the level in a bark bin for a boiler. These have been in service for at least 20 years and I am told the company that made these are not in busines anymore. I would like to replace these units with something other than a nuclear source due to LOTS of paper work involved. Has anybody used radar, sonar, vision systems, etc. to measure level. Have to have continous level measurment. Bark pile level is used to control the speed of the bark screws.