1. The problem statement, all variables and given/known data, I have to recommend a linear portion control sensor, that can be used in an explosive enviroment. Unsafe electrical contacts should be avoided and the case must not permit any dust or water. 2. Relevant equations 3. The attempt at a solution. My thoughts are either a LVDT sensor or a ultrasonic sensor for the task listed above. Anyone have any thoughts on which would be the best out of those or a better suggestion?