Hopper Level Help Needed

I work at a WWTP which has a single conveyor feeding a 4 ft deep hopper which diverts the sludge "cake" to one of two moyno pumps. The hopper has a steady vibration so the sensors have been mounted from the sidewalls to keep the vibration from effecting their operation. This system is currently using Banner T30UUPBQ level sensors mounted 12 inches above the hopper to determine the level in the hopper. The sensor output is 0 - 10 VDC and is sent to a A/B Micrologix 1400 controller to determine what speed the Toshiba G7 drive should run at to empty the hopper. The "cake" is basically the consistency of mashed potatoes and forms a cone shape against one side of the hopper after it falls off the conveyor. The Banner sensor is not working very well in this application. Can anyone recommend a good sensor capable of indicating the hopper level for this application? The sensor cannot touch the "cake" as it leaves a stick residue on whatever it touches. Probes cannot be used as "hammers" are used to help force the product into the moyno pumps.:001_huh: