Bro,
It would be better use a non contact level technology, of course not ultrasound, but what about pulsed radar or FMCW, Rosemount have a 5408 loop power transmitter maybe could be work fine, do you know the oil (grease) DK?
If the grease has high viscosity is recommended not stay in touch...
Pedro,
Are these transmitters having exactly the same heights on its taps?
I mean the high and low taps are at the same reference on the vessel.....
Your error or difference between the transmitter outputs is almost constant, so I believe that issue maybe is not created by the process itself...
