Ultrasonic Transmitter in a Water Storage Tank

[CuriousElectron]

Hi Gents,

Have any of you used Rosemount 3000 series ultrasonic for level monitoring in a large closed water storage tank? I'm particularly interested to know if the unit is rated for full submergence and if it would still function properly. The literature is not specific, but it does require at least 12" of clearance from the liquid surface to the sensor. I wonder if this is true for ultrasonic technology and if hydrostatic sensor would be better suited for tank level measuring when the full height of the tank needs to be monitored.

Thanks,
EE

 

[danw2]

That radar and all other top mounted 'non-contact' ultrasonic technology models will not operate if submerged, nor will they operate if the level comes within the 12" blanking zone. (they all have a blanking zone for technical reasons).

One work around is to fab a wide nozzle on the roof and mount the ultrasonic on the nozzle to provide the additional one foot height needed for the blanking zone. The wider the nozzle, the better so the cone of ultrasonic energy doesn't reflect off the sides or edge of the nozzle, creating a false echo.

For water level, hydrostatic head pressure works well. The specific gravity of water does not vary and engineering units are inherently inches/feet or mm/m of water. There are top mount submersible styles, but the vent tube that runs in the 'cable should have a dessicant to prevent humidity from condensing in the vent tube and creating an offset. The other style is a mounted down near grade level. The one downside is the requirement for freeze protection for outdoor tanks in northern climates (submersibles are exempt).