Rosemount 3095 - Example Installations

2-13
Level Controller Overview and Installation
EXAMPLE
INSTALLATIONS
Figure 2-9 illustrates example installations for the Model 3095 Level
Controller. “H” and “L” in the examples correspond to the H and L
stamped on the Level Controller sensor module and indicate which way
the controller is to be installed.
Open Tanks
In open vessels a pressure controller mounted near the bottom of the
tank will measure the pressure corresponding to the height of the fluid
above it.
The connection is made to the high pressure side of the controller. The
low pressure side is vented to atmosphere.
Process Connections Options: Impulse piping; one diaphragm seal,
(capillary or direct mount) level flange.
Open Tanks with Bubbler
A “bubbler” system using a top-mounted controller can be used in open
vessels. This system consists of an air supply, a constant flow regulator,
a controller, and tube extending down into the vessel.
Air is bubbled through the tube at a constant flow rate. The pressure
required to maintain flow is determined by the vertical height of the
liquid above the tube opening, process density, and local gravity.
Process Connections Option: Impulse piping,
Closed Tanks with Dry Leg
In closed vessels, the pressure above the liquid will affect the pressure
measured at the bottom. The pressure at the bottom of the vessel is
determined by the height of the liquid, the density of the liquid, plus
the vessel pressure.
To measure true level, the vessel pressure must be subtracted from the
measurement. This is accomplished by making a pressure tap at the top
of the vessel and connecting this to the low side of a differential pressure
controller. Vessel pressure is now equally applied to both the high and
low sides of the controller. The resulting differential pressure is
determined by liquid height, process density, and specific gravity.
If the gas above the liquid does not condense, the piping for the low side
of the controller will remain empty. Calculations for determining the
controller height will be the same as those shown for open vessel
bottom mounted controllers.
Process Connections Options: Impulse piping; one diaphragm seal
(capillary or direct mount); two diaphragm seals, level flange.
Closed Tanks with Wet Leg
If the gas above the liquid condenses, the piping for the low side of the
controller will slowly fill up with liquid. To eliminate this potential
error, the pipe is purposely filled with a convenient reference fluid.
The reference fluid exerts a head pressure on the low side of the
controller.
Process Connections Options: Impulse piping; one diaphragm seal
(capillary or direct mount); two diaphragm seals, level flange.