249W Level Sensor
Instruction Manual
Form 5729
March 2005
2
Figure 2. Torque Tube Arm Exploded View Showing Controller or Transmitter Mounting
W8150 / IL
CONTROLLER OR TRANSMITTER
(TYPE DLC3010 SHOWN)
RETAINING
FLANGE
POSITIONING
PLATE
GASKET
TORQUE TUBE
ARM
ROTARY SHAFT
OUTER
TUBE
END
MOUNTING HOLES ACCEPT
FOUR STUDS OR CAP
SCREWS DEPENDING ON
CONTROLLER OR TRANSMITTER
HEX NUTS OR CAP SCREWS
DEPENDING ON CONTROLLER
OR TRANSMITTER
Figure 3. Typical Cageless Displacer
KNIFE EDGE
BEARING
DISPLACER ROD
W1800-1*/IL
W8325
DISPLACER
TORQUE TUBE
Description
The Type 249W sensor is designed to measure
liquid level, interface level, or density/specific gravity
inside a process vessel.
A torque tube assembly (figure 3) and displacer
provide an indication of liquid level, interface level, or
density/specific gravity. The torque tube assembly
consists of a hollow torque tube with a shaft welded
inside it at one end and protruding from it at the
other end.
The unconnected end of the tube is sealed by a
gasket and clamped rigidly to the torque tube arm,
permitting the protruding end of the shaft to twist and
therefore transmit rotary motion. This allows the
interior of the torque tube to remain at atmospheric
pressure, thus eliminating packing and the
disadvantages of packing friction.
The displacer always exerts a downward force on
one end of the displacer rod. The other end of the
displacer rod rests on the knife-edge of the driver
bearing. A keyed shaft on the bearing end of the
displacer fits into a socket on the outside of the
welded end of the torque tube assembly.
A change in liquid level, interface level, or
density/specific gravity buoys up the displacer by a
force equal to the weight of the liquid displaced.
Corresponding vertical movement of the displacer
results in angular movement of the displacer rod
around the knife edge. Since the torque tube
assembly is a torsional spring which supports the
displacer and determines the amount of movement
of the displacer rod for a given displacement
change, it will twist a specific amount for each
increment of buoyancy change. This rotation is
brought through the torque tube arm by the
protruding rotary shaft. A controller or transmitter
attached to the end of the rotary shaft converts the
rotary motion into varying pneumatic or electric
signals. Figure 2 shows how the controller or
transmitter mounts on the torque tube arm.
Educational Services
For information on available courses for Type 249W
level sensors, as well as a variety of other products,
contact:
Emerson Process Management
Educational Services, Registration
P.O. Box 190; 301 S. 1st Ave.
Marshalltown, IA 50158 - 2823
Phone: 800 - 338 - 8158 or
Phone: 641 - 754 - 3771
FAX: 641 - 754 - 3431
e-mail: [email protected]
