Instruction Manual

Instruction Manual
D103216X012
L2sj Controller
January 2015
4
Principle of Operation
The operation of the L2sj controller in combination with the sensor is based on the Archimedes Principle, which states
that a body immersed in a liquid will be buoyed up by a force equal to the weight of the liquid displaced. The buoyant
force and resultant movement of the displacer in the liquid is transmitted to the controller which delivers a pneumatic
signal to a control valve.
Figure 2 shows a simple schematic of the controller and sensor. In its normal position, the counterclockwise moment
due to the weight of the displacer about pivot point O is balanced by the sum of the clockwise zero spring moment
and the counterclockwise relay force moment applied through lever A to the displacer rod. The weight of the displacer
decreases when the liquid level increases and the subsequent buoyant force increases causing a force imbalance
between the zero spring, relay, and displacer forces. This force imbalance is transmitted to the relay by levers A and B.
The relay compensates for the force imbalance by converting it to a pressure output to a control/dump valve and
bringing the forces back into equilibrium.
Figure 2. Operational Schematic
DISPLACER ROD
LEVER B
PROPORTIONAL BAND
ADJUSTMENT
PIVOT
POINT O
DISPLACER
LEVER A
ZERO SPRING
RELAY