4.2 Theory of Operation
The Electronic Modulevel Displacer Level Transmitter
relies on the principles of buoyancy to convert mechanical
movement to an electronic output. See Figure 23.
4.2.1 Displacer Buoyancy
The buoyancy force acting on an object is equal to the
weight of the liquid displaced by the object. As the level
changes, and more or less of the displacer is submerged in
liquid, the buoyancy force on the displacer changes. This
change is detected by the range spring from which the dis-
placer hangs. The compression or elongation of the range
spring, in turn, causes movement of the LVDT core
mounted on the rigid stem attached to the spring.
4.2.2 LVDT
An LVDT is a linear variable differential transformer made
up of a primary winding, two secondary windings and a
special magnetic steel core. The primary winding and the
two secondary windings form an open transformer. The
secondary windings are positioned, one above each other,
opposite the primary winding. The primary winding is
powered so that when the magnetic steel core is positioned
between the primary and one or both of the secondary
windings, a current is induced in the secondary winding(s).
By comparing the currents in the two secondary windings,
the exact position of the core, and therefore the liquid
level, can be measured.
4.3
Troubleshooting
The Electronic Modulevel Displacer Level Transmitter is
designed and engineered for trouble-free operation over a
wide range of operating conditions. Common transmitter
problems are discussed in terms of their symptoms and
corrective actions as recommended.
WARNING!
Explosion hazard. Do not connect or disconnect
equipment unless power has been switched off
or the area is known to be non-hazardous.
The table on the next page provides information on how
to troubleshoot transmitter-level problems.
26
48-618 ES/EZ Modulevel Displacer Level Transmitter (Top Hat Assembly Design)
