27
48-635 E3 Modulevel
®
Displacer Level Transmitter
3.0
Reference Information
This section presents an overview of the operation of the
E3 Electronic MODULEVEL Displacer Level Transmitter,
information on troubleshooting common problems, listings
of agency approvals, lists of replacement and recommended
spare parts, and detailed physical, functional, and perform-
ance specifications.
3.1
Description
The E3 MODULEVEL is a loop-powered, two-wire, 24 VDC
level transmitter which utilizes simple buoyancy principles
in combination with a precision range spring and a highly
accurate LVDT (linear variable differential transformer) to
detect and convert liquid level movement into a stable 4–20
mA output signal. The electronics are housed in an
ergonomic, dual-compartment enclosure which is angled for
ease of wiring and calibration.
3.2
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 14.
3.2.1 Displacer/Range Spring
According to Archimedes principle, the buoyancy force act-
ing on an object immersed in liquid is equal to the mass of
the liquid displaced. As the level changes, the volume of
displacer submerged in the liquid changes, thus varying the
buoyancy force acting on the displacer. This change is
detected by the precision range spring from which the dis-
placer hangs, causing it to elongate or compress. The change
in spring length causes movement of a special LVDT core
which is mounted on a rigid stem attached to the spring.
3.2.2 LVDT
E3 MODULEVEL utilizes highly precise LVDT technology
to convert the movement of the LVDT core within the
LVDT to a stable 4–20 mA output signal. The position of
the core with respect to a primary and two secondary wind-
ings within the LVDT, induces a voltage in each winding.
The comparison of the induced voltages within the micro-
processor of the E3 results in very accurate level output.
Moving
LVDT Core
Range Spring
Displacer
External cage
Electronics
Enclosure
Printed
Circuit Board
Wiring Board
LVDT
Stem
Keypad
Display
Enclosing Tube
Figure 14
Electronic Modulevel
®
Components
