ABB KM26 Operating Instruction page 20

20
KM26 | M AGN ETI C L EV EL G AU GE | O I/KM 26 -E N REV I
. . . 3 Mounting
Oversize chamber with guide rods
In applications where flashing is a concern (rapid change from
liquid to gas; boiling), the sudden presence of gas bubbles
expanding under the float can cause it to be forced upward
and then back down very erratically. If viewed on the visual
indicator, the operator would be unable to identify the true
liquid level because of the very abnormal performance.
Similarly, if a large number of small bubbles form underneath
and around the float, it will decrease the buoyant force that is
keeping the float on the surface. This could cause the float to
submerge completely in the liquid.
To combat this phenomenon, a oversize chamber with guide
rod design can be incorporated into the chamber design.
This provides simply a large open space surrounding the float
that allows the expansion of gasses to pass around it
unimpeded. In order for the float to operate the visual
indicator properly, the set of guide rods must be in place to
restrict lateral movement of the float so that it does not lose
coupling with any externally mounted components like
indicator, transmitter or switch.
Figure 23 - normal and oversize chamber with guide rods
Figure 24 - oversize chamber with guide rods
Cryogenic insulation
CAUTION
ABB does not recommend customer installation of
cryogenic insulation. Consult the factory.
Cryogenic insulations are used to maintain the required low
temperature of the service fluid to be measured. Cryogenic
units are offered with flipper styled magnetic bar graph
indicators with frost extension. The face of the frost
extension must always be exposed.
Figure 25 - cryogenic insulation
Mag wave (MW05)
The MW05 MLG is a twin-chamber design for use on
applications where redundant level measurement is critical.
MW05 combines MLG technology with a Guided wave
Radar(GWR), magnetostrictive, or other type of direct
insertion transmitter installed in the secondary chamber. It
provides precise visual measurement and reliable level data
transmission to a remote display or controller.
MW05 is available in a wide variety of configurations and is
offered in a broad range of pressure ratings, styles, sizes and
choice of process connections. Top and bottom MLG float
stop springs are standard in the primary MLG chamber. The
secondary chamber houses the transmitter sensor and allows
the GWR transmitter to provide a backup or remote level
measurement.
Figure 26 - Mag wave