February 2011: SiloPatrol®
SE Cable-Based
Level Sensor
SiloPatrol®
SE
SMU equipped with a
self-powered analog output
The SiloPatrol® SE cable-based level sensor
from Monitor Technologies is available with an Analog
4-20mA self-powered output. This SMU sensor is a standalone
transmitter that provides an updated (refreshed) direct
analog signal each time a new measurement is made. Measurements
are initiated either automatically as programmed within
the sensor electronics or as a direct response to receiving
a remotely activated electrical “sound” signal. This
sensor model is equipped with a relay output that can
be programmed to activate when a user established level
is reached or depleted, upon detection of a sensor
error, or when a measurement cycle is in progress. The
sensor can be programmed to hold the last output value,
to output <2 mA, or to output >23mA in the event
of a sensor failure. Choosing either of the last two
error signal choices allows your control system programmer
to provide timely error or alarm notification by whatever
means is appropriate for your plant operation.
The SiloPatrol
SE lowers a weight & cable into
the silo until it contacts the material surface. Upon
contact the weight & cable system is immediately
retracted and the measurement is fed to the plant control
system or operator interface. The sensor is also equipped
with a simple electrical lockout feature for those
applications where measuring during fill is not desirable.
These sensors are easy to install and are also virtually
maintenance free, requiring only a periodic inspection
usually once or twice per year.
This system also increases plant
safety by making it unnecessary for personnel to
climb silos on regular intervals in order to take
measurements of the material level. For more
information, please visit www.monitortech.com or
call 1-800-601-5953 / 1-630-365-9403.
Monitor Technologies LLC, located
in Elburn, Illinois, is a leading manufacturer of level
measurement instrumentation, solids flow indicators,
particle emission monitors and aeration devices for
the worldwide powder and bulk solids markets. The experience
and market knowledge gained over 50 years of business
has earned Monitor a reputation for providing high
quality and reliable product solutions backed with
trusted customer service. For more information please
visit www.monitortech.com.
The TrueCap® Model MK-2
RF Capacitance point level probe is designed to provide a superior
and stable sensitivity threshold making it suitable for a variety
of powder / bulk solids and some liquid or slurry applications.
Advanced features of the Model MK-2 include: > Automatic immunity to material build-up on
the probe by its driven shield design > Push-button calibration > Enhanced temperature compensation > Maximized reliability via smart sensing algorithms
like “self-validating” fail-safe protection > Visible status LED on ordinary location units > Versatility through a variety of configuration
options including: hazardous location version, split architecture
design, quick-connect process connection, stub probe, cable extensions,
solid extensions, Nylon® probes, Ryton® - equiv. probes,
etc.
A practical application for the TrueCap would be to use this level sensor where
a residual material build-up on a different sensor would cause a false material
level indication.
Principle of Operation for the TrueCap RF Capacitance Level
Probe:
The vessel wall and the active probe element establish an impedance reference
between each other when exposed to air which has a dielectric constant of 1.
When materials with a dielectric constant greater than 1 are in close proximity
to the probe, the impedance of the sensing field between the sensor and the vessel
wall will change. Once the amount of change exceeds a threshold that was electronically
determined during the calibration process, an output relay will either be energized
or de-energized depending upon the position of the fail-safe selector on the
probe’s electronic circuit board. A change of as little as .5 pico-farad
is all that is necessary for the probe to sense the presence of material.
