Introduction
3
1.2 Technology
Capacitance
In a simple capacitance measurement, the capacitance increases as the
process medium covers more of the sensing element. In an insulating medium,
this is due to the increase in dielectric constant (k) from air to that of the
medium. In a conductive medium, this is due to the decreased distance from
ground as the medium provides a conductive path from the ground reference,
typically the vessel wall, to the outer surface of the sensing element
insulation.
This change in capacitance causes an imbalance in a capacitance bridge which
is detected in the circuitry and converted to an output proportional to level.
Radio Frequency (RF) Admittance
RF Admittance is the next generation. Although similar to capacitance it
adds a valuable feature, the ability to compensate for conductive coatings.
The patented Cote-Shield™ circuitry of the Universal IV Pro Model measures
resistance and capacitance separately. The level component of the sensing
element capacitance has a negligible resistance however, a conductive coating
will have a much greater resistance. The design of the circuitry also produces
signals for the resistive and capacitive RF currents of a conductive coating
to be of identical magnitude but of opposite phase. This allows the Universal
IV to subtract the effect of the coating and produce an accurate level
measurement even in the most difficult applications.
This patented Cote-Shield™ circuitry is designed into the Universal IV Pro
Model and enables the instrument to ignore the effect of buildup or material
coating on the sensing element. The sensing element is mounted in the vessel
and provides a change in RF admittance indicating the level of material.
The Cote-Shield™ circuitry prevents the transmission of RF current through
the coating on the sensing element. The only path to ground available for the
RF current is through the material being measured.
The result is an accurate measurement regardless of the amount of coating on
the sensing element. By far the most versatile technology available, it works
with all types of materials in a vast array of conditions; from cryogenics to
high temperature, and from vacuum to 10,000psi pressure.
Lite Model
The Universal IV Lite Model is the entry level RF Capacitance measurement
system for use where Cote-Shield
™
is not required. Lite models can be used
in non-coating and insulating coating applications. Universal IV Lite is not
recommended for use in conductive
coating
applications. In addition, the
Lite model has a 20-7,000 pF range that may limit the measurement span on
conductive liquids.
Pro Model
The Universal IV Pro model has the most versatility with full capabilities
of Code-Shield and measurement span of 1-45,000 pF. The Pro can handle
shorter and longer measurement spans and is compatible with a vast array of
applications.
Содержание DREXELBROOK Universal IV Lite
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