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Section 1: Introduction
1.1
System Description
1.2
Technology
k
d
d
A
A
k
k
C
C
air
k
media
k A
k A
C =
C =
d
Figure 1-1
Simple Capacitance
Probe
Figure 1-2
RF Admittance Probe
with Cote-Shield
The AMETEK Drexelbrook, IntelliPoint RMT and RGT
Series point level switches detect the presence or absence of
material and provide a current output for control functions. The
RMT and RGT IntelliPoint™ switches are calibrated through
a simple potentiometer adjustment.
In a simple capacitance probe-type sensing element, when
the level rises and material covers the probe, the capacitance
within the circuit between the probe and the media (conductive
applications), or the probe and the vessel wall (insulating
applications), increases. This is due to the dielectric constant
(k) of the material which causes a bridge imbalance. The signal
is demodulated (rectified) and amplified, then the output is
increased. There are drawbacks, however, especially when
there is coating of the probe.
air
An RF Admittance level transmitter is the next generation.
Although similar to the capacitance concept, IntelliPoint
employs a radio frequency signal and adds the Cote-Shield
media
circuitry within the Electronics Unit. This patented Cote-Shield
circuitry is designed into the IntelliPoint series and enables
the instrument to ignore the effect of buildup, that is, material
coating on the sensing element. The sensing element is mounted
in the vessel and provides a change in RF admittance indicating
d
the presence or absence of material.
The Cote-Shield element of the sensor 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 probe, making it the most versatile
technology available by far. Not only does it work with all types
of materials, it's well suited to a very broad range of conditions,
from cryogenics to high temperature, from vacuum all the way
to 10,000psi
pressure.
1
Introduction
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