Ametek Drexelbrook ThePoint Series, Инструкция по установке и эксплуатации, Страница: 7 / 70

Introduction
1
Section 1: Introduction
1.1 System Description
The AMETEK Drexelbrook ThePoint™ Series uses No-Cal™
technology to detect the presence or absence of material without
calibration or initiation via setpoint adjustments, push-buttons
or magnets.
Installation is simple and easy. Simply apply power and
ThePoint system is ready to detect the presence or absence
of material. Since ThePoint instrument does not require
calibration or setpoint adjustments, it is capable of operating
in non-dedicated tanks regardless of the material being
measured.
1.2 Technology
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), amplified and the output is increased.
There are drawbacks, however, especially when there is coating
of the probe.
An RF Admittance level transmitter is the next generation.
Although similar to the capacitance concept, ThePoint employs
a radio frequency signal and adds the Cote-Shield™ circuitry
within the Electronics Unit.
This patented Cote-Shield™ circuitry is designed into ThePoint
series 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 presence or absence of material. The Cote-ShieldTM
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 by far the most versatile
technology, good for very wide range conditions from cryogenics
to high temperature, from vacuum to 10,000 psi pressure, and
works with all types of materials.
k
air
A
d
C
k
media
C =
k A
d
C =
k A
d
A
k
air
d
C
k
media
Material to be
measured must be below
sensor when power is
applied.
Figure 1-2
RF Admittance Probe
with Cote-Shield
Figure 1-1
Simple Capacitance
Probe
(Insulating Media)