Section One
Description
1-2
The resistive component of the coating is proportional to the capacitive component of the
coating and to the increased current flow produced by the coating. Therefore, by monitoring the
magnitude of the phase shift away from the -90º point, the signal processing circuitry of the
electronics is able to apply a proportional correction to the RF signal, thus subtracting out the
error caused by the coating. The corrected RF signal is ultimately rectified and amplified to
produce a proportional DC current output.
Many, if not most, process applications are water-based and, therefore, electrically conductive.
If the probe elements were both bare metal, the first contact with the process material would
short the capacitive plates producing an exceptionally high current flow. Covering one or both of
the probe elements with an insulating material such as Teflon or Kynar solves this problem.
Now, with no process material touching the probe, capacitance is determined by the combined
dielectrics of air and the probe insulation material in series. As the process rises, it displaces
the air and effectively shorts the gap between the two probe elements. Now, capacitance is
determined by the dielectric of the Teflon or Kynar insulation alone, producing a directly
proportional increase in capacitance and RF current flow as level rises. Process linearity is
determined solely by the uniformity of the thickness of the insulation material.
Linearity of non-conductive process measurements depends upon uniform, parallel spacing of
the probe elements. Probes used for non-conductive applications normally have at least one
element insulated. This is to reduce the magnitude of error that would be caused by a small
amount of conductive moisture in the process, such as might result from condensation.
2. Signal Processing
The L3610 is factory set on the appropriate RF capacitive measurement range as required for
the specific application, based on a capacitance span calculated for the specific application.
Normally, the range is not re-set in the field. The RF signal, proportional to level and corrected
for coating error, is rectified and filtered into a proportional DC voltage. This signal is processed
by a series of DC amplifiers and ultimately converted into a proportional DC current or DC
voltage output signal.
Front panel ZERO and SPAN adjustment pots set the span of the DC amplifiers within the pre-
set range. The pots are set at the factory relative to calculated zero and span capacitance
values for the specific probe and application. They are re-adjusted by the user if need requires.
3. Basic Features
•RF Impedance Sensing Technology with Null-Kote™
The L3610 uses RF impedance technology, proven in tens of thousands of applications.
With no moving parts, the measurement depends solely on its modern, electronic circuitry,
ensuring years of dependable operation.
•Coating Cancellation
Null-Kote™ technology allows the cancellation of the build-up on the probe of most process
materials. Units are factory set for either Mode A (non-conductive) or Mode B (conductive)
process coating cancellation. Coating cancellation is effective within specified limits.
•Superior Temperature Stability
The L3610 electronics is designed to provide temperature stability superior to that of
previous generations of level transmitters. This allows successful, repeatable
measurements in many short span, low dielectric applications.
•Self Diagnostic Feature
