MODEL AT3
1 – 1
SECTION I – INTRODUCTION
OVERVIEW
The AT3 monitor is a microprocessor based, real-time, in-line instrument used to monitor liquid-borne
particle concentration and oil contaminants in various process liquids. Use of the microprocessor
and graphics display provides a user friendly interface for setup and calibration. Because it is
acoustically based, Monitek’s patented transducer measures independent of the liquid’s color,
opacity, density, flowrate or photosensitivity. The sensor is relatively immune to the effects of
coatings that would blind an optical sensor. Sensors mount directly into process piping, thus
eliminating the handling error and dead time associated with grab sampling. The unit’s dot matrix
LCD display can present any user defined engineering unit (i.e., PPM, PCT, #/mI
,
etc.) along with
the ability to plot calibration curves. The raw data is displayed as “counts”.
Upset Monitor: The most common use of the AT3 is to monitor equipment upsets (i.e., oil separators,
filters, Dissolved Air Floatation devices, catalyst carryover). Here, the AT3 can be set up to read
in “counts” only. A reading in “counts” can be noted when a good or acceptable condition exists.
Then an “upset” can be simulated and an alarm point established. This eliminates the need for
taking samples to establish a calibration curve when all that is needed is for the AT3 to notify an
upset condition.
Concentration Monitor: The AT3 can also monitor suspended solids concentrations through the
microprocessor establishing a correlation between “counts” and the known concentration (PPM,
mg/L,
%,
etc.) can be determined, and the display will read out in engineering units.
However, to establish an accurate correlation a few conditions must be noted:
1.
The particle size distribution must remain relatively constant at the point of sampling.
2.
The temperature should be fairly constant. Temperature surges will affect the speed of
sound through the liquid medium.
Theory:
The AT3 transmits acoustic pulses across the path of a liquid; these pulses are created by
electrically exciting the transducer’s piezoelectric crystal. Acoustic energy is reflected off any
particles or bubbles encountered in the monitored liquid. Acoustic reflections received at the
transducer are converted back into an electrical signal, which is amplified by a preamplifier and
set to the receiver. Its amplitude is then compared to a reference voltage level known as the
detection threshold. The signal is also time-gated to process only reflections from particles in the
focal region. Signals that occur in the focal region and are greater than the detection threshold
are analyzed by the software algorithm that accumulates counts. The total counts are processed
by a mathematical curve fitting algorithm and a correspondent concentration value is displayed on
the front panel of the system.
In addition to the return signals from contaminants in the monitored liquid, there are also reflections from
the chamber wall opposite the transducer (far wall pulses) and from sound resonated in the
transducer (main bang). Figure 1-1 illustrates these signals as well as how the receiver window is
used to ensure that only reflections occurring in the focal region are processed.
Summary of Contents for Monitek AT3
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