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2150EX Area Velocity Flow Module
Section 1 Introduction
1-2
1.1.1 2150EX Area Velocity
Flow System Overview
The 2150EX measures liquid level and average stream velocity,
and calculates the flow rate and total flow. The liquid level and
velocity measurements are read from an attached Area Velocity
(AV) Sensor that is placed in the flow stream. Flow rate calcula-
tions are performed internally using the measured parameters
from the AV Sensor. Additionally, the 2150EX can measure its
input voltage.
The 2150EX is designed to provide durable operation with only a
minimal amount of routine maintenance, all of which may be
performed in the field, while keeping in mind restrictions for
potentially explosive atmospheres. Typically, the 2150EX and its
AV2150EX Sensor will only require that you keep the stream free
from excessive debris, and replace or recharge spent desiccant
and batteries. Sections 1.1.2 through 1.1.6 describe the 2150EX
and sensor in greater detail.
1.1.2 Level The AV Sensor’s internal differential pressure transducer mea-
sures the liquid level. The transducer is a small piezo-resistive
chip that detects the difference of the pressures felt on the inner
and outer face.
The stainless steel outer diaphragm is exposed to the flow stream
through the ports under the AV Sensor. The pressure felt on the
outer diaphragm is transferred to the outer face of the trans-
ducer through a silicone fluid medium. The outer diaphragm and
fluid isolate the sensitive transducer from direct exposure to the
stream. The inner face of the transducer is exposed, or refer-
enced, to the atmosphere through the internal vent tube that
runs the full length of the AV Sensor’s cable.
The difference between the pressures exerted on the transducer
is the hydrostatic pressure. Hydrostatic pressure is proportional
to the level of the stream. The Isco AV2150EX sensor uses state
of the art techniques to ensure accuracy throughout the environ-
mental operating range. At the factory each sensor is measured
at scores of pressure and temperature levels to precisely charac-
terize the unique transducer. These calibration results are digi-
tally stored within the sensor's flash memory. During readings
the sensor's microcontroller applies the known correction factor
to produce highly accurate level readings.
1.1.3 Velocity The AV Sensor measures average velocity by using ultrasonic
sound waves and the Doppler effect. The Doppler effect states
that the frequency of a sound wave (or other wave) passed from
one body to another is relative to both their motions. As the two
approach each other, the frequency increases; as they move
apart, the frequency decreases.
The AV Sensor contains a pair of ultrasonic transducers. One
transducer transmits the ultrasonic sound wave. As the trans-
mitted wave travels through the stream, particles and bubbles
carried by the stream reflect the sound wave back towards the
AV Sensor. The second transducer receives the reflected wave.
AV Module
AV Sensor
reference to
atmosphere
silicone
fluid
outer
diaphragm
piezo-
resistive
transducer
Particles or
air bubbles
Ultrasonic
sound waves
Flow