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Section 6
6.1 Downlook Ultrasonic Sensor
6.1.1 Installing the Downlook Ultrasonic Sensor
Sensor Installation
DANGER
Only qualified personnel should conduct the tasks described in this section of the
manual.
DANGER
Seul un technicien qualifié peut effectuer les tâches d'installation décrites dans
cette section du manuel.
DANGER
All connections to the flow meter must be made in a non-hazardous location.
DANGER
Tous les raccordements au débitmètre doivent être effectués dans un
environnement qui ne présente aucun danger.
The downlook ultrasonic sensor is mounted over the flow stream at the proper location for
level measurement for the primary device. See
information. The transducer emits a pulse of sound at a high frequency and awaits for the
echo to return from the surface of the water. The time it takes for this echo to return is
relative to the distance between the transducer and the surface water. As the level in the
flow stream increases, the time it takes for the echo to return to the transducer decreases
(distance is shorter).
By continuously transmitting these pulses and timing the returning echoes, the sensor
measures the level of the liquid on the flow stream. After measuring the level, the
microprocessor converts the level reading to a flow rate based on the user-defined
characteristics of the primary device.
Note: Do not suspend the sensor by the cable. Only use appropriate mounting hardware.
Site selection can greatly enhance system performance. Several important factors should
be considered when installing the downlook ultrasonic sensor at any primary device.
•
Locate the ultrasonic sensor at the proper head measurement point for that primary
device.
•
Determine the appropriate sensor height.
•
Suspend the ultrasonic sensor over the center of the flow stream where there is the
least surface turbulence.
•
Mount the sensor to a stable, secure location, isolated from vibration.
Invisible Range
The 940 Flow Meter is equipped with an invisible range (adjustable deadband feature) to
prevent false echoes from tops of channel walls, ladder rungs, shelves, etc. A user
selected range is defined which is invisible to the flow meter. Extend the invisible range to
where it meets or overlaps the highest expected level in the channel. Refer to
on page
44. A gap of at least 5 cm (2 in.) should be left between the invisible range and
the highest expected level. The minimum distance must be at least 29 cm (11 in.) The
Appendix A on page 75
for more
Figure 22
43
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Troubleshooting
